变极性等离子弧立焊穿孔熔池的稳定建立

改进焊接工艺控制时序，编制起弧系统控制平台及信号采集程序。采用改进的起弧系统对2219铝合金和LF6铝合金薄板及中厚板进行变极性等离子弧立焊工艺试验，利用红外线测温仪检测起弧过程中焊接熔池区域附近的点随预热时间的温度变化，并把该曲线上的临界温度作为检测穿孔熔池是否形成的标志，计算机根据穿孔时刻的临界温度控制焊件行走的使能信号。研究表明：改进的起弧系统能够简化设备操作，提高自动化程度与工作效率；在穿孔形成的瞬间，检测点的温度有一个从高到低的突变过程(穿孔前的瞬间温度达到临界值)，而且对于同一检测点，多次测量得到的临界温度基本稳定；起弧阶段向主焊接阶段过渡稳定，能够实现穿孔熔池的稳定建立，从而验证改进的起弧控制系统的可行性及可靠性。

ESTABLISHMENT OF STABLE KEYHOLE POOL DURING VARIABLE POLARITY VERTICAL-UP PLASMA ARC WELDING PROCESS

The original scheduling program of process control for arc starting system is improved.Console for controlling arc starting process and routine for collecting temperature signals are programmed.Experiments for aluminum alloys 2219 and LF6 are conducted via variable polarity plasma arc welding technique.Temperature history for the measured points near the molten pool are obtained using infrared thermoscope through trial and error.Critical values for the measured temperature history are utilized as the signals for formation of the keyhole weld pool,on the basis of which the computer controls the signal for the workpiece to travel.It is shown that the improved arc starting system reduces operation complexity and increases automation and efficiency.Moreover,temperature of the meas- ured points reaches the critical value and then decreases sharply at the moment of keyhole formation,and the measured critical value for a given point changes little despite repetitive meas- urements.Besides,the arc starting stage transits stably to the main welding stage which realizes the establishment of stable keyhole pool,thus feasibility and reliability of the improved arc starting system are experimentally verified.