Real-time measuring system design and application of thermal expansion displacement during resistance spot welding process

摘要

Resistance spot welding (RSW) technology is the most important joining method in auto-body manufacturing. Quality of spot weld not only determines reliability and safety of cars, but also has an important influence on assembly variation of auto-body. Many welding quality parameters, such as welding current, electric resistance, electrode pressure, and thermal expansion displacement, had been proposed to monitoring and controlling spot weld quality, in which thermal expansion displacement was thought as a very promising method. But the measurement of dynamic displacement encounters many difficulties in measuring precision, measuring speed and sensor installation, which limit the usage of this method. This paper introduced a kind of laser displacement sensor made in OMRON to overcome the limitations of displacement measuring precision and measuring speed, and at the same time designed an ingenious fixture to mount the sensor to welding gun. Calibration experiments showed that the fixture reduced vibration introduced by pneumatic welding gun and interference between sensor and welding gun, and have a good linearity with standard clearance gauge. Based on this measuring system, dynamic thermal expansion displacement during RSW process was real-time monitored. Analysis found thermal expansion displacement can be used to real-time distinguish weld quality, such as small nugget, splash.