Swingarm welding

[ola_martin]

I'modifying a RM swingarm. It's widened 25mm. and as you see I'm making a new "bridge" between the arms. what I also would like to do is to put a new bigger "ridge" on top of the arm from the shockmount and forward. My only reason to do this is for the looks.
But I have no experience on what will happen with heat disformation , will it pull out in all directions??
My welder says he can weld it bit by bit and let it cool in between, also as you can see I'm thinking about a jig to stiffen it up during welding.

Any thoughts on this?

Thanks!

[ola_martin]

pic

[maicomc490t]

We might need to call in the heavies for an opinion on this one.

Welding and even controlling distortion should not be a big deal with the right welder at the end of the TIG torch but many of the alloy swingarms were heat treated following the welding process.

The requirement as to heat treat or not would be worth investigating, but having said that there are probably thousands of swingarms around the world that have been successfully and safely welded without getting too carried away with additional work.

Perhaps Geoff from GMC can enlighten you or do the job for you if you are looking for a good TIG master

Dave Mac 

[Lozza]

Your jig will have to be much more substantial than that, I would have 3 or 4 fixing points on each arm as well as the pivot and axle. When you weld in your bridge leave the inner vertical where the bridge meets the arms NOT welded. For any sort of ductile weld spend time heating the whole arm up slowly all over(with LPG or such), then weld, then wrap in heat blankets ,spot lights anything to keep the heat in the job and lets it cool down slowly. Only after it's fully cooled (24hours) down then take it out of the jig. It should remain straight. Good Luck.

[GMC]

Aluminium usually welds okay without too much distortion, Stainless is one of the worst.
I woudn't worry about a jig, just check it for true after you have finished. It will be hard to build a jig to hold everything & allow access to weld everywhere too.
Aluminium needs to be hot to get decent penetration, & the heat will travel throughout the whole arm so welding it bit by bit isn't an option. Once you get it hot to weld you need to keep going till it's finished to get decent welds.
The fact that your welder thinks he can weld it bit by bit makes me think he hasn't got much experiance at welding aluminium or that he intends to use a MIG.
Some swingarms get chew marks from the chain, these are usually small & you can get in quick to fill these without detroying the heat treatment too much but to weld a gusset up the length of the arms will effect the heat treatment of the alloy.
You may get away without heat treating but I can tell you it will be weaker than it could be so if you want any peace of mind while riding it I would get it heat treated back to T6.

The tubing in my swingarms I have annealed to T0 in order to bend the banana shape into them. By the time I have finished welding them completely the whole swingarm is as soft as butter. Once welding is finished I check them for true, clamp a spacer inbetween the axle pivots & send them off to brought back up to T6.
Check your local trades guides for heat treatment companies, it's no big deal to get things done properly.

[brent j]

A bit off track and a bit late but why are you widening the swingarm? I assume to fit another bike?

A PE swingarm is wider by about the amount you are widening yours, I'd have to measure one of mine but I had both RM and PE and there is a noticable difference. THe PE arm is wider at the pivot and the back end. The RM swingarmn has the shock mounts about 25-30mm further forward.

Brent

[GMC]

At first I thought you were just widening the pivot area but on reflection it seems you are going to cut the arm in half & widen front & back, in which case a jig would be best to keep the arms parallel.
The jig will need to allow the half’s to move sideways but still be in alignment with each other.
It will still need checking for true when finished.
It will definitely need heat treating when done.

[ola_martin]

Thanks guys!

Yes, the arm is going to be cut in two and welded together with a wider bridge. My welder uses a TIG, he's done some alu-weld for me before with good results, but I don't think he has much experience with structural parts. That's why I'm on here asking for advice

About heat treating. I don't know what type of aluminium the swingarm is, and I don't know what type my new brackets are. Can all alloy be heat treated to T6 no mather what it was in the beginning? When I'm done welding and truing the swing afterwards, can the heat treating process cause it to loose it's form?

Sorry if my questions are stupid but I have little experience with structural aluminium.

-GMC, how's your plans looking on my exhausts?

Best Regards

[ola_martin]

Your jig will have to be much more substantial than that, I would have 3 or 4 fixing points on each arm as well as the pivot and axle. When you weld in your bridge leave the inner vertical where the bridge meets the arms NOT welded. For any sort of ductile weld spend time heating the whole arm up slowly all over(with LPG or such), then weld, then wrap in heat blankets ,spot lights anything to keep the heat in the job and lets it cool down slowly. Only after it's fully cooled (24hours) down then take it out of the jig. It should remain straight. Good Luck.

Lozza, I think i understand what you mean by inner vertical. But should all 4 not be welded or only the rear two?

BR

[Lozza]

Ola on every OEM swing arm I've noted it is ALWAYS on the rear, sometimes yes and sometimes no on the front.