Tool life improvement solution for cutting tool in cashew shell peeling machine by using finite element method

ĐẠI HỌC QUỐC GIA TP.HCM TRƯỜNG ĐẠI HỌC BÁCH KHOA --- THÁI VĂN BÌNH TOOL LIFE IMPROVEMENT SOLUTION FOR CUTTING TOOL IN CASHEW SHELL PEELING MACHINE BY USING FINITE ELEMENT METHOD C

ĐẠI HỌC QUỐC GIA TP.HCM

TRƯỜNG ĐẠI HỌC BÁCH KHOA

-

THÁI VĂN BÌNH

TOOL LIFE IMPROVEMENT SOLUTION FOR CUTTING TOOL

IN CASHEW SHELL PEELING MACHINE BY USING

FINITE ELEMENT METHOD

Chuyên ngành: KỸ THUẬT CƠ KHÍ

Mã số: 60 52 01 03

LUẬN VĂN THẠC SĨ

Tp Hồ Chí Minh, 2017

CÔNG TRÌNH ĐƯỢC HOÀN THÀNH TẠI TRƯỜNG ĐẠI HỌC BÁCH KHOA –ĐHQG -HCM

Cán bộ hướng dẫn khoa học: Phó giáo sư Trần Doãn Sơn

Cán bộ chấm nhận xét 1:

Cán bộ chấm nhận xét 2:

Luận văn thạc sĩ được bảo vệ tại Trường Đại học Bách Khoa, ĐHQG Tp HCM ngày tháng năm

Thành phần Hội đồng đánh giá luận văn thạc sĩ gồm: (Ghi rõ họ, tên, học hàm, học vị của Hội đồng chấm bảo vệ luận văn thạc sĩ) 1

2

3

4

5

Xác nhận của Chủ tịch Hội đồng đánh giá LV và Trưởng Khoa quản lý chuyên ngành sau khi luận văn đã được sửa chữa (nếu có)

ĐẠI HỌC QUỐC GIA TP.HCM

TRƯỜNG ĐẠI HỌC BÁCH KHOA CỘNG HÒA XÃ HỘI CHỦ NGHĨA VIỆT NAM Độc lập - Tự do - Hạnh phúc

NHIỆM VỤ LUẬN VĂN THẠC SĨ

Họ tên học viên: Thái Văn Bình MSHV:1570301 Ngày, tháng, năm sinh: 24/01/1983 Nơi sinh: Quy Nhơn

Chuyên ngành: Kỹ thuật cơ khí Mã số : 60520103

TÊN ĐỀ TÀI: Giải pháp cải tiến độ bền của dụng cụ cắt vỏ hạt điều của máy tách hạt

điều bằng phương pháp phần tử hữu hạn

I NHIỆM VỤ VÀ NỘI DUNG: nghiên cứu và phát triển để tìm ra giải pháp cải tiến độ bền của dụng cụ cắt vỏ hạt điều của máy tách hạt điều bằng phương pháp phần tử hữu hạn giúp cho nhà sản xuất máy có thể tối ưu hóa máy để phục vụ sản xuất hiệu quả cũng như đạt chất lượng khi xuất khẩu may

II NGÀY GIAO NHIỆM VỤ : 04/07/2016

III NGÀY HOÀN THÀNH NHIỆM VỤ:

IV CÁN BỘ HƯỚNG DẪN : PGS.TS Trần Doãn Sơn

Acknowledgements

First, I would also like to thank my small family for their constant encouragement and support; not only during my time at HCMUT, but throughout my life They are my dynamic which is encouraged me to overcome all difficulty during thesis time

I am greatly indebted to my Professor Tran Doan Son for his ideas and unending belief it me He supported me much on guideline how to complete the thesis with valuable research With his experience deeply on mechanical field, it helps me to have better overview any matters or easily approach any problem

Moreover I would like to thank Robert Bosch Vietnam for their support that has contributed this research They supplied workstation, software license and also technical opinions from some specialist on the related field It help me to acquire and access the insight

of knowledge

Last but not least, I swear this is my own research with guidance of Professor Tran Doan Son The contents, the result of the study are honest and not published in anywhere before The figures and data served for analysis, evaluation are collected from various sources have stated in the reference section

Thai Van Binh

Abstract

Cashew peeling machine is priority machine in cashew production process, therefore it decide whether the productivity and quality of production are optimized Nowadays many factory already applied current Peeling machine from My An Anh Company into production from over Vietnam and also export a few of machine to different countries such as Côte d'Ivoire, Bangladesh but just some machines which are a part of assembly line are accepted

by oversea users and Peeling machine is not proposed choice for their production because of unreliable cutting tool of machine Moreover, there are several feedbacks about quality of Peeling tool or cutting tool which is not long-lasting due to wearing and worker has to stop machine for more than 3 hours to do maintenance the cutting tool In order to overcome its life time, the wear phenomenon need to be take into account This research is a look at the feasibility of using possible methods to predict wear of tool during cutting process Two methods are investigated, one is incremental method utilizing traditional wear equations from Archard to predict wear volume and propose new material, and another is experimental for new material at factory to double check only

