EP3227095A1

EP3227095A1 - Mould for manufacturing a plastic part comprising a system for making openings in the part

Info

Publication number: EP3227095A1
Application number: EP15821105.2A
Authority: EP
Inventors: Jean-Yves Sozet
Original assignee: Plastic Omnium SE
Current assignee: Plastic Omnium SE
Priority date: 2014-12-05
Filing date: 2015-12-01
Publication date: 2017-10-11
Also published as: US20170361511A1; FR3029446A1; WO2016087769A1; MA41113A; CN107206635A; FR3029446B1

Abstract

The invention relates to a mould (1) for manufacturing a plastic part (MP), comprising a first element (3) and a second element (4) forming, in the closed position of the mould (1), a cavity (5) corresponding to the part (2) to be manufactured, in which the second element (4) comprises at least one system (6) for making moulding openings in said part (2), said system (6) comprising at least one member (7) forming a cavity of an opening for the finished part (2), said member (7) being movable relative to the second element (4) in the closing direction of the mould (1), between a retracted position and an position extending into the cavity (5). The system (6) comprises at least one positioning means (8) for positioning the member (7) in the extended position relative to the first element (3), said system (6) being sized such that, in the extended position of the member (7), the distance between a surface of the member (7) bearing on the plastic material (MP) and the first element (3) enables the formation of a thin layer of plastic material having a repeatable thickness.

Description

Mold for the manufacture of plastic parts having a system for making holes in the workpiece

The present invention relates to the technical field of manufacturing by molding plastic parts, including parts with orifices.

This may be in particular, but not exclusively, structural parts of a motor vehicle, such as technical front panels, wing supports and floors. This type of room has the particularity of having through holes while maintaining a good mechanical strength.

To make a plastic part, it is known to use a molding process, such as compression molding and / or injection and / or extrusion. Pressurized hot pressing molding in a mold is generally performed by moving a movable member of the mold (moved by a press) relative to a fixed member of the mold, these elements being typically made of steel.

Generally, a loading plane consisting of sheets of plastic material, typically a composite material called "SMC" (sheet molding compound), is placed in a compression mold.

Then we press the press to close the mold. It is said that the mold goes down (closes) to a closed position.

Then the press continues to operate to transmit a molding pressure to the plastic material. It is said that the mold is in the compaction phase. The plastic material can then flow and take the form of the mold cavity.

Finally, during a phase called "cooking", the plastic polymerizes to form a finished part.

To make an orifice in the final piece, it could be envisaged to design the mold with an orifice imprint, that is to say a local shape and molding for each orifice.

For example, the mold could comprise a pin located at the periphery of the cavity and not facing the loading plane, having the shape of the desired orifice, on one element of the mold that would come into contact with the other element when the closure of the mold.

However, during the creep of the plastic material, the reinforcing fibers preferentially orient themselves as a function of the creep directions, so they will go around the spindle and then join together by forming a gluing line. We no longer control the random orientation of the fibers. This results in a preferred orientation of the reinforcing fibers, which can lead to an anisotropy of the part, which will therefore have a different mechanical behavior depending on the directions of the forces undergone, which can induce less robustness as needed in certain areas of the finished part. In addition, the bonding lines do not generally comprise reinforcing fibers.

Therefore, to obtain a plastic part comprising through orifices, one must first mold the plastic part, then after leaving the mold, make with another equipment the holes in recovery, for example by machining, or by punching it at the desired locations so as to form through orifices.

The necessary equipment must therefore include, in addition to a molding equipment, a machining cell, or a punching system, integrated in the production cycle of the part. Such equipment is expensive and increases the cycle time, and leads to the generation of dust and falls from the removed material.

To avoid this recovery step, there is known a mold for making molding holes by means of movable pins. The pins are actuated by hydraulic cylinders. These pins are lowered into the mold cavity after creep of the plastic material and before polymerization.

However, such an in situ molding system deteriorates too much in use, because the pins come to tap against the face of the mold vis-à-vis, and rub against the reinforcing fibers which are abrasive. Because of this, the spindle and the mold are damaged.

