A question for those of you who do MIG welding on cars

Have a MIG welder (decent one on wheels bought new 30 years ago). Not done any welding on cars for years now. In the past I always disconnected the battery and the alternator to protect any electrical stuff on the car from the electric current put through the car by the  MIG welder. 

Cars in more recent years have much more electronic stuff on them of a complicated nature. So when MIG welding on modern cars is there a need to do more to protect the electronics from damage cause by the MIG electrical circuit.

(for anyone who does not MIG weld and is puzzled by the electrical current, A MIG welder works by putting a large electrical current through the car body and short circuiting it at the point where you are doing the welding. The heat that melts the metal is caused by the short circuit. The gas does not contribute to the heat, the gas is to shield the molten metal from oxygen in the air. Otherwise, without any shielding gas, the weld has lots of little air bubbles in it and is very weak and brittle)

 

 

That's really weird I was just watching some videos on the non gas version's you get and wondered what the clamp onto the metal was for so that cleared things right up. As far as I have found battery defo and as long as you keep as close enough to the weld with a clean connection should be fine.

i have never tried the non-gas version. I get the impression it's a bit rubbish compared to having the gas, but the gas does add cost of course,  for the bottle, gauges etc.  

so whilst on that subject can anyone comment from first hand experience of using both types how it compares in use, ease of getting good weld. do you get a load of slag on the surface like with arc welding .

plus any more comments on protection of electrical bits on the car please

42 minutes ago, isetta said:

i have never tried the non-gas version. I get the impression it's a bit rubbish compared to having the gas, but the gas does add cost of course,  for the bottle, gauges etc.  

so whilst on that subject can anyone comment from first hand experience of using both types how it compares in use, ease of getting good weld. do you get a load of slag on the surface like with arc welding .

I tried it briefly at a mates house once and didn't really like it. Then again I'm not a massive MIG welder myself. (Bit of a life-story here sorry!) Without sounding big-headed I'd like to say I'm better than most people who aren't a professional welder. I spent hours practising stick welding (and a hundred quids worth or so of scrap plate that I cut down to 2x6 to practice 90 degree joints). Ended up pretty decent at the end of it getting good penetration on all my welds, but have probably lost my touch after not welding for a few months. Also tried TIG on some 18 gauge stainless and a few pieces that were 2mm thick or so, but not had as much practice but is certainly the cleanest weld you can do. MIG just seemed like a point and hope for the best solution after doing the other two, but used gas for that. Funnily enough I forgot to crack the gas bottle open one day and was sat there wondering why I couldn't weld properly until it clicked.

I guess what I'm trying to get at is MIG welding isn't the best welding to start off with (not enough 'control' for my liking. I like to control the wire feed myself). Many of our professional welders only use it to tac stuff together, then TIG weld it, so gas-less isn't going to make the best penetrating weld there is but I suppose it would be ok for gluing two bits together for a makeshift guard or something. I certainly wouldn't trust it for anything structural. Then again I like my trusty stick welding now, which every DIYer seems to hate lol. Removing the slag is the best bit, especially with stainless as it eventually just pops off after a couple minutes and goes everywhere haha.

42 minutes ago, isetta said:

do you get a load of slag on the surface like with arc welding .

Yes, and it was harder for me to remove and came in little pieces rather than 1 long strip as my penetration was off and the weld wasn't uniform/consistent. The slag is caused by the flux coating on the wire, which is replaced by the inert gas (argon for me) when TIG welding/ proper MIG welding.

about 30 yrs ago I did a course at evening classes on welding. It was quite good, it was a real old school workshop (it literally had been a school in the 2nd world war and then the germans bombed the railway viaduct next to it causing structural cracking and it was going to be demolished but never was and then years later was reopened as an enginering workshop linked to the local technical college. (it is still standing but don't know what current use is) There was enough oxy-acetylene equip for everyone to have their own kit and workbench. We all got quite good at welding metal boxes etc including welding from underneath with stuff hanging upside down over the bench, but they only had one mig welder and one TIG so we did not get so much chance to practice on that.  I bought the MIG welder as my main use was for car bodies - like patches on sills etc and inner sills. very commonly needed on old cars 30 years ago. Many cars needed patches when 10 years old and some less than that. Oxy-acetylene gave a nicer more controlled weld but more tendancy to set more stuff alight if under a car.

Never actually used acetylene for anything, it got banned from site from everyone but like 2 or 3 authorised people because health and safety crap. I was going to get a welder for home, but the £1500 one at work will do a job much better on nights :).

Stick welding vertical is always fun trying to keep your concentration as small bits of molten metal land on you and burn your hair.