TABLE OF CONTENTS

ABSTRACT 1

ACKNOWLEDGEMENTS 2

LIST OF FIGURES 5

LIST OF TABLES 8

1 INTRODUCTION 9

1.1 Cashew overview 9

1.2 Cashew manufacturing overview 10

1.3 Current equipment status 12

1.4 Current cashew machine design study 12

1.4.1 Machine overview 12

1.4.2 Cutting tool 14

1.5 Wear 17

1.6 Problem Statement 20

2 THEORY AND TOOL USED 22

2.1 Heat treating 22

2.1.1 Physical processes 22

2.1.2 Effects of composition 23

2.1.3 Effects of time and temperature 25

2.1.4 Techniques 27

2.2 Cutting Tool Material Used 30

2.2.1 Current material used 30

2.2.1 Proposed material – SKD11 32

2.3 Wear Parameters 35

2.4 FEA wear simulation procedure 37

2.4.1 Finite element theory 37

2.4.1 Constraints and Lagrange Multiplier Method [19] 37

2.4.2 Ansys Mechanical Advanced Connections via MADPL version 17.0 [11] 39

3 INCREMENTAL METHOD DEVELOPMENT 44

3.1 Model 44

3.2 Mesh Validation and Setting 47

3.3 Contact 50

3.4 Pressure Distribution Sensitivity 52

3.5 Incremental Method Script 54

3.6 Simulation procedure 54

4 INCREMENT METHOD RESULTS AND DISCUSSION 56

4.1 Discussion 58

4.2 Equivalent stress 59

4.3 Pressure 64

4.4 Volume wear due to loss 66

4.5 Result summary 68

5 EXPERIMENT PROCESS AND RESULT 68

5.1 Device for experiment preparation 68

5.2 Preparation 68

5.3 Experiment process 70

5.4 Experiment results 71

6 SUMMARY AND CONCLUSIONS 72

6.1 Incremental method 72

6.1.1 Conclusions 72

6.1.2 Areas for Future Improvement 73

6.2 Experiment method 73

6.2.1 Conclusions 73

6.2.2 Areas for Future Improvement 74

7 REFERENCE 74

APPENDIX A SCIENCE PAPER 76

APPENDIX B DETAIL EQUIVALENT STRESS FORMATION (SKD11-FILLED FOR EXAMPLE) 81

APPENDIX C DETAIL EQUIVALENT PRESSURE FORMATION (SKD11-FILLED FOR EXAMPLE) 85

List of Figures

Figure 1: Cashew nut 9

Figure 2: Cashew peeling machine 11

Figure 3: Peeling cutting tool manufactured by unnamed material 11

Figure 4: Machine imported from Sri-lanka 12

Figure 5: Peeling machine mechanism 13

Figure 6: Cutting process 14

Figure 7: Peeling cutting tool design isoview 14

Figure 8: Peeling cutting tool design 2D view 15

Figure 9: Separated tool isoview 15

Figure 10: Separated tool 2D view 16

Figure 11: Cutting tool isoview 16

Figure 12: Cutting tool 2D view 17

Figure 13: Tooling holder 17

Figure 14: Lim and Ashby's wear map for steels 19

Figure 15: Approach process 21

Figure 16: Phase diagram of an iron-carbon alloying system 24

Figure 17: Time-temperature transformation (TTT) diagram for steel 26

Figure 18: Heat treatment graph for SKD11 35

Figure 19: APDL command in Ansys 40

Figure 20: Contact type 40

Figure 21: List of Key options 41

Figure 22: Contact command 42

Figure 23: Command insert method 42

Figure 24: Archard wear formula 43

Figure 25: Cutting tool modelling options 45

Figure 26: Cashew nut 45

Figure 27: Overall modeling 45

Figure 28: Meshing of Rectangle model 47

Figure 29: Boundary condition 48

Figure 30: Remote displacement set up 48

Figure 31: Analysis settings 50

Figure 32: Contact physical 51

Figure 33: Contact and Target body 51

Figure 34: High pressure case 54

Figure 35: Wear simulation process 56

Figure 36: Equivalent stress all cases comparison of SKD11 60

Figure 37: Maximum stress after wear – load case 1 61

Figure 38: Maximum stress after wear – load case 2 61

Figure 39: Maximum stress after wear – load case 3 62

Figure 40: Maximum stress after wear – load case 4 62

Figure 41: Maximum stress after wear – load case 5 63

Figure 42: Maximum stress after wear – load case 6 63

Figure 43: Pressure distribution graph of SKD61 65

Figure 44: Volume wear due to loss graph 67

Figure 45: 8 Cutting tools 69

Figure 46: Peeling machine at Hanh Phuong factory 69

Figure 47: Cutting mechanism on the machine 70

Figure 48: Stress at 0.7s 81

Figure 49: Stress at 1.1s 81

Figure 50: Stress at 3.7s 81

Figure 51: Stress at 4.1s 82

Figure 52: Stress at 8.7s 82

Figure 53: Stress at 9.1s 82

Figure 54: Stress at 20.7s 83

Figure 55: Stress at 21.1s 83

Figure 56: Stress at 39.7s 83

Figure 57: Stress at 40.1s 84

Figure 58: Stress at 48.7s 84

Figure 59: Stress at 49.1s 84

Figure 60: Pressure at 1.1s 85

Figure 61: Pressure at 2.1s 85

Figure 62: Pressure at 3.1s 85

Figure 63: Pressure at 3.7s 86

Figure 64: Pressure at 4.1s 86

Figure 65: Pressure at 4.7s 86

Figure 66: Pressure at 4.1s 87

Figure 67: Pressure at 6.1s 87

Figure 68: Pressure at 15.1s 87

Figure 69: Pressure at 30.1s 88

Figure 70: Pressure at 40.1s 88

Figure 71: Pressure at 48.1s 88

List of Tables

Table 1: Temperature experiment value 20

Table 2: Chemical composition of current used material by experiment 31

Table 3: Physical properties of SKD61 32

Table 4: Chemical composition of SKD11 (Hitachi) 33

Table 5: Wear resistant test by Ogoshi method (Hitachi) 33

Table 6: SKD11 physical properties 34

Table 7: SKD 61 physical properties 46

Table 8: SKD 11 physical properties 46

Table 9: Cashew material properties [1] 46

Table 10: Simulation cases for SKD61 46

Table 11: Simulation cases for SKD11 46

Table 12: Input for Remote displacement 49

Table 13: Friction contact setting 52

a light reddish to yellow fruit, whose pulp can be processed into a sweet, astringent fruit drink

or distilled into liquor

The shell of the cashew seed yields derivatives that can be used in many applications from lubricants to paints

