Method for manufacturing a composite work piece for a drug delivery device, comprising the steps: A) providing a first work piece part and a second work piece part, B) arranging both work piece parts (1, 2) with respect to each other in such a way that both work piece parts (1, 2) are in mechanical contact with one another in a contact area, wherein the first work piece part and the second work piece part are held in mechanical contact with each other in the contact area by an elastic force which is exerted by one of the work piece parts on the other one of the work piece parts on account of an elastic deformation, C) irradiating a surface of the first work piece part with electromagnetic radiation, thereby softening the first work piece part and/or the second work piece part in a region adjacent to the contact area, and D) joining the first work piece part to the second work piece part in the contact area for the composite work piece, wherein for the first work piece part a part is used which is impervious for the electromagnetic radiation of step C) and absorbs the electromagnetic radiation of step C) to an extent sufficient for softening the first work piece part and/or the second work piece part, wherein the method is characterized by one of: - wherein in step B) the second work piece part is introduced at least partly into the first work piece part, whereby the work piece parts (1, 2) are brought in mechanical contact with one another in the contact area, or - wherein in step B) the first work piece part is introduced at least partly into the second work piece part, whereby the work piece parts (1, 2) are brought in mechanical contact with one another in the contact area and wherein in step C) the electromagnetic irradiation is emitted from a hollow space inside the first work piece part, the electromagnetic radiation being directed essentially radially outward. A) providing a first work piece part and a second work piece part, B) arranging both work piece parts (1, 2) with respect to each other in such a way that both work piece parts (1, 2) are in mechanical contact with one another in a contact area, wherein the first work piece part and the second work piece part are held in mechanical contact with each other in the contact area by an elastic force which is exerted by one of the work piece parts on the other one of the work piece parts on account of an elastic deformation, C) irradiating a surface of the first work piece part with electromagnetic radiation, thereby softening the first work piece part and/or the second work piece part in a region adjacent to the contact area, and D) joining the first work piece part to the second work piece part in the contact area for the composite work piece, - wherein in step B) the second work piece part is introduced at least partly into the first work piece part, whereby the work piece parts (1, 2) are brought in mechanical contact with one another in the contact area, or - wherein in step B) the first work piece part is introduced at least partly into the second work piece part, whereby the work piece parts (1, 2) are brought in mechanical contact with one another in the contact area and wherein in step C) the electromagnetic irradiation is emitted from a hollow space inside the first work piece part, the electromagnetic radiation being directed essentially radially outward.