Talat Lecture 3402: Forging Process
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Talat Lecture 3402: Forging Process as PDF for free.
More details
- Words: 3,034
- Pages: 17
TALAT Lecture 3402
Forging Process 17 pages, 20 figures Basic Level prepared by K. Siegert, R. Malek and R. Neher, Institut für Umformtechnik, Universität Stuttgart
Objectives: − to understand the basic principles of die forging and the characteristic features of special aluminium die forging processes − to learn about the basic design of dies in order to obtain optimum part qualities and tool life
Prerequisites: − general understanding of metallurgy and deformation processes
Date of Issue: 1994 EAA - European Aluminium Association
3402 Forging Process Table of Contents 3402 Forging Process ....................................................................................................2 3402.01 Principles of the Forging Process ................................................................ 3 Fabricating Processes of Forging..................................................................................3 Processes for Changing Cross-Sections .......................................................................4 Processes for changing direction ..................................................................................5 Processes for Creating Hollow spaces..........................................................................5 Separating Processes.....................................................................................................6 Die Forging Processes...................................................................................................6 Open-Die Forging ................................................................................................... 7 Die Forging.............................................................................................................. 7 3402.02 Special Forging Processes for Aluminium.................................................. 8 List of the aims of various special die forging processes.............................................8 List of characteristic features of precision forging.......................................................9 List of characteristic features of high precision forging...............................................9 Characteristic features of closed die forging without flash....................................... 10 Characteristic features of isothermal forging ............................................................ 10 3402.03 Forging Dies ................................................................................................. 11 Types of Forging Dies................................................................................................ 11 Parting of Forging Dies.............................................................................................. 12 Rules for design of partings of forging dies .............................................................. 13 Die Inserts .................................................................................................................. 14 Fabricating Forging Dies ........................................................................................... 15 Failure and Damaging of Forging Dies ..................................................................... 16 3402.04 Literature:....................................................................................................... 17 3402.05 List of Figures................................................................................................. 17
TALAT 3402
2
3402.01
Principles of the Forging Process • • • • • •
Fabricating processes of forging Processes for changing cross-sections Processes for changing direction Processes for creating hollow spaces Separating processes Die forging processes
Fabricating Processes of Forging The term forging is used to define a group of processes which are mainly forming processes (see Figure 3402.01.01). Additionally included are processes of separating (splitting) and joining, if large or complicated workpieces are built up out of individual parts. The exact processes of separating and joining are not listed here in detail. According to the characteristic differences in free forming (or unrestricted forming) and die forming (restricted forming), forging can be divided into open-die forging and die forging.
Fabrication Process of Forging Separating
Forming Compressive forming
Tensile forming Bulge forming Bulge forming with mandrel Free bending
Rolling
Open-die forming
Rollforging
Drawing out solid and hollow bodies
Discrolling Ringrolling
Expanding Spreading
Upsetting Lateral rolling of shaped parts Heading Cross rolling of shaped parts
Stepping Radial or rotary forging alu
Closed-die forming
Bend forming
Drawing out in a die Fullering Radial forging in a die Upsetting in a die
Shear forming
Forming by bending with linear motion of tool
Displacing
Twisting
Offsetting
Setting spiral twisting
Die bending
Bending by buckling
Indenting Punching Through punching Piercing with a hollow mandrel
Closed die forging Embossing without flash Hobbing Impression die forging with flash
Extruding Solid forward impact extrusion Backward cup impact extrusion Solid lateral impact extrusion
Fabrication Process of Forging
Training in Aluminium Application Technologies
TALAT 3402
Joining
3
Source: K. Lange
3402.01.01
Processes for Changing Cross-Sections The processes for changing cross-sections build-up the fundamentals of forging, see Figure 3402.01.02. According to the law of constant volumes, changes in cross-section lead to corresponding changes in length. The cross-section can be changed by material displacement and material accumulation, whereby the processes of material displacement dominate.
