GMAW welding using ShopBot

[ron_cleaver]

Has anyone tried mounting a GMAW (aka MIG) welding gun on a ShopBot? It seems a perfect application because you can control the path of the gun and the height. You would just need a way to start and stop the gun (maybe by just raising the gun for some modes).

[gerald_d]

Ron, we do a lot of MIG welding in my full-time job and have considered using a SB type machine to drag the torch. But I discarded the idea quite early. The torch must be rotated quite a lot during a typical weld job and a special rotator needs be designed/constructed/programmed.

If you only want to do straight weld runs, then there are simple little "tractors" commercially available.

For any weld run, a good manual operator doesn't keep a constant speed during the run. At the start the speed is slow while the job pre-heats. Once the job is hot, the speed is increased. If the two plates are of unequal thickness then the gun is slightly twisted or "weaved" to get both to the same heat, judged by redness color. If the plates don't fit exactly (and they seldom do, because they distort during the weld) then the gun is slowed down to fill gaps. At the end of the weld run, the gun is slowed, sometimes even reversed slightly.

Commercially available welding robots are only used for very high volume runs and a lot of scrap is produced while the settings are optimised. It is quite simple to program a commercial robot because you can move their torches by hand to tell the robot where it must work. They learn by example - something that the SB will not do.

[ron_cleaver]

Gerald,

I understand that ShopBot is working on a fourth axis that would allow rotation. And the speed could be changed easily if there's an algorithm for it, based on a variety of parameters some of which you mentioned.

[gerald_d]

Ron, there is another factor in all this. The most efficient (and neatest) MIG welds are normally run about 45 degrees downhill. The tables for MIG robots are also controlled in about 2 axes so that the job is rotated into the most ideal position.

It's just my gut feel that the SB is just a little too far away from a weld robot - but then again we only pay around $3 per hour for human MIG operators here.

[ron_cleaver]

Gerald,

Maybe automated GMAW welding is cheap there too but not here.

I've seen bid specs that require robot welding for repeatability and weld quality. For a large quantity of the same welds, I would think ShopBot would be a winner if the details can be worked out.

[gerald_d]

Ron, the automated MIG welding that I have experience of, is in Germany, where I spend a lot of time. Here in South Africa the labour is too cheap, and the volumes too low, to use widespread automation. (except for some specialised applications)

Another factor, which actually makes the use of a SB easier, is the fact that the pro robots use a slightly flexible head. The robot pushes the copper gas shield against the job and sort of spring loads it. The rubbing gas shield (shroud) gives the exact location of the feedwire.

[gerald_d]

Here is a typical welding robot (http://www.piel.co.uk/robots/vr006c.htm). Notice all the features and axes of movement - plus the "teach" control.

[ron_cleaver]

Maybe someone from ShopBot could indicate the feasibility of this. The Panasonic robot seems to have some AI software with it, and if that's a requirement, then making it work might be a lot more difficult.

Also, I don't know when the fourth axis will be available. I couldn't find any mention of it on the ShopBot Web site.