On the Analysis of Metal Droplets During Cold Metal Transfer

Cold metal transfer (CMT) is an advanced gas metal arc welding (GMAW) process that features a reduced thermal input and improved stability of arc. This report examines the correlations between welder parameters and droplet properties in a one-cycle CMT characteristic where a single droplet was transferred. Through design of experiment and statistical analysis, it is revealed that the weight of the deposited metal droplet has a linear relationship with the output energy of CMT, and the weight can be precisely controlled by adjusting CMT parameters. The droplet surface contact angle is independent of the output energy and has no clear correlation with CMT parameters due to the relatively large thermal conductivity of copper and the heat capacity of the coupon. However, when the thickness of the copper coupon was reduced, the substrate temperature did increase, and the droplet had a smaller contact angle. In addition, the metal droplet transfer during the CMT process is subjected to a phenomenon known as magnetic arc blow which affects the landing position. When the ground connection was not in line with the electrode, the bent electric current path deflected the welding arc away from the ground connection. When the ground connection was attached underneath the projection path of the electrode, the droplet deflection disappeared. The knowledge obtained in this study is crucial to optimizing the CMT process and improving the quality of the subsequent copper joining processes.