Question regarding DC Drive on welding positioner

Gentlemen,

I have a few welding positioners here that are lacking in the controls department, and I would like to "upgrade" them to allow better speed regulation. I am concerned somewhat about what the interference from the welding process may do to the control that I install. For the first unit, I only have a DC gearmotor being driven from a simple DC drive with a pot. No feedback, nor any way to tell what the commanded speed is. To top it off, the knob is loose on the pot shaft, so even the pointer of the knob is not accurate. Im thinking about a simple DART control with digital display, and I saw one model with a feedback device that would allow me to "see" the actual speed (not closed loop). What I'm not sure of is how well this controller will work in the environment. We do all autogenous (fusion)welding. I just hoped that someone out there had a recommendation about what may work best, or what to watch out for.

Thanks in advance.

Never saw term autogenous welding so looked up. Now that I know it is done without filler I am more curios about what is being welded and what you are using for heat source.

How big is positioner? How much combined weight of weldment and positioner?

IF you are doing complete overhaul my first thought may be to hydraulics. Dont have to worry about dust grindings etc in motors etc. Also if you jam it would not hurt hydraulic motor.

Second thought may be VFD and 3 phase motor.

IF just a minor mod to get existing DC to work better
first thought is what do you want it to do? Just hold a steady speed or be able to vary speed as you weld or ??

Dan Bentler

The material is sanitary grade stainless steel process tubing and components. Most go in food/beverage, liquid systems like paint, or consumer goods like cosmetics, shampoo etc. My main goal is to reduce or eliminate the many variables that we currently have, in favor of a more controlled process, with quatifiable parameters. Currently, I don't really have defined speed (RPM} on this unit, so I wanted to get that out of the way as simply as I can. I don't know that I need closed loop control, maybe (down the road)just a digital display that I could select a speed (maybe even scaled), that can be manually entered according to the weld schedule for that part. I have a pretty good process now, but there are many opportunities there for improvement. Eventually, it would be nice to integrate the positioner to the welder to create a homemande orbital welder. That way I could vary weld parameters in real time based on the position of the weld. The only thing I'm not sure of is what are the possible issues with interference from the welder, and what , if anything can I do to reduce it?
The positioner is about 12" in diameter, and the parts are .25" to 12" diameter, up to about 10 ft. in length. Most parts are not very heavy, they are mostly pipe, tube or some kind of fitting.

Thanks for your response.

So what are you using as heat source - high freq TIG or adaption of it?

I did not do well as food grade stainless weldor - too much penetration and rough pipe interior.

I suppose the starting point is to make a chart of pipe size wall thickness travel speed at a welding voltage and current. Will require a lot of testing and tinkering to get right.

I think the HF will be major problem for filtering.
Assuming you are using transformer rectifier for weld power the transformer itself may not have the HF on primary so you could use primary current for your weld current and use instrument transformer on weld circuit to obtain weld voltage. Maybe CTs on xfmer secondary between transformer and rectifiers will eliminate HF also - not sure.

Dan Bentler

DC will not give you really tight speed control without an encoder but it will be fairly resistant to upset, error, or damage from the welding process. I would use shielded wire for the control inputs but otherwise, the Dart controller and a permanent magnet DC motor should be pretty rugged. You might find that the incoming AC power is just too dirty for the little drive. In that case, buy an isolation transformer for the drive and that problem should go away.

Dan,
The power source is a Miller TIG machine, and that is basically the process. I have weld schedule info. for the differing sizes and thickness materials. The harder part of it, as you seem to know, is to get proper penetration so that both sides of the tube or pipe has a slightly convex bead, so that the weld bead can be remvoed, and then polished out. There is a fine line between too much, and too little heat at the joint, so fit up and arc length (among other things) are critical.

Dick,
Thanks for the info. I think I'll try the dart controller, as the drive motor is a small dayton gearmotor. That at least will move me to the next step.......