脉冲后沿斜率可调的受控穿孔PAW系统

Controlled Keyhole PAW System with Adjustable Slopes of Pulse-trailing Edge

在穿孔等离子弧焊接过程中,为使小孔的'开—闭—开'状态转换更加平稳,对研制出的方波脉冲穿孔等离子弧焊接系统做出进一步的改进。设计出脉冲后沿带两个缓降坡度的脉冲焊接电流波形,通过调节这两个下降斜率的大小,可以更加灵活地控制热输入和等离子流力;在优化脉冲参数的基础上,提高穿孔状态转变的平稳性。以表征小孔尺寸的等离子弧尾焰电压为被控制量,脉冲电流峰值及其两个后沿下降斜率为控制量,采用PI控制算法和受控脉冲穿孔的控制策略,建立受控脉冲穿孔等离子弧焊接控制系统。工艺试验结果表明,系统准确工作在'一脉一孔'状态,既保证穿孔,又使小孔尺寸维持在预定值附近;与原来的方波相比,小孔的'开—闭'状态转换更加平稳,焊缝成形良好,控制效果显著。

To make the keyhole status transformation of ＂open-closure-open＂ more stable and smooth during keyhole plasma arc welding（PAW）,further improvement is made on the previously developed system of pulsed keyhole PAW with square waveform of welding current.The current waveform with two dropping slopes at the pulse trailing-edge is specially designed and employed.Through adjusting the magnitudes of these two dropping slopes,both heat input and plasma force can be controlled more flexibly.Based on the optimization of pulse parameters,the keyhole status transformation from open to closure becomes more smooth.The improved system takes the plasma efflux voltage depicting the keyhole size as the controlled variable,and the pulse current level and its two dropping slopes at the trailing-edge as the controlling variables.The control algorithm PI（proportional and integral） and the strategy of controlled pulse keyholing are employed to ensure the formation of a complete keyhole and maintain the keyhole size close to the preset value.The experimental results show that the system accurately operates in the mode of one keyhole per pulse.Compared to the square waveform,the specially designed current waveform can make the keyhole shift between open and closed states more stable and smooth.Thus,the weld formation quality is fine,and the improved system has significant control effects.