Tool Engg I-practical

Tool Engg. I EXPERIMENT NO. 1 AIM: - Determination of the forces acting on single point cutting tool by lathe tool Dynamometer. INTRODUCTION: It is essential to study metal cutting process for economical aspects and the manufacturing of the components. To investigate performance of cutting tools during metal cutting the measurement of the cutting forces is essential this helps the analysis of metal cutting as below. 1) Effects of speed and feed on the action of cutting tool. 2) Effects of mechanical properties of work material a cutting forces. 3) Values of forces exerted on machine component of jig and fixture. 4) Uses and effect of these forces on geometrical accuries of the work piece. In short the tool force measurement is that tool dynamometry is an essential tool to analysis the process of metal cutting theoretically. Orthogonal Cutting Process :-

In this process the cutting edge of a tool is set at an approach angle < 900 resulting in the resultant forces acting oblique on cutting edge the resulting force ( r ) can be acting oblique an cutting edge the resulting force ( r ) can be resolved in three component forces this process is known as oblique cutting. To simplify this process geometrically the radial force component is dominated by taking a follow work piece and cutting with tool having an approach angle as 900 the resulting cutting force ( R ) is now resolved in only two component Fc and Ft are named a vertical force i.e. cutting force i.e. cutting force i.e. entrust force.

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Tool Engg. I LATHE TOOL DYNAMOMETER It unable us to measure Ft and Fc at difference working condition and further makes it possible to merchants circle diagram for orthogonal cutting.

PERFORMANCE 1) Sensing unit of the dynamometer is placed in proper position with the help of cables carefully connected to Pv. Socket on the string gauge amplifier unit the some is repeated for PV2 channel. 2) The instrument is connected to 230-v supply. Do not switch on the supply. 3) Ensured that when range selected S/W is in fall clockwise position channel s/w selected in mid position. 4) By putting Sw2 in battery check position so if the battery were in good condition if the meter pointer does not show a reading between 4-4.5 replaced the batteries. For battery replacement back side cover was removed .On the back cover you would and laid a battery using which accommodate 6 no and 1.5 m dry all on standard variety. 5) Switch Sw2 is now kept in grid position and fork the range selector switch is kept in most 3

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Tool Engg. I sensitive position and if the micro voltmeters (m1) is not indicating zero (w.e. to user) adjust on the L.H.S. of the instrument. This adjustment must be done very carefully or 22 turn rimming not which make the zero adjustment very delicate. Again the balls range was selected a sw to its least sensitive range. 6) Then instrument was ready for use the A c mains are switched on by putting Sw1 in down word position. 7) Sw5 is turned to L.H.S. and observe that bridge excitation voltage of 5 V is indicated on M2 meter, when Sw5 was taken to RMs bridge excitation voltage if S V or Pv2 channel would be indicated by m2 meter. 8) The balanced is obtained at 300 m V range by operating balance not the voltmeter for both channel under specified condition referring to the ration caps provided you would come to know about the magnitude of forces with both the channel. PROCEDURE Lathe tool dynamometer operation – 1) The dynamometer is mounted on lathe occur across slide and is was rigidly clamped with balls. 2) An orthogonal cutting tool area used. 3) A below work piece was mounted in the clock of the machine. 4) The dynamometer was connected to bridge balancing circuit by means of connected cables supplies as follows. Dynamometer socket marked as Fr1 was connected to the socket at bridge balancing circuit marked Pn/V i.e. verto and similarly Pr was connected to Pv2 i.e. horizontal. 5) The supply as a bridge balance was switched as and the initial balance a both the bridge was carried starting from coder to pipe range dst as the voltmeter. 6) The speed and feed of lathe machine was adjusted and machine was started the tool is feed manually to start cutting 0 though n feed adjusted automatically. 7) Wait to stabilize the output of the bridge and measured the o/p for vesto and Hori graphs were used to know forcer values. 8) To vertical and horizontal forces on the dynamometer should not be exceed the limit as 500 kg.

