Desenvolvimento e avaliação de um algoritmo alternativo para soldagem MIG sinérgica de alumínio

Abstract

Although the pulsed GMAW allows overcoming limitations of the metal transfer in the conventional GMAW, the pulse parameter selection remains still a serious obstacle hindering its wide utilization. The synergic "command" helps to solve this problem due to an automatic determination of process variables. The algorithm of the conventional synergic command is based on the main premise that a stable arc is conditioned to only one droplet per pulse (ODPP). To simplify calculus, this commercial synergic command uses linear models which ignore any influence of the electrical parameters at the base period (base current and its duration) on the droplet formation. As a consequence of such simplifications, synergic command algorithms might conduct to wrong values of preset parameters and to not satisfy the main premise. The main objective of this work was to develop and assess a new synergic command algorithm that adopts more realistic calculus of the pulse parameters. It is aimed also to verify the influence of the pulse parameters on the ODPP conditions. Another objective was to determine possibilities and limitations of a new technique of visualization and measuring regarding metal transfer phenomenon, which is called Synchronized Shadowgraph method. In order to fulfil these tasks, primarily the ODPP conditions for base fixed parameters were determined. This was done using an electronic power supply, a data acquisition system (for welding current and arc voltage signals) and a Synchronized Shadowgraph system, consisting of a laser beam head, optics components, a high speed video camera and an interface unit to synchronize the current and voltage signals with the camera images. After the ODPP conditions had been determined, the base current parameters were altered, keeping the same peak current parameters, in order to verify whether the time point of the droplet detachment at the end of the current pulse was being shifted. It has been established that the ODPP region can be accurately determined by Synchronized Shadowgraph technique and the base current parameters did not seriously affect the ODPP conditions. Thus, by principie, both the commercial synergic command and the proposed one could be used. However, the new algorithm has a great advantage; it guarantees more precise calculation of the pulse parameters and the wire feed speed rate, leading to an arc length closer to the desired one and it provides formation of droplets of a size closer to the electrode diameter.