Hi everyone
Learning SMA with 7018 / low-hydrogen / basic rods
I want to get a good penetration bead shape on the inside corner of an outside-corner weld. Very often there is a quite "extruded" / prominent / standing-up penetration bead, which to me looks like it presents a stress-raiser down the plate-to-bead juntions. So I have been trying to get a "flat" underbead profile which looks like a T-joint fillet weld profile.
- am I right to be concerned that an "unblended shape" is a stress-raiser?
- if so, what can I do about it ?
The joint as fully as I can describe
- SMA, basic/7018/LoHi (college std. is rutile/6013)
- outside corner, with plates at 45deg from vertical presenting channel in the "flat"/"downhand" position
- 2mm root gap (or whatever gives a good result)
- 10mm (3/8th inch) plate thickness mild steel
The college will insist for the test piece on 2.5mm (3/32nd) rods for the root and 3.2mm (1/8th) rod for fill - but I can practice and build an image of how to do a commercial weld with whatever I like.
The technique is to maintain a "keyhole" through the root, riding the arc forward to arc straight onto the plate if the keyhole is being lost and to riding back up the weld pool if the size of the melt-through and keyhole is getting too large.
I have been experimenting trying to get a penetration bead shape which looks like a T-joint fillet - i.e. it is flat, blending into the plate with a 135deg intersection
I have got that sometimes, but cannot be sure what I am doing to get that. I'll take a risk and venture - I think it is when the root run is thin but the weld has been performed "hot" in the root with an upright (about 70deg to 80deg off the plate) rod tilt, "good" keyhole and a reasonably fast travel speed. Maybe I'm trying to be too clever by half - I want to believe that I am controlling surface tension, with fluidity making it happen but small root bead depth preventing gravity pushing a deep extruded penetration bead
A completely different "operating point" which gave good results was with "an enormous tilt" of about 40deg off the plate, with the arc playing very short onto the big front edge of the weld pool, with the force of the arc holding the metal back in this steep edge. In this case, I could use a smaller root separation and a larger 4mm 7018 rod. I would say "economically" this was a very favourable weld, getting the job done is fewer passes.
Guidance gratefully accepted.
Regards
Richard Smith