The present invention relates to a method and a device for producing a multi-part plastic product. The device possesses first means for the provision of a first plastic part, second means (for the production of a second plastic part and third means for the connection of the two plastic parts. The device according to the invention is characterized in that the third means contain a heating unit for heating the first plastic part to a defined temperature, and in that the heating unit has an actuating element, by means of which the defined temperature can be set in such a way that a thermal shrinkage of the first plastic part during cooling is equal to an ageing shrinkage of the second plastic part.