The species is originally native to north eastern Brazil Today, major production of cashews occurs in Vietnam, Nigeria, India and Ivory Coast

Figure 1: Cashew nut

In the 21st Century, cashew cultivation increased in several African countries to meet the demands for manufacturing cashew milk, a plant milk alternative to dairy milk [9]

1.2 Cashew manufacturing overview

Cashew producing industry of Vietnam has been constantly evolving and growing In

2015, exports reached more than two billion dollars Vietnam cashew was ranked No 1 in the world regarding exports Currently, the countries where the producing technology have good development as Indian, Brazilian, experts are sent specialist to Vietnam to study and exchange of experience in the produced processing of cashew Currently, the technology and equipment in Vietnam are quite synchronized The entire device was self-built, only colour sorting equipment still must import A process of cashew production is peeling the hard shell This device for this process must work in extreme environments large capacity, high heat; therefore this equipment is often damaged and unstable work and the rate of peeling is not high Basic reasons are including from designing, selecting and processing materials to manufacture without a unified standard The equipment manufacturing base is very unprofessional, no drawings, no advanced studying from design till materials selection or manufacturing process, maintenance and replacement Because of these characteristics, technology can‟t meet to the world, but the device has not dominated to the world market Some oversea customer order a few lines from Vietnam They complained a lot because of unstable operation and usually occur damage, then ưiil affect to the reputation of our industry There are no any comprehensive research from design, process and material selection, manufacturing process and the management and maintenance record of equipment This is a basic mandatory standard in order to exporte equipments to other countries

Figure 2: Cashew peeling machine

Current equipment nowadays, just according the experience of workers without design documents as figure 2 and the cutting tools as figure 3

Figure 3: Peeling cutting tool manufactured by unnamed material

1.3 Current equipment status

 Equipment: currently, all equipment manufacturing for cashew nuts in Vietnam are manufactured a Sri-lanka form But this original form vertical shape as below figure 4

Figure 4: Machine imported from Sri-lanka

 However nowadays, all manufacturer of Vietnam has converted from vertical shape into horizontal shape and add some line (currently popular machine has 6 lines and productivity can reach 200 kg/hour)

 Due to unfair competition about price, most of manufacturers are using low quality material, components such as drive motor, cutting material, components for mechanism from China

 The materials used in the manufacturing are largely black steel and low carbon then can‟t be heat treated to improve quality, so the bond strength and the relative movement often worn rapidly after a short period of use

1.4 Current cashew machine design study

 The cashew nut transmission mechanism including chain conveyor with the task of bringing the cashews to cutting tool assembly and guide bar to navigate cashews

 The cutting tool assembly including top and bottom guild bar to guild cashew nuts, two upper and lower tool and one tool with separation function at the end of assembly

Figure 5: Peeling machine mechanism

Motor (1) will make continuous transmission cashew nut motion via chain conveyor to bring it to the knife The machine have six lines with capacity until 200kg/h Designed with only one motor can drive all the conveyors machine This design helps the machine consumes less power consumption but the transmission system will be more complicated

The cutting process is described as figure 6 The cashew nut will route to two V-clamps (6) and is held by these V-clamps then the Pushing rod (7) will push the cashew nut to two Cutting tools (8) After cut, the cashew will be continuously pushed to V-tool until two haft-shell can be separated

Figure 6: Cutting process

1.4.2 Cutting tool

 Cutting tool design of current machine in design as figure 7 to figure 13

Figure 7: Peeling cutting tool design isoview

Figure 8: Peeling cutting tool design 2D view

 Main assembly of cutting tool including: (1)-separated tool, (2)-cutting tool, (3)-upper clamp, (4)-bottom clamp

Figure 9: Separated tool isoview

Figure 10: Separated tool 2D view

Figure 11: Cutting tool isoview

Figure 12: Cutting tool 2D view

Figure 13: Tooling holder

1.5 Wear

Wear is a complex phenomenon that is not well understood Humans have been aware of wear for many millennia It has been avoided by choosing harder materials for things that are more likely to wear However, wear is not always something to be avoided, many times it is desired; for example a pencil writes because the lead wears, and metal is polished by wearing the surface smooth Despite the fact that the occurrence of wear has been well documented throughout history, the scientific study of wear is relatively new because wear is such a new

field of study, there is not always agreement on theories or meanings of terms, the classifications and definitions presented in this paper are by no means the only ones that have been proposed [20]

