Press Tool Master File.doc

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PART - 1

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CONTENTS 1. Sheet metal processing using press tools. 2. Theory of shearing. 3. Cutting force. 4. Cutting clearance. 5. Land and angular clearance. 6. Strip layout. 7. Punches. 8. Buckling of punches. 9. Die block. 10. Stoppers. 11. Strippers. 12. Gauge. 13. Pilots. 14. Side cutters for a tool. 15. Ejectors and shedders. 16. Fasteners and dowel in a press tool. 17. Shank location. 18. Die set. 19. Progressive tool. 20. Compound tool. 21. Shaving. 22. Bending tool. 23. Deep drawing. 24. Presses. 25. Tool failure.

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CHAPTER -01 INTRODUCTION TO PRESS TOOL

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INTRODUCTION: The word tooling refers to the hardware necessary to produce a particular product. The most common classification of tooling is as follows: 1. Sheet metal press working tools. 2. Molds and tools for plastic molding and die-casting. 3. Forging tools for hot and cold forging. 4. Jigs and fixtures for guiding the tool and holding the work piece. 5. Gauges and measuring instruments. 6. Cutting tools such as drills, reamers, milling cutters broaches, taps, etc.

PRESS TOOLS: Press tools are special tools custom built to produce a component mainly out of sheet metal. Press tool is of stampings include cutting operations (shearing, blanking, piercing, etc.) and forming operations (bending, drawing, etc.) Sheet metal items such as automobile parts (roofs, fenders, caps, etc.), components of aircrafts, parts of business machines, household appliances, sheet metal parts of electronic equipments Precision parts required for homological industry etc, are manufacture by press tools.

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PRESS TOOL OPERATIONS: Blanking: Blanking is a process of producing flat stampings. The entire periphery is cut and cut out piece is called the blank.

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Piercing: It is the operation of making hole in the stamping. Here also the entire Periphery is cut and cut piece is waste.

Cut - off: Cut off operation separates the work material along a straight line in a single cut. No scrap is produced in cutting off operation. The process of cutting off is similar to shearing in a shearing machine.

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Parting - off: The parting off operation separates the work material along a straight line in a double line cut. The piece, which is removed by the punch, is a scrap.

Parting of

Notching: This operation removes a small amount of material from the edges of a strip or a blank. Notching serves to shape the outer contours, of the work piece in a progressive die or to remove excess metal before a drawing of forming operation in a progressive die.

Notching

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Trimming: It is the operation of cutting the edges of the drawn components, which are wavy and irregular.

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Shaving: It is operation of removing a chip from around the edges of a previously blanked stampings to get finished edges and accurate dimensions.

Perforating: If more number of holes are pierced, it is called perforating.

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Lancing: It is a combination of bending and cutting operation along a line in the work material. No metal is cut free during lancing operation.

Dinking: To cut paper, leather, cloth, rubber and other soft materials a dinking tool is used. The cutting edges penetrate the material and cut (like knives).

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Broaching: It is similar to shaving operation; in this a tool having a series teeth profile removes metal from the edges of the blanked component.

Extrusion: This is a special process to manufacture collapsible tubes, shells etc. The blank, which is loaded in the die, is forged upward or downward under high pressure between punch and die.

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Planishing: Planishing tool is used to straighten, blanked components. Very fine serration points penetrate all around the surface of the component.

Serrations

Embossing: The embossing tool is used to press letters and numbers into a sheet metal or on pre drawn piece part. Usually the punch will have the raised form and the die will have the corresponding cavity.

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Coining: It is the process of pressing cold material in a tool so that it flows into the engraved profiles on the die face. Coining differs from embossing such that in coining the metal flows, where as in embossing the metal does not change in thickness to a great extent.

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It is the shaping the material around a straight axis, which extends completely across the material. The result is a plane surface at an angle to the original plane of the flat blanked component.

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It is similar to bending except that the line of bend is along a curved axis instead of a straight one. Metal flow is not uniform. It will be localized depending upon the shape of the work piece.

Drawing:

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In drawing a flat blank is transformed into a cup or shell. The parent metal is subjected to severe plastic deformation. Shell forms produced may be cylindrical or rectangular with straight or tapered sides.

Flaring or lugging:

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The process of forming an outward flange on parts is called flaring operation.

Curling: It is an operation of rolling the edges of a sheet metal into a curl or roll. It improves the appearance of the piece part. It is also increase strength.

Bulging: It is an internal forming operation used to expand portions of a drawn shell or tube. The forming force is applied from inside the work piece and is

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transmitted through a medium that will flow but will not get compressed. The more common media are rubber, urethane, oil, or water.

Swaging: The operation of swaging some times called necking is exactly the opposite of bulging. When a work piece is swaged a portion is reduced in size and this causes the part to become longer than it was before swaging.

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Sub press tool: Sub press tools blank and form very small parts. The die components are retained in the sub press. The sub press is a small press operated in a larger one.

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Assembly tool: Assembly tool assemble two or more parts together by press fittings, riveting or other means. Components are assembled in very short time and the relationship between parts can be maintained closely.

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Side cam tool: Side cam transforms vertical motion from the press ram into horizontal or angular motion in the tool.

Horning:

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Horn tools are provided with an arbor or horn over which parts are placed for secondary operations.

Combination tool: In combination tool two or more operations such as forming, drawing, extruding, embossing may be combined on the component with various cutting operations like blanking, piercing, broaching and cut off.

CHAPTER -02 THEORY OF SHEARING

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1.

Plastic deformation:

The pressure applied by the punch on the stock material tends to deform it into the die opening when the elastic limit is exceeded by further loading, a portion of the material will be forced into the die opening in the form of an embossed on the lower face of the material and will result in a corresponding depression on its upper face. This stage imparts a radius on the upper edge of the punched out material. This is called the stage of “plastic deformation”.

2.

Penetration stage:

As the load is further increased, the punch will penetrate the material to a certain depth and force an equally thick portion of metal into the die. This stage imparts a bright polished finish (cut band) on both the strip and the blank or slug. On optimum cutting conditions the cut band will be 1/3 rd of the sheet thickness. This is “penetration stage”.

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3.

Fracture stage:

In this stage, fracture will starts from both upper and lower cutting edges. As the punch travels further, these fractures will extend towards each other and eventually meet, causing complete separation. This stage imparts a dull fractured edge. This is the “fracture stage”.

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CHAPTER -03 CUTTING FORCE

CUTTING FORCE: “Cutting force is the force which has to on the stock material in order to cut out the blank or slug ”. This determines the capacity of the press to be used for particular tool. The cutting force is also determines the cut length

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area for straight cuts are performed in the shearing and some cut off operations, the area to be cut is found by multiplying the length of cut by stock thickness. Formula for calculating the cutting force: Cutting force = L x S x T max L = Length of periphery to be cut in ‘mm’. S = Sheet thickness in ‘mm’ T max = Shear strength in N/mm2, (taken from the table) = 80% of tensile strength (σ max) The fig. Represents the typical load curve of cutting force of blanking or piercing punch.

Formula to calculate the press force: Press force = Cutting force + stripping force (Stripping force = 10% - 20% of cutting force) The following table gives the shear strength (T max = 0.2 for tensile strength σ max) of several materials.

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MATERIAL

T max in N/mm2

Steel with 0.1% carbon Steel with 0.2% carbon content (deep draw steel) Steel with 0.3% carbon Steel with 0.4% carbon Steel with 0.6% carbon Steel with 0.9% carbon Silicon steel Stainless steel MATERIAL

240 – 300 320 - 400 360 - 420 450 - 560 550 - 700 700 - 900 450 - 550 350 - 450 T max in N/mm2

Copper Brass Bronze German silver (2 - 20% Ni, 45 - 75% Cu) Tin Zinc Lead Aluminum 99% pure Aluminum manganese alloy Aluminum silicon alloy Paper & card board Hard board Laminated paper or rosin impregnated paper Laminated fabrics Mica Plywood Leather Soft rubber Hard rubber Celluloid

200 – 400 350 – 400 360 – 450 300 – 320 30 – 40 100 – 120 20 – 30 20 – 120 150 – 320 120 – 250 20 – 50 70 – 90 100 – 140 90 – 120 50 – 20 20 – 40 7 7 20 – 60 40 - 60

Example: Calculate the press force required t produce the following component. Sheet thickness 2mm. Material is brass. Cutting force

= L x S x T max = 126 x 2 x 400 = 100800 N = 100.8 KN

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Press force

= Cutting force +Stripping force = 100800 + 20% 100800 = 120960 N = 120.960 KN.

METHODS OF REDUCING THE CUTTING FORCE: It sometimes becomes necessary to reduce the cutting force to prevent press over loading. 1. 2.

The punch length is to be reduced. Stepped punches to be used.

3. To grind the face of the punch or die to a small shear angle.

DIFFERENT TYPES OF SHEAR ANGLES

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CHAPTER -04 CUTTING CLEARANCE

Cutting clearance: Cutting clearance is the gap between the side of the punch and the corresponding side of the die opening on one side of the edge, when the punch is entered into the die opening. It is expressed in the amount of clearance per side.

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Importance Of Cutting Clearance: Proper cutting clearance is necessary to: 1. Aid the life of the die. 2. Increase the quality of the piece part. 3. Improve the characteristics of piece part. 4. Causes the undue stress and wear on the cutting edges of the tool.

Optimum Cutting Clearance:

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Fig shows the blank or slug made under optimum cutting conditions. The edge radius (die roll) is the result of initial plastic deformation, which occurred during the first stage of plastic shear action. Highly burnished cut band results from the second stage (penetration) of shear action. The width of the cut band is approximately 1/3 rd of the thickness of stock material. The balance of the cut is the break, which results from the third stage (fracture) of the shearing action.

Excessive Cutting Clearance:

In this the large gap between the punch and die cutting edges allows the stock material to react to the initial pressure on a manner approaching that of forming rather than cutting. Therefore the edge radius becomes larger and the cut band becomes smaller.

Insufficient Cutting Clearance:

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When the cutting clearance is slightly less the condition can be identified by greater width of the cut band. Because of steeper angle between the punch and die cut edges the resistance of the stock material to fracture is increased. In case of excessive clearance the burr results from dragging of the material. While insufficient clearance compressive forces cause the burr.

Burr Side: The burr side is the adjacent to the break. The burr side is also called because of a noticeable burr condition develops it will occur in this side. Burr should be practically non-existence if the cutting clearance between the punch and die is correct and if the cutting edges are sharp. The burr side of the blank or slug is always towards the punch (die starts shearing) the burr side of the punched opening is always towards the die opening.

Determination of punch and die size: For Piercing: Piercing punch = Pierced hole size. Die = Hole size + total clearance. For Blanking: Blanking punch = Blanking size – total clearance. Die = Blanking size. For finding the cutting clearance following formula to be used. Clearance for ‘s’ up to 3mm = c X s X  tmax/10 For ‘s’ above 3mm clearance = (1.5 X s) X (s – 0.015) X  tmax/10

Problems: 1. Calculating the clearance for punching a 2mm sheet. Tmax to be assumed to be 300 N/mm2. Clearance

= c X s X  tmax/10 = 0.01 X 2 X  300/10 = 0.02 X  300/10 = 0.12 mm/side

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Therefore clearance on one side = 0.12 mm 2. Determine the punch and die dimension for the component given below. Sheet thickness 0.5mm, stainless steel sheet, T max is 400 N/mm. C = 0.01 Clearance = c X s X  tmax/10 = 0.01 X 0.5 X  400/10 = 0.03 mm/side

Blanking punch:

 Blanking die dimension is the same as that of component dimension.  Piercing punch size is the size of the pierced hole

Piercing Die:

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1. Determine the punch and die dimension for the component given below. Sheet thickness 2mm MS, T max is 400N/mm and C=0.01.

Clearance

= c X s X  tmax/10 = 0.01 X 2.0 X  tmax/10 = 0.13 mm/side

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 Blanking die dimension is the same as that of component dimensions.  Piercing punch size is same as component size. Piercing Die size

= component size + clearance = 10.00 + 0.26 = 10.26mm

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CHAPTER -05 LAND AND ANGULAR CLEARANCE

LAND: The inner walls of a die opening are not usually made straight through as the blanks or slugs tend to get jammed inside, which may result undue stress build up. This may lead to the breakage of the punch and die. To avoid such situation the die walls are kept straight only to a certain amount from the cutting edge. The straight wall is called “THE LAND”.  An amount of 3mm land for stock thickness up to 3mm.  For thicker materials equal to their sheet thickness.

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ANGULAR CLEARANCE OR ANGULAR RELIEF: Generally, soft materials require greater angular clearance than hard materials. Soft thicker materials above 3mm require more angular clearance. An angular Clearance of 1.5°per side will meet the usual requirements.

In special cases, the angular clearance extends from top to bottom of the die wall completely eliminating the land.

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Dies employing an ejector to clear the blanks will have straight walls without any angular clearance, as the blanks do not get accumulated in the die.

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CHAPTER -06 STRIP LAYOUT

STRIP LAYOUT: A strip layout represents the sequence of the logical, workable operations, which is to say a sequence of ideas. If this sequence of operations has error, the error will be surely emerge in a try out press. Factors to be considered while designing the layout are: 1. Shape of the blank. 2. Production requirement. 3. Grain direction. 4. Burr side. 5. Stock material.

