EP3131737A1

EP3131737A1 - Method for manufacturing a large-dimension plastics shell by moulding and overmoulding, shell portion and shell obtained by this method

Info

Publication number: EP3131737A1
Application number: EP15731636.5A
Authority: EP
Inventors: Frank Arrivet; François MAUDET; Abdessamad MOQNI
Original assignee: Automotive Lighting Rear Lamps France SAS
Current assignee: Marelli Automotive Lighting France SAS
Priority date: 2014-04-18
Filing date: 2015-04-20
Publication date: 2017-02-22
Also published as: FR3020006A1; FR3020006B1; WO2015159038A1

Abstract

The invention relates to a method for manufacturing a plastics shell which comprises two opposite large faces (2, 3) and has a greatest dimension (L), measured along one large face, that is greater than or equal to 10 times the greatest thickness of the shell measured between the large faces and is greater than or equal to 100 mm, said manufacturing method comprising at least the following steps of: -moulding a first shell portion (C1) comprising at least a part of one of the large faces (2) of the shell (C) and, away from the large face, an overmoulding surface (10) that is at least partially grooved and/or toothed with grooves (11) and/or teeth (12) which have a width (I) or thickness less than or equal to 5 mm and which are spaced apart from one another at a pitch (P) less than or equal to 5 mm, -overmoulding, on an overmoulding surface (10), a final shell portion (C2) comprising at least a part of the other large face (3) of the shell (C), all the shell portions being made of the same material as the first shell portion and the local thickness of each shell portion being greater than or equal to 1 mm in the regions at least 1 mm away from the edges of the corresponding shell portion. The invention also relates to the first shell portion and to the shell incorporating the first and final shell portions.

Description

Process for manufacturing a large plastic shell by molding and overmoulding, shell portion and shell obtained by this process

[01] The present invention relates to the technical field of molding, preferably by injection, plastic parts of large thickness.

[02] In the field below, it is known to injection mold thick plastic parts by implementing heated molds and adopting relatively long cycle times so as to control withdrawals and avoid defects and deformations induced by the cooling of the injected plastic material. This way of proceeding makes it possible to obtain quality parts but has the major disadvantage of inducing machine occupation times by parts manufactured too large, so that the manufacturing cost is too high and production rates do not increase. are not compatible with the needs for large series parts.

[03] It has therefore emerged the need for a new process for manufacturing a large and large piece of equipment that makes it possible to reduce the cycle times while having a satisfactory quality.

[04] In order to achieve this object the invention relates to a method of manufacturing a plastic shell which comprises two large opposite faces and has a larger dimension, measured along a large face, greater than or equal to 10 times the largest thickness of the shell measured between the large faces and greater than or equal to 100 mm, the manufacturing method comprising at least the following steps:

molding a first portion of shell comprising at least part of one of the large faces of the shell and, opposite the large face, an overmoulding surface at least partially grooved and / or toothed with grooves and / or teeth having a width or thickness less than or equal to 5 mm and spaced from each other by not less than 5 mm,

overmolding, on a molding surface, a last portion of shell comprising at least part of the other large face of the shell, all the shell portions being in the same material as the first shell portion and local thickness of each shell portion is greater than or equal to 1 mm in areas at least 1 mm away from the edges of the corresponding shell portion. [05] The method according to the invention makes it possible to manufacture without deformation or unacceptable shrinkage for the appearance and optical performance of large parts. According to the invention, it is more generally to manufacture hulls of large sizes whose largest dimension is greater than or equal to 100 mm and the largest thickness is greater than or equal to 5 mm. Such parts may also have a height H measured transversely to the thickness E between two opposite faces of the shell, greater than or equal to 30 mm. Such dimensions of parts pose technical problems in particular as regards their appearance and their optical performance unrelated to the technical problems related to the manufacture of small parts, such as generally less than 50 mm. The invention therefore allows the manufacture of large parts where the prior art did not allow it.

[06] According to the invention depending on the thickness of the shell, the latter may be formed by overmolding on the first shell portion of more than one other shell portion. Thus, according to an alternative embodiment of the invention, the method comprises a molding step, on a so-called overmolding surface of reception, of an intermediate shell portion which comprises an overmolding surface at least partially grooved and / or toothed with grooves and / or teeth which have a width or thickness less than or equal to 5 mm and which are spaced from each other by a pitch less than or equal to 5 mm. In this case the last portion of shell will be overmolded on an intermediate shell portion.

[07] According to another embodiment of the invention, the last portion of the shell is overmolded directly on the overmolding surface of the first shell portion.

[08] According to one feature of the invention, one of the large faces has a generally concave shape and the other large face has a generally convex shape. This feature takes advantage of the possibilities offered by the process according to the invention to produce hulls of complex shapes that have no defect in appearance or shape, insofar as the method according to the invention makes it possible to control the phenomena of withdrawal.

