WO2002078930A1

WO2002078930A1 - Device and method for injection moulding plastic parts having differences in thickness

Info

Publication number: WO2002078930A1
Application number: PCT/EP2002/003225
Authority: WO
Inventors: Bernd Klotz; Edmund Theiss
Original assignee: Krauss-Maffei Kunststofftechnik Gmbh
Priority date: 2001-03-30
Filing date: 2002-03-22
Publication date: 2002-10-10
Also published as: DE10115647A1; DE10115647B4

Abstract

The invention relates to a device for producing plastic moulded parts (13) having a cuneiform cross-section. According to the invention, a mould clamping element (3) can be tilted in relation to another mould clamping element (7) in such a way that material losses resulting from different thicknesses can be compensated for in one injection compression moulding process.

Description

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the thinner side of the partial cross section cools and is therefore hard.

The known injection molding is therefore only of limited suitability for the production of molded plastic parts with large differences in thickness, for example with a wedge cross section or gradations. This problem is particularly critical when plastic molded parts with large differences in thickness are to be used for optical purposes, for example lighting elements for the backlighting of flat screens, special scattering elements for fluorescent tubes or dimmable interior mirrors for motor vehicles. With some of these plastic molded parts, the surface bears optical elements such as prisms, reflecting surfaces or the like, which cannot be produced in the required quality with the conventional injection stamping technology due to the problems described above.

In contrast, the invention has for its object to provide a device with which plastic parts with large differences in thickness with good surface quality and low internal stresses can be produced; a corresponding procedure is also to be specified.

This object is achieved by a device according to claim 1, a method according to claim 4 and by molding tools according to claims 8 and 9; the dependent claims make advantageous further developments of the invention.

The inventors have recognized that in the case of a molded plastic part with a wedge-shaped cross section or with a stepped cross section made of, for example, thermoplastic, the percentage material shrinkage of the plastic mass is essentially constant, but not the shrinkage as an absolute value. Due to the different thickness dimensions about The partial cross-section results in different vibration dimensions at positions with different thicknesses.

According to the invention it is therefore proposed to form mold clamping elements in a device in such a way that they can be tilted relative to one another, so that the absolute values of the shrinkage are compensated for at the same time and uninspired parts can be produced.

In the closed position of a mold, the mold clamping elements are preferably at an angle other than 0 °, in the case of a wedge-shaped plastic molded part, preferably at the angle predetermined by the wedge of the molded part.

The device according to the invention is particularly simple to implement in that one of the mold clamping elements is mounted in a pivot bearing.

In terms of process engineering, the procedure is in particular such that one tool element of a molding tool is tilted against the other tool element; this preferably takes place towards the end of the casting process, an embossing process preferably being carried out by tilting.

The method according to the invention can also be carried out on a conventional injection molding machine which has, for example, two spaced-apart linear drives for a mold clamping element. For this purpose, the linear drives are operated differently, at least towards the end of the closing process or for carrying out the embossing process, so that the mold clamping element connected to the linear drives is tilted.

A mold is particularly suitable for use in a conventional injection molding machine, in which guides are provided for tilting a mold element against the other.

Basically, it is also possible to design a mold so that tool elements interlock with play, which is designed so that the mold elements can be tilted against each other.

Embodiments of the invention are explained with reference to the accompanying drawings. Show it:

1 is a schematic cross-sectional view of a mold in side view,

Fig. 2 is a schematic representation of two coupled molds in side view and

Fig. 3 is a schematic cross-sectional view in side view of a mold with games.

1, the device according to the invention comprises a movable mold clamping element 3, which carries a first tool element 9, and a fixed mold clamping element 7, which carries a further tool element 5. The movable mold clamping element 3 is mounted in a pivot bearing 11 with respect to the fixed mold clamping element 7 and can be pivoted in the direction of the arrow P.

The device shown is used to produce a wedge-shaped plastic molded part 13. In this case, the pivot point 15 of the pivot bearing 11 is preferably defined by the wedge angle of the plastic molded part to be produced.

Fig. 2 shows a structure with two symmetrically arranged devices according to the invention. cn P ^* er er ^ d P α? s! hi et <J er Φ N ^ cn HP α P σ rt ^ iQ P I- ¹ N et er N

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the, as indicated by the dashed position in Fig. 3.

If a large play is not desired or is not possible, the side walls of the molding tool and / or the mold clamping elements can alternatively be designed as guides which permit a corresponding pivoting movement of the elements. Such a guide is shown, for example, in FIG. 1 on the mold clamping element 7 as a curved guide 16, on which the tool element 9 is guided during the tilting movement.

The symmetrical structure of the shaping devices shown in FIG. 2 represents a preferred embodiment, since here, because of the symmetrical structure, the force is introduced into the device in the center and not, as in FIG. 1, to the side of the center line. The structure shown in FIG. 2 thus introduces no asymmetry with regard to the balance of forces and is therefore also suitable for use in otherwise conventionally constructed machines.

Claims

New claims

1. Device with a first mold clamping element (3) and a second mold clamping element (7), at least one of the mold clamping elements being movable relative to the other for closing or opening a mold (5, 9) that forms a cavity, and at least the movable one Mold clamping element (3) is designed to be tiltable relative to the other mold clamping element (7), characterized in that the cavity is designed to produce plastic molded parts with larger differences in thickness.

2. Device according to claim 1, characterized in that the mold clamping elements are plate-shaped and form an angle different from 0 ° with one another in the closed position of the mold.

3. Device according to claim 1 or 2, characterized g e k e n n z e i c h n e t that the movable mold clamping element is mounted in a pivot bearing (11).

4. The method with a mold from at least two tool elements (5, 9), wherein at least one tool element (9) is moved to open or close the mold and when the mold is closed, the tool elements are tilted against each other, characterized in that it is used for manufacturing of plastic molded parts with larger differences in thickness is suitable.

5. The method according to claim 4, characterized in that the tool elements are only tilted towards the end of the closing process.

6. The method according to claim 4 or 5, characterized in that an embossing operation is carried out on the plastic molded part (13) by tilting.

7. A method for operating a plastic molding machine with two mold clamping elements, one of which is movable via at least two parallel linear drives for opening or closing a mold, and one operates the linear drives with different feeds at least towards the end of the closing process, characterized in that Manufactures molded plastic parts with larger differences in thickness.

8. Forming tool with at least two tool elements (5,

9), which can be closed to form a mold cavity, and have guides (16) for tilting one tool element against the other, thereby ensuring that the mold cavity is designed to produce plastic molded parts with greater differences in thickness.

9. Molding tool for the production of plastic moldings with at least two tool elements which can be closed to form a mold cavity, characterized in that the tool elements (20, 21) engage in the closed position with play (S), which is dimensioned such that the tool elements can be tilted towards each other.

10. Device according to one of claims 1 to 3, g e k e n n z e i c h n e t, through guides (16) for tilting the movable mold clamping element.