Stitch mig welding

[cyber_drifter]

I have a cheap mig welder that I would like to fit a stitch welding control, to weld thin metal. Expensive mig welders already have this function, but unfortunately I can't afford that amount of money. Anyway, seeing that the welder is controlled by a relay, i thought it might be possible to use either continuous controls, using a ADC and a pic, or a couple of 555 timers for switched settings. Just wondering if anyone as done anything like this already?

Thank's,
Tom

[solutions]

What does the control do to turn a continuous weld into a stitch weld?

[FTL]

Can you explain more about what algorithm the automated stitching welder follows?

I also have a cheap MIG welder and regularly manually stitch thin (almost rusted through) auto body metal. I like the manual control in that I can tell when the metal is about to burn though so it is time to let it cool a bit and when it is cool enough to start again. With partially rusted metal the thickness and heat sinking capabilities of the metal are very inconsistent, so a simple cycling algorithm might not work well.

I would think it would be a bit strange to have the welder suddenly start up again after a second or two of being off. If you've moved the torch a bit it would start welding in a different place.

I can think of one feature that might be useful over manual stitching: You could keep the gas on while the arc power and wire feed is off. That way the shielding gas would help cool the weld and keep it un-corroded for when you start welding again.

One idea I can think of is: Could you put some sort of radiant heat sensor near the end of the torch? That way it might be able to use intelligent feedback to determine when to kill the arc and when to re-start it.

[gan_canny]

A dozen years ago I got a stitch attachment for a stick welder from an auto repair magazine advertisement. It replaces the regular stick holder. It consists of a solenoid that vibrates retracting the rod from the weld pool at a few hertz and breaking the arc. For MIG probably the same needs to be done. The wire would need to be reversed withdrawing it from the pool and then quickly reinserting it. The shielding gas would not be stopped. The weld pool needs to cool to prevent burn through on thin sheet metal. Breaking the arc without stopping the wire feed and withdrawing the wire probably causes the MIG wire to stick to the joint. Then again a thick copper backing plate (assuming you can get behind the joint) can help support the weld and withdraw heat. Also welding short distances ( long tacks) alternatively filling in until the full joint is made can help.

[bbarney]

It should be easy enough on a Mig welder but an arc welder would be easier to buy the attachment
The wire feed motor is usally 24VDC  the relay turns the wire on and off when you pull the trigger so using a pic should be possible
keeping it simple put your best Led Blinky program in the pic to run the relay  - 2 led blinky if you need to reverse the motor  
here's a link I found for a wire feed circuit for a mig welder to give you an idea of the wire feed circuit, it will be a little more complicated than the blinky led but it's the general idea, the stitch is the same as you repeatly pulling the trigger on and off you will still have to set the wire feed and heat  setting's manually unless you want to really make thing's complicated


http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=8&sqi=2&ved=0CHgQFjAH&url=http%3A%2F%2Fwww.astrosa.com%2Fn03%2Fspeed-control.pdf&ei=mkUJUMvsCOb00gG5wpHRAw&usg=AFQjCNEid2918xvmOkpFdixw-a86dTW9yQ&sig2=EYvpGjI9OuBIQoBq1I3L8w

[cyber_drifter]

Thank you for your replies. I'm not very good at expressing myself in what I'm trying to do, so here is a video of that a stitch function is about. You could just press the trigger, like most people do, but this seems like a nice project to get my teeth into.

http://www.youtube.com/watch?v=z3p1UTHndso

Thanks,
Tom