Study On Metal Transfer Behavior Of CMT+P Welding For Aluminum Alloys

The cold metal transfer(CMT)with addition of pulses(CMT + P)process is a new CMT welding method.The CMT + P process is based on the composition of traditional CMT welding and pulsed MIG welding.The primary aim of this paper is to investigate the metal transfer behavior of the CMT + P welding to evaluate welding stability and joint formation of this process.This research has important theoretical meaning and practical value in the mechanism research and practical application for CMT+P welding.First of all,the metal transfer behavior of the CMT + P welding for aluminum alloys is explored,and is compared with the CMT welding.The results indicate that the CMT + P transfer mode is a combination of a projected transfer mode with one droplet per pulse during the pulse period and a short circuit transfer mode during the cold metal transfer period.Secondly,the principle of waveform control of the CMT+P welding process is analyzed.Precisely controlled current and voltage waveforms are applied into the CMT + P welding process.The appearance of the high initial arcing current and the current pulse steps as well as the low current for the pulse time phase for the first CMT period indicate a stable,smooth CMT + P transfer process.Thirdly,the effects of the welding parameters on the metal transfer behavior are studied.The results show that the different wire feed speeds,the CMT short circuit numbers or the pulse numbers do not change the mode of metal transfer behavior of the CMT + P welding.But the size of the droplet changes with the change of the wire feed speed.Then,the effects of waveform control on metal transfer behavior are studied to precisely control the CMT + P welding process.The too small or too large pulse base current both causes change of the mode of metal transfer behavior.With pulse base current,pulse base time or CMT base current increase,the size of droplet increases.Finally,the influences of metal transfer behavior on the welded joint formation are analyzed.When the wire feed speed,pulse number or CMT base current increases(or the CMT short circuit number decreases),the weld penetration,weld width and contact angle all increase.The contact angle increases with increasing pulse base current or pulse base time,which means better wettability.The CMT + P welding process solves the problem of insufficient weld penetration in traditional CMT process and expands applications of CMT welding technology for welding thick aluminum plates.