STITCH WELDING

By - Date 07-17-2001 18:05

This question can only really be answered if you give an indication of why you are performing the intermittent welding. Can you also state very clearly what you mean by "stitch welding", because I believe that it is a term used in more than one circumstance.

By C.R.ZUBI Date 07-17-2001 18:30

IT DOESN'T REALLY MATTER "WHY" (ENG.DESIGN DWGS., IN THIS CASE), BUT IS THE HOW THAT CONCERNS ME. "STITCH" WELDS ARE THOSE THAT ARE NOT CONTINUOS IN NATURE (i.e. 2" LONG EVERY 4" O.C.) OR INTERMITTENT. "STITCH" IS MORE OR LESS A LAYMANS TERM. INTERMITTENT WELD IS DEFINED UNDER D1-1-96 AS: "A WELD IN WHICH THE CONTINUITY IS BROKEN BY RECURRING UNWELDED SPACES".
THANKS FOR TAKING THE TIME TO ANSWER BACK!!

C.R.

By - Date 07-18-2001 18:42

Ouch - Why do I feel like I asked a moronic question?

Just to clarify:

In my experience, the "slang" term "stitch welding" is applied to:

1) Intermittent welding as you describe it.
2) "Back step" welding to reduce distortion.
3) A low heat input welding technique used when welding some cast irons. (Random welding)

As I now also understand what you mean, my next question becomes relevant. Why are you stitch welding? I understand that the drawing may ask for it, but why did the designer ask for it on the drawing? Often it is merely a means of reducing welding costs, when full length welds are not required. Often it is of primary importance to reduce distortion of the weldment by balancing the welding around the neutral axis, or to maintain some sort of a "root gap" in the joint. If for some or other reason you need to maintain a 1mm gap in the root of the weld, then starting on one side and "just going" will pull this gap closed. By doing "space welding" (The South African slang term.) and choosing your welding sequence correctly, you will minimize this problem.

If distortion is not a problem, then it does not matter where you begin and end. Make sure how long the welded portions must be and the unwelded portion, mark this out and "let the welder experience freedom of expression". (No, South African welders are not frustrated artists, I am just feeling a bit dramatic this evening.)

If distortion is the issue, then as Prof. Crisi indicated, it must be handled on a job by job basis. It would be very difficult to really comment in this case, unless you VERY CLEARLY describe your particular situation.

Hope this helps

Regards
Niekie Jooste

By G.S.Crisi (****)

Date 07-17-2001 19:09

The answer depends greatly from the geometry of the piece (i.e., what it looks like). Is it flat bar or an angle iron to be welded on a plate? Is it a pipe or a vessel where you apply some stitches before making the final weld?
Giovanni S. Crisi
Sao Paulo - Brazil
P.S. Niekie, you're South African and your slang is different than that spoken in America. Stitch welds, in American welding slang, means "intermittent welds" and are a little longer than just "tack welds".
Giovanni S. Crisi
Sao Paulo - Brazil

By R. Johnson (**)

Date 07-18-2001 18:29

Intermitent fillets welds are usually used because the load does not require a continuous weld or more commonly to keep the distortion to a minimum.
Unless the engineering drawings call out specific requirements, it is usually up to the manufacturers (welders) standard practices. I have seen shops where the intermitent fillet welds were either laid out from the center of the part to be welded or laid out from one one of the part. I believe the important issue is not where the intermitent welds starts but how is it stopped. Our practice was to not allow any unwelded area at the end of the parts being joined. Hope this helps.