MIG brazing for car body panels

[atlantis]

Hi

I'm new to the forum and would like to introduce myself in a few words. I'm a hobbyist mechanic and builder - I work on anything mechanical and electrical that I find interesting. Welding wise I can weld and braze oxy-acetylene and MIG/MAG, but I don't weld very often. I'm also a car nut and do maintenance on my own cars. I think I can make pretty nice welds on most applications but I never got friends with body panels. Even though I did as they say I always kept producing holes until last time when it was going quite well the welder broke down...

From what I've read I think the danger of producing holes is much smaller with mig brazing - unfortunately the specialized welders body shops use are far too expensive for hobbyists like me. I know that some on the forum have tried mig brazing with ordinary mig sets and were quite successful. Would you mind answering a few questions (I beg your pardon if there are details somewhere on the forum and I just didn't find them):

- how low should the amps go to make the welder usable for brazing
- would the same wire diameter be used as for normal mig welding
- do you think there's any doable modification to the set that would improve it's usability
- does anyone know what the professional sets that have a mig brazing program do different when set to brazing?

I have 2 mig sets, one is my main one (20-180 amp) and the other is the backup one I bought when the other one broke down (25-160 amp), but both are pretty basic transformer ones. I have only one gas cylinder which is filled with a mixture of 82% ar and 18% co2 at the moment.

Regards
Martin

 

[Justme]

Did you find this

http://www.mig-welding.co.uk/brazing.htm

 

[atlantis]

Yes I did. It's interesting, but unfortunately there's hardly any detail info. Wire thickness used, wire alloy, amp setting, welder used etc.

 

[hotrodder]

The usual suspect for brazing wire is CuSi3 (designation C9), available in 0.8, 1.0, 1.2mm. Be prepared for a shock when pricing a spool. The usual gas is pure argon, your current mix has way too much CO2 for brazing.

Don't own a MIG and haven't used one for years so can't help with parameters except to be pedantic and point out that with MIG you adjust the voltage, the amperage is variable and related to wire diameter and speed

This goes into more detail but at the same time is more specific to pulse/synergic MIG... http://www.fronius.com/cps/rde/xbcr/SID-77B07941-CDBE1FC2/fronius_usa/13_mig_loeten_gb.pdf

 

[HughF]

I have a regular mig machine, about 150a and i have some experience with running brazing wire in it. When I am home (working overseas this week) I will run some test for you and show you some settings.

Hugh

 

[tiger99]

Please be aware that if you are in the UK, MIG brazing is illegal for car body repairs in stressed areas (most of the shell) and if spotted will fail the MOT. But I think you would be allowed to use it on door skins and such like.

It is an attractive process for many other applications, but the cost of a reel of wire is horrendous. I don't know why, maybe there is not much demand so it is made in amaller quantities than steel wire? You would expect it to be a bit more expensive, but over £1000 for a reel is just ridiculous.

 

[Burdekin]

Hi Martin, why don't you just oxy weld your panels?

Regarding mig welding, if you don't burn the occasional hole you probably have your amps too low. I v prep my edges and fully butt the joins together, then just ensure you get full penetration. If you leave a gap you are more likely to blow through more often and get more distortion as the panels will move more. Mig is good as you can keep the heat down and weld small areas at a time but oxy you'll have less grinding to do, the weld will be more malleable to planish or shape if you need as well. The guys I know who make panels by hand all use oxy welding for steel and aluminium panels.

 

[tiger99]

Or, use a backing bar. Must be copper, no other metal will do. Some people make them from a flattened piece of copper water pipe. You will find that even a simple one does wonders for burn-through and reduces distortion as it conducts a lot of the heat away.

An even better backing bar can be made from something like 1" * 1/4" copper bar, with a small groove machined down the middle, so it will allow some clearance for a bead to form on the reverse side, for extra strength.

 

[Justme]

Please be aware that if you are in the UK, MIG brazing is illegal for car body repairs in stressed areas (most of the shell) and if spotted will fail the MOT.

You might want to re think that statement. Some new cars are made out of a metal that should not be welded as the heat will alter the temper, so they have to be brazed to repair them.

 

[Robotstar5]

Please be aware that if you are in the UK, MIG brazing is illegal for car body repairs in stressed areas (most of the shell) and if spotted will fail the MOT. But I think you would be allowed to use it on door skins and such like.

MIG brazing is the only form of repair allowed by insurers on some modern cars.

 

[squazy84]

the guy that decided brazing should fail an mot on a car obviously never tried to remove a panel brazed to a car. my 76 celica has some factory brazed joints,obviously mig brazing is the way forward for the modern steel on cars,I think its boron steel?

 

[TechnicAl]

As someone has already posted.
MIG Brazing is the recommended process for joining Boron Steels which are now used extensively to reduce weight. Their higher strength allows thinner section without reducing design strength.

£1000 a spool..........

If anyone wants a spool for a lot less just let me know

 

[gulf]

hehe....i wont say anything

 

[matt1978]

Maybe the guy was getting confused with O/A Brazing and not Mig Brazing. I do think conventional Brazing with a flame is banned for MOT is it not?

 

[PTvor]

Not acceptable for anything structural, or within a given distance of anything structural, I think.

 

[Justme]

Maybe the guy was getting confused with O/A Brazing and not Mig Brazing. I do think conventional Brazing with a flame is banned for MOT is it not?

This is what the MOT manual says

MIG brazing, a combination of adhesive bonding and riveting, or amalgamations of these with other joining methods may be the vehicle manufacturers recommended method of repair. Such repairs must therefore be accepted unless they are clearly inadequate.

So I guess its down to the makers recommended repair method statement.

 

[matt1978]

As a lot have already said, Mig Brazing is a very well accepted form of repair AND manufacture of cars, a lot of car repair garages, both main dealer and independent, had to invest in new machines specifically for Mig brazing repairs to the newer models which contained the high strength steels, so it definitely wouldn't be an issue for MOT's.

But I think he will of got his wires crossed between Mig brazing and conventional Gas brazing.

 

[zardoz]

As someone has already posted.
MIG Brazing is the recommended process for joining Boron Steels which are now used extensively to reduce weight. Their higher strength allows thinner section without reducing design strength.

£1000 a spool..........

If anyone wants a spool for a lot less just let me know

eh?A grand a spool !?

I have seen a 4KG spool of Mig Brazing Wire C9 1.0mm (Copper wire containing 3% silicon and 1% Manganese ) for £137+ VAT or a 12.5Kg spool for £295+VAT ?

and similar prices for phosphor bronze MIG brazing wire

Still bloody expensive in my opinion though

 

[MCKDAVID]

"Not acceptable for anything structural, or within a given distance of anything structural, I think."

Maybe I'm getting senile, but I seem to remember that most of the older cars (70s / 80s) the roof / pillar sections were brazed to the body by the factories???? that would be structural...

Certainly the trick frames for the motorbikes of that era and before were all gas brazed, so the stength is clearly acceptable, perhaps its the individual method that was in question.... gas versus mig... both being done properly, I don't see the difference, the end strength result should be the same? I would guess that mig being the modern preference as faster in terms of production, with less distortion, or am I talking bolloks....

 

[backpurge]

It is not really anything to do with the strength of the joint it is how the applied heat effects the properties of the parent material now used for most car bodies