The lack of understanding of wear is not merely due to it not being studied; it is an inherently difficult phenomenon to study Because wear occurs when objects are in contact, it

is difficult to directly observe the process of wear as it happens Therefore, experimenters generally rely on observations made after the test, and then infer what caused the wear This

is not the only difficulty; many of the causes and effects of wear only occur on a microscopic level A third reason that wear is not well understood is that it involves many different variables that make it difficult to generalize results

Conditions used to classify wear include whether or not there is a lubricant present, and whether or not there are hard, abrasive particles present If there is a lubricant present, it is referred to as lubricated wear, otherwise it is dry wear If there are abrasive particles causing wear, then it is referred to as abrasive wear, otherwise it is called sliding wear The current study focuses on lubricated sliding wear

Lim and Ashby classified wear according to four mechanisms: seizure, melt, oxidation, and plasticity Seizure occurs at high pressures when local asperity contacts deform until large areas of the surfaces are in contact and seize Melt occurs when the local temperature at the surface exceeds the melt temperature of the material and forms a thin layer of liquid Oxidational wear occurs when a thin layer of material on the surface oxidizes and then wears away Lim and Ashby's plastic wear encompasses several mechanisms, including adhesion of asperities, delamination and fatigue crack growth While plasticity is an important factor in each of these, it is not the direct mechanism causing wear [12] Therefore, this category will

be referred to as mechanical wear, following the example of Cameron [13] The current research focuses on mechanical wear, though the methods developed will hopefully be extensible to other wear mechanisms

Besides classifying wear, Lim and Ashby also sorted much of the available wear data and developed equations for each mechanism This data was mostly from pin-on disk type wear experiments For mechanical wear, they used Archard's wear law [12]:

̃ ̃ where

̃ = non-dimensional wear rate

̃ = non-dimensional pressure

Figure 14: Lim and Ashby's wear map for steels

More information about the equation will be discussed in more detail in Chapter 2 Archard's wear law has also been used by many other researchers to model mechanical wear [14], [15], [16]

According Lim and Ashby, they created contour plots of wear rate as a function of normalized pressure and normalized velocity using the equations they developed They then combined the plots for each mechanism onto a single graph showing where each mechanism

dominates and this type of graph they called a wear map A wear map for steel is shown in Figure 14

Since finite element analysis (FEA) has become more accessible, popular, therefore many researchers have looked for ways to use it to calculate wear Each has their own unique details, but the general formula is to alternate between a finite element analysis to determine pressures and a calculation of wear which adjusts the model [4], [17] Podra and Andersson say that this method is best suited to the comparison of different design options due to the modeling simplifications and the uncertainty in the input data Benabdallah and Olender use a similar method to determine the profile generated on a pin in a pin-on-disk wear experiment, and produced good agreement with experiment They also found that the wear profile eventually reaches a steady state condition, where any subsequent wear is distributed evenly across the surface

1.6 Problem Statement

Before proposed the problem statement, all potential problems which are related to this operation cutting already investigated Besides of wear investigation, two potential problems which were concerned were affection of Cashew Nut Shell Liquid (CNSL) and thermal Studying from available science paper, it proved that CNSL doesn‟t only affect to tool wear but also it is alternative corrosion inhibitor according JYN Philip, J Buchweishaija and LL Mkayula [2] Another is thermal, experiment to measure temperature at cutting area has been conducted to study temperature level as table 1, the result indicated that the temperature emit

at the contacting between cutting tool and cashew are not really effect to the failure So wear due to sliding contact will be the target of this research

Table 1: Temperature experiment value

Machine 1 Machine 2 Machine 3 Machine 4 Machine 5 Machine 6 Machine 7 Machine 8

43.8 43.9 45 43.8 43.9 44.3 44.1 43.5 44.1 42.6 44.3 43.8 44.3 43.5 44.1 42.6 42.5 44 44.9 43.8 44 44.8 44.3 43.2 44.3 43 44.8 43.8 44.8 43.2 44.3 43 43.7 43.9 45.2 43.7 43.9 45 43.9 43.5 44.1 42.9 45 43.7 45 43.5 44.1 42.9 44.3 45 43.9 43.5 44.1 42.6 44 45.1 43 45 44.1 43.5 42.6 43.8 43 43.8 44.8 45.2 44 43.2 44.3 43 43.9 45.1 42.5 45.2 44.3 43.2 43 42.5 42.5 43.8

45 45.1 43.9 43.5 44.1 42.9 42.9 45.3 43 45.1 44.1 43.5 42.9 43.7 43 43.7 44.1 43.5 42.6 43.8 43.9 43.8 43.9 44.3 44.3 43.8 42.6 44.5 43.9 44.3 43.9 43.2 44.3 43.2 43 42.5 44 43.8 43.8 44.8 44.8 43.8 43 44.6 44 44.8 44 43.5 44.1 43.5 42.9 43.7 43.9 43.7 43.7 44.6 44.7 43.7 42.9 44.7 43.9 44.5 43.9 43

The goal of this research is to find a method to predict the wear by simulation using Ansys between different cutting tool material and cashew material in order to choose more proper material and experience also be conducted to compare with simulation result The particular difficulty of this problem comes from how to conduct experiment to measure at every period time in production Therefore, the research will base on life time of cutting tool Wear simulation is conducted to find the time of execution machine then interpolate to real time of experiment for each material and compare

