An evaluation of the production of magnesium base alloy castings by the expendable pattern ...

324 Pages·2017·10.98 MB·English

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An evaluation of the
production of magnesium
base alloy castings by the
expendable pattern casting
process
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An Evaluation of The Production
of Magnesium Base Alloy Castings
by the Expendable Pattern Casting Process
by
T ANTIPAIBULV UT, CHAIRAT H
BEng (KMITI); MSc (UMIST)
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Master ;;rphiiosophy of LougQb.orough University
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©b"y'TantipaibulvuCCftairath 1997

TABLE OF CONTENTS
page
Table of Contents ........................................................................ ii
S y no ps is ................................................................................... viii
Certificate of Originality .............................................................. ix
Acknowledgements ...................................................................... x
Chapter 1 Introduction ................................................................. I
1.1 Objectives of the research .................................................. 2
Chapter 2 Magnesium base alloy .................................................... 3
2.1 Introduction .................................................................. 3
2.2 The reasons for using magnesium base alloys ........................... 3
2.3 Engineering design aspects of magnesium .............................. .4
2.4 Applications .................................................................. 6
Examples of Magnesium Applications .................................... 7
2.5 Advantages & Disadvantages of Magnesium in Comparison with
Other Materials ............................................................... 9
2.6 Casting processes suitable for magnesium base alloys ................ 11
2.7 Metallurgical aspects of Magnesium base alloys ........................ 12
2.7.1 The classification of Magnesium base alIoys ..................... 12
2.7.2 Designation of commercial alloys in the ASTM Standard ..... 19
2.7.3 The relevant designation of different standards in
different countries .................................................. 21
2.7.4 The influence of various alloying elements in
magnesium base alloys ............................................. 23
2.7.5 The properties of cast alloys ....................................... 25
2.8 Cast alloys in current use ..................................................3 1
2.9 Casting processes ..........................................................3 7
2.9.1 The development of magnesium alloy casting ...................3 7
2.9.2 Casting methods .....................................................3 8
2.9.2.1 Melting and auxiliary pouring equipment .............. 38
2.9.2.2 Physical Chemistry of Magnesium Melting and
Precautions ............................................... .40
2.9.2.3 Melting Procedure and Process Parameters ........... .42
2.9.3 Various Casting Processes ........................................ .48
2.9.3.1 Sand Casting ............................................. .49
2.9.3.2 Permanent Mould Casting, .............................. 54
11
page
2.9.3.3 Investment Casting ....................................... 55
2.9.3.4 Low-Pressure Die Casting Process .....................5 6
2.9.3.5 High-Pressure Die Casting Process ....................5 6
Chapter 3 Expendable Pattern Casting (EPC process) ..................... 60
3.1 Introduction and History ..................................................6 0
3.2 Sequences in EPC Process in brief.. ..................................... 60
3.3 Process Technique .........................................................6 1
3.4 Part Selection and Tooling ................................................6 2
3.5 Processing Parameters .....................................................6 2
3.5.1 The Foam Pattern .................................................... 62
3.5.2 Bead pre-expansion .................................................6 3
3.5.3 Pattern moulding .................................................... 63
3.5.4 Pattern Shrinkage .................................................... 64
3.5.5 Surface Finish .......................................................6 4
3.5.6 Tolerances ............................................................6 5
3.5.6.1 Estimated Tolerances of EPS patterns ..................6 5
3.5.7 Gating design ........................................................6 5
3.5.8 Pattern Assembly ....................................................6 5
3.5.9 Coating ............................................................... 66
3.5.9.1 Functions of Coating and Coating Types ..............6 6
3.5.9.2 Application of the Coating ...............................6 7
3.5.10 Sand System ........................................................ 67
3.5.10.1 Sand Process ............................................. 67
3.5.10.l.l Unbonded Sand Process .................. 67
3.5.10.1.2 Bonded Sand Process .....................6 8
3.5.10.2 Flasks .....................................................6 8
3.5.10.3 Venting ................................................... 68
3.5.10.4 Sand compaction ........................................6 8
3.6 Pouring a EPC Casting .................................................... 69
3.7 Cleaning and Finishing .................................................... 69
3.8 Safety Considerations ...................................................... 69
3.9 Advantages and Disadvantages ofEPC Casting ........................7 0
3.9.1 Advantages of EPC Casting ........................................ 70
3.9.2 Disadvantages of EPC Casting ....................................7 0
3. 10 EPC Casting Features ....................................................7 1
3.11 Dimensional precision and dimension accuracy of EPC castings ... 71
111
page
3.12 Defect Problems ........................................................... 72
3.13 Properties of expandable polystyrene ..................................7 2
3.14 Casting Costs .............................................................. 74
3.15 Environmental Factors ...................................................7 4
3.15.1 Health and Hygiene .............................................7 4
3.15.2 Environment. .................................... : ................ 75
3.15.3 Waste Disposal.. ................................................. 75
Chapter 4 Modelling development for the casting process ................ 76
Introduction ......................................................................7 6