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Tool Engg. I EXPERIMENT NO. 2 AIM : To study forces acting on twist drill and its measurement on tool dynamometer. Forces acting on drill tool : All elements as drill are subjected to certain forces in drilling resolving resultant forces resistance to cutting or each pt. or lip are obtained three forces Fx , Fy , fz acting on direction mutually 1st to each other. The horizontal forces Fr acting upward impede the penetration as the drill into work. Force F of chisel edge acting in some direction further and more the advancing of drill is impeded by friction forces on drill margined and frictional forces Ft due to chip flow. In order to penetrate the work, the axial force applied to it by machine must overcome the some of forces of resistance along drill axis. F1 = Σ [ 2 Fv + F + Ft ] It has been found that Fv, Fy, Ft over 40% , 51% , 3% of resistance thrust force F) respectively. The force F which impede the advance of drill into the material are overcome by feed mechanism. The total forces of resistance acting along maximum force Fmox permitted by feed mechanism. I.e. f is less than Fmax permitted by feed mechanical i.e.e F is less than Fmax is necessary drilling condition forces Fx set up moment of resistance ( F3x – Mx) to cutting make up of the moment of force F3 moment of force due to shaping and friction of chisel add Mc. Mx moment of the friction forces on margin Mm the moment of the forces to the friction of the chip on the drill and machine surface Mc open. M = Mx + Mce + Mm + Mc Investigation shows that about 80% of force moment of resistance of cutting is accurate for by lips, 8% of chisel and drill chip, hole and drill margin and machine surface [Mm + Mc ]. To perform drilling in drilling machine it will necessary that total moment of resistance be overcome by the available torque to drill press i.e. mt ≥ m The torque of drill forces is determined by the formulae – Mt =

Nsp h

Where, Nsp = available power of spindle m h = Speed of machine spindle in rpm.

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The total moment of resistance to cutting cm should not only be less or equal to torque Mt developed by motor drill at given spindle speed but less or equal to maximum torque cut) permitted by weakest link in main drive gear train tm ≥ m tm can be calculated in designing the machine if threshold force F and torque in use known. -0-0-0-

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Tool Engg. I EXPERIMENT NO. 3 AIM: Design a circular form tool for two step work-piece. THEORY : It is one in which the cutting edge is a shape that produce desired contour on the work piece. In the turning operation most of the form tool are made of H.S.S. but cemented carbide being mostly are the extensively used for this purpose. The use of counter cemented carbide tip for the form tool enables the productivity to rate by 30-40% C in compression with H.S.S. form tool on circular form tool relief angle γ = 10.120 and rake angle v depends upon type of material to be machined. 1) From ∆OaA ,

a

Sin r1 = ht/r1 = ht/15 or Sin 120 = ht/15 or

ht

A1

ht = 15 Sin 120 γ

= 3.12 mm COS r =

A1 r1

A1 = r1 cos12

O

r1

A

A1 = 14.68 mm 2) From ∆ QOB , Sin r1 = ht/r2 = 3.12/25

a

r1 = Sin -1 = 0.1248

A2

0

r1 = 7.16 A COS r1 = 2 , ∴ A 2 = r2 COS 7.16 r2 = 24.80 mm

γ1 O

r1

A

3) From ∆ AO2E, Σ 1 = α + r = 220

O2

Now, from fig. measure, R1 = 34 mm. H Sin Σ1 = R1

R1 H

H = R1.sin Σ , = 34 sin 220

A

= 12.74 mm

ε1 B1 E

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Tool Engg. I COS Σ 1 =

B1 R1

B1 = R1 COS Σ1 = 34 cos 220 4) From ∆ O2 BF ,

O2

Sin Σ2 = H/R2 =

12.74 24

R2

Σ1 = Sin-1 0.530

H

Σ1 = Sin-1 0.530 = 32.060 cos Σ2 =

B2 R2

ε1

B2 = R2 cos Σ2

B

B2

E

B2 = 24 cos 32.06 B2 = 20.33 mm

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Tool Engg. I EXPERIMENT NO. 4 AIM : Design of circular form cutting tool for the given job Design of circular form tool :

Form tool is one in which cutting edge is a shape that produce exact counter shape on w/p in the turning operation. Most of the form tool are made a high speed steel but connected carbide are be more and more extensively used for this purpose. The use of countered resulted carbide are be more and more tool tips for form tool unable the productivity raised by 30 to 40 %. ( In comparison with H.S.S. form tools ) On circular form tools relief angle λ = 100 to 150 an flat form tool 6 = 12 – 150 while rake angle r (gama) depends upon the type of material to machine and its mechanical properties like tensile strength and its hardness. But the range is 8 – 250 and rake angles specified for various materials given in following tables on next pages K = The minimum distance required to permit the chip disposal from the tool force and range is 3 – 12 mm M = wall distance and range is 6 to 10 mm. Rake angles for Turning various materials

