Warpage Control Due To Heat Treatment Process On Conventional Furnace.
WARPAGE CONTROL DUE TO HEAT TREATMENT PROCESS ON CONVENTIONAL FURNACE
MUHAMMAD ASIF BIN MD YUSOF
This report had been done in partial fulfillment for
Bachelor of Mechanical Engineering (Thermal – Fluid)
Faculty of Mechanical Engineering Universiti Teknikal Malaysia Melaka
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I declare that I have been done reading this report and in my opinion, this report fulfill the condition in all aspect that must be in project writing as need in partial fulfillment
for Bachelor of Mechanical Engineering ( Thermal – Fluid )
Signature : ………
Supervisor Name : En. Hamzah Bin Mohd Dom
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“I declare that this report had been done originally from me except some of them where I have been explain each one of them with its sources”
Signature : ………
Name : Muhammad Asif Bin Md Yusof
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For my beloved parents:
Mr. Md Yusof Bin Jamil
Mrs. Noraishah Binti Hussin
For my supportive siblings:
Mohamad Arif Bin Md Yusof
Nurul Adila Binti Md Yusof
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ACKNOWLEDGEMENT
First of all, I would like to thank Allah S.W.T. because with His permission I can finish my “Final Year Project” (FYP) to complete the requirement for my graduation.
Secondly, I would like to thank to my supervisor, Mr Hamzah Mohd Dom, Lecturer of Faculty of Mechanical Engineering in UTeM, for giving me the opportunity in doing my FYP under his supervision. I also would like to thank to him for teaching me in understanding about the warpage control during the heat treatment process. He also guided me and given advised based on his experience during my progress of this project. I have learned many new things from him.
I would also like to thank to all the staff in the Faculty of Mechanical Engineering Laboratory whether they are directly or indirectly involved in this project. I would appreciate all their effort to making this project successful. I thank all of you for all your cooperation with me since the beginning of this project by giving permission to use the lab for my experiments.
I would also like to thank to all my friends especially class of 4 BMCT (G2) for being kind and helpful to me until the project is finished. The comments and advices helped me to improve the quality of this report.
Last but not least, thank to my beloved parents and family who had give me the courage and support in finishing this project. I hope that this report will be a guidance and as a reference to other students of UTeM in the future.
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ABSTRAK
Tesis ini berkaitan tentang kajian terhadap masalah meleding yang terjadi semasa rawatan haba dijalankan dengan menggunakan relau. Kini, terdapat pelbagai jenis proses rawatan haba yang dijalankan seperti sepuh lindap, sepuh lazim, lindap kejut dan pembajaan. Sewaktu menggunakan relau apabila proses rawatan haba dilakukan, besi keluli mengalami perubahan isipadu sewaktu berlakunya perubahan struktur dalaman besi keluli. Apabila bahagian tersebut mengalami proses lindap kejut, perubahan kepada struktur dalaman berlaku sekali lagi dan perubahan isipadu kali ini tidak dapat mengimbangkan perubahan pada struktur besi keluli sewaktu proses pemanasan. Perkara ini telah menyebabkan perubahan bentuk ataupun meleding terutamanya kepada bahagian yang nipis sewaktu proses rawatan haba di dalam relau. Maka, projek ini bertujuan bagi mengoptimumkan parameter proses rawatan haba yang dapat menyebabkan meleding kepada bahagian yang nipis di struktur besi keluli. Projek ini juga difokuskan kepada relau konvensional dan material keluli lembut menggunakan Teknik Taguchi bagi menganalisis parameter tersebut.
