FR2789623A1 - Molding equipment employs pressurized, liquid-filled shell halves with resilient membranes in parting plane, to embrace model closely before solidifying liquid to form mold for short production runs - Google Patents

Abstract

The mold is in two halves (4, 5) closing about a cavity (26). The rigid, concave mold shell resists high internal pressures. Elastic membranes sealed to edges of each shell, deform to embrace the model (6) placed inside, forming with the mold shell, internal chambers around the model. These are filled with liquid, which is placed under pressure, to lay the membrane against the model. The liquid is solidified. An Independent claim is included for the corresponding method of molding. Following solidification of the liquid as described, the model is removed. The mold is re-closed, and a molding is produced in the cavity so formed. Preferred features: A support (7) locates the model in the mold. Equipment in the mold, is able to re-liquefy the molding. The mold may include flexible membranes between the elastic membrane and the shell to which it is sealed. The first chamber between elastic and flexible membranes is filled with liquid. A second chamber defined between flexible membrane and the shell is filled with a liquid under pressure. The elastic membrane includes pockets of fluid in its thickness, connected to a pressure control, permitting local variation of the thickness of the elastic membrane. The elastic membrane is preformed. When under no pressure, its shape corresponds with that of the model.

Description

REUSABLE MOLD AND MOLDING METHOD USING SUCH

  The invention relates to a reusable mold and to a molding method using such a mold. It relates more particularly to the production of parts by a rapid and economical molding process, using a reusable mold, and in particular offering the possibility of easily modifying certain dimensions.

  of the part compared to the model.

  The invention finds in particular applications for the production in small series, even the unit production. For example, in the field of footwear, there is a need to reproduce foot shapes, commonly called "shape", on which the uppers, pieces of leather or fabric previously sewn forming the top of the shoes are shaped. Then, on said shapes, the upper and the sole are sewn or glued together, thus forming a shoe corresponding to the shape used. In the case of custom shoes, it is therefore useful, if these shoes are to be manufactured according to the same methods as standard shoes, to have shapes derived from standard shapes after modification of

certain dimensions.

  Generally, to reproduce a shape, we have the choice, conventionally, between two solutions:

machining or molding.

  Machining has the disadvantages of requiring expensive machine tools to purchase and operate. The part can be produced: either by copying and conventional machining - or by numerical control machining, a solution which has the advantage of giving great precision and the possibility of modifying, using a parameter program, some of the dimensions of the room for

adapt it to customer demand.

  In the current state of the art, and in particular for the manufacture of forms for shoes, these two methods are used, which allow the manufacture of complex forms such as those of a foot. The second method requires a program, possibly parameter, and

  consequently involves significant study costs.

  Also, only copying gives the possibility of making parts at relatively low cost, but it does not allow to easily modify only certain

dimensions of the model.

  The other solution is molding. In general molding processes, three types of mold are traditionally used: - sand molds which are produced from models or model plates, and intended to mold steel, cast iron, aluminum or bronze parts ; - steel molds for casting bronze, aluminum or plastic parts; - aluminum molds for parts in

plastic, PVC, rubber.

  The main disadvantage of sand molds is that they are not directly reusable. As for metal molds, if they are reusable, they are costly to produce since they must be machined, which makes them unsuitable for production in small series, a

let alone a unitary production.

  Until now, to modify some of the dimensions of a part compared to a basic model, it was known to place inserts directly on the model, inserts which can be reshaped if necessary after installation on the model, in order to obtain the desired shape, as is done today for the manufacture of orthopedic shoes. Furthermore, it was also known to place inserts no longer on the model but in the mold, such as for example those described in patent JP 3 248 822. However, such devices are hardly adapted to high rates and prove to be costly in labor, the operator having to act differently for each new part if it must be different from the model. The invention aims to propose an alternative solution to the prior art, a more economical and simpler solution to implement. It aims in particular to propose a reusable mold allowing the reproduction of complex shapes and, according to specific provisions, offering the possibility of modifying some of the dimensions of the model without inducing

  fundamental change in the operating protocol.

  The invention also relates to a molding process.

using in particular such molds.

  With these objectives in view, the invention relates to a reusable mold characterized in that it comprises at least two mold elements and closing means for holding the mold elements assembled so as to define between them a molding space , at least one of the mold elements comprising: - a rigid shell of concave shape; - An elastic membrane tightly linked to the edges of the shell, capable of deforming elastically to match the shapes of a model placed in the molding space, and defining between it and the shell at least one chamber; - A liquid filling said chamber, this liquid being capable of solidifying and, from the solid state, to return to the initial liquid state; means for pressurizing the liquid sufficient to apply the membrane to the model, and

  - Means for solidifying the liquid.