Material

New properties and work material

R degrees

Aluminium, copper

-

-

20 to 28

Bronze,Loaded

-

-

0 to 5

Up to 50

Up to 150

25

From 50-80

150-235

20-25

Hard steel

80 – 100

235 –290

12 – 20

Very hard steel

100 – 120

290 – 350

8 – 12

Soft cost iron

-

Up to 150

15

Hard art iron

-

150 – 200

12

Very hard cost iron

-

200 – 250

8

bross Mild Steel Medium hard steel

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EXPERIMENT NO. 5 AIM : Design of flat form tool. METHOD :

As for circular form tool the w/p profile is constructed into projection and parallel lines are passed the top views. The points of intersection of uel lines and the w/p profile are projected on the corresponding circles of radii E 1 r 2 r3 etc to obtain pts 1' 2' 3' etc. the apex of the tool should lie on the w/p axis. From pt and ( tLO apex) we draw the line representing tool and ace at an angle and r and the line of tool and lank as angle λ. From the pts. 1, 2 and 3 we draw lines 11el to the and lank. To construct the cross – section of the tool perpendicular to the flank (Section N-N) we draw line LL ( perpendicular to the and flank ) from line LL we lay off the lengths L1 , L2 since the dimension of the total profile measure along the w/p are equal to the corresponding axial dimension of total w/p at angle lences L1,L2 since the dinmention of total l1 we denote by 2" 3" the pts. of intersection as these lines 0 with the lines drawn from pts. 2 & 3 are parallel to the tool flank pts. 1", 2" and 3" etc are Pts of profile of the and lat form tool in section N-N. Analytical calculation of a flat form tool can also be carried out

To determine the dimensions denoted by P2 and P3 in this figure shown if the dimension C2 and C3 are known or they can be calculated by a system or equation identical to more used in the calculations or circular form tool. Dimensions P2 and P3 can be radialy determine since they are sides as the right angle ∆ A2 and B3. The following equation are you have to solve the right angle. r1 = λ + r ,

P2 = c1 cos r , and

P3 = c3 cos r ,

The dimensions P2 and P3 should be calculated to at accuracy with 0.001 mm.

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PROBLEM:

FLAT FORM TOOL

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EXPERIMENT NO - 6 AIM :To study the forces acting on a straight flute plain milling cutter and helical flute cutter. THEORY :

The total resultant force of resistance R of the layer of stock being cut by

straight flute plain milling cutter can be resolved into following forces :Tangent 'f3' and radial 'fy' or horizontal force c & r and vertical force 'fe' The tangential force f3 set up the moment of resistance to the cutting , M=

f 3× d kg/mm and tends to bend the cutter arbor. 2

This moment of resistance should be over come by the torque developed by electric motor of the milling machine. Thus the main drive mechanism is designed and the power required in milling is calculated on the basis of f3. Thus radial force fy exerts pressure on the cutter spindle bearing and also tends to bend cutter arbour, therefore cutter arbor is subjected to bending by the action of two forces 'f3' & 'fy' or their resultant. In addition to bending the arbor is also subjected to torsion from the action of momentum resistance to cutting their force in arbor design calculations are based on resistance to combined stresses. The horizontal force 'fb' ( feed force ) is used in designing the feed mechanism the of milling machine in calculating the rad. Damping force for the work piece and in designing various component of milling fixtures. Force 'Fv' fever the cutter against the work piece. The reaction 'fv' acting on the work piece is directed upwards where in this case, it’s the force tending to lift work piece from the table. Since the w/p is clamped firmly to the table. Force 'fv' tends to press the work piece to the table and the table to the bed wag or saddle while 'fv' tends to separate the cutter. Force 'fv' tends to lift the table inclined. If the basically flute milling cutter is used the cutting force f3. fy and fn and fv will be supplemented by axial force fa ; acting in direction depending on the flute beside, which has a helix angle 'v'. It follows from the diagram in (fig b) that fa = f3 tan w Investigations conducted by a Rosenberg have should that a friction force T act cuts along the teeth, in direction in which it reduces force fa , therefore, to calculate force 'fa' following formulae can be used. 14

