Q: We tack weld many of our aluminum parts manually with gas metal arc welding (GMAW) in a fixture before final robotic welding takes place. We are having difficulty getting good fusion from the robot station in the areas where it welds over the tack weld. The aluminum material is 6061-T6, the manual tack weld wire is 5356, and the robot welds with 4043, all done with argon shielding gas. Any ideas how to resolve this? A: There are several things to consider, but ultimately it could be one small change or several things combined to resolve your issues. As a refresher, cleaning the weld joint, selecting the right GMAW parameter settings, and using the proper weld technique are all necessary to achieve good results. Two things we noticed right away that might be partially to blame for the lack of fusion (LOF) are the pure argon shielding gas and the two different filler metals. Not that these are uncommon combinations, but they may cause some problems. Pure argon shielding gas is common for welding specialty alloys including aluminum because it is a nonreactive gas. With regards to aluminum, it provides good cleaning action, stable arc characteristics, good arc initiation, and mod...