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UNlVERSITI TUN HUSSEIN ONN MALAYSIA

BORANG PENGESAHAN STATUS TESIS·

1111\ I.. PREDICTION OF PUNCHING LIFE SPAN FOR PHOSPHOR BRONZE STAMPING OPERATION

SESI l'ENGAjIA:\i: _______ _

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No 7 lalan Wira 2 , Taman Wjra, J>t 86400 Pt Raja , Batu Pahat, lohor

"I hereby declared that I have read this thesis and in my opinion this thesis in terms

of contents and quality requirements fulfill the purpose for the award of the

Master of Mechanical Engineering".

Signature

Name of Supervisor PROF. DR. SULAIMAN BIN HASSAN

Date ·······7!:/~~/~1.: ................... .

PRJEDJICTJION OF PlUNCJB[][NG lLJIFE SPAN FOR PHOSPHOR BRONZE STAMPJING OPERATJION

MOHID 18' ADZJIlL MIDN 3JIN HASHJIM

Thesis submitted in fulfillment of the requirements for the award of Master of Mechanical Engineering

Faculty of Mechanical and Manufacturing Universiti Tun Hussein Onn Malaysia

AUGUST 2007

Thesis submitted in fulfillment of the requirements

for the award of

Master of Mechanical Engineering.

"I hereby declare that the work in this thesis is my own except for quotations and summaries which have been duly acknowledged"

Signature

Name of Student MOHD F ADZIL MUIN BIN HASHIM

Date 9., b/([)~1 Q:j 'f ................... 7. .. ~ ............................................... .

11

To my dear wife, Zohaida, the most positive person I know and a constant

source of encouragement. She believed in me before I believed in myself

iii

To my dear children Firdaus, Iman, Naeem, and Syifa. Also to my dear parents.

They would have been pleased and proud to see the results of this undertaking.

Acknowledgements

Praise be to Him only, with His Grace and Mercy, He had given me the strength and courage to do and complete this project.

iv

Firstly I want to thank my supervisor Prof. Dr Sulaiman Hj. Hassan from

UTHM for his support and guidance during the project period.

Special thanks to Mr. Takahiro Yoshiike who is a stamping die designer and

had supported me. Also special thanks to small group of skillful world class die

maintenance technicians with dedicated production staffs and subordinates who had

worked together with me to achieve these results.

I want to thank Vba programmers who have guided me to write a customized

program for punch re-sharpening level using advanced Vba source codes world wide

especially John Walken Bach (USA). In addition, thanks to Krueger from UK for the

opens source Constrained Cubic Spline Vba subroutine. Finally, to countless friends,

local and international who had guided me directly or indirectly.

v

ABSTRAK

Meramal hayat mata alat punch adalah kritikal untuk produk kerana ianya

akan menyebabkan kualiti produk menjadi kurang baik, merendahkan kadar

pengeluaran dan membazir masa bagi proses penajaman. Mata alat perlu diasah

selepas digunakan beberapa kali kerana dimensinya akan merosot dan ini

menyebabkan ketidak tepatan yang akan menyebabkan dimensi produk tidak

mengikut yang ditentukan. Salah satu kaedah yang digunakan bagi penentuan masa

penajaman mata alat ialah melalui anggaran kasar mengunakan unit kshots.

Selalunya anggaran ini tidak tepat dan ianya menyebabkan proses penajaman dan

proses mencetak yang tidak ekonomi. Kajian ini dilakukan untuk mengatasi

kelemahan ini. Mata alat yang digunakan dalam kajian ini adalah dari jenis

Cementite Tungsten Carbide dan bahan keIja yang digunakan ialah Phosphor Bronze

Strip. DaIjah kekerasan relatifbahan adalah lebih kurang 6.3. Proses pencetakan

yang digunakan ialah proses pencetakan progresif dan ianya dijalankan di sebuah

kilang elektronik yang termuka. Untuk kadar kshots yang tertentu, profil kehausan

mata alat diukur dan ketidak tepatan dimensi produk dikaji. Peningkatan burr pad a

