NiTi形状记忆合金超声波焊接温度场数值计算与分析

Numerical Calculation and Analysis of Temperature Distribution during Ultrasonic Welding Process for NiTi Shape Memory Alloy

NiTi形状记忆合金因具有优异的超弹性、形状记忆效应而被广泛应用。超声波焊接作为一种固相连接技术,在NiTi合金薄片材料的连接方面具有一定的优势,由于超声波焊接方法具有瞬时性且焊接过程十分复杂,所以难以通过试验观察的手段来研究其连接机理。针对NiTi形状记忆合金超声波焊接过程中温度难以监测的问题,采用ANSYS有限元分析软件建立NiTi合金的超声波焊接二维有限元分析模型,探究了超声波振幅对焊接温度场分布的影响规律,搭建热电偶测温平台采集焊接试验过程的温度数据对模型进行验证,结合数值模拟结果,分析了NiTi合金超声波焊接的连接机理。结果表明,焊接温度场与振幅呈正相关,在固定焊接条件下,振幅每增加5μm,焊接最高温度约提高45℃。经试验测定,模拟结果与试验数据吻合较好,最高温度仅相差4℃,误差不超过最高温度的3%。将试验结果与模拟结果相结合,NiTi合金的超声波过程中铝没有熔化,接头为固相连接。

NiTi shape memory alloy is widely used for its excellent superelasticity and shape memory effect. As a solid phase bonding technology, it has certain advantages in the bonding of NiTi shape memory alloy flakes. It is difficult to study the mechanism of ultrasonic welding by means of experimental observation because of its instantaneous and complicated welding process. Aiming at the problem that the temperature is difficult to monitor in the ultrasonic welding process, a two-dimensional finite element analysis model of NiTi shape memory alloy ultrasonic welding is established by ANSYS, the influence of ultrasonic amplitude on the distribution of welding temperature field is investigated. The thermocouple temperature measuring platform is built to collect the temperature data of welding test process, and the validity of the finite element analysis model is verified. Based on the numerical simulation results, the connection mechanism of NiTi alloy ultrasonic welding is analyzed. The results show that the welding temperature field is positively correlated with the amplitude. The maximum welding temperature increases by about 45 ℃ for every 5 μm increase in amplitude under the fixed welding condition. The test results show that the simulation results are in good agreement with the test data. The maximum temperature differs only by 4 ℃, and the error does not exceed 3% of the maximum temperature. Combining the test results with the simulation results, the NiTi alloy does not melt during the ultrasonic process, and the joint is a solid phase connection.