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Tool Engg. I

Interlocking cutters with helical flutes of different hands 15

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Tool Engg. I Fa = 0.28 f3 tan w Depending upon the land of flute spiral force 'fa' either tends to slide the cutter off the arbor or bolds it against the shoulder or against spindle nose. Force 'fa' also acts on milling friction cross feed screw stable ways. The axial force can be compensated by using inter loading cutter with helical flute of different bands shown in fig. Force 'fs' can be determined by emphirical formulae given in various hand books ; more often handbook gives form was to calculate power in kw required for cutting in the milling process. This being known the force 'fa' can be calculated by the following formulae – f3 =

60 × 102 N cut v

Kg-F

For plain milling cutter of H.S.ST18 in machining steel with tensile strength , 67 = 75 2

lgf/mm . N cut = 3.5 x 10-5

D14 . t86. S3.12 Bn Kw

The required power of the drive motor of milling machine is , Nm=

Ncat η

Where, η = efficiency of machine. -0-0-0-

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Tool Engg. I EXPERIMENT NO – 7 AIM :- Study of geometry of various types of milling cutters. THEORY :Milling Cutters :-

Milling cutter is the cutting tool used in used in milling machines. It has a cylindrical body, rotation on its axis, and is provided equally spaced teeth which engage the work piece internally. The cutter teeth are machined to give cutting edge on the periphery. They may meshed either axially or spirally. Materials :-

All important tool materials like carbon steel, high speed steel cost non ferrous cutting alloys, sintered carbide, etc. are used for milling cutters. Solid type of cutters may be made of carbon steel, or generally of HSS. CLASSIFICATION :

The broad classification of milling cutters is according to the shape of teeth they carry, such as plain, inserted, formed or saw teeth, etc. Under this classification are covered a large number of milling cutters. TYPES OF MILLING CUTTERS:-

1) Plain milling cutters 2) Side milling cutters 3) End milling cutters 4) Face milling cutters 5) Metal slitting cutters 6) Angle milling cutters 7) Formed milling cutters 8) Wood ruff-key milling cutters 9) T-slot milling cutters 10) Fly cutter GEOMETRY OF VARIOUS TYPES OF MILLING CUTTERS :1) PLAIN MILLING CUTTERS :-

It has straight or helical teeth cut on the periphery of a disc or a cylindrical surface. It may be solid inserted blade or tipped type, and is usually profile sharpened but may be form relieved also. Generally helical teeth are used it the width of the cutter exceeds 75 mm. The 17

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Tool Engg. I plain milling cutter is generally used for milling flat surfaces parallel to cutter axis. Helical teeth cutter is used where large stock removal is required.

Helical angle

permits several teeth to cut simultaneously which results in smoother cutting action. Heavy duty plain cutters have fewer teeth and helix angle 350-450. There are sometimes nicked on their periphery a helical pattern for chip breaking and smooth operation. Types a) Light duty plain milling cutter

b) Helical plain milling cutter

c) Plain side milling cutter 1)

d) Face milling cutter shell end mill – type

SIDE MILLING CUTTERS :-

This cutter is similar to plain cutter except that it has teeth on the side. However, side-milling cutter may have teeth on the periphery and on one or (more) both sides of the tool. These cutters may have straight, spiral or staggered teeth. Further these may be solid, inserted blade or tipped construction and may be profile sharpened on farm relieved. HALF SIDE MILLING CUTTER :-

It has teeth only on one side in addition to circumferential teeth. These cutters are usually used in pair for milling both ends of work to a given dimension. 2)

END MILLING CUTTERS: -

These cutters have an integral shaft for driving and have teeth on both periphery and ends. These are cutters with teeth on the periphery and end integral with a shank 18

for

holding

and

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Tool Engg. I driving. These are used to mill flat, horizontal, vertical, bevel, chamber and slant surfaces, grooves and keyways, to cut slot which is a process in die marking etc. The end mill cutter has either taper shank or straight shank. Types : 1) Common type end milling cutters 2) Two lipped end mill 3) Steel end milling cutters 4) FACE MILLING CUTTERS :-

These

cutters

are

made in two common forms. The smaller type almost resembles

a

shell

end-

milling cutter and is known as shell typeface milling cutter. It carries teeth on the periphery as well as the end face.

