Abstract
This document relates to a molding tool for forming and back-injecting a bendable sheet including a mold that includes a first mold half and a second mold half. The first half is arranged opposite the second half forming a cavity for receiving the bendable sheet and a melt. Further, the mold includes at least one pin for holding the bendable sheet and the pin is retractable in response to a force exerted on the pin by a pressure of the injected melt during back injection.
Claims
1. A molding tool for forming and back-injecting a bendable sheet comprising: a mold, comprising a first mold half and a second mold half, wherein the first mold half is arranged opposite the second mold half forming a cavity for receiving the bendable sheet and a melt; and at least one pin for holding the bendable sheet against the second mold half, wherein the at least one pin is elastically mounted to or in the first mold half and points towards the second mold half; and wherein the at least one pin is retractable into the first mold half in response to a force exerted on the at least one pin by a pressure of the injected melt during back injecting the bendable sheet; and wherein the at least one pin includes a tiltably mounted head.
2. The molding tool of claim 1, wherein the molding tool comprises at least three retractable pins.
3. The molding tool of claim 1, wherein at least one retractable pin comprises a spring.
4. The molding tool of claim 3, wherein at least one of a spring compression force of the spring is inferior to the force exerted on the retractable pin by the injected melt and a spring compression force is superior to a force needed to form the bendable sheet.
5. The molding tool of claim 1, wherein the at least one pin comprises a suction pad for holding the bendable sheet.
6. The molding tool of claim 1, wherein the tiltably mounted head is connected with a ball joint or a cylindrical joint.
7. The molding tool of claim 1, wherein a top of the at least one pin is divided into sections, wherein at least one section is flat and at least another section is cut at an angle.
8. The molding tool of claim 1, wherein the melt is a plastic material.
9. The molding tool of claim 1, wherein the material of the bendable sheet comprises glass, metal, wood or plastic.
10. A method for forming and back-injecting a bendable sheet using a molding tool comprising the steps of: providing the molding tool; providing a bendable sheet with a frontside and a backside; inserting the bendable sheet into a cavity between a first half of a mold and a second half of the mold; closing the mold for bending the bendable sheet, wherein at least one pin is maintaining the sheet and is at least partially retracted during the closing process; holding the sheet in shape; injecting a melt under pressure on the backside of the bent sheet, wherein the at least one pin is retracted due to a force exerted on the at least one pin by the injected melt and wherein the at least one pin includes a tiltably mounted head; and curing the melt.
11. The method of claim 10, wherein the at least one pin comprises a spring with a compression force, wherein at least one of the force exerted on the at least one pin by the injected melt is superior to the compression force and the spring compression force is superior to a force needed to form the bendable sheet.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Exemplary embodiments will be described in conjunction with the following figures.
(2) FIG. 1 shows a perspective view of a first half of a molding tool with extended pins, according to embodiments of the disclosure,
(3) FIG. 2 shows a side view of the first half of the molding tool, according to embodiments of the disclosure,
(4) FIG. 3 shows a perspective view of the first half of the molding tool with retracted pins, according to embodiments of the disclosure,
(5) FIG. 4(a) shows a schematic view of the pin comprising a spring, according to embodiments of the disclosure,
(6) FIG. 4(b) shows a schematic top view of a head of the pin, according to embodiments of the disclosure,
(7) FIG. 5(a) shows a schematic sectional view of the closed molding tool with the extended pin during an injection process, according to embodiments of the disclosure,
(8) FIG. 5(b) shows a schematic sectional view of the closed molding tool with the completely retracted pin during an injection process, according to embodiments of the disclosure,
(9) FIG. 6(a) to show a schematic sectional view of the molding tool during a
(10) FIG. 6(c) bending process, according to embodiments of the disclosure,
(11) FIG. 7(a) shows a perspective view of an extended pin, according to embodiments of the disclosure,
(12) FIG. 7(b) shows a schematic view of the extended pin, according to embodiments of the disclosure.
DETAILED DESCRIPTION
(13) FIG. 1 shows a first mold half 1 of a molding tool for forming and back-injecting a bendable sheet. The first mold half 1 comprises bores 2 for accommodating retractable pins, as an example one of the pins is denoted with the reference sign 3. The pins 3 are shown in an extended position and point towards the second half of the mold (the second half of the mold is not shown). The first half of the mold 1 further comprises an opening for injecting a melt for back-injecting the bendable sheet. However, this opening is not shown in FIG. 1. The pins 3 comprise a tiltably mounted head 5 connected with a ball joint. However, in embodiments, the head 5 may be connected with a cylindrical joint. The head 5 comprises a low friction surface at its upper surface 6. Thus, a back-injected bent sheet comprising a layer of cured melt may be easily removed after a bending and back-injecting process. Corresponding features are denoted using the same reference signs in FIG. 2 and the following figures.
(14) In FIG. 2 the first mold half 1 is shown in a side view. The pins 3 are extended such that the pins can hold a bendable flat sheet. When the molding tool is open and the first and a second half of the mold have a maximum distance between each other, the pins 3 are extended in the shown position.
(15) FIG. 3 shows the first mold half 1 with retracted pins 3. The pins 3 are completely embedded into the bores such that they do not protrude beyond the surface of the first mold half 1. During a closing phase of the mold, the sheet is bent (the bending process is described in more detail below). After the bending process, a melt is injected under pressure for back-injecting the bent sheet. Thereby, the melt displaces the pins by exerting a force on the pins. Therefore, the embedded position of the pins 3 shown in FIG. 3 corresponds to a closed position of the mold and after back-injecting the bent sheet. To enable a retraction of the pins 3, the pins 3 are mounted on a spring. However, in embodiments the pins 3 may be mounted elastically in a different way, for example by using an elastic material.
