Abstract: The application relates to a method for producing a moulded part assembly from a first plastic moulded part and a second plastic moulded part by means of laser welding, wherein the first plastic moulded part consists at least partially of a first material and the second plastic moulded part consists at least partially of a second material that can be welded to the first material, wherein a welding region of the second plastic moulded part is arranged in a stepped receiving means of the first plastic moulded part, or vice versa. According to the invention, during the laser welding, the first plastic moulded part and the second plastic moulded part are to be shifted onto one another in a shifting direction. The invention also relates to a production device for producing a moulded part assembly.