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研究生：	陳麒翰 Chen, Chi-Han
論文名稱：	考慮晶粒尺寸效應對精微薄板成形之成形極限預測 Forming Limit Prediction of Micro Sheet Metal Forming due to Grain Size Effect
指導教授：	李榮顯 Lee, Rong-Shean
共同指導教授:	高振騰 Gau, Jenn-Terng
學位類別：	博士 Doctor
系所名稱：	工學院 - 機械工程學系 Department of Mechanical Engineering
論文出版年：	2010
畢業學年度：	98
語文別：	英文
論文頁數：	148
中文關鍵詞：	精微薄板成形、晶粒尺寸效應、成形極限圖、延性破壞準則
外文關鍵詞：	micro sheet metal forming, grain size effect, forming limit diagram, ductile fracture criterion
相關次數：	點閱：146 下載：3
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由於光電、資訊以及3C產品輕薄短小的趨勢，提升精微金屬元件的製造效率與品質是維持競爭優勢的重要手段。精微金屬成形具有大量生產及品質穩定的優點，是精微金屬元件製造中相當具有競爭力的製程。然而精微金屬成形製程由於在塑性變形區的特徵尺寸可能只有數個晶粒，其微觀組織或是晶粒尺寸對於金屬流動以及可成形性的影響變得顯著，使得精微工業無法直接套用巨觀金屬成形的經驗與準則至精微金屬成形製程。因此本論文探討晶粒尺寸效應對於精微成形製程與成形極限之影響此一重要課題。本文在實驗方面，進行不同厚度與晶粒尺寸304不銹鋼與C2600黃銅薄板之拉伸試驗、張伸試驗以及深引伸實驗，探討晶粒尺寸比(T/D ratio)對於機械性質的影響。在試件表面製作微小網格以及隨機斑點後，以自行設計的精微模具組配合萬能試驗機進行張伸試驗以及深引伸實驗並以影像處理方式進行變形後網格以及斑點的局部應變來建立精微薄板成形之成形極限圖。在理論預測方面，以有限元素模擬軟體LS-DYNA進行拉伸試驗模擬並藉由應力以及應變累積獲得延性破壞準則能量常數並藉由異向性降伏準則建立預測的成形曲線。在比對實驗與預測之成形極限後，本文提出修正的延性破壞準則來預測精微薄板成形之成形極限，在考慮應變路徑以及晶粒尺寸比後，所提出的延性破壞模式可以較準確地預測304不銹鋼與C2600黃銅精微薄板之成形極限。

Due to the miniaturization trend of the devices in electronic, medical and 3C industries, the improvements for manufacturing efficiency and product quality are important means to keep competitive. Micro metal forming is the most suitable and cost effective manufacturing process for mass production of micro metal parts because of its high production rate, low material scrap rate, net shape production and superior mechanical properties. However, when the material deforms in the micrometer range, the forming feature may only have few grains. The microstructure becomes more important when miniaturization and exhibits grain size effect which influences material flow and formability in micro metal forming process. The plasticity theory and the know-how of conventional metal forming technology developed under macro scale cannot directly apply to micro metal forming. In this paper, the influence of grain size effect on forming process and formability of micro sheet metal forming was investigated. For the experimental study, a series of micro scale tensile tests, dome height tests and deep drawing experiments were conducted for investigating the grain size effect on mechanical properties and formability of stainless steel 304 and C2600 brass alloy foils. The FLDs of micro sheet metal forming were established by local strain measurements of the micro grids and spots through image measurement and management processes. In forming limit prediction, finite element code LS-DYNA was used to calculate the ductile fracture constants in the ductile fracture criteria and develop predicted forming limit curves. Based on the experimental results, simulation results and Oh’s fracture criterion, two new models were proposed in this paper for predicting the forming limit of stainless steel 304 and C2600 brass alloy foils in micro sheet metal forming. The first proposed model includes the effect of strain path while the second proposed model considers the coupling effect of strain path and thickness to grain size ratio. The first model is superior to the Oh’s criterion on predicting forming limit strain of the foils, but it is not suitable for the foils that are thinner than 100μm. However, the second proposed model can be used for forming limit prediction of the stainless steel 304 and C2600 brass alloy foils with the foil thickness less than 100μm where the grain size effect must be considered.

CHINESE ABSTRACT	I
ABSTRACT	II
ACKNOWLEDGEMENT	IV
TABLE OF CONTENTS	V
LIST OF TABLES	VIII
LIST OF FIGURES	XI
NOTATION	XVIII
CHAPTER 1   INTRODUCTION	1
1 Motivation	1
2 Micro Metal Forming Process	1
2.1 Micro Metal Forming Development and Application	1
2.2 Micro Metal Forming Bottleneck	3
3 Failure Criteria and Forming Limit Diagram	7
3.1 Forming Limit Diagram	8
3.2 Necking and Fracture Criteria	9
3.3 Formability Experiments and Simulations	13
4 Objective and Methodology of the Study	15
5 Outline of the Study	16
CHAPTER 2   THEORETICAL METHODS	18
1 Ductile Fracture Criteria	19
2 Proposed New Criteria for Formability Prediction	21
3 Material Properties Theory	23
3.1 Strain Hardening Coefficient	23
3.2 Normal Plastic Anisotropy Ratio	23
3.3 Anisotropic Yielding Criterion	24
4 Finite Element Analysis	29
4.1 LS-DYNA Introduction	29
4.2 Finite Element Settings	29
CHAPTER 3   EXPERIMENT METHODS	32
1 Materials	32
2 Thickness to Grain Size Ratio	33
2.1 Heat Treatment	33
2.2 Thickness to Grain Size Ratio Determination	37
3 Mechanical Property Testing	45
3.1 Strength Coefficient and Strain Hardening Coefficient	46
3.2 Normal Plastic Anisotropy Ratio	48
3.3 Fracture Strain	50
4 Formability Testing	50
4.1 Formability Die Design	50
4.2 Dome Height Test	51
4.3 Deep Drawing Test	54
5 Grid and Spot Marking Process	55
5.1 Grid Marking Process	55
5.2 Spot Marking Process	59
5.3 Local Strain Measurement	61
CHAPTER 4   RESULTS AND DISCUSSION	71
1 Grain Size Effect	71
1.1 Effect of Grain Size on Mechanical Properties	71
1.1.1 Flow Stress (n, K)	71
1.1.2 R-value and Fracture Strain	82
1.2 Effect of Grain Size on Forming Limit	85
1.2.1 Deep Drawing Experiment	85
1.2.2 Dome Height Test	94
1.2.3 Local Strain	99
2	Prediction of Failure	104
2.1 Forming Limit for Micro Sheet Metal	104
2.2 Fracture Prediction by Ductile Fracture Criterion	108
CHAPTER 5   CONCLUSIONS AND SUGGESTIONS	130
1 Conclusions	130
2 Suggestions	133
REFERENCES	135
APPENDIX A	144
APPENDIX B	147

                                    

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