The Error Compensation Strategy Using Step Approach For Machining Thin-Wall Low Rigidity Component.

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

THE ERROR COMPENSATION STRATEGY USING STEP

APPROACH FOR MACHINING THIN-WALL LOW RIGIDITY

COMPONENT

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Manufacturing Process) (Hons.)

IZZUAN BIN AHMAD B050910260 880413-26-5479

FACULTY OF MANUFACTURING ENGINEERING 2012

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: The Error Compensation Strategy Using Step Approach for Machining Thin-wall Low Rigidity Component

SESI PENGAJIAN: 2011/12 Semester 2 Saya IZZUAN BIN AHMAD

mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut: 1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis.

3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan (√)

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia yang termaktub di dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Alamat Tetap: 559B, Jln Sg Aceh, Sg Setar Besar,

14310 Nibong Tebal, Pulau Pinang Tarikh: 29 JUNE 2012

Disahkan oleh:

COP RASMI:

Tarikh: 29 JUNE 2012

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.

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DECLARATION

I hereby, declared this report entitled “The Error Compensation Strategy Using Step Approach for Machining Thin-Wall Low Rigidity Component” is the results of my

own research except as cited in references.

Signature : ………. Author’s Name : ...IZZUAN BIN AHMAD... Date : ...29 JUNE 2012...

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APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Process). The member of the supervisory committee is as follow:

. . . Dr. Raja Izamshah Bin Raja Abdullah

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ABSTRAK

Ketepatan komponen yang dimesin adalah salah satu perkara yang paling penting untuk dipertimbangkan bagi mana-mana pengilang. Salah satu bidang yang yang agak sukar dan mencabar bagi pengeluar adalah pengeluaran komponen monolitik yang biasanya dikaitkan dengan industri aeroangkasa. Komponen monolitik ini terdiri daripada beberapa rasuk berdinding nipis dan bahagian bebibir yang perlu dimesin. Oleh kerana komponen monolitik mempunyai kawasan yang besar dan ketegaran rendah, komponen berdinding nipis sentiasa dimesin dalam kawalan berangka (NC) proses akhir pengilangan. Walaubagaimanapun, oleh kerana pelbagai sebab dalam proses pemesinan, ciri-ciri bagi komponen berdinding nipis sangat mudah untuk berubah bentuk di bawah kuasa pemotongan yang akan mempengaruhi ketepatan dan kualiti.

Laporan ini adalah untuk menyiasat prestasi pemesinan menggunakan langkah strategi untuk pemesinan komponen berdinding nipis dengan ketegaran yang rendah. Empat langkah strategi berbeza iaitu langkah garis air, langkah bertindih, tiga langkah bijak dan kaedah 4-to-1 yang akan disiasat dengan menilai prestasi pemesinan pada pemesinan komponen berdinding nipis yang diperbuat daripada aloi aluminium.

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ABSTRACT

Accuracy of machined components is one of the most critical considerations for any manufacturer. One of the challenging difficult areas for manufacturer is the production of monolithic component that is usually associated with aerospace industries. This monolithic component consists of several thin-wall rib and flange sections that need to be machined. Due to the large area and low rigidity of monolithic component, the thin-walled are always machined using numerical control (NC) end milling process. However, owing to various reasons in the machining process, the thin-walled features are very easy to deform under the cutting force which will influence the accuracy and quality.

This report investigates the machining performance using the step strategy for machining thin-wall low rigidity component. Four different step strategies namely waterline-step, overlapping-step, three wise-steps and 4-to-1 rule method are investigated by evaluating their machining performance on machining the thin-wall component made of aluminum alloy.

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DEDICATION

This study is dedicated to my beloved family, Aishah Binti Salleh and Noor Hidayah Binti Ahmad.