Processes for Changing Cross-Sections Open-die forming Closed-die Forming Pushing through
Rolling
Solid forward impact extrusion
Material displacement
Drawing out
Spreading
Drawing out over a mandrel
Radial forging
Draw
Upsetting in a die
Radial forging in a die
Heading in a die
Heading in a horizontal upsetting machine
Stretch rolling
Backward cup impact extrusion
Solid lateral impact extrusion
Ring rolling
Cross rolling
Material accumulation Upsetting
Combined material displacement and accumulation
Heading
Upset die forging
alu
Processes for Changing Cross-Sections
Training in Aluminium Application Technologies
TALAT 3402
4
Source: K.Lange
3402.01.02
Processes for changing direction These processes include bending processes (free bending, die bending) and shear forming processes (Figure 3402.01.03). Processes for Changing Direction Punch (Top die) Bending die (Bottom die)
Forming
Top die Bottom die
Without elongation
With elongation
Bending in a die
Preformed workpiece
Shear Forming
Top die Displaced crank stroke pin
Bottom die
Twisting
Displacing Source: K.Lange alu
Processes for Changing Direction
Training in Aluminium Application Technologies
3402.01.03
Processes for Creating Hollow spaces Hollow spaces (cavities) are produced by the methods of indentation forming and extrusion forming (Figure 3402.01.04). Processes for Creating Hollow Spaces Hollow mandrel
Punch(rounded, not sharp)
Punch
Indentation Forming Scrap
Punching
Through Punching
Piercing with a hollow mandrel
Holing punch Receiver
Pressing Through
Holed plate Counter punch
Backward cup impact extrusion
Bulk holing
Source: K.Lange alu
Processes for Creating Hollow Spaces
Training in Aluminium Application Technologies
TALAT 3402
5
3402.01.04
Separating Processes Separating processes used for forging are mostly cutting processes (Figure 3402.01.05). Shear cutting processes are used for the loss-free cutting of raw parts with a given crosssection (extruded sections) and defined lengths or volumes. Separating Processes
Shear cutting Cutting
Closed cutting with cutting edge
Punch
Holing punch
Flash
Holed plate
Cutting plate
Flash removal
Holing
Chisel
Wedge cutting
Chisel
Anvil
Chisel
Anvil
Cutting with chisel
Anvil
Chopping
Slitting
Source: K.Lange alu
Separating Processes
3402.01.05
Training in Alum inium Application Technologies
Die Forging Processes These are processes which are used to produce a defined workpiece geometry having good dimension and volume accuracy. Such processes are: form pressing with flash, form pressing without flash and compressing in a die, see Figure 3402.01.06. Die Forging Processes in a Narrow Sense Clamping jaws
Top die
Upsetting
Flash
Punch Workpiece
Workpiece
Container Stripper Bottom die
Upsetting
Closed-die forging without flash
Closed-die forging with flash
Source: K. Lange alu
Die Forging Process
Training in Aluminium Application Technologies
TALAT 3402
6
3402.01.06
Open-Die Forging The chacteristics of open-die forging are listed in Figure 3402.01.07.
Characteristics of Open Die Forging Merits:
# #
No special tools (costs, fabricating time) Simple forms
Problems:
# # #
High machining costs Material not optimally used Grain flow (fibre structure) not optimal
Applications: $ For low production series $ Test samples and prototypes $ Especially large dimensions $ Shortest delivery times Alloys:
! Mainly medium and high-strength
Source: H.G. Roczyn alu
Characteristics of Open-Die Forging
3402.01.07
Training in Aluminium Application Technologies
Die Forging The characteristics of die forging are listed in Figure 3402.01.08.
Characteristics of Die Forging Merits:
# Optimal microstructure # Grain flow (fibre structure) made to suit # Complicated forms # Low amount of machining # Efficient use of material
Problems:
# Tool costs
Applications:
$ For large production series $ Highest demands on strength + toughness $ Safety parts
Alloys:
! Mainly medium to high-strength materials
Source: H.G. Roczyn alu Training in Aluminium Application Technologies
TALAT 3402
Characteristics of Die Forging
7
3402.01.08
3402.02
Special Forging Processes for Aluminium • • • •
List of characteristic features of precision forging List of characteristic features of high precision forging Characteristic features of closed die forging without flash Characteristic features of isothermal forging
List of the aims of various special die forging processes (Figure 3402.02.01)
