基于高动态压电致动伺服的铝合金电阻点焊热力耦合特性及形核机理研究

Aluminum alloy resistance spot welding is to face the development needs of aerospace and new energy vehicles, which is the key common technology in improving the basic metal joining process. As the spot welding is a highly nonlinear and multi variable coupling dynamic thermal interaction process, a macro-micro pressure control technology of aluminum alloy spot welding process based on piezoelectric actuation has been proposed to solve the pressure control difficulty in a real short time. Based on the medium frequency inverter electric servo spot welding equipment, the high-frequency Piezoelectric actuators are applied to provide pressure supplement in micro level. These scientific problems need to be studied, including the thermal interaction in the nugget formation process, mechanism of metal micro fluid flow and molten pool mixing, and the coupling mechanism of composite force with thermo and fluid in the nugget formation process. Combined with mechanical testing and metallographic analysis, the microstructure evolution and grain refinement of spot welding joints are studied, and the range of resistance spot welding process of aluminum alloy based on piezoelectric actuation is determined. Finally, a four-parameters’ welding and detection integrated intelligent control system is expected to be constructed based on the high-frequency Piezoelectric actuators and the Matching Pursuit method to meet the demand for the precision welding of light vehicle and high end equipment.

针对铝合金点焊焊接时间短、形核过程控制难的问题，本课题提出一种基于压电致动器辅助的点焊过程宏-微压力可编程调控技术，即在电伺服加压的基础上，串入一级高动态响应的压电致动器提供高动态脉动压力输出，从而在点焊过程中既能保持必要的静压，又能对形核区域形成高频激振(通电中)或微区锤锻(断电后)，期望借此能够改善铝合金点焊形核稳定性，细化熔核晶粒，提高焊点综合力学性能。课题首先研究高动态压电伺服下宏-微压力耦合输出特性，进而建立铝合金形核过程力-热-流交互模型，分析工件接合面金属熔化形核、熔核金属流动与熔池搅拌机制，结合试验研究分析不同宏微压力耦合输出波形下焊点微观组织和力学性能演变规律。在此基础上，研究焊点未熔合和飞溅缺陷的高速匹配追踪识别算法，建立耦合电极压力波形参数与缺陷发生的相关性模型，利用压电致动器的高动态特性，以压力输出为调节因子，探索铝合金点焊在线闭环质量控制的可行性。

电阻点焊在汽车、航空航天等工业领域应用极为广泛，但是现有电阻焊方法对各类新型轻质高强材料的焊接往往存在强度损失大、易发生飞溅等问题。电阻点焊是一个瞬时焊接过程，而现有焊接设备在电流、电极压力两方面的动态控制性能都相对非常有限，从而导致电阻点焊过程的热力传输难以高动态精确调控，在过程可控性这一源头上就大大制约了各类新型轻质高强材料焊接质量的提升空间。本课题从实现高动态电极压力输出、进而赋予电阻点焊全新质量调控能力的角度开展研究，提出了一种压电致动器辅助的“宏-微复合压力编程”新思想和方法，传统压力设备提供必要的静态压力，同时由压电致动组件提供动态的脉冲压力，振荡冲击熔核，调控其熔化形核和凝固结晶过程。本文所述方法革新了传统电阻点焊加压方式，突破了现有电极加压方法动态响应能力不足的局限，具体研究以薄板铝合金为研究载体，从设备研制、工艺特性、增强机理、过程飞溅质量预测及控制这四个方面展开。研究表面高动态压电致动加入，可在相同焊接电流下，增大焊核直径约27%，同时能够显著抑制焊接飞溅缺陷的发生。焊接过程动态产热、传热行为的分析表明，压电致动的加入并没有增加焊接产热，而是降低了熔核中心到边缘的温度梯度，以及熔核中心过热度，从而更有效利用电阻热熔化更多边缘金属，增大焊核尺寸，抑制焊接飞溅。