nelson_stud welding_updated-dec12

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Report Number: F/MAE/NG/2015-3

Forging Progression Sequence Development for Bolt Shank

Submitted to

Nelson Stud Welding

By

Fnu Aktaruzzaman – Research Assistant

James Lowrie – Research Assistant

Gracious Ngaile – Associate Professor

North Carolina State University

Department of Mechanical & Aerospace Engineering

Advanced Metal Forming and Tribology Laboratory (AMTL)

December 5, 2015

Confidential Report

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Foreword

This document has been prepared by the Advanced Metal Forming and Tribology Laboratory in

the Department of Mechanical and Aerospace Engineering at North Carolina State University.

The research focus of this Lab includes manufacturing process modeling and optimization,

triboscience and tribotechnology, tool design, and computational tools. In addition to conducting

industry relevant engineering research, the Lab has the objectives a) establish close cooperation

between industry and the university, b) train students, and c) transfer the research results to

interested companies.

This report, entitled “Forging Progression Sequence Development for Bolt Shank”, presents FE

simulation results for several alternative progression sequences.

For further information, contact Dr. Gracious Ngaile, located at North Carolina State University,

Department of Mechanical & Aerospace Engineering, 911 Oval Drive – 3160 Engineering

Building III, BOX 7910, Raleigh, NC, 27695-7910, phone: 919-515-5222,

email:[email protected], webpage:http://www.mae.ncsu.edu/ngaile.

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Table of Contents

Foreword …………………………………………….…...2

Table of contents …………………………………………………3

Chapter 1: Introduction …………………………………………………4

1.0 Introduction ………………………………………………....4

1.1 Objectives …………………………………………………5

1.2 Approach …………………………………………………5

1.3 Finite Element Setups ………………………………………………....6

Chapter 2: Forging Progression Alternatives for Part# 1…………………………7

2.1 Progression Alternative – I …………………………………………………7

2.2 Progression Alternative – II …………………………………………………11

2.3 Progression Alternative –III ………………………………………………....18

Chapter 3: Forging Progression Alternatives for Part# 2…………………………28

3.1 Progression Alternative – I …………………………………………………28

3.2 Progression Alternative – II …………………………………………………34

3.3 Progression Alternative – III …………………………………………………41

3.4 Repeated Simulation of Progression Alternative -III ……………………………..54

Chapter 4: Conclusions …………………………………………………51

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Chapter 1

Introduction

1. Introduction

Nelson stud welding plans to produce bolt shank shown in Figures 1 and 2 by forging. Due to

complex flow of material, these parts can only be produced in several stages. NCSU was asked

to determine potential progression sequences and study material flow using the finite element

method. Conventional forging techniques for forward-backward extrusion of similar parts have

shown to produce folding defects. Thus, in the course of developing progression sequences,

emphasis was given to material follow modes, strain induced, fold formation, under fill and other

defects.

Figure1: Dimensional details of Part-1

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Figure2: Dimensional details of Part-2

1.1 Objectives

(a) Conduct finite element analysis of the baseline progression provided by Nelson. Reproduce

fold defect that has been encountered in industry when forming these parts. (Reported in

progress report). (b) Establish potential alternative forging sequence for Part 1 and Part 2 that

lead to sound product.

1.2 Approach

Preform design methodology based on geometric resemblance developed at NCSU was used to

narrow down potential progression sequences. Finite element software DEFORM was used in

the study. The baseline progression provided by Nelson was used as a starting point to develop

alternative progression sequences. Before looking for other progression alternatives, fold defect

had to be reproduced by simulating the baseline sequence.

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1. 3 Finite Element Model Setups

The simulations were carried out using 2D DEFORM software package. The following

assumptions were made to facilitate the solution process.

The process can be considered a quasi-static problem (No kinetic effects)

The process is not strain rate dependent because it is a cold forging process (rigid-plasic

material)

AISI 4140 was used in the simulations

The dies used in the process do not deform

All preform and final form shapes are rotationally symmetric about their center axis

Friction between the dies and workpiece was approximated by a constant shear friction

factor of 0.12

A number of simulations were carried out. This report, however, presents three different

alternatives for each part. The alternative progressions for Part 1 are presented in Chapter 2 and

altenative progressions for Part 2 are presented in Chapter 3.

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Chapter 2

Forging Progression Alternatives for Part # 1

2.1 Progression Alternative – I

In this alternative progression sequence the bolt shank is formed in two stages, one preform stage

and final stage.