  According to a particular arrangement, the thickness of the elastic membrane can be modified at least locally either before the solidification of the liquid, or before the casting of the part, so as to generate differences of certain dimensions between the model and the part. The thickness of the elastic membrane may for example be increased locally before the solidification of the liquid, to generate an increase in certain dimensions between the model and the part which will be molded.

  after the membrane has returned to its normal thickness.

  Conversely, the thickness of the elastic membrane may be increased locally before the casting of the part, so as to generate in the molded part a reduction in

  certain dimensions compared to the model.

  In addition, this provision allows, using variations in thickness of the membrane both at the time of the impression and at the time of molding.

  proper, slight undercuts.

  According to other provisions of the invention, the mold may include: a support for holding the model in position in the molding space, this being particularly useful when a variable thickness membrane as described below is used -above; - Means for bringing the solidified liquid back to the liquid state, which can make it possible to reduce the cycle time and to facilitate the release of the part from the mold; - a flexible membrane located between the elastic membrane and the shell, tightly connected to said shell, a first chamber defined between the elastic membrane and the flexible membrane being filled with liquid, and a second chamber defined between the flexible membrane

  and the hull being filled with a pressurized fluid.

  If this fluid is a gas, this arrangement has the particular advantage that the liquid can be automatically pressurized when the mold is closed, by reducing the volume of this gas; - In the thickness of the elastic membrane, pockets of fluid connected to means for adjusting the pressure of said fluid, in order to locally vary the thickness of said elastic membrane; - A pre-form of the elastic membrane, when it is not subjected to any liquid or fluid pressure, corresponding to a blank of the shape which the model must give it, this arrangement promoting good conformation of the elastic membrane to the model. The invention also relates to a method of

  molding, which can in particular use the mold described above

  above. This molding process is characterized in that it consists in: using at least two mold elements jointly forming a mold and defining between them a molding space, at least one of the mold elements comprising a rigid shell of concave shape and a elastic membrane which is tightly bonded to the edges of the shell and enclosing a liquid in at least one chamber defined between the elastic membrane and said shell; - place a model in the molding space; close the mold; - pressurize the liquid; - solidify the liquid, and keep it in the solid state; - open the mold and remove the model; - close the mold; - form the part in the imprint left by the

  model, then unmold it after solidification.

  If there is a mold according to the invention provided with means for bringing the solidified liquid back to the liquid state, it is possible to add to the process described above a provision according to which as soon as the part is sufficiently resistant, the liquid solidified is brought back at least partly to the liquid state in order to facilitate demolding. If there is a mold according to the invention provided with means for locally varying the thickness of the elastic membrane, it is possible to add to the process described above: - an arrangement according to which, before solidifying the liquid and when the model is already in place in the molding space, the thickness of the elastic membrane is varied locally, in order to modify the dimensions of the imprint left in the solidified liquid relative to the dimensions of the model; - An arrangement according to which, after the extraction of the model and before molding the part, the thickness of the elastic membrane is varied locally in order to modify dimensions of the shape given to the part compared to those of the imprint left in the solidified liquid; - An arrangement according to which, the thickness of the elastic membrane having the possibility of decreasing in certain zones, said thickness is reduced in the

  say zones before extracting the model and / or the part.

  This provision allows slight undercuts

  in the model and / or in the room.

  We will now describe, purely by way of non-limiting example, a possible embodiment of the invention. It is about a machine intended for the realization of forms for the manufacture of shoes, forms presented in the statement of the state of

the technique done above.

  Reference is made to the appended figures: - Figure 1 is a general view of the machine, - Figure 2 is a perspective view of a mold element according to the invention, - Figure 3 is a schematic view, in section , of a mold according to the invention, comprising two mold elements, shown before taking the imprint, - Figures 4a to 4h are schematic sectional views of two mold elements according to the invention during the different stages molding according to an example of a method according to the invention, - Figure 5 shows a first means for locally varying the thickness of the elastic membrane, - Figures 6a to 6c show another way to vary the thickness of the elastic membrane, and a use of these means, - Figure 7 is a view of one of the two elements of a mold according to an alternative embodiment, with the model placed in the molding space, - Figure 8 represents yet another variant of an element mold according to the invention, comprising a solidifiable liquid chamber and a pressurizing fluid chamber, - Figure 9 shows a particular arrangement of the membrane ensuring good adhesion of the elastic membrane with the solidified liquid, - Figure 10 shows an embodiment of the mold according to the invention comprising three mold elements. The machine as a whole, represented in FIG. 1, comprises a frame 1, provided with a command and control panel 9, with a sub-assembly 2 which can undergo a