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ABSTRACT
This thesis is about analyzing warpage problem due to heat treatment process on conventional furnace. Nowdays, there are various types of heat treatment employed in heat treatment process such as annealing normalizing, hardening and tempering. By using furnace during heat treatment process, steel parts change volume as they change their inner structure. When these parts are quenched, their internal structure changes again, thus making the volume change is not sufficient to offset the change upon heating. This change of volume causes shape distortion especially on thin parts during heat treatment process in the furnace. So, this project is to optimize heat treatment parameter that can cause warpage on thin parts. It is focusing on conventional furnace and material of mild steel to be used with Taguchi Method is selected for parameter analysis.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION i
ACKNOWLEDGEMENT iv
ABSTRAK v
ABSTRACT vi
CONTENTS vii
LIST OF FIGURES xi
LIST OF TABLES xii
LIST OF SYMBOLS xv
CHAPTER 1 INTRODUCTION 1
1.1 Overview 1
1.2 Objective of the project 2
1.3 Scope of Research 2
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CHAPTER 2 LITERATURE REVIEW 4
2.1 Distortion 4
2.1.1 Size Distortion 5
2.1.2 Warpage (Shape Distortion) 5
2.1.2.1 Causes of Warpage 6
2.1.2.2 Minimizing Warpage 7
2.2 Heat Treatment 10
2.2.1 Objective of Heat Treatment 11
2.2.2 Types of Heat Treatment 12
2.2.2.1 Annealing 12
2.2.2.2 Normalizing 13
2.2.2.3 Surface Hardening 14
2.2.2.3.1 Carburizing 15
2.2.2.3.2 Carbonitriding 15
2.2.2.3.3 Nitriding 15
2.2.2.3.4 Nitrocarburising 16
2.2.2.4 Tempering 16
2.3 Furnace 17
2.3.1 Silicone Carbide Furnace 18
2.3.2 Conventional Standard Furnace 19
2.3.3 Round and Stationary Furnace 19
2.4 Design of Experiment (DOE) 21
2.5 Taguchi's Background 23
2.5.1 Taguchi Basic Steps in Engineering 24
2.5.1.1 Concept design 25
2.5.1.2 Parameter design 26
2.5.1.3 Tolerance design 27
2.5.2 Taguchi Method Approaches 28
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2.5.2.2 Robust Function 34
2.5.2.3 Orthogonal Arrays 35
2.5.2.4 Signal to Noise (S/N) Ratio 38
CHAPTER 3 METHODOLOGY 40
3.1 Introduction 40
3.2 Title Confirmation and Compilation 41
3.2.1 Chapter 1 : Introduction 41
3.2.2 Literature Review 42
3.2.3 Field Observation Analysis 43
3.2.4 Experimental Setup 43
3.2.4.1 Material Composition 43
3.2.4.2 Specimen Preparation 44
3.2.4.3 Experiment Flow Process 45
3.2.4.4 Experiment Procedure 47
3.2.5 Methodology Construction 48
3.2.6 Data Result and Calculation 49
3.2.7 Data analysis 49
3.2.8 Report Writing 49
3.2.9 Conclusion and Recommendation 50
3.3 Taguchi Method of Procedure 50
3.3.1 Material and Methods 51
3.3.2 Sample Inspection 54
3.3.3 L9 Orthogonal Array Experiments 57
CHAPTER 4 RESULT AND ANALYSIS 60
4.1 Introduction 60
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4.3 Warped Sample Measurement Data Sheet 66 4.4 Result of Total Defect Due to Warpage 67
4.5 Signal-to-Noise Ratio 68
4.5.1 Main Effect of Signal-to-Noise 69 Ratio (S/N) Response
CHAPTER 5 DISCUSSION 71
5.1 Introduction 71
5.2 Experiment Discussion 72
5.2.1 Signal-to-Noise ratio 74 5.2.2 Main Effect of Signal-to-Noise 75
Ratio (S/N) Response
5.3 Problems Encountered during Project 77 CHAPTER 6 CONCLUSION AND RECOMMENDATION 78 6.1 Conclusion 78 6.2 Recommendation 80
REFERENCE S 81
BIBLIOGRAPHY 84
APPENDIX A 85
APPENDIX B 88
APPENDIX C 90
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LIST OF FIGURES
NO. TITLE PAGE
2.1 Warpage of Thin Plate Specimen 6
2.2 Temperature Ranges for Normalizing and Hardening 14 Treatment
2.3 Typical Furnace Components 18
2.4 Silicone Carbide Furnace 18
2.5 Conventional Standard Furnace 19
2.6 Round and Stationary Furnace 20
2.7 Stage of optimize a process or product design 25
2.8 Parameter Diagram of a Dynamic Product or 27
