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Old April 9th, 2010, 07:11 PM   #1
lgottler
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Default Checking for a good weld

Any professional welders give advice for visual checking a weld?

I'm running a job at our shop and because of some weld failures from the last supplier (along with fit problems), we won the job, but I don't want a single failure from us.

Aside from destructive testing, do you think its possible to accurately check a weld visually?

The welds I'm putting on now, (robotic welder) I set it as high as I could go without blowing through the metal (only .075 thick). The back side of the weld would glow bright red while welding. After a weld, the back of the area has a scale on it, I'm assuming is the metal de-carbing from the heat.

Now destructively, these welds are strong, I tore the metal next to the welds right off. Visually looking at the backside, can I use that grey scale buildup as a sign of good penetration, or not? Its a sign of heat, but what about penetration? Would that go hand in hand?

We hand welded the first 100 and I had to TIG repair about 40 of them because visually, the back of the welds didn't look like they got hot enough, so I hit it again with a bit of filler.

This picture shows how the robotic welder is set right now, sorry, no back side shot, can't get in there. I'm running a bead straight down, then I come back on itself at the end to add filler and keep from blowing out the edge.



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Old April 9th, 2010, 08:07 PM   #2
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The main thing you need to look at for what you are doing is the edge of the weld where it meets the metal. You are looking for cold roll. If it is tied in nice and sharp you should be good if you can see a small lip where it isn't tied in properly chances are it isn't. Also is your metal nice and clean where you are welding?
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Old April 9th, 2010, 08:08 PM   #3
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whats the application?
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Old April 9th, 2010, 08:11 PM   #4
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Also running the weld downhill you are getting the least penetration.
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Old April 9th, 2010, 08:22 PM   #5
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Originally Posted by chadcooper55 View Post
Also running the weld downhill you are getting the least penetration.
This weld is actually horizontal. Face a wall and weld on the wall right to left. Thats what I meant...so down would be the small tab.
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Old April 9th, 2010, 08:23 PM   #6
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whats the application?
monitor bracket, joints monitor mount to wall mount. Metal in pic: .130 and .075
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Old April 9th, 2010, 08:29 PM   #7
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...Also is your metal nice and clean where you are welding?
Its actually pretty good stuff. The laser blanks were sent through a time saver, then when we formed them. I had the guys wipe off the part before loading it in the press and after forming they wiped off any oil residue. I tried to think ahead on this part, I wanted a good weld.

The edge on the thicker piece is actually a laser edge, the face of it we orbital sanded smooth with 60 grit, then wiped clean.

I had to think ahead to the painter, so all surfaces were dust, oil, free.
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Old April 10th, 2010, 10:26 AM   #8
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I would do some destructive testing to see just how well the filler metal from the mig penetrated the laser cut edge. Laser cut edges (same as plasma but laser seems harder to burn through) have a coating on them and it can just about block any penetration in that area because the surface of the cut edge has nowhere to go when it melts. It might be worth a sample piece to bead blast or wire wheel the surface off the laser cut edge and do a side by side comparison to see what fails first, if anything. If you get the same quality test out of the cleaned edge as the un clean edge then it should be good. The .075 will probably deform before you have to worry about the weld breaking. The only thing that stands out is the laser cut edge. It's bitten me in the ass before I realized it had to get cleaned up for a prefectly clean weld.

If you want more detail give me a call, I dont feel like typing for an hour.

Looks good as it is though, should be trouble free.
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Old April 13th, 2010, 03:43 PM   #9
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I agree with 95geo on destructive testing being a very helpful tool. Laser cuts generally have cleaner edges and less dross than plasma arc cutting but can be problematic if the assist gas is not able to "blow" the molten metal out of the cut. A picture of the cut edge before you weld it would be helpful!
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Old April 13th, 2010, 09:22 PM   #10
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I did a destructive test, I clamped it in a vice and bent it all the hell and back trying to rip it off

If I find one that has any defects, I'll try to get a cross section to see penetration.

I need a good check for the guy pushing the buttons. When its welding a new one, the operator is removing any spatter, verifying positions, and then finally checking weld quality on the last one.
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Old April 24th, 2010, 08:47 PM   #11
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Finally got around to doing a more scientific test. I took a bad part and cut the welds in half on both sides. Then sanded it flat, from 60 to about 400 grit. Then put it in a small glass jar of hydrochloric acid (muriatic acid, $6/gallon pool store) for about 10 minutes. removed with pliers, hosed off with windex, rinsed in cool water, blow dry. Of course I used gloves, long sleeve shirt, and full face shield.

It revealed the depth of weld penetration really well. It appears that the center is the worst part of the weld. I ended up with acceptable (to me) depth at start and end. The start is where I first held the weld a split second longer and the end is where I backtracked the weld a bit.

I sliced out the center area on the other side (least penetration) and did a pull test, bend test, twist test. I only ended up tearing out base metal, so I think it will pass. If I run another lot, I'm going to figure out the adjustments for amp and wire speed (on the fly adjustments) so I can fine tune the welds on this thinner stuff better.
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