Preform stage: The first simulation was set up by considering the first stage of forging as a

simple two die system, a fixed bottom die and a moving punch. The dimensions of the original

billet and the desired shape of the part at the end of the first preform is shown in figure 3. The

workpiece was meshed with about 2000 elements, as shown in figure 4, and a clear picture of the

die set used in the first operation can be seen in figure 5. The predicted load required to form the

first preform is 103 ton (228 klbf) and there is no evidence of defects at this stage in the forming

process (see figure 5 and figure 6). Load goes up just before the final step to fill the corners of

the die cavity.

Figure 3: Initial billet and the preform dimensions

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Figure 4: (left) Initial mesh used in the first preforming stage (right) die set used to carry out the

first preforming stage

Figure 5: Strain distribution of the 127th step of first preforming

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Figure 6: Magnified view of final step of first preforming (no forming defect found)

Final forming stage: The final stage of the previous simulation is used as the starting point for

this simulation. The mesh and dies used in the final stage are shown in figure 8. According to

the simulation, it takes 132 tons (292 klbf) to form the part. Load goes up just before the final

step to fill the corners of the die cavity. A seen in figure 9 and figure 10, there is no evidence of a

forming defect. The maximum strain induced in the final stage is 2.16 and occurs around the

edge of the bottom surface of the part and the top backward extruded cup.

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Figure 7: Final forming drawing

Figure 8: (left) Initial mesh used in the final stage (right) die set used to carry out the final

forming operation

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Figure 9: Strain distribution of the 190th step of final forming

Figure 10: Magnified view of final step of final forming (no forming defect found)

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2.2 Progression Alternative- II

In this alternative progression sequence the bolt shank is formed in three stages; 1st preform, 2nd

preform and final stage.

Preform stage 1: The first simulation was set up by considering the first stage of forging as a


billet and the desired shape of the part at the end of the first preform is shown in figure 11. Note

that in this alternative, the initial billet has a smaller diameter compared to the alternative 1. The

workpiece was meshed with about 2000 elements, as shown in figure 12, and a clear picture of

the die set used in the first operation can be seen in figure 12. The predicted load required to

form the first preform is 30 ton (65.9 klbf) and there is no evidence of defects at this stage in the

forming process (see figure 13 and figure 14). Load goes up just before the final step to fill the

corners of the die cavity.

Figure 11: Initial billet and 1st preform dimensions

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Figure 12: (left) Initial mesh used in the first preforming stage (right) die set used to carry out

the first preforming stage

Figure 13: Strain Distribution in the First Preform

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Figure 14: Magnified view of last step of first preform (no forming defect found)

Preform stage 2: The second preforming stage utilizes the geometry and strain from the final

step of the simulation of the first preforming stage. The mesh and die set used to carry out this

stage of the forming process is shown in figure 15. A load of 62 tons (137klbf) was required to

form the second preform and there is still no evidence of forming defects, as can be seen in

figure 16 and figure 17. Load goes up just before the final step to fill the corners of the die cavity.

The maximum strain in the second preforming occurs at around the edge of the bottom surface of

the part and is about 1.65.

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Figure 15: (left) Initial mesh used in the second preforming stage (right) die set used to carry out

the second preforming stage

Figure 16: Strain distribution in the second preform

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Figure 17: Magnified view of last step of second preform (no forming defect found)

Final stage: The final stage of the previous simulation is used as the starting point for this

simulation. The mesh and dies used in the third preforming stage are shown in figure 19.

According to the simulation, it takes 108 tons (239 klbf) to carry out the final forming stage.

Load goes up just before the final step to fill the corners of the die cavity. As shown in figures 20

and 21, there is no evidence of a forming defect. The maximum strain in the final stage occurs at

around the edge of the bottom surface of the extruded cup and is about 3.11. This strain is rather

high for cold forming. However it is localized at the center of the cup.

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the final forming stage

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Figure 20: Strain distribution in the final forming operation

Figure 21: Magnified view of last step of final forming operation (no forming defect found)

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2.3 Progression Alternative - III (Baseline given by Nelson)

In this alternative progression sequence the bolt shank is formed in four stages; 1st preform, 2nd

preform, 3rd and final stage.

