EP3174697A2

EP3174697A2 - Mould for manufacturing a component made of plastics material

Info

Publication number: EP3174697A2
Application number: EP15753126.0A
Authority: EP
Inventors: Olivier TORRES; Damien BOISSON
Original assignee: Plastic Omnium SE
Current assignee: Plastic Omnium SE
Priority date: 2014-08-01
Filing date: 2015-07-24
Publication date: 2017-06-07
Also published as: WO2016016559A3; FR3024387B1; FR3024387A1; WO2016016559A2

Abstract

Compression mould (1) for manufacturing a component made of plastics material (MP), comprising a first element (2) and a second element (3), the two elements (2, 3) forming a moulding chamber (4) in the closed position of the mould, characterized in that at least one of the elements (2, 3) is equipped with at least one compression system (5) for the plastics material (MP), said compression system (5) comprising at least one movable compression block (6) that is able to move towards the moulding chamber (4) in order to compress the plastics material (MP) therein.

Description

Mold for the manufacture of plastic parts having an optimized compression system

The present invention relates to the technical field of manufacturing plastic parts, especially automotive body parts, by a compression molding process.

To manufacture plastic parts, it is known to use a compression molding process. Such a method uses molding equipment comprising:

a mold provided with a movable element and a fixed element, the two elements, typically made of steel, forming a molding chamber in the closed position of the mold;

- A press for moving the movable element to the fixed element.

Generally, at least one plastic sheet is placed in the compression mold, typically a "SMC" ("sheet molding compound") composite material consisting of thermosetting resin, reinforcing fibers, and often fillers and / or catalyst (hardener).

Then moving the movable member to the fixed member by means of the press until closing the mold. Finally, a molding pressure is applied to the plastics material.

The production of large components, for example pieces having a projected area greater than 0.5 m ^2, it is necessary to use a powerful press, i.e. a press tonnage. For example, to manufacture a tailgate liner it is customary to use a press having a maximum closing force of the order of

2000 tons.

The press applies a given force which, depending on the projected surface of the part, is felt in pressure in the compressed material.

Such a press is then used as a means of compressing the plastic material, since the latter requires a high pressure (greater than 30 bars) to cause the material to flow into the molding cavity, to polymerize the material ...

To make smaller parts, such as a door reinforcement for example, the pressure in the molding chamber must be much lower. Typically, for these small parts the required pressure is less than 30 bar.

However, such a low pressure can not be finely controlled, or even can not be guaranteed or obtained, with a large tonnage press. Indeed, it is difficult to precisely slave compression cylinders of the press on values much lower than the maximum tonnage. For example, with a press having a maximum closing force of 2500T, it is nevertheless possible to make it work at 500T, but there are then significant force variations around the nominal point at 500T, especially at the beginning of the molding cycle.

As a result, variations (in particular peaks) of high pressures occur within the plastic at the beginning of the compression, during the rise in pressure. These can deteriorate the quality of the room. These pressure peaks do not guarantee a homogeneous pressure during molding.

It is therefore not possible to use a heavy-weight press in combination with a small-piece mold.

It is therefore necessary to associate the mold of the small room, a low power press (low tonnage) to control this low pressure.

However, such a solution is not feasible industrially because of the price and size for the installation of one or more new smaller presses.

In addition, the pressure required to mold the material in the molding chamber, may also depend on the type of material used, not just the size of the piece. Thus, it is possible to mold a large piece in a so-called "low pressure" material or a small piece with a difficult to mold material requiring high pressure.

It is therefore necessary to associate with the workpiece, depending on the material and its surface, a suitable power press for stably controlling the pressure required for molding.

Again, such a solution is not feasible industrially because of the price and space for the installation of one or more new presses less powerful.

The object of the invention is to remedy these drawbacks and to allow the use of the same press for manufacturing plastic parts of all sizes, in particular for making small parts on an "oversized" press, since it was originally intended for produce only large pieces ..

For this purpose, the invention particularly relates to a compression mold for the manufacture of plastic part, comprising a first element (fixed) and a second element (movable), the two elements forming a molding chamber in the closed position of the mold. At least one of the elements is equipped with at least one compression system of the plastic material, the compression system comprising at least one movable compression block capable of moving towards the molding chamber to compress the plastic material therein.

The compression system within one of the elements (fixed or mobile) of the mold, makes it possible to apply a molding pressure on a surface greater than that of the material placed in the mold before compression, in order not to start compressing the material during the closing of the mold, and to avoid that the parameters of implementation degrade the final properties of the material of the piece produced. This lower power system than the press also allows to guarantee a more constant molding pressure, especially without peak overload.

It is thus no longer necessary to use the power of the press to transmit the transformation pressure to the plastic material. Thus, for small parts, depending on the desired pressure, it is possible to use only the compression system integrated in one of the elements. The power of the press is only used to open / close the mold and ensure its sealing plating in the closed position.

Advantageously, the mobile compression block is movably mounted in a wall of at least one of the elements with a piston-type movement, and the mobile compression block has a surface adapted to constitute a molding surface with the plastic material, when the block mobile compression is pushed into the molding chamber of the mold.

