UNIVERSITI PUTRA MALAYSIA

DEVELOPMENT OF CAD/CAM SYSTEM FOR COLD WORKING CLOSED DIE FORGING PROCESS

MOHAMED A. ABDULMAWLLA

FK 2000 11

DEVELOPMENT OF CAD/CAM SYSTEM FOR COLD WORKING CLOSED DIE FORGING PROCESS

By

MOHAMED A. ABDULMA WLLA

Thesis Submitted in Fulfilment of Requirements for the Degree of Master of Science in the Faculty of Engineering

U niversiti Putra Malaysia

June 2000

11

DEDICATED TO

MY PARENTS

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirements for the degree of Master of Science.

DEVELOPMENT OF CAD/CAM SYSTEM FOR CLOSE DIE FORGING PROCESS

By

MOHAMED A. ABDULMA WLLA

June 2000

Chairman: A. M. S. Ramouda, Ph D.

Faculty: Engineering

iii

The application of computer-aided engineering (CAE), design (CAD), and

manufacturing (CAM), is essential in modern metal forming technology. Thus,

process of modelling for the investigation and understanding of deformation

mechanics has become a major concern in recent and advanced research, and the

finite element method (FEM.) has assumed increased importance, particularly in the

modelling of deformation processes.

This work is devoted to the development of CAD/CAM system for closed die

forging process. The system development consists of three stages: namely, metal

flow simulation, die failure analysis and design optimisation, and development and

implementation of machining code. In the first stage, the finite element method was

used to simulate the axisymmetric closed die forging process of copper material. The

method was used to study the metal flow, die filling retaining the non-linearity

involved in the large change in the geometry, the continuous change in the contact

surface condition and the isotropic material work-hardening characteristics. In the

second stage, a finite element analysis and optimisation algorithm was developed to

IV

examine the die fatigue life and to optimise the die design. The finite element

analysis in the first and second stage was carried out using commercially available

finite element software called LUSAS. In the third stage, a machining code for the

optimised die was developed and implemented using CAD/CAM software called

UniGraphics and CNC machine. A qualitative comparison between the

computational results and experiments ware made.

It had been found that the early stage of the metal flow in closed die forging

was very similar to a simple upsetting, then the material flows into the die cavity and

towards the flash land leading to a very sharp increase in forging load. The die was

designed to sustain the forging load and withstand 1000 load cycles.

v

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Abstrak tesis yang dikemukakan kepada Senat UiuverslTIPUffa Malay��\' SlA sebagai memenuhi keperluan untuk ijazah Master Sains,

PEMBANGUNAN SISTEM CAD/CAM BAGI PROSES ACUAN TEMPAAN TERTUTUP

Oleh

MOHAMED A. ABDULMA WLLA

June 2000

Pengerusi: A.M.S. Hamouda, Ph.D.

Fakulti: Kejuruteraan

Aplikasi kejuruteraan terbantu komputer (CAE), reka bentuk terbantu

komputer (CAD) dan pembuatan terbantu komputer (CAM) adalah penting dalam

teknologi pembentukan logam moden. Jadi, pemodelan proses bagi kajian dan

pemahaman mekanik ubah bentuk telah menjadi satu tumpuan utama dalam

penyelidikan terkini dan maju, dan kaedah unsur terhingga (FEM) telah menjadi

begitu penting, terutamanya dalam pemodelan proses ubah bentuk.

