the invention disclosed hereunder is a process and a device for the preparation and formation of a plastic weld connection between a workpiece and a second component to be attached thereto by heating by means of a heating device . if force is applied , the heating element tends to deform the contact surface especially in the case of hollow , thin - walled workpieces such as plastic containers . so far , methods were disclosed for the measuring of the degree of deformation by means of a sensor , subsequently readjusting the position of the heating device according to the determined deformation . the invention disclosed here under dispenses with any measurement of deformation , instead using an elastic element which automatically readjusts the position of the heating element in the case of deformation of the workpiece to effect a pre - load between the heating device positioned at the contact surface of the work - piece and the workpiece .