有限元素法應用於7075鋁合金銲接模擬之研究

Abstract

本研究使用有限元素分析軟體ANSYS,使用雙橢圓移動熱源,以元素的生與死技術模擬三維單V形槽之對接銲,重現銲料的填入過程,並比較在不同之單V形槽角度之條件下其溫度場、應力場與角變形量之差異。 對於溫度場的分析,研究結果顯示對於有開槽角度的銲接方式,使用體熱源比表面熱源之熔融區較接近實際銲接情況。且由熱循環曲線圖可以看出,銲道中之元素於銲接熱源到達時才升溫,與實際有填充金屬銲接情況相同,因此使用元素的生與死方法較符合實際銲接的溫度變化情形。 在應力場的研究中,由於銲道金屬於填入銲道時處於熔點,此時並無應力應變存在,因此利用元素的生與死技術使模型中尚未填入銲道之元素與銲道中高於熔點的元素不發生作用,待低於熔點時才啟動元素參與應力計算,於殘留應力分析時,殘留應力之分佈與實驗之趨勢吻合。 對於有開槽角度之角變形分析,研究結果顯示如直接於銲道施加熱量,角變形方向將與實際結果相反。本研究採用元素的生與死技術,並且定義計算銲道元素熱應變之參考溫度為熔點溫度,使得銲道於熱通量施加時不產生膨脹變形,模擬角變形方向與實際變形方向一致,而角變形量會隨單V形槽角度增加而增加,與實驗結果相同。
Welding is used in industry in a broad number of ways. In the past, in order to measure welding temperature fields, stress fields and deformation, one had to conduct a physical experiment. Unfortunately, conducting experiments has many restrictions such as budget, time, and the requirement of a large amount of labor. However, with the use of the finite element method in the welding process, one can quickly forecast welding temperature fields, stress fields and deformation. The calculation in the welding process is a nonlinear procedure in which the material properties change with the temperature. Furthermore the analytical results of the temperature fields adjacent to the heat source are rather steep. The problem of the fusion and solidification of material has been solved by the method of “Element Birth and Death”, and the thermal stress and residual stress in welding can be predicted by using the simulative analysis method. In this paper, heat flux is modeled with double ellipsoid heat source model, a feasible dynamic simulation method on 7075 Al alloy’s 3D welding temperature fields, stress fields has been established, which provides theory foundation and instruction on optimizing the welding technology and parameters. Single V-groove butt welding on three types of heat treatable aluminum alloys 7075-T6 and compared the angular distortion levels of the aluminum alloys at different Vee preparation angles. Simulations of the angular distortion by the reference temperature of the melting point on fusion volume for the thermal strain calculations have been used, and the results demonstrated the single Vee preparation angle (amount of filler metal) in butt welding affected the angular distortion of the weldment. The angular distortion tended to increase with the single Vee preparation angle.

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Keywords

有限元素, 銲接, 溫度場, 角變形, 殘留應力, 數值模擬, Finite Element, Welding, Temperature Field, Angular Distortion, Residual Stresses, Numerical Simulation

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