Special Forging Processes and their Aims Process
Characteristics
Advantages
1. Precision forging
better forging quality
narrower tolerances, better replication of final form
2. High precision forging
best forging quality
narrower tolerances, better replication of final form, better surfaces
3. Closed die forging without flash
forging in closed dies
material savings
4. Powder forging (mostly combined with 3.)
sintered raw parts
material savings, fewer forming process steps, narrower tolerances
5. Isothermal forging
tool temperature ~ work temperature
better replication of final form
6. Superplastic forging (mostly combined with 3)
as in 5. ; very low forming speeds
material savings, fewer forming process steps, better replication of final form
7.Squeeze casting
pressing in pasty state
fewer forming process steps, better replication of final form
8. Partial forging
stepwise fabrication
better replication of final form
9.Thermomechanical working
combined forging and structure change
better mechanical properties
Soerce: K. Lange, H. Meyer-Nolkemper alu
Special Forging Processes and their Aims
Training in Aluminium Application Technologies
TALAT 3402
8
3402.02.01
List of characteristic features of precision forging (Figure 3402.02.02)
Characteristics of Precision Forging Precision Forging is a die forging process which saves at least one finishing or supplementary operation compared to conventional die forging. Its merits are:
# # # # $ $
Problem:
Higher tooling costs
0° - 1° side tapers (draft) Thinner work-piece sections Narrower tolerances Smaller radii High quality surface finish Shorter production times for finished product
Source: K. Lange, H. Meyer-Nolkemper alu
Characteristics of Precision Forging
Training in Aluminium Application Technologies
3402.02.02
List of characteristic features of high precision forging (Figure3402.02.03)
Characteristics of High Precision Forging - Special case of precision forging - Production of "ready-to-use" parts # 0° - 1° side tapers # Thin work-piece regions # Narrow tolerances # Small radii $ High quality surface finish $ Shorter production times for finished product $ Little or no machining required $ Weight savings $ Good reproducibility Source: K. Lange, H. Meyer-Nolkemper alu Training in Aluminium Application Technologies
TALAT 3402
Characteristics of High Precision Forging
9
3402.02.03
Characteristic features of closed die forging without flash (Figure 3402.02.04)
Closed Die Forging without Flash Characteristics: =
Die forms in closed tools from which no material is lost
# # # #
Constant volume of hot starting, intermediate and final form Exact mass distribution Exact positioning No flash
$ $ $
Weight savings No flash Shorter production times for finished part
Source: K. Lange, H. Meyer-Nolkemper
Closed-Die Forging
alu
3402.02.04
Training in Aluminium Application Technologies
Characteristic features of isothermal forging (Figure 3402.02.05)
Isothermal Forging - Form pressing with die temperatures almost equal to the work temperature # Melted pockets due to local overheating caused by too high forming rates # Low temperature gradient tool / work piece # No flashed removal $ $
High quality parts in almost "ready-to-use" shape Shorter production times for finished part
Source: K. Lange, H. Meyer-Nolkemper alu
Isothermal Forging
Training in Aluminium Application Technologies
TALAT 3402
10
3402.02.05
3402.03
Forging Dies • • • • • •
Types of forging dies Parting of forging dies Rules for design of partings of forging dies Die inserts Fabricating forging dies Failure and damaging of forging dies
Types of Forging Dies The following types of forging dies are encountered in die forging: Figure 3402.03.01: - Single-cavity die - Multiple-cavity die: a number of identical cavities in one die - Multiple-stage die: more than one forming step for the workpiece in a die
Types of Forging Dies closed die
die with flash simple
multiple-cavity die
multi-stage die
die with multiple parts multi-stage die
upsetting punch punch holder full die
simple die
holing punch
insert with a number of identical cavities
block inserts clamping blocks
die insert Source: K. Lange alu Training in Aluminium Application Technologies
Types of Forging Dies
3402.03.01
The elements of forging dies are shown in Figure 3402.03.02 for a hammer die.
TALAT 3402
11
The Elements of Forging Dies (shown for a hammer die) h H impact area cavity reference areas clamping area hole for holding pin support area
B
h: cavity depth b: cavity width a, a1: web thicknesses
Source: K. Lange alu
L
a
b a1 b a
The Elements of Forging Dies
a
a H: block height L: block length B: block width
3402.03.02
Training in Aluminium Application Technologies
While designing forging dies, the following aspects must be taken into consideration: • Design to meet the stresses Forging dies are mostly subjected to repeated stress. The fatigue strength depends on the surface, cracks, residual stress and top-layer hardness. • Design for dimensions Shrinkage of the formed part is taken into account. Particular attention must be given to the fact that both die (steel) and workpiece (aluminium) have different coefficients of thermal expansion and that the die geometry has various sources of errors. • Design for machining • Machining tolerances are to be considered. • Design for optimal material flow The tool stress can be reduced by avoiding sharp edges, abrupt transitions, long narrow fins (ribs) etc. (see also TALAT Lecture 3403).
Parting of Forging Dies Dividing the cavity between top and bottom die (parting line of a forging) is of particular importance. The position of the parting line influences the tolerance of the forging and several other properties of the forging as well as die wear (see Figure 3402.03.03).
TALAT 3402
12
Partings of Forging Dies The parting plane of dies determines the proportion of volume of the forging in the upper and lower die.
The parting has an influence on further values and properties: - geometry of the forging - fibre structure - strength properties - mass of material - forging process (force required, form filling) - further working - wear of dies Source: H.G. Roczyn alu
Partings of Forging Dies
3402.03.03
Training in Aluminium Application Technologies
Rules for design of partings of forging dies Rules for design of partings of forging dies: 1. Symmetrical parting: The effort for making the tool with a given wall taper is lowest. 2. Plane parting: The die block height is the lowest; the mechanical working is simplified. 3. Parting for good material flow: This makes the material flow easy. 4. Parting for good machining: This makes it easy to machine or to remove flash.
Basic rules for the positioning of the parting of forging dies are collected in Figure 3402.03.04.
TALAT 3402
13
Basic Rules for Designing Partings for Forging Dies Construction aspects
Principle
Example
1 symmetrical parting flash not at edge of the workpiece
favourable, breaks rule 2
right wrong
right wrong
wrong 2 plane parting
favourable, breaks rule 2
preferential, simple die fabrication 3 parting for good material flow
breaks rule 3
favourable
favourable, breaks rule 2
unfavourable
"interrupted", flow optimised 4 parting for good machining
few areas with side taper sufficient allowance on machining areas
unfavourable
unfavourable
Source: K. Lange alu Training in Aluminium Application Technologies
Design Rules for Partings of Forging Dies
favourable
favourable, breaks rule
3402.03.04
Die Inserts Die inserts are blocks which can accommodate the complete die cavity (see Figure 3402.03.05). One can save expensive die steel for the die holder if die inserts are used. Die inserts are made of tempered alloy steel. due to the lowered stress acting on the die holders, these can be made of low alloy steel or tempered steel (e.g. steel 1.2713), thereby saving costs. The die insert is fastened to the die holder in a force or form locked type of joint.
