GB1411196A - Electrical resistance welding apparatus - Google Patents

Abstract

1411196 Dental pillars etc ORALTECHNIC ANSTALT 21 March 1973 [22 March 1972 (2)] 13575/73 Heading A5R [Also in Division B3] Apparatus for resistance welding comprises a welding tool, two variable transformers connected to a condenser and a cyclic switching arrangement to produce charging of the condenser to a first weld charge from the first variable transformer followed by discharge of the condenser through the tool to provide a preliminary weld pulse and charging of the condenser from the second transformer to a second weld charge followed by discharge of the condenser through the tool to provide a second weld pulse of greater energy than the first one. The invention is particularly related to welding pins, studs or wires of high melting point metals such as tantalum or titanium in dental or orthodontic work e.g. where pins or studs of these metals fixed in the maxillary bones are welded in situ to form supporting pillars for tooth grafts. The first, lower intensity pulse provides an improved contact between the parts to be be welded capable of carrying the subsequent higher intensity pulse so that arcing and excessive heating in the patients mouth are avoided. A suitable tool, Fig 6, for effecting the welds comprises a scissors-form tongs carrying welding electrodes 51, 52. A detent mechanism 54 . . . . 57 serves to lock the electrodes in the pressure applying welding position. In a circuit Fig 5 for generating two successive pulses of the required intensities motor driven cams 12, 13 control the operation of relays 26, 30, 28, 33 so that a capacitor 37 is charged to a first power level from variable transformer 17, is then discharged through a transformer 35 the secondary of which is connected to the welding tool thereby providing the first weld pulse; capacitor 37 is then charged to a second power level from variable transformer 18 and discharged the second time through transformer 35 to provide the second weld pulse.