EFFECT OF TOOL PATH GENERATION WHEN MACHINING MOLD.CAVITY

ROI{ANA BINTI SARIP

A project report submitted in partial firlfilment of the

requirements for the award of the degree of

Master of Mechanical Engineering (Advanced Manufacturing Technology)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

DECEMBER 2OO9

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Dedicofed to my beloved fomily...

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ACKNOWLEDGEMENT

I would like to express my sincere gratitude and grateful appreciation to my

main supervisor, Prof. Dr. Safian bin Sharif and my co-supervisor, Mr. Rozaimi bin

Mohd Saad for their guidance, encouragement, advice, motivation and friendship.

Without their support and trust, this thesis would not have been the same as presented

here.

I am also wanted to thank to all staff at Production Laboratory and Machine

Shop for their support and guidance throughout my research.

Thank you to Allah for giving me strength to accomplish this thesis.

ABSTRACT

Studies on the tool path generation for free form surface have been conducted

extensively and most of these studies were focused on the effect of tool path

generation on the tool wear and surface texture. In this study, the effect of tool path

generation on tool wear, surface finish, machining time and dimensional accuracy

were evaluated during ball end milling of a mold cavity. UGS CAD/CAM software

was used to simulate the tool path and actual during machining at various cutting

parameters was conducted on CNC machining centre to machine a concave shape of

the mold-cavity component. Workpiece of 6061 aluminium alloy and HSS ball end

mill were used in this study. Four types of tool path strategies were investigated;

they are Follow Periphery, Parallel Line, Concentric Arc and Radial Lines. Result

showed that the highest value of 0.04pm flank wear was obtained when using

Concentric Arc and the lowest value of 0.01pm was recorded with Parallel Line.

Follow Periphery tool path strategy demonstrates the shortest machining time of 115

min and radial line recorded the longest machining time of 352 min. Radial Line and

Follow Periphery recorded the lowest and highest surface roughness of 0.95pm and

2-76pm respectively. In average, the smallest error value in dimension was from

Radial Line strategy with 0.04% while the biggest effor was recorded using Follow

Periphery with 0.6%. Based on the result obtained, it can be concluded that Parallel

Line and Radial Line produce lower tool wear, smaller error in dimensional accuracy

and better in surface finish but longer in cutting time while Follow Periphery and

Concentric Arc produce shorter cutting time, higher tool wear, bigger error in

dimensional accuracy and poor in surface finish.

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ABSTRAK

Kajian terhadap penjanaan peqalanan matalat bagi permukaan pelbagai

bentuk telah djalankan secara meluas dan kebanyakan kajian tertumpu kepada kesan

ke atas penjanaan perjalan mata alat terhadap geometri mata alat dan tekstur

permukaan. Di dalam kajian ini, kesan penjanaan mata alat terhadap kehausan,

kemasan permukaan, masa pemesinan dan ketepatan dimensi telah dinilai sepanjang

menjalankan pemesinan kaviti acuan cekung. Perisian UGS CAD/CAM telah

digunakan untuk simulasi perjalanan mata alat dan pemesinan sebenar pada

pelbagai parameter pemotongan dengan menggunakan mesin berangka computer

berpusat. Bendakerja yang digunakan di dalam kajian ini adalah 6061 aluminium

alloy dan matalat pengisar bebola berhalaju tinggi. Empat jenis strategi perjalanan

matalat yang diselidik adalah Follow Periphery, Porallel Line, Concentric Arc dan

Radial Lines. Keputusan menunjukkan nilai tertinggi bagi kehausan rusuk adalah

0.04pm yang diperolehi dari Concentric Arc dan nilai terendah adalah 0.01pm dari

Parallel Line. Strategi perjalanan matalat Follow Periphery merupakan masa

pemesinan terpendek iaitu 115 minit dan Radial Line mencatatkan masa pemesinan

terpanjang iaitu 352 minit. Radial Line dan Follow Periphery mencatatkan bacaan

kekasaran permukaan terendah dan tertinggi iaitu masing-masing sebanyak 0.95pm

dan2.76 pm. Secara purata, nilai ralat terkecil di dalam dimensi adalah dat'' Radial

Line \aitu sebanyak 0.04% manakala ralat terbesar yang direkod adalah dari Follow

Periphery dengan 0.6%. Berdasarkan kepada keputusan yang dicapai, boleh

disimpulkan bahawa Parallel Line dan Radial Line menghasilkan kehausan matalat

yang rendah, ralat dimensi yang kecil dan kemasan permukaan yang baik tetapi

mengambil masa pemesinan yang panjang manakala Follow Periphery dan

Concentric Arc menghasilkan masa pemesinan yang pendek tetapi kehausan mataLat

yang tinggi, ralat yang besar di dalam ketepatan dimensi dan kemasan permukaan

yang kasar.