[09] According to another characteristic of the invention, the grooves and / or the teeth of each overmoulding surface all have substantially the same width and the same depth and are spaced at the same pitch. [10] According to another characteristic of the invention, the local thickness of any portion of a shell portion is less than or equal to 5 mm, preferably less than 3.5 mm. According to a feature of the invention the The local thickness is between 1 mm and 5 mm and more preferably between 1.5 mm and 3.5 mm, the local thickness being measured at a distance greater than 1 mm from the edges of the shell portion. By local thickness, it is to be understood the smallest of the distances between two opposite faces, separated continuously by plastic, of a portion of a shell portion. According to a variant of the invention, the local thickness is less than or equal to one third of the total thickness of the shell.

According to another characteristic of the invention, the difference between the smallest thickness of the shell and the largest thickness of the shell is less than half the greatest thickness, said thicknesses being measured between the large faces of the shell. the hull and at a distance a distance from the edges of the hull greater than 2 mm.

[12] According to a preferred embodiment of the invention, the molding and overmolding steps are performed by injection molding the plastic material.

[13] According to a variant of this preferred form of implementation, the injected plastic material is chosen from the following plastics:

- polymethylmethacrylate (PMMA)

- Polycarbonate (PC)

Acrylonitrile butadiene styrene (ABS)

or mixtures thereof, without this list being neither exhaustive nor exhaustive.

[14] The invention also relates to a portion of a plastic shell which comprises two large opposite faces and has a larger dimension, measured along a large face, greater than or equal to 10 times the greatest thickness of the shell measured between the large faces, shell portion characterized in that it comprises one of the large faces of the shell and, opposite the large face, an overmoulding surface at least partially grooved and / or toothed with grooves and / or teeth which have a width or thickness less than or equal to 5 mm and which are spaced from each other by one step, measured parallel to the large face, less than or equal to 5 mm.

[15] The invention also relates to a shell comprising two large opposite faces and having a larger dimension, measured along a large face, greater than or equal to 10 times the greatest thickness of the shell measured between the large faces and greater than or equal to 100 mm, characterized in that it comprises a first shell portion according to the invention and a last portion of shell which is overmoulded and which includes the other large face of the hull.

[16] According to a feature of the invention, one of the large faces of the shell has a generally concave shape and the other large face of the shell has a generally convex shape.

[17] According to yet another feature of the invention the shell comprises at least one overmolded intermediate shell portion and located between the first shell portion and the last shell portion.

[18] The shell obtained by means of the manufacturing method according to the invention can be used for various applications. So this shell can be opaque and not let the light. The shell may also be intended to form a light guide or part of a lighting optics.

[19] According to a feature of the invention, the width of the grooves, the thickness of the teeth and the spacing pitch of the grooves are less than 3.5 mm.

[20] According to another characteristic of the invention, the width of the grooves, the thickness of the teeth and the spacing pitch of the grooves are between 1 mm and 5 mm.

[21] According to yet another characteristic of the invention, the width of the grooves, the thickness of the teeth and the spacing pitch of the grooves are between 1.5 mm and 3.5 mm. Such dimensions allow to adopt short cycle times without risk of defects such as shrinkage.

[22] Thus, according to one characteristic of the invention, the shell has at least one translucent and / or transparent zone.

[23] According to another characteristic of the invention, the shell comprises at least one opaque portion and at least one transparent or translucent portion.

[24] According to yet another characteristic of the invention, the shell is intended to form a light guide and the first shell portion comprises an entrance face of the light and the last shell portion comprises an exit face of light or vice versa. It must therefore be understood that the first portion of the shell may comprise an exit face of the light while the last portion of the shell comprises an entrance face of the light. [25] Of course, the various features, variants and forms of implementation of the method according to the invention can be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.

[26] Similarly, the various features, variants and embodiments of the shell according to the invention can be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.

[27] Furthermore, various other features of the invention appear from the attached description with reference to the drawings which illustrate a non-limiting embodiment of a shell according to the invention by the implementation of the method according to the invention. invention.

- Figure 1 is a schematic perspective of a shell according to the invention.

- Figure 2 is a front view of the shell shown in Figure 1.

- Figure 3 is a section along the lines III-III of Figure 2 at a tongue or tooth of the first shell portion.

- Figure 4 is a section along the line IV-IV of Figure 2 at a groove of the first shell portion.

FIG. 5 is an exploded perspective view of the shell illustrated in FIG.

- Figure 6 is a partial longitudinal section of a portion of the shell shown in Figure 1.

It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references.

[28] The invention proposes to make a plastic shell preferably injected so that the shell has no structural defect or deformation induced by the removal and / or cooling of the material after injection.