According to one embodiment, the mold comprises at least a first compression system implanted in the first element and at least a second compression system implanted in the second element.

According to this embodiment, the two blocks of the two compression systems can be vis-à-vis, and able to apply the same pressure on the plastic, when pushed into the molding chamber.

The two pavers of the two compression systems can be facing each other, and able to simultaneously apply a pressure on the plastic, so as to balance forces on either side of the plastic material in the molding chamber. .

The two blocks can be controlled by at least one moving means, such as a hydraulic cylinder or an electric worm motor.

According to one embodiment, at least one of the elements (2, 3) is adapted to compress the plastic material (MP) in the molding chamber (4).

The invention also relates to a compression molding process in which a mold according to the invention is used.

The invention will be better understood on reading the appended figures, which are provided by way of examples and are in no way limiting, in which:

FIG. 1 schematically shows a mold according to a first embodiment of the invention, in the open position (top), closed (in the middle) and then in the compression phase (at the bottom), this mold being adapted to a molding process by compression.

FIG. 2 schematically shows a mold according to one embodiment of the invention, comprising a single compression system on the side of the fixed element.

FIG. 3 schematically shows a mold according to one embodiment of the invention, comprising two compression systems.

Figure 4 illustrates a mold and an implementation for overmolding an insert.

FIG. 5 illustrates a particular embodiment of the mold according to the invention, in which the mold comprises two compression systems which are not facing each other and which do not have molding surfaces of the same dimensions.

FIG. 6 illustrates a particular embodiment of the mold according to the invention, in which the mold comprises two compression systems facing each other but which do not have molding surfaces of the same size.

Referring now to Figure 1, which shows an example of mold (1) according to the invention, for the manufacture of a plastic part (MP) by means of a compression molding, the mold being in position opened.

The mold (1) comprises a first element (2), fixed, and a second element (3), movable and movable in a closing direction of the mold.

The two elements (2, 3) form a molding chamber (4) when the mold is closed.

The molding chamber (4) is equipped with at least one compression system (5) of the plastics material (MP).

At least one of the elements (2, 3) is equipped with at least one compression system

(5) plastic material (MP).

This compression system (5) comprises at least one mobile compression block

(6) able to move to the molding chamber (4) to compress the plastic material (MP). This moving block (6) thus makes it possible to apply the required pressure to the plastics material present in the molding chamber (4).

Thus, it is the displacement of the mobile compression pad (6) which causes compression of the plastic material (MP), when the mold is in the closed position.

The movable compression pad (6) is movably mounted in the thickness of one or the other of the elements (2, 3) with a piston-like movement. According to the example of Figure 1, the movable compression pad (6) moves (see arrow) in the closing direction of the mold (1).

There is a clearance and possibly an offset of flush between the mobile compression pad (6) and the other steel molding zones (2, 3) interfaced with the movable pad. The person skilled in the art knows how to define the conditions of adjustment of this game and of this outcropping to limit undesired effects, such as, for example, infiltrations of material at the interface between the movable pad and mold elements (2, 3), or an outcropping in the direction of movement of the mold. movable block, between the movable block and the other steel forming zones (2, 3).

The mobile compression block (6) has a surface (7) adapted to constitute a molding surface with the plastic material (MP), when the mobile compression pad (6) is in contact with the plastic material, that is to say say when the keypad is in the compression position.

The compression system (5) comprises displacement means (8) for the movable compression pad (6). It can be a mechanical means, such as a hydraulic cylinder connected to the mobile compression pad (6) by a rod, or an electric worm motor.

Such a compression system makes it possible to finely manage the pressure applied to the plastic material. Indeed the local management at the mold of the movement of the block is more accurate than the overall level of the press (item 3 according to the example of Figure 1).

According to one embodiment (Figure 2), the mold is adapted to apply a pressure on either side of the plastic material (on the side of the movable element and the side of the fixed element).

Thus, as illustrated in Figure 2, the movable element (3) of the mold can also be used to compress the plastic material (MP) in the molding chamber (4), on the side of the element (3) movable . The other side of the plastic material (MP) being pressed by the compression system (5). This configuration offers the advantage of providing a more homogeneous pressure in the plastics material (MP), whether the molding is large or small. Indeed, the pressure experienced by the plastic material on its lower and upper surfaces is directly transmitted to them, unlike a conventional mold, in which the pressure received by the surface opposite the movable member undergoes a pressure transmitted through the plastic material. from its opposite surface. This results in a loss of pressure, creating a differential between the top and the bottom of the room.

According to another embodiment (FIG. 3), the mold (1) comprises two compression systems (5). Thus, the molding chamber (4) is equipped with at least one first compression system (5) implanted in the first element (1) and at least one second compression system (5) implanted in the second element ( 2). The two compression systems (5) may have substantially the same molding surfaces, as shown in Figures 3 and 4. But as illustrated in Figures 5 and 6, the molding surfaces may have different dimensions. The two compression systems (5) can be positioned vis-a-vis (FIGS. 3, 4 and 6) or offset relative to one another (FIG. 5).

