Approximate entropy analysis of arc stability in VPPA-GMAW hybrid welding

Variable polarity plasma arc-gas metal arc welding (VPPA-GMAW) integrates the advantages of VPPA and GMAW, and it is particularly applied to weld thick-plates aluminum alloys. High-speed camera and data acquisition system were used to analyze the arc shape and the welding process electrical signal. According to the analysis of arc swing amplitude and the approximate entropy of arc voltage signal denoised by wavelet threshold method, the influence of VPPA frequency on the arc stability was studied. The results show that the approximate entropy of GMAW arc voltage decreases with the increase of VPPA frequency in a certain range, and the stability of the hybrid arc is significantly improved. The spectral analysis shows that the arc stability is reduced due to the resonance effect between the VPPA and the GMAW arc when the VPPA frequency closes to the GMAW arc pulse frequency. The results are helpful to understand hybrid welding mechanism and the selection of welding process parameters.