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ACKNOWLEDGEMENT

Alhamdulillah, all my praise to Allah S.W.T for the bless that been given to complete Project Sarjana Muda 1 (PSM I) and successfully finished writing this report. In this rare opportunity, I would like to thank you to all people that involved directly or indirectly in completing this technical report. Firstly, I would like to thank you to my supervisor, Dr. Raja Izamshah Bin Raja Abdullah for his guidance, advices, ideas and support all the way through the execution of this project. My appreciation also goes to all technicians from Faculty of Manufacturing Engineering (FKP) for all the supports, contribution and cooperation during my investigation and completing my project. Finally, I would like to thanks to my family especially to my mother and my sister for their love and support from behind. Not forget to all my colleagues and members that help and give their opinions for completing this project and report either directly or indirectly.

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TABLE OF CONTENT

Declaration ii

Approval iii

Abstrak iv

Abstract v

Dedication vi

Acknowledgement vii

Table of Content viii

List of Table xi

List of Figures xii

List of Abbreviations, Symbols and Nomenclature xiv

1.0 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 3

1.3 Objective 4

1.4 Scope of Project 5

1.5 Report Outline 5

2.0 LITERATURE REVIEW 6

2.1 Introduction 6

2.2 Milling 6

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2.3 Cutting Tool 8

2.3.1 End Mill 8

2.3.1.1 Two-Flute 9

2.4 Cutting Tool Material 11

2.4.1 Factor Affecting the Selection of Cutting Tool 11

2.4.2 High-Speed Steel (HSS) 12

2.4.3 Carbides 14

2.5 Workpiece (Aluminum) 15

2.6 Step Machining Strategy 16

2.6.1 4-to-1 Rule 17

2.6.2 Waterline Step 19

2.6.3 Overlapping Step 21

2.6.4 Tree-Wise Step 22

3.0 METHODOLOGY 23

3.1 Introduction 23

3.2 Machining Parameters 25

3.3 Jig/Fixture 26

3.4 Part Modeling (CAD) 27

3.5 Machining Programming (CAM) 31

3.6 Machining Performance Measurement 32

3.6.1 Geometrical Accuracy 32

3.6.2 Surface Roughness 33

3.6.3 Cutting Force 35

3.6.3.1 Dynamometer 35

3.6.3.2 DynoWare Software 36

3.6.4 Machining Time 37

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4.0 RESULT AND DISCUSSION 38

4.1 Introduction 38

4.2 Geometrical Accuracy Measurement 38

4.2.1 4-to-1 Rule 39

4.2.2 Waterline Step 40

4.2.3 Overlapping Step 41

4.2.4 Tree-wise Step 42

4.3 Surface Roughness Measurement 46

4.3.1 4-to-1 Rule 47

4.3.2 Waterline Step 48

4.3.3 Overlapping Step 48

4.3.4 Tree-wise Step 49

4.4 Cutting Force 52

4.4.1 4-to-1 Rule 52

4.4.2 Waterline Step 53

4.4.3 Overlapping Step 53

4.4.4 Tree-wise Step 54

4.5 Machining Time 55

5.0 CONCLUSION AND RECOMMENDATION 57

5.1 Conclusion 57

5.2 Recommendation 58

REFERENCES 59

APPENDICE

A Gantt Chart FYP I B Gantt Chart FYP II

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LIST OF TABLES

3.1 Machining Parameter of Milling of Thin Wall 25 4.1 The values of CMM for 4-to-1 Rule 39 4.2 The values of CMM for Waterline Step 40 4.3 The values of CMM for Overlapping Step 41 4.4 The values of CMM for Tree-wise Step 42 4.5 Surface roughness value for 4-to-1 Rule 47 4.6 Surface roughness value for Waterline Step 48 4.7 Surface roughness value for Overlapping Step 48 4.8 Surface roughness value for Tree-wise Step 49 4.9 Machining time for step machining approach 55

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LIST OF FIGURES

1.1 Dimensional surface errors produce in machining thin-wall feature. 3

2.1 Peripheral milling 7

2.2 An end mill cutter with two flutes 10

2.3 HSS cutting tool 12

2.4 Carbide cutting tool 14

2.5 Aluminum block 15

2.6 The application of the 8:1 rule 18

2.7 Pocket wall milled in a single pass at full depth 18

2.8 Waterline Steps 19

2.9 One-way machining direction 20

2.10 Bi-directional machining direction 20

2.11 Overlapping steps 21

2.12 Tree-wise steps 22

3.1 Process Plan Flowchart 24

3.2 The base of thin-wall workpiece with four holes at each corner 26 3.3 The thin wall assembled by bolt and nut to another base that will

be clamped by fixture in the 3-Axis CNC 27 3.4 Sketch the rectangular shape with dimension 70mm x 120mm 27 3.5 Extrude the sketch with 50mm length 28