Process System
2.9 The Four Phase of the Methodology 29
2.10 A Quadratic Loss Function 30
2.11 Nominal-is-Better Loss Functions 32
2.12 Smaller- Is-Better Loss Functions 33
2.13 Larger-Is-Better Loss Functions 33
3.1 General Flow Chart of Project Planning 41
3.2 Experiment Flow Chart of Heat Treatment in 48
Controlling Warpage using Taguchi Method
3.3 Achieved Warped Sample From Experiment 55
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LIST OF TABLES
NO. TITLE PAGE
2.1 The Orthogonal Array of L9 type 36
2.2 Standard Orthogonal Array 37
3.1 Composition and Properties of Mild Steel 44
3.2 Description of Specimen (Sample) 44
3.3 Measurement of Material 45
3.4 Shearing Process 45
3.5 Experiment of Heat Treatment in Furnace 46
3.6 Measurement of Warped Material 46
3.7 Heat Treatment Process of Each Material 47
3.8 The Parameter for Three Levels of Selected Factors 51
3.9 List of Equipment Used in the Experiment 56
3.10 Experiment Layout using L9 (32) Orthogonal Array 57
3.11 Selected Process Parameter and their Respective 58
Levels in Experimental Design 3.12 Taguchi L9 (32) Orthogonal Array Design 58
3.13 The Process Parameter Used in the Experiment 59
4.1 Experiment Result for Hardening Time Interval of 61
30 minute and Flat Arrangement in the Furnace 4.2 Experiment Result for Hardening Time Interval of 61
30 minute and Straight Arrangement in the Furnace 4.3 Experiment Result for Hardening Time Interval of 62
30 minute and Sideways Arrangement in the Furnace 4.4 Experiment Result for Hardening Time Interval of 62
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4.5 Experiment Result for Hardening Time Interval of 63
60 minute and Straight Arrangement in the Furnace 4.6 Experiment Result for Hardening Time Interval of 63
60 minute and Sideways Arrangement in the Furnace 4.7 Experiment Result for Hardening Time Interval of 64
90 minute and Flat Arrangement in the Furnace 4.8 Experiment Result for Hardening Time Interval of 64
90 minute and Straight Arrangement in the Furnace 4.9 Experiment Result for Hardening Time Interval of 65
90 minute and Sideways Arrangement in the Furnace 4.10 Warped Sample Measurement Data Sheet 66
4.11 Experiment Trial and Total Defect due to Warpage 67
4.12 Calculation for S/N ratio (Larger-the-better) 68
4.13 Response Table for Signal to Noise Ratio 70
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LIST OF SYMBOLS
ANOVA = Analysis of Variance DOE = Design of Experiment
OA = Orthogonal Array
ECL = Electrical Communication Lab QFD = Quality Function Deployment S/N = Signal-to-Noise
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CHAPTER 1
Introduction
1.1 Overview
Heat treatment is known to be a controlled heating and cooling of metals in changing their physical and mechanical properties. This process happened without altering the product shape. Heat treatment is sometimes done due to manufacturing processes that either heating or cooling the metal such as welding or forming.
Heat treatment is made to increase the strength of material and enables the manufacturing process in the steel industry. It also improve the material performance by increasing the strength or other desirable characteristics.Warpage or shape distortion is due to the process of heat treatment are different because it is usually a result of process and design issues thus affecting the phase changes of the material. While furnace is a tool which heat is discharged and transferred directly or indirectly for the purpose of effecting a physical or chemical change in the material.
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1.2 Objective of the project
The objective of this project are as follows:
1) To conduct an experiment and analyze warpage problem due to heat treatment on conventional furnace using Taguchi Method.
2) To optimize the heat treatment parameter on controlling warpage by conventional furnace.
