Welding near paint - heat sink options

[Rhyscar]

Hey OS, I've got a job on the Levin that requires a bit of welding finesse, so wanting to query the collective brain of OS before I charge ahead and screw something up. 

 

I decided to solve my rear tyre rub issues properly by cutting out the offending sheetmetal, which will be replaced by 1.6mm trailer guard material. I've cut the inner guard approx 25-30mm up from the lip, which will butt into the inner of the trailer guard. Car is fully painted/finished so need to be careful to avoid massively screwing up the exterior. Inside the car it's not in a noticeable area so I'm confident I can tidy it up. 

 

Was thinking something like this;

 

 

A few questions I have before I embark

1. Can either Tig or Mig it - which process produces less heat? Mig? Any tips/tricks? Planning on a few stitches in the sensitive areas, then panel bond/seam sealer on both sides. 

2. Also after experience/opinions on heat sink options to draw heat away from the paint;

• Welders Putty/heat blocker? 
• Wet cotton pillowcase full of wet sand?? 
• Wet cloth/towels?
• Any others?

 

Thanks in advance for your help!

[Bling]

Not steel, but when I used to braise copper pipe where it went into a building, i'd wrap a wet rag around the pipe which stopped any heat getting past it. I can't comment on how the electrons will react to a wet rag, but I feel like if you had one tucked in against the exterior panel and in that wheel arch lip on the right, it would help a lot. I've only ever done MIG on my cars and a single spot weld in one area, then moving to another area to put one does keep the heat down a lot. Just my thoughts anyway, i'm sure others have done very similar jobs to yours. Only mentioning it as the wet rag wrapped around the pipe was a very simple solution but worked perfectly.

[ThePog]

You can buy a gel that does just this; https://www.bearingandengineering.co.nz/shop/ENGINEERING/WeldingPlasmaGas/WireRodsElectrodes/COOL+GEL+HEAT+BARRIER+SPRAY+473ml+LACO.html

I have used it a bit.

[Rhyscar]

Pretty cool stuff. Example is with copper, and eventually the heat capacity of the gel will be exceeded, but it looks to be pretty effective. 

 

[tortron]

Wet rag on the area and blowing an air duster gun between tacks should about do it

[azzurro]

Id think its probably far enough from the outer skin yould probably be fine there.

A good fitment for your patch will be key! big gaps = more weld = more heat

Just take it slow (tack, wait, tack cool, tack..)  so the wider area doesnt heat up, and make sure any paint you care about is protected, not just direct weld but also from splatter and wire hedgehogs incl from the inside - accidentally zapping the outer skin from the inside would grind my gears!

I dunno about leaving a damp rag in there while welding or having water touching the actual weld, but have it on hand for cooling the metal around the area in case you forget rule 1 (take it slow!), but imo a air line would be safter/better.  some copper (or aluminium) backing for belts and braces esp if your fitment isnt good.

[mjrstar]

My personal preference would be to mig it with .6 wire and co2 for the gas as i reckon you can get better penetration at a lower amperage (just my opinion on gas selectionhete). Run a longer post flow for extra cooling if it's adjustable on your machine, if not a second click of the trigger will give you another dose of gas

I think the access sucks enough for tig to be annoying, even though I hardly ever use my mig these days..And agree with others around  tack wait method.

If you want some extra insurance you could get someone with a purge cup to backpurge the HAZ with argon as that will cool the back side of the weld very quickly. This is a bit unconventional with mig and maybe overkill but hey.

Cover up the inside of the outer skin to stop any splatter finding it's way into the seam. 

TL:DR

I reckon inert gas is the best cooling method.