氏名　NGUYEN TIEN DONG
学位の種類　博士（工学）
学位記番号　博甲第512号
学位授与の日付　平成21年3月25日
学位論文題目　Abrasive Grain Efficiency for Grinding Sapphire Substrates as well as a Magnesium Alloy and the Development of its Evaluation Method by Surface Roughness Measurements　（サファイア及びマグネシウム合金研削加工の砥粒効率と表面粗さ測定によるその評価法の開発）
論文審査委員
　主査　教授　石崎　幸三
　副査　教授　松下　和正
　副査　教授　岡崎　正和
　副査　教授　鎌土　重晴
　副査　准教授　磯部　浩己
　副査　産学技術総合研究所主任研究員（本学客員教授）　杵鞭　義明

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成20（2008）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

CONTENTS
Acknowledgements　p.i
Declaration　p.ii
Abstract　p.1
Nomenclature　p.3
Contents　p.5
Chapter 1　GENERAL INTRODUCTION
　1.1　The Grinding Process in the Industrial Fields　p.9
　1.2　The Development of Abrasive Materials　p.9
　1.3　Grinding Process with Diamond Grinding Tools　p.10
　1.4　Grinding if Hard and Brittle Materials　p.10
　1.4.1　Single crystal sapphire　p.10
　1.4.2　Ceramics machining process　p.11
　1.4.3　The effects of grinding parameters on ceramics ground surface　p.12
　1.5　Grinding of Light Materials　p.13
　1.5.1　Industrial requirements　p.13
　1.5.2　Magnesium and its alloys　p.13
　1.5.3　Light metals machining process　p.14
　1.6　The Development of Grinding Wheels and grinding Techniques　p.17
　1.7　The Dermination of the Number of Cutting Points　p.19
　1.8　Research Aims　p.20
Chapter 2　EXPERIMENTAL PROCEDURES
　2.1　Grinding Machine　p.25
　2.2　Vacume Vises　p.27
　2.3　Force Measurements　p.29
　2.4　Sample Preparations　p.31
　2.4.1　Single crystal sapphire　p.31
　2.4.2　Magnesium alloy AZ31B　p.33
　2.5　Newly Developed Cup-type Diamond Grinding Wheels　p.34
　2.6　Setup and Balancing of Grinding Wheels　p.36
　2.7　Truing and Dressing of Grinding Wheels　p.38
　2.8　Surface Evaluation　p.41
　2.8.1　Surface texture and contour measuring　p.41
　2.8.2　Scanning electron microscope （SEM）　p.42
　2.9　Experimental Setup　p.43
Chapter 3　EXPERIMENTAL RESULTS
　3.1　Table Feeding Speed　p.45
　3.2　Table Feeding Speed and Sample Surface Roughness　p.45
　3.2.1　Grinding sapphire substrates　p.45
　3.2.2　Grinding magnesium alloys　p.48
　3.3　Grinding Wheel-loading　p.52
Chapter 4　DISCUSSION
　4.1　Surface Roughness　p.55
　4.2　The Ideal Surface Roughness by Working Abrasive Grains　p.56
　4.3　The Method of Estimating Total Number of Abrasive Grains　p.58
　4.4　Abrasive Grain Efficiency and Surface Roughness　p.62
　4.4.1　Machining sapphire substrates　p.62
　4.4.2　Machining magnesium alloys　p.64
　4.5　Mechanism of Grinding Wheel-loading　p.67
　4.6　Abrasive Grain Efficiency and Surface Roughness under Wheel loading　p.70
Chapter 5　CONCLUSIONS
　5.1　Conclusions　p.75
　5.1　Suggestions for Further Researches　p.77
References　p.79
Publications　p.iii
Conferenes　p.v