[29] Within the meaning of the invention a shell is a part whose thickness is small relative to its length developed or measured along one of its large faces when the shell is not developable. As shown in FIGS. 1 and 2, a shell according to the invention and generally designated by the reference C, comprises two large opposite faces 2 and 3. Thus, the shell C has a larger dimension L, measured along a large face, for example the large face 2, greater than or equal to 10 times the largest thickness E of the shell measured between the large faces 2 and 3. The largest dimension L corresponds to the developed length of the large face 2. According to the invention the largest dimension L is preferably greater than or equal to 100 mm, while the height H of the shell is preferably greater than or equal to 30 mm. Furthermore, the width _L of the shell is preferably greater than or equal to 40 mm. The hull C can therefore be described as a large piece.

[30] Moreover, according to the illustrated example and as shown by the cross sections of Figures 3 and 4, the difference between the smallest thickness El of the shell C and the greater thickness E2 of the shell C is less than half of the greater thickness E2, said thicknesses being measured between the large faces 2 and 3 of the shell C. Moreover, according to the illustrated example, the large face 2 has a generally concave shape while the large face 3 has a shape general convex.

[31] The largest thickness E has, for example, a value greater than or equal to 10 mm. However, this thickness is too large to be injected at one time in a manufacturing cycle of less than 200 seconds counted between the start of the injection and the ejection out of the mold of the injected part, while offering satisfactory structural, aesthetic and dimensional characteristics.

[32] Also in order to overcome this drawback, the invention proposes to design the shell C in several parts or portion of shells that can be molded and overmolded on each other so that at each stage of manufacture the thickness the maximum local area of each shell portion is less than 5 mm and preferably less than 3.5 mm, the maximum local thickness corresponding to the smallest of the distances between two opposite faces, separated continuously by plastic, from a part of a hull portion. This local thickness therefore corresponds to the maximum thickness of plastic injected at each stage of manufacture. In general, the local thickness may be chosen to be less than one-third of the total thickness of the shell while remaining greater than 1 mm in areas at least 1 mm away from the edges of the shell portions.

[33] According to the illustrated example and as shown in Figure 5, it is proposed to break the shell C into two shell portions C1 and C2, said first and last. The first portion of shell C1 then comprises part of the first large face 2 while the last shell portion C2 includes a portion of the large opposite face 3.

[34] The first shell portion C1 comprises opposite the large face 2, an overmolding surface 10 at least partially grooved and / or toothed. According to the illustrated example, overmolding surface 10 comprises an alternation of grooves 11 and tongues 12. In this case, the tongues 12 form, beyond the large face 2, teeth.

[35] As shown in Figure 6, the grooves have a width i less than or equal to 5 mm. The width i is, here, measured perpendicularly to the large face 2, the grooves extending parallel to said large face 2. Moreover, the grooves 11 are spaced apart by a pitch P less than or equal to 5 mm. The pitch P then corresponds to the thickness of the tongue / tooth 12 defined by two successive grooves 11. Furthermore, it may be noted that the distance d separating the bottom of the grooves 11 of the large face 2 is less than or equal to 5 mm.

[36] The last portion of shell C2 has a shape complementary to that of the first portion of shell to form in combination therewith the shell C as a whole.

[37] The manufacture of the hull according to the invention thus constituted is carried out in the following manner in accordance with the process according to the invention.

[38] In a first step the first shell portion Cl and injection molded plastic in a mold designed for this purpose. The plastic material used may be, for example, PMMA.

[39] Then, it is overmolded the last portion of shell C2 by injection of a plastic compatible with that used for the first portion of shell C2. Preferably, it will be used the same plastic material that constitutes the first shell portion Cl. The injected plastic material, during overmolding of the second shell portion C2 on the first shell portion Cl, matches the overmolding surface 10 of the first shell portion C1 and forms part of the large face 3 and in this case a part of the other large large face 2. At the end of the overmoulding process is obtained the shell C as illustrated figure 1. [40] It will also be noted that the overmolding surface 10 occupies on the first shell C2 the major part of the surface or face opposite the part of the large face 2. Thus, the first C1 and last C2 portions of shell have similar dimensions. In addition, the first shell portion Cl forms part of the large face 2 which has a length (greater dimension) substantially equal to the length of the large face 2 of the shell C. Similarly, the last portion of the shell C2 forms part of the large face 2 which has a length (greater dimension) substantially equal to the length of the large face 3 of the shell C.

[41] According to the illustrated example, the shell C is intended to form an optical part. Also, the overmolding of the last portion of the shell is made on the first portion of the shell C1 while the latter has a temperature sufficient to prevent the formation of a diopter between the two shell portions C1 and C2.

[42] Moreover, in the present case, the first C1 and last C2 shell portions are defined or designed to each form an entire optical face of either input or output of the light. Thus the first shell C1 here forms the entirety of an input face of the light Fe while the last shell C2 forms the entirety of the output face Fs of the light.

