Abstract
Derivative welding processes are in many cases capable of altering phenomena that determine fundamental aspects of weld bead formation. Some of these evolutions act over the wire feed dynamics. However, in this scenario, the effects of the wire feed pulsation on the weld bead formation governing factors have not been fully explored yet. Therefore, this work aimed at examining how a wire feed pulsation approach affects the droplet transfer in gas metal arc welding and how its interaction with the molten pool defines the weld bead penetration. Bead-on-plate weldments were produced by varying the wire feed pulsation frequency, yet keeping the same levels of arc energy and wire feed speed, with the power source operating in constant voltage and current modes. To assess the droplet transfer behavior, high-speed imaging was used. The geometry of the weld beads was compared in terms of fusion penetration. The results showed that an increase in the wire feed pulsation frequency intensifies the detachment frequency of the droplets, being possible to accomplish a stable metal transfer with them straightly projected toward the weld pool, which contributed to a centralized-increased penetration profile. Based on a descriptive model, it was demonstrated that the increase in droplet momentum or kinetic energy, due to the wire feed pulsation, was not enough to justify the penetration enhancement. It was concluded that the wire feed dynamics can also stimulate surface tension variations in the weld pool and therefore disrupt the behavior of its mass and heat convection, supporting fusion penetration.
Highlights
In welding, as it happens in other manufacturing fields, the derivative processes have been under intensive development
A high standard deviation in the detachment period indicates a large variability in the time available for the droplets to grow, which leads to wide variability in the volume of the detached droplets
The experiment without wire feed pulsation is characterized by large droplet sizes and high variability in the volume of the detached droplets, which is typical of a metal transfer without any control
Summary
As it happens in other manufacturing fields, the derivative processes (hereafter understood as process versions that were developed from more basic ones) have been under intensive development. They are implemented, in many cases, due to the capability of acting on phenomena that govern important outputs, such as weld bead formation. In gas metal arc welding (GMAW), many of these developments are possible due to technological enhancements in the power sources, generally using fine real-time control of fundamental variables (such as arc voltage and welding current) in order to improve process stability and metal transfer regularity. Besides allowing an efficient control of the power source electric signals, other developments act over the metal
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