Sounds like a weld process issue rather than a robot issue ; I may be able to help you with either. 1 mm is pretty thin , what size is your wire?? What shielding gas?? Are you pulse welding or standard mig?? Are the leaks at the start,end, or random on the weld??? Is the stickout, torch angle, and speed constant throughout the weld?? More issues could apply .. Drop me a line ,, I'll get back soon as I can........
Larry