MOLD FOR MANUFACTURING PLASTIC PARTS

Abstract

The invention relates to a mold for manufacturing a plastic part, including a first element and a second element forming, in the closed position of the mold, a cavity corresponding to the part to be manufactured, in which the second element includes at least one system for making molding openings in said part, said system including at least one member forming a cavity of an opening for the finished part, said member being movable relative to the second element in the closing direction of the mold, between a retracted position and an position extending into the cavity. The system includes at least one positioning means for positioning the member in the extended position relative to the first element, said system being sized such that, in the extended position of the member, the distance between a surface of the member bearing on the plastic material and the first element enables the formation of a thin layer of plastic material having a repeatable thickness.

Claims

1. A mold for manufacturing a part made from plastic material, the mold comprising: a first element and a second element forming, in a closed position of the mold, a cavity corresponding to the part, wherein the second element includes at least one system for making molding openings in said part, said system including at least one member forming a cavity of an opening for the part, said at least one member being movable relative to the second element between a retracted position and an extended position extending into the cavity, wherein said system includes at least one positioning means for positioning the member in the extended position relative to the first element, said system being sized such that, in the extended position of the member, a distance between a surface of the member bearing on the plastic material and the first element enables formation of a thin layer of plastic material having a repeatable thickness.

2. The mold according to claim 1, wherein the at least one positioning means is configured to position the bearing surface of the member relative to the surface of the first element opposite the member, at a fixed distance when the member is in the extended position.

3. The mold according to claim 1, wherein the at least one positioning means comprises at least one movable plate having at least one mechanical stop, the movable plate being movable relative to the second element.

4. The mold according to claim 3, wherein the mechanical stop rests against the first element in a packing phase of the mold.

5. The mold according to claim 3, wherein in the extended position of the movable member, a distance between the surface of the member bearing on the plastic material and the first element is not zero and less than 0.2 mm.

6. A method for manufacturing a part made from plastic material having at least one opening, using the mold according to claim 1, the method comprising: positioning the plastic material in the cavity of the mold; closing the mold; packing the plastic material in the cavity up to a nominal dimension of the part; after flow of the plastic material and before polymerization of the plastic material, lowering the at least one positioning means until a mechanical stop comes into contact with the mold; opening the mold and ejecting the part; and removing the layer formed in the opening.

7. The method according to claim 6, wherein the layer is removed via one of shot-peening, projection of CO.sub.2 crystals, washing with water jet or compressed air or a brush.

8. A mold for manufacturing a part made from plastic material, the mold comprising: a first element and a second element forming, in a closed position of the mold, a cavity corresponding to the part, wherein the second element includes at least one system for making molding openings in said part, said system including at least one member forming a cavity of an opening for the part, said at least one member being movable relative to the second element between a retracted position and an extended position extending into the cavity, wherein said system includes at least one moveable plate and at least one mechanical stop configured to position the member in the extended position relative to the first element, said system being sized such that, in the extended position of the member, a distance between a surface of the member bearing on the plastic material and the first element enables formation of a thin layer of plastic material having a repeatable thickness.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will be better understood on reading the accompanying figures, which are given solely by way of example and not limiting in any way, in which:

[0036] FIG. 1A illustrates a mold according to the invention in the closed position.

[0037] FIG. 1B illustrates a mold according to the invention in the open position.

[0038] FIG. 2 illustrates a section of the mold according to the invention in the open position.

[0039] FIG. 3 illustrates a section of the mold according to the invention in packing phase.

[0040] FIG. 4 illustrates a section of the mold according to the invention in packing phase with the pins in the lowered position.

[0041] FIG. 5 illustrates a section of the mold according to the invention in the open position after packing.

MORE DETAILED DESCRIPTION

[0042] We now refer to FIGS. 1A and 1B which illustrate a mold (1) according to the invention for manufacturing a part (2) made from plastic material (MP). The mold (1) comprises a first element (3), fixed according to the example of FIGS. 1A and 1B, and, opposite, a second element (4) movable according to this example. The two elements form, in the closed position of the mold (1), a cavity (5) corresponding to the part (2) to be produced.

