A question about welding

[MillCreek]

The inert atmosphere is only critical at the point of molten metal, hence the Tig torch flows gas around the tungsten electrode , also when welding tubing in a closed joint like a bikeframe it is common to "backpurge" the tube while welding , that involves injecting a flow of inert gas inside the tube while welding the outside.Ray

Now that is interesting.  Independent Fabrications, who makes my titanium frame, talks about using these welding jigs with airtight plugs that plug up the frame openings, and they drill small holes in the frame and inject argon into the tubes while welding.  So that is why it is done.  

I tell you, I learn more useful things from this website here....

[lupinus]

it depends on the welding process and the individual welder.  So long as it looks otherwise good, no skips or pits or gap it is probably alright

However, a bead that sits high on the metal or has a curve under it (this a C laying on its side) are signs of a weld that doesn't have proper penitration.  A very shallow bead either shows a welder who pushes into the weld with his wire or rod or can show one that moves to fast, can be hard to tell.

A properly laid bead should be consistant and rise a little bit over the base material that was welded.

As to looks keep in mind a lot of production things are put together by the lowest bidder in a third world rat hole by guys making ten cents an hour and working like a slave, I have seen some welds that just make me shake my head, its been about five years I can could probably pick up an arc welder and lay better beads then that.  But in the end unless it is a high stress joint it isn't to likly to break even if its done half ass.

I'm not a welder but I did go to school for it for a year and decided as an industry it wasn't for me.

When you can stick weld and make the slag curve off on its own you know you did a damn good job (and I used to do it constantly, which annoyed the teacher cause he couldn't)

[charby]

I'm not a welder but I did go to school for it for a year and decided as an industry it wasn't for me.

When you can stick weld and make the slag curve off on its own you know you did a damn good job (and I used to do it constantly, which annoyed the teacher cause he couldn't)

Same boat here, went to trade school to be a welder.  I used to get the slag to roll right off with a 6018 rod. I worked as a welder for about 18 months and decided that getting a BA would be a better career decision.

I do miss TIG welding though, just nice and clean welding.

-C

[lupinus]

TIG is fun, I never cared for mig though it just never worked out for me to well.  I always prefered stick and when I have to do a quick welding chore it is still stick for me.

[charby]

Regrading MIG once I figured out it is better to push a wire than drag one it worked out great. But anything over a 3/8" I used stick, just got better penetration over all.

MIG is nice becuase you can just lay a bead and go, no cleaning slag off.

-C

[French G.]

Well, I are a certified TIG welder, and I have taught myself to passably torch and stick weld. I grew up around a welding mastermind.  My opinion is there are way too many people calling themselves welders out there.

Now if you are judging a weld by looks, hopefully you will see a consistent bead pattern. Hopefully you will see it fused into the base metal at the edge of the bead. Beyond that, sometimes pretty is not what you want to see. It is good I think that bike riders thought big welds looked macho. A weld requires adequate penetration. On aluminum of any thickness this will result in a big bead. Lots of heat, plenty of rod laid in equals a decent weld if the welder is decent. As for the 41XX series steel seen in bike frames, it helps to burn the weld in good there too. Chrome moly ought to be pre and post heated. Unless you are building a space shuttle this can be adequately accomplished skillfully using a torch and temp. indicating crayons.

-Often custom car people judge a weld by how pretty it is, small and neat. Those same people then weld race car frames and people get hurt.

-MIG welders should be banned. They just help more monkeys call themselves welders.

-I suspect anyone who tells me they can weld Ti without a totally inert atmosphere, the issue is it is reactive at such low temps (above 850-900 F) and does not play well with atmospheric nitrogen, Oxygen, etc. Yes you can run back-up gas, tons of torch gas and such, but if you weld for any great amount you travel away from heated areas, or you heat surrounding metal to the point it is reactive.

[CatsDieNow]

Titanium and aluminium are usually heat-treated to improve the strength.  Welding (heating) affects the heat-treating.  When you've got something that is weight-critical the safety margins get shaved.   I'd be curious to know at what point the welding is done, before or after the furnace.  

Re-welding a broken frame is probably not such a good idea if you are routinely bouncing down trails.

I have always prefered pretty welds - it's not the weld that will break anyway (if it's a good weld), but the area a fraction of an inch away due to the partial annealing that occurs.  I am not a fan of grinding them off, though.

[MillCreek]

Titanium and aluminium are usually heat-treated to improve the strength.  Welding (heating) affects the heat-treating.  When you've got something that is weight-critical the safety margins get shaved.   I'd be curious to know at what point the welding is done, before or after the furnace.

Most of the custom titanium frame builders talk about using 'aerospace grade' seamless 3/2.5 alloy tubes.  A friend of mine who works at Boeing with titanium says that a company called Sandvik supplies the majority of high-end titanium tubes in this country.  He doesn't know about any heat-treatment, but says that Sandvik uses a process called 'cold-working' to increase the strength of the tubing, the tubing is produced from billets by extrusion, and that Sandvik custom-makes tubing to the desired specs.

[CatsDieNow]

I don't know anything about bike-making...but that sounds good to me.   Extrusion is cold-working.