3.6 Solid raw material 28

3.7 Sketch on the top of the block 29

3.8 Pocketing the sketch with 40mm length 29

3.9 Final product 30

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3.11 Machining Program 31 3.12 Coordinate Measuring Machine (CMM) 32 3.13 Marking points on the milled side to be measured using CMM 33 3.14 Surface Roughness Tester (Mitutoyo) 34

3.15 Kistler Dynamometer 35

4.1 Graph of comparison of geometrical accuracy for line # 1 43 4.2 Graph of comparison of geometrical accuracy for line # 2 43 4.3 Graph of comparison of geometrical accuracy for line # 3 44 4.4 Graph of comparison of geometrical accuracy for line # 4 44 4.5 Graph of comparison of geometrical accuracy for line # 5 45 4.6 Graph of comparison of geometrical accuracy for line # 6 45 4.7 The workpiece with point for surface roughness measurement 47 4.8 Graph of comparison of surface roughness for side A 50 4.9 Graph of comparison of surface roughness for side B 50 4.10 Graph of cutting force against time for 4-to-1 Rule on Fx axis 52 4.11 Graph of cutting force against time for Waterline Step on Fx axis 53 4.12 Graph of cutting force against time for Overlapping Step on Fx axis 53 4.13 Graph of cutting force against time for Tree-wise Step on Fx axis 54 4.14 Graph of machining time for step machining approach 56

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LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURE

% - Percentage

° - Degree

°C - Degree Celsius °F - Degree Fahrenheit CAD - Computer Aided Design

CAM - Computer Aided Manufacturing CMM - Coordinate Measuring Machine CNC - Computer Numerical Control

Co - Cobalt

Cr - Chromium

g/cm3 _- _{Gram per centimeter cube} HEM - High Efficiency Machining HSM - High-Speed Machining HSS - High-Speed Steel NC - Numerical Control Ra - Average Roughness

V - Vanadium

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CHAPTER 1 INTRODUCTION

1.1 Background

Many components used in the aerospace industry are usually thin-walled structures. Due to the gradual reduced thickness during cutting, the end milling of thin-walled plate is a very complicated process. The tight dimensional tolerance of aerospace component poses a great challenge for the manufacturer especially for machining a component that contains a thin-wall feature (Tang and Liu, 2007).

Traditionally, aircrafts were fabricated from thin sheets of aluminum which were bent or folded for strength and then riveted to form light weight, rigid and strong air frame components. Several bent and riveted components were then riveted and bolded together into larger and more complex assembles. These were in turn riveted on to the aircraft frame.

In today’s highly competitive commercial aircraft market, this manual method has many disadvantages such as slow processes, expensive, labor intensive, highly error prone and highly non uniform which is depend on the operator. Each assembly is just slightly different from the next which adversely affects how each assembly is mounted on to the aircraft frame.

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This manual production method has been replaced by an automated, highly uniform and very accurate method called monolithic machining. The monolithic components are commonly used as structural parts in the aeronautical industry due to the homogeneity and excellent strength to weight ratio. The components are milled starting from a raw block of material and removing up to 95% of the weight of the initial block (Campa et al, 2007).

In end milling process, the thickness of the plates is reduced gradually, which makes it even more difficult to control the accuracy of machining. The end milling of such component is complicated, where periodically varying milling forces excite the flexible plate structures both statically and dynamically and leading to significant deformations (Ratchev et al., 2005).

