By the welding of plastic material, said plastic material is placed between a welding electrode (9) of a profile and pattern mating the welding to be performed, and a counter electrode (10) comprising one or several pulse heating wires (22). Together the pulse heating wires cover the pattern of the welding electrode (9) and project preferably a short distance beyond said welding electrode. The pulse heating wires are furthermore mutually and outwardly electrically insulated. A separating tape of a higher melting point than the plastic material has been inserted between the pulse heating wires (22) and the plastic material. The used welding press comprises a welding plane with the welding electrode (9) and a fixing plane (32) for the counter electrode (10). The temperature of the welding electrode (9) can be kept constant and within a temperature range of approximately 20 DEG C to approximately 250 DEG C. The fixing plane (32) is non-heated. The pulse heating wires (22) are secured to the fixing plane and are mutually and outwardly electrically insulated. Each pulse heating wire (22) communicates with a current source and an electronic regulator capable of setting and regulating the temperature and heating period of each pulse heating wire (22) very accurately.