produk juga dikaji pad a setiap 4000 unit produk. Hayat mata alat adalah ditentukan

apabila produk yang dihasilkan rosak. Semasa ini, mata alat akan membulat,

kehausan dapat dikenalpasti dan kerekahan pada hujung mata alat dilihat. Dapatan

dari kajian ini ialah hubungan kadar kehausan berkadar terns kepada kshots dan ini

memudahkan algorithma bagi penentuan hayat mata alat dibuat. Model simulasi

dicipta dengan mengunakan 'Constraint Cubic Spline algorithm', pengkaji telah

dapat meramal keturnpulan dan kehausan mata alat dengan lebih tepat. Walau

bagaimanapun bentuk dan bahan mata alat serta kekerasan relatif akan

mempengaruhi algorithma ini. Kajian ini menjimatkan kos proses pencetakan

melalui mengurangkan ketidak tepatan ramalan kehausan dan hayat mata alat yang

seternsnya mengurangkan kerosakan produk, mengurangkan burr dan membolehkan

penajaman dibuat dengan lebih tepat. Secara keseluruhan, algorithma yang didapati

dapat menambah baik kecekapan dan menambah produktiviti.

VI

ABSTRACT

Predictions of punching life span for stamping process is critical since affect the

quality of product, the production rate and cause waste in time and cost. The punch

need to be sharpened correctly after a number of punches since its dimensional

accuracy will deteriorate and cause inaccuracy in the dimensions of the product and

thus do not satisfy the quality requirements. One of the method that are normally

used to determine the point where re-sharpening should be carried out is through

estimating the number of shots or unit kshots that will produce products that are

dimensionally inaccurate and the occurrence of burr on the product. The research

was carried out to overcome this problem. The punch that was used is made of

Cementite Tungsten Carbide and the work piece is Phosphor Bronze Strip. The

relative hardness is about 6.3. The stamping process is a progressive stamping

process carried out in a well known electronic factory. The profile of the wear of the

punch is measured and the error in product dimension is identified. The increase

presence of burr is also studied and identified for every 4000 product. The end of

punch life span is determined when there is a dimensional inaccuracy on the product

and the product is rejected. This research found that at this point punch is rounded,

wear is present and cracks occurred at the cutting edge of the tool. As a result of this

research, relation between the punch wear and kshots are found to be proportionate

and this enable an algorithm to be formulated. Simulation model is built to enable

more accurate algorithm is developed. The simulation model used 'Constraint Cubic

Spline algorithm'. The researcher is able to forecast a more accurately the kshots that

relates to punch wear and thus save products dimensional inaccuracy and product

rejects. An improved sharpening process is also possible and this provide accurate rc-

sharpening work. The accuracy of the sharpening prediction also reduce burr and

have enhance the efficiency of the resharpening process. In conclusion, the algorithm

has improved productivity and save cost to the company.

\'11

CONTENTS

CHAPTER TItLE PAGES

ACKNOWLEDGEMENTS iv

ABSTRACT "i T ABLES OF CONTENTS "II

LtST OF FIGURES xi

LlST OF TABLES X" liST OF SYMBOLS xvi

LiST OF DEFINITION xvii

LlST OF APPENDIXS xxiii

CHAPTER 1 INtRODUCTION

1.1 Needs For Prediction of Punching

Life Span

1.2 Research Motivation 2

1.3 Aim 2

1.4 Research Objectives -. .)

1.5 Research Scope 3

Vlll

CHAPTER 2 LITERATURE REVIEW 4

2.1 Introduction 4 2.2 Punch Wear Characteristics 4 2.3 Wear Mechanism and Quantification 12 2.4 Quantification of Adhesive Wear 14 2.5 Punch Wear At The Cutting Edge 16 2.6 Summary 19

