Some constructions need spot welds fullfilment which is a problem when such constructions cannot be inserted to service zone of spot resistance welding machines because of specific constructions configuration, their big dimensions or unusual location. That is why this problem is still relevant now (please, see - Tkachenko A.N. and Voskresensky A.S. "Applications of the arc spot welding on fabrication of car bodies", "Paton Welding Journal", N.12, 2005, p.22-23).

As it is written in the article "Plasma-Punktscweissen..." ("Technica" - Suisse - 2003, 52, N.23, 52-57), plasma spot welding provides for: a suitable access to the place that has to be welded, the stability of process, a high quality of the goods surfaces and welded spots, low costs of equipment and of its exploitation, possibilities to assemble parcels consisting of 3 and more sheets. It may be added that plasma spot welding permits to produce thin details connections without loading them by noticeable pressing forces. It is not seldom possible to find such parameters of spot plasma welding that allows to do this process without the spot sign at the outer side of the last detail, as opposed to the plasma torch.

At the begining of our professional career (please, see our author rubric) we had devoted special attention to arc spot welding. Later we turned to spot plasma welding (please, see (47) of our previous site

We developed equipment and technology of spot plasma welding which were aimed, first of all, at goods made of stainless steel 0,5 - 2,5 mm thick. At the beginning we used our blocked plasma set. Later we added to it a control block, including relays of time, contact breakers, ballast resistances, gas and water valves, and this set became a spot plasma welder . A standard rectifier for manual welding was used as a base-convential welding set. It was complemented by plasma torch, simple above mentioned block, as well as by blocks of communication and of pilot arc, which provide supply by gases, water, pilot arc current and also provide time control of shielding gas switching on and off and changing of the welding current. The logic of these parts of spot welder work is that, firstly, we have to supply it by water and argon, then switch on a shielding gas, and later - switch on the welding current, reduce and switch it off. Obviously, shielding gas, argon and water have to be switched off in the inverse sequence.

According to requirements for spot welds, as shielding gas may be used CO2, nitrogen, helium, argon or mixtures of argon with hydrogen or with helium.

The main principle of spot plasma welding is: first - melting of a detail that is most close to plasma torch, then - melting of a more remote detail or details with making a common welding pool-puddle, which, after rather slow cooling of gathered liquid metal becomes a spot weld. Because of constant pilot arc burning (usually it is 5-8 A), the process is highly stable.Welding current has to be usually 40-180A, and it changes step by step - in order to avoid crater arise in spot weld. Time it takes to weld one spot ranges from one small fraction of a second upto a few seconds. It takes much longer than during contact spot welding. On the other hand, the energy expenses are 2-3 times lower then during contact - resistance welding. This process is mainly used when welding various goods with complex form structures, such as boxes that contain regidity ribs, screens and other supplementary elements.Examples of them could be radiators, plate heat exchangers, fuel cans, metal furniture, washing machines, different vehicles, boats, etc. Usually plasma spots have nice appearance - much better than after contact welding , because they have not the typical places of connected details local deepening - and they do not require cleaning after welding.

Sometimes, when using spot welds, we have an oppotunity to eleminate small surface cracks. It is possible to add an additional material in order to carry out welding, brazing processes or their different combinations. For these purposes the special automatical plasma torch has been developed.

That is why the Spot Plasma welder may be very useful for manufacturing and repairing many precision structures, different tools, scientific instruments, military goods, etc., which need single side spots fulfillment or interrupted welds producing.

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