I found that the flux-core wire carries more heat to the metal than the MIG process. The wire diameter is larger to accomodate the flux inside the wire so it has to be rigid enough so it won't collapse. It is hard to get the heat low enough. So, more burn-throughs and lots of spatter. I prefer argon/CO2 mix with sheet metal; have used flux-core for heavier repairs like subframe connectors, rear back brace, etc.