CHAPTER]U THEORY OF STAMPING AND FACTORS 20 THAT ASSOCIATES WITH PUNCHING LIFE SPAN

3.1 Introduction 20 3.2 The Theory of Stamping 20

3.2.1 Classification of Stamping 21 3.2.2 Progressive Stamping 25

3.3 Basic Characteristics of Shear Cutting 26 3.4 Factors For Stamping Accuracy 29

3.4.1 Machine Accuracy 29 3.4.2 Static Accuracy 29 3.4.3 Dynamic Accuracy 30

3.4.4 Die Set Accuracy 31 3.4.5 Influence of punch

die clearance 32 3.4.6 Insufficient Clearance 33 3.4.7 Excessive Clearance 34 3.4.8 Stock Material 35

Accuracy 35

3.4.9 Phosphor Bronze Strip 35 3.5 Summary 36

IX

CHAPTER IV EXPERIMENT AL METHOD 38

4.1 Introduction 38 4.2 Experimental Procedure Flow Chart 39 4.3 Selection Of Punches 40 4.4 Preparation Of Stamping Machine 44 4.5 Stamping Die Set 44

4.6 Equipments 45 4.7 Scientific Imaging Software 47 4.8 Data Analysis Software 47

4.8.1 Interpolation Algorithms 48 4.8.2 Linear Piecewise Interpolation 48

4.8.3 Constrained Cubic Spline

Interpolation 49 4.8.4 Measures For The

Estimation of Predicted 51

Error

4.9 Punching Operation 52

4.10 SEM Micrograph of Punch Dull

Surface 53 4.11 Measuring The Punch Wear 55 4.12 Equation of The Wear Profile 55 4.13 Computation of Punching Life

Span and Wear Characteristics 58

4.14 Summary 59

CHAPTER V RESULTS AND DISCUSSIOl\S

5.1 Introduction

5.2 Punching Life Span

5.3 Validation of Punching Life Span

5.3.1 Validation of Punch SI Life

Span

5.3.2 Validation of Punch S2 Life

Span

5.3.3 Validation of Punch S3 Li fe

Span

5.4 Prediction of Optimum Re-sharpening

Length ofWom Punch Program

5.5 Validation of Punch SI Side Wear

Length

5.6 Validation of Punch S2 Side Wear

Length

5.7 Validation of Punch S3 Side Wear

Length

5.8 Summary

CHAPTER VI CONCLUSION

6.1 Conclusion

6.2 Contribution to Science

6.3 Future Works

REFERENCES

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XI

LIST OF FIGURES

FIGURES TITLE PAGES

2.1 Characteristics factors related to occurrence of 5

burr (After Kanno, 1986)

2.2 Relationship between the surface abrasion of the 6

punch and the occurrence of burr (After

Kanno,1986)

2.3 Schematic area of side wear (Mter Mitsumi 8

Corp,2002)

2.4 Transition of area of side wear (After Mitsumi 8

Corp,2002)

2.5 Transition of burr height with different punch 9

materials (After Mitsumi Corp,2002)

2.6 Transition of burr height with increase in number II

of shots (After Mitsumi Corp,2002)

2.7 Mechanism of adhesive wear by plasticity (After 13

Roberts,2003)

2.8 Model for derivation of Archard wear equation 14

(After Roberts, 2003)

2.9 Forces reacting on tooling surface during 17

punching process (After Lange, I 975)

2.10 Tooling conditions of the shearing process (After 17

Yoshida 2001)

2.11 SEM Micrograph of crack initiation (After 18

Yoshida, 2001)

3.1 Plastic deformations phase (After Lascoe, 1986) 21

XlI

3.2 Penetration deformations phase (After 21

Lascoe,1986)

3.3 Fracture phase (After Lascoe,1986) 22

3.4 Stamping operations using shearing principles 24

(After Lascoe,1986)

3.5 Comparison of cutting off and parting operation 25

(After Lascoe ,1986)

3.6 A progressive stamping skeleton (After 26

Shinano,1985)

3.7 The four basic characteristics of shearing cutting 27

(After Lascoe,1986)

3.8 Theoretical part edge after blanking (After 28

Taupin, ,1996)

3.9 Actual part edge after stamping using phosphor 28

bronze material

3.10 The effects of clearance towards part's e (After 33

David, 2000)