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ECONOMY FACTOR: The designer should try out every possible means to attain a good percentage of any strips, without sacrificing the accuracy of the piece part. Economy Factor = Area of the blank x No of rows x 100 Width of the strip x pitch A minimum economy of 60% should be aimed. The position of the blank in the strip decides the economy factor

Strip Layout for blanking tools:  Blanking tools produce blanks entirely from the strip or unit stock.  Blanking is a most efficient and popular way of producing intricate and closely tolerated blanks.

Shape of the blank:  The contour of the blank, decides the position of the strip.  Some of the blanks are laid at an angle.

Production Requirement: If production requirement is less, then material conservation is necessary. This must not increase the tool cost. Gang die may be suitable for the mass production.

Grain Direction:  The grains are found in the sheets when they are rolled.  Bending the strip along the grain direction results in crack and fracture.

Burr Side:  It is a decisive factor in laying the strip.  In blanking, burr is found on the punch.  In piercing, burr is found on the die.

Stock Material:

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 Every means is necessary to conserve the stock material.  A double pass layout would justify the cost of stock material conserved.

Single Row One Pass layout: Here the blanks are arranged in a single row and the strip is passed through the tool only once to the punch and blanks from it.

Blanks having at least two Straight parallel sides: Here the strip width should be equal to the distance between two parallel sides. The blanks are produced by cut off or parting off operation.

Blanks having Irregular Counters: Factors considered for best method of positioning a blank in the strip. 1. 2. 3. 4. 5. 6. 7.

Contour. Minimum material wastage. Less tool cost. No scrap strip to handle, which renders the production faster. Accuracy in strip width. Accuracy of the blank. Flatness.

Strip layout for Cut Off and Parting Off:  Cut off and parting are the operations, which shear the strip across the entire width either, in straight or curved lines. ICDP TECHNICAL TRAINING CENTER

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 The difference is cut off punch cut s only one edge producing no scrap where as parting punch cuts two opposite edges producing the scrap.

Different layouts: There are two ways of laying the strip, Narrow run and wide run. Wide run is generally desirable due to,  Shorter advance distance of the strip promotes easy feeding.  More blanks can be produced from a given length of strip. Narrow run is used when the grain direction of the piece part is important.

Single row two pass method: A two-pass tool requires minimum of two stops. The stops used for the first pass have to be removed. Or made to disappear from the working surface so as not to interfere with the second pass. For double pass the front and back scrap as well as the scrap bridge should be wider than those for single pass (about 50-100). Two pass layouts are justified only when the wastage is considered and the stock material is costly.

Double row layout: Further economy can be attained by double rows. Strips for double row layout will be wider and require the back and front scrap to be more than usual amount.

Gang die: It consists of two or more similar sets of tool members so as to produce two or more number of components during the single stroke of press ram.

Gang die is the most economical means of mass production of stampings. But still gang dies are not recommended for very complex work.

Angular layouts: Some of the piece parts will be require to be laid out to an angular position to make the layout more economical.

Different types of strip layout:

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CHAPTER -07 ICDP TECHNICAL TRAINING CENTER

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PUNCHES

Punch: Punch is the male member of a press tool. There are three categories of punches: 1. Cutting punches. 2. Non – cutting punches. 3. Hybrid punches.

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CUTTING PUNCHES: These punches perform operations like blanking, piercing, notching, trimming etc.

NON - CUTTING PUNCHES: These punches perform operations like bending, forming, drawing, extruding etc.

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These punches perform both cutting and non-cutting operations, like shear and form, punch-trim etc.

PUNCH GROUPS: There are two groups of punches: 1. Segregated punches. Self mounted punches, which are positioned and retained by means of self-contained screws and dowels. 2. Integrated punches. Punches depend on other component such as punch plate, to locate and position them.

TYPES OF PUNCHES: 1) Plain punches  Rectangular in cross section.  These are self-mounting straight punches.

Advantages:  Material saving.  Machine time saving.  Easy mounting.

2) Pedestal punches  They are also called as broad based punches.  Load distribution qualities are excellent.  Used for heavy-duty work. 3) Pedestal offset punches    

Base is offset. Reason for offsetting Space consideration for other components. Machining and grinding accessibility.

Disadvantages: ICDP TECHNICAL TRAINING CENTER

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 Non-uniform distribution of forces.

4) BOSSED PUNCHES  Punches made with positioning boss. 5) FLANGED PUNCHES  Punches having a flange with boss.  Allows the possibility of providing clamping screws. 6) HEADLESS PUNCHES  Plain punch, which does not contain dowels.  Positioning is done by opening provided on the punch plate.  Fastening is done by means of screws. 7) STEPHEAD PUNCHES (SHOULDERED PUNCHES)  Punches fitted in punch plate without screws and dowels. 8) BEVELED HEAD PUNCHES  Punches are made to angular sitting.  Bevel angle is made to 30-45deg.  Beveled portion may be machined or pinned. 9) CLAMPED PUNCHES  A headless punch except the manner in which it clamped. 10) FLOATING PUNCHES  Punches made loose in the punch plate.  Well guided in the stripper plate.  Alignment of the stripper to the die plate is maintained precisely.

PERFORATORS:  Punches of dia 2.5mm or below.

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 Punches whose working contour are other than round. Commonly used perforators:

Step head perforator: Consists of stepped head shank and point diameter.

Step head shank less: Similar to step head perforator. Shank dia is more than point diameter.

Pyramid perforator: It is used when there is a disparity between point dia and shank.

Bevel head perforator: Consists of bevel seating.

Headless perforator: Does not have a shoulder. A whistle notch is milled on the shank for fastening.

Slug ejector perforator: To prevent slug pulling, air pressure or spring pins are commonly used.

Quilled perforator: Slender perforators are quilled, to prevent buckling.

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CHAPTER -08 BUCKLING THEOREM

Buckling of Punches:

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Whenever Press tool is worked upon within the press, The punches mounted in that tool, are subjected to compression stresses. But if due consideration of stresses are overlooked during designing of the tool, the thin punch within the tool may fail by buckling. Hence by maximum force, which a punch can withstand without buckling can be calculated by using the following formula. Fb = [² × E × I] / Lp² Fb = Maximum Force beyond which buckling occurs. E = Modulus of Elasticity (For steel Modulus of Elasticity varies from 200 to 220 GN /m²) I = Moment of Inertia in mm4 Lp = Length of punch in mm The ultimate condition is when, Buckling Force

= Cutting Force required for the operation = Shear force on the punch.

Example 1: To find the smallest diameter of the punch to pierce 2mm Mild Steel sheet. Length of the punch = 60mm E = 210GN/m² Assume Fb = 800N Fb = [² × E × I] / Lp² 800 × 10-9 = [² × 210 × I] / 0.06² 800 × 10-9 × 0.06² = ² × 210 × I I = [800 × 10-9 × 0.06²] / [² × 210] = [2.88 × 10-9] / [2070.516] I = 1.389547 × 10-12 mm4 I = 1.389547 × 10-12 mm4 I = [d4] / 64 1.389547 × 10-12 = [d4] / 64 d4 = 1.389547 × 10-12 × 64 d4 = 2.8307619 × 10-11 d = 2.3066mm ~ 2.31mm

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CHAPTER -09 DIE BLOCKS FACTORS INFLUENCE THE DESIGN OF A DIE BLOCK: 1. 2. 3. 4. 5.

Piece part size Stock thickness Intricacy of the piece part contour Type of tool Machinery available for manufacturing the tool

SOLID DIES: 1. Made up of non shrinking tool steels 2. Hardened & tempered to 58-62hrc

CONSIDERATIONS OF SOLID DIES: 1. 2. 3. 4. 5. 6. 7.

Critical nature of the Dimensions involved Extreme Pressures & Wear conditions while Shearing Sheet thickness Press force Strength & Life of the Die: Sufficient wall thickness at the weakest points Sufficient Die thickness according to the Severity of the specific operations.

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DIES THICKNESS: STOCK MATERIAL FOR DIE BLOCK LENGTH THICKNESS IN mm upto125mm 125-200mm 200-400mm upto 1 16 20 24 1 to 2 20 24 28 2 to 3 24 28 32 3 to 4 28 32 36 4 to 6 32 36 50 6 & above 36 40 60 DIE BUSHES: Advantages:  

Easily replaceable. Reduces cost of the die manufacturing.

Application: 

In large piercing dies.

SPLIT or SECTIONAL DIE BLOCKS: These are the dies having more than One Section.

Deciding Factors of SOLID or SPLIT DIES:

SOLID DIE

SPLIT DIE SIZE OF THE DIE BLOCK

Small

Bigger Reduces cost, Machining Time, Hardening Failures SIZE OF THE DIE OPENING Sufficient to performinternal Too working small for Internal working Eases the machining process. COMPLEXITY OF THE DIE OPENING Intricate cotours, Sharp Corners in the Simple contours component Eases machining Avoids Cracks at hardening. PERISHABILITY No possibility of Breakage High Possibility of Breakage Simplify the manufacture of relatively perishable portions of the die block PROFILE GROUND DIE OPENING When internal grinding is WTRAINING hen internal grinding is impossible ICDP TECHNICAL CENTER possible wherever required wherever required

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SPLIT DIES: Locating & Clamping of Die Sections: Considerations:  

Tilting Due to Downward Thrust. Lateral Displacement due to Lateral Thrust created by the Punching Action.

Methods:  

For Thin Stock materials, Dowels and Screws. As the Stock material thickness increases, Need of Nesting arises.

NESTING: METHODS OF NESTING:   

Nesting in Die set pockets. Nesting in Retainer Plate, which is of Mild steel. Nesting in the above methods incorporating Liners.

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NESTING IN DIE SET with LINERS:

DIE SECTIONS LINER DIE SHOE

Section X-X

LINER

LINER

LINER

LINER

NEST BLOCKS: Advantages:   

They do not weaken the die set. Can be easily hardened for heavy work. Can be easily ground, when Die needs to regrind. As the Whole assembly of Die Sections are ground together.

Disadvantage:

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

Costly compared to pocket milled Die set type nesting, as the separate nest block has to be machined & clamped to the die set.

NESTING in Retainer Plate:

Locating & Keying of Circular Sections: DIE INSERT:

CARBIDE DIES: Die Material: Tungsten Carbide. Applications: Blanking, Piercing, Trimming, Forming, Drawing, and swaging operation.  Where production rates are high.  Parts having Close tolerances. DESIGN PRINCIPLE: 

  

Draw radii or approach angles. Punch & die clearance. Relief

All remains the same as that of the steel dies. 

Supporting of Carbide Dies inserts:

Inserts must be supported externally by pressing or shrinking them into a Hardened steel case.

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CHAPTER -10 STOPPERS ICDP TECHNICAL TRAINING CENTER

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STOPPERS: After each and every stroke of the press, the strip has to be fed forward for one pitch length. This can be accomplished by means of stopper. The function of the stopper is to arrest the movement of the strip when it is fed forward to one pitch length.

Basic stop principles: It is essential that two basic definitions be associated with the fundamental principles of stops,  

Stop position. Registry position.

Stop position: This is the location of the actual stopper position surface against which the stock strip is halted.

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Registry position: This is the exact location in which the stock strip must be established in order that the work will be dimensionally correct. The registry position may or may not be the same as the stop position.

Relationship between stop position & registry position:  

The work is located by the stop and is registered by the pilots. The Relationship between stop position & registry position depends upon the function of the stop. if a stop acts a true gauge, stop position & registry position are one end the same. If stop function as an approximation gauge, the stop position doesn’t coincide with the registry position. It can be said generally that if the stock strip is piloted, it is necessary for the stop to act only as an approximation gauge, allowing the strip to be overfed. If a stock strip is not piloted the stop then function as a true gauge.

Stop Categories: Primary: Primary stop is the first stop in the die, which act as true gauges, registering the stock strip. This locates stock position to coincide with the registry position.

Secondary: The stops in between are secondary stops. The secondary stop acts as a approximation gauge, therefore allows the overfeed when installed. Final: The final stop is the last stop in the die. It may or may not register the stock strip, when mounting them locate the stopping position as required.

Stop types: Solid stop: It is simply a hardened steel block mounted at required location.

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Plain pin stop: The stop is the plain cylindrical pin. The stop pin is mounted in a die Block. The pin is a light drive fit on the mounted hole. The mounted hole is generally made to suit standard pin size (dowel size).

A clearance hole for the pin should be provided in the die shoe for three reasons:  To permit adjusting the height of the stop pin without removing the die block from the die shoe.  To allow the stop pin to be removed in order to sharpen the die with the die block fastened to the die shoe.  To allow the pin to be driven down in the event of a miss-feed, thus reducing the chance of damage to the die

Headed pin stop: It frequently occurs that a stop must be located close to the die opening. In such cases the use of plain pin stop is prohibited because the proximity of the mounting hole to the die opening will make the die weak. For such an applications a headed pin stop may be employed. The mounting hole can be located at the safe distance from the die opening.