Maximum cutting is

done by teeth on the periphery and these end face perform finishing operation. The farmer type is used for small work whereas the latter for longer surface. The shell type cutters are usually held in a stab corer and lagers type can be mounted directly on the spindle nose. 3)

METAL SLITTING CUTTERS :-

These are used for cutting thin slate or for posting off. They are manufactured in two types – 1) Plain slitting saws 2) Staggered teeth saw These cutters are also called

'metal slitting saw'.

6) ANGLE MILLING CUTTERS :-

These cutters carry sharp angular teeth which are neither parallel nor normal to their axis. Their specific use is in milling v-grooves, notches; dovetail slot, reamer teeth and other angular surfaces. The two types – 1) Single angle cutters 2) Double angle cutters

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Tool Engg. I 7) FORM MILLING CUTTERS :- They are also called as form

relieved milling cutters or radius cutters. This category includes a fairly large variety at milling cutters used for producing different shaped contours. Their teeth are provided with a certain angle or relief so that their form and size are retained even after recompensing. Their common types are as follows – 1) Corner rounding cutters 2) Concave & convex cutters 3) Gear cutter 4) Tap & reamer flating cutters 5) Gear hubs 6) Thread milling cutters 8) WOODRUFF – KEY MILLING CUTTERS :-

It is a small type of end milling cutter which resembles with plain and side mills. Smaller sizes say up to 50 mm diameter are made to have solid shank, to be fitted in the machine spindle, whereas larger sizes are rounded with a hole for mounting the same on an arbor. Smaller size have straight teeth and larger size have staggered teeth. 9) T-SLOT MILLING CUTTER: -

It is a single operation cutter which is used only for cutting T-slots. In operation the narrow groove at the top is first milled by means of a slotting cutter or end milling cutter. The

- slot milling cutter is then

employed for milling the wider grove.

10) FLY CUTTER: -

It is actually a single point tool. It is either mounted on cylindrical body, known as a bar , exactly in the same way as the boring tool in a boring bor.

It is generally used for

experimental of purposes such a cutter, if 20

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Tool Engg. I properly designed, is capable of producing a very accurate surface. ELEMENTS OF FLUTED MILLING CUTTER :-

A typical milling cutter with various angles and center nomenclature is shown in fig.

1) ARBOR :-

It is the shaft on which the milling cutter is mounted and driven. 2) SHANK :-

It is the parallel or tapered extension along the axis of the cutter employed for holding and driving. 3) CUTTER BODY :-

This is the main frame of the cutter on which the teeth are brazed or integrated mechanically or hold mechanically. 4) PERIPHERY :-

It is locus of the cutting edge of the cutter and is an imaginary cylindrical surface enveloping the tips of the cutting teeth. 5) CUTTING EDGE :-

It of a milling cutter is the only portion that touches the work. It is the intersection of the tooth face and the tooth flank of beds surface. 6) GASH :-

It is the chip space or flute between the back and one tooth and face of the next tooth. 21

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Tool Engg. I 7) FACE :-

It is that portion of the gash adjacent to the cutting edge and which the chip impinges as it is cut from the work. 8) FILLET :-

It is the curved surface at the bottom of the gash which joins the face of one tooth to the back of the tooth immediately ahead. 9) LAND :-

This is narrow surface back of the cutting edge resulting from providing a clearance angle. It never touches the work and is less than 1.5 mm in width. 10) TOOT FACE :-

This is the surface upon which the chip is formed when the cutter is cutting. It may be either flat or curved surface. 11) BACK OF TOOTH :-

The back of flank of the tooth is created by the gallet and relief angle. It may be flat or curved surface. 12) LIP ANGLE :-

It is the angle which is inclined between the land and the face of the tooth. 13) CLEARANCE ANGLE :-

This is the angle between a line through the surface of the land and a tangent to the periphery at the cutting edge. It is necessary to prevent the back of tooth from rubbing against the work. 14) RELIEF ANGLE :-

A secondary clearance is generally ground back of the land to keep the width of the land within the proper limits. It is necessary because after several sharpening of the cutter, the width of the land increase to a pt. where it begins to interface with the work. It is usually 30 > clearance angle. 15) RAKE :-