3.11 Effects of insufficient clearance towards facture

zone (After David, 2000) 33

4.1 Flowchart for the experimental procedure 39

4.2 Location of punches in the stamping die 40

4.3 The pilot punch identified as S 1 41

4.4 The oblong pilot punch identified as S2 42

4.5 The punch identified as S3 42

4.6 Stamping machine 44

4.7 The stamping die set 45

4.8 The Scanning Electron Microscope 46

4.9 Overshooting of Cubic Spline and Smoothness of 51

Constrained Cubic Spline

4.10 Cleaning the punch before analyzing 53

4.11 Mounting the punch on the SEM stage 54

4.12 SEM micrograph of the punch wear cutting edge 54

4.13 Screenshot of SCION imaging software 55

Xlll

4.14 Screenshot of the Excel Function to extract 56

coefficients

4.15 Screenshot of tabulated data points 58

4.16 Equations of punch wear profile after 5.1 Mshots 57

4.17 Screen shot of the computed worn punch loss area 59

5.1 (a) Measured variables of worn punch 62

5.1 (b) Schematic of punch re-sharpening length 63

5.1 (c) Comparison of burr height between (a) sharp 66

punch and a (b) worn punch when life span is

reached

5.1 (d) SEM micrograph of worn punch ex 1200) 67

5.1 (e) SEM micrograph of a failed punch 67

5.2 Comparison between shots-dependent of average 69

area loss on different punches S 1, S2 and S3

5.3 Agreement between shot -dependence on average 72

area loss and recorded area loss of punch S 1 is

reached between 0 Mshots to 4.7 Mshots

5.4 Agreement between shot-dependent average area 73

loss and recorded area loss of punch S2 is reached

between 0 Mshots to 5.2 Mshots

5.5 Agreement between shot-dependent average area 74

loss and recorded area loss of punch S3 is reached

between 0 Mshots to 5.4 Mshots

5.6 Process flow for predicting and validating the side 76

wear length

5.7 Agreement between shot-dependent side wear 78

lengths of recorded and predicted curve of punch

S1 is reached between 0 Mshots to 4.7 Mshots.

5.8 Agreement between shot-dependent side wear 79

lengths of recorded and predicted curve of punch

S2 is reached between 0 Mshots to 4.9 Mshots.

