I'm doing some 1/8" 5052 & 6061 aluminum but welds and they are cracking at the beginning of the weld. I've been able to minimize the cracking, but not eliminate it. I know the cracking is caused by heat/cooling cycle, but I could use any help I can get to eliminate this problem. 

Anybody know anything about rapid arc? Using a Lincoln power wave s500 I'm working in manufacturing so quality is important, until it slows down production. I've been going through different trim and ultimarc settings generally around 1.03-1.06 and the ultimarc I kinda am all over the place -2.0-+10.0 wire speed generally around 485-500 Ipm on 1/4"-3/8 carbon. I feel like some robots in the shop are making the power fluctuate which is extremely frustrating. Complained about it but ya'kno how that goes. I run miles of flat fillet welds and horizontal lap joints every week as fast as I can while trying to make it look good. The minimum weld size is 1/4. Any tips on how to deal with the fluctuating power that is probably not ever going to change? Any tips on better settings for this fast paced environment to get pretty welds fast? for pmig and/or rapid arc. Pics for critique and suggestions. Have a couple videos but it won't let me attach.