Study On ARC Length Tracking System Of TIG Welding Based On SCM Control

TIG is widely used in chemical industry, energy equipment, marine, rail transportation, aerospace and other high-tech manufacturing field for its advantages of good welding quality and beautiful welding seam. In the process of welding, the change of arc length can lead to welding defects such as the not fusion or penetration phenomenon, in order to ensure the welding quality, there is need to use the TIG arc length tracing system.The paper analyzes the problems in the process of TIG arc length trace control on the foundation of the papers about the arc lengthcontrol. In view of the problems about the slow dynamic response and the high frequency and the high expense and the highvoltageduring TIG arc length tracing process,the paper designs hardware and software o farc length tracking system based on SCM, and carry out the relevant tests.(1)The paper analyzes the relationship between the Voltage, arc current and arc length and draw the picture about the curve based on the dates of the welding test.(2)The paper tests the tracking precision anddynamic response speed of the TIG arc tracker which has been applied in the market, and determine the new system design objectives.(3)The paper designs hardware of arc length tracking system based on SCM of STC12C 5A60S2. The hardware includes arc voltage sampling circuit, SCM detection and control sys tem, and drive circuit of arc length control motor.(4)The paper designs software of arc length tracking system based on hardware.The soft ware includes the the acquisition process of the arc voltage, current and arc voltage of the set, the control algorithm of the arc length and the generating program of PWM control signal.The paper determines the relevant control parameters ofcontrol algorithm of PD based on thearc length tracing test.The welding experiments show that:(1)The signal frequency about the PWM of the microcontroller duringthe arc length tracing influences the loadcapacity, tracking precision and dynamic response speed of DC motor. The contradiction between the load capacityand dynamic response speedcan not be increased at the same time, then the paper determines the best frequency of the PWM control signalafter lots of tests;(2)The design of sampling circuit in TIG welding arc can effectively protect the circuit during the process of arc length tracing. The system works well during the arcbreaking;(3)The system can be a very good implementation of TIG welding arc length tra cking, and the control system can overcome the influence of high frequency during arc strike , and the system has the advantages of fast dynamic response, high controlling precision, and stable and reliable working performance.