1/8in TIG weld concave convex?

admin

So Im going to college to get my degree in welding. Im taking an advanced tig class and the teacher asked for 1/8in tig weld on 1/8in material. So most my steel tig welding ive done before and for other teachers say a semi concave to flat weld is perfect as long as there is no under cut ect. My advanced tig welding teacher now want us to run a bead that is some convex to it. In order to do this you must run cooler and use alot more filler rod. How does everyone else fill a correct 1/8in mild steel weld should look? Many of my other welds were alot more consitant but barley had a concave to the weld. My teacher was finally happy when I welded it like this with some convex to the weld. How do you feel about concave vs convex mild steel tig welds?Link to my convex 1/8in tig weld on 1/8in steel.http://fabricationzone.com/forum/index.php?topic=4.0
Reply:If you are being graded on your welds, what the instructor wants should be your concern, I would think.Rex
Reply:A weld should always be flat to slightly convex as that is the reinforcement, if it is concave the effective leg length of the weld is smaller.
Reply:too much concavity or too much concavity are both bad. they have limits on how convex or concave they can be when it comes to acceptance criteria. this is whi i always aim for flush. although slightly conves or convave isnt the end of the world. convexity "too much of it" is a waste of weld metal if you ask me.
Reply:wow i can't spell tonight! why convex concave.....what the bloody hell?
Reply:Well I ask this because one teacher tells you to do it one way and the next tells you to do it the other way. I welded it the way he asked for the grade but I want to know for my own best way. Ive always felt flat is about perfect with most steel tig welds.
Reply:Concave welds place the surface of the weld metal in tension as it cools- more prone to cracks, particually at the toes. A convex weld isn't in tension but the bead has a sharp(er) transition into the base metal- sharp edges, particually at a change of section make for great stress risers and poor fatigue life. Too much of either is also a waste of weld metal/timeAs said, there are acceptance criteria for excessive concavity/convexity depending on the job.
Reply:I like a lot of these answers. Some good points, I favour what rode2rouen said. And maybe its just an exersize. In Oz. our welds are mainly measured on leg length, so a concave 10mm (leg length) weld on 10mm steel plate is a bit weak, but may have less stress than a convex weld like hottrodder said. The same weld I like to grow the leg to 11 or 12 mm and concave the weld but still maintain a good strong throat thickness.   But then you need to work out how the metal is going to cope with the extra heat? As I understand, tig is the process that will put the most heat into a job. If you are working on stainless, its always a consideration. Work out your variables for that welding joint.