TALAT 3402
14
Die Inserts Die insert in a die holder Merits of die inserts % Easy handling due to reduced weight % Insert can be constructed with high-strength materials % Die holder can be made of unalloyed or low alloyed material % Cost savings with replacements
Source: Thyssen alu
Die Inserts
3402.03.05
Training in Aluminium Application Technologies
Fabricating Forging Dies
Fabricating forging dies Fabrication & finishing block
rolling forging milling
Heat treating
Forming cavity
casting
annealing
heating
cold hobbing
warm hobbing
Post treatment
diffusion annealing machining
tempering
eroding
electrochemical milling
smoothing
Heat treating
tempering
Post treatment
stressrelieving
pressure jet lapping
Surface treatment Source: K.Lange / H. Meyer-Nolkemper alu Training in Aluminium Application Technologies
TALAT 3402
Fabricating Forging Dies
15
3402.03.06
The steps of fabrication of forging dies are described in Figure 3402.03.06. • The die block is produced by casting or rolling/forging and finally mechanically working. • The cavity is fabricated by machining, cold hobbing, eroding, electrochemical milling, etc.. • The die inserts (and die holder) are heat-treated to improve strength. • After polishing, the cavity has a surface roughness of 3 µm. Since aluminium has a lower flow stress than steel, the contours of the die cavity are reproduced more exactly on aluminium forgings. Failure and Damaging of Forging Dies Damages occur on forging dies due to thermal and mechanical fatigue as well as due to wear and permanent deformation (see Figure 3402.03.07). The individual effects occur in combinations of: 1. Warm fatigue cracks can occur due to thermal stresses in the tool. The temperature gradients depend on the geometry and forming conditions. 2. Plastic deformation occurs as a result of local stresses exceeding the yield strength, as may be the case in protruding form elements. 3. Fatigue cracks are initiated due to repeated die stresses occurring over the forming operation cycle. Thus, notches and abrupt transitions in the die should be avoided as far as possible. 4. Wear occurs due to small particles which detach from the surface. The degree of wear depends on the tribological system between tool and workpiece.
Failure and damaging of forging dies Damage is a result of : - the mechanical loading (repeated) due to forming resistance and geometrical conditions, - the thermal stressing due to workpiece and tool temperature as well as pressure contact time, - the tribological conditions at the contact zone between workpiece and tool.
mechanical fatigue permanent deformation
Wear (abrasion) thermal fatigue Source: A. Kannappan alu
Failure and Damaging of Forging Dies
Training in Aluminium Application Technologies
TALAT 3402
16
3402.03.07
3402.04 Literature: 1. Lange, K.: Benennung und Begriffsbestimmungen im Bereich der Umformtechnik. Ind. Anz. 86 (1964) 84-85 2. Lange, K.: Lehrbuch der Umformtechnik, Bd.2: Massivumformung, 2.Aufl. Berlin, Heidelberg, New York, Paris, Tokyo: Springer 1988. 3. Roczyn, H.G.: Vortrag Schmieden von Aluminium am IFU Stuttgart WS 92/93. 4. Lange, K.: Meyer-Nolkemper, H.: Gesenkschmieden, 2.Aufl. Berlin, New York: Springer 1977. 5. Nussbaum, A.I.: Forging Technology for the Nineties. Light Metal Age, 50 (1992) 7/8. 6. Thyssen Edelstahlwerke AG, Werkstoffblätter für Warmarbeitsstähle 7. Kannappan: Wear in forging dies. A review of world experience. Metal forming 36(1969) 335 - 342, Metal forming 37(1970) 6-14 and 21.
