Tig car panel repairs

[franky]

Howdy all.

I've a R-tech 161 i've been trying to teach tig weld with. I've made some brackets and my car(240Z) is now on a spit upside down.

I've got a few repairs to make to the floor(cars from arizona so never welded yet). I can have the car upside down so I can lean on it in a nice position.

Floor and sheet for repair is 1.0mm.

Basically is it possible to get nice welds without distorting the panel? What are the best shapes to cut out to prevent the floor distorting? I've about 4 bits the same shape/size of a credit card to do. what is the best way to hold the repair sections in position?

Also 2 new frame rails where the others have been subjected to dodgy jacking. They're spot welded on, so drilled the welds out to remove. I'm thinking using some cleco's to hold them in position then from the inside creating a weld pool to weld back in position, basically to join the floor back to the rails.... Does this sound like the best way to go about it?

Sorry for all the questions!

 

[hotrodder]

Metal expands and contracts as it's heated and cooled. Welds shrink. Everything being equal you'll typically get more distortion with TIG than MIG, the 'thin metal' MIG technique of basically tack welding until the weld is continous typically gives the least distortion.

Oxyfuel and TIG have a lot more to offer for someone who's a dab hand with hammers 'n dollies... the extra distortion being less of a deal than the welds being softer with less reinforcement i.e. instead of finishing the welding quickly and then having to grind it all back before reaching for the plod the welds are hammered/planished out (which helps reverse the shrinkage that occured during welding) and metal finished. Overkill for a floor repair 9.5 times out of 10 and obviously you need access to both sides of the panel anyway

Patch shape... if welds can be placed in areas with some shape to them distortion will be less than a flat sheet, it's also far easier to finish a curved surface than a dead flat one. Again not really that applicable to floor repairs as they're generally flat with stiffening ribs. If you take your time then less of a difference but in the case of a rectangular/square patch + rushing (letting the heat build up) the square corners can distort more than a round patch would

Holding things in place... whatever gets the job done which includes sticky tape, magnets, clamps, a bit of scrap tacked in place so the patch sits in the hole nicely etc etc. Magnets can mess with the welding arc if you weld near them, more so with TIG which is also the least tolerant of dirt.
The clecos thing... if i'm picturing it correctly you're thinking to use them through the some of the spot weld holes? Yes than can work, obviously you'll need a bit of scrap drilled to suit the cleco size as they'll fall through the old spot weld holes

Thread here which goes into a bit more detail on the typical approach when using TIG for coachwork... http://www.mig-welding.co.uk/forum/showthread.php?t=19656&highlight=coachwork

 

[ChrisJohnsSculpture]

There is a lot you can do to help minimise distortion :

-Using pulse mode may help, although how useful it is will depend on your technique.
-Make sure that the metal is surgically clean
-Get as good a fit as you possibly can ie minimise gaps.
-Use the thinnest filler rod you can and keep the weld as flat as possible
-Use lots of tacks and seam weld in short sections, keeping alternating sections opposite each other and widely spaced
-make sure tungstens are sharp
-Keep a short arc

One approach which can help with TIG welding thin sheet is to have a slight overlap on the joint, maybe 1mm or so and do an autogenous weld (no filler rod). This reduces the heat you need to put into the weld and, increases travel speed and reduces time between welds. May not be suitable for all applications though.

The general procedure is to do pairs of opposite welds as quickly as possible so both are done before the first cools too much and allow plenty of time in between pairs for the work to cool.

Square patches are probably best for minimising distortion as the symmetry will help to equalise the stresses. Circular may be ideal in theory but are likely to compromise fit. In general avoid complex shapes which will create uneven residual stresses.