Two methods are investigated The first is an incremental, macro-scale approach that follows previous work to predict wear with finite elements, especially that done by Benabdallah and Olender [4] and John M Thompson This is done by means of a script that calculates wear according to Archard's wear law and finite element analysis outputs This method will give output of wear shape with machine time of different materials then time machine will be interpolated to real time of experiment according figure 15 Two material were conducted in the thesis is SKD-61 (current use) and SKD-11 The second, new material SKD-11 will be conducted experiment by replacing current cutting to run production then see real life time of new tool According figure 15, value B can be interpolated once value A and

C are acknowledged from simulation results

Figure 15: Approach process

Some background information and theory is presented in Chapter 2 The development of the incremental wear method is in Chapter 3, and some results are discussed in Chapter 4 The experiment of SKD11 will be mentioned in Chapter 5 Finally, Chapter 6 will conclude the documents and contains some points for further study

2 Theory and Tool Used

2.1 Heat treating

According purpose of this research, the heat treatment is the process which enhance the hardness of cutting tool Depend on methodology of heat treating, the cutting tool will have different characteristic

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material The most common application is metallurgical Heat treatments are also used in the manufacture of many other materials, such

as glass Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, normalizing and quenching It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding [3]

2.1.1 Physical processes

Metallic materials consist of a microstructure of small crystals called "grains" or crystallites The nature of the grains (i.e grain size and composition) is one of the most effective factors that can determine the overall mechanical behavior of the metal Heat treatment provides an efficient way to manipulate the properties of the metal by controlling the rate of diffusion and the rate of cooling within the microstructure Heat treating is often used to alter the mechanical properties of a metallic alloy, manipulating properties such as the hardness, strength, toughness, ductility, and elasticity [3]

There are two mechanisms that may change an alloy's properties during heat treatment: the formation of martensite causes the crystals to deform intrinsically, and the diffusion mechanism causes changes in the homogeneity of the alloy [3]

The crystal structure consists of atoms that are grouped in a very specific arrangement, called a lattice In most elements, this order will rearrange itself, depending on conditions like

temperature and pressure This rearrangement, called allotropy or polymorphism, may occur several times, at many different temperatures for a particular metal In alloys, this rearrangement may cause an element that will not normally dissolve into the base metal to suddenly become soluble, while a reversal of the allotropy will make the elements either partially or completely insoluble [3]

When in the soluble state, the process of diffusion causes the atoms of the dissolved element to spread out, attempting to form a homogenous distribution within the crystals of the base metal If the alloy is cooled to an insoluble state, the atoms of the dissolved constituents (solutes) may migrate out of the solution This type of diffusion, called precipitation, leads to nucleation, where the migrating atoms group together at the grain-boundaries This forms a microstructure generally consisting of two or more distinct phases Steel that has been cooled slowly, for instance, forms a laminated structure composed of alternating layers of ferrite and cementite, becoming soft pearlite [3]

Unlike iron-based alloys, most heat treatable alloys do not experience a ferrite transformation In these alloys, the nucleation at the grain-boundaries often reinforces the structure of the crystal matrix These metals harden by precipitation Typically a slow process, depending on temperature, this is often referred to as "age hardening" [3]

Many metals and non-metals exhibit a martensite transformation when cooled quickly (with external media like oil, polymer, water etc.) When a metal is cooled very quickly, the insoluble atoms may not be able to migrate out of the solution in time This is called a

"diffusion less." When the crystal matrix changes to its low temperature arrangement, the atoms of the solute become trapped within the lattice The trapped atoms prevent the crystal matrix from completely changing into its low temperature allotrope, creating shearing stresses within the lattice When some alloys are cooled quickly, such as steel, the martensite transformation hardens the metal, while in others, like aluminum, the alloy becomes softer [3]

2.1.2 Effects of composition

The specific composition of an alloy system will usually have a great effect on the results

of heat treating If the percentage of each constituent is just right, the alloy will form a single,

continuous microstructure upon cooling Such a mixture is said to be eutectoid However, if the percentage of the solutes varies from the eutectoid mixture, two or more different microstructures will usually form simultaneously A hypoeutectoid solution contains less of the solute than the eutectoid mix, while a hypereutectoid solution contains more [3]

Phase changes occur at different temperatures (vertical axis) for different compositions (horizontal axis) The dotted lines mark the eutectoid (A) and eutectic (B) compositions according figure 16

Figure 16: Phase diagram of an iron-carbon alloying system

 Eutectoid alloys: A eutectoid (eutectic-like) alloy is similar in behaviour to a eutectic alloy A eutectic alloy is characterized by having a single melting point This melting point is lower than that of any of the constituents, and no change in the mixture will lower the melting point any further When a molten eutectic alloy is cooled, all of the constituents will crystallize into their respective phases at the same temperature [3]

 Hypoeutectoid alloy: a hypoeutectic alloy has two separate melting points Both are above the eutectic melting point for the system, but are below the melting points of any

constituent forming the system Between these two melting points, the alloy will exist

as part solid and part liquid The constituent with the lower melting point will solidify first When completely solidified, a hypoeutectic alloy will often be in solid solution [3]