3402.05 List of Figures
Figure No. 3402.01.01 3402.01.02 3402.01.03 3402.01.04 3402.01.05 3402.01.06 3402.01.07 3402.01.08 3402.02.01 3402.02.02 3402.02.03 3402.02.04 3402.02.05 3402.03.01 3402.03.02 3402.03.03 3402.03.04 3402.03.05 3402.03.06 3402.03.07
TALAT 3402
Figure Title (Overhead) Fabrication Process of Forging Processes for Changing Cross-Sections Processes for Changing Direction Processes for Creating Hollow Spaces Separating Processes Die Forging Process Characteristics of Open-Die Forging Characteristics of Die Forging Special Forging Processes and Their Aims Characteristics of Precision Forging Characteristics of High Precision Forging Closed Die Forging Isothermal Forging Types of Forging Dies The Elements of Forging Dies Partings of Forging Dies Design Rules for Partings of Forging Dies Die Inserts Fabricating Forging Dies Failure and Damaging of Forging Dies
17
Forging Process 17 pages, 20 figures Basic Level prepared by K. Siegert, R. Malek and R. Neher, Institut für Umformtechnik, Universität Stuttgart
Objectives: − to understand the basic principles of die forging and the characteristic features of special aluminium die forging processes − to learn about the basic design of dies in order to obtain optimum part qualities and tool life
Prerequisites: − general understanding of metallurgy and deformation processes
Date of Issue: 1994 EAA - European Aluminium Association
3402 Forging Process Table of Contents 3402 Forging Process ....................................................................................................2 3402.01 Principles of the Forging Process ................................................................ 3 Fabricating Processes of Forging..................................................................................3 Processes for Changing Cross-Sections .......................................................................4 Processes for changing direction ..................................................................................5 Processes for Creating Hollow spaces..........................................................................5 Separating Processes.....................................................................................................6 Die Forging Processes...................................................................................................6 Open-Die Forging ................................................................................................... 7 Die Forging.............................................................................................................. 7 3402.02 Special Forging Processes for Aluminium.................................................. 8 List of the aims of various special die forging processes.............................................8 List of characteristic features of precision forging.......................................................9 List of characteristic features of high precision forging...............................................9 Characteristic features of closed die forging without flash....................................... 10 Characteristic features of isothermal forging ............................................................ 10 3402.03 Forging Dies ................................................................................................. 11 Types of Forging Dies................................................................................................ 11 Parting of Forging Dies.............................................................................................. 12 Rules for design of partings of forging dies .............................................................. 13 Die Inserts .................................................................................................................. 14 Fabricating Forging Dies ........................................................................................... 15 Failure and Damaging of Forging Dies ..................................................................... 16 3402.04 Literature:....................................................................................................... 17 3402.05 List of Figures................................................................................................. 17
TALAT 3402
2
3402.01
Principles of the Forging Process • • • • • •
Fabricating processes of forging Processes for changing cross-sections Processes for changing direction Processes for creating hollow spaces Separating processes Die forging processes
Fabricating Processes of Forging The term forging is used to define a group of processes which are mainly forming processes (see Figure 3402.01.01). Additionally included are processes of separating (splitting) and joining, if large or complicated workpieces are built up out of individual parts. The exact processes of separating and joining are not listed here in detail. According to the characteristic differences in free forming (or unrestricted forming) and die forming (restricted forming), forging can be divided into open-die forging and die forging.
Fabrication Process of Forging Separating
Forming Compressive forming
Tensile forming Bulge forming Bulge forming with mandrel Free bending
Rolling
Open-die forming
Rollforging
Drawing out solid and hollow bodies
Discrolling Ringrolling
Expanding Spreading
Upsetting Lateral rolling of shaped parts Heading Cross rolling of shaped parts
Stepping Radial or rotary forging alu
Closed-die forming
Bend forming
Drawing out in a die Fullering Radial forging in a die Upsetting in a die
Shear forming
Forming by bending with linear motion of tool
Displacing
Twisting
Offsetting
Setting spiral twisting
Die bending
Bending by buckling
Indenting Punching Through punching Piercing with a hollow mandrel
Closed die forging Embossing without flash Hobbing Impression die forging with flash
Extruding Solid forward impact extrusion Backward cup impact extrusion Solid lateral impact extrusion
Fabrication Process of Forging
Training in Aluminium Application Technologies
TALAT 3402
Joining
3
Source: K. Lange
3402.01.01
Processes for Changing Cross-Sections The processes for changing cross-sections build-up the fundamentals of forging, see Figure 3402.01.02. According to the law of constant volumes, changes in cross-section lead to corresponding changes in length. The cross-section can be changed by material displacement and material accumulation, whereby the processes of material displacement dominate.