  translation along guide rails 3. This sub-

  assembly 2 carries two molds pivoting respectively around the axes 8 and 8 ', and each composed of two mold elements, respectively 4 and 5, 4' and 5 '. On the molds are provided orifices 29 and 29 'to allow, by means of supports 7 and 7', the maintenance of models 6 and 6 'in the respective mold spaces 26 and 26'. Each of the supports 7 and 7 'is adjustable in rotation and in translation along the vertical axis. Each of the mold elements 4, 5, 4 ', 5' is connected to compressors by conduits not shown in the

figure 1.

  Each mold is composed of two mold elements 4 and 5, as for example shown in FIGS. 2 and 3 according to a configuration slightly different from that illustrated in FIG. 1, which moreover illustrates the wide possibilities of adaptation of the invention, readily accessible to those skilled in the art. Each of the mold elements is provided with means for pivoting around the axis 8, with closure means known per se (for example screws or other tightening means symbolized by the axes 10) to keep the mold elements 4 and 5 assembled. and ensuring good positioning of the mold elements, so as to define a space between them

molding 26.

  Each of the mold elements 4 or 5 comprises: - a rigid shell, for example metallic, of concave shape, supporting the closure means 10 and the means for ensuring the articulation of the two mold elements 4 and 5 around their axis of rotation 8, provided with an inspection hatch 11 tightly connected to the shell 30; - An elastic membrane 12, for example of rubber-based material, tightly bonded to the edges of the shell 30, the elastic membrane 12 being capable of deforming elastically to conform to the shapes of the model 6, and defining between it and the shell a chamber 27 filled with a liquid 17 (for example liquid water); - An orifice 29 allowing the passage of a support 7 for adjusting and maintaining the position of the model; - refrigeration means 15 capable of solidifying the liquid 17; means 16 for reheating the solidified liquid

  17 to return it to a sufficiently liquid state.

  Furthermore, each mold element is connected to means, not shown, for pressurizing the liquid 17, such as for example a reserve of pressurized water. It will also be necessary to provide means to compensate for variations in the volume of water.

  during his physical state changes.

  The liquid 17 chosen here is water, but this in no way excludes other liquids, or even mixtures containing solid particles such as grains of sand. It will only be necessary to choose a material whose solidification temperature is not too far from the ambient temperature, this in order to save energy. It will also be noted that it is possible to choose a material which is solid at room temperature and liquid at a higher temperature, for example wax; the device described below then applies in a similar manner, by adapting the working temperatures by means of refrigeration and / or heating, and can moreover allow the molding of parts made of materials at higher melting temperature. The material and the shape of the shell 30 must be chosen so that the shell 30 has sufficient elasticity to withstand the pressures which will be exerted on it, in particular during the solidification of the water 17. The shell 30 can for example be made of steel or aluminum, this second solution presenting

the advantage of being lighter.

  It will also be necessary to provide the vents necessary for the evacuation of the air present in the mold at the time of molding. It is also possible to add a vacuum pump to evacuate the air when the impression is taken, as well as during the subsequent pouring of the

material in the mold.

  The elastic membrane 12 is held tight against the shell 30 by a flat iron held in place with the screws 14 at a sufficient number of points to ensure a

  regular tightening and good sealing.

  To be suitable, the elastic membrane 12 must have particular characteristics: it must resist frequent changes in temperature, it must be sufficiently elastic in the operating temperature range to conform to the shapes of the model, and it adheres to the ice for good support during the extraction of the model, or also during the mold release of the part if you want to reuse the mold several times to make a small series of identical parts. Silicone rubber has interesting characteristics for this use, because it can be strongly stretched, withstands relatively high temperatures, and is not very adherent on the plastic of molded parts. The membrane has for example a thickness of 1 to

1.5 mm.

  Preferably, a device can be used to vary the thickness of the membrane 12. In FIG. 5, pockets 18 are created between the membrane 12 and suction cups 21 whose shape is adapted to the deformation which it is desired to induce . the suction cup 21 can be connected in a sealed manner to the membrane 12, for example by gluing, so that the pressurization or depression of the pockets 18 by means of conduits 19 varies the position of the membrane 12, adding or thereby removing additional volume between

  the solidified water and the model, or the part produced.

  According to a preferred variant illustrated in FIG. 6a, pockets 18 are made in the thickness

  of the membrane 12 and are connected to non-compressors

  represented by conduit 19. When the model 6 is in place in the mold and the liquid 17 is still in the liquid state, a fluid 20 is injected under pressure, thus causing a deformation of the membrane 12, as shown in Figure 6b. During the molding of the part 22, the fluid 20 is released, which allows the part 22 to be of a larger size i1 than the model 6, as shown in FIG. 6c. The pockets of the elastic membrane 12 are arranged on said membrane 12 so as to obtain shape modifications at the desired locations on the model. Figure 7 shows a possible arrangement of pockets 18 on a mold element (the mold element of Figure 7

  representing a possible variant of the invention).

  It will be noted that the inflatable bags may also play, to a certain extent, the role of compensating for variations in the volume of water during the passage of

  the liquid state to the solid state and vice versa.

  Preferably, to improve the adhesion of the elastic membrane 12 to the solidified liquid 17, it is possible to use an elastic membrane 12 provided, on its face in contact with the liquid 17, with pins 31, which can for example be produced by same material as the elastic membrane 12. These pins 31 will be taken in the solidified liquid 17, their elastic nature allowing them to

  withstand the pressure due to the solidification of water.

  The holding function will be all the better ensured as the pins 31 flare towards the ice, like those

shown in Figure 9.

  According to a particular arrangement, provision may be made, for example for the production of parts of large volume, to give the elastic membrane 12 a preform corresponding to a rough outline of the shape of the models 6, for better application of the

  elastic membrane 12 on model 6.

  It is possible to provide, if the support 7 of the model 6 is not linked to the frame of the machine 1, a device allowing the positioning of the model 6 as quickly and as precisely as possible in the molding space 26, this positioning

  position always effected through hole 29.

  It will be necessary to adapt the location of the cooling devices 15 and heating 16 as well as the pockets 18 of the elastic membrane 12 to the model which it is envisaged to have in the molding space 26. An elastic membrane 12 comprising pockets 18 of given shape can therefore generally be suitable only for a certain number of models of fairly similar sizes and shapes, while nevertheless keeping

  very wide possibilities of adjustments.

  We can, according to a particular arrangement, design a similar system, the heating means 16 and cooling 15, possibly flexible and elastic, are arranged so as to suit models 6 of various sizes and shapes, within the limit of the size of the shell 30, and in which the pockets 18 of the elastic membrane 12 are numerous, so as to form a more or less dense matrix, the pressure in each of the pockets 18 of fluid 20 being then determined for example by computer in function

  of the model 6 used and of the part 22 to be obtained.

  According to the needs of the user, the mold can comprise more than two elements 4 or 5. FIG. 10 represents such a mold with three elements. The multiplication of mold elements can allow better application of the elastic membrane 12 and

  facilitate the extraction of model 6 and / or part 22.

  The invention also relates to the method of implementing the mold described above; we will refer to

  Figures 4a to 4h for the description we are going to make

now.

  We start by opening the mold (Figure 4a) and then positioning the model 6 relative to the pockets 18 of the elastic membrane 12 using the means 7 for positioning the model (Figure 4b). Then the mold is closed and the liquid 17 is pressurized. Optionally, the fluid pressure 20 in each of the pockets 18 is adjusted to the values making it possible to obtain an additional volume of the elastic membrane 12 corresponding to that to be added to the model 6 to obtain the desired shape (FIG. 4c and 6b). Then, the liquid 17 is cooled until it solidifies (FIG. 4d). While maintaining the liquid 17 in the solid state, after possibly reducing as much as possible the pressure in the pockets 18 in order to facilitate the extraction of the model 6, the mold is opened and the model 6 is removed (FIG. 4e). By tilting the support 7, it is replaced by a particular support 23, intended to be taken in the part 22 (Figure 4f). We can then close the mold, possibly adjust the pressure in the pockets 18 to new values, making it possible to obtain an additional volume of the elastic membrane 12 corresponding to that to be removed from the imprint left by the model and over thicknesses of the elastic membrane 12 introduced during the solidification of the liquid 17 to obtain the desired shape. Then can start the casting of the part 22, the constituent material, for example a two-component polyurethane which flows cold, being introduced into the mold through the support 23 (FIG. 4g and 6c). As soon as the part is sufficiently resistant, it is possible to demold (FIG. 4h), after having possibly reduced as much as possible the pressure in the pockets 18 in order to facilitate the extraction of the part 22. Demolding can be facilitated if the we start even before the opening of the

  mold the heating of the solidified liquid 17.

  The use of the mold as described above is in no way limiting. One can in fact consider manufacturing no longer solid forms by casting, but hollow forms, in particular by the blowing method. This blowing will preferably be carried out using the same orifice 29 and the imprint left

by support 7 of model 6.

  One can also imagine variants to the mold elements 4 or 5 described above. We can for example, as shown in Figure 8, place a flexible membrane 25 in the bottom of the shell 30 and tightly connected to said shell 30, thereby creating a chamber 28, which can be filled with compressed gas 24. This automatically pressurizes the liquid 17 when the mold is closed. This also makes it possible to reduce the volume of water 17 to solidify and therefore a saving in frigories and a reduction in cycle time. Furthermore, the presence of the compressible gas in the chamber 28 makes it possible, in a simple manner, to compensate for the variations in volume of the water during the passage from the liquid phase to

the solid phase, and vice versa.

Claims (12)

  1. Reusable mold characterized in that it comprises at least two mold elements (4, 5) and closing means (10) to hold the mold elements (4, 5) assembled so as to define a space between them molding (26), at least one of the mold elements (4 or 5) comprising: - a shell (30) rigid and of concave shape, capable of withstanding high pressures; - An elastic membrane (12) tightly connected to the edges of the shell (30), capable of deforming elastically to match the shapes of a model (6) placed in the molding space (26), and defining between it and the shell (30) at least one chamber (27); - a liquid (17) filling said chamber (27), this liquid (17) being capable of solidifying and, from the solid state, returning to the initial liquid state; means for pressurizing the liquid (17), sufficient to apply the membrane (12) to the model (6), and   - Means (15) for solidifying the liquid.   2. Reusable mold according to claim 1 characterized in that it also comprises a support (7) for holding the model (6) in position in the space of molding (26).   3. Reusable mold according to claim 1 characterized in that it comprises means (16) for   return the solidified liquid (17) to the liquid state.   4. Reusable mold according to claim 1 characterized in that at least one of the mold elements (4, 5) comprises a flexible membrane (25) located between the elastic membrane (12) and the shell (30), so linked tight to said shell (30), and in that the first chamber (27) defined between the elastic membrane (12) and the flexible membrane (25) is filled with liquid (17), and a second chamber (28) defined between the flexible membrane (25) and the shell (30) is filled with a fluid (24) under pressure. 5. Reusable mold according to claim 1 characterized in that the elastic membrane (12) comprises in its thickness pockets (18) of fluid (20) connected to means for adjusting the pressure of said fluid (20), in order to make locally vary the thickness of said elastic membrane (12).   6. Reusable mold according to claim 1 characterized in that the elastic membrane (12) has, when it is not subjected to any pressure of liquid (17) or fluid (20), a pre-form corresponding to a   outline of the form that the model should give it (6).   7. Molding process characterized in that it consists in: - using at least two mold elements (4,5) jointly forming a mold and defining between them a molding space (26), at least one of the mold elements (4,5) comprising a rigid concave shell and an elastic membrane (12) which is tightly connected to the edges of the shell (30) and contains a liquid (17) in at least one chamber (27) defined between the elastic membrane (12) and said shell (30); - place a model (6) in the molding space (26); - close the mold; - pressurize the liquid (17); - solidify the liquid (17), and maintain it in the solid state; - open the mold and remove the model (6); - close the mold; - form the part (22) in the imprint left by   the model (6), then unmold it after solidification.   8. Molding method according to claim 7 characterized in that as soon as the part (22) is sufficiently resistant, the solidified liquid (17) is returned at least partially to the liquid state in order to facilitate demolding. 9. A molding method according to claim 7 characterized in that, before solidifying the liquid (17) and when the model (6) is already in place in the molding space (26), the thickness is varied locally. of the elastic membrane (12), in order to modify the dimensions of the imprint left in the solidified liquid (17) relative to the dimensions of the model (6).   10. Molding method according to claim 7 characterized in that, after the extraction of the model (6), the liquid (17) being solidified, and before molding the part (22), the thickness of the material is varied locally. the elastic membrane (12) in order to modify the dimensions of the shape given to the part (22) relative to those   of the imprint left in the solidified liquid (17).   11. Molding method according to claim 9 characterized in that, the thickness of the elastic membrane (12) having the possibility of decreasing in certain areas, the thickness of the elastic membrane (12) is reduced in said front areas to extract the model (6) and / or the part (22).   12. Molding method according to claim 7 characterized in that the pressurization of the liquid (17) is due, when the mold is closed, to the thrust   exerted by the model (6) on the elastic membrane (12).