摘 要
了解動態電阻的模式對電阻點銲過程中傳遞現像的預測與銲接品質的監控是必要的，在本研究中，動態電阻值取電極端半徑內有效面積中之上下工件本身電阻值、上下工件間接觸電阻值及工件-電極界面間接觸電阻值之總和。接觸電阻包括集束電阻與膜電阻，其值為硬度、溫度、電極力、電阻率及表面情況之函數。電阻點銲過程中，工件中具相變化非穩態之軸對稱質量、動量、能量、溶質及磁場強度傳遞與在電極中之溫度及磁場強度傳遞，已被系統化地探討。電磁力、焦耳熱、電極-工件界面與工件-工件界面之熱生成、不同相間之不同性質及電極幾何形狀皆被考慮。所預測之熔區厚度及動態電阻曲線與實驗數據有良好的吻合。除了熔區飛濺現像外，動態電阻曲線被概分為四個階段，第一階段之迅速下降乃因絕緣膜電阻之快速下降造成，第二階段曲線之上升乃因材料本身電阻係數隨溫度增加而變大所造成材料本身電阻及接觸電阻之增加所造成的，當接觸電阻又開始下阪時，曲線上將出現有一反曲點，由於此時材料本身電阻之增加率仍大過接觸電阻之下降，故曲線仍維持上升趨勢，第三階段曲線反轉向下折形成峰部，下降主因乃高溫時材料電阻係數增加率明顯變小，其所造成之電阻上升率小過界面接觸面積增加所造成之電阻下降，以致動態電阻曲線向下遞減，另在第三階段末尾，主要工件-工件界面溫度已接近熔點，第四階段，界面開始熔合，逐漸消失，動態電阻曲線出現一折點，且下降趨勢減緩。
電磁力對熔區流場之影響已被證明，電流增加、磁擴散係數減小及電極端半徑減小皆可造成電極角部位有較高電流密度，有時甚至高到可將電 極角部位工件熔化，傷及工件表面及損害電極。

Abstract
Dynamic electrical resistance during resistance spot welding has been quantitatively modeled and analyzed in this work. A determination of dynamic resistance is necessary for predicting the transport processes and monitoring the weld quality during resistance spot welding. In this study, dynamic resistance is obtained by taking the sum of temperature dependent bulk resistance of the workpieces and contact resistances at the faying surface and electrode-workpiece interface within an effective area corresponding to the electrode tip where welding current primarily flows. A contact resistance is composed of constriction and film resistances, which are functions of hardness, temperature, electrode force, electrical resistivity and surface condition. Unsteady, axisymmetric transport of mass, momentum, energy, species, and magnetic field intensity with a mushy-zone phase change in workpieces and temperature, and magnetic fields in electrodes during resistance spot welding, are systematically investigated. Electromagnetic force, joule heat, heat generation at the electrode-workpiece interface and faying surface between workpieces, different properties between phase, and geometries of electrodes are taken into account. The predicted nugget thickness and dynamic resistance versus time show quite good agreement with available experimental data. Excluding expulsion, the dynamic resistance curve can be divided into four stages. A rapid decrease of dynamic resistance in stage 1 is attributed to decreases in film resistances at the faying surface and electrode-workpiece interface. In stage 2, the increase in dynamic resistance results from the primary increase of bulk resistance in the workpieces and an increase of the sum of contact resistances at the faying surface and electrode-workpiece interface. Dynamic resistance in stage 3 decreases, because increasing rate of bulk resistance in the workpieces and contact resistances decrease. In stage 4 decrease of dynamic resistance is mainly due to the formation of the molten nugget at the faying surface. The molten nugget is found to occur in stage 4 rather than stage 2 or 3 as qualitatively proposed in the literature. The effects of different parameters on the dynamic resistence curve are also presented. Besides, electromagnetic force effect on velocity field of molten nugget was proven to be crucial. Higher current, smaller magnetic diffusivity and decreasing the radius of electrode tip will lead to high current density around the corner between electrode and workpiece. Sometimes the corner of electrode and surface of workpieces will be melted due to local high current density.

第一章 緒論 1
1-1 簡介 1
1-2 文獻回顧 1
1-3 研究目的 5
第二章 理論分析 6
2-1 座標系與假設條件 6
2-2 接觸電阻 7
2-3 工件之統御方程式 9
2-4 電極之統御方程式 11
2-5 邊界條件及初始條件 12
2-6 數值方法 17
第三章 結果與討論 18
3-1 動態電阻模擬 18
3-2 熱流模擬 21
第四章 結論 25
4-1 動態電阻變化 25
4-2 電流場、溫度場、速度場及熔區之成長 26
參考文獻 28
圖表 33
附錄 A 60
附錄 B

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