[0043] The closed position is defined as being the first position, during the descent of the movable element (4), in which the movable element (4) is in contact with the plastic material (MP) introduced into the mold for molding the part (2). When the mold starts to close, therefore, there is a space and thus a free volume of material between the two elements (3, 4) of the mold (1), necessary for the packing phase.

[0044] The second element (4) comprises at least one system (6) for producing molding openings in the part (2). This system (6) comprises: [0045] at least one member (7) forming a cavity of an opening, in other words a local and molding shape for each opening, this member (7) being movable relative to the second element (4) in the closing direction the mold (1) between a retracted position (in the second element (4)) and an extended position (in the cavity (5)); and [0046] at least one positioning means (8) for positioning the member (7) in the extended position relative to the first element (3).

[0047] An opening means an area with no material over at least substantially its entire thickness. According to the invention, when the part leaves the mold, the opening comprises a layer blocking it.

[0048] However, on the finished part, the opening is said to be a through opening since the layer has been removed. Thus, a through opening is an area with no material over its entire thickness.

[0049] 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 shown on the figures.

[0050] The member (7) comprises a surface (7a) forming a surface bearing 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 element (3) is called the “retracted position”. In this retracted position, the surface (7a) is preferably recessed (FIGS. 2, 3 and 5) relative to the surface of the element (4) forming the cavity (5). The bearing surface (7a) may also be positioned at the same level (FIGS. 1A and 1B) as the surface of the cavity, so that it does 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 the “extended position”. In this extended position, the surface (7a) is inside the cavity (5).

[0051] According to the particular embodiment illustrated on the figures, the member (7) may be a pin, i.e. a rod, for example metallic, of height D1. The height D1 is at least close to the thickness of the part (2).

[0052] The pin (7) comprises a surface, called the upper surface with reference to FIG. 1B, and a second surface (7a), called the lower surface with reference to FIG. 1B. The lower surface (7a) forms the surface bearing on the plastic material (MP) in the mold cavity. The shape of this surface (7a) corresponds to that of the opening to be produced in the part (2).

[0053] The positioning means (8) positions the bearing surface (7a) of the member (7) relative to the surface of the fixed element (3) opposite, at a fixed distance, constant from one opening to another and repeatable from one part to another (in the meaning of the production variation) when the member (7) is in the extended position.

[0054] The positioning means (8) comprises, for example as shown on FIG. 1A: at least one movable plate (9) forming a plate for driving 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 be able to move the movable member (7) in the thickness of the second element (4) between its retracted position and its extended position.

[0055] 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).

[0056] The plate (9) carries the movable pin (7) under its side located opposite the cavity (5). The plate (9) carries at least one mechanical stop (10) on its periphery, not opposite the cavity. This stop (10), parallel to the axis of closure of the mold (1) has a length D2. In the closed position of the mold (1), the stop (10) is initially not in contact with the other element (3) of the mold. However, in the packing phase of the mold (1), the movable plate (9) descends until the bearing surface (10a) of the stop (10) rests on the first element (3). Thus, the stop (10) positions the plate (9) at a fixed distance from the element (3), and therefore, positions the pin (7) in the extended position at a fixed distance from the element (3) irrespective of the relative position between the elements (3) and (4).

[0057] The distance between the bearing surface (7a) of the member (7) and the surface of the fixed element (3) in the cavity, surface opposite the member (7), is defined only with respect to fixed dimensions, and not with respect to the thickness of the plastic material in the cavity, and therefore not with respect to the position of the movable element (4).

[0058] This distance only depends on: [0059] the distance (D1) between the bearing surface (7a) and the movable plate (9); [0060] the distance (D2) between the bearing surface (10a) of the mechanical stop and the movable plate (9); [0061] the distance (D3) between the dimension of the point of the element in contact with the stop (10) and the dimension of the surface of the element (3) opposite the pin (7). Note that this distance may be zero.