(16) FIG. 4(a) illustrates a pin 3 comprising a head 5 and a spring 7. The head 5 of the pin 3 has a low friction surface, wherein the surface is divided into 2 sections 8, 9. Further, the surface of the pin is of a heat-resistant material, for example PTFE. The material of the different sections may differ from each other. The first section 8 is cut at an angle of 20 degrees. The section second 9 is flat. Thus, a retracting process of the pin 3 due to the injected melt may be improved. The melt can apply a pressure onto the angled section 8 while the flat section 9 may stay in contact with the bent sheet. The flat section 9 may have another shape that fits better to the shape of the bendable sheet after bending. Due to the pressure applied on the first section, the spring 7 can be compressed and the pin may be retracted, losing the contact with the bent sheet. The melt may pass the head of the pin covering the bent sheet.
(17) FIG. 4(b) shows a top view of the head 5 of the pin 3. The first section 8 is cut at the mentioned angle and the second section 9 is flat. This head 5 of the pin 3 comprises two sections 8, 9 each forming a semicircle. However, in embodiments the head 5 may comprise at least one of more sections cut at different angles and having other shapes. The head may have a spheric shape or any shape that allows the force provided by the melt front to be, at least partly, transferred into the retraction direction of the pin. In FIG. 4(b) the diameter of the head 5 of the pin 3 amounts to 10 mm. However, the heads 5 of the pins 3 may have other diameters. A diameter of a bore 2 matches the diameter of the pins head 5, such that the pins 3 are retractable. A gap between the pins 3 and the surface 4 of the first mold half 1 may be sealed, such that melt may not enter the bore when the pins 3 are retracted and the melt is injected.
(18) FIG. 5(a) shows a closed mold 10 comprising the first mold half 1 and the second mold half 11 when a melt 12 is injected. The melt is a polypropylene. The bendable sheet 13 is arranged between the mold halves and the pins 3 maintain the bent sheet 11. More in particular, the sheet is positoned against the second mold half. Therefore, the pin 3 is partly extended and the head 5 of the pin 3 protrudes at least partially beyond the surface 4 of the first mold half 1. The arrow 14 shows the flow direction of the melt. The inclined surface of the pin is directed towards the melt front.
(19) FIG. 5(b) shows a schematic snapshot of an injection process, after the melt has displaced the pin 3. The pin 3 is retracted due to a force exerted on the surface of the head 5 of the pin 3 by the melt 12. The force compresses the spring 7 and the pin 3 is pressed into the bore 2 of the first mold half 1. In embodiments, an injection pressure amounts to 800 bars.
(20) The example of mold 10 shown in the FIGS. 1 and 3 comprises twenty-eight pins 3 with a diameter of the head 5 of 10 mm.
(21) FIGS. 6(a), 6(b) and 6(c) show snapshots of a bending process of a bendable sheet 13 with the molding tool. In FIG. 6(a) the molding tool is opened and the pins 3 are extended. A bendable sheet 13 is positioned between the first half 1 of the mold and the second half 11 of the mold. The pins 3 maintain the bendable sheet 13. In this example, the bendable sheet is a glass sheet. In the example shown, the thickness of the bendable sheet 13 is 0.8 mm. However, in embodiments, the bendable sheet 13 can have another thickness.
(22) FIG. 6(b) shows a mold-closing step during the bending process, in which the pins 3 hold in position the glass sheet. The second half 11 of the mold moves toward the first half 1 of the mold. Thereby, the second mold half 11 applies at least locally a pressure to the bendable sheet 13. Where the pressure is too high, the retractable pins 3 can retract at least partly to avoid a damage of the bendable sheet because of local stresses. Further, the pins 3 comprise tiltably mounted heads 5, such that they are able to hold the sheet in position even though it is no longer in a flat shape.
(23) FIG. 6(c) shows a closed position of the molding tool, when the bending process is finished. The bendable sheet 13 is bent and adapted its shape to the shape of the mold. Between the first half 1 and the second half 11 of the mold is still a cavity for injecting the melt. The pins 3 are at least partially protruding beyond the surface of the first half 1 of the mold to hold the bent sheet 13 in shape. In another step the melt 12 will be injected into the cavity 15 to back-inject the bent sheet 13 (as described in FIGS. 5(a) and 5(b)).
(24) If the gravitational force in the FIGS. 6(a), 6(b) and 6(c) is in the direction from the second mold half to the first mold half than the sheet may be solely supported by the pins. In other geometries, for example when the gravitational force is directed from the first mold half to the second mold half, additional support for the sheet is needed. Such additional support may be an edge of the second mold half. In a geometry where the gravitational force is in a direction parallel to the sheet, additional clamping of the sheet may be foreseen, for example suction pads or clamps in the head of the pins.
(25) FIGS. 7(a) and 7(b) illustrate an extended pin 3 in a perspective view and a schematic view. The pin comprises a tiltably mounted head 5 that is connected with a cylindrical joint 16. An upper surface 6 of the shown pin 3 only comprises one section that is angled with respect to the melt flow direction. A bore 2 comprises a diameter that complies with the diameter of the head 5. Therefore, the pin 3 is completely embeddable into the mold half 1. A tiltably mounted head may improve the application of the sheet to the second mold half.