Processes for Changing Cross-Sections Open-die forming Closed-die Forming Pushing through
Rolling
Solid forward impact extrusion
Material displacement
Drawing out
Spreading
Drawing out over a mandrel
Radial forging
Draw
Upsetting in a die
Radial forging in a die
Heading in a die
Heading in a horizontal upsetting machine
Stretch rolling
Backward cup impact extrusion
Solid lateral impact extrusion
Ring rolling
Cross rolling
Material accumulation Upsetting
Combined material displacement and accumulation
Heading
Upset die forging
alu
Processes for Changing Cross-Sections
Training in Aluminium Application Technologies
TALAT 3402
4
Source: K.Lange
3402.01.02
Processes for changing direction These processes include bending processes (free bending, die bending) and shear forming processes (Figure 3402.01.03). Processes for Changing Direction Punch (Top die) Bending die (Bottom die)
Forming
Top die Bottom die
Without elongation
With elongation
Bending in a die
Preformed workpiece
Shear Forming
Top die Displaced crank stroke pin
Bottom die
Twisting
Displacing Source: K.Lange alu
Processes for Changing Direction
Training in Aluminium Application Technologies
3402.01.03
Processes for Creating Hollow spaces Hollow spaces (cavities) are produced by the methods of indentation forming and extrusion forming (Figure 3402.01.04). Processes for Creating Hollow Spaces Hollow mandrel
Punch(rounded, not sharp)
Punch
Indentation Forming Scrap
Punching
Through Punching
Piercing with a hollow mandrel
Holing punch Receiver
Pressing Through
Holed plate Counter punch
Backward cup impact extrusion
Bulk holing
Source: K.Lange alu
Processes for Creating Hollow Spaces
Training in Aluminium Application Technologies
TALAT 3402
5
3402.01.04
Separating Processes Separating processes used for forging are mostly cutting processes (Figure 3402.01.05). Shear cutting processes are used for the loss-free cutting of raw parts with a given crosssection (extruded sections) and defined lengths or volumes. Separating Processes
Shear cutting Cutting
Closed cutting with cutting edge
Punch
Holing punch
Flash
Holed plate
Cutting plate
Flash removal
Holing
Chisel
Wedge cutting
Chisel
Anvil
Chisel
Anvil
Cutting with chisel
Anvil
Chopping
Slitting
Source: K.Lange alu
Separating Processes
3402.01.05
Training in Alum inium Application Technologies
Die Forging Processes These are processes which are used to produce a defined workpiece geometry having good dimension and volume accuracy. Such processes are: form pressing with flash, form pressing without flash and compressing in a die, see Figure 3402.01.06. Die Forging Processes in a Narrow Sense Clamping jaws
Top die
Upsetting
Flash
Punch Workpiece
Workpiece
Container Stripper Bottom die
Upsetting
Closed-die forging without flash
Closed-die forging with flash
Source: K. Lange alu
Die Forging Process
Training in Aluminium Application Technologies
TALAT 3402
6
3402.01.06
Open-Die Forging The chacteristics of open-die forging are listed in Figure 3402.01.07.
Characteristics of Open Die Forging Merits:
# #
No special tools (costs, fabricating time) Simple forms
Problems:
# # #
High machining costs Material not optimally used Grain flow (fibre structure) not optimal
Applications: $ For low production series $ Test samples and prototypes $ Especially large dimensions $ Shortest delivery times Alloys:
! Mainly medium and high-strength
Source: H.G. Roczyn alu
Characteristics of Open-Die Forging
3402.01.07
Training in Aluminium Application Technologies
Die Forging The characteristics of die forging are listed in Figure 3402.01.08.
Characteristics of Die Forging Merits:
# Optimal microstructure # Grain flow (fibre structure) made to suit # Complicated forms # Low amount of machining # Efficient use of material
Problems:
# Tool costs
Applications:
$ For large production series $ Highest demands on strength + toughness $ Safety parts
Alloys:
! Mainly medium to high-strength materials
Source: H.G. Roczyn alu Training in Aluminium Application Technologies
TALAT 3402
Characteristics of Die Forging
7
3402.01.08
3402.02
Special Forging Processes for Aluminium • • • •
List of characteristic features of precision forging List of characteristic features of high precision forging Characteristic features of closed die forging without flash Characteristic features of isothermal forging
List of the aims of various special die forging processes (Figure 3402.02.01)
Special Forging Processes and their Aims Process
Characteristics
Advantages
1. Precision forging
better forging quality
narrower tolerances, better replication of final form
2. High precision forging
best forging quality
narrower tolerances, better replication of final form, better surfaces
3. Closed die forging without flash
forging in closed dies
material savings
4. Powder forging (mostly combined with 3.)
sintered raw parts
material savings, fewer forming process steps, narrower tolerances
5. Isothermal forging
tool temperature ~ work temperature
better replication of final form
6. Superplastic forging (mostly combined with 3)
as in 5. ; very low forming speeds
material savings, fewer forming process steps, better replication of final form
7.Squeeze casting
pressing in pasty state
fewer forming process steps, better replication of final form
8. Partial forging
stepwise fabrication
better replication of final form
9.Thermomechanical working
combined forging and structure change
better mechanical properties
Soerce: K. Lange, H. Meyer-Nolkemper alu
Special Forging Processes and their Aims
Training in Aluminium Application Technologies
TALAT 3402
8
3402.02.01
List of characteristic features of precision forging (Figure 3402.02.02)
Characteristics of Precision Forging Precision Forging is a die forging process which saves at least one finishing or supplementary operation compared to conventional die forging. Its merits are:
# # # # $ $
Problem:
Higher tooling costs
0° - 1° side tapers (draft) Thinner work-piece sections Narrower tolerances Smaller radii High quality surface finish Shorter production times for finished product
Source: K. Lange, H. Meyer-Nolkemper alu
Characteristics of Precision Forging
Training in Aluminium Application Technologies
