Resumo:
This work has the aim to analyze the influence of parameters welding current, polarity and
arc length in the arc stability and geometrical weld bead characteristics of a Shielded Metal
Arc Welding SMAW process. In order to complain with the objectives a prototype of
an automatic welding equipment was developed. Based on this equipment a set of tests
were design by the use of statistical tools based on the Design of Experiments techniques
through a Minitab software. The electrical arc signals, in particular, voltage, were recorded
by a data acquisition system and after processed by the use of a fast Fourier Transform
(FFT) technique with a low-pass filter with a cut-off frequency of 4 kHz. The arc stability
analysis were based on the variation coefficient by the voltage arc signal filtered. The
geometrical characteristics and productivity of the welding bead specimens were evaluated
by direct recorded dimensions after cross-sectioning, polishing and measuring of the
penetration, dilution and bead convexity index, deposition and fusion rate, and deposition
efficiency by the use of three different kind of covered electrodes, i.e., rutile, basic and
celulosic. It was found that the automatic welding increased the arc stability compared
with the manual welding procedure for all covered electrodes. Also the polarity had an
important effect in the arc welding stability. The celulosic electrode had a higher arc
stability in straight and reverse polarity, despite of its non recommended use in straight
polarity, followed by rutile and basic electrodes, but this electrodes not showed conduct
variations with the polarity.