In order not to damage such pins, a mold is known comprising, in the cavity, in front of the movable pin, an interchangeable wear part, sometimes called a fixed pin, which can be removed from the mold and exchanged when is too damaged.

Another technique for not damaging the pins (mobile or fixed) is to leave, in the closed position of the mold, a minimum clearance between the pin and the face of the mold vis-à-vis. This minimum clearance is set to preserve a minimum distance between the two parts of the mold, taking into account the production dispersions on the thickness of the parts (0.4mm for example), in particular when the thickness of the part is minimal. Thus, the material is not completely pushed back in thickness, and a non-repetitive thickness material web from one room to another is left at the bottom of the orifice. This residual veil is then removed in an additional production step. In molding, there is a dispersion of thickness of the molded part, related to variations in the industrial process due to different parameters, such as the amount of material used. Thus, given the variations in the density of the material, the weight used and the operation of the press, the residual haze can vary from 0.2 to 0.6 mm. It is therefore necessary to provide a significant mechanical action to remove this veil. For example, it may be necessary to use heavy equipment for drilling, grinding or milling. In addition, such equipment includes tools (forest, grindstone, milling cutter) that need to be replaced regularly due to wear or damage. Finally, such tools may be accompanied by alignment problems with respect to the orifice to be molded.

The object of the invention is to remedy these drawbacks by providing a mold for the manufacture of plastic parts, such as structural parts of a motor vehicle, allowing the production of orifices directly in the mold obstructed by a very thin web, controlled thickness of the order of 0.1 mm. These orifices are therefore intended to be through on the part mounted on the vehicle.

Thus, the object of the invention relates to a mold for the manufacture of plastic part, comprising a first element and a second element forming, in the closed position of the mold, an impression corresponding to the part to be produced. The second element comprises at least one system for producing molding orifices in the part, said system comprises at least one positioning means relative to the first element, the member in the extended position, said system being dimensioned so that in position output of the member, the distance between a bearing surface of the member on the plastic material and the first element allow the formation of a thin plastic film of repeatable thickness at the bottom of the orifice.

The mold according to the invention thus makes it possible to produce openings directly in the mold obstructed by a veil, so fine that it can be removed by simple mechanical actions.

Furthermore, the thickness of this web being fixed regardless of the actual thickness of the part, it is possible to guarantee this simple mechanical action to remove the sails of each hole and each piece.

In addition, the mechanical elements involved in the mold not coming into contact with each other during closure, the mold according to the invention is not damaged during the production of the orifices.

According to the invention, the positioning means can make it possible to position the bearing surface of the member relative to the surface of the fixed element vis-à-vis the member is in the extended position.

According to one embodiment, the positioning means comprises at least one movable plate provided with at least one mechanical stop, the movable plate being movable relative to the second element.

The mechanical stop can be supported on the first element in compacting phase of the mold. Furthermore, this mechanical stop and the movable member are advantageously dimensioned so that in the output position of the movable member, the distance between the bearing surface of the member on the plastic material and the first element is not zero and less than 0.2mm, preferably substantially equal to 0.1 mm.

The invention also relates to a method of manufacturing a plastic part comprising at least one orifice, by means of the mold according to the invention, the method comprising at least the following steps:

positioning the plastic material in the mold cavity;

- the mold is closed;

the plastic material is compacted in the cavity, up to the nominal dimension of the piece to be molded;

after creep of the plastic material and before polymerization of the plastic material, the positioning means are lowered until the abutment comes into contact with the mold element;

- we open the mold and eject the piece; and

the veil formed in the orifice created by the spindle is removed.

According to the invention, the haze can be removed by means of a shot blasting process, CO 2 crystal blasting, water jet scrubbing or compressed air or a brush.

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:

- Figure 1 A illustrates a mold according to the invention in the closed position.

- Figure 1 B illustrates a mold according to the invention in the open position.

- Figure 2 illustrates a portion of the mold according to the invention in the open position.