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Disappearing stopper: It is a spring pin located at the required stopping position disappearing stops offer one important advantages over other pin stops is that they do not require clearance in apposing die members

Finger stops: The stop is actuated manually. It is pushed inward until the stop shoulder contacts the front edge of the stripper. When the stop is in close position, the nose of the stop extends into the stock channel, obstructing the stock strip. The stop is held in closed position and the leading end of the stock strip is fed against the stop. Then operator trips the press and releases the stop. The spring returns the stop to its open position where its remains until a new stock strip are fed into the die.

Pusher Stops: These stops are special types of finger stop. They serve a duel purpose as both stops and pushers–the spring forces inward where it obstructs the stock strip channel. In operation the leading end of the stock strip is fed against the pusher stop. After the press cycle, the stop is manually pulled outward, permitting the strip to advance the next stop. When released, the stop in effect becomes a pusher.

Trigger stoppers: For the fast productions mostly trigger stopper are used. They are also called as automatic stoppers. They are of two types 1. Front acting & 2. Side acting. In general, the working mechanism is same in both but one is mounted in the front end of the tool & other one at the side of the tool. The lever shaped trigger stop fits freely in the slot milled in the guide plate. One sidewall of the slot is provided with the taper angle, which gives the necessary movement to the trigger. An inclined set spring set at the other end of the trigger.

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CHAPTER -11 STRIPPERS

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STRIPPERS: The main function of the stripper is to strip the stock material off the punches after each stroke. In addition the stripper may act as a guide for the punches, as well as hold the strip flat and tight, while the strip is being worked on.

STRIPPER CATEGORIES AND TYPES: Stripper can be classified into 2 groups,  Fixed stripper,  Traveling stripper. Fixed stripper is easier to make than the traveling strippers. Fewer components are required in the construction of fixed strippers when compared to the equivalent traveling stripper. Therefore the fixed strippers are economically desirable as far as the die construction cost is concerned, mechanically, fixed stripper are solid in performance. This is an advantage where the stripping force is necessary. But, In some situations a fixed stripper may be impracticable. i.e. 1. When it is necessary to clamp the strip in addition to it’s stripping function. 2. When it is necessary to keep the punches engaged in the stripper during the entire press cycle. 3. A traveling stripper permits the operator to observe the work while the tool is operating.

Box Stripper: A typical box pin stripper is shown The tunnel dimensions are as fallows The tunnel width X can be determined as X=W+F W F

= Stock strip width at maximum tolerance. = Desired horizontal feeding distance.

For the average progressive die, assuming there are no other specific requirement, Clearance F may be 0.3 per 100mm tunnel length. ICDP TECHNICAL TRAINING CENTER

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Tunnel height H=S+G, G is the required vertical feeding clearance, G may be= 0.5s for flat work cutting dies with short tunnel length. Or it may be several times larger than the ‘S’

s

H

G

W

X

HOOK STRIPPER:

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Hook pins are made from cold drawn steel. The function is as shown in

hook pin

figure.

PRESSURE PAD STRIPPERS: Pressure pad strippers hold the material during cutting and strips it from the punch in the upward stroke. They may be actuated by the spring, rubber or hydraulically.

SPRING STRIPPERS: Spring stripper is a pressure pad stripper. They are used when it is necessary or desirable to hold the stock material flat (or very nearly flat), or to provide better visibility and access when the tool is mounted on the press. ICDP TECHNICAL TRAINING CENTER

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Inverted dies have stationary punches & therefore require traveling pressure pad strippers. Pressure pad strippers are also used for push back applications.

Stripper Plate

CLAMPING SPRING STRIPPERS: They are true pressure pads. They bear against the stock material, applying pressure to it. The material is clamped between stripper and die. Clearance must be large enough to ensure clamping.

Spring Stripper Die NON CLAMPING SPRING STRIPPER: These kinds of strippers are used when the material is not to be clamped. There will be clearance between the stock strip and the strip for obtaining good flatness, clearance within 0.05 to 0.4mm is recommended. The pilot registers the stock strip. In most cases, spring strippers are an effective device for producing good flat piece parts.

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It is often necessary to employ pilots in conjunction with spring stripper. If the stripper is the clamping stripper, it cannot be used to strip the pilot completely, this is because the pilot should register the stock strip before the strip contact the material. To strip the material from the pilot, the guide rails are used. If the pilots however are too far away from the hooking action of the guide rail legs, the stock material may pull up, bowing the strip even if the stock material doesn’t pull out of the rail confinement, there will be bowing action. It can causes the excessive pilot wear, seriously deteriorate the quality of the pierced opening and adversely affect the ultimate flatness of the piece part. When the pilot position too far away, then non-clamping strippers are applied, so that the stripper strips the stock strip also from the pilot.

COMPENSATING WASHER: When cutting punches are sharpened they become shorter. In many applications, the springs are compressed a little more and are not always desirable. A practical method to eliminate this is to install the cylindrical washer as shown in the figure. Each time the punches are sharpened the washer is reduced for the amount

SPRING AROUND THE STRIPPER BOLTS: Such a construction is shown figure. This construction has desirable features and undesirable features

Desirable features are  The bolt retains the stripper at center of spring pressure

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 The bolt acts to confine the spring in location so that the double spring pocket can be eliminated

Undesirable features are  The assembly needs considerable vertical space often than available

STRIPPER BOLT SUSPENSION: Bolt hole B is drilled larger than shoulder diameter A. (clearance hole is provided). When the die fully closed and the stripper bolt is at its maximum travel position E must be sufficient to assure adequate punch grinding life (E is about 6mm). Normally, a space G Should exists between the end of the stripper bolt and the stripper (G = 0.5mm). To ensure stripping a spring stripper should over travel a distance S, when the stripper is at its extended position. The over travel is between 0.1 for every light work to 1.5 for heavy work. In any case each time the punch is sharpened, the over travel increases. This should be corrected from time to time by inserting the compensator under striper bolt head as shone in figure.

STRIPPER BOLT SUSPENSION:

STRIPPER BOLT SPRING

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GUIDE STRIPPERS: Two typical stripper guide pins arrangements are shown in figure. The drawings are self-explanatory.

STRIPPING FORCE: Stripping force for most operations range from 10 to 20% of the cutting force. If the die has more than one punch the stripping force for that die is the sum of stripping force required for each punch.

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Stripping Force for the Blanking and Piercing: The following factor affects stripping force, 1. Stock material: Material, which has high friction, value and material, which tend to cling, are more difficult to strip. 2. Surface condition of sidewalls: A punch, which has smooth finish on its side, wall strip more easily than punch, which is not as smooth. 3. Area of the stock material to be stripped: Figure shows two-piece parts one larger than other. The thickness and the type of stock material. The pierced opening is the same size in both parts. The cutting is the same for both the parts. But the larger piece part requires the greater stripping effort. The larger area of the stock material surrounding the punch is stronger and causes the material to cling more tightly to the punches.

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CHAPTER -12 GAUGES

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GAUGES: Gauges must be considered in the design of press tool because theses component position the strip longitudinally in its travel through the die. In second operation dies, gauges locate the previously blanked or formed part for further processing operations. Design consideration includes: Material choice: Finished tool steel is used for gauges in first class die. Cold rolled steel should be used only when low production n requirements exists. Adequate thickness: The back gauge and the front spacer must be thick enough to avoid binding of the strip between stripper plate and die block. Good doweling practice: Since the gauges locate the strip they should always be doweled in position.

Back Gauge Strip Support

Front Gauge

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Accuracy of location surfaces. The gauging surfaces, which actually bear against the strip or part, should be ground, and so marked on the die drawing.

BACK GAUGE AND FRONT GAUGE: In passing through at two station piece and blank die the strip is positioned against back gauge by the operator. Strips support helps to align the bottom of the strip with the top surface of the die block to prevent binding. Back gauge is the actual guiding member and the function of the front gauge is only to provide an approximately gauging. The required dimensional relations are mentioned from the back gauge to the die opening.

BULGE CLEARENCE: Thick and soft material tends to bulge sidewise as soon as blanking operation is performed. This makes it quite difficult to feed as well as to gauge the strip further unless a bulge clearance is provided in such stations. Bulge clearance is provided usually in the back gauge only.

SIZE OF BACK GAUGE AND FRONT GAUGE:

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The gauge should be thick enough to avoid binding of the strip between the stripper and the die block. The recommended thickness of 3mm for sheet up to 1.5 mm and strip thickness +1.5 mm for heavier (more than 1.5mm) strip is found to be satisfactory if automatic stops are employed in the tool. The space between back gauge and the front spacer is made to strip width +0.5mm if roll feeding is used and strip thickness +1mm for hand feed.

EXTENDED BACK GAUGE: For easier gauging usually the gauge is extended beyond the die on the feeding side. An amount equal to 2and ½ times the strip width for hand feeding and equal to the strip width for roll feeding is sufficient.

STRIP SUPPORT: While hands feeding the strip to reduce fatigue to the operator a strip support should be provided. The strip support should be made wider and brought closer to the die block to provide better support and guidance. Roll feed doesn’t require strip support.

PUSHERS: These are provided to keep the strip firm against the back gauge during its travel through the tool. Spring loaded pushers are often employed to achieve this.

EASY AND QUICK LOADING AND UNLOADING: Nest gauges should be facilitated fast and easy loading and unloading of the components. The main factors, which decide this, are good visibility and ICDP TECHNICAL TRAINING CENTER

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accessibility to the nest. Adequate lead angle should be provided around the nesting profile for easy loading. Unloading more difficult than loading. For low production tools simple pick of slots machined in the nest would be sufficient to allow the operator to manually pick the piece out of the nest. Ejection of piece parts out of the nest by means of lever-operated ejectors is another solution. If the piece part is thin it can be ejected from the nest by means of compressed air jets.

NESTING GAUGES: Nest gauges are used in secondary operation tool or whenever limit stock is fed in to the tool. There are three conditions to be met to achieve the best result.

ACCURACY: The fit between the gauge part and the gauge should be perfect. For gauging purpose it is not necessary of the nest to fit entire contour of the piece part. All that is required to provide sufficient number of locating points. The number of locating points required for certain nest depends upon the size and the shape of the piece part. A minimum of three part for circular and angular shape and 4 points for other shapes are required.

FOOL PROOFING Any possibility of the piece part being loaded in the incorrect manner by the operator should be prevented by the nest. Foolproof pins could easily accomplish this as shown in the fig.

TYPES OF NEST GAUGES PIN TYPE NEST GAAUGES: The simplest form of nest gauges comprises of plains or headed cylindrical pins arranged in such way as to provide enough number o f locating points for the piece part. These hardened and ground pins are press fritted in to the die block. The arrangement of the pins should be such that a total clearance of at least 0.03mm results between them. The upper end of the pins must be doweled for easy loading and unloading. The opposing member should have relief holes drilled in to it to receive these pins. Inverted tools, the nest pins are fitted in to the traveling stripper and the relief holes are to be drilled in the die block. If these holes happened to appear in the near vicinity of the die opening the die will be weekend in such case the nest pins should be of the spring loaded type and made to disappear below the face of the stripper, upon contact with the die block. It is obvious

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that disappearing nest pins are less accurate and should be used only if inevitable

PLATE TYPE NEST GAUGE: This type nest is a plate in to which an opening is machined to receive the piece part. As mentioned already the opening need not fit the entire contour of the piece part. Plate type nest could of sectional constructions for easiness in machining and hardening. Plate type nest gauges should be perfectly

screwed and dowelled in position. As a general rule, all gauging elements should be made out of tool steels and hardened to 48-52 HRC.

NESTING IN DIE SET: Simplest nesting method is to fit the section in to the pocket that is milled directly in the die set. The die section should be fit tightly into the pocket but the assembly pressure should be so great as to distort the die set. It should be noted that nesting does not eliminate the need for the use of screw.

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Liners made out of hardened tool steel facilitate easy and accurate assembly of sectional dies into the pocket. 1. Liners expedite accurate assembly of the sections. Liners being last to be fitted in the die assembly permit 2. Liners eliminate the possible shearing of the walls of pocket 3. Adjustments to made for the discrepancies in size and position of the pocket. The section free in the pocket. Therefore, knock out holes should be provided in the nest or pocket directly under the liners as shown.

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CHAPTER -13 PILOTS

PILOTS: Pilots play a vital role in the operation on multiple-station dies, and many press lines troubles can be traced to their faulty design. In applying pilots the following factors should always be considered:

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1. They must be strong enough so repeated shock will not cause fracture. 2. Slender pilots must be sufficiently guided and supported to prevent bending, which can cause faulty strip positioning. 3. Provision should be made for quick and easy removal of he pilots for punch sharpening.

PURPOSE OF PILOT: The pilot positions the stock strip relation with die opening. This is termed as registering the stock strip in the required position. Usually the stock strip is over fed than the actual pitch length. The max over feeding of the strip is about 0.1mm. When the press is tripped the pilot comes down and engages the pierced hole thus dragging the strip back into the registry position stock strip is fed by mechanical means pilot action is the same principal. However, the direction in which the feeding is qualified is normally reversed. Instead of being over feed the stock is under fed.