4.1 Modelling in general and its benefits .....................................7 6
4.2 The development of modelling in an empty cavity mould process ...7 7
4.2.1 Fluid flow modelling in mould filling of
an empty cavity mould process ....................................7 8
4.3 The development of modelling in the expendable pattern casting
process ......................................................................9 3
4.4 Objectives of this modelling research .................................. 106
4.4.1 The purpose of this research modelling ......................... 106
4.4.2 The benefit of the experimental work in modelling ............ 106
4.4.3 Solutions of mould filling in EPC process ..................... 106
Chapter 5 Experimental Methods and Materials ............................ 108
Part A : Experimental Work on the Casting Process
5.1 Introduction ............................................................... 108
5.2 Equipment and Materials ................................................ 109
5.2.1 Counter gravity pouring method ................................. 109
5.2.2 Gravity pouring method .......................................... 118
5.2.3 Tensile testing ...................................................... 121
5.2.4 Metallography ...................................................... 127
5.3 Casting Trial Experience ................................................. 134
5.3.1 Gravity Pouring method .......................................... 134
5.3.1.1 Stage I ................................................... 134
5.3.1.2 Stage 2 ................................................... 135
5.3.1.3 Stage 3 ................................................... 136
5.3.1.4 Stage 4 ................................................... 137
5.3.1.5 Stage 5 ................................................... 138
IV
page
5.3.2 Counter Gravity Pouring method ................................ 139
5.3.2.1 Stage 1 ................................................... 139
5.3.2.2 Stage 2 ................................................... 140
5.3.2.3 Stage 3 ................................................... 141
5.3.2.4 Stage 4 ................................................... 142
5.3.2.5 Stage 5 ................................................... 143
5.3.2.6 Stage 6 ................................................... 144
5.3.2.7 Stage 7 ................................................... 144
5.3.2.8 Stage 8 ................................................... 146
5.3.2.9 Stage 9 ................................................... 146
5.3.2.10 Stage 10 ................................................ 147
5.3.2.11 Stage 11 ................................................ 147
5.3.3 The last stage of test bars' casting in EPC Counter
Gravity Pouring ................................................... 148
Objectives of the Experiment .................................... 148
5.3.3.1 Sand Casting Gravity Pouring ........................ 149
5.3.3.2 EPC Counter Gravity Pouring ........................ 149
Photographs for Chapter 5 ................................................... 152
Chapter 6 Results and Observations ............................................ 165
6.1 Introduction ............................................................... 166
Part A: Experimental Work on the Casting Process
6.2 Casting Trial Experience ................................................. 166
6.2.1 Gravity Pouring method .......................................... 166
6.2.1.1 Examination & Diagnosis .............................. 166
6.2.1.2 Problems & Solutions .................................. 170
6.2.2 Counter Gravity Pouring method ................................ 170
6.2.2.1 Examination & Diagnosis .............................. 170
6.2.2.2 Problems & Solutions .................................. 186
6.3 The last stage of test bars' casting in EPC Counter
Gravity Pouring ........................................................... 191
6.3.1 Problems & Solutions ............................................ 191
6.3.2 Microstructure ..................................................... 193
6.3.2.1 Sand Casting Gravity Pouring ........................ 194
6.3.2.2 EPC Counter Gravity Pouring ........................ 196
v
page
6.3.3 Tensile Test ........................................................ 200
6.3.3.1 Sand Casting Gravity Pouring ........................ 200
6.3.3.1.1 Tensile properties ........................... 200
6.3.3.1.2 Fracture ..................................... 200
6.3.3.2 EPC Counter Gravity Pouring ........................ 201
6.3.3.2.1 Tensile properties ........................... 201
6.3.3.2.2 Fracture ..................................... 202
Part B : Mould Filling Model of Casting Processes
Analysis of Different Pouring Methods
6.4 Summary .................................................................. 203
6.5 An Empty Cavity Mould Pouring Process ............................ 203
6.5.1 Introduction ........................................................ 203
6.5.2 Gravity Pouring with Bottom Gated Filling .................... 204
6.5.3 Counter Gravity Pouring ......................................... 206
6.6 Expendable Pattern Casting process ................................... 209
6.6.1 Introduction ........................................................ 209
6.6.2 Mechanism of EPC process ...................................... 209
6.6.3 Factors affecting the EPC Process .............................. 210
6.6.4 Polymeric pattern material concern in EPC process ........... 213
6.6.5 Fluidity, Mould Filling and Gating System .................... 214
6.6.6 Conclusion ......................................................... 214
6.6.7 Counter Gravity pouring in EPC process ...................... 215
Photographs for Chapter 6 ................................................... 234
Chapter 7 Discussion ................................................................ 251
7.1 Introduction ............................................................... 251
Part A: Experimental Work on the Casting Process
7.2 Comparison between Flux and Fluxless Melting ..................... 251
7.3 Discussion of practical experiments during
the trial casting experience ............................................... 253
7.3.1 Gravity Pouring Method .......................................... 253
7.3.2 Counter Gravity Pouring Method ............................... 257
7.4 Discussion of the research results ...................................... 263
7.4.1 Gravity Pouring Method .......................................... 263
7.4.2 Counter Gravity Pouring Method ............................... 264
7.4.3 The comparison of gravity pouring and
counter gravity pouring methods ................................ 267
vi