- Figure 3 illustrates a portion of the mold according to the invention in the compaction phase.

FIG. 4 illustrates a part of the mold according to the invention in the compaction phase and in the lowered position of the pins.

- Figure 5 illustrates a portion of the mold according to the invention in the open position after compacting.

Referring now to Figures 1 A and 1 B which illustrate a mold (1) according to the invention for the manufacture of a part (2) of plastic material (MP). The mold (1) comprises a first element (3), fixed in the example of Figures 1A and 1B, and vis-à-vis a second element (4), movable according to this example. The two elements form in the closed position of the mold (1) an impression (5) corresponding to the part (2) to be produced.

The closed position is defined as the first position, when the moving element (4) is lowered, in which the movable element (4) is in contact with the plastic material (MP) introduced into the mold for molding of the piece (2). There is thus at the beginning of closure a space and therefore a free volume of material between the two elements (3, 4) of the mold (1), necessary for the compacting phase. The second element (4) comprises at least one system (6) for producing molding orifices in the part (2). This system (6) comprises:

at least one orifice-forming member (7), that is to say a local shape and molding for each orifice, this member (7) being movable relative to the second element (4) in the closing direction of the mold (1), between a retracted position (in the second element (4)) and an extended position (in the cavity (5)); and at least one positioning means (8) relative to the first element (3), of the member (7) in the extended position.

A hole is understood to mean a zone with a material evident at least over substantially all of its thickness. According to the invention, the orifice at the outlet of the mold comprises a veil obstructing it.

On the other hand, on the finished part, the orifice is said to pass through, because the veil has been removed. Thus, a through hole is an area with a material evident over its entire thickness.

The member (7) is movable in translation relative to the second element (4): it is adapted to slide in the second element (4), for example in the closing direction of the mold (1) as illustrated in the figures.

The member (7) has a surface (7a) constituting a bearing surface on the plastic material (MP) in the cavity (5) of the mold. The position of the member (7) when the bearing surface (7a) is farthest from the fixed member (3), is called "retracted position". In this retracted position, the surface (7a) is preferably recessed (Figures 2, 3 and 5) relative to the surface of the element (4) forming the cavity (5). The bearing surface (7a) can also be positioned at the same level (FIGS. 1A and 1B) as the surface of the cavity, so that it can not modify the volume of the cavity of the mold (1). Conversely, the position of the member (7) when the bearing surface (7a) is closest to the fixed element (3), is called "output position". Indeed, in this extended position, the surface (7a) is in the cavity (5).

According to the particular embodiment illustrated in the figures, the member (7) may be a pin, that is to say a rod, for example metallic, of height D1. The height D1 is at least close to the thickness of the piece (2).

The pin (7) has a surface, said upper with reference to Figure 1B, and a second surface (7a), said lower with reference to Figure 1 B. The lower surface (7a) constitutes the bearing surface on the plastic material (MP) in the mold cavity. This surface (7a) has a shape corresponding to that of the orifice that is to be made in the part (2).

The positioning means (8) makes it possible to position the bearing surface (7a) of the member (7) with respect to the surface of the fixed element (3) vis-à-vis, at a fixed distance, constant from one orifice to another and repeatable from one part to another (in the sense of the variation of production), when the member (7) is in the extended position.

The positioning means (8) comprises, for example, as shown in FIG. 1A: at least one movable plate (9) constituting a drive plate of the member (7), provided with at least one mechanical stop (10). The movable plate (9) is connected to the movable member (7) so as to move the movable member (7) in the thickness of the second member (4) between its retracted position and its extended position.

According to the embodiment of the figures, the movable plate (9) is substantially perpendicular to the closing direction of the mold (1). The plate (9) is movable in translation relative to the second element (4). The plate is adapted to move in the closing direction of the mold (1).