PILOT SIZE: The accuracy with which the work can be registered depends upon the proper location and the diameter of pilot. The following will indicate the pilot diameter; For an average work Ø of pilot

= (Ø of hole to be piloted-0.05 to 0.1mm)

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For close work Ø of pilot For an accurate work Ø of pilot

= (Ø of hole to be piloted-0.03to 0.05mm) = (Ø of hole to be piloted – 0.01to 0.2mm)

However the thick stock materials & the stock materials like aluminum and copper need often bigger tolerances between the pilot and the pierced hole.

PILOT LENGTH: Registering the strip must be complete before the cutting punches come and engage the strip. Therefore the pilot must be longer than the punches. If the pilots are too short they cannot perform their function This creates serious consequences ranging from spoiled work to damaged pilots. Care must be taken while setting the stroke of the press so throes pilots clear the stock strip without obstructing the future feeding of the strip in any case the piloting length should be extended beyond the punch face equal to the sheet thickness.

PILOT OPENING IN THE DIE: The opening of the pilot in the die should not be too large. If so, the stock strip may tend to draw into the opening. In case of the thin material pilot may nit displace the material into registry position but may instead draw the material on one side therefore it is advisable to have the opening Ø as pilot dia+double clearance. Weaker pilots are guided in the stripper.

PILOT OPENING IN DIE SHOE: Through hole is provided in the die shoe for the pilot so that slugs produced during miss feed are cleared. It also helps in clearing the accumulated burrs dislodged from the pierced hole.  Step headed shank less  Step head shank type  Step head pyramid type  Bevelled head  Headless whistle notched

PILOT NOSE PROFILE: The main function of the pilot nose profile is to allow smooth riding of the pilot into the stock strip. The most commonly used nose profiles are described below:

BULLET NOSE: The most common pilot nose profile is bullet nose. The bullet shape is formed by radius ‘R’, which is equal to piloting diameter. For piloting in holes less than 6mm the length of radius R can be increased to reduce the lateral force during piloting. Bullet nose is strong simple to make and smooth in action.

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The other three commonly used pilot nose profiles are: 1.45º conical stub nose 2.30º conical stub nose 3.16º angular long nose

45º CONICAL STUB NOSE PILOT: The profile is used when a shorter nose profile is desired. 45º cone increased the relative lateral forces hence not recommended for delicate pilots used for piloting thin soft material.

30º CONICAL STUB NOSE PROFILE: This is same as the above pilot except the nose angle is30º this is a compromise between the 45º stub nose pilot and the conventional bullet nose

15º ANGULAR NOSE: This small angle provides good mechanical advantages. they are used for small pilots and for thin materials.

TYPES OF PILOTS: RETRACTABLE PILOTS: In many occasions especially during hand feeding misfeeding occurs due to over shooting of the stock strip over the stoppers. This creates the problem when a tool is having pilot s in it. Pilots may break or buckle obstructing smooth function of the tool. Generally retractable pilots are spring loaded in such away that they will be lifted upwards when they come in contact with the un pierced area during press descends. Care should be taken while selecting spring so that springs allow more telescopic movement of the pilot.

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REMOVABLE TYPE PILOTS: Pilots break very often due to misfeeding of the stock strip. Much consideration must be given for changing quickly the broken pilots, preventing greater time loss during production. Removable type of pilots can over come this difficulty. These pilot inserted through top bolster into the punch holder and fastened with a back up screw as shown in fig:

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METHODS OF PILOTING: Direct piloting: It consists of piloting in holes pierced in that area of the strip, which will become the blank. All pilots decided so for have been direct pilot which are retained in the blanking punch.

Indirect piloting: Indirect piloting consist of piercing hole in the scrap area of the strip and locating in these holes at subsequent operations direct piloting is the preferred

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method but certain blank condition require explained.

indirect piloting, as will be

PART CONDITION: There

are

seven

conditions

that

required

in

indirect

Close tolerance on hole: Pilots can enlarge holes in pulling a heavy strip to position.

Holes too small: Frail pilots can break or deflect in operation.

Holes too close to edge of the blank: Distortion can occur in blank because of enlargement of holes

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piloting.

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Holes in weak area: Piloting in projecting tabs is impractical because they may deflect before the strip is pulled to position.

Holes placed too closely: Piloting in closely placed hole does not provide an accurate relation between two holes and edge of the blank.

Blank without holes: Piloting is done in the scrap area wherever the blank does not contain holes.

Projection in hole: Whenever the hole in the blank

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contains weak projection, which could be bent down by the pilot, indirect piloting should be selected.

CHAPTER -14 SIDE CUTTERS

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SIDE CUTTERS: Side cutter is an accurate method of stopping arrangement used mainly for thinner strips where it is difficult to accommodate the other type of stoppers. A side cutter is a trimming punch, which trims the side of the stock material, providing a shoulder. This shoulder is stopped against a hardened insert provided in the spacer. In small tools the spacer may be fully hardened to avoid the insert. The width of the side cutter is equal to the pitch. The allowance for side cutting depends upon the type and thickness of the stock material. Table gives the allowance for side cutting for different materials. No

Materials

sheet thick

C

1 2 3

Steel Brass Bronze

4 5 6 7 8 9

Copper Zinc Aluminium Leather paper Fibers Card board

0.2-0.4 0.2-0.6 1.0-1.5 1.5 0.2-0.5 0.5-0.1 1-1.5 0.4 0.4-1 1

2.5 1.5 2.5 1.5xS 3 2 2.5 5 4 3xS

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The size of the side cutter will be more than the pitch by 0.05-0.1 for the purpose of registry the strip with the pilot. But in case of tools without pilot, the side cutter is made equal to the pitch. The stop position and registry position will be the same. Due to the unbalanced cutting force cutting force acting on the side cutter, the side cutters are provided with heels. The undercut provided on thee side cutter eliminates the difficulties of feeding due to thorn formation. Thorns are small projection, which occurs at the side of the strips due to the punch wear out. In side cutting there is a tendency of the slugs being coming up with the punch, causing difficulties in further punching. Slug pushers are used to avoid this. A standard side cutter shape is shown in the fig.

THE ADVANTAGES OF SIDE CUTTER: 1. It is a safer method than stop pin 2. Avoids the danger of the deformation of margins of thinner strips by the stop pins, when pressed against it. 3. Preferred for small punching where it could be difficult to employ other types of stops. 4. It is economical and avoids complications in tools where numbers of stages are more. 5. Pilots can be avoided for punching components with moderate accuracy.

SIDE CUTTER: The side cutter is installed in the first position of the tool.this eliminates extra stops and simplifies both construction and operation of the tool. Usually the side cutter is located along the front edge of stock strip, because of the fact that the strip are usually meant to gauge of the tool Two side cutters, one on each side is used where the number of stages are more or if pitch is less.

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Side cutter

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CHAPTER -15 EJECTORS & SHEDDERS ICDP TECHNICAL TRAINING CENTER

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EJECTORS AND SHEDDERS: In conventional drop through type blanking tools, the punch forces the blanking to the die. The blank will be retain within the die cavity till the subsequent blanks push it pass the land. Then it falls down through the opening in the die shoe and subsequently through the opening in the press bed.

Shedders and ejectors are used when it is not possible to remove the blanks in the conventional method due to the following reasons. 1. Size of the blank does not allow it to conveniently pass through the opening in the press bed. 2. Counter of the blank is such that it tends to stick and get distorted during its travel through the die cavity. 3. Opening in the press bed fitted with die cushion, which will interfere with the piece part disposal. 4. Close tolerance specified for the flatness of the blank. 5. Tools of Inverted nature.

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EJECTORS: In the conventional position, die is the lower member of the tool. If the expulsion of the blank is achieved by forcing it upwards, the action is known as “ejection”. The element of the tool, which ejects the blank, is called as “ejector”.  Ejectors may be actuated by compression springs, rubber, pneumatic devices or hydraulic devices.  Ejectors if used with spring stripper always return the blank into the spring due to the simultaneous stripping and ejecting action.  In some progressive tools, the blanking station is provided with an ejector to return the blank into the strip to be carried forward to the next station for further operations, known as the cut and carry method.

SHEDDERS: Another way to accomplish the expulsion of the blank from the die cavity is by making use of the knock out mechanism on the press. For this purpose, the tool should be of the inverted design. In inverted tools, Die becomes the upper member of the tool, being clamped to the press ram. The expulsion of the blank is achieved by forcing them downwards. This action is generally known as “shedding” and the element of the tool, which sheds the blanks, is known as the “shedder”.

COMPRESSION SHEDDERS: Shedders hacked up by compression springs; hard rubbers or disc springs called compression shedders. Such shedders always tend to return the blank in to the strip if employed with compression type traveling stripper. Compression shedders could be used to great advantage to produce flatter and neatly sheared blanks. They are also used if the blanks are too large to allow the in corporation of an efficient positive knock out system.

SHEDDER PINS: The stock material is usually coated with rust preventive solution. It is obvious that any liquid or oil deposit left on the stock material will cause the blank to stick to the face of the shedder. Spring loaded shedding pins are employed to overcome this problem. Even absolutely clean and dry stock material tends to adhere to the shedders, due to the atmosphere pressure. Therefore regardless of the conditions of the stock, the illustration of shedding has to be considered to be absolutely necessary. Shedding pins will be more effective if applied to one side of shedder face rather than in the center. ICDP TECHNICAL TRAINING CENTER

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KNOCKOUTS: Positive knockouts are classified in to two groups  Direct knockouts  Indirect knockouts

DIRECT KNOCKOUT: In a knock out system if the knock out rod is directly in contact with the shedder the system is known as direct knock out system.

INDIRECT KNOCKOUT: As the passage of the knockout rod is through the shank, any punch which comes in line with or near to the center line of the shank will obstruct the knockout rod from coming in direct contact with the shedder. In such cases an indirect knock out system should be employed. In addition to the shedder and the knock out rod, it consists of a knock out plate and transfer pins as shown in the fig. The location and number of transfer pins depend on the size and shape of the blank.

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CHAPTER -16 ICDP TECHNICAL TRAINING CENTER

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FASTENERS

FASTENERS: The subject of fastener is an important one because these components are applied so frequently and employed in such large quantity. Although small, they perform important function. In design of tool and dies, fasteners are often the weakest link in the tool and, if they are not selected and applied correctly, they can become cause of the entire tool and die.

DIE FASTNERS: In this exploded view of typical die for producing blank from the strip, all fasteners have been shown removed from the components, which they locate and hold. From this drawing it is apparent that fasteners, all though small individually, from the substantial portion of the entire tool when taken together.

TYPES OF FASTNERS

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These are the types of fasteners most commonly used in die construction. They are 1. 2. 3. 4. 5. 6. 7. 8.

Socket cap screw Counter sunk screw Grub screw or set screw Eyebolt Rivets Cotter pins Dowels Removable dowels

Less frequently employed type include the following:Hexagon nuts, washers, studs, rivets, and wood screw.

SOCKET HEAD CAP SCREW: These are generally used to fasten the plate elements of the press tool like punch holder assembly to the die top and die stripper assembly to the die sleeve.

COUNTER SUNK SCREW: These are used to fasten elements like nest gauges, spacers, plate stoppers etc.

GRUB SCREW OR SET SCREW: These are used to fasten parts, which are to be confined within a hole, like springs etc.

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EYEBOLTS: Eyebolts are used for lifting heavy die sets or mould housings. It is also called as carrier blots.

NON-THREADED FASTENERS: This group includes the elements like rivets and cotter pins.

RIVETS: Rivets are generally used to fasten support plate of an extension table in press tool. They are made of MS, aluminium, copper, or brass.

COTTER PIN: These are used to prevent the loose parts from coming out of holes.

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DOWEL: Dowel holds parts in perfect related alignment by absorbing side pressure and lateral thrust. also; they facilitate quick disassembly of components and reassembly in their exact former relationship.

REMOVABLE DOWELS: One type of removable dowel is illustrated these dowel are used in blind application

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CHAPTER -17 SHANK & SHANK POINT LOCATION

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Shank is an element of the press tool and acts as connecting link from tool to the press platen. Five ways of mounting the shank. By Riveting By Press fitting By means of threading By making it as integral part of top plate By making flange fastening

1

2

3

4 Self-Aligning Type Shank:

PRESS RAM

FEMALE COUPLE

MALE COUPLE

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Location of a Shank on a Tool: Balancing of the punches is the most important aspect during punching operation. Un balanced force on the tool may lead to undue wear on punch and die as well as pillars. The resultant forces of all cutting forces acting on many punches should pass through the shank centre. The position of the resultant forces of all partially cutting forces can be found by the following methods By calculation. By polygon system (graphical)

By Calculation:

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By Polygon System: Polygon system: To find the line of the action of resultant then follow the reference below: 1. Draw the forces to scale in a straight line. 2. Draw the arrowheads at the ending points of each force as shown. 3. Draw two more lines at 450 angle from the starting and finishing points of the total length of the forces so as to form an equilateral triangle and call the intersecting point as pole. 4. Draw the lines from each arrowhead joining the pole point and call them as pole beams. 5. Draw the forces to scale at the given distance. 6. Draw the lines parallel to the pole beams, cutting force line graphically. 7. The line of action of the action of the resultant goes through that point where those two- pole beams intersect.