1.3 Scopes of the project
The scopes of this project are as follows:
1) To do a survey on warpage problems due to heat treatment process.
2) To conduct an experiment on studying heat treatment parameter of racking arrangement at controlling warpage by conventional furnace.
3) To find solution of improvement in reducing warpage using Taguchi Method during heat treatment.
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1.4 Problem statements of the project
It is understand that furnace is an apparatus in which heat is used in order to change the physical and chemical substance of the treated material. There are various types of heat treatment used today such as annealing, normalizing, hardening, and tempering. Thus, by using furnace when heat treatment is made, upon heating, the steel parts changes volume as they change their inner structure. When these heated parts are quenched, their internal structure changes again, so the volume change is not sufficient to offset the change upon heating. This change of volume causes warpage especially on thin parts during the heat treatment in the furnace. So, this project is to make an analysis of warpage control due to heat treatment using Taguchi Method and it is focusing on conventional furnace. Then, it is to find a solution of improvement in reducing warpage during heat treatment.
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CHAPTER II
LITERATURE REVIEW
This chapter will explain about the literature review that have been done to guide the research in the future. It will explain all about Warpage, Heat Treatment, Design of Experiment (DOE) and Taguchi Method in detail.
2.1. Distortion
Prabhudev (2004) states that distortion is defined as a permanent and an unpredictable change in shape or size of component during processing. It is probably the biggest problem in heat treatment operation. Then, Sinha (2003) states that distortion is an irreversible and unpredictable dimensional change in the component while doing the processing from heat treatment and from temperature variations and loading in service. The usage of term dimensional change is used in denoting the changes in both shape and size. Thus, distortion is known to be a general term often use by engineers in describing the irreversible dimensional changes in a heated part during heat treatment operations in steel during hardening and tempering. Sinha (2003) also states it is known as one of the most difficult and troublesome problem that is encountered by the heat treater and heat-treatment industries on a daily basis. Distortion occurred due to combined effect of thermal and transformation stresses. This refers at the dimensional changes after
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5 hardening process that takes place as a result of volume change during phase transformation.
Distortion can be classified into two categories that is size distortion that is the changes in volume and shape distortion that is warpage which is due to changes in geometrical form of the steel component.
2.1.1 Size Distortion
Sinha (2003) states that size distortion is the net change in specific volume between the parent and transformation product produced by phase transformation without a change in geometrical form. Size distortion occurs due to the expansion or contraction in steel component. This type of distortion is less problematic than size distortion
2.1.2 Warpage (Shape Distortion)
Warpage is a physical distortion where there is a change in geometrical form or shape of the workpiece and is revealed by changes of curvature (angular relations) or curving, bending, twisting and nonsymmetrical dimensional change without any volume change (Sinha, A. K. 2003). Warpage is also known to be an irreversible change in shape of the component that occurs during heat treat processing. The change in shape can be resulted due to nonuniform heating or cooling (quenching), metallurgical structure or prior residual stresses (Dossett e. al. 2006).
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6 For designers and heat treaters, this type of distortion poses greater problem than size distortion. Upon heat treatment, part movement could occur immediately and sometimes later in a subsequent processing operation. Parts that is machined, cast or formed to achieve the accurate dimensions due to heat treatment, often came out from the heat treatment process with apparent changes in their dimensional structure. There are a lot of cases which the distortion that occurs is shown by warpage such as bowing or twisting of sheet metal, canning of machined pocket areas, and other forms of part movement.