Penyelidikan ini ditumpukan kepada pembangunan sistem CAD/CAM bagi

proses tempaan acuan tertutup. Pembangunan sistem terdiri dari 3 tahap: iaitu

penyelakuan aliran logam, analisis kegagalan acuan dan pengoptimuman reka

bentuk, dan pembangunan dan pelaksanaan kod pemesinan. Dalam tahap pertama,

kaedah unsur terhingga telah digunakan untuk menyelaku proses tempaan acuan

tertutup paksi simetri bagi bahan tembaga. Kaedah ini telah digunakan untuk

mengkaj i aliran logam, pengisian acuan dengan mengekalkan ketaklelurusan yang

terlibat dalam perubahan besar geometri, perubahan berterusan dalam keadaan

permukaan sentuhan dan ciri-ciri pengerasan kerja bahan isotropi. Dalam tahap

vi

kedua, satu analisis unsur terhingga dan algorithma pengoptimuman telah

dibangunkan untuk memeriksa hay at lesu acuan dan mengoptimum reka bentuk

acuan. Analisis unsur terhingga dalam tahap pertama dan kedua telah dilaksanakan

menggunakan peri sian unsur terhingga yang wujud secara komersial yang dipanggil

LUSAS. Dalam tahap ketiga, kod pemesinan bagi acuan teroptimum telah

dibangunkan dan dilaksanakan menggunakan peri sian CAD/CAM yang dipanggil

UniGraphics dan mesin CNC. Satu perbandingan kualitatif di antara keputusan

perkomputeran dan ujikaji telah dilakukan.

Telah dapat diperhatikan bahwa pengaliran logam diperingkat awal

penempaan acuan tertutup adalah bersamaan dengan tempa-dempak mudah. Bahan

kemudiannya mengalir ke rongga acuan menuju ke flash-land. Fonomema ini

mengakibatkan beban tempaan meningkat dengan mendadak.Acuan tersebut telah

direkabentuk agar mampu menerima beban tempaan dengan selamat dan dapat

menahan beban sehingga 1000 kitaran.

VB

ACKNOWLEDGEMENTS

First of all, I would hke to express my greatest thanks and gratitude to Allah

(S W T ) the most gracious and merciful for giving me the ability to carry out this

work

I would like to express my great respect and gratitude to the chairman of the

supervisory committee, Dr A M S Hamouda, for his support, excellent

supervision, guidance and constructIve suggestion and valuable comments through

the duration of the project

I would like also to thank the members of the supervisory committee, Assoc

Prof Dr Shamsuddin bin Suialman and Dr Megat M Hamdan, Head of

Manufacturing and Mechamcal Engineering Department for their guidance and

assistance during the period of this work

Appreciation also to the assistance rendered by the respective lecturers,

technicians and staff of the facuIty of engineering for providing the facilities required

for undertaking this project

I am grateful to my beloved country LIbya and the Engineering Academy,

Tajoura for offering me the scholarship for pursuing the Master degree at Universiti

Putra Malaysia SpeCIal thanks go to all the lovely members of my family and

relatives without their encouragement and overwhelming support this work would

not have been possible

V1l1

I certify that an Examination Committee met on 19th June 2000 to conduct the final examination of Mohamed A Abdulmawlla on his Master of Science thesis entitled "Development of CAD/CAM System for Closed Die Forging Process" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 198 1 The Committee recommends that the candidate be awarded the relevant degree Members of the Examination Committee are as follows

Md Yusof Ismail, Ph.D Faculty of Engineering Universiti Putra Malaysia (Chairman)

A M. S Hamouda, Ph.D Faculty of Engineering Universiti Putra Malaysia (Member)

Shamsuddin bin Sulaiman, Ph D Faculty of Engineering Universiti Putra Malaysia (Member)

Megat M. Hamdan, Ph D Faculty of Engineering Universiti Putra Malaysia (Member)

GHAZALI MOHA YIDIN, Ph.D, ProfessorlDeputy Dean of Graduate School, Universiti Putra Malaysia

Date 2 7 JUN 2000

IX

This thesis submitted to the Senate of Universiti Putra Malaysia and was accepted as fulfilment of the requirements for the degree of Master of Science.

KAMIS A WANG, Ph.D, Associate Professor Dean of Graduate School, Universiti Putra Malaysia

Date: 1 3 JUL 2000

DECLARATION FORM

I hereby declare that the thesis is based on my original work except for quotations and citations, which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.