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CHAPTER -18 DIE SETS

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DIE SET: The following elements are considered before selecting the die set. 1. Make or manufacture, 2. Type, 3. Size, 4. Material, 5. Thickness of the die holder, 6. Type & length of the bushing, 7. Thickness of the punch holder, 8. Length of guidepost, 9. Shank diameter, 10. Grade of precision.

DIE SET COMPONENTS: These are, A. Top plate. B. Guide bushing. C. Guide pillar. D. Bottom plate.

•TOP

PLATE:

The upper working member of the die set is called the top plate. The upper surface of the top plate is bears against the under side of the press ram. Punch components are fastened to the lower finished surface. The top plate is generally made out of MS.

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PUNCH SHANK: The punch shank projects above the top plate and it align the centre the die with the centre line of press. In operation the shank is securely clamp to the press ram and it drives the punch portion of the die, rising and lowering the die. For semi steel die sets, the punch shank is cast integrally with the body of the top plate and it is then machined. To supplement their holding power of the shank, cap screws are often inserted upward to engage tapped in the press ram.

SHANK

BOTTOM PLATE: The bottom plate is the lower working member of the die sets. Usually the bottom plate is made thicker than the top plate to compensate the weakening effect of the slug and blank holes, which must be machined through it. Generally it is made up of MS.

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GUIDE PILLAR: Guide pillars are precision-ground pins which are press fitted into accurately bored holes in the bottom plate. They aligns punch & die components with the high degree of accuracy. Guide pillars are used for precision die sets are chromium plated to provide high degree of accuracy of resistance to wear. The addition of chromium reduces wear up to 50%. They are specified at least ¼ inch shorter than the shut height.

REMOVABLE GUIDE PILLAR: Pillars may be removed for die sharpening, specially in large dies. In first kind of removable pillar have an axial hole machined through them are tapered at one end to engage a taper pin. In second type of removable pillar, the taper pin is advanced for locking by means of a socket cap screw. In third type of removable pillar a socket head cap screw is engaged In retaining cap to clamp the pillar to the bushing.

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NON STICKING GUIDE PILLARS: In initial engagement the jamming of top plate and bottom plate is problem to avoid this kind of problem non sticking pillars are used. Sticking occurs until the bushings have engaged the pillars sufficiently for complete alignment.

GUIDE BUSHINGS: Guide bushings are engaged with the guide pillars for aligning the top plate with the bottom plate. Most bushings are made up of tool steel they are also available in bronze. There are two types: 1. 2.

Plain bushing are simple sleeves, pressed into the top plate. Shouldered bushings are turned down at one end and they are

Pressed into the top plate against the shoulder thus formed.

BALL BEARING DIE SETS:

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Some die sets are provided with ball bearing. Guide pillars are pressed into the top plate and thy engage linear ball bearings. Lubrication is provided by cup greasing and this is sufficient for entire run. Ball bearings should take more place than conventional guiding and they reduce die space a small extend.

PILLAR ARRANGEMENT: Ways of positioning the pillars in a die set. A. Two pillars are applied at the back of the die sets. This is most commonly used two pillar arrangement. B. Pillars are applied at the sides force feeding strip from front to back. C. The pillars are arranged diagonally. D. Four pillars are used the foregoing are standard pillar arrangement as listed in die set catalogue.

TWO PILLAR DIE SETS:

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Most tools are provided with two guide pillars applied at the back of the die set because this type gives maximum visibility and accessibility since it is open on three sides. There are three most distinct types of back pillar die sets. 1. Regular: This type is employed with average proportions. 2. Long: This type is used for dies, which are long and narrow. 3. Reverse: This type is used for dies, which are relatively longer in measurement from front to back than their measurement from side to side.

THREE PILAR DIE SETS: It provides increased stability for unbalanced cuts. These are incorporated only in square or rectangular steel sets. For hand feeding, the extra pillar is applied as shone in fig A, at the front. When the feed is automatic it is centered as shown in fig B.

FOUR PILLAR DIE SET: These die sets are selected for retaining round disc as drawing tools, trimming tools, and the like. There are two back pillar style as shown in figure

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A and center pillar style as shone in fig B are available in diameters ranging from 4 to 48 inches.

LONG NARROW DIE SETS: This type of die set is used to retain tools for cutting, bending and forming of long, narrow parts. They are back pillars sets, and they are available with either two or three pillars. Two pillars are specified for sets ranging from 12 to 72 inches in length and three pillars for sets ranging from 84 to 240 inches.

ROUND DIE SETS: Three die sets are selected for retaining round dies such as drawing tools, trimming dies, and the like. There are two back style pillar as shown in fig A and center pillar style as shown in fig B are available in diameters ranging from 4-48 inches. ICDP TECHNICAL TRAINING CENTER

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CENTER POST DIE SET: These die sets are used for secondary operation work such as coining, piercing and left & right hand. Parts of one hand may be conveniently loaded from one side. When the other hand is to be run the die set is turned around 180ºin the press for ease in loading.

FOOL PROOFING: Center pillar and diagonal pillar die set are provided with different diameter pillars, dimension A and B Thus, the top plate cannot be reversed on the bottom plate.

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FLOATING –ADAPTER DIES: In blanking and piercing thin stock and for shaving and broaching operations very little clearance. Can be allowed between the punch and die members. Long should be used with these die sets because; in operation the guide pillar must always be guided within them.

LARGE DIE SET: Large die sets are made of plate. They have ground surfaces and are square or rectangular in shape. Three pillars arrangements are shown in fig.

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RECOMMENDED THICKNESS: The thickness is illustrated in this example. E.g. If the die set area for a particular die measures 30 by 20 inches and the force in tons is less than 30, the values of 1 x 3/4 th inches for C and 2 inches for D would be selected. However, if the force is in tons were 60, we would use the values opposite pressure in tons of 50-70,and the value for C would be 2½ inches and for D3 inches.

HEAVY DUTY DIE SETS: The heavy duty die sets are particularly used for long runs. They are assembled with removable boss bushings to provide adequate alignment between top & bottom plate.

SPECIAL DIE SETS: These are designed for specific jobs. In this type ribs are provided at high stressed areas or sections. Specific rules cannot be given because of variety of conditions encountered.

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CHAPTER -19 COMPOUND TOOL

Compound Tool: A common characteristic of compound dies is the inverted construction. The blanking die is on the upper die shoe and blanking die on the lower half. The pierced slugs pass through the lower die shoe. Compound tools are usually used for manufacturing pierced blanks of close dimensional tolerances. The sheet material is lifted off the blanking punch by spring actuated stripper, which provides guide to feed the material. The blank remains in the die that is removed by spring stripper or by knock out. Blank holder is used when blanking thin and springy material and accuracy and flatness is required. Ejection of the blank from the die by springs

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or positive knock out makes angular clearance unnecessary

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Blank, Pierce and Notching Dies: For producing gray fiber spool heads, a sheet of 2.39mm stock is fed and is located by finger stopper. The blanking punch is mounted on the lower die shoe. 01 is the projection to cut the notches on the periphery of the blank is inserts in the die. 02are the key holes shaped in the die. Circular portions having tapped holes are used in securing it to the die plate. The knockout 03 is made in two pieces to facilitate the construction o guide the four punches 04. The piercing punches for the center hole are guided by a knock out bushing. The round & rectangular punches are secured in the die by same retainer 05. The knockout is actuated by positive knockout bar in the press through shedder pins. The blanking punch die 06 is made in two sections. The outer profile of the outer section is same as that of the blank. The inner profile of this section is circular with notches and small perforation. The inner section is circular with flats to serve as inner edge of the die for piercing punches

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Trim and Pierce Dies: Most drawn shells are trimmed. This type of dies piercing and trimming of edges of previously drawn. Shells can be trimmed as shown in fig A. After trimming if the shell is carried up by upper die then it is stripped from the die and punches by knockout. An inverted die for trimming and piercing shallow shells is shown in fig B

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Shave and Pierce Dies: A compound shave and pierce die shaves and pierces holes of a component. A knockout is provided to prevent the part from remaining in the die, stripper strips the part from the punch & shedder pin prevents the part adhering the knockout

Broach, Cutoff & Pierce Die: When the die is in operation the broach engages the work almost immediately at the start of press stroke. When the broach completed 2/3rd stroke the cutoff punch cuts the stock to its length. Broaches hold the work securely and locate the part securely so the piercing punches come into contact piercing the work in relation to the broached notches.

Inverted Die: In this type of die the arrangement of die and punch is reversed and the punch is mounted on the die shoe with the knockout pins and the combined pressure pad and the stripper. This type of die is known as inverted die.

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The inverted die has the advantages that the cutting edges are kept clear of chips by the operation of the stripper and ejector.

Shedders and Knockouts: Positive Shedders: Positives shedder is shedder, which is not actuated by springs or other compression media. Fig below illustrates the basic positive shedder actuated by means of a knockout rod. This type of assembly is used for inverted type dies. The flanges are an integral part of the shedder; act as keepers, retaining the shedders within the die cavity.

Fig depicts the shedder relationships at the bottom of the press stroke E T A

= punch entry distance. = sheet thickness. = the upward distance of the shedder is equal to die opening

Therefore A = E +T Gap D should be minimum of 2½ T or 3 mm, which ever is greater. It should accumulate at least 2 extra piece parts with in the die cavity.

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The assembly fig shown is more sophisticated because of the nature of shedder counter. It is essential for distributing the knockout force with respect to shedder counter. The gap D can be derived by association from fig B In fig B D=E+T+A+ 2½ T where

E T

minimum = punch entry distance =stock material thickness.

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In this fig E, the transfer pins are assembled by pinning them in the pin plate. In view A the pin plate and knockout rod are also fitted together and secured by pining. This method is for light duty, where the knockout forces are evenly distributed and balanced in relation to the shedder counter. The knockout assembly shown in view B is stringer, since knockout rod is welded to pin plate.

In fig F laminated construction is used. The shedder in fig F is for compound, pierce & blank die. The flange is a separate ring, secured to the shedder body by screws. The size and counter make laminated construction possible. Its size permits installation of the screws, adequate in size and sufficient in number. In this fig G the knockout rod is pined to the assembly to the shedder. A collar ring is assembled to the knockout rod by means of a cross pin. The collar acts as a stopper limiting the protrusion distance of the shedder.

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In this fig the knockout shaft is threaded in the shedder and secured by a lock nut. Two lock nut are jam tightened on the shaft, stopping the shedder travel.

In fig I the stripper strips either the work piece or the stock material from the punch. A spider type bridge plate 02 is shown. It operates within a suitably countered recess, which is milled in the punch holder. In this case the transfer pin is a threaded stud secured with lock nuts to maintain the spacing between the stripper 04 and spider.

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A knockout arrangement for large work pieces is shown in fig J where it is applied to a positive knock off stripper. The center distance between the knockout rods must be met to suite the press

In fig K shedding pin is located at the center of the shedder. There is no edge advantage for the shedding pin. This error can result in failure in shedding pin. Length L is too short it does not provide grinding life on the shedder

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The basic spring actuated shedder is shown in fig L. This is a flanged shedder having the proportions indicated by H and W. H= 2W minimum For light gauge materials two or more shedding pins should be installed in the shedder. The springs must be strong. If they are, or if the shedding pin location are not balanced the blank may be pushed through the stock strip L

In fig M the shedder actuating spring is contained in the punch holder shank. The spring applies pressure to the plunger 02 and transfer pins 03 transmit the spring pressure to the shedder 04.

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CHAPTER -20 PROGRESSIVE TOOL

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PROGRESSIVE TOOL: In a progressive tool strip is moved in stages from station to station. Different operations are performed on it at each station except idle stage. A complete strip is removed at the final stage. Progressive tool may be considered as series of tools placed side by side with the strip passing through each successively. Before designing the tool the piece part may be studied carefully. This is to plan the operation to be carried out in different stations. For this process strip lay out is made. The strip lay out carries the following information. 1. 2. 3. 4. 5.

Feed direction. Pitch maintained. Position of stopper. Width of the strip. Scrap bridge.

The method employed in laying out the strip influences the economic success. The strip lay out is such that maximum area of strip is utilized for the production of the stamping. The tool shown in figure the finish part is produced through three stations. The strip is stopped at the first station by the auxiliary stopper, and 2 holes are pierced. In second station the pilot enters into the holes. In third station the piece part is blanked and pierced component is obtained.

STRIP LAYOUT FOR PROGRESIVE TOOLS: The following guidelines are used for designing the progressive tools.      

The solid margin around the die is 1.2 times the sheet thickness. Margin between 2 blanks, strip edges should be adequate. The shank should be loaded at the centre of the press. Scrap disposal should be provided. For precision pilots must be provided. The tonnage, table area, ram face area must bead equate.

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PILOTS: The blanking punch is fitted with pilot for accurate centralization of the piercing hole. Pilots can be spring loaded with a grub screw for adjusting the spring compression. Generally the trigger stopper of blanking tool with pilots is adjusted in such away that the strip is fed about 0.1mm more than the pitch. This allows the strip to move freely towards left as the pilot centralizes the pierced holes.

SCRAP DISPOSAL: In progressive tools the scrap is spread in a wider area. The shank must be placed in such a way that all the scrap falling through the die has got clear passage through the press table.