It the face of a milling cutter lies along a radius of the cutter, it is said to have zero rake. It the face of cutter lies along a line on either side of the radius, it has +ve/-ve raks. -0-0-0-

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Tool Engg. I EXPERIMENT NO – 8 AIM :- To study various types of broach and its geometrical elements. THEORY :- Broaching is a machining operation in which a tooth having a series of cutting

teeth called "broach' i.e. pulled or postured by the broaching machine part the surface of a work piece. In doing so , each tooth of the tool takes a small cut through metal surface of a work piece. Most of the cutting is done by the first and intermediate teeth whereas the last two teeth finish the surface to the required size: -

TYPES

Broaches can be classified as follow :1) A/c to the 'Method of OPERATION ' a) Push broach b) Pull broach c) Stationary broach 2) A/C to the KIND OF OPERATIONS THEY PERFORM. a) Internal broach b) External broach 3) A/c to 'THEIR CONSTRUCTION' a) Solid b) Built – up c) Rotor – cut d) Progressive 4) A/c to THEIR USE a) Single purpose b) Combination broach 5) A/c to ' FUNCTION ' a) Keyway b) Burnishing c) Roughing d) Spiral 23

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Tool Engg. I Push broaches are shorter in length than pull broaches and the same cross section in order to ensure adequate stiffness to resist bending. The former type is usually employed where a shorter length is to be broached and less material is to be removed. The push broaches exerts compressive stresses on the work piece being broached. So it is preferred of short length so as to avoid bending or oraching of broach. ELEMENTS OF A BROACH

1) PULL END :The end of a pull broach, which contains shank is the pull end. The broaching machines puller head grips this end of the broach. 2) FRONT PILOT :It guides the broach into the hole and keeps it concentric with the latter. This helps in starting a straight cut. 3) REAR PILLOT :Its size and shape conforms to those of the finished hole and provides. Support to the broach after the cutting process is over. After the operation, this portion of the broach is gripped by the machine to pull back the broach to the starting position. 24

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Tool Engg. I 4) LAND :It is the extreme tap part on the tooth and is normally ground slightly to provide clearance. 5) TOOTH GULLET :It is also known as face gullet or chip space. This provides space for the chips to cost and escape. If this space is not provided, or is too small to accommodate the cut chips, the chips will rub against the hole surface and spoil it. Its size varies directly on the pitch of the teeth. 6) PITCH To linear distance measured between cutting edge of one tooth and the corresponding point on the next tooth is called 'pitch'. But it is not be same for all the teeth of the broach. 7) CUT PER TOOTH It corresponds to the depth of the gullet, which varies (increases) gradually from the first tooth near the shank to the finishing teeth, where it is almost constant. This gradual various in the height of the tooth or depth of gullets is known as cut per tooth. 8) BACK OFF ANGLE It is also known as clearance angle and is ground on the land to provide relief. Therefore, it is sometimes called a relief angle also. Its value normally varies from 0.50 to 30 , values from 1.50 to 20 being very common. However, for finishing teeth either no clearance is provided or a very small angle between 00 – 10 is provided because, if at all, a very nominal cutting is done by those teeth. 9) HOOK OFF RAKE ANGLE It is also known as face angle. It is similar to the rake angle provided on a single point tool of a lathe and purpose is also the same. Its value depends on the material to be cut and varies from 30 to 150, the most commonly used value varying between 120 and 150. 10) HOOK RADIUS It is the radius contained by the bottom of the gullet. It should have a very highly polished and smooth surface so as to prevent sticking of chips in the gullet. -0-0-0-

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Tool Engg. I EXPERIMENT NO. 9 AIM :- Design of circular broach for machining and cylindrical hole , diameter d = 29 h7 ( +

0.021 ) and length lo = 50 + 0.55 in a toothed wheel blank of free cutting speed 6t = 70 kgf/mm2. SOLUTION :-

1. The broach material selected for this purpose is H.S.S. 2. Broaching allowance 'A' and diameter of premachined hole bore A = 0.005 D + 0.12 √ L = 0.9735 ≈ 1 mm D0 = D – A = 25 – 1 = 24 mm 3) Cut per tooth S2 from standard table is selected as 0.03 mm for steel. Assuming the no.of semi finishing teeth as 3 the S2 is determined as – 1

