FR3020006A1 - METHOD FOR MANUFACTURING A HULL OF PLASTIC MATERIAL BY MOLDING AND OVERMOLDING, HULL PORTION AND HULL OBTAINED BY THIS PROCESS - Google Patents

Abstract

The invention relates to 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 the largest thickness of the shell measured between the large faces, the manufacturing method comprising at least the following steps: molding a first shell portion (C1) comprising at least part of one of the large faces (2) ) of the shell (C) and, opposite the large face, an overmolding surface (10) partially at least 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 from one another by a pitch (P) less than or equal to 5 mm, -molding, on an overmoulding surface (10), a last shell portion (C2) comprising at least a portion of the other large face (3) of the shell (C). The invention also relates to the first hull portion and the hull incorporating the first and last hull portions.

Description

The present invention relates to the technical field of molding, preferably by injection, of plastic parts of great thickness. [2] In the field below, it is known to injection mold plastic parts of large thickness by implementing heated molds and adopting relatively long cycle times so as to master the withdrawals and avoid the 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. [3] It has therefore become apparent that there is a need for a new process for manufacturing a large piece of material which 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, 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 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 5mm and which are spaced from each other a step less than or equal to 5 mm, overmolding, on a molding surface, a last portion of shell comprising at least a portion of the other large face of the shell. [05] 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. [6] According to another variant of the invention, the last portion of the shell is overmolded directly on the overmolding surface of the first shell portion. [7] According to a 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 makes use of the possibilities offered by the process according to the invention to produce hulls of complex shapes having no defect in appearance or shape, insofar as the process according to the invention makes it possible to control the phenomena of withdrawal. [8] According to another characteristic of the invention, the grooves and / or the teeth of each overmolding surface all have substantially the same width and the same depth and are spaced at the same pitch. [09] 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 necessary to hear the smallest of the distances between two opposite faces, separated continuously by plastic, of a portion of a portion of shell. 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. [10] 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. [11] According to a preferred embodiment of the invention, the molding and overmolding steps are performed by injection molding the plastic material. [12] According to a variant of this preferred embodiment, the injected plastics material is chosen from the following plastics: polymethyl methacrylate (PMMA), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), or mixtures thereof. these, without this list being neither exhaustive nor exhaustive. [13] 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. [14] 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 largest thickness of the hull measured between large faces, characterized in that it comprises a first portion of shell according to the invention and a last portion of shell which is overmolded and which comprises the other large face of the shell. [15] 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. [16] 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. [17] The hull 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. According to one characteristic 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. [19] 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. [20] According to yet another feature 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. [21] Thus, according to one characteristic of the invention, the shell has at least one translucent and / or transparent zone. [22] According to another characteristic of the invention, the shell comprises at least one opaque portion and at least one transparent or translucent portion. [23] 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 portion of the shell 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. [24] 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. [25] Similarly, the various features, variants and embodiments of the hull 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] 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 hull according to the invention. Figure 2 is a front view of the shell shown in Figure 1. Figure 3 is a section along 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. 2. FIG. 6 is a partial longitudinal section of a portion of the shell illustrated in FIG. 1. It should be noted that in these figures the structural elements and / or functions common to the different variants may have the same references. [27] 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 following its injection. [28] For the purposes 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 Figures 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 In addition, 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 greatest thickness E2, said thicknesses being measured between the large faces 2 and 3 of the shell C. Furthermore, according to the illustrated example, the large face 2 has a generally concave shape while the large face 3 has a general shape convex. [29] 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. [30] 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 local maximum of each shell portion is less than 5mm 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 the plastic, 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. [31] According to the illustrated example and as shown in Figure 5, it is proposed to decompose the shell C into two shell portions C1 and C2, said first and last.

The first shell portion C1 then comprises a portion of the first large face 2 while the last shell portion C2 comprises a portion of the large opposite face 3. [32] The first shell portion Cl comprises the opposite of 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. [33] As shown in Figure 6, the grooves have a width e less than or equal to 5 mm. The width e is, here, measured perpendicular 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. [34] 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. [35] 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. [36] 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. [37] Then, it is overmolded the last shell portion C2 by injection of a plastic compatible with that used for the first shell portion 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 overmoulding 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 FIG. 1. [38] It will also be noted that the overmoulding surface 10 occupies on the first shell C2 the majority of the surface or face opposite the part of the large face 2. Thus, the first and last C1 C2 shell portions 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 a 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. [39] According to the illustrated example, the shell C is intended to form a part optical. 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. [40] Moreover, in the present case, the first C1 and last C2 shell portions are defined or designed to each form the entirety of an 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. [41] Of course, a shell C according to the invention is not necessarily an optical part and can form a structural part and / or decorative. [42] 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. [43] Similarly, a shell according to the invention may have any shape other than that of a C. [44] Furthermore, various other modifications may be made to the invention within the scope of the appended claims.

Claims (15)

REVENDICATIONS1. 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 greatest thickness of the shell measured between the large faces, the manufacturing method comprising at least the following steps: molding of a first shell portion (C1) comprising at least part of one of the large faces (2) of the shell ( C) and, opposite the large face, an overmolding surface (10) partially at least grooved and / or toothed with grooves (11) and / or teeth (12) which have a width (e) or thickness less than or equal to 5 mm and which are spaced from one another by a pitch (P) less than or equal to 5 mm, - overmoulding, on a molding surface (10), a last portion of shell (C2 ) comprising at least part of the other large face (3) of the shell (C). 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. The manufacturing method according to claim 1, characterized in that the last shell portion (C2) is overmolded directly on the overmoulding surface first shell portion (C1). 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 (e) 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. The manufacturing method according to the preceding claim, characterized in that the injected plastic material is selected from: - polymethyl methacrylate (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 process 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 (C1) 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), shell portion (C2) characterized in that it comprises at least part of one of the large faces (2) of the hull and, opposite the large face (2), an overmolding surface (10) partially at least grooved and / or toothed with grooves and / or teeth which have a width (e) or thickness 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. 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), characterized in that it comprises a first shell portion (C1) according to claim 12 and a last shell portion (C2) which is overmoulded and which comprises at least a part of the other large face 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 (C1) comprises an inlet face (Fe) of the light and the last shell portion (C2) includes an exit face (Fs) of the light or vice versa.10