Signed

Name: Mohamed A. Abdulmawlla Date: 26 June 2000

TABLE OF CONTENTS

DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL SHEETS DECLARATION FORM LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS AND NOMENCLATURES

CHAPTER I INTRODUCTION

Importance of the Study Problem Definition and Scope of the Work Objective Thesis Layout

II LITERATURE REVIEW Classifications of Forging Operations

Open Die Forging Close Die Forging

Material for Forging Force and Energy Requirement Friction and Lubrication Selection of Die Material Die Design Factors Methods of AnalysIs

S lab Method Slip-line Analysis Upper-Bound Technique Fimte Element Method

Finite Element Method History of Finite Element Method Method of AnalysIs Basis for Finite Element Formulation Fmite Element Procedure

History of CAD/CAM

ill RESEARCH METHODOLOGY Research Methodology Finite Element Software (LUSAS)

IV FINITE ELEMENT FLOW SIMULATION AND DIE ANALYSIS

Page

11 111 V VB Vlll X Xlll XIV XVll

1 1 2 6 6

7 8 9 9 1 0 1 1 1 3 1 3 1 5 1 5 1 6 1 6 1 7 1 8 20 20 27 29 3 1 35

3 8 38 41

AND OPTIMISATION OF CLOSE DIE FORGING PROCESS 44 Die Design and Specifications

Die Cavity Shape Billet Calculations

44 44 47

V

VI

Code VerificatIon Finite Element Flow S Imulation

Modelling Steps Load Deformation Curve Stress-Stram Distribution

Die AnalysIs And Optimisation Die Blocks Finite Element Model for the Die

Matenal PropertIes Support Condition Loading

Equivalent S tress Contours Fatigue AnalysIs Damage Contours Log-life Contours Die cost

COMPUTER AIDED MANUFACTURING OF CLOSED DIE FORGING Die Specifications UniGraphics Software

Selectmg the Proper Machinmg Operations Planar Mill Cavity Mill Fixed Contour Mil l ing

RESUL TS AND DISCUSSIONS Billet Deformation Die Analysis

'.11

47 49 49 54 56 61 62 63 63 64 64 65 71 73 74 74

76 76 77 80 81 82 84

87 87 92

VII CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK 94 System Limitations 95 Thesis Contribution 96 Recommendations for Future Work 96

REFERENCES 98

APPENDICES 103 APPENDIX A Lusas Data File For Closed Die Forging Displacement

Dnven 48 18% Of Total Height 104 APPENDIX B Part of CNC Code for the Machining OperatIOn