[0062] Thus, the system (6) is sized such that in the packing phase of the mold (1) and in the extended position of the movable member (7), the distance between the surface of the member (7) bearing on the plastic material and the first element (3) allows the formation of a thin layer of plastic material. Thus, the stop (10) and the pin (7) are sized, in particular the distance D2 and the distance D1, so that in the packing phase of the mold (1) and in the extended position of the pin (7), the distance between the bearing surface of the pin (7) and the first element (3) is not zero and less than 0.2 mm, preferably substantially equal to 0.1 mm.

[0063] Thus, the pin (7) forms on the part (2) an opening having a thin layer of approximately 0.1 mm to 0.2 mm.

[0064] 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 DF.

DF=D2−D1−D3

[0065] We want: DF =0.1 mm

[0066] According to the example described, the plate (9) is connected to the upper surface of the pin (7). It is clear that the plate (9) can be connected to a different part of the pin (7), and those skilled in the art will know how to adapt the dimensions of the pin (7) and of the stop (10) to respect the minimum value imposed (DF) between the bearing surface (7a) and the element (3).

[0067] It is obvious that the mold (1) has the same number of pins (7) as the number of openings to be produced in the part (2). These pins (7) can each be carried by a different plate (9) or, preferably, carried by the same plate (9) or a set of plates (9), each plate (9) carrying several movable pins (7).

[0068] According to a preferred embodiment, the system (6) comprises a plate (9) carrying a set of pins (7) and at least one stop (10).

[0069] 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 start of the packing phase, the plastic material (MP) flowing enters a volume formed between the bearing surface (7a) and the cavity (5). When the member (7) moves to the extended position, this material is forced into the cavity (5). If the cavity is already full, then the movable element (4) rises, releasing the volume required for this plastic material in the cavity (5).

[0070] Similarly, in the retracted position of the member (7), the rod (10) is preferably recessed in the moving element (4).

[0071] The invention also relates to a method for manufacturing a part (2) made of plastic material (MP) comprising at least one opening, using a mold (1) according to the invention. FIGS. 2 to 5 illustrate the operation of the mold (1) and the method according to the invention.

[0072] The method according to the invention comprises at least the following steps: [0073] positioning (FIG. 2) the plastic material (MP) in the cavity (5) of the mold (1); [0074] closing the mold (1) and packing (FIG. 3) the plastic material (MP) in the cavity, up to the nominal dimension of the part (2) to be molded; [0075] after flow of the plastic material (MP) and before polymerization of the plastic material (MP), lowering (FIG. 4) the positioning means (8) until the stop (10) comes into contact with the mold element (3); the movable pin (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 (from one part to another) layer at the bottom of the opening; [0076] opening the mold and ejecting the part (2); and [0077] removing the layer formed in the opening created by the pin (7), for example by a method of shot-peening, projection of CO2 crystals, washing with water jet or compressed air or a brush.

[0078] Thus, the system (6) descends during the mold closing step, in other words at the same time as the step of lowering the movable element (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 towards the fixed element (3).

[0079] The movable element (4) comes into contact with the material, leaving a space (gap) between the two elements (3, 4) of the mold (1). The plastic material (MP) is then compressed and starts to flow into the cavity (5). Due to the industrial production uncertainty regarding the quantity of plastic material actually introduced into the cavity (5), there is a dispersion in the thickness of material in the mold, and therefore, the space between the two elements (3, 4) of the mold (1) has a variable dimension.

[0080] Before the plastic material (MP) starts to polymerize, in other words to harden, the positioning means (8) descends independently of the movable member (4), taking 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 therefore independent, disconnected from the movement of the movable element (4). Note that the movable member (4) can continue to move relative to the element (3). There may in fact be a variation in the position of this moving element (4) due to the flow of the material which fills the cavity. The element (4) continues to descend until the cavity is completely full, or the movable element (4) rises under the effect of the plastic material pushed into the cavity by the volume taken by the pin (7) entering the thickness of the material.