 Hypereutectoid alloys: a hypereutectic alloy also has different melting points However, between these points, it is the constituent with the higher melting point that will be solid Similarly, a hypereutectoid alloy has two critical temperatures When cooling a hypereutectoid alloy from the upper transformation temperature, it will usually be the excess solutes that crystallize-out first, forming the proeutectoid This continues until the concentration in the remaining alloy becomes eutectoid, which then crystallizes into a separate microstructure [3]

2.1.3 Effects of time and temperature

Proper heat treating requires precise control over temperature, time held at a certain temperature and cooling rate With the exception of stress-relieving, tempering, and aging, most heat treatments begin by heating an alloy beyond the upper transformation (A3) temperature This temperature is referred to as an "arrest" because at the A3 temperature the metal experiences a period of hysteresis At this point, all of the heat energy is used to cause the crystal change, so the temperature stops rising for a short time (arrests) and then continues climbing once the change is complete Therefore, the alloy must be heated above the critical temperature for a transformation to occur The alloy will usually be held at this temperature long enough for the heat to completely penetrate the alloy, thereby bringing it into a complete solid solution [3]

In the diagram in figure 17, the red curves represent different cooling rates (velocity) when cooled from the upper critical (A3) temperature V1 produces martensite V2 has pearlite mixed with martensite, V3 produces bainite, along with pearlite and matensite

Figure 17: Time-temperature transformation (TTT) diagram for steel

Because a smaller grain size usually enhances mechanical properties, such as toughness, shear strength and tensile strength, these metals are often heated to a temperature that is just above the upper critical-temperature, in order to prevent the grains of solution from growing too large For instance, when steel is heated above the upper critical-temperature, small grains

of austenite form These grow larger as temperature is increased When cooled very quickly, during a martensite transformation, the austenite grain-size directly affects the martensitic grain-size Larger grains have large grain-boundaries, which serve as weak spots in the structure The grain size is usually controlled to reduce the probability of breakage [3]

The diffusion transformation is very time-dependent Cooling a metal will usually suppress the precipitation to a much lower temperature Austenite, for example, usually only exists above the upper critical temperature However, if the austenite is cooled quickly enough, the transformation may be suppressed for hundreds of degrees below the lower critical temperature Such austenite is highly unstable and, if given enough time, will precipitate into various microstructures of ferrite and cementite The cooling rate can be used

to control the rate of grain growth or can even be used to produce partially martensitic microstructures However, the martensite transformation is time-independent If the alloy is

cooled to the martensite transformation temperature before other microstructures can fully form, the transformation will usually occur at just under the speed of sound [3]

When austenite is cooled slow enough that a martensite transformation does not occur, the austenite grain size will have an effect on the rate of nucleation, but it is generally temperature and the rate of cooling that controls the grain size and microstructure When austenite is cooled extremely slowly, it will form large ferrite crystals filled with spherical inclusions of cementite This microstructure is referred to as "sphereoidite." If cooled a little faster, then coarse pearlite will form Even faster, and fine pearlite will form If cooled even faster, bainite will form Similarly, these microstructures will also form if cooled to a specific temperature and then held there for a certain time [3]

Most non-ferrous alloys are also heated in order to form a solution Most often, these are then cooled very quickly to produce a martensite transformation, putting the solution into a supersaturated state The alloy, being in a much softer state, may then be cold worked This cold working increases the strength and hardness of the alloy, and the defects caused by plastic deformation tend to speed up precipitation, increasing the hardness beyond what is normal for the alloy Even if not cold worked, the solutes in these alloys will usually precipitate, although the process may take much longer Sometimes these metals are then heated to a temperature that is below the lower critical (A1) temperature, preventing recrystallization, in order to speed-up the precipitation [3]

2.1.4 Techniques

Complex heat treating schedules, or "cycles," are often devised by metallurgists to optimize an alloy's mechanical properties In the aerospace industry, a super alloy may undergo five or more different heat treating operations to develop the desired properties This can lead to quality problems depending on the accuracy of the furnace's temperature controls and timer These operations can usually be divided into several basic techniques [3]

 Annealing

Annealing is a rather generalized term Annealing consists of heating a metal to a specific temperature and then cooling at a rate that will produce a refined microstructure, either fully

or partially separating the constituents The rate of cooling is generally slow Annealing is most often used to soften a metal for cold working, to improve machinability, or to enhance properties like electrical conductivity [3]

In ferrous alloys, annealing is usually accomplished by heating the metal beyond the upper critical temperature and then cooling very slowly, resulting in the formation of pearlite

In both pure metals and many alloys that cannot be heat treated, annealing is used to remove the hardness caused by cold working The metal is heated to a temperature where recrystallization can occur, thereby repairing the defects caused by plastic deformation In these metals, the rate of cooling will usually have little effect Most non-ferrous alloys that are heat-treatable are also annealed to relieve the hardness of cold working These may be slowly cooled to allow full precipitation of the constituents and produce a refined microstructure [3]

Ferrous alloys are usually either "full annealed" or "process annealed." Full annealing requires very slow cooling rates, in order to form coarse pearlite In process annealing, the cooling rate may be faster; up to, and including normalizing The main goal of process annealing is to produce a uniform microstructure Non-ferrous alloys are often subjected to a variety of annealing techniques, including "recrystallization annealing," "partial annealing,"

"full annealing," and "final annealing." Not all annealing techniques involve recrystallization, such as stress relieving [3]

