A special-purpose welder to weld railway car wall elements allows the welding of flat metal sheet, e.g. a railway car wall of 6000x1000mm maximum dimensions, various types of strengthening, spacing and carrying supports. Intended for the welding with previously tacked elements, the unit, fixed with manual clamps to the slide, makes a longitudinal travel, whereas the welder moves perpendicularly to the bench.

The workplace comprises:
• Three-phase D.C. spot welder type ZP4PS
• Bench with rollers to arrange and move the elements being welded
• Slide to locate, clamp and move the unit being welded
• Control cubicle with a control system to control the travel magnitude of the welder and of the slide with the elements being welded
• Water-cooling unit (option)
• System of fences and optical barriers to protect the workplace operation.

The three-phase D.C welder type ZP4PS allows the welding of heavily weldable materials, such as some grades of alloy steels, brass and aluminum. The welder is adapted to move using its trolley system. Greaseless hold-down systems are fastened to the welder outrigger arms. The top hold-down is designed to exert the necessary pressure on the elements being welded during the spot welding, on the hand, the bottom hold-down system is intended to transfer the pressure force produced by the top hold-down system onto the body.
The magnitude of the compressed-air pressure needed to reach the required pressure force is set on the welding process control system and adjusted by a proportional valve. The run of the welding process is controlled via a microprocessor control system. During the flow of the welding current there exists a capacity to change the pressure of electrodes. The welding current switch-on and switch-off follows with a thyristor contactor. The welder is provided with a transformer/diode unit with three transformers and a set of rectifying diodes.
The thyristor contactors, the transformer/diode unit, secondary circuit elements and electrode plugs are water-cooled. The flow of water via the thyristor contactors and the transformer/diode unit is protected with signalling devices that lock the current flow in case of a small quantity of water in the circuits. Servomotors are installed in the drive system of the bench slide and the longitudinal travel of the welder, whereas absolute encoders are fitted to control the speed and position of the bench slide and welder arm. The whole travel and positioning process is controlled from a PLC controller type Simatic-S7. The communication with operators follows via the software installed on a PC that plays the role of a visualizing and reporting station. The inverters, PLC controller and the PC are installed in the control cubicle directly at the workplace. Program sets to define the coordinates of individual welding spots as well as welding processes are read into the operator station, e.g. from a diskette, and over there, they are memorized in the data basis. There is a capacity to supply input data on the distribution of welding spots in the form of a DxF format file. The choice of the proper wall to be welded follows on specifying the name or type under which it will be written into the data basis. The control of the welding process parameter follows directly from the PC.
The system can operate in two modes:
Manual mode, when the control of the movements of the bench and the welder follows through the manual initiation by the operators from the control desk, or automatically, in the event when the control of the movements of the bench and the welder occurs automatically according to the set algorithm. The machine comprises two identical benches: a feeding bench and a receiving bench. Each of the benches is equipped with a set of rollers to move the elements being welded.
On one side of the bench there is a movable slide that is used to arrange the elements prepared for the performance of the welding operation, and to move them. The slide is provided with a special structure adapted to catch hold of elements being welded. The travel of the slide and of the welder is performed by servo-drives.