The plate (9) carries under its face located opposite the cavity (5), the movable pin (7). The plate (9) carries peripherally, not facing the cavity, at least one stop (10) mechanical. This stop (10), parallel to the closing axis of the mold (1), has a length D2. In the closed position of the mold (1), the abutment (10) is not initially in contact with the other element of the mold (3). On the other hand, in the compaction phase of the mold (1), the movable plate (9) descends until the abutment (10) bears, by a bearing surface (10a), on the first element (3) . In this way, the stop (10) positions the plate (9) at a fixed distance from the element (3), and thus positions the pin (7) in the extended position at a fixed distance from the element (3) regardless of the relative position between elements (3) and (4).

Indeed, the distance between the bearing surface (7a) of the member (7) and the surface of the fixed element (3) in the cavity, surface facing the body (7). ), is defined only with respect to fixed dimensions, and not with respect to the thickness of the plastic in the cavity, and therefore not with respect to the position of the movable element (4). This distance is in fact only dependent on:

- the distance (D1) between the bearing surface (7a) and the movable plate (9);

- the distance (D2) between the bearing surface (10a) of the mechanical stop and the movable plate (9);

the distance (D3) between the point dimension of the element in contact with the stop (10) and the dimension of the surface of the element (3) vis-à-vis the spindle (7). It should be noted that this distance may be zero

Thus, the system (6) is sized so that in compacting phase of the mold (1) and in the extended position of the movable member (7), the distance between the bearing surface of the member (7) on the plastic material and the first element (3) allow the formation of a thin plastic film. Thus, the abutment (10) and the spindle (7) are dimensioned, in particular the distance D2 and the distance D1, so that in the compaction phase of the mold (1) and in the output position of the spindle (7), the distance between the bearing surface of the spindle (7) and the first element (3) is not zero and less than 0.2 mm, preferably substantially equal to at 0.1 mm.

Thus, the pin (7) forms on the part (2) an orifice having a thin veil, of the order of 0.1 to 0.2mm.

Referring to FIG. 3, the distance between the bearing surface (7a) of the pin (7) in the extended position and the element (3) is denoted DR

DF = D2 - D1 - D3

And we wish that: DF = 0.1 mm

According to the example described, the plate (9) is linked to the upper surface of the spindle (7). It is clear that the plate (9) can be linked to different level of the spindle (7), and the skilled person will be able to adapt the dimensions of the spindle (7) and the stop (10) to respect the minimum coast imposed (DF) between the bearing surface (7a) and the element (3).

It is obvious that the mold (1) has as many pins (7) that the part (2) must have orifices. These pins (7) may each be carried by a different plate (9), or preferably carried by the same plate (9), or a plate assembly (9), each plate (9) carrying a plurality of movable pins (7). ).

According to a preferred embodiment, the system (6) comprises a plate (9) carrying a set of pins (7) and at least one stop (10).

According to one embodiment, the surface (7a) of the member (7) is recessed relative to the surface of the element (4) forming the cavity (5), when the member is in the retracted position. Thus, at the beginning of the compacting phase, the plastic material (MP) fluent, enters a volume formed between the bearing surface (7a) and the cavity (5). When the member (7) goes into the extended position, this material is driven into the cavity (5). If it is already filled, then the movable member (4) rises, releasing the volume necessary for this plastic material in the cavity (5).

Similarly, in the retracted position of the member (7) the rod (10) is preferably recessed in the movable member (4). The invention also relates to a method of manufacturing a piece (2) of plastic material (MP) comprising at least one orifice, by means of a mold (1) according to the invention. Figures 2 to 5 illustrates the operation of the mold (1) and the method according to the invention. The method according to the invention comprises at least the following steps:

- Positioning (Figure 2) the plastic material (MP) in the cavity (5) of the mold (1); the mold (1) is closed and the plastic (MP) in the cavity is compacted (FIG. 3) to the nominal dimension of the piece (2) to be molded;

- after creep of the plastic material (MP) and before polymerization of the material plastic (MP) is lowered (Figure 4) the positioning means (8) until the stop (10) come into contact with the element (3) of the mold; the movable spindle (7) is then in its extended position at a fixed and constant distance from the element (3) allowing the formation of a thin and repeatable veil (from one room to another) at the bottom of the orifice ;

the mold is opened and the piece (2) is ejected; and

the veil formed in the orifice created by the spindle (7) is removed, for example by means of a shot blasting process, the projection of C02 crystals, the washing with a jet of water or with compressed air or of a brush.