Preform 1: The first simulation was set up by considering the first stage of forging as a simple

two die system, a fixed bottom die and a moving punch. The dimensions of the origonal billet

and the desired shape of the part at the end of the first preform is shown in figure 22. The



form the first preform is 86 ton (191 klbf) and there is no evedence of defects at this stage in the

forming process (see figure 24 and 25). Load goes up just before the final step to fill the corners

of the die cavity. As shown in Figure 24 the extrusion load was in the order of 60klbf before

sudden rise at the end of the stroke. The maximum strain exhibited at this is stage is 1.71.

Figure 22: Initial billet and final stage of 1st preform

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the 1st preforming stage

Figure 24: Strain Distribution in the First Preform

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step of the simulation of the first preforming stage. The desired geometry of the second preform

is shown in figure 26. The mesh and die set used to carry out this stage of the forming process is

shown in figure 27. A load of 85 tons (187klbf) was required to form the second preform and

there is still no evidence of forming defects, as can be seen in figure 28 and figure 29. Load goes

up just before the final step to fill the corners of the die cavity. The maximum strain in the

second preforming occurs at around the edge of the bottom surface of the part and is about 2.00

according to this model of the forging process.

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Figure 26: Second preform drawing and die-punch design

Figure 27: (left) Initial mesh used in the 2nd preforming stage (right) die set used to carry out the

second preforming stage

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Figure 28: Strain distribution in the 2nd preform

Figure 29: Magnified view of last step of 2nd preform (no forming defect found)

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Preform stage 3: The desired shape of the workpiece at the end of the third preforming stage is

shown in figure 30. Again, the final stage of the previous simulation is used as the starting point

for this simulation. The mesh and dies used in the third preforming stage are shown in figure 31.

According to the simulation, it takes 3.6 tons (8 klbf) to carry out the third preforming step. As

seen in figure 32 and figure 33, there is no evidence of a forming defect. The maximum strain in

the third preforming occurs at around the edge of the bottom surface of the part and is about 1.79.

Figure 30: Third preform drawing and die-punch design

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Figure 31: (left) Initial mesh used in the third preforming stage (right) die set used to carry out

the third preforming stage

Figure 32: Strain distribution in the third preform

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Figure 33: Magnified view of last step of 3rd preform (no forming defect found)

Final stage 4: The first step of the final step in the forging process was carried over from the

results of the previous simulation. The desired shape of the forging is shown in figure 34 and the

mesh and dies used in the forming process are shown in figure 35. The predicted load to carry

out this stage of the forming is 72.5 tons (160 klbf) and no folding defect was observed for this

forming process. Figure 36 and figure 37 show forming load and strain distribution for the final

stage. Load goes up just before the final step to fill the corners of the die cavity. The maximum

strain in the final forming occurs at around the center of the part and is about 1.79 according to

this model of the forging process.

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Figure 34: Final forming drawing and die-punch design


stage

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Figure 36: Strain distribution of the 630th step of fourth preform

Figure 37: Magnified view of the final forming stage (no forming defect found)

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Chapter 3

Forging Progression Alternatives for Part # 2

3.1 Alternative progression- I

In this alternative progression sequence the bolt shank is formed in two stages, one preform stage

and final stage.

Preform stage: The first simulation was set up by considering the first stage of forging as a



workpiece was meshed with about 2000 elements, as shown in figure39, and a clear picture of


form the first preform is about 100 ton (225 klbf) and there is no evidence of defects at this stage

in the forming process (see figure 40 and figure 41). The punch load goes up just before the final

step to fill the corners of the die cavity. As seen in Figure 40, the punch load increase from

145klb to 225llbf at the final stroke.

Figure 38: Initial billet and 1st stage preform dimensions

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Figure 40: Load and strain distribution at the final punch stroke of the preforming stage

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Figure 41: Magnified view of final step of first preforming (no forming defect found)

Final state: The final stage of the previous simulation is used as the starting point for this


According to the simulation, it takes 139 tons (307 klbf) to carry out the third preforming step,

Figure 44. It should be noted that the load goes up from 150klbf to 305 klbf just before the final

step to fill the corners of the die cavity. The strain map figures (Figs 44 and 45) show no

evidence of a forming defect. The maximum strain of 2.63 occurs at the center of the backward

extruded cup.

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forming operation

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Figure 44: Load and strain distribution of the 496th step of final forming stage

Figure 45: Magnified view of final step of forming (no forming defect found)

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3.2 Progression Alternative - II

In this alternative progression sequence the bolt shank is formed in three stages, 1st preform, 2nd

preform and final stage.





the die set used in the first operation can be seen in figure 47. Note that in this alternative and

small diameter billet is used. The predicted load required to form the first preform is 21 ton (46.7

klbf) and there is no evidence of defects at this stage in the forming process (see figure 48 and

figure 49). A maximum effective strain of 1.58 was exhibited at this stage.

