Electronics > Projects, Designs, and Technical Stuff
tig microwelder feasible?
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LaserSteve:
The reason the spark start is used is to get a high enough surface temperature on one side of the arc to form a cathode spot and obtain electron emission.  A very high  Dc start voltage  generally does not provide enough Di/Dt to get a cathode spot and ionize enough air to get a  self confining arc going.

So one of the big expenses and more difficult design problems is to keep the start pulse or start HF out of the current regulating electronics.  I spent many an evening designing DC coupled low pass filters and protection circuits for this  task.

Steve

coppercone2:
how come the HF is better at doing that? Because of the skin effect?

I thought it was just to make a conductive path.. from what you are saying its actually to kinda heat some point on the surface to be welded like a induction heater? Not saying you are wrong its just non intuitive for me, I only ever used mig/stick for electric welding.

What exactly is happening? The only reason I can think of why HF would work here is because it would not penetrate as much so it would make metal vapor on the surface that would aid in plasma conduction? (since you don't want to vaporize the electrode).

In that case would it be good to negative bias the HF so that the ions are drawn towards the electrode too?
LaserSteve:
A few systems we have at  work use a low current and a retracting sharp pin. A few tens of mA are flowing into the future weld area and the pin is pulled back by a very well controlled linear solenoid.

A few microseconds after the sense current starts declining, a IGBT fires and dumps in the ignite spark,  the inert gas pulses in, then a second IGBT dumps capacitor one into the weld probe, then the main regulated weld current is gated in. Used mainly in pulsed welders for jewelry and thermocouples and test sample wire bonding. The timing is incredibly tricky.

Steve
 
LaserSteve:
Yes, you need a glowing orange to white hot emission spot in TIG, ion and electron bombardment do the heating, as well as localized resistance heating.

Steve
coppercone2:
Would you say the start HF does a job with more ideality (less heating that negatively effects the bond area)? The way you put it sounds like either way could possibly work if you time it right or figure out a way to protect the current source.

Do you have things like filters which get shorted out electronically (slow) compared to the instantaous response of the filter, kind of like shorting out a inrush limiter in a power supply? Or is HF prefered because you can filter it out easily (easy of electrical control implementation), rather then any physical process control reason?
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