中文摘要：

穿孔等离子弧焊接过程中存在的一些问题制约了该工艺在现代工业中的推广和应用，如焊接工艺合理参数区间窄，可调裕度小，导致焊接过程中小孔的稳定性较差等。熔池的小孔行为是直接影响焊接过程稳定性和接头质量的关键因素，为拓展合理工艺参数范围，提高焊接过程稳定性和焊缝质量，研制出受控脉冲穿孔等离子弧焊接控制系统。基于简易测试装置，实时采集焊接过程中的尾焰电压信号，可靠描述焊缝熔池穿孔与否以及小孔尺寸；采用受控脉冲穿孔的控制策略，适时调整峰值电流和基值电流的作用时间，使得小孔一直处于“准稳态”。实现“一脉一孔”，但脉冲时间和基值电流并不固定，取决于每个脉冲过程小孔的建立时间和存在时间；保证穿孔，使小孔尺寸在预定值附近波动，并防止烧穿的发生；大幅拓展穿孔等离子弧焊接合理工艺参数区间。工艺试验结果表明，当工件散热条件和厚度发生变化时，控制系统能够迅速做出调节，运行稳定可靠，控制效果显著。

英文摘要：

Narrow applicable ranges and low adjustability of process parameters of keyhole plasma arc welding result in poor stability of the keyhole and limit the wide application of this welding method. The keyhole behavior determines the stability of the welding processes and the final quality of the weld joints. Therefore, a system of controlled pulse key-holing in plasma arc welding is developed to expand the parameter ranges and improve the welding quality. Based on simple detecting device, efflux plasma voltage signal is measured in real-time during the welding process, which is employed to determine whether a keyhole is formed or not and to describe the keyhole dimension. A control strategy termed as controlled pulse key-holing is used to adjust the duration of peak and base current in time, thus the keyhole is kept in quasi-steady state. One keyhole per pulse is achieved while the duration of both peak and base currents is not constant. Key-holing is ensured, the keyhole dimension only fluctuates around the preset value, and burn-through is avoided. The usable ranges of welding process parameters are widened significantly. Plasma arc welding experiments show that the control system can make prompt adjustments when thermal loss conditions and work-piece thickness are changed so that it runs steadily and reliably and has marked control effect.