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Old 05-16-2009, 07:39 PM
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How to fix pinholes in welds?

I've been practicing welding sheet metal and have gotten to the point where I can butt weld two pieces without burning a hole in it. I am stitch welding it, but I am finding that after I grind the weld down and shine a light from the back there are pinholes in the weld. I have tried little tack welds over the pinholes and then grinding that down, but I often find there is still a pinhole there. What causes the pinhole in the first place, and how do you fix them after they occur?

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Old 05-16-2009, 08:33 PM
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What is your gas mix? Wire size?
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Old 05-16-2009, 08:42 PM
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I'm using .023 wire and 75% Argon/25% CO2 gas. The welder settings are set for 24 gauge.
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Old 05-16-2009, 10:04 PM
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Make sure the metal is CLEAN on both sides, flow about 25 CFM with no wind in the shop, no fans etc. blowing and see if that helps. Also make sure the wire is clean with no rust on it. Perosity is caused from the trash in the metal or oxy. getting to the weld when it is molten.
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Old 05-16-2009, 10:07 PM
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Quote:
flow about 25 CFM
You mean 25 CFH.

I don't run that much, but it will work.

In addition to what MikeH said, a poor technique can also cause voids and pinholes, no penetration will wind up being pinholes after grinding..


When I weld thin gauge sheetmetal, I use the same wire and gas, but have found stitch welding piles up on top some, and does not lay smoothe without pinholes unless I do a little backwelding motion.

For stitch welding using single spots:

Instead of starting at the previous bead, and advancing in the direction of the weld, try starting your bead about .050" or.060 ahead of your last bead, and welding back towards the previous bead..this takes advantage of the heat buildup, and will blend the bead into the previous bead, getting them both flatter.

You can use the same backwelding technique for longer stitches, and it is fairly well known that it will reduce warpage on long welds.

Showing direction of weld, direction of stitch, angle of torch and start point.



Finish point of stitch.


You can stand the torch up some if you want, I lay it down so I can see better. When MIG welding,I also use a straight line motion, advance some then back up a little, advance some more then back up a little.

Backwelding on .035" with .023 wire with about a .4" -.5" stitchlength. No backup metal was used.


The backside of the same weld.


after grinding.


Some guys trim the ball on the end of the wire off after every stitch, it does make a cleaner weld, and better penetration at the start, I don't. It helps keep me from burning through at the start.
I don't use anything less than 20 gauge in the shop. 24 gauge is tough to weld, and too flimsey for the old stuff I work on.

Hope this helps,
later, mikey
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Last edited by powerrodsmike; 05-16-2009 at 10:28 PM.
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Old 05-16-2009, 10:10 PM
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Sometimes spot blasting the pinholed areas cleans enough contamination away to get a better weld.
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Old 05-18-2009, 07:46 AM
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Thanks, guys, for all the suggestions. I am looking forward to giving them a try so I can improve my technique. My welds sure don't look as good as yours, Powerrodsmike, especially from the back side. It's going to be a few days before I get a chance to get back to my project, but I will practice some more using these suggestions and hopefully I will start getting better results.
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