FOUR STAGE TOOL FOR WASHER: In this tool the strip fed is stopped by auxiliary stopper in first stage. In second stage a hole is pierced. IN next stage piloting is done, and in fourth stage the punch blank the strip & piece part is obtained. In this tool the punches should be spaced widely to provide healthy margin.

STAGE STOPS: When a new strip is taken, the first stage stop is pushed against the spring end is held against the stage stop to pierce one central hole in the strip. In second stage the strip is fed to second stage stop, which too must be held, pressed against the spring during the second stage feeding. Stage stopper stops the strip at each station of the tool.

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If the work piece has got no holes additional pilot holes can be provided to utilize the strip area. The additional holes are also provided in the case where the accuracy requirements are high, or the holes are very smaller in diameter. In such cases the pilots are provided on the scrap bridge or where the adequate space is available accept blanking area.

PILOTING

PIERCING

BLANKING AREA

FOUR STAGE TOOL WITH SIDE CUTTING STOP: Figure shows progressive tool for a pointer. Blanking punch for this component is rather difficult. It is more convenient to sacrifice the strip material and make sturdy punches and dies. The utilizes less than 1/3 rd of the raw material but runs trouble free.

SIDE CUTTING STOPS:

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The side cutting stop controls the pitch during feeding. The side cutting stop uses two punches that sheared the strip width accurately. The width of the side cutting stop is equal to the pitch. The side cutting punches have a step. The non-cutting rear side of the punch is made longer than the cutting side so that it engages with the die cut out before the punch commences cutting.

SIDE CUTTER

PRIMARY STRIP SECONDARY STRIP

PROGRESSIVE DIE DESIGN: Selection of progressive die: Following factors are considered for the selection of progressive die. 1. 2. 3. 4. 5.

Stock material thickness overall size of the die. Number of station. Total press tonnage. Quick change die and flexible manufacturing requirement exits. Press level and condition. Problems with worn bearings that can damage precision tooling

STRIP DEVELOPMENT FOR PROGRESSIVE DIES: The following strip development sequence is applicable. STEP1: Analyze the part.  Material thickness.  Size and critical dimension.  Form required.  Direction of metal grain. STEP2: Analyze the tooling required:  Production required per month.  Press availability.  Safety conditions. STEP3: Make dummy drawings. Tips for dummy drawing.  Show the complete part.  Show all necessary views.

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 Show over bend position if they are critical.  Show work lines and set up lines. STEP4: Make strip layout. STEP5: Draw plan view & draw plan of the punch over plan of the die. Make views and notes properly. STEP6: Problem areas:  Part lifter.  Part gages.  Pilot controls.  Pad travels.  Poor die steel conditions.  Will the die fit the press?  Will the die fit to production requirement?

CHAPTER -21 SHAVING

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SHAVING: Shaving is the secondary cutting operation. It is done by removing (shaving) a small amount of material from the previously cut edge. The purpose of shaving is 1. To improve the dimensional accuracy of the piece part. 2. To improve the cut edge characteristics of the piece part. 3. To improve the flatness of the piece part

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SHAVING CLEARANCE: The cutting clearance in shaving operation may be practically non-existent. It is common practice to use close fit between punch and die with minimum clearance possible. However in the case of larger shaving allowance a cutting clearance of 5% of shaving allowance will be acceptable. Size of blank for blanking Size of hole for piercing Out side Ǿ Inside Ǿ

= Ǿ40 + (2 x 0.14) =Ǿ10 – (2 x 0.14) = Ǿ40.28. = Ǿ9.72.

SHAVING ALLOWANCE: The width of the scrap web removed by shaving operation is the shave allowance. Shave allowance for steel A=C+0.04s. Or minimum =0.08. A1=C/2 or min 0.04. Shaving allowance for brass, copper, German silver etc. A= Ze or min 0.08. A1= C or minimum 0.04. C=Cutting clearance used for previous cutting operation (prior to shaving). A=Shave allowance for single shaving operation is employed.

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To improve the flatness of blank used to produce a better square cut edge, it is necessary to keep up side down in the shaving. The cutting action is opposite to that of the previous cutting and a more flat blank will be obtained. The striking force required for shaving operation is two to three times that of the stripping force required for the blanking, piercing. Example: A blank o outside diameter 40 and inside diameter 10 is to be shaved and outside in a single stage. Calculate the allowance and decide the component size for blanking. Material MS Thickness 2mm Tmax =60N/mm². Shaving allowance of M.S. In single stage A =C+0.04s. C = 0.005 x 2 x√360/10. =0.06/side. A =0.06 x 0.04 x2 =0.14/side.

CHAPTER -22 BENDING

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PRINCIPLES OF BENDING: The principle of bending involves.  

Selection of material of length equal to neutral fibre. Stressing it beyond elastic limit.

PLASTIC DEFORMATION DUE TO BENDING:

Factors influence the bend severity:   

Increasing the stock material thickness increases the severity. Increasing the bend angle increases the severity. Decreasing the bend radius increases the severity.

PLASTIC DEFORMATION DUE TO BENDING:

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PLASTIC DEFORMATION DUE TO BENDING:

Neutral Plane: The neutral plane is theoretical plane originated by inherent bending stresses. The Neutral plane accurs at a distance of 0.33 to 0.5 S, from the inner surface.

Bend Angle:

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The bend angle is the angle included between the two extreme positions of the bend radius. It originates at the bend axis.

BEND ELEMENTS: 3T 0.3

T 0.5

BEND AXIS

T

OUTER SURFACE

BEN DA REA BEN DA NG LE

R

90°

90 °

BEND LINES INNER SURFACE

BEND ALLOWANCE

CALCULATION FOR DEVOLOPED LENGTH: Formula for Calculating: Centre Fibre (C F) = (/180) x ri + S x;(ri + s/2) Neutral Fibre (N F) = ( /180) x [ri + (s/2 x ξ)] Lo = A + B + ( / 180) x [ri + (s/2 3 ξ)] Where, Lo = Original Length  Ri = Internal radius ξ = correction factor [to be chosen from graph] Note; If the value of (ri/s) exceeds r in the graph length of the strip should be calculated by using center fibre formula.

CALCULATION FOR DEVOLOPED LENGTH:

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CALCULATION OF MAXIMUM & MINIMUM RADIUS: The work piece if sy (yield point) In order to obtain a permanent set the stress which occurs on bending must be higher than yield point of the material. The above formula therefore gives the condition for Rmax. Radius which produces a permanent set.

CALCULATION OF MAXIMUM & MINIMUM RADIUS: The Rmax value of radius to which a particular material could be bent  b is just equal to  y according to the previous formula, y = SE  (2 ri + S) i.e, 2 Rmax. + S = (SE / y) – S Rmax = (SE  2y) – (S 2) In this case S/2 can be neglected comparing to the value of Rmax. Therefore, Rmax = SE / 2y

• • •

There is also a limit for bend radius on minimum side. If the bend radius compared with the thickness of the sheet is below certain, the stress in the outside fibre exceedes the ultimate tensile stress therefore rupture occurs. So, R min could be calculated by following formula. Rmin = C  S

CALCULATION OF MAXIMUM & MINIMUM RADIUS: Where, C =Constant referred to the following table. If ri is greater than the Rmax, no permanent deformation takes place. 1. Mild steel 2. Deep drawing tool 3. Construction steel

1.5 0.5 2.0

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4. Copper 5. German Silver 6. Brass 7. Aluminium hard 8. Aluminium pure 9. Aluminium half hard 10. Gun Metal 11. Stainless Steel 12. Brass

0.27 0.45 0.4 0.4 0.7 1.4 1.2 0.5 0.3

BENDING FORCE: FOR ‘V’ BENDING DIES Bending Force = [ C bs²   ]  W Where, C is a constant b = width s = sheet thickness W = width of the Die The value of constant ‘C’ can be takes from the graph or can be calculated using the formula, C = 1 +[ (4S)/W] [ The formula can be used up to W=20 S]

BENDING FORCE: FOR ‘U’ BENDING DIES Bending Force, Fb = [ C bs²   ]  W But instead of W, two times the Distance of point of contact of punch and die is considered. Thus, W= 2(R1 + cb + R2) Bending Force = [{ C bs²   }  W] [2(R1+ cb + R2)] Where, C= Constant B= width of the bend S= Sheet thickness = Ultimate tensile stress R1 = Die Radius Cb = Bending clearance ICDP TECHNICAL TRAINING CENTER R2 = Punch radius

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EFFECT OF GRAIN DIRECTION: 1. The most favorable condition exists when the axis of the bend is perpendicular to the grain direction. 2. The most reverse bends practical for the type of material can be made in this direction. 3. The least favorable condition exists when the axis of the bend is parallel to the grain direction. 4. The ability of the material to withstand bending strain as the angle ‘p’ approach 908.

EFFECT OF GRAIN DIRECTION:

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BEND RADIUS FOR ‘V’ DIES: Optimum size for bending radii depends upon the particular job. For average conditions bending radii of “0.5S” to “s” are generally practical. However, smooth material requires, proportionally larger bending radii than harder materials.

SPRING BACK: In bending operations the elastic limit of the metal in process is exceeded but is ultimate strength is not. Therefore some of the original elasticity of the stock material will be present on the material after bending operation is over. Because of this when the force (punch) is withdrawn the material on the compression side of the bend, tends to expand slightly and the material on the compression side of the bend tends to expand slightly and the material on the tension side is tends to contract. The combined result is that the work piece tends to resume its original shape. This causes the bend to spring open a small amount.

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HOW TO AVOID SPRING BACK? 4 METHODS to OVERCOME SPRING BACK in ‘V’BENDING DIES    

Over Bending Corner Setting Offset Punch Method Angular Punch Relief

1. Over bending IN ‘V’ BENDING: Over bending is the simplest way to correct spring back. It is done by making the punch angle (angle m) smaller by the required amount. For soft steel, Brass, aluminium or copper spring back For ¼ to ½ hard material For hardened material more

-

0 to 18 1 to 58 12 to

158

or

2. Corner Setting on ‘V’ Dies: This is the most effective way of avoiding the spring back. This is a method of eliminating spring back than making compensating allowances.

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3. Offset Punch Method: The face of the punch is offset in order to achieve coining penetration in the bend area. Offset dimensions should not be made unnecessarily deep, as this can weaken the piece part. An offset depth of 5% of ‘S’ is normally used.

4. Angular Punch Relief: An angular differential is provided between the included angle of the punch and the included angle of the die opening.

5 METHODS to OVERCOME SPRING BACK in ‘U’ BENDING DIES 1. 2. 3. 4. 5.

Convex pad method. Punch sidewall relief – Angular Punch sidewall relief – straight under cut. Over Bending Corner setting ICDP TECHNICAL TRAINING CENTER

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SPRING BACK IN ‘U’ BENDING DIES:

Using convex pad

Punch side wall relif- angular

straight undercut

OVER BENDING:

Formed while bending

CORNER SETTING IN PRESSURE PAD DIES:

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EFFECT OF BURR SIDE: It is undesirable for the burr side to be located in the outer surface of the formed piece part, because the burr drags around the bend radius and into the die opening. This causes excessive wear in the die members. If the piece part is loaded such that burr is located on the inner surface of the formed piece part, the burr will face towards the punch. Since there is no drag between the work piece and the punch, burr cannot erode the punch.

BENDING IN PROXIMITY TO PIERCED HOLES: Holes pierced before bending will be distorted if they are very close to the bend area. As a rule distortion will be minimized if the distance P is held to minimum of 1.5 s

HOW TO STRIP THE BENT COMPONENT? Spring actuated plungers:

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Positive Knock off:

POSITIVE KNOCKOUT WITH PINS:

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Hook Stripper:

BENDING DIES:    

‘V’ Bending Dies ‘U’ Bending Dies Multiple Bending Dies L’ Bending Dies

‘V’ BENDING DIES:

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‘U’ BENDING DIES:

‘L’ BENDS ON PRESSURE PAD DIES: ‘L’ Bends are produced in V dies. They are also produced in pad type dies. An L bend is one side of U bend. Since the other leg of U is missing, selfequalizing qualities of U bend are not available.

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Draw backs of ‘L’ Bending: The two problems encountered are:  The one sided lateral thrust imposed upon the punch.  The work piece tends to pullout of the die opening.

‘V’ BENDING DIES IN PRESS BRAKES:

OTHER TYPE OF CLASSIFICATION:    

•ACUTE ANGLE DIE •GOOSENECK DIE •OFFSET DIE •ROTARY BENDING DIE

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MATERIALS FOR BENDING: HARD: Avery stiff; springy, cold rolled strips intended for flat work, where ability to withstand cold forming is not required.

HALF HARD: A moderately stiff cold-rolled strip suitable for limited bending. Rightangled bends may be at 908 to the grain direction around a radius equal to thickness

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QUARTER HARD: A medium soft cold-rolled strip suitable for limited bending, forming, forming and drawing. May be bent to 1808 across the grain and to the 908 parallel with the grain and a radius equal to the thickness.

SOFT: A soft, ductile cold rolled strip suitable for fairly deep drawing operations where surface disturbances such as stretcher strains are objectionable. Strip of this temper is capable of being bent flat upon it self in any direction.

DEAD SOFT: A soft ductile, cold rolled strip produced without definite control of stretcher and fluting it is suitable for difficult draw applications where such surface disturbances may be tolerated. It is suitable for bending flat upon itself in any direction.