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CHAPTER

TABLE OF CONTENS

TITLE

DECLARATION

DEDICATION

ACKNOWLEDGEMMENTS

ABSTRACT

ABSTRAK

TABLE OF CONTENTS

LIST OF TABLE

LIST OF FIGURE,S

INTRODUCTION

1.1 Background of Study

1.2 Problem Statement

1.3 Objectives of the Study

I.4 Scope of Work

1.5 Significant of the Study

LITERATURE REVIEW

2.1 Introduction

2.2 The Metal Cutting Process

2.3 Milling Operation

2.4 CAD/CAM

2.4.1 Cutter Path Strategy

2.4.2 Step Over

2.4.3 Gouging

2.5 Type of Cutting Tool

2.5.1 Ball End Mill

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2.6

2.7

Material of Cutting Tool

2.6.1 High Speed Steel

Surface Finish

2.7.1 Method To Measure Surface Finish

2.7.2 Shape and Waviness of the Surface

2.7.3 Surface Roughness

2.7.4 Surface Finish in Milling

Tool Wear

2.8.1 Tool Wear Pattern in Ball Mill

METHODOLOGY

3.1 Introduction

3.2 Milling Machine

3.3 Cutting Tools

3.4 Workpiece Material

3.5 MeasurementEquipment

3.5.1 Tool Wear Measurement

3.5.2 Surface Roughness Measurement

3.5.3 Dimensional Accuracy Measurement

RESULT AND DATA ANALYSIS

4.1 Introduction

4.2 Tool Wear

4.3 Cutting Time

4.4 Surface Roughness

4.4.1 Six Location Result for Surface Finish

4-4-2 Flat, Flat to Curve and Curve

4.5 Average Value for Surface Finish

4.6 DimensionalAccuracy

CONCLUSION

REFERENCES

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LIST OF TABLE

TABLE NO. TITLE PAGE

3.1 Spesification of the CNC Milling Machine 24

3.2 Tool spesification 24

3.3 Properties of 6061 aluminium alloy 25

3.4 Chemical composition of 6061 aluminium alloy (Wt%) 25

3.5 Spesification of Mitutoyo Formtracer 27

3.6 Specification of Coordinat Measuring Machine 28

4.I Tool wear pattern for Concentric Arc, Follow Periphery,Parallel line and Radial Line 31

4.2 Flank wear value for Concentric Arc, Follow Periphery,Parallel line and Radial Line 32

4.3 Data for actual and simulation time in machining 33

4.4 Surface finish dataat six locations 35

4.5 Surface finish data at flat, flat to curve and curveLocation 35

4.6 Surface finish data in average 37

4.7 Dimensional accuracy Dataatx, Y, Z axis for FollowPeriphery tool path strategy 39

4.8 Dimensional accuracy dataatX, Y, Z Axis for ParallelLine tool path strategy 4A

4.9 Dimensional accuracy dataat X, Yo Z axis for ConcentricArc tool path strategy 40

4.10 Dimensional accuracy data at X, Y, Z axis for RadialLine tool path strategy 4I

4.II Dimensional accuracy error data at X, Y, Z axis for FollowPeriphery tool path strategy 4I

4.12 Dimensional accuracy error data in average at X, Y andZ axis for Follow Periphery tool path strategy 42

4.13 Dimensional accuracy error data at X, Y and Z Axisfor Parallel Line tool path strategy 43

4.14 Dimensional acattacy enor datain average at X, YandZ axis for Parallel Line tool path strategy

4.15 Dimensional accuracy error data at X, Y andZ axisfor Concentric Arc tool path strategy

4.16 Dimensional accuracy error data in average at X, YandZ axis for Concentric Arc tool path strategy

4.I7 Dimensional accuracy error data at X, Y andZ axisfor Radial Line tool path strategy

4.18 Dimensional accuracy error data in average at X, Yand Z axis for Radial Line tool path strategy

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FIGURE NO.

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LIST OF FIGURE

TITLE PAGE

Photomicrograph of partially formed chip 5

Schematic illustration of a two-dimensional cutting process 6

Milling process (a) Slab milling (b) End milling 7

Ball end mill 7

Modern Mold Design Flowchart 8

Cutter path strategies: (a) Single Direction Raster Strategy(One direction) (b) Raster (Ztg-ZaglBack and Forth) and(c) Spiral

Step over of milling operation

Scallop height

Over cut and under cut in NC machining

(a) Gouging with neighboring surface (b) Surface overlap(c) Surface gap T2

Geometrical characteristics of two flute ball mill 13

The shape, waviness and roughness ofa surface 17

An overview of the causes, mechanisms, types andConsequences of the tool wear 19

Different wear types observed at the cutting edges of

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the end-mill

Mold cavity

Methodology flow chart

Milling Machine

Ball Mill

Zeiss Axiotech-high power optical microscope

Mitutoyo Formtracer C S-5000

Coordinate Measuring Machine

The tool path strategy: (a) Follow Periphery (b) Parallel Line(c) Concentric Arc (d) Radial Lines

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4.2 Tool wear comparison for each tool path strategy 32

