Guide rail, device and method for the injection moulding of this rail
A guide rail made from an injected plastic material includes at least one portion having the shape of a tubular profile longitudinally split over at least one portion of the length. The guide rail is configured to be straight or curved in the shape of an arc of a circle.
1. A method of injection moulding of a guide rail of a guide shoe fastened to a sliding window of a motor vehicle door, the guide rail having no draft angles, wherein the guide rail is made from an injected plastic material, wherein the guide rail comprises at least one portion having a shape of a tubular profile, which has a recess over the entire length of the tubular profile and which is provided over at least one portion of the length of the tubular profile with a longitudinal slot and wherein the tubular profile is curved in a shape of an arc of a circle, the arc of a circle being inscribed in a plane, so that an outer surface of the tubular profile has a concave longitudinal zone, an opposite convex longitudinal zone and two opposite lateral longitudinal zones, with each lateral longitudinal zone extending from the concave longitudinal zone to the opposite convex longitudinal zone, and wherein the longitudinal slot extends along one of the two opposite lateral longitudinal zones or along the concave longitudinal zone, wherein the method comprises the steps of:
providing an injection moulding device comprising:
a mould comprising a male portion and a female portion together delimiting a moulding cavity the shape of which corresponds to that of a contour of the guide rail to be moulded, the guide rail to be moulded having no draft angles, comprising at least one portion having a shape of a tubular profile, which has a recess over an entire length of the tubular profile and which is provided over at least one portion of the length of the tubular profile with a longitudinal slot, the tubular profile being curved in a shape of an arc of a circle, the arc of a circle being inscribed in a plane, so that an outer surface of the tubular profile has a concave longitudinal zone, an opposite convex longitudinal zone and two opposite lateral longitudinal zones, with each lateral longitudinal zone extending from the concave longitudinal zone to the opposite convex longitudinal zone, and the longitudinal slot extending along one of the two opposite lateral longitudinal zones or along the concave longitudinal zone,
the female portion of the mould comprising at least two parts, the moulding cavity comprising a moulding cell with two ends, the shape of which corresponds to that of the at least one portion of the guide rail having the shape of the tubular profile,
the male portion of the mould comprising at least one core for the formation of the recess of the guide rail and an intermediate part for the formation of the longitudinal slot of the guide rail, the core being curved in the shape of an arc of a circle inscribed in a plane,
a device for injecting under pressure inside the moulding cavity, plastic material configured to manufacture the guide rail, and
an extraction device for extracting the at least one core of the male portion outside the moulding cell of the mould, the extraction device being configured to displace the core from one of the two ends of the moulding cell in a trajectory of an arc of a circle of the same radius as a radius of the arc of a circle of the core in order to extract the core from one of the two ends of the moulding cell,
injecting at least one plastic material under pressure inside the moulding cavity of the mould of the injection moulding device,
hardening the at least one plastic material,
actuating the extraction device to slide the male portion of the mould outside the female portion of the mould to extract the male portion from the female portion; and
separating the at least two parts of the female portion of the mould to unmould the guide rail thus obtained.
2. The method of injection moulding according to claim 1 , wherein an outer surface of the core of the male portion of the mould has a concave longitudinal zone, an opposite convex longitudinal zone and two opposite lateral longitudinal zones, with each lateral longitudinal zone of the core extending from the concave longitudinal zone of the core to the opposite convex longitudinal zone of the core and wherein either the concave longitudinal zone of the core, or one of the two opposite lateral longitudinal zones of the core extends outwards and over at least one portion of the length of the core by the intermediate part.
3. The method of injection moulding according to claim 1 , wherein the recess of the guide rail has a shape of a portion of a torus with a circular cross-section and wherein the core of the male portion of the mould has a shape of a cross-section circular torus the diameter of which corresponds to the inner diameter of the recess of the profile of the guide rail to be moulded.
4. The method of injection moulding according to claim 1 , wherein the tubular profile of the guide rail has a radius of curvature comprised between 300 mm and infinity.
5. The method of injection moulding according to claim 1 , wherein the tubular profile of the guide rail comprises at least one longitudinal wing extending from the outer surface of the tubular profile to form a single piece with the tubular profile and wherein the moulding cavity comprises portions used to form the at least one longitudinal wing of the guide rail.
6. The method of injection moulding according to claim 1 , wherein the at least one plastic material is one composite material.
7. The method of injection moulding according to claim 1 , wherein the at least one plastic material is chosen among polypropylene, polyoxymethylene, acrylonitrile butadiene styrene, acrylonitrile butadiene styrene/polycarbonate, poly methyl methacrylate, acrylonitrile styrene acrylate, or styrene acrylonitrile.
8. The method of injection moulding according to claim 1 , wherein the male portion of the mould further comprises a cooperation part which cooperate with the extraction device, the core extending outwards and over at least one portion of its length by the intermediate part of the formation of the slot of the guide rail, the thickness of the intermediate part corresponding to the thickness of the guide rail to be obtained.
9. The method of injection moulding according to claim 8 , wherein the cooperation part comprises a rack with teeth, wherein the extraction device comprises a pinion driven in rotation by a displacement device, the pinion meshing with the teeth of the rack, to displace the rack, and jointly the core of the male portion of the mould, so that the core exits from the moulding cell.
10. The method of injection moulding according to claim 9 , wherein the rack with teeth is in a shape of an arc of a circle, wherein the pinion is disposed in such a way that the axis of rotation of the pinion is parallel to a central axis of the circle of the core in the shape of an arc of a circle of the male portion of the mould and wherein the pinion meshes with the teeth of the rack in such a way as to displace the rack and jointly the core in a trajectory in the shape of an arc of a circle of the same radius as the radius of the arc of the circle of the core that joins the central axis of the circle of the core to the centre of the cross-section of the core, in such a way as to cause the core to exit outside the moulding cell.