Tig welding machine

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BY ROSARIO CASANUEVA, FRANCISCO J. AZCONDO, F R A N C I S C O J . D´A Z , & I ˜ CHRISTIAN BRANAS

PHOTO COURTESY OF U.S. NAVY

A

MULTIPLE TWO-PHASE resonant converter module connected in parallel is the chosen architecture for a

tungsten inert gas (TIG) welding power supply. Connection to the utility is performed through a frontend power factor correction stage. Fine tuning is performedby overlapping the control signals of the resonant converter phases. Output ripple is reduced by interleaving each module, and the arc strike is achieved with no extra circuitry and at low voltage. DC and multiple pulsating operations from 20 Hz to 5 kHz with different pulse widths have been tested. The resulting arc stability, welding parameters, and efficiency are analyzed in this article. Theexperimental results show the welding performance and near unity power factor.
IEEE INDUSTRY APPLICATIONS MAGAZINE  SEPT j OCT 2011  WWW.IEEE.ORG/IAS

A design for multiple two-phase resonant converter modules
Digital Object Identifier 10.1109/MIAS.2010.939654 Date of publication: 5 July 2011

53
1077-2618/11/$26.00©2011 IEEE

IEEE INDUSTRY APPLICATIONS MAGAZINE  SEPT j OCT 2011 WWW.IEEE.ORG/IAS

TIG or GTAW Welding TIG or gas-tungsten-arc welding (GTAW) is a widely used high-quality, high-precision welding process. In TIG welding (Figure 1), an arc is established between a nonconsumable tungsten electrode and the metal that is heated and melted. Filler wire may be added for the weld. The inert gas: 1) shields the welding area from the air, preventing oxidation, 2)transfers heat from the electrode to metal, and 3) helps to start and maintain a stable arc (due to the low ionization potential). This process can be used for many types of materials in all welding positions, and it provides a concentrated, stable arc and a high-quality and neat weld deposit. Before the arc is initiated, the electrode is too cold to emit electrons to establish the arc. Any of thefollowing three methods can be used to start the arc: 1) touching the electrodes together and then separating them, 2) applying a high-voltage pulse, or 3) high-voltage, high-frequency (HF) ac pulses [1]–[3]. In TIG welding, dc, pulsed dc, or ac power supply is used [4]–[12]. DC current sources provide constant polarity current, resulting in high arc stability. Pulsed power supplies provide currentpulses between two current levels: a maximum current value, enough to melt the base material, and a background current level, sufficient to maintain a stable arc. The duration of the current pulses can be changed to weld different thicknesses of the same material, and the current levels are set for each material [13]. AC power supplies provide a combination of negative and positive current at bothpolarities, which are suitable for welding aluminum or its alloys. Auxiliary arc starters are commonly added to the power source to supply the high-voltage or HF, high-voltage ac pulses (2 kV, 1 MHz) across the weld terminals, and their operation can be seen in [3], [14]. Arc-welding machines are potential sources of harmonics as the nonlinear behavior of the process and the use of pulsed supplieslead to unwanted frequencies superimposed on the supply voltage. To improve the input behavior and power factor, active power rectifiers are used. Resonant converters have applications in the control of discharges including arc welding [15]–[17]. These converters are known for their advantages such as HF dc-to-dc power supplies, which in turn result in small size, lightweight, and high-efficiencysystems. These converters can be operated to achieve zero voltage and/or zero current

switching, which results in minimum switching losses. The HF operation minimizes the size of magnetic components. This article proposes a design of multiple two-phase resonant converter modules connected in parallel operating at a constant switching frequency to generate a highly flexible power supply for...
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