3402.02.02
List of characteristic features of high precision forging (Figure3402.02.03)
Characteristics of High Precision Forging - Special case of precision forging - Production of "ready-to-use" parts # 0° - 1° side tapers # Thin work-piece regions # Narrow tolerances # Small radii $ High quality surface finish $ Shorter production times for finished product $ Little or no machining required $ Weight savings $ Good reproducibility Source: K. Lange, H. Meyer-Nolkemper alu Training in Aluminium Application Technologies
TALAT 3402
Characteristics of High Precision Forging
9
3402.02.03
Characteristic features of closed die forging without flash (Figure 3402.02.04)
Closed Die Forging without Flash Characteristics: =
Die forms in closed tools from which no material is lost
# # # #
Constant volume of hot starting, intermediate and final form Exact mass distribution Exact positioning No flash
$ $ $
Weight savings No flash Shorter production times for finished part
Source: K. Lange, H. Meyer-Nolkemper
Closed-Die Forging
alu
3402.02.04
Training in Aluminium Application Technologies
Characteristic features of isothermal forging (Figure 3402.02.05)
Isothermal Forging - Form pressing with die temperatures almost equal to the work temperature # Melted pockets due to local overheating caused by too high forming rates # Low temperature gradient tool / work piece # No flashed removal $ $
High quality parts in almost "ready-to-use" shape Shorter production times for finished part
Source: K. Lange, H. Meyer-Nolkemper alu
Isothermal Forging
Training in Aluminium Application Technologies
TALAT 3402
10
3402.02.05
3402.03
Forging Dies • • • • • •
Types of forging dies Parting of forging dies Rules for design of partings of forging dies Die inserts Fabricating forging dies Failure and damaging of forging dies
Types of Forging Dies The following types of forging dies are encountered in die forging: Figure 3402.03.01: - Single-cavity die - Multiple-cavity die: a number of identical cavities in one die - Multiple-stage die: more than one forming step for the workpiece in a die
Types of Forging Dies closed die
die with flash simple
multiple-cavity die
multi-stage die
die with multiple parts multi-stage die
upsetting punch punch holder full die
simple die
holing punch
insert with a number of identical cavities
block inserts clamping blocks
die insert Source: K. Lange alu Training in Aluminium Application Technologies
Types of Forging Dies
3402.03.01
The elements of forging dies are shown in Figure 3402.03.02 for a hammer die.
TALAT 3402
11
The Elements of Forging Dies (shown for a hammer die) h H impact area cavity reference areas clamping area hole for holding pin support area
B
h: cavity depth b: cavity width a, a1: web thicknesses
Source: K. Lange alu
L
a
b a1 b a
The Elements of Forging Dies
a
a H: block height L: block length B: block width
3402.03.02
Training in Aluminium Application Technologies
While designing forging dies, the following aspects must be taken into consideration: • Design to meet the stresses Forging dies are mostly subjected to repeated stress. The fatigue strength depends on the surface, cracks, residual stress and top-layer hardness. • Design for dimensions Shrinkage of the formed part is taken into account. Particular attention must be given to the fact that both die (steel) and workpiece (aluminium) have different coefficients of thermal expansion and that the die geometry has various sources of errors. • Design for machining • Machining tolerances are to be considered. • Design for optimal material flow The tool stress can be reduced by avoiding sharp edges, abrupt transitions, long narrow fins (ribs) etc. (see also TALAT Lecture 3403).
Parting of Forging Dies Dividing the cavity between top and bottom die (parting line of a forging) is of particular importance. The position of the parting line influences the tolerance of the forging and several other properties of the forging as well as die wear (see Figure 3402.03.03).
TALAT 3402
12
Partings of Forging Dies The parting plane of dies determines the proportion of volume of the forging in the upper and lower die.
The parting has an influence on further values and properties: - geometry of the forging - fibre structure - strength properties - mass of material - forging process (force required, form filling) - further working - wear of dies Source: H.G. Roczyn alu
Partings of Forging Dies
3402.03.03
Training in Aluminium Application Technologies
Rules for design of partings of forging dies Rules for design of partings of forging dies: 1. Symmetrical parting: The effort for making the tool with a given wall taper is lowest. 2. Plane parting: The die block height is the lowest; the mechanical working is simplified. 3. Parting for good material flow: This makes the material flow easy. 4. Parting for good machining: This makes it easy to machine or to remove flash.
Basic rules for the positioning of the parting of forging dies are collected in Figure 3402.03.04.
TALAT 3402
13
Basic Rules for Designing Partings for Forging Dies Construction aspects
Principle
Example
1 symmetrical parting flash not at edge of the workpiece
favourable, breaks rule 2
right wrong
right wrong
wrong 2 plane parting
favourable, breaks rule 2
preferential, simple die fabrication 3 parting for good material flow
breaks rule 3
favourable
favourable, breaks rule 2
unfavourable
"interrupted", flow optimised 4 parting for good machining
few areas with side taper sufficient allowance on machining areas
unfavourable
unfavourable
Source: K. Lange alu Training in Aluminium Application Technologies
Design Rules for Partings of Forging Dies
favourable
favourable, breaks rule
3402.03.04
Die Inserts Die inserts are blocks which can accommodate the complete die cavity (see Figure 3402.03.05). One can save expensive die steel for the die holder if die inserts are used. Die inserts are made of tempered alloy steel. due to the lowered stress acting on the die holders, these can be made of low alloy steel or tempered steel (e.g. steel 1.2713), thereby saving costs. The die insert is fastened to the die holder in a force or form locked type of joint.