4.3 Tool path generation comparison for actual, simulation anderror machining time 33

4.4 Six location to measure the surface finish 34

4.5 Surface finish datafor comparison for flat, flatto curve andCurve area 36

4.6 Surface finish data for comparison in average 37

4.7 Point for dimensional accuracy in Z axis 38

4.8 Point for dimensional accuracy in X and Y axis 39

4.9 Dimensional accuracy er:ror in X, Y and Z axis forFollow Periphery tool path strategy 42

4.I0 Dimensional accuracy error in average at X, Y andZ axis for Follow Periphery tool path strategy 42

4.II Dimensional accuracy error at X, Y and Z axis forParallel Line tool path strategy 43

4.12 Dimensional accuracy error in average at X, Y andZ axis for Parallel Line tool path strategy 44

4.13 Dimensional accuracy error at X, Y and Z axis forConcentric Arc tool path strategy 45

4.I4 Dimensional accuracy error in average at X, Y andZ axis for Concentric Arc tool path strategy 45

4.1,5 Dimensional accuracy error at X, Y and Z axis forRadial Line tool path strategy 46

4.16 Dimensional accuracy error in average at X, Y andZ axis for Radial Line tool path strategy 47

CHAPTER I

INTRODUCTION

1.1 Background of the study

Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) is one

of the versatile tools used in engineering practice in many ways including drafting,

design, simulation, analysis and manufacturing. There are various applications of

existing CAD/CAM system whereby each application has its strength which is

usually targeted to a specific market and group of users. According to Ibrahim Zeid

(2005), CAD/CAM system is classified into four groups depending on the market

they serve, the tools, functionalities and flexibilities they provide. The four groups

are low end, mid range, high end and specialized.

Low-end systems are used for unsophisticated and simple product which

consists of small number of product and uncomplicated geometry. The user can focus

on basic geometry modeling and drafting such as AutoCAD, Autodesk Inventor and

CADKEY. The midrange system is for users who require complex modeling and a

large number of parts per product. Unlike low end system, midrange system support

design together with manufacturing application such as SolidWorks, Pro/E and

MasterCAM. High-end system supports modeling, analysis and manufacturing of

complex products such as airplains, cars and others. Examples of this high-end

system are Unigraphics, Parasolid, SDRC I-DEARS and CATIA (Ibrahim Zeid,

2005).

One of the most important technique in manufacturing is to produce a part

with free-fofin or parametric surfaces. Efficient machining of these surfaces has

become very important in many manufacturing industries, such as the automobile,

consumer electronics, die-making and toy industries (Jian-Zhong Yang et aL,2007).

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Research on cutter path generation techniques has been carried extensively

over the past decade. Proper selection of cutter path strategy is crucial in achieving

desired and quality machined surfaces. Without considering the effect of cutter path

selection with adequate consideration of the machining outcome such as cutting

forces, vibration analysis, tool life, cutting temperature and workpiece surface

integrity, the result can lead to catastrophic cutter failure and therefore lead to

unnecessary waste of time, cost and poor surface quality (C. K Toh,20A4).

This study is conducted in order to gain a better understanding on the type ofcutter path strategies and their effect when ball end milling of mold cavity part.

1.2 Problem Statement

The development of the aeronautic and automobile industries brought new

technological challenges, related to the growing complexity of the products and the

new geometries modeled in Computer Aided Design (CAD) systems. These more

complex geometries impose new challenging manufacturing situation for milling of

moulds and stamping tools (R. Baptista,1999).

The utilization of Computer Numerical Control (CNC) machine to

manufacture complex surfaces has driven extensive research works especially in the

area of tool path generation. According to Cevdet Gologlu (2008), the

implementation and selection of cutting path strategies with appropriate cuffing

parameters have significant effect on surface roughness. Study on optimal tool path

generation has been aiming at achieving two conflicting objectives which is quality

and efficiency. Hui wen Li. et al, (20A1) reported that a large tool path interval

results in a rough surface while a small interval increases machining time, resulting in

the inefficient of the process.

Most of previous studies were focused on the effect of tool path generation on

tool geometry and surface texture. In this study, the effect of tool path generation on

tool wear, surface finish, machining time and dimensional accuracy is being

evaluated when ball end milling of mould cavity.

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1.3 Objective of the study

The main objective of this study is to evaluate the effect of various tool path

strategies via CAD/CAM on tool wear, surface finish, machining time and

dimensional accuracy of a mold cavity.

1.4 Scope of work

The scope of the study covers the following aspects:

1. UGS CAD/CAM software was use to run the simulation and

experiment with selected cutting parameters.

2. MAHO 7005 CNC machining centre was used to machine the mold-

cavity component.

3. 6061 aluminium alloy was selected as the workpiece.

4. High Speed Steel (HSS) ball end mill was used as the cutting tool.

5. Focus on the study was on finishing operation.

6. Cutting conditions such as cutting speed, feed rate and depth of cut

were kept constant.

1.5 Significant of the Study

It is expected that the study will contribute to the following achievement:

1. Better understanding on the effects of tool path generation when ball

end milling a mold-cavity part.

2. Proposed predictive results that can be achieved by using UGS

software that is currently used in Production laboratory, Faculty of

Mechanical Engineering, UTM.

3. Established the tool path generation and their outcomes when milling

6061 aluminium alloy.

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