Advice needed please

[Dunnby]

Afternoon, can anyone shed some light on this for me! I have a company welding up a titanium bike frame for me. It's been welded, then cracked near the weld. Welded again and cracked along the weld. What is best to sort this out?? Any advise will be great

This is the best picture I can get.

Thanks

 

[gordon stephenson]

No image showing for me,

 

[hotrodder]

I can't either. Permission settings in the album?

Was there any heat tint in the area welded? Pic below of a Ti exhaust collector isn't great due to reflections but the slight hint of 'straw colour' is visible surrounding the weld

and as a general rule of thumb with Ti the more heat discolouration the more brittle the weld [/gross generalisation]. More info in this thread http://www.mig-welding.co.uk/forum/threads/titanium-weld-cracking.62966/page-2#post-799862 Obviously if whoever tried repairing it attacked it with wire brushes or scotchbrite type abrasives they could have cooked the crap out of it and then removed the evidence...

Cracking near the weld could be the result of embrittlement due to poor shielding and/or poor purge. Cracking through the weld suggests someone welded (badly) over the crack so it just grew back.

While you're sorting the pics out do you know what grade of wire they used?

 

[Dunnby]

They used Cold- worked, tapered/butted 3Al/2.5V tubing (seat tube) and bladed 6Al/4V downtube (diagonal)

This is all the information I can find about it. Thanks for replying

 

[Dunnby]

 

[Dunnby]

hopefully this picture stays up! what shielding gas should be used for this type of welding?

 

[WorkshopChris]

My limited knowledge of titanium is you need huge amounts of gas. Normally argon with a purge and flow inside the parts(if tube/open bore and either a separate flood of gas around the torch or weld in a small purged tent like structure depending on the size of the parts. As far as i know once its getting brittle from excessive heat the only option is to replace. BUT that's just my gaining of things from one industrial part i was involved with, i know absolutely nothing about building bikes.

 

[Dunnby]

My limited knowledge of titanium is you need huge amounts of gas. Normally argon with a purge and flow inside the parts(if tube/open bore and either a separate flood of gas around the torch or weld in a small purged tent like structure depending on the size of the parts. As far as i know once its getting brittle from excessive heat the only option is to replace. BUT that's just my gaining of things from one industrial part i was involved with, i know absolutely nothing about building bikes.

thanks very much for your reply Chris, I was thinking this as its been welded a few times in the same spot, not sure if this is making it weaker and weaker. one more try then I may need to replace the frame

 

[Brad93]

I'd suggest getting a firm that specialise in titanium or exotic metals to weld it up. Ideally you want to weld titanium in a purge chamber, however using gas lenses, trailing shields and a good purge on the backside of the weld you can get satisfactory results, if, you know what you are doing.

 

[hotrodder]

hopefully this picture stays up! what shielding gas should be used for this type of welding?

Still no pic showing

 

[Elmo Putney]

Not a bike frame but not far off...

http://www.pistonheads.com/gassing/topic.asp?t=1266026

 

[hotrodder]

I've been out of the bike trade for years now but FWIW the vast majority (if not all?) Ti frames were built 'in the open' with just large gas cups and several purge lines. A fairly common technique was to weld in two passes i.e. an autogenous pass to fuse the root and then a pulsed filler pass
Smaller components were more commonly welded in purge chambers as you can set up and weld several parts with just one evacuation and argon fill making it cheaper. DeKerf used to make a beautiful one piece Ti handlebar/stem combo this way