 Aging

Some metals are classified as precipitation hardening metals When a precipitation hardening alloy is quenched, its alloying elements will be trapped in solution, resulting in a soft metal Aging a "solutionized" metal will allow the alloying elements to diffuse through the microstructure and form intermetallic particles These intermetallic particles will nucleate and fall out of solution and act as a reinforcing phase, thereby increasing the strength of the alloy Alloys may age "naturally" meaning that the precipitates form at room temperature, or they may age "artificially" when precipitates only form at elevated temperatures In some applications, naturally aging alloys may be stored in a freezer to prevent hardening until after further operations - assembly of rivets, for example, may be easier with a softer part [3]

 Quenching

Quenching is a process of cooling a metal at a rapid rate This is most often done to produce a martensite transformation In ferrous alloys, this will often produce a harder metal, while non-ferrous alloys will usually become softer than normal [3]

To harden by quenching, a metal (usually steel or cast iron) must be heated above the upper critical temperature and then quickly cooled Depending on the alloy and other considerations (such as concern for maximum hardness vs cracking and distortion), cooling may be done with forced air or other gases, (such as nitrogen) Liquids may be used, due to their better thermal conductivity, such as oil, water, a polymer dissolved in water, or a brine Upon being rapidly cooled, a portion of austenite (dependent on alloy composition) will transform to martensite, a hard, brittle crystalline structure The quenched hardness of a metal depends on its chemical composition and quenching method Cooling speeds, from fastest to slowest, go from fresh water, brine, polymer (i.e mixtures of water + glycol polymers), oil, and forced air However, quenching a certain steel too fast can result in cracking, which is why high-tensile steels such as AISI 4140 should be quenched in oil, tool steels such as ISO 1.2767 or H13 hot work tool steel should be quenched in forced air, and low alloy or medium-tensile steels such as XK1320 or AISI 1040 should be quenched in brine [3]

However, most non-ferrous metals, like alloys of copper, aluminium, or nickel, and some high alloy steels such as austenitic stainless steel (304, 316), produce an opposite effect when these are quenched: they soften Austenitic stainless steels must be quenched to become fully corrosion resistant, as they work-harden significantly [3]

 Tempering

Untampered martensitic steel, while very hard, is too brittle to be useful for most applications A method for alleviating this problem is called tempering Most applications require that quenched parts be tempered Tempering consists of heating steel below the lower critical temperature, (often from 400 to 1105 ˚F or 205 to 595 ˚C, depending on the desired results), to impart some toughness Higher tempering temperatures (may be up to 1,300 ˚F or

700 ˚C, depending on the alloy and application) are sometimes used to impart further ductility, although some yield strength is lost [3]

Tempering may also be performed on normalized steels Other methods of tempering consist of quenching to a specific temperature, which is above the martensite start temperature, and then holding it there until pure bainite can form or internal stresses can be relieved These include austempering and martempering [3]

Steel that has been freshly ground or polished will form oxide layers when heated At a very specific temperature, the iron oxide will form a layer with a very specific thickness, causing thin-film interference This causes colours to appear on the surface of the steel As temperature is increased, the iron oxide layer grows in thickness, changing the colour These colours, called tempering colours, have been used for centuries to gauge the temperature of the metal At around 350˚F (176˚C) the steel will start to take on a very light, yellowish hue

At 400˚F (204˚C), the steel will become a noticeable light-straw colour, and at 440˚F (226˚C), the colour will become dark-straw At 500˚F (260˚C), steel will turn brown, while at 540˚F (282˚C) it will turn purple At 590˚F (310˚C) the steel turns a very deep blue, but at 640˚F (337˚C) it becomes a rather light blue [3]

The tempering colours can be used to judge the final properties of the tempered steel Very hard tool steel is often tempered in the light to dark straw range, whereas spring steel is often tempered to the blue However, the final hardness of the tempered steel will vary, depending on the composition of the steel The oxide film will also increase in thickness over time Therefore, steel that has been held at 400˚F for a very long time may turn brown or purple, even though the temperature never exceeded that needed to produce a light straw color Other factors affecting the final outcome are oil films on the surface and the type of heat source used [3]

2.2 Cutting Tool Material Used

2.2.1 Current material used

 Overview

Materials used to manufacture the current cutting tool are used inconsistently and used available materials on the market, such as using material of wired knives sawing, and then cutting into desired shapes One of the materials used today is chromium steel structure, chemical composition shown in Table 2

Table 2: Chemical composition of current used material by experiment

Mn

% 0.375

P

% 0.030

S

% 0.032

Cr

% 5.030

Mo

% 0.099

Ni

% 0.128

Nb

% 0.029

Ti

% 0.006

V

% 0.326

W

% 1.18

Ca

% 0.000

Ce

% 0.024

This is the material of stainless steel group, mainly chromium substances Uses mainly is for manufacturing machine parts with corrosion resistance and the aesthetic of device It's not the kind of material tools, especially when working under high friction and high temperature

as well as high cutting speed In fact the cutting tools durability have from three to four days only then it need to be rework or replace