½ S2 = 0.015 ;

1

/3 S2 = 0.01 mm ;

/6 S2 = 0.04 mm

4) Selection of broach tooth and chip space dimension Longitudinal cross sectional area of chip = LS2 = 50 x 0.03 = 1.5 mm. From the table, rectangular profile nearest value of Ag is 5.8 Ag = cross sectional area of gullet = K x 3.16 = 4.5 mm2 and of pitch is 7 mm and h = 2.3 , h = 3.0, r = 1.25 on these dimensions can also be selected by imperical formulae as under T = 1.25 √ L = 8.8 ≈ 9 mm h = 0.4 t

= 3.6 mm

h = 0.5 h

= 1.8 mm

b = 0.3 t

= 2.7 mm

Let us assume the value selected from standard table i.e. t = 7 ; h = 2.3 ; b = 3 r = 1.25 mm The pitch for finishing or sizing teeth = ts = 1.25 mm. Now checking for 2 max i.e. maximum no.of teeth in contact = L/t + 1 = 1.873 Hence, the condition that 2 maximum should be greater than or equal to 3 is satisfied and selected value of pitch is safe.

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Tool Engg. I 5. Selection of geometry from table, we get Roughing

= 30.30'

γ = 150

semi finishing = 20 10' Sizing

=

γ = 150

10 15'

γ = sizing = 50

6. Selection of number of chip breakers from table D = 25 mm, the number of chip breakers is equal to 12 and width m = 1 mm ρ r = 0.3 mm. 7) Determination and number of cutting and sizing teeth. 8) Selection of pay end rear pilot dimension from table , φ = 22 mm ;

d 2 = 17 mm ;

d 3 = 22 mm ;

c = 0.5 mm ; L1 = 140 mm ,

L2

= L 3 = 25 mm ;

L 4 = 16 mm , ϒ1 = 0.3 mm & r2 = 1 mm α = 300 for pull and Dt = 24.00 – 0.073 from table , Drp = minimum diameter of broach hole = 25 – 0.041 Lrp = 25 t = 1.5 11) Length of broach ( L' ) Length of toothed portion , = Tc Zc + t 5 25 = 7.20 + 5.6 x 6 = 173.6 Length of front pilot = L1 + 65 ( for tapered pilot ) = L1 + 75 ( for cylindrical front pilot ) = 140 + 65 + 75 = 280 mm Length of rear pilot = 25 L = 173.6 + 280 + 25 = 478.6 mm 12.

Force and strength calculation F = Ks ∏ DS2 Z max K K s = 425 kgf/mm2 27

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Tool Engg. I D = 25 mm ; S2 = 0.03 mm ; Zmax = 8K = 1.25 F = 425 x 25 x 0.03 x 8 x 1.25 = 10008.75 Kgf Cross sectional area of critical section = ∏ ( Dt – 2b2 )2/4 = 29S mm2 Permissible stress for HSS = 3 S lgf/mm2 permissible pulling force = F1 = 35 x 29 S.44 = 10 34 kg/mm2 ∴ F1 > F ,

hence, design is safe. -0-0-0-

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Tool Engg. I

EXPERIMENT NO. 10 AIM :-

Study of taps and dies.

GEOMETRY OF TAPS :-

A tap is a screw like tool which has threads like a bolt and three or four flutes cut across the thread. It is used to cut threads on the inside of a hole as in a nut. The edges of a thread formed by the flutes are cutting. The lower part of top is somewhat tapered so what it can well dig into the walls of the drilled hole. The upper part of the tap consist of a shank ending in a square for holding the tap in a medicine spindle or by a tap wrench. Taps are made from carbon steel or high speed steel and hardened and tempered. Taps are classified as – (1) Hand taps (2) Machine taps Hand taps : The hand taps are illustrated in figure are usually made in sets of these (1) tapered tap , 29

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Tool Engg. I (2) Second tap (3) bottoming top. They are rougher intermediate and finisher respectively. Machine taps : It has straight a basic flutes. In machine tapping it is necessary to see that chip always clear the cutting edge. Elements of Tap :

