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Main Forums => The Roundtable => Topic started by: Nick1911 on June 09, 2008, 09:17:32 AM

Title: TIG technical welding question
Post by: Nick1911 on June 09, 2008, 09:17:32 AM

When one wants to join aluminum with TIG, AC is used instead of DC.  What frequency range of AC is used?  Is it just 60HZ crackling away?  Would a higher frequency (saw 40kHZ) be usable for TIG welding current?

Thanks!

 

Title: Re: TIG technical welding question
Post by: never_retreat on June 09, 2008, 09:24:29 AM

I'm not sure what the frequency actually is but is fairly high. It can interfere with cable tv signals.
Someone else will chime it with cable tv freq. Most likely.
What are you trying to do?

Title: Re: TIG technical welding question
Post by: Nick1911 on June 09, 2008, 09:33:10 AM

I believe that RF interference might be because of the "high frequency, high voltage" circuit used for starting the arc without having to scratch-start.  I'm aware that this can range up to and beyond 1Mhz, but that's not the welding current AC supply.

Basically, I'm looking into the possibility of hardware hacking a DC-only inverter machine to run AC out.  After pouring over the schematics for a while, I've determined that it would be very easy to get AC out of it, but the inverter circuit I'd pull from runs at 40kHz.  These higher frequencies drastically reduce the transformer sizes needed in the machines, which makes them lighter and smaller.

Title: Re: TIG technical welding question
Post by: French G. on June 09, 2008, 06:36:36 PM

I wish I could tell you but I have no weld books at home with me. It's not 60hz, the "high frequency" setting must be used when welding aluminum or you will never get a stable arc, I believe it is because the air gap does not stay ionized.

Title: Re: TIG technical welding question
Post by: Nick1911 on June 10, 2008, 04:27:29 AM

Alright, for those interested in the thread; I've found my answer.  Old, linear style power supplies ran at 60Hz, but also imposed a high frequency, high-voltage, low current wave on the same wire.  This is the "high-frequency" circuit.  It kept the argon gap ionized, which gives it low resistance.  Once that's happens, the source puts a low voltage, high current, low frequency current across the gap, which heats the metals.

In a typical welder, you might see the HF circuit running 1Mhz, 5000 volts, 15ma.  The "skin effect" that occurs at these higher frequencies makes this high voltage fairly non-dangerous to humans.  Once the arc is established, welding current can flow through it.  Typical welding current would be more like 15vac, 60Hz, 110 Amps.

Inverter style machine typically run the AC output at more like 100Hz.

Title: Re: TIG technical welding question
Post by: zahc on June 10, 2008, 05:56:11 AM

interesting.