All welding power sources have two kinds of HF Welding., static characteristic and dynamic characteristic. The static output characteristic can be easily established by measuring the steady-state output voltage and current by conventional method of loading by variable resistors. Thus, a curve showing the output current versus output voltage for a given power source constitutes its static characteristic. The dynamic characteristic of an arc welding power source is determined by recording the transient variations occurring over a short intervals in the welding current and the arc voltage. Thus, it describes instantaneous variations occurring over a short interval of time say a millisecond. Arc stability is determined by the combined interaction of the static and dynamic colt ampere (V-I) characteristics of the welding machine power source. The intrinsic transient nature of a welding arc is the main reason for great importance of the dynamic characteristics of an arc welding power source. Most welding arcs have continuously changing conditions which are mainly associated with striking of the arc, metal transfer from the electrode to the weld pool, and arc extinction and reignition during each half cycle of ac welding. The transient nature of the welding arc is also due to variation in arc length, arc temperature and electron emission characteristic of the cathode. The rate of change of voltage and current in arc welding machine is so fast that the static volt-ampere characteristic of a power source can hardly be of any significance in predicting the dynamic characteristic of a welding arc. However, it is only the static volt-ampere characteristics of a welding power source which are supplied by the manufacturer. Through they cannot give the nature of behaviour of the power source regarding its dynamic response but they are of considerable importance in determining the general overall response in controlling the process parameters. Wanna learn how to TIG weld aluminum? First you need a decent TIG welding machine. Not a great one, just a decent one. Already got one? You might have an old Synrowave 300 or a DialArc, an old Hobart CyberTIG or you might have a brand new Miller Dynasty 350. Know what? It doesn't really matter. The same principles apply. If you have an old as dirt TIG welding machine, you can still make good aluminum TIG welds. Weld beads that look like a stack of dimes. First lets look at machine settings: Set the polarity to A/c (alternating currrent) Make sure to set the high frequency to continuous Set the amperage to about one and one half amps per one thousandths of inch of thickness. (up to about 250 amps then things change quite a bit) Set both the contactor and amperage switches to the remote positon. Set the argon or argon/helium torch shielding gas to around 15 cfh. (if you are using a #7 cup) less if the cup is smaller. Notice I said argon or argon/helium? Argon is not the only game in town. In fact, if you TIG weld any aluminum over about .063" thick, adding helium to the mix makes a huge difference. Now lets talk tungsten electrodes 2% thoriated have received a lot of bad press for the radioactivity issue but they do work. 2% lanthanated electrodes are a really good all purpose electrode...good for TIG welding aluminum as well as steel. Use the smallest electrode that will get the job done without quivering at max amperage. Remote amperage control...you need a foot pedal. Period.
