Direct current resistance welding machine circuit - for difficult aero- and space applications, using controlled alternating current ripple

摘要

The machine uses a 50 Hz mains supply and three single-phase transformers delta-connected on their prim. sides and the sec. windings connected in 3-phase 1/2-wave with intermediate-phase choke; or in 3 phase-star or -delta; or in a 3-6-phase circuit. In each case a residual ripple is obtd. on the welding electrodes with an amplitude of 4% of the average current and 300 hz. The circuit has three opposed pairs of electronic valves for controlling the prim. sides, and rectifiers in the branches of the sec. windings arranged for complete dynamic balancing. The circuit permits the use of welding times down to one-sixth of a cycle and also a welding wave with rising, constant, or falling current for controlled preheating and/or cooling or for a second heating cycle. The machine is useful for welding heat-resistant and stainless steels where the thickness ratio is 20:1, hitherto a very difficult problem when using e.g. US RENE 41 or other Ni or Co alloys.