TIG Welding queries

By teamunwired Date 06-25-2009 14:36

Hello!
We students here at NIT Calicut,India are competing for a vehicle design & fabrication contest- Baja SAE Asia 2010. We have chosen 4130 Chromoly Alloy Steel tubings/pipes as the material for our Roll Cage(Chassis). The following are the specs:

Tubing Material: 4130 Chromoly Alloy Steel
Outer Dia(OD)= 1.25 inch
Wall Thickness= 0.065 inch (1.65 mm)

The roll cage has to survive the harshest of punishment of a 4 hour endurance race on an off-road track. I would really appreciate if answer the following queries:
1. Does TIG Welding have a clear advantage over MIG and Arc Welding in our case? If so, what are the advantages?
2. Does TIG Welding require stress relieving/ heat treatment?

Thanking you in anticipation

Kind Regards
Prateek Kalyankar
NIT Calicut,India

By MMyers

Date 06-25-2009 15:03

I would suggest spending a few minutes with Google. 4130 in those thicknesses and applications has been TIG welded for decades. No post weld, no nothing. Weld it with 80S wire and go. Once you get to thicker sections, then you're into a different place, but for thin wall tubing, TIG it.

By teamunwired Date 06-25-2009 17:47

Thank you so much for the prompt and may i say encouraging response.
Could you please answer the query on whether stress relieving is required? If yes, does it require local or global stress relieving?

By MMyers

Date 06-25-2009 22:02

Not at those thicknesses. That's what I was inferring about "weld it and go". When you get to about 1/8" or heavier, you increase the cooling rate and you can run into high hardness which require stress relief. You can combat this by preheating, but I would want proof (tensiles & bends) that the preheat is giving you the weld properties you think you're getting.

http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

By teamunwired Date 06-25-2009 22:39

Thank you so much for that. The link sure cleared up quite a few doubts.

By cwi49cwe (*)

Date 06-28-2009 22:24

The only thing I would like to add to the comments of my previous friends is, if there is any way possible, I would make every effort to purge the inside with straight argon, I have even went so far as to drill 3/16 to 3/8 in. holes at T-joints to keep contamination to and absolute minimum. It might seem to be an added expense but well worth the effort.

By teamunwired Date 07-02-2009 12:23

[deleted]

By teamunwired Date 07-02-2009 12:28

Would you advise using purge bladders? Is there a simpler/cheaper alternative?

By teamunwired Date 07-02-2009 12:32

Thank you so much. We are complete amateurs at TIG and would really appreciate if you answer the following queries

1. What was the approx location of the holes w.r.t the T joint
2. Is Argon purged through the holes or through the open ends of the tube?
3. Is purging required even before & after the weld has been done?

Could you send some images/links of the process you described? We'd love to get a clearer picture

By 803056

Date 07-02-2009 16:42

Search the forum using "purge" or "purging" as your key words.

We've discussed purging at length recently. There is some good information in those discussions.

Best regards -Al