[43] Of course, a shell C according to the invention is not necessarily an optical part and can form a structural part and / or decorative.

[44] In addition, according to the illustrated example the shell C forms a "C" whose ends of the branches are connected by a bar for facilitating the attachment of the shell on a support. However, the implementation of such a bar is not strictly necessary and the shell C may not include said bar.

[45] Similarly, a shell according to the invention may have any shape other than that of a C.

[46] Finally, it should be recalled that the invention makes it possible to produce a large piece having a quality at least equal to a total manufacturing time shorter than that required for the manufacture in a single injection of the same large piece. .

[47] Furthermore, various other modifications may be made to the invention within the scope of the appended claims.

Claims

A method of manufacturing a plastic shell which comprises two large opposite faces (2,3) and has a larger dimension (L), measured along a large face, greater than or equal to 10 times the most large thickness of the shell measured between the large faces and greater than or equal to 100 mm, the manufacturing method comprising at least the following steps:

molding a first shell portion (Cl) comprising at least part of one of the large faces (2) of the shell (C) and, opposite the large face, an overmolding surface (10); ) at least partly grooved and / or toothed with grooves (11) and / or teeth (12) which have a width (t) or thickness of less than or equal to 5 mm and which are spaced from each other by one step (P) less than or equal to 5 mm,

- overmolding, on a molding surface (10), a last shell portion (C2) comprising at least part of the other large face (3) of the shell (C), all the hull portions being in the same material as the first shell portion and the local thickness of each shell portion is greater than or equal to 1 mm in areas at least 1 mm away from the edges of the corresponding shell portion.

2. Manufacturing process according to the preceding claim, characterized in that it comprises a molding step, on a so-called overmolding surface receiving, an intermediate shell portion which comprises a molding surface at least partially grooved and / or toothed with grooves and / or teeth which have a width or thickness less than or equal to 5 mm and which are spaced from each other by one step, measured parallel to the large face, less than or equal to 5 mm.

3. Manufacturing process according to claim 1, characterized in that the last shell portion (C2) is overmolded directly on the overmolding surface of the first shell portion (Cl).

4. Manufacturing process according to one of the preceding claims, characterized in that one of the large faces (2) has a generally concave shape and the other large face (3) has a generally convex shape.

5. Manufacturing process according to one of the preceding claims, characterized in that the grooves (11) and / or the teeth (12) of each overmolding surface all have substantially the same width (t) and are spaced apart by not even (P).

6. Manufacturing process according to one of the preceding claims, characterized in that the local thickness of any portion of a shell portion is less than or equal to 5 mm.

7. Production method according to one of the preceding claims, characterized in that the difference between the smallest thickness (E3) of the shell (C) and the largest thickness (E2) of the shell is less than half of the largest thickness (E2), said thicknesses being measured between the large faces (2,3) of the shell (C).

8. Manufacturing process according to one of the preceding claims, characterized in that the molding and overmolding steps are performed by injection of the plastic material.

9. Manufacturing process according to the preceding claim, characterized in that the injected plastic material is chosen from:

- polymethylmethacrylate (PMMA)

- Polycarbonate (PC)

Acrylonitrile butadiene styrene (ABS)

- or mixtures thereof.

10. Manufacturing process according to one of the preceding claims, characterized in that the shell has at least one translucent or transparent zone.

11. Manufacturing method according to one of the preceding claims, characterized in that the shell characterized in that it is intended to form a light guide and in that the first shell portion (Cl) comprises an inlet face light and the last portion of the shell comprises an exit face of the light or vice versa.

12. Portion of a plastic shell that includes two large opposite faces (2,3) and has a larger dimension (L), measured along a large face, greater than or equal to 10 times the greatest thickness (E) of the shell (C) measured between the large faces (2, 3) and greater than or equal to 100 mm, shell portion (C2) characterized in that it comprises at least part of one of the large faces (2) of the shell and, opposite the large face (2), an overmoulding surface (10) partially at least grooved and / or toothed with grooves and / or teeth which have a width (t ) or thickness less than or equal to 5 mm and which are spaced from each other by a pitch (P) less than or equal to 5 mm.

13. Hull comprising two large opposite faces and having a larger dimension (L), measured along a large face (2), greater than or equal to 10 times the largest thickness (E) of the hull measured between large faces (2, 3) and greater than or equal to 100 mm, characterized in that it comprises a first shell portion (Cl) according to claim 12 and a last shell portion (C2) which is overmolded and which comprises a part at least on the other side of the hull.

14. Shell according to claim 13, characterized in that one of the large faces (2) has a generally concave shape and the other large face (3) has a generally convex shape.

15. Shell according to one of claims 13 or 14, characterized in that it is intended to form a light guide and in that the first shell portion (Cl) comprises an inlet face (Fe) of the light and the last shell portion (C2) comprises an output face (Fs) of the light or vice versa.