Influence of Process Parameter on the Clad Surface Characteristics in Pulsed Current GMAW Process

The clad surface characteristics, which have an important role on the clad quality, have been influenced by the parameters of pulsed current GMAW (GMAW-P) viz. peak current (Ip), peak duration (Tp), background current (I_B) and background duration (T_B) (Fig. 1). Selection of the most suitable combination of pulse parameters is very difficult due to the complex interdependence of the above parameters of pulsed current (1-4). To resolve this problem, studies have been carried out for different types of droplet detachments namely background detachment, one droplet detachment per peak, two droplets detachment per peak and three droplets detachment per peak by varying pulse cycle time. Effect of the GMAW-P parameters on clad surface characteristics has been studied. The suitable type of droplet detachment for cladding, using 1.2 mm diameter of ER 5356 filler metal, has been selected on the basis of uniformity in clad surface undulation. This is done to obtain good quality clad For this a quantitative evaluation of the quality of clad was carried out by measuring the surface characteristics of the clad using a computerized measuring system based on a Linear Variable Differential Transformer (Sylvac). Fluctuations on the top of the clad surface were displayed numerically on the digital-indicating unit of a LVDT (1 micron accuracy). All the displayed digital output values were transferred to a personal computer through a data acquisition card and analyzed statistically to calculate the standard deviation (o) and coefficient of variation (C.V.) of the same. Among these four types of droplet detachments, the lowest standard deviation (0.0553) and the lowest coefficient of variation (0.0252) were found for the clad made with one-droplet detachment during peak-per-pulse. Smaller the standard deviation and the coefficient of variation, the smoother the clad surface. Hence, one-droplet detachment per peak was considered to be capable of providing smoother clad surface than other types of droplet detachments. Based on this, the following parameters of the pulsed current were found to be more suitable than other combinations of pulsed current (Clad No.C4). I_p = 196.8 A; Tp = 5.0 ms; I_B = 20A; T_B = 6 ms; W_F = 6 m/min; l_AV = 99.7 A and W_S =10.0 mm/s. The peak energy was found to be low for background detachments.