TALAT 3402
14
Die Inserts Die insert in a die holder Merits of die inserts % Easy handling due to reduced weight % Insert can be constructed with high-strength materials % Die holder can be made of unalloyed or low alloyed material % Cost savings with replacements
Source: Thyssen alu
Die Inserts
3402.03.05
Training in Aluminium Application Technologies
Fabricating Forging Dies
Fabricating forging dies Fabrication & finishing block
rolling forging milling
Heat treating
Forming cavity
casting
annealing
heating
cold hobbing
warm hobbing
Post treatment
diffusion annealing machining
tempering
eroding
electrochemical milling
smoothing
Heat treating
tempering
Post treatment
stressrelieving
pressure jet lapping
Surface treatment Source: K.Lange / H. Meyer-Nolkemper alu Training in Aluminium Application Technologies
TALAT 3402
Fabricating Forging Dies
15
3402.03.06
The steps of fabrication of forging dies are described in Figure 3402.03.06. • The die block is produced by casting or rolling/forging and finally mechanically working. • The cavity is fabricated by machining, cold hobbing, eroding, electrochemical milling, etc.. • The die inserts (and die holder) are heat-treated to improve strength. • After polishing, the cavity has a surface roughness of 3 µm. Since aluminium has a lower flow stress than steel, the contours of the die cavity are reproduced more exactly on aluminium forgings. Failure and Damaging of Forging Dies Damages occur on forging dies due to thermal and mechanical fatigue as well as due to wear and permanent deformation (see Figure 3402.03.07). The individual effects occur in combinations of: 1. Warm fatigue cracks can occur due to thermal stresses in the tool. The temperature gradients depend on the geometry and forming conditions. 2. Plastic deformation occurs as a result of local stresses exceeding the yield strength, as may be the case in protruding form elements. 3. Fatigue cracks are initiated due to repeated die stresses occurring over the forming operation cycle. Thus, notches and abrupt transitions in the die should be avoided as far as possible. 4. Wear occurs due to small particles which detach from the surface. The degree of wear depends on the tribological system between tool and workpiece.
Failure and damaging of forging dies Damage is a result of : - the mechanical loading (repeated) due to forming resistance and geometrical conditions, - the thermal stressing due to workpiece and tool temperature as well as pressure contact time, - the tribological conditions at the contact zone between workpiece and tool.
mechanical fatigue permanent deformation
Wear (abrasion) thermal fatigue Source: A. Kannappan alu
Failure and Damaging of Forging Dies
Training in Aluminium Application Technologies
TALAT 3402
16
3402.03.07
3402.04 Literature: 1. Lange, K.: Benennung und Begriffsbestimmungen im Bereich der Umformtechnik. Ind. Anz. 86 (1964) 84-85 2. Lange, K.: Lehrbuch der Umformtechnik, Bd.2: Massivumformung, 2.Aufl. Berlin, Heidelberg, New York, Paris, Tokyo: Springer 1988. 3. Roczyn, H.G.: Vortrag Schmieden von Aluminium am IFU Stuttgart WS 92/93. 4. Lange, K.: Meyer-Nolkemper, H.: Gesenkschmieden, 2.Aufl. Berlin, New York: Springer 1977. 5. Nussbaum, A.I.: Forging Technology for the Nineties. Light Metal Age, 50 (1992) 7/8. 6. Thyssen Edelstahlwerke AG, Werkstoffblätter für Warmarbeitsstähle 7. Kannappan: Wear in forging dies. A review of world experience. Metal forming 36(1969) 335 - 342, Metal forming 37(1970) 6-14 and 21.
3402.05 List of Figures
Figure No. 3402.01.01 3402.01.02 3402.01.03 3402.01.04 3402.01.05 3402.01.06 3402.01.07 3402.01.08 3402.02.01 3402.02.02 3402.02.03 3402.02.04 3402.02.05 3402.03.01 3402.03.02 3402.03.03 3402.03.04 3402.03.05 3402.03.06 3402.03.07
TALAT 3402
Figure Title (Overhead) Fabrication Process of Forging Processes for Changing Cross-Sections Processes for Changing Direction Processes for Creating Hollow Spaces Separating Processes Die Forging Process Characteristics of Open-Die Forging Characteristics of Die Forging Special Forging Processes and Their Aims Characteristics of Precision Forging Characteristics of High Precision Forging Closed Die Forging Isothermal Forging Types of Forging Dies The Elements of Forging Dies Partings of Forging Dies Design Rules for Partings of Forging Dies Die Inserts Fabricating Forging Dies Failure and Damaging of Forging Dies
17
Related Documents
Talat Lecture 3402: Forging Process
June 2020 2
Talat Lecture 3401: Forging Alloys
June 2020 6
Talat Lecture 3803: Process Technologies
June 2020 4
Forging Process Analysis
November 2019 16
Talat Lecture 4102: Clinching
June 2020 11More Documents from "CORE Materials"
Talat Lecture 2406: Annex 1
June 2020 2