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1.2 Problem Statement

The tight dimensional tolerance of aerospace component poses a great challenge to manufacturer especially for machining a component that contains a thin-wall feature. Because of the poor stiffness of thin-wall feature, deformation is more likely to occur in the machining of thin-wall part which resulting a dimensional surface errors. Figure 1.1 shows the dimensional surface errors produced in machining thin-wall feature. Material in the shaded areas MNOP as depicted in Figure 1.1 (b) is to be removed ideally. However, due to the milling force the wall is deflected which make point M moves to point M′ as well as point N to point N′. As a result of the wall deflection, only material MN′OP is removed resulting a dimensional surface errors in

NON’ areas.

Figure 1.1: Dimensional surface errors produce in machining thin-wall feature. (a) Deflection of wall resulting from cutting force. (b) Machining sketch of thin-wall component.

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In current industry practice, the strategies for machining the thin-wall component are using one or more of the following techniques:

(i) Using a repetitive feeding and final ‘float’ cut to bring the machined surface within tolerance.

(ii)Manual calibration to determine ‘tolerable’ machining conditions.

(iii)A lengthy and expensive trial and error numerical control validation process. (iv)Using a step machining approach, this alternately is milling each side of the

wall.

The last technique of using a step machining approach is favorable in industry practice. This project investigated the machining performance using step machining approach or strategy for machining thin-wall low rigidity component.

1.3 Objective

The objectives of the project are:

i. To study the step machining strategies namely 4-to-1 rule, waterline-step, overlapping-step and tree wise-step for machining the thin-wall component.

ii. To evaluate the machining performance of each strategy for machining the thin-wall component.

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1.4 Project Scope

This project focuses on the effects of different step machining strategies on the machining performances for milling thin-wall workpiece. Four different step machining strategies namely 4-to-1 rule, waterline-step, overlapping-step and tree wise-step are generated. A 12 mm carbide endmill cutter is used for machining of aluminum workpiece. The machining performance includes dimensional accuracy, machining time, cutting forces and surface finish were measured for results evaluation.

1.5 Report Outline

This report writing consists of three chapters for Final Year Project (FYP) 1. The Chapter 1 is explaining about the introduction; which is includes the project background, problem statement, objectives of the project, scope of the project and the significant of this project. Then the Chapter 2 was stressed on the literature review of the related issues in this project. Meanwhile, Chapter 3 is more about the project methodology which is includes the process planning for this project, flowchart, data gathering method and data analytical techniques in this project. Then the second phase report writing of Final Year Project, which is FYP 2, was covered with two more chapters. It continues with the Chapter 4 that is all about the result and discussion of experimental that have been done. Lastly in Chapter 5, it had state the conclusion and recommendation to improve the experimental or analysis of this project for the next time.

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CHAPTER 2 LITERATURE REVIEW

2.1 Introduction

This literature review will discuss in detail on the issue that is related with the step approach for machining thin-wall low rigidity component. This chapter is included explanation about the related study based on this project and the machining process that need to be considered in the cutting process. The other related topic is about the cutting tool and material of the workpiece and cutting tool that will used for machining process in this project.

2.2 Milling

Milling is a process of generating machined surfaces by progressively removing a predetermined amount of material or stock from the workpiece at a relatively slow rate of movement or feed by a milling cutter rotating at a comparatively high speed. The characteristic feature of the milling process is that each milling cutter tooth removes its share of the stock in the form of small individual chips.

Milling tends to be an expensive manufacturing process because the bits and cutters operate at high temperatures and burn coolant that is sprayed on them in the process to keep them from overheating. The cutting bits themselves are also very expensive as they must be hardened to a degree where they can repeatedly cut into metals such as aluminum and stainless steel (Hawk, 2012).

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2.2.1 Peripheral Milling

Peripheral milling of very flexible components is a common manufacturing process in the aerospace industry. Very flexible components are considered to have a wall thickness thinner than 5 mm and an axial depth of cut larger than 30 mm. The wall thickness of the component is reduced further by peripheral milling operation using a long and helical slender end mill (Budak, Altintas et al., 1995).

In peripheral milling (also called slab milling), the axis of cutter rotation is parallel to the workpiece surface, as shown in Figure 2.1. The cutter body which is generally is made of high-speed steel (HSS). It has a number of teeth along its circumstances and each tooth acts like a single-point cutting tool. When the cutter is longer than the width of the cut, the process is called slab milling (Kalpakjian, 2006).