(1) AXIS :- It is the longitudinal center line of the tap. (2) BODY :- The threaded portion extending from the entering end of the tap of the shank. (3) CHAMFER OR TAPERED LEAD :- The tapered cutting portion provided with cutting clearance at the entering end of the tap to distribute the cutting action over several thread forms and to facilitate the entry of the tap into the hole. (4) CHAMPER RELIEF :- The gradual decrease in land height from the cutting edge to heel on the chamfered portion on the land to provide clearance for the cutting edge. (5) CUTTING EDGE : The edge formed by the intersection of the flute face and the form of the thread imposed on the land. (6) DRIVING SQUARE :- The portion of the extreme end of the tap shank by which the tap is held and driven. (7) FLUTE :- The flute is groves in the body of the tap to provide cutting edge, permit the removal of chip and to allow lubricant or coolant to reach the cutting edges. (8) FACE : The portion of the flute surface adjacent to the cutting edge upon which the chip impinges as it is cut from the work. (9) FLUTE RELIEF :Radial relief in the thread form starting at the cutting edge and continuing to the heel. (10) HEEL :The edge formed by intersection of relieved surface behind the cutting edge and the flute. (11) LAND :The portion of the body at tap left standing between the flutes, also the surface between the cutting edge and the heel. (12) RADIAL RELIEF :Radial relief is thread form provided behind unrelieved end.

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Tool Engg. I (13) SHANK :The portion of the tap which it is held or located and driven. (14) THREAD RELIEF :The clearance produced on the tap by which reducing the diameter of entire thread between the cutting edge and heel. (15) WEB :The central portion of the tap situated between the tools of the flutes and extending along the flute portion of the tap. (16) WEB TAPER :The increase of web thickness from the entering end of the tap towards the shank end of the flutes. (17) BACK TAPER :The reduction in diameter of tap body of the threaded pattern from the entering and towards the shank. (18) EFFECTIVE / PITCH DIAMETER :On a tap having a parallel threaded portion , the effective diameter is the diameter of an imaginary co-axial cylinder which would pass through the threads and the width of the spaces between the threads equal at these points measured at cutting edges. (19) MAJOR DIAMETER : On a tap having a parallel threaded portion, the major diameter is dio metral measurement over the rest of the threads form at the edges. (20) MINOR DIAMETER : On a tap having a parallel , the major diameter is measurement over the roots of the thread form at the cutting edge. (21) OVERALL LENGTH : The axial length over the extreme ends of the tap. THREAD CUTTING EDGES :A threading die is an extremely internally threaded tool used to cut external screw threads by screwing on the work piece. The threads are usually cut in one part. Threading dies may be solid or split, they may be round, square or hexagon spring or two piece adjustable dies for a hand stock.

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Tool Engg. I A threading die operates in a manner resembling the operation of a tap , except that it cuts external and not internal threads. Round thread cutting dies are use to cut threads and to size previously cut threads. Thread cutting is accompanied by the removal of a considerable amount of chips and the clearance holes may be large enough to avoid being dogged by the chips. Only a very thin layer of metal is removed in sizing screw threads and therefore dies for this purpose do not require large clearance holes. Such may be also of lower strength. No. of cutting teeth , 3c =

A + 2 or 3 2(S3 )

3c =

1 +3 2 (0.03)

= 16.66 + 3 = 20 Out of total cutting teeth, it teeth are used for roughing and three are used for semi finishing where the value of S3 is reduced gradually. No of sizing teeth = 16

DETERMINATION OF DIMENSION OF CUTTING TEETH

Diameter of first order tooth = diameter of pilot = 24 mm. The value of various teeth diameter are entered in the working drawing of broach. The dimension of tooth 2.17 are obtained by adding 2 S3 i.e. to previous diameter. The 2 S3 is distributed as 21/2 S3 21/3 S3 ; 21/6 S3 for tooth no. 18, 19 and 20 as stated earlier

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Tool Engg. I co.03 , 0.02 , 0.0067 for the six finished and sizing teeth the dimension is kept constant i.e. 25/6 mm. DIMENSION AND TOLERENCE OF SIZING TEETH :

DS = D – A = 25 . 021 – 0.05 = 25.016 mm assuming the diameter will be oversized by 0.0058. Tolerance on cutting teeth = ±

1 = 0.006 5S3

Tolerance on finishing teeth = -

1 tolerance of hole = - 0.0007. 3 -0-0-0-

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