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rangerod
11-16-2002, 10:17 PM
What does touch start TIG compared to HF start mean?

chip hayden
11-16-2002, 11:32 PM
hf[high frequency] allows you to initate the arc without touching the workpiece. touch or lift start means the tungsten electrode has to be in contact with the workpiece to start the arc.

Roger
11-16-2002, 11:57 PM
There are places that you shouldn't or can't use HF but lift start or touch start are ok.

Need HF when using square wave TIG for aluminum as tend to lose arc as polarity changes.

rangerod
11-17-2002, 02:26 AM
O.K. If you touch the tungsten to the metal to get the arc started won't there be little pieces of the tungsten left in the metal you are going to weld?

Roger
11-17-2002, 07:14 AM
When not welding a CC welder's output voltage (called open circuit or no load volts) is 50 to 80 Volts. When welding a CC welder's output voltage (closed circuit or operating volts) is 17 to 40 volts. When not welding in lift start mode the welder's output is low voltage low amp trigger current before and while electrode is touched to work. When electrode is lifted from work trigger current flow is interrupted. This interruption of trigger current after slight delay switches welders output to normal CC welder open circuit voltage starting arc while voltage droops under load to closed circuit voltage. Hot start could be involved that would flatten slope of voltage droop during start extending time voltage is near OCV before drooping to CCV.

Lift start because of the slight time delay switching to starting voltage cause tungsten to be away from work when arc is started. The lift start process doesn't blast chunks of tungsten electrode into work causing tungsten inclusions any more than HF starts. Lift start doesn't cause significant contamination that happens when scratch starting.
Lift start/touch start regardless of tm names is different than scratch start and should not be confused.

chip hayden
11-17-2002, 09:17 AM
Roger, I'm not being a smartass, I'm jut trying to think of a situation where you wouldn't want to use hi-freq to initiate the arc.[unless my wife is having a long winded phone conversation!]
chip

Roger
11-17-2002, 02:39 PM
HF start in a hospital or close to some electronics might not be allowed.

rangerod
11-17-2002, 05:08 PM
Thanks Roger. I was getting them both mixed up, I tought they were the same process. Can anyone tell me the difference between touch start & scratch start TIG.

Roger
11-17-2002, 08:45 PM
When you learn arc welding in school you start with stick welding now called SMAW, Shielded Metal Arc welding. You start SMAW arc by gripping electrode holder that holding rod and taping working end of electrode on grounded work (metal to be welded). Quickly raising rod end about rod diameter above work after tap. You should then be holding arc between work and rod end. Repeat until you get desired result. this is called "Tap Start". Often beginners stick rod (tac weld rod) to work trying this start and use higher amp settings to make starts easier.

The other way to start the arc is by scratching rod end onto work ending with rod end about 1 diameter distance above work. This is somewhat like striking a match. Beginners find this "Scratch Start" method easier. More often used when AC welding which is a little harder starting. Beginners also often stick rod to work with this method. Not good to leave starting arc scars all over critical work as they cause stress/weak points.

TIG welds are started about same way but you have foot/hand remote amp control (amptrol) to help control arc.

rangerod
11-17-2002, 11:48 PM
Roger

Thanks for the info. You gave me a good understanding of all these processes. :)