電阻點銲過程中，工件的熔區冷卻率、溶質分佈、以及固化形狀影響熔區的微結構，而交流與直流電源對其作用被廣泛探討；於加熱、熔化、冷卻、以及固化期間，本文採用有限差分法，預測工件及電極的輸送現象；研究模式可說明電磁力、電極-工件介面與工件-工件接合面的生成熱、以及動態電阻，後者為工件本身電阻、工件-工件接合面接觸電阻、以及電極-工件介面接觸電阻的總和；其中接觸電阻包含收縮電阻與薄膜電阻，受工件硬度、工件溫度、電極力、以及工件表面狀況影響。電阻點銲採用交流電源所產生橢圓形熔區，不同於直流電源所產生者；熔區的邊界薄層與內部所含溶質量多於其它位置。
交流電源電阻點銲過程中，動態電阻對工件的熔區冷卻率、溶質分佈、以及固化形狀的影響被深入探討。計算結果：顯示增加收縮電阻與居禮溫度，熔區提早成長，高居禮溫度可加強溶質的傳遞與混合，但電極底部錐角處的工件產生熔化，因此可調節溶質含量，改變居禮溫度，控制銲接質量。

The effects of AC and DC on cooling rate, solute distribution and nugget shape after solidification, which are responsible for microstructure of the fusion zone, during resistance spot welding are realistically and extensively investigated. The finite difference method is used to predict transport variables in workpieces and electrodes during heating, melting, cooling and freezing periods. The model accounts for electromagnetic force, heat generations at the electrode-workpiece interface and faying surface between workpieces, and dynamic electrical resistance including bulk resistance and contact resistances at the faying surface and electrode-wokpiece interfaces, which are function of hardness, temperature, electrode force, and surface condition. The computed results show that in contrast to DC, using AC readily produces the nugget in an ellipse shape. Deficit and excess of solute content occur in a thin layer around the boundary and interior of the nugget, respectively.
The effects of dynamic electrical resistance subject to AC (Alternative current) on transport variables, cooling rate, solute distribution and nugget shape after solidification during resistance spot welding are realistically and extensively investigated. The model accounts for electromagnetic force, heat generation and contact resistances at the faying surface and electrode-workpiece interfaces and bulk resistance in workpieces. Contact resistance are comprised of constriction and film resistances, which are functions of hardness, temperature, electrode force and surface condition. The computed results show that the weld nugget readily occurs by increasing constriction resistance and Curie temperature. High Curie temperature enhances convection and solute mixing, and readily melts through the workpiece surface near the electrode edge. Aside from finding the significant effect of Curie temperature on resistance spot welding, this study indicates that any mean (For example, adjusting solute content) to reduce Curie temperature can be a new way to control weld quality.

目錄
中文摘要........................................................................................................................I
英文摘要.......................................................................................................................II
謝誌...............................................................................................................................IV
目錄.....................................................................................................................….....V
圖表索引..........................................................................................................….…..VII
符號說明............................................................................................................…....XII
第一章 緒論...........................................................................................................1
1-1 簡介...........................................................................................................1
1-2 研究目的..................................................................................................3
1-3 文獻回顧 ................................................................................................4
第二章 理論分析...................................................................................................14
2-1 座標系與假設條件 ............................................................................14
2-2 接觸電阻(Electrical contact resistance ).............................................15
2-3 工件之統御方程式 ............................................................................18
2-4 電極之統御方程式 ............................................................................20
2-5 邊界條件與初始條件..........................................................................21
2-6 數值方法...............................................................................................24
第三章 結果與討論..............................................................................................28
3-1 動態電阻之模擬..................................................................................28
3 -2 熱.流場之模擬......................................................................................31
第四章 結論..........................................................................................................68
4-1 動態電阻變化.....................................................................................68
4-2 溫度場、速度場、生成熱、濃度、熔區成形、以及熱傳遞...69
參考文獻 ..............................................................................................................71
附錄........................................................................................................................78

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