I have seen several post that are anti sheet metal welding and I am curious as to why so many people are against it. I am not a welder but I do have access to a very nice mig welder and with some practice I believe I could do a good job with it. Of course I love welding and do it as often as possible. Yes I am aware of potential problems if something goes wrong.

sheetmetal welding is a black art. with metal so thin, you can burn thru easily. you also have a major heat issue with warping panels. it all adds up to a PITA. A good quality mig is a good start. the big question is can you turn it down far enough for sheetmetal. need to be able to get your wire size to the smallest stuff they sell. I think i'm using .023. Even with that, it requires stitch welding. also get yourself some of the heat sink paste and use it religiously. that really helps with the warping. be very patient. the issue with stitch welding is your first strike must be spot on. Now add the fact that you are welding inside wheel wells, on past vertical surfaces and rust pitted metal. I'm lucky to get one decent weld out of ten. you find yourself grinding alot to do it over. Use gas.

i use .030 wire with a 75/25 argon co2 mix. my welder is very expensive, because im stupid and prefer snap-on i also have a ac/dc tig welder from miller. i like the tig on very light steel. but i can just as well weld with the mig. the bigest problem is making sure what you are welding is clean, not kinda clean. remove rust and undercoating (which burns very well)
take on 2 or 3 repairs at one time. work for a minute on one spot then move to another, this will help you keep excessive heat out of the metal. everyone once started wants to finish immediatly. so to cure this work on multiple areas that way you can keep welding (which is fun)

I hate welding thin metal but almost any wirefeed will do, the trick is to only lay about 1-2mm welds and to keep them seperated as you go, working back and forth and spreading the heat with lots of breaks. Keep cleaning before welding. Sometimes fiberglass is the easy and cheap repair but welding in new metal is probably best.

I just use a cheap Deca 120V flux cored wirefeed with two heat settings and infinate wire speed settings - the cheap welder. I also have a nice quality stick welder but even with the smallest rods i could find i had no luck with sheet metal.

Welding is a trade, it takes time to learn and master and on thin material you have a smaller window of opportunity. As a general rule of thumb the cheaper the machine the cheaper the result. Mig is easier to learn but tig will give a better cleaner less brittle and if done properly no grinding finish.

I have been having good results with a thick copper backing plate. Either clamped on back or pressed up against the bottom with a floor jack. This dissipates the heat.
I found it as a piece of thick-walled copper pipe and I cut it down one side and flattened it out.

smartobject wrote:I have been having good results with a thick copper backing plate. Either clamped on back or pressed up against the bottom with a floor jack. This dissipates the heat.
I found it as a piece of thick-walled copper pipe and I cut it down one side and flattened it out.

good tip!!

I haven't been on this site in awhile but I missed alot of these for some reason I didn't get notifications on them. Thanks guys