Figure 46: initial billet and final stage of first preform

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Figure 47: (left) Initial mesh used in the 1st preforming stage (right) die set used to carry out the

1st preforming stage

Figure 48: Load and strain distribution in the 1st preform

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Figure 49: Magnified view of last step of 1st preform (no forming defect found)


step of the simulation of the first preforming stage. The mesh and die set used to carry out this

stage of the forming process is shown in figure 50. A load of 43 tons (95.1klbf) was required to

form the second preform and there is still no evidence of forming defects, as can be seen in

figure 51 and figure 52. The punch load slightly goes up just before the final step to fill the

corners of the die cavity. The maximum strain in the second preforming occurs at around the

edge of the bottom surface of the part and is about 1.93.

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Figure 51: Strain distribution in the second preform

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Final stage: The final stage of the previous simulation is used as the starting point for this


According to the simulation, it takes 108 tons (239 klbf) to carry out the third preforming step.

Load goes up just before the final step to fill the corners of the die cavity. Figures 55 and 56

show that at the end of the punch stroke there is no evidence of a forming defect. The maximum

strain in the final stage occurs at around the center of the backward extruded cup and is about

3.01 (Figure 56). This strain is rather high for cold forging but it is localized at the center of the

extruded cup.

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stage

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Figure 55: Load and strain distribution in the final forming operation

Figure 56: Magnified view of last step of final forming operation (no forming defect found)

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3.3 Progression Alternative -III (Baseline given by Nelson)




simple two die system, a fixed bottom die and a moving punch. The dimensions of the origonal




form the first preform is 21.5 ton (47.4 klbf) and there is no evedence of defects at this stage in

the forming process (see figure 59 and figure 60).


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Preform stage 1 (repeat):

The first simulation (following given baseline) was repeated due to inconsistant strain rate

comparing to strain rate of first preform simulation (given baseline design for part-1) of part-1

(Figure 24). For this step maximum strain for part-1 was 1.71 but for part-2 it is 1.33 which is

considerablly lowar then part-1 first preform strain. To analyse this issure we repeat this

simulation again. Simulation was set up as a simple two die system, a fixed bottom die and a

moving punch. The dimensions of the origonal billet and the desired shape of the part at the end

of the first preform is shown in figure 57. The workpiece was meshed with about 2000 elements,

as shown in figure 61, and a clear picture of the die set used in the first operation can be seen in

figure 61. The predicted load required to form the first preform is 97 ton (213 klbf) (previous

step’s load and strain was 48.7 klbf and 1.55 in/in respectively) and there is no evedence of

defects at this stage in the forming process (see figure 62 and figure 63).

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Strain comparison of preform1 of part-1 and part-2:

Figure 64: (a) first preform of part-2 (b) repeated first preform of part-2 (c) first preform of part -

1 (figure 24)

Part -2 Part -2 Part -1

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In Figure 64 shows the strain distribution of (a) first preform of part-2, (b) repeated first preform

of part-2 and (c) first preform of part -1. In this three figure parts are extruding from .615 starting

diameter to .430 finish diameter but the maximum strains are not same. Strain concentretration at

the bottom corner of the bolt shank (Figure 64 –(b) and (c)) incraced the maximum strains but

strain distributions along the bolt shank (~ 1.33 in/in) are similer for all the preforms which

confirm the consistancy of forming process. We repeated the all the preforming process of part-2

(folloing given basieline design) to see the reproducebility of the process. Repeated preforms for

part-2 are discuss at the end of this chapter.




shown in figure 66. A load of 117.5 tons (259 klbf) was required to form the second preform

and there is still no evidence of forming defects, as can be seen in figure 67 and figure 68. Load

goes up just before the final step to fill the corners of the die cavity. The maximum strain in the

second preforming occurs at the center of the backward extruded and is about 1.71.


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Figure 67: Load and strain distribution in the second preform

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According to the simulation, it takes 43 tons (95.2 klbf) to carry out the third preforming step.

Figures 71 and 72 show that at the end of the third simulation, there is no evidence of a forming

defect. The maximum strain in the third preforming occurs at the center of the backward

extruded cup and is about 2.97.

