Welding enclosures for welding

By Lawrence (*****)

Date 08-28-2002 19:11

Alan,

Very few aerospace manufacturers or repair vendors employ large enclosures for welding titanium and as you say *other aerospace materials* What "other" alloys could possibly demand a purge enclosure? I have seen miles of titanium duct fabricated and repaired a good share of it, never have I seen an enclosure employed for either fab or fix. Does your engineering doccumentation actually call out a requirement for this chamber?

Excellent results are obtained in GTA titanium welds (manual and semi/automaitc) with well engineered argon backups, trailing shields and purging fixtures.

My advice is for you to get a tour of other duct manufacturers (Boieng/Douglas, Lockheed etc.) and take a peek at how they do their work. Also if you are using automatic or semi-automatic equipment to weld your tubes and ducts, the manufactures of this equipment (Liburdi/Dimetrics comes to mind) most likely have testamonial and data sheets that prove the benefit of good trailing shields.

Numerous considerations need to be taken to produce consistantly sound Titanium welds, but a 100% inert atmosphere enclosing the componant is rare indeed, not unheard of just rare.

The Navy Joining center has published extensively on this subject as has EWI and TWI.

Persuasive salesmen have for years been selling chambers-bubbles-boxes (we have our share) that end up collecting dust in shop corners while production continues to increase due to careful planning and quality process control.

Lastly, if you are selling your ducts to Boeing, Pratt Whitney, Lear or any other Major, perhaps you can get your hands on a copy of there "Standard Practice" manuals for welding. These will tell you what is viable and as well as the latest cutting edge in process control.

This is a great question! I'm really looking forward to other responces

Lawrence

By ALAN RIDDLE (*)

Date 08-29-2002 10:18

Thanks for the info. We weld our Ti ducts 97% out of a chamber BUT we have had some problems with "doubler" welds onto the tubing. It is virtually impossible to purge behind the doubler when seal welding it to the tube. We cut some samples apart on Ti, Inco and SS and the oxidation and color indicates the need for a purge. This is the driving reason to weld doublers, mounting brackets and a few other attachment welds in a chamber.

Alan

By Lawrence (*****)

Date 08-29-2002 18:04

Alan,

Now that's a horse of a different color! You really have me thinking. Your high standards are impressive and I'm eager to hear your gonna solve this one. Maybe the chamber is the best way to handle it after all.

Tho I'm still a bit skeptical about the need for dry boxing inco and 300 series stainless, I would think a well-fit lap would eliminate the possibility of any "Sugar" developing in unwanted areas.

Now with Ti a little color can be indicative of a light surface Alpha Case rather than embritteling contamination absorbed into solution throughout the weld. Does testing indicate the surface color you find is truly associated with embrittlement in the Titanium doublers?

This is simply stated and you are prolly already quite familiar but, "Weld contamination, which occurs in the molten weld puddle, is especially hazardous. The impurities go into solution, and do not cause discoloration. Although discolored welds may have been improperly shielded while molten, weld discoloration is usually caused by contamination which occurs after the weld has solidified". With varying degrees of embrittlement

There is still much discussion about alpha case in particular and color in general when it comes to acceptability of hot worked Titanium. I wouldn't be surprised if some of the "Rules of Thumb" we have applied for many years don't change a bit when considering surface coloration when mechanical performance and ductility are unaffected. (Hardness testing for fieldwork and difficult part geometries are being explored)

It's still hard for me to get my brain around this. I would think a well-fit doubler welded with proper purge and trailer would not have a loss in ductility when compared to work done in a chamber. The difference ought to be negligible