Machsupport Forum
General CNC Chat => Show"N"Tell ( What you have made with your CNC machine.) => Topic started by: tesart on May 24, 2009, 10:03:14 AM
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Has anybody here used their plasma table for an automatic welder? I have a bunch of 1/4"aluminum plates to weld up and keep thinking about using my table. Any suggestions would be great!
Thanks
Tom
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I have mounted a mig gun to a bridgeport table, and used the power feed to travel. It worked just dandy. I would not want to do the same on my cnc machine, however. I would be to worried that all that current would fry something in the electronics, but that's just me being overcautious I suppose.
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For automated welding the first hurdle is keeping your parts accurate enough. Humans can account for misfit parts, machines can't. The next task is properly fixturing the parts. Automation won't change the basic properties of the type of welding you are doing; if you couldn't weld vertically with the material/filler that you are using when welding it by hand automation won't change that.
For seaming there are two basic type of fixturing. One uses a continuous series of fingers on each side of the seam that hold the material down and in registration with each other. You close one set of fingers, run one plate up against them to square it, and then close the other set on top the inserted plate to hold it in place. Next you open the first set of fingers and push the second plate up to the edge of the first and then close the fingers on top of it. This should give you a pretty straight seam but some tracking adjustments might need to be made depending on length. Many times this is done manually with a joystick, etc.
The second basic type is used for situations where the seams are less perfectly aligned. It uses some sort of seam tracking to keep the torch on track. Seam tracking devices can vary from laser tracking, to mechanical probes to through arc seam tracking (with specialized equipment.)
To control the welding process you will need to at least sense that you have established and maintained an arc (similar to plasma cutting). Some newer welding power supplies will have an output for this. If you don't have one you can use a current sensing relay. You will probably also want to have better control of the gas flow if your going to do it a lot. That way you can turn the gas on a second or two before starting to weld (pre-flow) and keep it on several seconds after the weld (post-flow). Fancy welding controllers will also let you set different current profiles for starting and finishing the weld.
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Thanks, The parts are all water jet cut so fit up is good. My thought was to just use stops on each panel and some hold down clamps. The G code would be very simple, just point to point at a set speed and the starting/stopping of the torch would just be by hand. A pretty crude setup I know but there are only 60 or so welds each 6 feet long. If I can do it and end up with less cleanup in the end I think it might be worth it.
Thanks Again for the responces and I'll post pics if it works ;D
Tom
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Hey I like this topic.
I did this on a few scrap bits of steel. Here look at these pics, pretty good for only one go at it mucking around.
Peter
http://www.learn-how-to-weld.com (http://www.learn-how-to-weld.com)
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That looks good, appears that you got the welding power supply up into spray mode. One nice side effect of welding automation is that is almost impossible to do by hand, like spray transfer on thinning materials. If you add a bit of dwell at the end of the cycle you can reduce the crater/low spot caused when welding and motion stop together.
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Looks great Apples! I'll be doing my samples next week. its 1/4 inch aluminum 6 feet long, do you think I should tack it first by hand or just go for it? Well clamped?
Tom
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Tack and clamp as much as possible. That is sort of the cardinal rule when welding anyway.
Put it this way. There is a machine called a "beam welding machine". Basically it welds 3 bits of flat steel together to make them into an I beam. This particular machine is being used for welding the chassis rails for low loader truck trailers ( to put heavy bulldozers etc on). And on this machine they use rollers with hydraulic rams pushing and clamping it all the steel together. Then there is a welding machine either side of the plates of steel and away it goes.
There must be some serious clamping forces there with those hydraulics.
But yeah, heat makes metal expand and get bigger and warping and twisting is very common.
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Did some tests and they look pretty good. Will be doing the actual parts next week.
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It's working great! here is some pics of of the set up. I'm useing 3/64 wire with a travel speed of 70 ipms. Tacks and welds both "legs" in 1 min!!
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Are you inspecting your welds by sawing a sample piece in half so you can see the profile? You need to insure that the penitration and HAZ is proper? It is very easy to make a really nice looking but complelty useless bead with an automated welder.
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Yes I have and am getting good penetration. I have read that you set these up(real ones anyways). is there any data on feed rates? I just guessed until I got it right. It seems as thou you could up the wire speed in proportion to travel speed... is this right?
Thanks
Tom
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I used to do automated welding/cutting. For the last seven years I have been building test and automation equipment for a local university.
You can find a starting point by using a welding 'calculator' like Miller Electric Part # 086446 . It is slide rule type device that will give you a good starting point with a given material thickness, wire, gas, etc. There are so many combinations of base materials, wire, etc that it takes some experimentation to get it right. You might also be able to find some more info on MIller's website: http://www.millerwelds.com/education/articles/articles10.html.
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This is a photo of the seam welding rig we use. It is basically little more than a cannibalised MIG set with the wire feed and torch put on a motorised, track-riding carriage. Welding current and control signals are fed to it via an umbillical cable which is supported along a clothesline over the track. It's seriously dumb and ugly.
(http://qpreflectors.com/DSCF0874.JPG)
All it does is ride along at a fixed speed, with the current and wire speed constant. All settings are adjustable of course, but there's really nothing clever about it. It is designed to weld up to 4m in one shot, for making spinning blanks for satellite communications "dish" antennas, which usually means we're welding 1050 soft sheet with 1050 filler wire, real chewy stuff.
The clamping jaws have copper bars in them for chilling the weld and preventing distortion, and there's a copper plate with a channel under the weld line so that the molten bead can flow down.
Penetration is 100%, weld quality is excellent and distortion is negligible - For starting and stopping, we just do it on a bit of scrap at each end, lead in and lead out.
I'm sure a half-decent CNC rig could do a very nice job of welding - use the coolant trigger for gas, and you can control pre and post flow, dwell to build up weld at start and finish, and if your welder won't accept a digital input you could do worse than stick a small stepper on the current knob and call it an axis... set your wire feed up controlled by Mach3 as a spindle... More than one way to skin a cat, and I reckon there's real potential here.