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CHAPTER -23 DEEP DRAWING

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DEEP DRAWING: Drawing is a process of cold forming and flat precut metal blank into a hollow vessel.

DEEP DRAWING OF CYLINDRICAL CUPS: When the punch of the drawing tool forces the metal blank through the bore of the drawing die, different forces come into the action to cause rather complicated plastic flow of the material. The volume and the thickness of the material of the metal remain essentially constant and final shape of the component will be similar to the contour of the punch. The relationship between the diameters and depth of the drawn sheets vary widely and relationship is an important factor in the design of the drawing dies.

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If the drawing ratio exceeds a certain limit the material will fail due to excessive stresses. Then it is necessary to draw the component in two or more stages. This increases the tool cost.

TO REDUCE No. OF DRAWS: To reduce the number of draws the following methods can be employed.  Use of special sheets.  Annealing the work piece for each draw. Annealing permits greater drawing ratio and consequently lesser number of stages.

A SIMPLE DRAW DIE:

FORCES ACTING ON THE COMPONENT WHILE DRAWING:

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Compression Circumferential Radial tension Blank Holding

Bendi ng

Friction Tension

METAL FLOW DURING DRAWING CYLINDRICAL CUPS:

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SUMMARY OF METAL FLOW: Little or no metal deformation takes place in the blank area, which forms the bottom of the cup. The metal flow taking place during the forming of the cup wall uniformly increases with the cup height. The metal flow of the volume elements at the periphery of the extensive and involves an increase in metal thickness caused by severe circumferential compression. This increase in the wall thickness caused by severe circumferential compression. This increase in the wall thickness is at the open end of the cup wall. The increase is usually slight because it is restricted by the clearance between the punch and the bore wall of the die ring.

WRINKLING: Deep drawing necessitates severe cold working and involves plastic flow of the metal. The metal may buckle rather than shrink, ‘wrinkles’ occur at the edge of the blank and ‘puckers’ appear on only one part of the blank.

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PUCKERING:

BLANK DEVELOPMENT: (FOR CYLINDRCAL SHELLS) WHY BLANK DEVELOPMENT? The development to approximate blank size should be done to.  Determine the size of the blank to produce the shell to required depth.

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 To determine how many draws will be necessary to produce the shell. This is determined by the ratio of the blank size to the shell size. Various methods have been developed to determine the size of the blank of the draw shell.

METHODS:  Algebraic calculation.  Simple graphical method  A combination layout and mathematics.

ALGEBRAIC METHOD: The following equations may be used to calculate the blank size for cylindrical shells of relatively thin metal. The ratio of shell diameter to corner radius can effect the diameter and should be taken into consideration. The cylindrical shells can be considered as consisting of circular pipes or disc. Total area = [(pd²)÷4] + pdh Surface area of the blank is = (pD²)÷4 ‘D’ is the diameter of the blank ‘d’ is the diameter of the cup. By the principle of equal area. [(pd²)÷4] + pdh = (pD²)÷4 D² = 4d² + 4dh D = √ {(4d²+4dh)} This equation will hold good if (d÷r) is 20 or more. When (d÷r) is in between 15-20 D= √ {(d²+4dh)-0.5r} When d÷r is between 10-15 D= √ {(d-2r)² + 4d(h-r) + 2pr(d- 0.7r)}

SIMPLE GRAPHICAL METHOD: A simple graphical method of determining the diameter ‘D’ of a circular. Knowing the height ‘h’ and the diameter ‘d’ of the cylindrical shell to be drawn is as follows:

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 From a reference plane, raise the perpendicular of height ‘h’  From top of the perpendicular, draw a hypotenuse of length h+(d/2), to intersect the reference plane.  The horizontal component X, between the intersections on the reference plane, equals the radius of the necessary circular blank of diameter D.

AREA OF ELEMENT METHOD: To calculate the blank diameter for complex circular shells, it can be divided into simple elements of shapes. The elements are numbered 1,2,3, ……….etc., Element 1 is a cylinder, element 2 is a portion of the sphere and element 3 is a disc. The area of each segment may be found by using the equation. From the total area the diameter of the blank can be calculated.

LAYOUT METHOD:        

Make an accurate layout of the part including a line through the center of the stock. Number each dissimilar edge starting from extreme edge of part. Draw a vertical line XY and mark off the length of each section accurately starting from section from section 1 at the top of the line. Number each section to correspond with the same section of the shell. Through the center of gravity of each section draw a line downward parallel to XY. The center of gravity of an arc lies on a line, which is perpendicular to bisects the chord, and is perpendicular to 2/3rd the distance from the chord to the arc. From point X draw a line A at 458 to point P. Point P is midway between X&Y. Draw a line parallel to A intersecting the lines drawn through the centers of gravity. P to the ends of the section. On line XY obtaining lies B, C and D. Draw parallel lines B`, C` & D`. B` starts where A` intersect the first center of gravity line and so on until where D` where C` intersects the third center of gravity line and continues to intersect A`.

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    

Through the intersection of A` & D` draw a horizontal line Z to centerline of the shell. Construct a circle using y as center and z as diameter. Using x as center draw an arc tangent the circle. Draw a horizontal line tangent to the top of the circle until it intersects the large arc. The distance from this intersection to the line xy is the radius of the blank.

CENTRE OF GRAVITY METHOD: The blank size for a cylindrical drawn cup can be determined by Gouldinus theorem. The theorem states that the area is equal to the length of the area to the length of the profile the length of the path of its center of gravity. A= Lp + g The center of gravity point in this method can be found out graphically or can be calculated arithmetically. (pD²)÷4 = L1+ L2 +L3 ……………………(2p X) pD² = L1+ L2 +L3 ……………………(2p X)×4 D² = L1+ L2 +L3 ……………………(2p X) ×4 D = √ {(L1+ L2 +L3) 8X} The center of gravity distance can be calculated arithmetically from the formula. X = L1 X1 + L2 X2 + L3 X3 L1 + L2 + L3 Area = length of the profile X length of the path of the center of the gravity.

CLEARANCE: 1. The clearance between the punch and the die must be greater than the thickness of the material to be drawn. 2. Too large clearance will result in wrinkled and 3. Too small clearance will result in tearing of the component. The formula will help to calculate the clearance for draw dies. For deep drawing quality steel, = s + (0.07 × √ (10s) Aluminium,………………….. = s + (0.02 × √ (10s)

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Non ferrous…………………... = s + (0.04 × √ (10s) The table also provides guidelines for determining the above clearance.

Blank thickness in mm Sizing draws upto 0.4mm 0.4 to 1.3mm 1.3 to 3.3mm 3.3 and above

First Draw 1.07-1.09s 1.08-1.1s 1.1-1.12s 1.12-1.14s

1.08-1.10s 1.09-1.12s 1.12-1.14s 1.15-1.12s

Redraws 1.04-1.05s 1.05-1.06s 1.07-1.09s 1.08-1.10s

DIE & PUNCH RADIUS: The draw radius of the die should be kept as large as possible to aid the metal flow but if it is too large the material will be released by the blank holder too soon and wrinkling will result. When the radius is too small the material will rupture as it is bent around the draw edge. The nose radius and side walls of the punch should be polished with vertical stroked especially when drawing soft materials to eliminate any cross packets in which the metal flow and cause fracture when the is stripped from the punch.

DRAWING FORCE: Drawing Force can be calculated the Percentage shearing force. The percentage depends on the draw ratio d/D or ‘m’ F = d × Su ×A d = diameter of the cup in mm S = thickness of the material in mm Su = ultimate strength in N/mm² A = constant Values of a:

a m F d S Sy

0.4 0.8

0.4 0.5 0.6 0.7 5 0.7 0.7 7 5 = d × S × Sy (D/d-c) 5 = diameter of the cup in mm

0.6 0.7 0.8 1 0.6 6 0.6 2 0.6 6 0.5 7 5 5 5

= thickness of the material in mm = yield strength in N/mm² ICDP TECHNICAL TRAINING CENTER

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C

= constant (between 0.6 to 0.9)

PRESS CAPACITY: BLANK HOLDING FORCE: Optimum blank holding Pressure is necessary for the successful draw. Very low blank holding pressures lead to wrinkle formation and high blank holding pressure leads to tearing. It is difficult to control the pressure in the pressure in the spring loaded blank holder, when compared with the hydraulic or pneumatic blank holder.

BLANK HOLDING FORCE CALCULATION: The recommended blank holding pressure varies from 80 to 200 N/mm². Bigger values are used for thinner materials. By knowing the blank holding areas, the blank holding force can be calculated. Blank holding Force = blank holding pressure × blank holding area

BLANK HOLDING FORCE CALCULATION: Blank holding pressure is inversely proportional to the blank thickness. The blank holding factor X, can be taken from the graph depending on the stock thickness. In this method blank holding force is not calculated separately, but the total drawing force (including the total drawing force) is arrived at. Total drawing force = ‘X’ × Drawing force.

BLANK HOLDING FORCE CALCULATION: Blank holding pressure can be calculated from the graph. The pressure varies according to the sheet thickness, cup diameter, D/d ratio (b) and the strength of the material. The blank holding force can be calculated by multiplying the value by blank holding area.

DIE REQUIREMENTS FOR DEEP DRAWING OF CYLINDRICAL SHELLS: 1. The clearance between the punch and the die must be greater than the thickness of the material to be drawn. 2. Too large clearance will result in wrinkled and too small clearance will result in tearing of the component. 3. The clearance should be proportional to the material thickness plus an allowance to prevent wall friction. This allowance ranges from 7ICDP TECHNICAL TRAINING CENTER

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20percent of the material thickness depending on the type of operation and the metal. 4. As the shear strength of the stock decreases the allowance should be increased.

CALCULATION: The formula will help to calculate the clearance for draw dies. For deep drawing quality steel, = s + (0.07 × √ (10s) Aluminium, = s + (0.02 × √ (10s) Non ferrous = s + (0.04 × √ (10s)

DRAW BEEDS: One of the functions of the draw beed in a blank holder is to provide additional resistance to metal flow, thus helping to control the movement of metal into the die cavity.

AIRVENT: An air vent should be provided in the punch and the die to eliminate air pockets, which tend to collapse the cup when stripped from the die. On noncylindrical shapes two or more air vents are provided. To prevent plugging of the air vents with the drawing compound and dirt they must be placed in such apposition that they can be easily cleaned.

LUBRICATION:  

Necessary due to the higher frictional forces between the punch & sheet metal, die & sheet metal. The purpose of the lubricant is to provide a film between the work piece and the punch and the die

QUALITIES of LUBRICANTS: The film must be strong enough to permit metal deformation without being squeezed from the surface. Table gives various compositions for press lubricants for stamping and drawing.

LUBRICANTS: For Normal Draws: ICDP TECHNICAL TRAINING CENTER

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  

Straight mineral oil General purpose soluble oil Diluted soap solution

For Higher Draws:  Polar material such as fatty oils  Waxes  Concentrated soaps For Extreme Draws:  Extreme Pressure Agents such as loosely combined Chlorine or Sulphur  Pigment such as Chalk, Graphite and Molybdenum Disulphide

DRAWING TOOLS: The simplest method of producing the shell is by the use of a drawing tool, on what is known as a single action press. This is the general form of power press, in which there is only one tool slide. The flat circular blank is located in the turned recess in the die. When the punch descends, the blank flows in to the die. The punch continues to descend until the top edge of what is now the drawn shell is below the sharp edge of the die.

DRAWING FLANGED COMPONENTS: While drawing flanged cups the cup diameter d should be considered and not the diameter at the flange. While taking d/D ratio if the flange diameter is considered.

RAW MATERIAL: Lamination may occur as if two sheets are positioned one over the other while drawing. This is caused due to the segregation in the sheet. The quality of the sheet metal must tested and be ensured before drawing.

FAULTS IN EQUIPMENT AND DESIGN OF TOOLS:   

Bottom of the drawn cup is torn if the D/d ratio is too large. Increasing the number of stages or the using the steels with better drawing quality will result in successful draw. Tearing at the bottom corners occurs at the bottom of the shells if the sheet thickness is not uniform, the draw clearance is less. Increasing the draw clearance is the remedial action. Bulges will occur if the draw clearance is more. Increasing the blank holding pressure will help in controlling the defect.

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CHAPTER -24 PRESSES

PRESSES: PARTS OF PRESSES: CAPACITY OF PRESS: The rated capacity of press is the force, which the slide will exert near the bottom of the stroke.

PRESS BED:

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Press bed serves as table to which the bolster plate or the lower tool assembly is mounted.

PRESS SLIDE It is the reciprocating member of the press. It is guided in the press frame. The upper tool member is called plunger slide. On a Hydraulic press it is called as platen.

PLUNGER SLIDE The inner slide of double action is called plunger slide. In a double action press the punch is mounted on this slide.

BLANK HOLDER SLIDE The outer slide of double action press is called blank holder slide.

BOLSTER PLATE It is the plate secured to the press bed for locating and supporting the tool.

PITMAN Pitman is the connecting rod, which conveys power and motion for the main shaft to the press slide.