ReqUIred to Produce the Die 125 BIODATA OF AUTHORS 128

LIST OF TABLES

TAB LE

1 Metal forming system

2 Ratio of endurance limit to tensIle strength

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Page

4

72

Xl\

LIST OF FIGURES

FIGURE Page

1 Open die forgIng 9

2 Closed die forging 10

3 Typical load stroke curve for closed die forgIng 1 2

4 FE simulation of open die forgIng 1 9

5 SchematIc representatIon of the Newton-Raphson method 34

6 Method of approach 39

7 3D drawing of the machined part 40

8 The sequence ofLUSAS system 42

9 The machined part 45

1 0 Draft angles 45

1 1 Corner and fillets radii 45

1 2 The flash and the gutter 46

1 3 The die cavity 46

14 Billet dimenslOns 47

15 The geometric propertIes in aXIsymmetnc elements 48

1 6 True stress strain curve 48

1 7 Modelling the die and bIllet surfaces 50

1 8 Elements used in the simulatlOn 50

1 9 The undeformed mesh 51

20 Nonlinear Hardemng Curve for the Von Mlses YIeld Model 52

2 1 The boundary conditlOns 53

22 Load distribution on the die line 55

23 Load-displacement curve 55

24 Mesh dIstortIOn at dIfferent stages 56

25 Displacement vectors at different stages 57

26 Stress contours at dIfferent stages 59

27 Strain distribution at different stages 60

28 Deformed and undeformed mesh 65

29 Stresses and displacement distnbutions for 40mm die 68

3 0 Stresses and displacement distnbutions for 60mmdie 69

3 1 Stresses and displacement distnbutions for 80mm die 7 1

3 2 Typical S -N curve for steel 72

33 Contour of damage 73

34 Log-life contour 74

3 5 Mechanical drawing of the die 75

36 2D drawing of optimIsed dIe 77

3 7 Operational sequence 78

3 8 The operation manager 79

3 9 Machining operatIOns 8 1

40 Tool paths for planar mIll ing operatIon 82

4 1 Parts where Planar and CavIty Mill are useful 83

42 Tool paths for first cavIty millmg operatlOn 83

43 Tool paths for the second cavIty mtlling operation 84

44 Fixed contour tool diameter and comer radius 85

45 Isometric view of the tool path m fixed contour operation 85

46 Front view of the tool path m fixed contour operation 86

47 Deformed mesh 20% reduction 88

48 Deformed mesh 40% reductlOn 88

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49 Deformed mesh just before the final stage 89

50 Deformed mesh final stage 89

51 Effective stress distnbution at 30% reduction 90

52 Effective stress distribution In final stage 91

53 Strain distribution at the final stage 91

54 Effective stress distributIon in the die and the billet at final stage 93

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ABBREVIA TIONS AND NOMENCLATURES

FE Finite Element

CNC Computer Numerical Control

NC Numerical Control

CLSF Cutter Location Source File

APT Automatically Programmed Tools

D Diameter

H Height

Pt Total load on the die

P Load

Py Yielding load

O'y Yield stress of the forged material

A Cross sectional area of the billet

E Modulus of elasticity

CAD Computer Aided Design

CAA Computer Aided Analysis

CAM Computer Aided Manufacturing

FEM Finite Element Method

f (al;) Yield function

all Cauchy stress

all Deviatoric stress

CY Effective stress, flow stress

A Lagrangian multiplier

vo Initial velocity vector at nodal point

v : Velocity vector at nodal point

v : Poisson's ratio

8 : Effective strain

8 : Effective strain rate

i : Proportionality factor (rate) in flow rules

c : Constant

BI] : Strain rate

UI : Velocity component tangent to a surface

K : Penalty constant

F/ : Traction

ex : Deceleration coefficient

V : Volume

S : Surface

SF : Surface where traction is prescribed

E ( BI] ) : Work function

1C : Functional

01C : Variation of functional 1C

Bv : Volumetric strain rate

Su : Surface where velocity is prescribed

�v : Velocity corrections of nodal values

K : Stiffness matrix

f : Nodal point force vector

xviii

CHAPTER I

INTRODUCTION

In this chapter, the undertaking of the work is justified, identify the aims of

the study and outline the method of approach adopted to achieve the set objectives.

Finally, a summary of the content of different chapters is provided under the heading

" Layout of thesis" .

Importance of the Study

In manufacturing operations many parts are fonned into various shapes by

applying external forces to the workpiece by means of tools and dies. Typical

operations are forging, extrusion and rolling. Because defonnation in these processes

is carried out by mechanical means, an understanding of the behaviour of the

materials in response to applied forces is important. In addition, the behaviour of

manufactured part during its expected service life is an important consideration.

Unlike rolling operation, which generally produce continuous plates, sheets,

and strips, forging operation produce wide variety of discrete parts. Metal flow and

the grain structure can be controlled, so forged parts have good strength and

toughness. Thus they can be used reliably for highly stressed and critical

applications. Die design material behaviour during deformation, as well as friction,

and material flow characteristics in a die cavity, are important in design

2

consideration. Also important is the proper selection of die-materials, temperature,

speed, lubricant and equipment.

Recently, computer-aided design and manufacturing are being implemented

increasingly in all aspects of forging design and manufacturing. Techniques being

used include modelling of the deformation of the workpiece and finite element

analysis during forging in the dies, die design, calculation of forces, and prediction of

die failure.

Problem Definition and Scope of the Work

The ultimate goal of manufacturing engineer is to produce component of

selected material with a required geometrical shape and a structure optimised for the

proposed service environment. In general, forging processes tend to be complex

system of independent variables, dependent variables and independent-dependent

interrelations. Independent variables are those aspects of the process over which the

engineer has a direct control and are generally selected or set up when setting up the

process. Among the typical independent variables considered are: -

• S tarting material. The engmeer must specify the chemistry and the

condition of the material to be machined.