　Grinding process is a complex material removal operation involving cutting, plowing and rubbing depending on the extent of interaction between abrasive grains and a work-piece under the condition of grinding. On a conventional grinding-wheel, abrasive grains are distributed randomly with different protrusion heights on the whole wheel surface. Working abrasive grains are defined as those that act directly to grind work-piece surfaces. In this thesis, newly developed cup-type diamond grinding-wheels with hexagonal pattern were used to grind hard-to-machine ceramic materials and light metals, which were represented by a single crystal sapphire and magnesium alloy AZ31B, respectively. A new method to evaluate the effective number of grinding grains has been developed.
　In Chapter 1 which is entitled as “General Introduction”, a state-of-the-art grinding technology is presented in details. A grinding process utilizes various tiny and hard abrasive particles formed in a binder as a multitude of cutting edges to remove unwanted material on a work-piece at very high speed. The number of abrasive grains on a grinding-wheel surface is the most essential parameter, which directly affects ground surface of the work-piece. A smoother surface can be obtained by grinding process than by the other machining processes. Two typical difficult cases were selected for the present work. They were hard-to-machine ceramics and light metals, i.e., single crystal sapphire and a magnesium alloy, respectively. Finally, research aims are written.
　Chapter 2, “Experimental Procedures” describes the grinding installation and methods of experimental measurements. All the grinding experiments were carried out on regulated-force-feeding （RFF） grinding-system. The table feeding force in this advanced grinding-system is kept constant instead of keeping table feeding speed as a conventional machine. Samples are placed on a vise surface by air suction. Newly developed diamond grinding-wheels with hexagonal pattern, which contain abrasive diamond grains in the hexagon edges, and porous green carborundum without diamond grains in inside of the hexagons, are presented. Grinding stone ratio, R is defined as the ratio between the hexagonal edge area containing abrasive grains and the total area of wheels. Four hexagonal grinding-wheels with different R （13, 19, 25 and 36.0%） and a conventional wheel with R 100% were used. Before each experiment, grinding-wheels were balanced using a dynamic balancing instrument in order to reduce vibration. After that, grinding-wheels were trued and dressed in order to obtain flatness on the wheel surface and sharpen abrasive grains, respectively. The measurement of surface roughness was conducted by a contour measuring instrument. Finally, grinding parameters such as wheel speed, cutting depth and coolant water are presented.
　Chapter 3, which is entitled as “Experimental Results”, describes all experimental results, such as table feeding speed and sample surface roughness for ground sapphire and magnesium alloy samples. The time for each grinding pass was obtained from raw data of grinding forces as function of grinding time in order to calculate the table feeding speed. Sample surface roughness was obtained by measuring several points on work-piece sample surfaces. The wheel-loading phenomenon in grinding magnesium alloys occurred at wheel speed of 3000 rpm. The pictures of grinding-wheel surfaces under loading conditions are shown.
　Chapter 4 entitled “Discussion” shows the establishment of evaluation method to estimate abrasive grain efficiency by measuring sample surface roughness for ground sapphire and magnesium alloy samples. The effects of grinding stone ratio, R, on surface roughness, Ra, are discussed. The number of abrasive grains that passed through a unit length of sample, Ng, is investigated to show the advantages of the newly developed cup-type diamond grinding-wheels. There are about five times more effective grains in the hexagonal wheels than in a conventional wheel. A new mechanism of wheel-loading in grinding light metals is proposed. It is not related to local positioning of abrasive grains, but related macroscopic positions of active grains in order of mm distance. The evaluation of the integrity of grinding-wheel surfaces and sample surface based on wheel-loading phenomenon are discussed.
　Finally, conclusions and suggestions for further research are given in Chapter 5 entitled “Conclusions”. The new evaluation method of effective abrasive grains in grinding-wheel was established by measuring sample surface roughness. Abrasive grain efficiency for grinding sapphire substrates as well as a magnesium alloy and the new mechanism of wheel-loading phenomenon allow designing efficient grinding-wheels. Recommendations for further researches are also presented.

　本論文は、「Abrasive Grain Efficiency for Grinding Sapphire Substrates as well as a Magnesium Alloy and the Development of its 　Evaluation Method by Surface Roughness Measurements （サファイア及びマグネシウム合金研削加工の砥粒効率と表面粗さ測定によるその評価法の開発）」と題し、5章より構成されている。
　第1章「General Introduction」では、研削法の進歩を鳥瞰すると共に最近の研削法の進歩と問題点を明らかにし最も大きな二つの問題、つまり難加工材の研削と軽金属研削時の目詰まり問題、に絞り研究を進めることが述べられている。また本研究では、精密加工用に優れているにもかかわらず，研究の少ないカップ型砥石について研究をすることも述べられている。
　第2章「Experimental Procedures」では、本研究で用いた定荷重被研削材送り式研削盤についてその特徴を述べ、単結晶サファイア、マグネシウム合金の詳細、砥石の詳細、被研削材送り速さ測定法、表面粗さ測定法を述べている。
　第3章「Experimental Results」では，被研削材送り速さ、表面粗さ、目詰まりの状況の実験結果を述べている。
　第4章「Discussion」では，砥粒と表面粗さの関係、実効砥粒数の論理的計算方法、砥石形状の違いによる実効砥粒数の違いを述べており、「どのような形状にすることにより実効砥粒数を増加させることが出来るか」、つまり「どのような形状が効率良く表面を滑らかに研削することが出来るか」と言う観点から，新しい実効砥粒数の求め方による，砥石の評価方法を述べている。また、目詰まり状態を詳細に述べ、今までの目詰まりの理論では説明出来ない現象を解明すると共に新しい目詰まりのメカニズムに関する理論を述べている。
　第5章「Conclusions」では本論文で得られた結論を要約し、新しい砥石評価法を見つけ出したこと、新しい六角型砥石が通常砥石より効率良く，サファイア、マグネシウム合金が研削されることを結論づけ、今後の展開も論じている。
　よって、本論文は工学上及び工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。