method for treating a plastic part , which comprises a surface , comprising the steps : a ) irradiating at least a part of the surface with a treatment radiation to obtain a modified surface area , the modified surface area being capable of absorbing a heating radiation to an extent greater than the unmodified surface area , and b ) irradiating the modified surface area with the heating radiation at least in a section so that the plastic part is heated and softened in a region defined by the irradiated section of the modified surface area .