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Straight answers to the questions people ask most when choosing and using DC TIG welders for steel, stainless and other metals.
A DC TIG welder is the right tool for steel, stainless steel, copper and copper alloys, nickel alloys and titanium. It gives a stable, quiet arc and very clean welds when the metal and gas coverage are right.It cannot properly weld aluminium or magnesium alloys. Those need alternating current to break up the oxide skin on the surface. If you expect to weld aluminium now or in future, choose an AC/DC machine instead. For stainless, mild steel and thin-walled tube, DC is the usual choice.
High frequency start ignites the arc without touching the tungsten to the workpiece, so there is no risk of contaminating the tip. It is usual on workshop machines. The high frequency can interfere with nearby electronics, so follow the manufacturer's installation advice.Lift-arc start has you touch the tungsten to the work and lift away, and the machine starts the arc with low current. It avoids high frequency interference and is common on compact site machines. It works well with a little practice and clean material.
For DC TIG the torch is normally connected to the negative terminal, with the earth lead on the positive. Most of the heat then goes into the work rather than the tungsten, which gives good penetration and a long tungsten life.Connecting the torch to the positive terminal overheats the tungsten very quickly and can ruin it. Follow the manual, check the terminal connections every time you change leads, and confirm the polarity if you also use the machine for stick welding, where the polarity depends on the electrode type.
Some DC TIG machines also have a stick mode, which can be useful for site repairs and for thicker or dirtier material. Others do not, so check the specification of the machine you are considering.Where a stick mode is fitted, an electrode holder and work return lead are used in place of the torch, and the machine is switched to its stick setting. The electrode types, sizes, current range and duty cycle that it can handle vary from machine to machine, so read the data plate and manual before choosing electrodes. Do not assume that every electrode type will run well on a machine designed mainly for TIG.
Pulse alternates between a high peak and a lower background current. It gives better control of heat on thin sheet, reduces distortion, and helps with out-of-position and root welds on stainless. Many welders also find it helps them time the filler additions.It is not essential for thick material or for general fabrication where heat is not a concern. Decide based on the kind of work you do most. Pulse needs practice to set well, so start with the manufacturer's guidance and adjust on offcuts.
A gas-cooled torch relies on the shielding gas and air to carry away heat. It is light and simple, and suits lower currents and shorter weld times. A water-cooled torch uses a separate cooling unit, and is the better choice for higher current, long continuous welds and hot ambient conditions.If you notice the torch getting hot to hold, or you need to rest it often, the job probably needs water cooling. Look at the duty cycle at your working current, not only the maximum current.