Figure 2.1 : Warpage of Thin Plate Specimen (Sources :Rajan et all. (2011)) 2.1.2.1 Causes of Warpage
Based from the latest research (Croucher 2008), warpage of heated parts during and after the heat treating process is due to many factors. Some parts will warp for reasons the heat treater can control, but others will distort for causes that occurred before the heat treater received the parts and are beyond control. Thus, by understanding and
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7 controlling these factors, this allows the heat treater to minimize the occurrence of heat treating warpage. The factors are:
a. Relief of pre-heat treat residual stresses
b. Expansion and contraction of parts during processing of heat treatment c. Inadequate racking procedures in the furnace
d. The process of quenching is too fast e. Improper quenchant selection
f. Uneven quenching due to inadequate agitation or spacing g. Improper quench immersion rates
h. Furnace air flow design in relation to part orientation
2.1.2.2 Minimizing Warpage
According to Rajan et. all. (2011), in minimizing warpage or known as shape distortion during heat treatment, a number of factors must be taken into consideration such as:
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8 a. Stress Relieving
The presence of residual stress due to the previous machining or forging operation will enhance the tendency of warpage. Thus, fabrication stresses caused by these operations must be relieved by subcritical annealing or normalizing operation.
b. Heating Rate
The components heating rate must not be too fast or the components may crack or warp as sections are having different heat up at different rates. So, the difference in temperature can be controlled by preheating the components to a temperature below the lower transformation of steel.
c. Preheating
Preheating can reduce shape distortion in steels by reducing the thermal stresses that is made. This is due to the gradient temperature prevailing between the surface and interior part of component. Then, for large cross-section, complicated parts and high alloy steels that has poor thermal conductivity, it is preferable to carry out two-stage preheating.
d. Quenching Media
The basic aim of hardening of steels is to get martensitic structure and avoiding the formation of pearlite and bainite. So, the rate of cooling of heated component must be fast enough in producing a fully martensitic structure but faster cooling rate will increases the severity of quench. Thus, it is essential to use the least quenching medium that made martensite happened. Shape distortion can be further reduced while quenching if the cooling conditions are made uniform as possible. Usually, basic quenching media used are water, brine and conventional oils. Even salt baths, hot quenching oils and polymer quenchants is still considered as quenching media as they gave good results.
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9 e. Press Quenching
Press quenching or die quenching of steel is not common to most of commercial heat treating industries. So, during press quenching, warpage can be minimized by physical restraint of part during its rapid cooling from austenitic condition. So, quenching jigs are used for this purpose.
The part is clamped in a jig and then placed in a hydraulically operated press after heating. Then, the jig should be preheated in avoiding rapid cooling of the surface of component which comes in contact with the jigs. Along with the closing of the press, oil is flown over the component. This will resulted in maintaining the plane shape during the quenching operation.
f. Trays, Fixtures and Supports.
It is achieved that odd shaped components and unsymmetrical sizes needed to use the holding trays and fixtures. This will maintain the shape of the components during heating and rapid cooling from austenitizing temperature. The parts should lie on a flat surface.
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CHAPTER II
LITERATURE REVIEW
This chapter will explain about the literature review that have been done to guide the research in the future. It will explain all about Warpage, Heat Treatment, Design of Experiment (DOE) and Taguchi Method in detail.
2.1. Distortion
Prabhudev (2004) states that distortion is defined as a permanent and an unpredictable change in shape or size of component during processing. It is probably the biggest problem in heat treatment operation. Then, Sinha (2003) states that distortion is an irreversible and unpredictable dimensional change in the component while doing the processing from heat treatment and from temperature variations and loading in service. The usage of term dimensional change is used in denoting the changes in both shape and size. Thus, distortion is known to be a general term often use by engineers in describing the irreversible dimensional changes in a heated part during heat treatment operations in steel during hardening and tempering. Sinha (2003) also states it is known as one of the most difficult and troublesome problem that is encountered by the heat treater and heat-treatment industries on a daily basis. Distortion occurred due to combined effect of thermal and transformation stresses. This refers at the dimensional changes after
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hardening process that takes place as a result of volume change during phase transformation.
Distortion can be classified into two categories that is size distortion that is the changes in volume and shape distortion that is warpage which is due to changes in geometrical form of the steel component.
