Re-melting TIG welds

Igor,

I do it all the time to clean up "blemishes" I don't know of any problems with doing so. Now that may not be the case for any pressure vessel or structural instance but take for example, one of my sheet-metal intake manifolds. I will always find "ugly" spots and I do just what you are inquiring about. I just take the torch and wiggle it into a puddle that removes my blemish if there is enough base and filler, I can always add more rod in some cases. Little circle motions work best and I hold the torch over the end of the weld and cut the arc power but leave the torch over the HAZ and let the postflow gasses cover the area until it cools or the postflow cycle ends. It has been very successful for me. Now I'm only speaking to non load bearing stuff. That might be a different game but I have yet to have a manifold or set of headers come back to me with a fabrication defect using the process you are asking about. Keep up the welds sir, they look better each time I see them posted. Quite an addictive hobby isn't it?

All the best sir,

Rob

It is a very addictive hobby indeed. Thanks for your tips. I am going to make a couple of structural things. One is a pullup bar so that I can continue practicing pullups. There used to be nice scaffolding near where I work, where I practiced, but they removed it. This pullup bar will be a 2" OD pipe welded to a plate on one end and with a triangular like supporting thing:

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See this.

Quote:

************************************* Cannondale also uses a different welding technique than other bike manufacturers. ?Instead of the traditional stacked-dime TIG weld bead appearance and welding the joint in a single pass, we break the rules a little bit by making two passes,? says Crawford. ?With our technique, the first pass ensures complete penetration. We then make a second pass that smoothes the weld bead to the point where the joint looks like it was molded.? Because the cosmetic second takes the crown off the weld, operators continue to add filler wire to maintain throat thickness.

?Our welding method improves fatigue life,? states Pahl. ?Our welding method creates a smooth transition from the weld joint to the rest of the tube, and this helps prevent stress risers. Stress risers occur at the outer edge of an unfinished weld where the weld abruptly ends. At that point, the tube wall suddenly gets thinner, so it?s more prone to the accumulated stress that builds up with riding. Our technique tapers the walls more gradually, which disperses the stress over a wider area. As a result, our frames last longer.? It also allows Cannondale to use thinner wall tubes for a lighter frame.

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Thanks, that was very helpful. If cannondale does it, so can I.

i

Keep in mind that they also heatreat frames so the extra heat might make a little difference in the strength.

Be mindful that excessive welding heat on many aluminum alloys is not desired. Most alloys are heat treated to some extent and it is very rare that the weld bead matches the strength of the aluminum alloy. I worked as a fitter for two years on large aluminum ferries. The cold looking welds on the lifting lugs seemed to hold up much better than if my welder put in a really hot weld. I took a lifting lug on the chin from a hot weld. Really flat hot welds on aluminum is not the way to go ... unless you are going to heat treat afterwards. Most welds on steel are stronger than the parent metal as welded. Randy

By the way, why do some welds turn out to be concave instead of convex. Should I use less filler and run my torch slower, or some such?

Can I, in these instances of bad looking welds, run the tig torch over that weld again, without a filler rod, in order to re-melt the bead and improve its appearance. As it turns out, doing that does get rid of warts and it does turn concave fillet welds into convex fillet welds.

The question is, does doing so increase, decrease or does not change the strength of the weld. Any thoughts?

thanks.

As an aside, I am hugely impressed with tig. I could weld thin things (1/8") to thick things (1/2) and the weld looked really nice too.

What I really like about it is that I can weld very small things, like welding little nuts to steel plates, etc.

i