 Feature

 Good balance of both strength at elevated temperature and toughness

 Good machinability with less distortion after heat treatment

 Application

 General die for Aluminium Die-casting

 Die for Zinc Die-casting

 Die for low pressure casting

 Hardened hardness

 45-48 HRC

 Physical properties as table 3

Table 3: Physical properties of SKD61

2.2.1 Proposed material – SKD11

Studying from existent supplier in Japan – Hitachi, they share one of wear resistance testing of their materials as table 4 and table 5 We learned that the wear of SKD11 is better than SKD61 Based on current steel material market in Vietnam, application of cutting tool, testing from Hitachi and costing (around 135K VND/kg equivalent to SKD61), we propose SKD11 for the thesis

SKD11 is cold-work tool steel This steels is used to cut or form materials that are at low temperatures This group possesses high hardenability and wear resistance, and average toughness and heat softening resistance They are used in production of larger parts or parts that require minimal distortion during hardening The use of oil quenching and air-hardening helps reduce distortion, avoiding the higher stresses caused by the quicker water quenching More alloying elements are used in these steels, as compared to the water-hardening class These alloys increase the steels' hardenability, and thus require a less severe quenching

process and as a result are less likely to crack They have high surface hardness and are often used to make knife blades The machinability of the oil hardening grades is high but for the high carbon-chromium types is low [6]

Table 4: Chemical composition of SKD11 (Hitachi)

Table 5: Wear resistant test by Ogoshi method (Hitachi)

 Feature

 Be a good impact, good abrasion resistance, less distortion

 Good machinability with less distortion after heat treatment

 Resistant to deformation, impact resistance and other characteristics

 Excellent harden-ability and minimal quench stress

 Application

 Bending die for automotive parts

 Die for hydroforming

 Most commonly used in all kinds of moulds

 Hardened hardness [5]

 57 - 63 HRC

 Physical properties as table 6 [5]

Table 6: SKD11 physical properties

 Heat treatment

With studying from previous theory of heat treatment and analysis heat treatment advice from Hitachi supplier plus proposal from LAB specialist, SKD11 is proposed using graph according figure 18

Figure 18: Heat treatment graph for SKD11

2.3 Wear Parameters

There are several parameters that are used to quantify wear The most important are: wear volume (V), wear height (h), wear rate (w) and wear coefficient (K) Wear volume is simply the volume of material that is lost due to wear It is often measured by comparing before and after volumes of wear specimens Wear height can be either the maximum, average, or minimum depth of the material removed; depending on what is most important to the experimenter These two measurements are often what is of most interest to engineers and designers, who are concerned with the life and durability of a part They are not, however, very useful for characterizing the process of wear in general terms, because they are heavily dependent on variables that may change significantly from problem to problem Some of these variables are: the distance traveled (s), the time over which the wear occurred (t), the normal force at the interface (Fn), and the hardness material that is wearing (H) Oftentimes, the distance and time are combined as velocity (v), and force is combined with area as pressure (P) [20]

Wear rate is a more general parameter for specifying wear It is not a time rate, but a distance rate Wear rate is defined as the volume removed per sliding distance, that is:

Wear rate, either with or without dimensions, is generally considered to be constant for a material pair This parameter is a function of only pressure and velocity, which makes it good for calculation with a single set of materials

The problem can be further non-dimensionalzed by using the wear coefficient and normalized force (P˜) and velocity (v˜) The force is normalized by:

̃ Because the force is normalized by the area, it can also be referred to as normalized pressure Velocity is normalized by the hardness and apparent contact area:

̃

where r0 is the radius of the pin, and a is the thermal diffusivity of the material in m2/s The wear coefficient comes from Archard's wear law [17]:

̃ ̃ where KA is Archard's wear coefficient:

The wear coefficient is intended to allow for the results from known experiments to be applied to predict wear for new geometries or materials However, in practice it needs to be determined experimentally for each contact configuration [17] This is because wear is not simply a material property, but a response of a system The unreliability of the wear coefficient is currently one of the major problems with wear predictions based on Archard's

wear law Because it may change with each configuration, the accuracy of any equations that use it is reduced This research intends to address this shortcoming

2.4 FEA wear simulation procedure

2.4.1 Finite element theory

The main task of the finite element method (FEM) in the wear calculations is to compute the fields of contact stresses The structure to be analyzed is discretized with a number of elements, assembled at nodes In FEM the function in question (displacement, temperature, etc.) is piecewise approximated by means of polynomials over every element and expressed

in terms of nodal values [5] The elements of different type and shape with complex loads and boundary conditions can be used simultaneously In the structural analysis the degrees of freedom are defined as nodal displacements The equations for every element are assembled into a set, expressed in the structural level as

[K]{u} = {F}

where [K] is the structural or global stiffness (N/m) matrix, {u} is the structural nodal displacement or deformation (m) vector and {F} is the vector of structural nodal loads (N) This equation system can be solved for {u} From deformations the nodal stresses are computed The commercial finite element (FE) software ANSYS can handle several material and structural non-linearity, such as plasticity, viscoelasticity, friction, etc., [6] The coupled-field analyses, for instance thermal–structural, can be performed as well [7]

The FE wear calculations involve solving the general contact problem with the area of contact between the bodies not known in advance The analysis is therefore non-linear The point-to-surface interface elements are used in those cases FEA software is equipped with many tools, enhancing the non-linear numerical procedure, the parameters of which are to be chosen with care

2.4.1 Constraints and Lagrange Multiplier Method [19]

According Ansys help, Constraints are generally implemented using the Lagrange Multiplier Method In this method, the internal energy term is augmented by a set of