2.1.1 Size Distortion
Sinha (2003) states that size distortion is the net change in specific volume between the parent and transformation product produced by phase transformation without a change in geometrical form. Size distortion occurs due to the expansion or contraction in steel component. This type of distortion is less problematic than size distortion
2.1.2 Warpage (Shape Distortion)
Warpage is a physical distortion where there is a change in geometrical form or shape of the workpiece and is revealed by changes of curvature (angular relations) or curving, bending, twisting and nonsymmetrical dimensional change without any volume change (Sinha, A. K. 2003). Warpage is also known to be an irreversible change in shape of the component that occurs during heat treat processing. The change in shape can be resulted due to nonuniform heating or cooling (quenching), metallurgical structure or prior residual stresses (Dossett e. al. 2006).
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For designers and heat treaters, this type of distortion poses greater problem than size distortion. Upon heat treatment, part movement could occur immediately and sometimes later in a subsequent processing operation. Parts that is machined, cast or formed to achieve the accurate dimensions due to heat treatment, often came out from the heat treatment process with apparent changes in their dimensional structure. There are a lot of cases which the distortion that occurs is shown by warpage such as bowing or twisting of sheet metal, canning of machined pocket areas, and other forms of part movement.
Figure 2.1 : Warpage of Thin Plate Specimen (Sources :Rajan et all. (2011)) 2.1.2.1 Causes of Warpage
Based from the latest research (Croucher 2008), warpage of heated parts during and after the heat treating process is due to many factors. Some parts will warp for reasons the heat treater can control, but others will distort for causes that occurred before the heat treater received the parts and are beyond control. Thus, by understanding and
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controlling these factors, this allows the heat treater to minimize the occurrence of heat treating warpage. The factors are:
a. Relief of pre-heat treat residual stresses
b. Expansion and contraction of parts during processing of heat treatment c. Inadequate racking procedures in the furnace
d. The process of quenching is too fast e. Improper quenchant selection
f. Uneven quenching due to inadequate agitation or spacing g. Improper quench immersion rates
h. Furnace air flow design in relation to part orientation
2.1.2.2 Minimizing Warpage
According to Rajan et. all. (2011), in minimizing warpage or known as shape distortion during heat treatment, a number of factors must be taken into consideration such as:
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a. Stress Relieving
The presence of residual stress due to the previous machining or forging operation will enhance the tendency of warpage. Thus, fabrication stresses caused by these operations must be relieved by subcritical annealing or normalizing operation.
b. Heating Rate
The components heating rate must not be too fast or the components may crack or warp as sections are having different heat up at different rates. So, the difference in temperature can be controlled by preheating the components to a temperature below the lower transformation of steel.
c. Preheating
Preheating can reduce shape distortion in steels by reducing the thermal stresses that is made. This is due to the gradient temperature prevailing between the surface and interior part of component. Then, for large cross-section, complicated parts and high alloy steels that has poor thermal conductivity, it is preferable to carry out two-stage preheating.
d. Quenching Media
The basic aim of hardening of steels is to get martensitic structure and avoiding the formation of pearlite and bainite. So, the rate of cooling of heated component must be fast enough in producing a fully martensitic structure but faster cooling rate will increases the severity of quench. Thus, it is essential to use the least quenching medium that made martensite happened. Shape distortion can be further reduced while quenching if the cooling conditions are made uniform as possible. Usually, basic quenching media used are water, brine and conventional oils. Even salt baths, hot quenching oils and polymer quenchants is still considered as quenching media as they gave good results.
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e. Press Quenching
Press quenching or die quenching of steel is not common to most of commercial heat treating industries. So, during press quenching, warpage can be minimized by physical restraint of part during its rapid cooling from austenitic condition. So, quenching jigs are used for this purpose.
The part is clamped in a jig and then placed in a hydraulically operated press after heating. Then, the jig should be preheated in avoiding rapid cooling of the surface of component which comes in contact with the jigs. Along with the closing of the press, oil is flown over the component. This will resulted in maintaining the plane shape during the quenching operation.
f. Trays, Fixtures and Supports.
It is achieved that odd shaped components and unsymmetrical sizes needed to use the holding trays and fixtures. This will maintain the shape of the components during heating and rapid cooling from austenitizing temperature. The parts should lie on a flat surface.