5.9 Agreement between shot-dependent side wear 80

lengths of recorded and predicted curve of punch

S3 is reached between 0 Mshots to 5.4 Mshots

XIV

B.l Recorded data for checking stamping machine 98

dynamic accuracy

E.l A straight is used to approximate the curve f(x) 101

between X 1 and x2

F1.1 Comparison between the cutting edge of the

punch S 1 taken at a different interval

F1.2 Shows the comparison of punch's wear profile at 106

different intervals

F1.3 The CCS interpolation has fitted a smooth line 108

between the observed data points

F1.4 Shows the screenshot of the simulation program 109

01.1 Wear profile of punch SI after run 01 110

01.2 Wear profile of punch SI after run 02 110

01.3 Wear profile of punch SI after run 03 111

01.4 Wear profile of punch Sl after validation process 111

02.1 Wear profile of punch S2 after run 01 112

02.2 Wear profile of punch S2 after run 02 112

02.3 Wear profile of punch S2 after run 03 113

02.4 Wear profile of punch S2 after validation process 113

03.1 Wear profile of punch S3 after run 01 114

03.2 Wear profile of punch S3 after run 02 114

03.3 Wear profile of punch S3 after run 03 115

03.4 Wear profile of punch S3 after validation process 115

H1.1 Samples of punch S 1 micrograph after run 02 116

H1.2 Samples of punch S 1 micrograph after run 03 116

H2.l Samples of punch S2 micrograph after run 02 117

H2.2 Samples of punch S2 micrograph after run 03 117

H3.l Samples of punch S3 micrograph after run 02 118

H3.2 Samples of punch S3 micrograph after run 03 118

xv

LIST OF 'fABLES

TABLES TITLE PAGES

2.1 List of punch material used to determine life span 7

3.1 Classification of stamping operation 23

4.1 The operational conditions of stamping machine 43

5.1 Area loss by worn punches 81,82 and 83 68

5.2 8ummary of observed wear rates between punches 70

81,82 and 83

5.3 Validation results of punches life span and wear 75

rate

5.4 Prediction accuracy and curve validation range 81

Fl.l An extract of the excel formula that generates the 104

coefficients

Fl.2 A detail list of data generated by the polynomial 105

equation of the punch model 81 at the 2nd

repetition of the industrial experiment

Fl.3 Data of punch model 81 107

Fl.4 Data generated by Constrained Cubic 8pline 107

Interpolation

A

H

V

W

Wsp R2

spm

K

K

L

Mshots

LIST OF SYMBOLS

Area loss due to wear at the punch cutting edge

Hardness

Volume loss due to wear at the punch cutting edge

Wear rate of a punch (mm2/Mshots)

Specific Wear Rate (mm2/m/N)

Coefficient of determination.

Unit of stamping velocity in strokes per minute.

Wear rate (mm2/m)

Archard wear coefficient

Life of a punch before next re-sharpening

The unit of punch hits through the stock material.

XVI

Abrasion

Abrasive

wear

Adhesion

Adhesive

wear

Blank

: Blanking

xvii

LIST OF DEFINITIONS

A process where hard particles are forced against and

moved along a solid surface.

It is a displacement of material, due to hard particles

or hard protuberances. A hard body plastically

deforms (with or without removal of matter) a softer

body.

(1) The attractive force between adjacent surfaces in a

frictional contact; (2) the state in which interfacial

forces hold two surfaces together.

At a certain moment, the force applied to the contact is

supported by the existing junctions. An adhesive

junction is produced. It is either hardly resistant at all

and the two bodies separate with no change, or the

junctions is relatively resistant, and a crack forms in

the less resistant body.

The piece of sheet or strip metal produced in cutting

dies. The produced pieces are discrete and have no

material carrier.

The process of cutting out a flat piece of the size and

shape necessary to produced the desired part.

Bolster plate

Burr

Burr side

Capacity of a

press

Clearance

Crank press

Die set

Die shoe

The static plate attached to the top of the bed of a

press.

xviii

A rough ridge, edge, protuberance, or area such as that

left on metal after cutting, drilling, punching, etc. In

stamping it occurs in cutting dies because of the

clearance between punch and die.

This term is refers to the side or face of a blank or

other stamping which comes in direct contact with

punch in a blanking operation, and the side or face of a

blank or other stamping which comes in direct contact

with the die in a punching operation.

The related capacity of a press is the pressure, in tons,

which the slide will safely exert at the bottom of the

stroke in doing work within the range of the press.

In punching and shearing dies, the gap between the die

and the punch.

A mechanical press the slide of which is actuated by a

crankshaft.

A tool holder held in alignment by guideposts and

bushings and consisting of a lower shoe, upper shoe or

punch holder, guideposts and bushings.

A plate or blocks which die holder is mounted. A die

shoe functions primarily as a base for the complete die

assembly and, when used, is bolted or clamped to the

bolster plate or face of slide.

Elastic limits

Flank of punch

Metal

Progression

Progressive die

Punch

Punching

XIX

The maximum stress to which a material or body can

be subjected and still return to its original shape and

dimension.

The position at the horizontal plane of punch where it

will shear the stock material.

A group of substance that can conduct electricity and

heat and can be hammered into shape or draw out in

sheets.

The precise linear travel of the stock strip at each press

stroke and is equal to the inter-station distance. Also

called pitch, advance, or feed.

A die with two or more stations arranged in line for

performing two or more operations on a part one

operation usually being performed at each station.

The parts are connected by a carrier strip until final

parting or cutoff operation.

i) The male part of the die, as distinguish the female

part called the die. The punch is the upper member of

the complete die and is mounted on the slide.

ii) The act of piercing or punching a hole. Also

referred to as punching

The die shearing of a closed contour in which the

sheared out sheet metal part is scrap.