Alu bike frame problem

[moleb]

Hello,

I'm having issues welding a bracket onto a Kawasaki bike frame. However much I clean it just keeps pulling black mud to the surface.
I made some progress by ramping up the frequency and setting the DCEN to -20 at which point I can get a pool on each piece and then 'walk' the 2 together but I don't fancy the strength of the result as it feels more like soldering than welding.

Any tips for this type of thing? My setup is working fine on other suff but this frame is old and defeating me.

Thanks all.

 

[WorkshopChris]

Are you welding aluminum with Direct Current Electrode Negative?

 

[moleb]

Sorry no, it's AC. I meant balance is -20 (my set goes from -30 to +30 on balance). Set to 180A with foot pedal but using about half that to get a muddy puddle. White tungsten, no pulse. Gas at 6LPM.

 

[WorkshopChris]

Ok that makes more sense. i did wonder if it was ballance that was set as neg.
Does you set have adjustable frequency?

 

[moleb]

Yes it does. I have that set at 140 as this is getting me a bit more control of the mud, but it's still mud rather than shiny.

 

[Jim Davey]

Not if his frequency function is working. Sounds like you should be heading the other way into positive bias, that's the way to get more cleaning.

 

[moleb]

Thanks, yes I think I have that the wrong way around. The -30 +30 thing confuses me as most seem to be by percent (20-80). -10 - 20 works well for me on new stuff so I'll try it in + and see. I ran out of gas yesterday so had to give up.

 

[WorkshopChris]

What sort of results do you get at about 120ish, .

I haven't done loads of ali tig but doesn't more negative attract more rubbish towards the electrode and positive push it away. same theory as penetration when stick welding with pos and neg setups.

 

[backpurge]

Be very careful welding bike frames, do you know what grade ally it is, some frames are manufactured from a grade that is heat treated to ensure mechanical strength etc and carrying out welding repairs/modifications without heat treating afterwards will wreck the mechanical properties

 

[moleb]

It's not a structural point, it holds a fairing bracket on. There are multiple brackets for the fairing so this one is not alone. It has broken off so I don't think the original had much strength in the first place.

 

[Richard.]

Some of the modern frames and swing arms are nasty cast Alu to weld on and full of all sorts of unfriendly stuff to weld on to enhance its strength. The other thing as well is they are big thick lumps to try and get flowing I'd certainly be looking at a helium mix to start.
Backpurge is right you need to look into what your doing first with possibly pwht. It's not the area your welding that makes it risky or not it's another haz your adding which can crack and you can never predict where they will run too. On a frame that could be a problem.
Balance wants to be around 55-60% dcen.