Thus, the system (6) descends during the mold closing step, that is to say in parallel with the step of descent of the movable member (4). The system (6) can be temporarily secured to the movable element (4) (to follow its movement), or be controlled so as to accompany the movable element (4) during its descent to the fixed element (3). ).

The movable element (4) comes into contact with the material, leaving a space (air gap) between the two elements (3, 4) of the mold (1). The plastic material (MP) is then compressed and begins to flow in the impression (5). Due to the uncertainty in industrial production of the amount of plastic material actually introduced into the impression (5), there is then a dispersion of the thickness of material in the mold, and therefore, the space between the two elements (3, 4) of the mold (1) has a variable size.

Before the plastics material (MP) begins to polymerize, i.e. harden, the positioning means (8) descends independently of the movable member (4), driving with it the member (7) until it abuts against the fixed element (3). The movement of the positioning means (8), and therefore of the member (7), is independent, disengaged from the movement of the movable member (4). It should be noted that the movable element (4) can continue to move relative to the element (3). Indeed, there may be a variation in position of this movable element (4) due to the creep of the material that fills the cavity. The element (4) still descends until the cavity is completely filled, or the movable element (4) rises under the effect of the plastic material pushed into the cavity by the volume taken by the spindle (7) that enters the thickness of the material.

Claims

1. Mold (1) for the manufacture of plastics part (2) (MP), comprising a first element (3) and a second element (4) forming in the closed position of the mold (1) an impression (5) corresponding to the piece (2) to be produced, wherein the second element (4) comprises at least one system (6) for producing molding orifices in said part (2), said system (6) comprising at least one member (7) forming an orifice for the finished part (2), said member (7) being movable relative to the second element (4), between a retracted position and an output position in the cavity (5), characterized in that said system (6) comprises at least one positioning means (8) relative to the first element (3), the member (7) in the extended position, said system (6) being dimensioned so that in the extended position of the the member (7), the distance between a bearing surface (7a) of the member (7) on the plastics material (MP) and the first element (3) allows ent the formation of a thin web of plastic material of repeatable thickness.

2. Mold (1) according to claim 1, wherein the positioning means (8) allows to position the bearing surface (7a) of the member (7) relative to the surface of the fixed member (3). ) vis-à-vis the member (7) at a fixed distance when the member (7) is in the extended position.

3. Mold (1) according to one of the preceding claims, wherein the positioning means (8) comprises at least one movable plate (9) provided with at least one mechanical stop (10), the movable plate (9). being movable relative to the second element (4).

4. Mold (1) according to claim 3, wherein the stop (10) bears on the first element (3) in compacting phase of the mold (1).

5. Mold (1) according to one of claims 3 and 4, wherein the mechanical stop (10) and the movable member (7) are dimensioned so that in the output position of the movable member (7), the distance between the bearing surface of the member (7) on the plastic material and the first element (3) is not zero and less than 0.2mm, preferably substantially equal to 0.1 mm.

6. A method of manufacturing a piece (2) of plastic material (MP) comprising at least one orifice, by means of the mold (1) according to one of claims 1 to 5, the method comprising at least the following steps:

positioning the plastic material (MP) in the cavity (5) of the mold (1);

the mold (1) is closed;

the plastic material (MP) is compacted in the cavity (5) to the nominal dimension of the part (2) to be molded; - after creep of the plastic material (MP) and before polymerization of the plastic material (MP), the positioning means (8) are lowered until the stop (10) comes into contact with the element (3) mold;

the mold is opened and the piece (2) is ejected; and

- The veil formed in the hole created by the spindle (7) is removed.

The method of claim 6, wherein the haze is removed by a shot peening, CO 2 crystal blasting, water jet scrubbing or compressed air or brush method.