The two compression systems (5) are controlled by at least one moving means (8), such as hydraulic cylinders or an electric worm motor.

In order to ensure identical movement of the moving blocks (6), it is important to integrate a position control by motor or jack.

The movable pavers (6) represent most of the finished surface of the piece (high and low) resulting from the molding. This area is calculated according to the loading plan and the recovery rate of the latter.

According to one embodiment, the two moving blocks (6) of the two compression systems (5) are facing each other, and they are able to apply the same pressure to the plastics material (MP) when they are pushed into the molding chamber (4).

Preferably, the two blocks (6) of the two compression systems (5) are vis-à-vis, and able to simultaneously apply a pressure on the plastic material (MP), so as to balance forces of both sides. other of the plastics material (4).

Such a compression system allows to finely manage the pressure applied to the plastic material, and to apply an identical pressure on both sides of the plastic material (MP).

It is noted that the mold according to the invention can be used for the manufacture of composite parts comprising an insert, by allowing the overmolding of an insert (9) as illustrated in FIG. 4.

To produce a plastic part comprising an insert (9), it is known to overmold plastic material (MP) around the insert (9).

Generally, the insert (9) is placed in a compression mold between two sheets of plastic material, typically a composite material called "SMC". Then we close the mold. Then, the press is used to transmit a molding pressure to the plastic material above the insert (on the press side). Then the insert (9) transmits the pressure to the plastic material located under the insert (the opposite side to the insert).

As a result, it is difficult to control the pressure actually applied on either side of the insert (9), since it is difficult to predict the pressure effectively transmitted by the insert (9). It is therefore not possible with this type of process, to achieve a balancing of the compression forces on both sides (generally at the top and bottom) of the insert.

It is therefore impossible to guarantee the same thickness of plastic material around the insert (9). Such a defect implies, for the finished part, shortages of material, poor mechanical characteristics and dispersions of thickness of material overmolded around the insert.

With the mold (1) according to the invention, it is possible to finely manage the pressure applied in the material to be molded around the insert (9).

For this type of application, the mold (1) preferably comprises two compression systems vis-à-vis (Figure 4). These make it possible to apply a simultaneous and balanced pressure on the two vertical faces of the insert to guarantee a thickness chosen for the finished part.

The mold (1) preferably comprises a system for holding the insert (5) in the mold (1).

Advantageously, the holding system is a system also ensuring the sealing of the molding chamber (4), preventing the plastic material (MP) from flowing out of the molding chamber (4) of the insert (9) .

The invention also relates to a compression molding method using a mold (1) according to the invention.

According to an example, in which the mold (1) comprises two compression systems (5) facing each other, the method may comprise at least the following steps:

- The plastic material (MP) is cut and weighed;

The plastic material (MP) is positioned on the punch (2);

The press (3) closes the mold (1) and is positioned in position 0 (thickness of the finished part);

The two displacement means (8) of the compression systems (5) are controlled simultaneously and the blocks (6) apply a pressure to flow the plastic material (MP);

The mold (1) being at a temperature between 145 ° C and 160 ° C, the plastic (MP) polymerizes and baked according to its technical characteristics; Both moving means (8) are recalled;

- The press (3) rises and the piece is released from the mold (1).

Claims

1. Compression mold (1) for the manufacture of plastic part (PM), comprising a first element (2) and a second element (3), the two elements (2, 3) forming a molding chamber (4) in closed position of the mold, characterized in that at least one of the elements (2, 3) is equipped with at least one compression system (5) of the plastic material (MP), said compression system (5) comprising at least one less a movable compression block (6) able to move towards the molding chamber (4) to compress the plastic material (MP).

2. Mold (1) according to claim 1, wherein the movable compression pad (6) is movably mounted in a wall of at least one of the elements (1, 2) with a piston-like movement, and the movable pad of compression (6) comprises a surface (7) adapted to constitute a molding surface with the plastic material (MP), when the movable compression pad (6) is pushed into the molding chamber (4) of the mold (1) .

3. Mold (1) according to one of the preceding claims, comprising at least a first compression system (5) implanted in the first element (1) and at least a second compression system (5) implanted in the second element ( 2).

4. Mold (1) according to claim 3, wherein the two blocks (6) of the two compression systems (5) are vis-à-vis, and able to apply the same pressure on the plastic material (MP), when pushed into the molding chamber (4).

5. Mold (1) according to one of claims 3 and 4, wherein the two blocks (6) of the two compression systems (5) are vis-à-vis, and able to simultaneously apply pressure on the material plastic (MP), so as to balance forces on either side of the plastic material (MP) in the molding chamber (4).

6. Mold (1) according to one of claims 3 to 5, wherein the two blocks (6) are controlled by at least one displacement means (8), such as a hydraulic cylinder or an electric screw motor without end.

7. Mold (1) according to one of the preceding claims, wherein at least one of the elements (2, 3) is adapted to compress the plastic material (MP) in the molding chamber (4).

8. A method of compression molding, characterized in that one uses a mold according to one of claims 1 to 7.