Butt and flash welding
Two further variants of resistance pressure welding besides the well-known resistance spot and resistance projection welding are pressure butt welding and flash butt welding. These two lesser-known processes are used frequently, especially in the wire and chain industry and in rail welding. In these welding processes, the two joining partners are pressed directly onto each other and a current is then applied. The component shortening is compensated by means of feed. The welding power results from the contact force of the workpieces pressed together and the resulting contact resistance.
The welding time is determined by the carriage speed and the travel of the machine. With the help of these two welding methods, very large cross-sections can be joined. As a rule, butt welding applications range up to approx. 2000 qmm. The cross-sections to be welded go beyond this when flash welding. For chains, cross-sections up to approx. 14000 qmm are welded. In the field of pipeline welding, there are even applications up to 40000 qmm.
In pressure butt welding, the workpieces are pressed together and heated by the current flow until the required temperature is reached. This is done via set current and pressure values or also path-controlled pressure and / or current programmes, mostly current drop or rise. An upsetting is realised at the end of the welding.
In the flash welding process, the material is preheated via a reversing process so that the entire surface is heated evenly. In reversing mode, the workpieces briefly open and close in a programmed manner with different current settings. In the subsequent pure burn-off, the components are moved towards each other with lower speed and force. This results in the welding of the components. Depending on the application, it is then compressed and reheated.
You can find out more about these interesting and quite complex welding processes in DVS leaflets 2901 Part 1 and 2, in the book Resistance Pressure Welding by Mr. Krause and, of course, from your Harms & Wende partner.