Cutters for peripheral milling may have straight or helical teeth which are resulting in orthogonal or oblique cutting action. Helical teeth generally are preferred over straight teeth because the tooth is partially engaged with the workpiece as it rotates. Consequently, the cutting force and the torque on the cutter are lower which is resulting in a smoother operation and reduced chatter (Kalpakjian, 2006).

Figure 2.1: Peripheral milling (Source: Kalpakjian. S, 2006)

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2.3 Cutting Tool

In machining, a cutting tool (or cutter) is a tool that is used to remove material from the workpiece by means of shear deformation. Cutting tools must be made of a material harder than the material which is to be cut. The cutting tool also must be able to withstand the heat generated in the metal-cutting process.

2.3.1 End Mill

An end mill is a tool used on a milling machine. A milling machine is a machine found in a metal working shop that is used to remove material from a metal block to make it into a finished part. An end mill is one of the tools used on the milling machine to make a particular type of cut (Sunshine, 2012).

End mills come in single ended and double ended varieties. A single ended end mill has only one useful working end and the other end is just a smooth shank for holding the end mill in the tooling holder on the milling machine. A double ended end mill has two useful working ends. When one end becomes dull and no longer useful, the end mill can be installed such that the opposite end can be used (Sunshine, 2012).

End mills are made of carbide steels with the cutting surfaces sometimes made entirely of carbides. It is also common for end mills to be coated with a very thin layer of titanium nitrate. Titanium nitrate is a gold coloured coating that prevents the metal chips being removed from the part from sticking to the end mill, reducing its life and the quality of the cut. End mills come in a wide variety of shapes and sizes (Sunshine, 2012).

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End mill is an important and common machining operation because of its versatility and capability to produce various profiles and curve surfaces. The cutter called an end mill has either a straight shank (for small sizes) or a tapered shank (for larger cutter sizes) and is mounted into the spindle of the milling machine. End mills may be made of high-speed steels or with carbide inserts which are similar to those for face milling. The cutter usually rotates on an axis perpendicular to the workpiece surface (Kalpakjian, 2006).

The end mill is an important tool in the milling process. A typical example for the end mill is the milling of a pocket and slot in which a lot of material is removed from the workpiece. Therefore the proper selection of cutting parameters for end milling is one of the important factors affecting the cutting cost (Tsai and Liao, 1999).

2.3.1.1 Two-Flute

The flutes of the milling bit are the deep helical grooves running up the cutter while the sharp blade along the edge of the flute is known as the tooth. The tooth cuts the material and chips of this material are pulled up the flute by the rotation of the cutter. There is almost always one tooth per flute but some cutters have two teeth per flute. The words flute and tooth are used interchangeably. Milling cutters may have from one to many teeth with 2, 3 and 4 being most common. Typically, the more teeth a cutter has, the more rapidly it can remove material. So, a 4-tooth cutter can remove material at twice the rate of a 2-tooth cutter.

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In current industry practice, the strategies for machining the thin-wall component are using one or more of the following techniques:

(i) Using a repetitive feeding and final ‘float’ cut to bring the machined surface within tolerance.

(ii)Manual calibration to determine ‘tolerable’ machining conditions.

(iii)A lengthy and expensive trial and error numerical control validation process. (iv)Using a step machining approach, this alternately is milling each side of the

wall.

1.3 Objective

The objectives of the project are:

i. To study the step machining strategies namely 4-to-1 rule, waterline-step, overlapping-step and tree wise-step for machining the thin-wall component.

ii. To evaluate the machining performance of each strategy for machining the thin-wall component.

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1.4 Project Scope

1.5 Report Outline

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

2.2 Milling

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2.2.1 Peripheral Milling

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2.3 Cutting Tool

2.3.1 End Mill

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2.3.1.1 Two-Flute

The Error Compensation Strategy Using Step Approach For Machining Thin-Wall Low Rigidity Component.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA