FR2530985A1 - Mould for obtaining a grid, particularly by injection, method and means of manufacture and use. - Google Patents

Abstract

In a mould for a grid, of the type comprising a first and a second half-shell, at least one 21 of the half-shells has, formed on a substantially flat surface P', a system of elongated separate indentations 25 divided into two families 25a, 25b at least, the indentations in each family being disposed in parallel alignments, each indentation 25a, 25b of each family being bordered at each end by an indentation 25b, 25a of another family while itself separating two successive indentations of an alignment of another family. Application: moulding of grids, particularly for the protection of loud speakers, appearing like interlaced threads.

Description

The present invention relates generally to a grid mold, its application to obtaining grids by molding, a method of manufacturing such a mold, and an apparatus adapted to ensure the implementation of such a method and the resulting products. The invention applies in an interesting, but not exclusive, manner in the field of protective grilles for loudspeakers
As is known, most molds for grids currently known are especially suitable for manufacturing grids in the form of plates, planes or curves, pierced with holes.

There are also other grids obtained by means of wires, metallic, composite or plastic, which are intertwined, in the manner, for example, of canes for chairs. The aesthetics of such grids with interlacing of wires is generally more appreciated than that of grids pierced with the aforementioned holes
However, such wire interleaving grids have the disadvantage of leading to high cost prices. They are in fact generally manufactured in very long wide strips which are cut as required; this results in significant material losses, in particular in the case of circular grids. In addition, in the case of metallic wires, there are risks of corrosion while the conditioning of these grids is delicate: by painting there is a risk of obstruct certain holes in the grid and we cannot always avoid the formation and drying of drops detrimental to the aesthetic appearance of the grids in the final state.

 The invention aims to overcome these drawbacks and for this purpose proposes a mold for a grid of the kind comprising a first and second half-shell, characterized in that the first at least of the half-shells present, formed on a substantially flat surface , a network of separate elongated imprints divided into at least two families, the imprints in each family being arranged in parallel alignments, each imprint of each family being bordered at each end by an imprint of another family while separating itself two successive imprints of an alignment from another family.

 Such a mold makes it possible to produce parts having a texture close to that of a grid on a surface.

It is understood that the number of families of apparent parallel wires is arbitrary, ranging from two for the simplest grid, to-four-or # more depending on the complexity of the caning to be reproduced.

 In order to produce a complete grid, the invention recommends using a mold of the aforementioned type in which the second half-shell has, provided on a substantially flat surface intended to be faced with the substantially flat surface of the first half-shell, a network of disjointed elongated imprints arranged in parallel alignments and superimposed on those of the imprints of the first half-shell, this network being such that during the confrontation of said planar surfaces, each imprint of each alignment of each half-shell crossing a second imprint of the other half-shell and being disposed astride the third and fourth imprints of said other half-shell, separated by said second imprint, the abovementioned imprint and said third and fourth imprints delimiting a section of continuous hose.

 The invention of course recommends applying such molds to obtaining grids affecting the shape of interlaced wires. These wires are preferably made of colored plastic, which eliminates any paint problem.

 By way of example, the invention proposes to obtain a mold of the aforementioned type by EDM by using at least one electrode carrying teeth complementary to the imprints.

 The invention particularly recommends implementing this method by means of an electro-erosion device provided with means for translating and rotating an electrode relative to the future mold, this electrode carrying a plurality of teeth arranged according to an elementary pattern complementary to an elementary pattern adapted to allow all the mold imprints to be obtained by single reproduction of this pattern after translation and / or rotation.

Other objects, characteristics and advantages of the present invention appear from the following description, given by way of non-exhaustive example, with reference to the accompanying drawings in which
- Figure 1 is a top view of an interlacing of two families of perpendicular son square section
- Figure 2 is a sectional view of the above interlacing according to line II-II of Figure 1
FIG. 3 is a sectional view of a mold according to the invention in line with an "apparent" wire,
- Figure 4 is a partial perspective view of a half-shell of a mold according to the invention
- Figure 5 is a section through a variant of interlacing of wires, in line with a wire
- Figure 6 is a schematic perspective view of an interlacing of three families of son
- Figure 7 is a sectional view of a mold according to the invention during manufacture and the electrode used for this purpose
- Figure 8 is a diagram showing the procedure of tracing by electro-erosion of the impressions of a mold according to the invention;
- Figure 9 is a perspective view of an electrode for the manufacture of a mold according to the invention.

 Figures 1 and 2, 5 and 6 show conventional intertwining son arranged in two or three families of different direction.

 The interlacing 10 or cane represented by FIGS. 1 and 2 comprises two families 11 and 12 of wires which are parallel within the same family, but perpendicular from one family to the other. These wires are equidistant, defining openings 13 of square shape.

 As it appears in FIG. 2, a wire 12 of one family passes successively above and then below the wires II of the other family. It should be noted that the tangent zones 14 between crossed wires are all substantially included in the mean plane (P) of the interlacing or grid 10.

 A mold 20 according to the invention is designed from this coplanarity of the tangency zones 14, these zones becoming, after molding, weld zones between crossed wires.

 The mold 20 as shown in Figure 3 is composed of two half-shells 21 and 22 faced along a confrontation surface P '.

 As it appears in FIG. 4, the half-shell 21, as well as the half-shell 22, presents, formed on the confrontation surface P ′, a network of elongated indentations 25 separated by bosses 26 square located on the plant P '. These footprints are divided into two families 25a and 25b. The imprints of each family are arranged in alignments parallel to a given direction, D1 and D2 respectively, specific to the family, Dl and D2 being perpendicular; these footprints are themselves parallel to these directions.

 As it appears in FIG. 4, the imprints 25 are distinct although practically contiguous. Each imprint of each family is bordered at each end by an imprint of the other family, this same imprint itself separating two successive imprints of an alignment of the other family. However, it is observed that the periphery 27 of each imprint 25 is included in the plane P ', even at its quasi-junctions with the other imprints along junction edges 28. This distinct character from the imprints is necessary for obtaining apparently intertwined sons, without interpenetration.

 This half-shell 21 is sufficient to give, on the face of a solid molded part, the illusion of a coating in a grid, especially if the bosses are very small, or even zero.

 Obtaining a fine perforated grid requires the use of another half-shell 22 practically symmetrical with the half-shell 21 with respect to the plane of confrontation of the plane surfaces P 'and P2 (P2 not shown) of the two half shells respectively. This half-shell 22 is however offset with respect to the first half-shell 21.

 As it appears in FIG. 3, obtaining a continuous sinuous casing 50 by superposition of the half-shells 21, 22 requires that each imprint 25 or 25 'of one or the other of the half-shells 21 and 22 be straddling two footprints 25 'or 25 of the other half-shell, thereby ensuring the connection. It should be noted that the hollow casing thus obtained is included, successively, entirely in each of the half-shells. Each casing thus formed is open to all the casings of the other family which it crosses; in this way, after filling said mold with a moldable substance and then drying it, all the casings will be welded to each other in their crossing zone thus avoiding any subsequent parasitic displacement which would ruin the aesthetics of the assembly by default. parallelism of the wires, as can happen with an actual intertwining of wires, metallic in particular.

 The invention described with regard to the representation of a simple interlacing of identical equidistant wires distributed in two orthogonal families, is of course applicable to more complex interlacing, combining various forms of apparent wires, and variable numbers of families of parallel wires .

 FIG. 5 illustrates an intertwining of two families of orthogonal threads which a mold according to the invention can simply produce. These are non-sinuous threads, having breaks 30 at right angles. Such an ornamental pattern is very difficult to produce by real interlacing of threads, taking into account that it is necessary beforehand to bend these threads, which complicates the braiding of said threads. The pattern, on the other hand, is very simple to # relay - with a mold according to the invention, it suffices to replace the imprints 25 of constant width but of variable depth with parallelepipedic imprints, therefore having a constant depth, well separated from each other. It is within the reach of ordinary skill in the art to propose numerous variants of imprint shapes while remaining within the scope of the invention.

 The same is true of the number of families of sons. Figure 6 presents an interlacing with three families making different angles between their directions. The imprints of the associated mold according to the invention, not shown, no longer crossing at a right angle, no longer have a rectangular contour but affect the shape of a parallelogram although identical within each family the imprints have different lengths d family to family. It should be noted that within a given family, the imprints are arranged in alignments parallel to the directions of the three families. If we now consider Figure 6 as a schematic view of a half-shell adapted to achieve such interlacing, we see that the "footprints" designated by the reference 35 are aligned in the directions DI, D2, D3 of the three families 31, 32, 33.

 The invention is easily generalized to the case of four or more families of son, the fingerprints then no longer being identical within the same family and not necessarily admitting a parallelogram contour, but a trapezoid.

 It is thus understood that the invention makes it possible to vary at will the ornamental patterns which can be imagined based on interlacing of threads, including those in which the number of families and the shape of the threads is such that it would prove practically impossible. to make them by braiding or real intertwining of threads.

 In order to avoid any flow burrs at the openings between interlaced wires, the invention recommends facing the two half-shells before introducing the material to be molded, which is therefore preferably injected into the mold by any device. appropriate.

It is understood that the molded material can be any. The invention applies particularly well to materials
colorable plastics, insensitive to corrosion and requiring no painting; it can also be applied to the molding of metals for example (aluminum, gold in goldsmithery, etc ...).

 According to the invention, a mold as described above is advantageously obtained from a block 21 having a substantially flat surface in which impressions are hollowed out by electro-erosion. As is known, this technique consists in establishing a potential difference between a workpiece and an electrode in order to create and maintain an electric arc between these elements. The electrode is generally made of copper and carries for example a pattern that we want to imprint on the workpiece, or a blade or a wire when we want to perform cutting operations.

 Despite the complexity of the patterns that a mold according to the invention makes it possible, it is generally possible to identify an elementary pattern which alone allows it to reproduce the entire mold or its half-shells after translation and / or rotation relative of the pattern with respect to said half-shell. The invention recommends that this pattern be transferred to a negative on an electrode.

 In the case of the half-shell 21 of FIG. 4, an elementary pattern is for example a single imprint.

 The invention recommends choosing in this case one or more alignments of teeth, and making on the surface of an electrode one or more alignments of teeth projecting in a shape complementary to the desired imprints.

 As an example, FIG. 9 represents a single piece electrode 40 carrying two alignments 41 and 42 of aligned teeth 44. Such an electrode can be produced as follows.

First of all, the digging channels 43 between the teeth alignments are hollowed out by rectification by example, parallel to the arrow F1. These channels have a depth greater than the height of the teeth as will appear later.

 The teeth 44 are then cut according to the desired shape, by # rectification for example parallel to a direction F2 fa making with the direction Fl the angle existing between the associated directions D1 and D2 of alignments of imprints to be dug. In the case of FIG. 9, the tracing of the teeth 44 is obtained by cutting, in the projecting walls of the channels 43, a sinuous edge (S) substantially sinusoidal. The teeth 44, one of which is hatched in FIG. 9, are formed by the bosses delimited by the aforementioned sinuous edge and a plane tangent P to the hollows of said edge.

 FIG. 7 illustrates the production of an alignment of impressions 25 of a half-shell 21 using an electrode 40 carrying an alignment of teeth 44 of the aforementioned type.

The latter is advantageously longer than the alignment of imprints to be dug so as to n, having to provide for displacement of the teeth parallel to themselves. The cavities 25 are hollowed out by the teeth 44 by lowering the electrode 40 towards the half-shell 21, over a height H so as to superimpose the planes P ′ and P ″. It is advantageous for this purpose that the channels 43 are deeper than the plane P "so as not to risk attacking the plane P '. The imprints thus define by their bottom a sinusoid S 'substantially tangent to the plane P'.

 FIG. 8 shows diagrammatically the sequence of operations to be carried out to produce a half-shell according to FIG. 4 from a single alignment of teeth 44.

 It should be noted first of all that the imprints 25 or 25 'of the same family are staggered. By analogy with what has been said about the figure, it appears that the imprints of family 25a are aligned parallel to the direction D2 of family 25b only on condition of considering only one alignment out of two. The invention consequently recommends to carry out at first all the alignments parallel to D1 of odd number - or even (steps a to e), to carry out an offset of the electrode parallel to D1 and D2 over substantially distance distances alongside the square boss 26 (step e - f) and then digging the alignments of even - or odd number respectively (steps f to j). All the imprints of the family 25a are then dug. We then apply (step j - h) a rotation of 900 then an offset parallel to D2 over a distance substantially equal to the side of the boss 26. We then dig a first series of alignments of the same parity (steps k to q) then after appropriate offset (step q - r) we dig the alignments of the other parity. The electro-erosion device used for this purpose obviously includes organs adapted to ensure rotations and translations between the electrode and the part to be machined.

This procedure is of course particularly suitable for the use of an electrode carrying several alignments of parallel teeth corresponding to alignments of impressions of the same parity. It cannot be a question of successive alignments taking into account that the contour of the imprints at their ends is parallel to the direction of the other family: this requires that the tracing of the edges of the alignments of the teeth (cf. FIG. 9) of a family is made parallel to this other direction or in the case of two families, the teeth or the imprints of two adjacent alignments of a family are not aligned parallel to the direction of the other family, which prohibits obtain by rectification a monobloc electrode carrying alignments of teeth corresponding to adjacent alignments of teeth
This procedure can easily be generalized to the drawing of two families of non-orthogonal impressions.

 The invention is of course generalized to any other type of electrode, obtained or not by rectification, with or without added parts. Several electrodes can be implemented by EDM, although this process for obtaining a mold according to the invention proves to be particularly advantageous by the quality of the imprints to which it leads. It is understood that any other method, countermolding or the like, can be used without departing from the scope of the invention.

 It is understood, in fact, that the embodiments, method, procedure and means of implementation described above have only been described by way of non-exhaustive examples and that numerous variants can be proposed by those skilled in the art. art without departing from the scope of the invention.

Claims (14)

Rp1IE ~ NDIC TIONS  1. Mold for grid of the kind comprising a pre  first and second half-shells, characterized in that  the first at least of the half-shells (21, 22) present,  formed on a substantially flat surface (P '), a network  separate elongated imprints (25, 35) divided into  at least two families (25a, 25b, 31, 32, 33) imprint them  your in each family being arranged in parallel alignments  fièles in a given direction (D1, D2, D3), specific to the  so-called family, to which the footprints are themselves  parallel, each footprint (25a, 25b) of each family  being bordered at each end by an imprint (25b, 25a)  from another family while separating two fingerprints themselves  successive of an alignment of another family (25b, 25a).  2. Mold according to claim 1, characterized in that  that said fingerprints (25) within each family are  identical, and that the alignments they form are  equidistant.  3. Mold according to claim 1 or claim  2, characterized in that said fingerprints are distributed  in three families (31, 32, 33) aligned parallel to the  directions from two other families.  4. Mold according to claim 1 or claim 2, characterized in that said imprints (25) are divided into two families (25a, 25b).  5. Mold according to claim 4, characterized in that the directions (D1, D2) of the two families are orthogonal.  6. Mold according to any one of claims 1 to 5, characterized in that the imprints (25) have a constant width.  7. Mold according to claim 6, characterized in that the imprints (25) have a constant depth.  8. A mold according to claim 6, characterized in that the imprints of the same alignment define by their bottom a sinusoid (S ') substantially tangent to the above-mentioned substantially planar surface (P') of said half-shell.  9. Mold according to any one of claims 1 to 8, characterized in that the second half-shell (22, 21) has, formed on a substantially planar surface (P2)  intended to be faced on a substantially flat surface  (P ') of the first half-shell, a network of imprints  (25 ') elongated, disjointed, arranged in parallel alignments and superimposed on those of the indentations (25) of the first half-shell, this network being such that, during the confrontation of said flat surfaces, each indentation  (25, 25 ') of each alignment of each half-shell crosses a second imprint (25', 25) of the other half-shell and  is disposed astride the third and fourth imprints (25 ', 25) of said other half-shell, separated by said second imprint, the aforementioned imprint and said third and fourth imprints delimiting a section of hose continued.  10. Application of a mold according to any one of claims 1 to 9 to obtain by molding a grid  (10) affecting the shape of wires (11, 12) interlaced in a network.  11. Application according to claim 10, characterized in that the wires (11, 12) are made of plastic material of the chosen color.  12. Grid obtained by injection molding of colored plastic in a mold according to any one of claims 1 to 9.  13. A process for obtaining a mold according to any one of claims 1 to 9, characterized in that a hloc is produced having a substantially planar surface (P '), and that, in this block, perpendicularly on said surface, impressions are hollowed out by electro-erosion using at least one electrode (40) carrying complementary teeth (44) of the impressions (25.  14. electro-erosion apparatus for implementing the method of claim 13, of the type comprising an electrode (40) and means for applying a voltage difference between a block and the electrode, characterized in that that the electrode carries a plurality of teeth (44) arranged in a pattern complementary to an 'elementary pattern from which all of the mold cavities (25) can be obtained by translation and rotation, and means adapted to ensure translations and relative rotations between the block (22) and the electrode (40).