Resistance welding, the first instance of resistance welding dates back to 1856, when James Joule, the man behind the Joule heating principle, managed to fuse and weld a bundle of copper wires by electric resistance heating.
The first resistance welding machines were used for butt welding. Elihu Thomson, in the USA, made the first welding transformer in 1886 and patented the process the following year.
His transformer produced an output of 2000A at 2V open circuit voltage. Thomson later developed machines for spot welding, seam welding, projection welding and flash butt welding.
Spot welding later became the most common method of resistance welding and is, today, extensively used in the automotive industry and many other sheet metal applications. The first robots for resistance spot welding were delivered by Unimation to General Motors in 1964.
By Klas Weman, ESAB Welding Equipment AB, Laxå, Sweden.
Thomsons resistance welding transformer
Resistance Welding Benefits
- High speed welding
- Suitable for high rate production
- Easily automated
- Low energy consumption
- No consumables
MEDIUM FREQUENCY DIRECT CURRENT WELDING Ordinary welders use a single-phase welding transformer that supplies alternate welding current; the welding current is adjusted by the thyristors by means of the phase-shift technique. This new technology employs an inverter supplied by the three-phase mains. Inside the inverter the current is rectified, filtered by the capacitors and transformed by an IGBT bridge into alternate current at medium frequency (1000Hz). It is used a specific welding transformer equipped with a rectifier that supplies direct welding current.
ADVANTTAGES PROVIDED BY MEDIUM FREQUENCY WELDING
Current is affected neither by dimensions of the secondary circuit nor by the ferrous material inside the secondary circuit itself nor by the variations of the mains voltage. The welding current is supplied continuously and constantly. The fusion area heats up in a more homogeneous way improving the quality obtained. Constant and accurate welding current. The adjustment in milliseconds allows the best welding time set-up. Welding time reduction that allows an increase in productivity. Reduction of the used welding current. The electrodes lifetime is longer and a less required maintenance allows a better productivity. This effect is particularly emphasized on aluminum and galvanized sheets spot welding. Improved weldability of unlike and highly conductive materials. Aesthetically improved results due to a minor deformation of the piece to be welded and to a reduced electrode indentation. Reduced possibility that material spatters during the welding process. High speed of welding currant rise. Allows to weld the materials more easily and to solve problems of difficult welding. Reduced electric consumption. Reduced current absorption, balanced on the tree phases. Reduced installation costs and improved power factor (cos). Therefore, the inverter technology involves a remarkable improvement of the welding quality, an extreme precision of the welding time and current, a higher productivity and a reduction in costs.