• Starting workpiece geometry. This may be dictated by previous

processing or may be selected by the engineer from a variety of available

shapes, often on basis of economics.

3

• Tool or die geometry It has many aspects such as the die material, die

angles and cavity details, which have wide variety and so different effect

on the process

• Amount of deformation. The amount of deformation is limited by the

material properties and its ability to deform It should be taken in

consideration during die design according to the shape of the workpiece

material

After the manufacturing engmeer specifies the independent variables, the

process then determines the nature and values for a second set of variables, known as

dependent variables Examples include -

• Force and power requirements. To deform a given material from a given

starting shape to a specified final shape, with a specified friction

coefficient, speed and starting temperature, will require a certain amount

of force or power A change in any of the independent variables will bring

about a change in the force or power required

• Material properties of the product While the engineer can specify the

properties of the starting material, the combined deformation and

temperature changes imparted by the process will certainly modify them.

The customer is not interested in the starting properties, but rather the

final properties of the product. Thus, while it is often desirable to select

starting properties based on compatibility with the process, it is also

necessary to know or be able to predict how the process will alter them.

4

• Surface finIsh and precision. Both are product characteristic and depends

on the specific details of the process.

• Nature of material flow Deformation process exerts external constrains

on the material through control and movement of its surfaces. S ince

properties depend on the deformation history, control here is vital

As il lustrated in Table 1 the problem facing the metal forming engmeer

becomes quite obvious On one hand are the independent variables, those aspects of

the process over WhICh he/she has direct control On the other are the dependent

variables, those aspect over which he/she must have control but for which his/her

influence is indirect The dependent variables are determined by the process based on

proper selection of the independent variables If a dependent variable is to be

modified, the engineer must determine which independent variable (or variables) is

to be changed, in what manner, and by how much Thus, the engineer must have

knowledge of the independent-dependent variable interrelations

Table 1 Metal forming system

Independent variables Dependent variables

Starting material Force and power requirements

Starting workpiece geometry Experience Material properties of the

Tool or die geometry Experiment product Surface finish and

Lubricant and friction Theory . .

preCISIon

Amount of deformation Nature of metal flow

5

PERPUSTAKAAl\I The link between the independent and de���l-IamN �lA

important area of knowledge for the manufacturing engineer Unfortunately, such

l inks are often difficult to obtain Metal forming process is a complex system

composed of the material being deformed, the tool performing the deformation and

various other process parameters Also various materials often behave differently

The ability to predict and control dependent variables, therefore, comes about

in one of three ways -

1 Experience This reqUIres long-time exposure to the process and IS often

restricted in scope by the realm of past contact

2 Experiment While possibly the least likely to be in error, direct experiment is

both costly and time consuming

3 Modelling. Here one attempt to develop a mathematical model of the process

into which numerical values for the various independent variables can be

inserted and compute a prediction for the dependent variables. Most

techniques rely on the applied theory of plasticity with two-dimensional

stresses. Alternatives vary from first-order approximations, such as slab

equil ibrium or uniform deformation energy calculation, to sophisticated,

computer-based, solution, such as the finite element or finite difference

methods

6

Objective

The present work focuses on simulating non-steady forging process using a

finite element techmque III order to come up with a clear and better understanding of

metal flow and stress distribution in the process It is also to study the effect of

independent and dependent variables on the die So the aims of this work are -

• To develop a finite element algorithm to model forging process

• To conduct finite element analysis and optimisation on the die life

• To develop a CNC code for the manufacturing of the die

Thesis Layout

The thesis is organised into seven chapters The first chapter gives an

introduction to the research and its objectives The second chapter contains an up to

date literature review metal forming history, basic aspects of forging and some

important terms and definitions The third chapter contains a brief and general

overview about this work and the finite element software used in analysing the

forging process The fourth chapter contains application of FEA to non-steady state

closed die forging process, die optimisation and die fatigue analysis using LUSAS

software The fifth chapter contains die modelling using CAD/CAM software and

generating the machining code for die manufacturing The sixth chapter contains the

results and discussion The final chapter contains conclusion and suggestions for

future work