TIG (GTAW)Tig welding can be split into three categories, AC, DC+ and DC- depending on the polarity of the tungsten/work material. Some metals/alloys have an affinity for oxygen causing a thin layer of oxygen to form a film on the surface. While this film is what protects stainless/aluminium/titanium from rust/oxidization is has a very detrimental effect on the weld-ability**. AC welding while having a lower heat output and a less stable arc has the advantage of constantly changing the direction the electrons are flowing*. Cycling the polarity causes the oxygen film to break up exposing the metal.
AC welding is the preferred method for all aluminium alloys while DC- is recomended for Stainless and Titanium. DC+ is only used for thin sections where arc stability is an issue.
We bought our Lincoln Idealarc 300/300 from ebay for 809$ US, the same guy sold us a watercooler for 250$. Total cost with shipping and taxes came to 170.000isk (2800$ US). Although this is an older transformer based machine***, it has AC and DC capabilities up to 375Amps, High Frequency start****, watercooled torch and can be operated in stick mode. This is sufficient to weld just about any thickness of any metal around, but there is a 350kg (770lb) penalty to pay :D
There is a difference in the setup used in the Americas vs. Europe/Asia for TIG welding, the foot pedal seems to dominate the americas for current control while the rest of the world uses a torch with built-in current control and trigger. As a result we modified our US manufactured torch to include a current control but this proved to be a bad idea. We plan to replace the torch/leads with a Binzel torch with unified rubber leads, current control and a better trigger location. Tig Welding Videos
*Electricity is created by electrons moving from one terminal(pole/pin) to the other terminal(pole/pin)l. DC electricity is when these electrons flow one way, from the negative terminal to the positive terminal. AC electricity is when the terminals alternate the flow of electrons (one terminal becomes positive, the other negative and they then they switch), the number of time this happens is called cycles or hertz. In North America the AC electric grid uses 60 cycles/hertz per second, in Europe it cycles 50 times every second.
** Aluminum is the most affected due to the fact that aluminum oxide has a melting point of 1926 °C (3499 °F, 2199 °K) while pure aluminum melts at 660 °C (1220 °F,933 °K)
*** New welding machines are almost exclusively based on inverter technology rather than transformer technology. Transformers are huge ironcored spools which drop or raise AC volrage with very little loss. Inverters change the AC current into DC before dropping the voltage with more loss but they are much smaller resulting in less weight and cost. When inverters offer AC welding it is often called Square Wave, this is because the electricity has to be changed back into AC but it is impossible to recreate a perfect wave form. This is actually preferred over regular synewave AC because it allows more heat to be generated with less current.
**** Air conducts electricity poorly in a gas state but when it is superheated into plasma it becomes a superconductor and breaks Ohm's law (the more current it conducts the less the resistance is). Higher voltage causes less resistance and is therefor more likely to use poor conductors such as air.
20.000 volts are superimposed on the circuit to initiate an arc from the tungsten to the work piece. When using AC this is done for every cycle since the arc breaks down when the polarity is changed.
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