【作者】 李欢；

【导师】 曹彪；

【作者基本信息】 华南理工大学 ， 机械电子工程， 2018， 博士

【摘要】 超声波焊接(USW)是一种绿色、高效的连接方法。由于焊接过程中界面及焊接区域机械-热-冶金作用的复杂性以及过程观察与测量条件的制约,尽管近年来在该领域开展了较为广泛的研究,但焊接机理有待于进一步明晰、接头质量及可靠性有待进一步提高。电阻热辅助大功率超声焊接技术(RUSW),利用电流流过焊接区域原位生成的电阻热来促进界面连接,有望改善焊接过程和提高焊接质量,但相关研究较少,目前处于初步探索阶段。本课题针对新能源领域常见的Cu/Al超声焊接,采用有限元模拟结合部分试验,系统研究了超声焊和电流辅助超声焊的过程行为及界面连接机制,为超声焊以及复合焊的优化与应用提供理论依据。利用Ansys软件建立了超声焊接及电阻热辅助超声金属焊接的有限元模型。为了较准确的模拟电、热、力的交互作用,模型综合考虑了各接触面的摩擦产热、材料的塑性变形热、材料的动态超声变软率和接触电阻产热、随温度变化的材料性能。利用所测量的焊头振幅及上、下工件振幅计算了不同接触面的摩擦产热和材料的动态超声变软率。采用测量界面温度、焊头下压位移和焊接截面轮廓形貌的方式对超声及复合焊模拟进行了试验验证,模拟结果与实测结果吻合良好,模型可以用来研究超声及复合焊过程。利用上述所建的模型研究了Cu/Al超声焊中温度场、塑性应变分布和材料的动态嵌入过程,以及基于超声作用理论和扩散理论并结合模拟的界面的温度、塑性变形结果分析了界面中间相的生成。结果表明:最高温度出现在焊头与上工件接触面的中心;焊接过程中,焊头首先嵌入上工件表面并迅速达到完全嵌入,底座齿在下工件表面的嵌入滞后于上工件;工件塑性变形区域在开始阶段迅速增加,然后进入相对稳定阶段;焊头下压位移与焊接区域总塑性应变呈近似线性关系。为了深入理解RUSW的界面行为和焊接机制,首先通过与单一超声焊接在相同时间的温度场、塑性变形分布进行对比来揭示辅助的电阻热对焊接过程的影响,同时也与长时间超声焊情况进行了对比来体现复合焊的变化。随后分析了各种热源单独作用的过程规律。结果表明:在相同时间里,辅助的电阻热提升了界面温度并且加速了齿的嵌入材料过程;复合焊可以在较短时间达到与单一超声焊相近温度分布和塑性变形分布但获得更薄的中间相;复合作用条件下焊接区温升大于单独热源作用的温升之和。更多还原

【Abstract】 Ultrasonic welding(USW)is a green and efficient joining technology,which has recently been extensively study.However,the mechanisms of welding are still not clearly understood.This is due to the complex nature of mechanical-thermal-metallurgical interaction at the welding interface that occurs during the welding process,which leads to quality and robustness of the joints needing to be increased.Resistance heat assisted high power ultrasonic welding(RUSW)is a promising welding technology,which will hopefully improve the welding process and promote welding quality by the addition of resistance heat generated from the current flowing through the welding interface.There are very few studies about RUSW and it is still in the initial stage of research.This study investigates Cu/Al ultrasonic welding,which is widely used in the new energy field.Moreover,the finite element analyses and experimental methods are used to investigate the behavior and mechanism of USW and RUSW,which can provide theoretical basis for optimization and application of USW and RUSW.The finite element model of USW and RUSW have been developed based on the commercial ANSYS software.In order to accurately simulate the electrical-thermal-mechanical coupling,the work of friction at each contact,heat of plastic deformation in materials,contact resistance,ultrasonic softening,and temperature-dependant properties of materials have been considered in the models.These models were verified by comparison of predicted interface temperature,sonotrode displacement and the weld cross-section profile with the experimental results.The simulation results are in consistence with the experimental results.This demonstrates that the model can be used to investigate the USW and RUSW process.Along with the temperature and plastic strain distribution,the materials penetration during USW process has been investigated by the model.The results show that the maximum temperature occurs at the sonotrode/copper interface,sonotrode tip teeth penetration into the upper specimen starts at an earlier stage and increases rapidly,reaching the maximum,but anvil tip penetration into lower specimen starts later and increases slowly.The plastic deformation area of the welding zone increases exponentially,and then keeps constant.The total plastic strain of welding zone is approximate proportional to the displacement of the sonotrode tip.The thickness of intermetallic has been predicted by consideration of temperature and ultrasonic action at the plastic deformation area.The result shows that the thickness of intermetallic layer is dominated by ultrasonic action rather than interface temperature,and increases as the welding time increases.The mechanism of weld interface action in RUSW has been studied.The influence of additional resistance heat on ultrasonic welding has also been investigated by comparing of simulated interface temperature and plastic deformation at the same time.The advantage of RUSW is reflected by comparing the simulation results of RUSW with the longer USW duration.The resistance heat can significantly increase the interface temperature,accelerate the penetration process of the teeth and promote the plastic deformation in the specimens simultaneously.A thinner intermetallic compound(IMC)layer is obtained for distribution with similar interface temperature and plastic deformation.The interface temperature in RUSW is greater than the sum of single ultrasonic energy and resistance heat.The welding pressure affects friction work and contact resistance,which changes with temperature.The interface temperature in RUSW first increases and then decreases with increase in pressure.更多还原