CLUTCH It is the coupling used to connect or disconnect the driving machine member to or from driven machine member in a press it connects or disconnects the flywheel to the main shaft. The clutches are divided in to three main groups 1. Positive clutches in which driven and driving members of the clutch are inter touched in engagement. . Eddy current clutches. 2. Friction clutches

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The stroke of the press is the reciprocating motion of the press slide. It is the distance between terminal points of motion.

SHUT HEIGHT: It is the distance from the top of the bed to the bottom of the slide with the stroke down and the adjustment up.

DIE SPACE: Die space is the area available for mounting tools in the press.

CLASSIFICATION OF PRESSES: Presses are classified by following characteristics.  Source of power.  Method of actuation of slides.  Number of slides.  Frame types.  Intended use.

SOURCES OF POWER: The press is powered by one of the following sources, 1. 2. 3. 4.

Manual Mechanical Hydraulic Pneumatic

1.MANUAL: The presses are hand or foot operated through levers, screws, or gears.

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There are three major types of mechanical drives. 1. Non-geared or a fly type. 2. Single reduction gear type. 3. Multiple reduction gear type.

3.HYDRAULIC PRESSES In these types of presses oil pressure in a cylinder in a closed and reacting against a piston moves the slide. Constant pressure and speed can be maintained throughout the entire stroke.

4.PNEUMATIC PRESSES Such presses are operated by pneumatic, pneumatic cylinders provide the necessary forces.

FLY PRESS OR BALL PRESS: The fly press or ball press is the simplest type of all presses and is operated by hand.

POWER PRESS: The constructional feature of a power press is almost similar to the hand press, the ram instead of driven by hand is driven by power. (Ie: mechanical or hydraulic)

GAP PRESS: It has a Gap like opening in the frame for feeding the sheet metal from one side of the press.

INCLINED PRESS: The characteristics of inclinable press is its ability to tilt back on its base, permitting the scrap or finished products to be discharged from the gravity without the aid of any type of handling mechanism.

ADJUSTABLE BED PRESS: It has the mechanical arrangement for raising or lowering the table on which the die is fitted. This enables the setting of different sizes of work and dies on the machine.

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HORN PRESS: It has a cylindrical horn like projection from the machine frame, which serves as the dies support. The horn may be interchanged for the different sizes of work. The press is intended for cylindrical work pieces.

STRAIGHT SIDE PRESS: It has two vertical rigid frames mounted on two sides of the base, which are intended for absorbing severe load exerted by the ram. The machine is suitable for heavy work but due to presence of side frames, the sheet metal cannot be fed from the side.

PILLAR PRESS: It is a hydraulic press having four pillars mounted on the base. The pillars support and guide the ram.

POWER PRESS DRIVING MECHANISM: 1. 2. 3. 4. 5. 6. 7. 8.

Crank and connecting rod drive. Eccentric drive. Knuckle joint. Cam drive. Toggle leaver. Screw drive. Rack and Pinion drive. Hydraulic drive

ECCENTRIC DRIVE: It is used in presses for shorter length of stroke of the ram. The working is simpler to crank and connecting rod mechanism.

CAM DRIVE: It is used to give a specific type of movement to the ram the ram remains idle for some period at the bottom of the stroke.

KNUCKLE JOINT DRIVE: It has a high mechanical advantage near the bottom of the stroke. Theses presses are used for squeezing or coining operation.

TOGGLE DRIVE: It is mainly used in drawing operations for holding the blank.

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It is operated by a friction disc, which imparts a uniform acceleration movement to the ram in the downward stroke. They have longer stroke length and gentler action.

RACK AND PINION DRIVE: It is used for imparting a very long stroke length to the ram.

HYDRAULIC DRIVE: It is used for applying a very large pressure at a slow speed for forming, drawing operations, etc. The oil under high pressure is pumped on one side of the piston and then on the other to impart reciprocating movement to the ram.

PRESS SIZE: The size of the press is designated by its maximum applying load on a piece of blank and it is expressed in tonnes. The mechanical presses are built having capacities ranges from 5 to 4000 tonnes.

PRESS SELECTION: The first & foremost consideration for choosing a press is the tonnage required for the operation of tool, similarly the table size, throat, stroke & shut height of the press should be suit the press tool.

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CHAPTER -25 TOOL FAILURE ICDP TECHNICAL TRAINING CENTER

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TOOL FAILURE: PROBLEMS WITH CUTTING DIE PLATES: Die plates of cutting edges may cause trouble by: 1. Dulling of cutting edges and consequent excessive bur formation. 2. Breakage. 3. Cutting die plate performance.

DETERMINING FACTORS OF TOOL LIFE: The determining factors may be classified in to four groups depending on: 1. 2. 3. 4.

The stamping The tool The press The operation

PRESS SELECTION:

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Every C-frame press at the instant of cutting impact, deflects somewhat, misaligning the punch a little, if the deflection is too pronounced, then the misalignment becomes too great so that uneven wear is produced, and in extreme cases even damage to the cutting edge occurs.

CUTTING SPEED: The temperatures reached during high-speed cutting processes do not impair the hardness of the cutting edges.

DIE SETTING: The proper setting of the tool in press is of utmost importance. If the alignment is not correct, excess friction and certain dangerous lateral stress are produced which causes premature wear of the tool member.

OPERATION WITH THE TOOL: The periodic cleaning of the tool in order to avoid accumulation of dirt, chips, or foreign matter, which mix with the lubricants, act as abrasives and considerably increase tool wear. The press operator is supposed to co-operate in the prolongation of the useful life of the tool by A. Avoiding any irregularities rate feeding. B. Informing the Forman immediately when burr starts to become excessive. In general, giving the tool then it deserves as an expensive precision products.

SHARPENING OF PUNCHES: The punches are subjected to wear three times as fast as the die plates. The stock clings to punch slides like press fit. 1. Do not employ the same kind of tool steel for cutting members, punch and die plates. 2. Make the punch longer than strictly necessary and sharpen them more frequently than the corresponding die-plates.

REMOVE FEATHER EDGES: After grinding a die plate or a punch, featheredges are formed around the cutting edges.

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After sharpening a die plate or a punch, remove the feather with a fine oilstone. It is surprising what a favorable influence this little precaution has on the useful duration of the dies. A fringe benefit of this consists of improved surface finish of the cut surfaces.

PROTECTIVE COATINGS ARE HELPFUL: When blanking or punching sheet metal coated with either paper or plastics, both the bur formation and the wear decreases on the tool members that are in contact with the coated side of the stock. It is significant in the production of the laminations for the electrical devices. These stampings, made from highly abrasive silicon steel, which cause very rapid wear of tool members

BREAKAGE OF DIE-PLATES: During the operation of the operation of the tool the following details may be directly or indirectly cause the die plate failures. 1. Inaccurate feeding causes the cutting of half blanks or half holes results in the deflection of force and results in chipping of cutting edges. 2. In punching of small holes, slugs often clog the clearance holes, resulting in the punch breakage and damage to the die plate. Very dull cutting edges means overloading causes spoiling and breaking of die plates.

HOW TO GET MORE FROM DRAWING DIES: In a drawing die there are three main tool members: the die ring, the punch, and the blank holder. The cause for wear in a drawing die is the continuous friction between the stock and the tool members. The die ring can be polished after which its dimensions are enlarged beyond the tolerance limits.

PRESS SELECTION: Every press at the instant of impact deflects somewhat misaligning the punch a little. If the deflection is too pronounced, then the misalignment becomes too great so that uneven wear is produced and thus tool life is greatly reduced. By reducing the drawing speed the tool life is somewhat increased.

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STOCK: The stock should be clean, without scale, oxidation, or rust. The sheet metal must be perfectly uniform in texture, hardness, thickness, surface finish, etc.

STOCK LUBRICATION: In drawing operations, lubrication creates a film between the stock and the tool members, thus allowing the stock to slip easily between the active tool members. In this way the friction between the working surfaces of the tool and the stock that is being produced is reduced and the heat produced by the operation is greatly decreased.

PRESS ROOM: The cleaning of the tool in order to avoid accumulation of dirt, chips, and foreign matter, which when mixed with lubricant, act as an abrasive and considerably increase tool wear. Prolongation of tool life 1. Avoiding any irregularities. 2. Informing the foreman immediately as soon as appear in some shells.

wrinkles or cracks

PROBLEMS WITH SLUGS: Slugs sometimes cause problems, which involve expense, loss of time, labor costs, and lowering of the production efficiency of the corresponding press tools. The slug cause clogging of die opening and slug lifting or pulling.

JAMMING THE SLUG DISCHARGE HOLES: This is due to cut slugs becoming compressed together and building up in almost solid columns. Some slugs in the columns can shift to a crosswise position and literally clog the slug exit holes in die plates and die shoes.

SLUG PULLING: Slug pulling is the return of slugs above the die plate. The disagreeable consequences: Possibility of miss-feeds, if the slugs shift on to some cutting edges, punches and die-opening edges may be damaged, and punches may break.

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TOOL SETTING: The tool must be located on the bolster plate or the press table that the slugs have an absolutely pre discharge path, i.e. all the clearance holes of the plates and die shoes, must have correctly positioned discharge holes of the right size.

MAGNETISED PUNCHES: Punches some times become magnetized, either while being sharpened or punching action. This causes increase in damage of slug fitting, so always demagnetize the punches after resharpening and whenever they have become magnetized naturally.

REMIDIES OF UNSTICKING JAMMED PRESSES: 1. If the press is equipped with tie rods, loosen them. If the nuts are too hard to turn, heat the tie rods. 2. Apply external forces, such as wedges hydraulic jacks to die members, never use impacts. 3. Try to slide the ram together with die out of its seat in a forward direction. 4. Put dry ice around the tool and pitman screw to make them contract, thus reducing the jamming pressure. 5. For steel-frame press, heat the frame in order to expand.

PREVENTIVE METHODS: Put a piece of heavy paper or cardboard between the die bottom and bolster plate: and between the punch holder top and the ram bottom face. Then in case of jamming, burn out the paper. The yielding of rubber sheet compensates automatically for over thickness or double thickness of stock and thus any jamming is avoided. Machine a cylindrical in the ram top to hold a strong-flanged cup. In the interior of the cup place a cake made from Cerro metrics or from an alloy of tin and lead rest on the cake a properly shaped steel cylinder that will receive the thrust from the ball joint and the pitman screw. In case of jamming, take out two or more plugs of clearance holes, heat the cup so that the low melting alloy soften or melts outright. Thus the jamming pressure is removed.

MAGNETISED STAMPINGS:

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Product damage occurs when tiny particles of steels cling to magnetized stampings and score mating surfaces or in severe cases, jam moving parts. Magnetized punches have a tendency to lift small slugs and blanks out of the die plate opening and deposit them on the die plate top surface, which causes damage to punch and die plate breakage.

PREVENTION: STAMPINGS: Avoid the magnetic lifters for handling stock; use hook lifters instead; if possible change the type of steel with less carbon content or alloying elements.

TOOLS: Use non-magnetic materials for die members.

PRESSES: For press construction use mild steel that is magnetically “soft” and have low hysterias.

REMEDIES: Demagnetizing the stampings, tools and press components.

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STRIP LAYOUT FOR VARIOUS COMPONENTS

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component

STRIP WIDTH 23,5

PITCH 14,5

PITCH PUNCH

NOTCHING

NOTCHING

IDLE 0.08mm

45 DEG BEND FORM UP

IDLE

COINING DOWN FORM UP 90 DEG

NOTCHING

COINING

NOTCHING

FLAT

PART OFF

Component ICDP TECHNICAL TRAINING CENTER

P1

PL1

P1

CP1

P1

P2

BP

P1

EIGEN ENGINEERING

ICDP TECHNICAL TRAINING CENTER

EIGEN ENGINEERING

Width-16mm

Stage-1 piercing

Stage-3 Piercing

Pitch-6,5mm

Stage-2 Sidecutting

Stage-4 Piercing

Stage-5 Idle

Stage-6 Forming

Stage-7 Idle

Stage-8 Bending

Stage-9 Corner Setting

Stage-10 Idle

Stage-11 Forming

Stage-12 Idle

Stage-13 PartOf

ICDP TECHNICAL TRAINING CENTER

EIGEN ENGINEERING

PITCH

01 STATION

11

PIERCING

COMPONENT DEG

PILOTING

02 STATION NOTCHING

03 STATION IDLE

04 STATION NOTCHING

05 STATION IDLE

06 STATION TRIM

07 STATION IDLE

08 STATION PRE FORM

09 STATION RES

10 STATION FINAL FORM

11 STATION RES

12 STATION BLANK

ICDP TECHNICAL TRAINING CENTER

EIGEN ENGINEERING

ICDP TECHNICAL TRAINING CENTER

EIGEN ENGINEERING

Reference Books

Die Design Fundamentals.

-

Paquin.

Tool Design.

-

Donaldson.

Basic Die Making.

-

Ostrgarrd

Advanced Die making.

-

Ostrgarrd.

Fundamentals Of Tool Design.

-

A. S. T. M. E.

Tool Design.

-

C B Cole.

Punches And Dies.

-

Frank A Stanley.

Tool Engineering Hand Book. Die Design Hand Book. PSG Hand Book. CMTI Hand Book.

ICDP TECHNICAL TRAINING CENTER