Real-Time Quality Estimation of Resistance Spot Welding Based on Electrode Displacement Characteristics and HMM

Resistance spot welding (RSW) is applied widely in modern industry especially automobile manufacture. However, the quality of RSW is influenced by many factors, which make it difficult to control. In this paper, the electrode displacement was measured at real time using grating displacement sensor, and the displacement signals were sampled by the monitoring system developed using LabVIEW based on PC. One group of samples was welded under the fixed electrode pressure and welding time but the different welding current, and the fluctuation characteristics of the electrode displacement curves were mined and analyzed. Based on the electrode displacement fluctuation characteristics, the HMM was built with the electrode displacement as the observation and the tensile-shear strength as the state. The simulation results showed that the maximum estimation error can be 2%, which is 3% lower than the one when performing the same HMM simulation using the displacement curve filtered as observation.