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Figure 71: Load and strain distribution in the third preform

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Figure 72: Magnified view of last step of third preform (no forming defect found)

Final forming stage: The first step of the final step in the forging process was carried over from

the results of the previous simulation. The desired shape of the forging is shown in figure 69 and

the mesh and dies used in the forming process are shown in figure 73. The predicted load to

carry out this stage of the forming is 90 tons (199 klbf) and no folding defect was observed for

this forming process as shown in figures 74 and 75. Load goes up just before the final step to fill

the corners of the die cavity. The maximum strain in the final forming occurs at around the

center of the backward extruded section and is about 3.69 according to this model of the forging

process. The maximum strain exhibited in this alternative progression is rather high for cold

forming. It should be noted that the same progression was used for Part # 1. But the maximum

strain induced for Part # 1, was relatively low.

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stage

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Figure 76: Magnified view of final forming stage (no forming defect found)

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3.3 Repeated Simulation of Progression Alternative -III (Baseline given by Nelson)



Repeated preform stage 1.

The first simulation was set up as a simple two die system, a fixed bottom die and a moving

punch. The dimensions of the origonal billet and the desired shape of the part at the end of the

first preform is shown in figure 77. The workpiece was meshed with about 2000 elements, as

shown in figure 78, and a clear picture of the die set used in the first operation can be seen in

figure 78. The predicted load required to form the first preform is 22 ton (47.4 klbf) and there is

no evedence of defects at this stage in the forming process (see figure 79 and figure 80).


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shown in figure 82. A load of 112 tons (248 klbf) was required to form the second preform and

there is still no evidence of forming defects, as can be seen in figure 83 and figure 84. Load goes

up just before the final step to fill the corners of the die cavity. The maximum strain in the

second preforming occurs at the center of the backward extruded and is about 2.08.

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Figure 83: Load and strain distribution in the second preform


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According to the simulation, it takes 43 tons (93.4 klbf) to carry out the third preforming step.

Figures 87 and 88 show that at the end of the third simulation, there is no evidence of a forming

defect. The maximum strain in the third preforming occurs at the center of the backward

extruded cup and is about 2.92.


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Figure 87: Load and strain distribution in the third preform

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Figure 88: Magnified view of last step of third preform (no forming defect found)

Final forming stage: The first step of the final step in the forging process was carried over from

the results of the previous simulation. The desired shape of the forging is shown in figure 89 and

the mesh and dies used in the forming process are shown in figure 80. The predicted load to

carry out this stage of the forming is 79 tons (176 klbf) and no folding defect was observed for

this forming process as shown in figures 91 and 92. Load goes up just before the final step to fill

the corners of the die cavity. The maximum strain in the final forming occurs at around the

center of the backward extruded section and is about 3.23 according to this model of the forging

process. The maximum strain exhibited in this alternative progression is rather high for cold

forming. It should be noted that the same progression was used for Part # 1. But the maximum

strain induced for Part # 1, was relatively low.

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stage

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Figure 92: Magnified view of final forming stage (no forming defect found)

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Chapter 4

Conclusions

A number of simulations were carried out to determine potential progression sequences for both

Part 1 and Part 2. This report, however, presents three alternative progressions for each part. The

presented progressions were carefully studied to ensure that there is no defect. Tables 1 and 2

give the maximum strain values and punch loads exhibited in all the forming stages.

*- A previous step with strain of 1.79 was used in the next simulation.

Table 1: Forging summary for Part -1

Progression variants Maximum load

(klbf)

Maximum strain

(in/in)

Alternative # 1 Preform - 1 228 2.16

Final stage 292 2.16

Alternative # 2

Preform - 1 65.9 1.38

Preform - 2 137 1.65


Alternative # 3

(baseline provided by

Nelson)

Preform - 1 191 1.71

Preform - 2 187 2.00*

Preform - 3 8 1.79


Table 2: Forging summary for Part -2

Progression Variants Maximum load (klbf) Maximum strain

(in/in)

Alternative # 1 Preform - 1 225 2.25


Alternative # 2

Preform - 1 46.7 1.58

Preform - 2 95.1 1.93

Final stage 239 3.01 Repeated

preforms

Alternative # 3

(baseline provided

by Nelson)

Preform - 1 47.4 1.33 1.33

Preform - 2 259 1.71 2.08

Preform - 3 95.2 2.97 2.92

Final stage 199 3.69 3.23

nelson_stud welding_updated-dec12

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