Question About Automatic MIG Welding...

[Eric Nelson]

We were recently asked to quote building a machine to automatically spot weld a nameplate to a part. It's currently done by hand, and our customer just wants to automate this boring task. I have no issues with getting the parts transferred and positioned correctly in the system, but I have a question about the MIG welding. The only welding I've ever done was stick, and that was back in the 80s...

Every part is identical, and the welding needs to be done in the same 4 spots every time, all on the same horizontal plane, so there's really no need for a fancy (read: $$$) articulated robot. A servo X/Y motion will get me to the 4 positions, and allow horizontal motion during the welding process. What I'm not sure about is the vertical motion (moving the gun to the material). Can I just move down to a preset location every time, or do I need to go with a servo to allow me to vary the distance of the welding gun to the material? If I need to vary the distance, what dictates the distance? Or, do I need to be able to stop at some position, start welding, then move slightly closer?

Also, any thoughts on how to automatically ground the plate being welded? These are 12" x 48" x 1/4" thick raw steel plates that will be moved from station to station via a walking beam.



-Eric

 

[JeffKiper]

Eric I would use a air cyl. to lower the weld head to the plate. How do you plan to rotate the weld head to catch all for side or it on the corners only.

The grounding is easy. You have seen Warner magnetic clutch and brakes right. Use the magnet housing to complete he path. Once inplace turn on the 90 VDC on the coil and you have 1 heck of a magnetinc ground clamp. Look in any welding supply magazine and you will see the magnet with a 3/8" stud on a magnet.

 

[jstolaruk]

yeah, servo would be overkill. But as far as the grounding we've always clamped the part down on to a copper rest pad connected directly to the welder's return wire and keep it as short as possible; your weld quality will impacted by the quality of the ground. And, yes, the copper rest pad does become a part that has to replaced every so often. Also, if you got other wires nearby (prox & such) and if you can't shield them completely, there are weld splatter resistance wires you can get; the weld splatter will find any exposed wire. Just stuff I've learned from experience.

 

[Eric Nelson]

Thanks for the info, guys. I was thinking along the lines of a magnet for the ground, but it could also be an air actuated clamp. Is this a commercial item, or do I just 'roll my own' as usual?

I'm now wondering if I really even need servo for the X/Y motion. See the attached picture of the actual piece we need to weld. It's a thin aluminum plate, about 4" x 4", with their logo stamped into it (I scribbled out the logo). The 4 corners are chamfered. This gets welded onto the BACK side of the steel plate, and the logo is visible from the front through a cutout in the plate. It's really just 4 little tack welds, so do you guys think I even HAVE to move horizontally while welding? If that's the case, I could just use air cylinders instead of servo actuators and really cut the cost!...

I plan to shroud the gun, so hopefully splatter shouldn't be too much of an issue.



-Eric

 

[TimWilborne]

Don't see any reason you couldn't use air cylinders to do the whole thing...

I did something similar once. Lots of problems with weld splatter on the tip. Jstolaruk has much more experience at this than me but we found that angling the gun so it wasn't perpendicular with the welding surface reduced the weld splatter problem

 

[jstolaruk]

Yes, being able to change the gun's angle relative to the work piece can be handy.

And thanks, but seriously I call in the weld equipment guys and pick their brain as much as I can. I have a friend that has a bachelor's degree in welding, that's how much there is to this stuff.

 

[SkullZipper]

Miller electric own a company called Jetline you should check them out for ideas. I have used their pneumatic operated MIG/TIG positioners and they work fine for what you want to do.

 

[leitmotif]

We were recently asked to quote building a machine to automatically spot weld a nameplate to a part. It's currently done by hand, and our customer just wants to automate this boring task. I have no issues with getting the parts transferred and positioned correctly in the system, but I have a question about the MIG welding. The only welding I've ever done was stick, and that was back in the 80s...

Every part is identical, and the welding needs to be done in the same 4 spots every time, all on the same horizontal plane, so there's really no need for a fancy (read: $$$) articulated robot. A servo X/Y motion will get me to the 4 positions, and allow horizontal motion during the welding process. What I'm not sure about is the vertical motion (moving the gun to the material). Can I just move down to a preset location every time, or do I need to go with a servo to allow me to vary the distance of the welding gun to the material? If I need to vary the distance, what dictates the distance? Or, do I need to be able to stop at some position, start welding, then move slightly closer?

Also, any thoughts on how to automatically ground the plate being welded? These are 12" x 48" x 1/4" thick raw steel plates that will be moved from station to station via a walking beam.

-Eric

Eric
I think you should try a little manual MIG welding first. The main reason for this recommendation is to see that the wire feed does not always stop in the same position. Granted you will be new to this and the wire will not always be the same length sticking out because you do not release feed / current switch at the same time every time. Good controls on the weld process may be able to ensure this problem is overcome.

I think this is a perfect application for spot welding.

Another good method would be automated TIG - but in that case you must have good fitup. With good fitup TIG would give a real pretty product.

Regardless what weld process you do I think the major issues are how to position the plate and the nameplate in the same position and orientation every time. The other issue is how to clamp such that you dont weld your clamps AND your material handling equipment - ground path has to be completely independent of any moving equipment - welding thru bearings wrecks em pretty quick.

Dan Bentler

 

[Eric Nelson]

Thanks to everyone for the info so far!... :site:

Dan - This customer has a limited budget (seems they ALL do... ), so he really wants to use his existing Miller welder. In this application, a 'pretty' weld is not needed. The welds are completely hidden from view after installation. Heck, this part doesn't even get painted! As long as HE doesn't have to weld it, and the nameplate doesn't fall off during normal use, he'll be thrilled...

They currently clamp the nameplate down with a with "+" shaped hold-down on a Destaco clamp, leaving the corners wide open. This works well, so I plan to duplicate this, but with a pneumatic Destaco instead.

Locating the plate and precisely positioning the nameplate is 'old hat' for us. It's just the welding portion that I'm a little wary about. I'll have to try my hand at a little TIG to see what I can glean from the experience...

Thanks as always!



-Eric