In a lamp such as a rear combination lamp for a motor vehicle, which has auxiliary lamps each with a plurality of functions, the lens fitted to the front opening of the lamp body is formed by integrally molding differently colored resin lens members corresponding to the respective auxiliary lamps. The composite lens described above has been formed generally through a molding process called multi-color molding. In this process, one lens member is molded using a predetermined color resin in a die, and then another lens member is further molded with a different color resin in another die while the first molded lens member is set therein. The lens obtained is a composite lens formed by combining one lens member with another.
The resin molding process first performed is referred to as "pre-molding," and the resin molding process performed next is referred to as "post-molding." A composite lens for a rear combination lamp is formed by integrating a red lens for a tail & stop lamp and a white (clear) lens for a backup lamp. For manufacturing this composite lens, the white lens is first formed in the pre-molding process and the red lens is formed with the pre-molded white lens in the post-molding process. Each of the pre-molded lens (the white lens) and the post-molded lens (the red lens) has projection ribs, projecting from the lens surface along the boundary where the respective lens members are bonded at their respective sides to integrate the members tightly.
In forming a composite lens, an upper movable die and a lower pre-molding die are used for molding a pre-molded lens, and the same upper movable die and a lower post-molding die are used for molding a post-molded lens.
The molding of the pre-molded lens is accomplished by bringing the movable die into contact with the pre-molding die. The formed pre-molded lens is separated from the pre-molding die while being held in the movable die. Then, the movable die is brought into contact with the post-molding die to mold the post-molded lens next to the pre-molded lens.
However, a problem often occurs during the separation process of the movable die from the lower pre-molding die after the pre-molded lens is formed. Because the protection rib of the pre-molded lens contacts the pre-molding die so tightly due to frictional forces, the pre-molded lens remains with the pre-molding die rather than being separated with the movable die. When this happens, the subsequent process cannot be performed, and the formation of a high quality composite lens is prevented.