Projected spray in one droplet per pulse (ODPP) mode in combination with closed loop feedback control of droplet detachment is the most effective approach to guarantee high weld quality for gas metal arc welding (GMAW) of steel in argon-rich shielding. Three groups of experiments are performed according to the different welding current wave forms in this paper: pure square wave, square wave combined with sine wave (combined wave), and pure sine wave. Compared with the pure square wave form, the combined wave form can generate a weld bead with narrower and shallower penetration (the width and depth are respectively 3.048 mm and 0.228 mm). The direction of the droplet is still very straight even though the corresponding frequency of the droplet transfer is as low as 18 Hz. In pure sine wave form pulsed GMAW, the droplet is forced to oscillate once (the oscillation cycle equals the pulse cycle) at the wire tip and then detaches smoothly. The process is accompanied with a harmoniously characteristic sound. The images also show that the droplet is forced to oscillate twice (the oscillation cycle equals half of the pulsed cycle) at the wire tip and then detaches in square wave form or combined wave form pulsed GMAW. Careful selection of parameters is also required to generate more oscillations for the droplet at the tip of the wire before it detaches. The cross section of a weld bead show that the penetration profile can be greatly improved using a combined waveform. The results achieved are beneficial for the investigation of the mass and heat control in GMA welding of thin materials.
展开▼
