the invention relates to the automatic welding of plastic parts possessing a built - in winding . in order to carry out an automatic welding operation without risking damaging the parts by subjecting them to an excessive welding temperature , there are regulating means for varying the electrical energy supplied to the winding , in order , during the welding phase , to maintain the temperature of the winding between a minimum temperature , below which welding cannot be carried out , and a maximum temperature , beyond which the parts will be damaged . the invention is used particularly for the production of systems for the distribution of gas under pressure by means of plastic pipelines .