Abstract:
A mold ( 10 ) comprising a plurality of blocks ( 11, 13 ) that, in an assembled position, define a mold cavity, the mold being characterized in that it includes at least one pusher ( 21 ), said pusher ( 21 ) being configured to be housed in a first block ( 11 ) of said plurality, in a side facing the mold cavity, and, when the pusher ( 21 ) is housed in said first block ( 11 ), to present a first surface (S 1 ) flush with the mold cavity, and in that the mold ( 10 ) also includes actuator means ( 23, 25 ) enabling the pusher ( 21 ) to be moved relative to the first block ( 11 ), and sealing means ( 19, 27 ) configured to isolate the actuator means ( 23, 25 ) from the mold cavity. An associated molding method.

Description:
FIELD OF THE INVENTION 
       [0001]    The present description relates to a mold, and more particularly to a mold made up of a plurality of blocks, in particular for injection molding, and it also relates to a molding method using a mold. 
       BACKGROUND 
       [0002]    Molds are known, in particular injection molds, that are made of a plurality of blocks that define a mold cavity when they are in an assembled position. Such molds are normally used for injection molding, e.g. for injection molding turbine engine blades. The closed mold cavity defines the shape of the part to be molded. Injection is often performed at high temperature, in which case the temperature of the mold is reduced at the end of injection in order to unmold the part under good conditions without harming its properties. Nevertheless, since the part and the blocks of the mold are made of different materials (e.g. blocks made of metal and part made of carbon) differential expansion occurs that may have the effect of jamming the part in the mold. 
         [0003]    Furthermore, when the mold cavity is opened by separating at least one block of the mold from the remainder of the mold, the part is subjected to cooling that is non-uniform as a result of the temperature difference between the air in the workshop that is in contact with a portion of the part, and the remaining block of the mold that are in contact with another portion of the part. This temperature gradient gives rise to residual stresses in the part. These residual stresses increase with increasing length of the time taken to perform unmolding. It is therefore necessary to provide special methods or appropriate tools for unjamming and extracting the part quickly from the mold. 
         [0004]    A known solution to the problem of unmolding consists in providing a mold made up of numerous blocks, and in removing the blocks one by one until the part is completely disengaged. Such a solution is lengthy to perform and generally requires the mold to be handled (rotated, turned upside-down, tilted, etc.), and this can be found to be complex once the mold exceeds a certain size or its temperature is relatively high. 
         [0005]    Another known solution consists in using an external tool for applying a force on the part and for separating it from the mold, e.g. wedges or a crowbar. However, the force that needs to be exerted is relatively large and such a technique often damages the molded part, in particular by leaving marks on the part. 
         [0006]    An improvement to that problem consists in leaving a narrow through hole in a block of the mold, the through hole then connecting the mold cavity to the outside of the mold. The hole is plugged temporarily before and during molding, generally by means of a screw and a resin of the room temperature vulcanization (RTV) silicone type. At the end of injection, the mold is opened by separating at least one block of the mold from the remainder of the mold, the RTV resin is removed, and a rod is inserted in the through hole from the outside in order to exert a force on the part so as to separate it from the mold. Nevertheless, that method suffers from the above-mentioned drawbacks concerning the use of an external tool. Furthermore, the sealing provided by the RTV resin is of limited reliability and it can happen that the material injected into the mold pushes back the resin and escapes via the through hole during molding. Such a solution is thus not satisfactory. There therefore exists a need for a novel type of mold. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to remedy the above-mentioned drawbacks, at least substantially. This object is achieved by the fact that the mold comprises at least one pusher, said pusher being configured to be housed in a first block of said plurality, in a side facing the mold cavity, and to present a first surface flush with the mold cavity when the pusher is housed in said first block, and by the fact that the mold also includes actuator means enabling the pusher to be moved relative to the first block, and sealing means configured to isolate the actuator means from the mold cavity. 
         [0008]    The term “pusher” designates a part capable of transmitting thrust. The pusher has a first surface flush with the mold cavity so that after molding it is in direct contact with the molded part. The first surface of the pusher thus matches the shape of the mold cavity, i.e. the negative of the shape of the part. The pusher is thus suitable for transmitting thrust to the part, which thrust creates a lever effect for separating the part from the mold. In order to transmit thrust, the pusher is movably mounted in the first block. In particular, the pusher is capable of being moved in one direction. 
         [0009]    Furthermore, the first surface of the pusher may be dimensioned to be of arbitrarily large area. The larger the area of the first surface, the smaller the amount of force that needs to be applied to unjam the part from the first block. 
         [0010]    The actuator means enable the pusher to be moved. They may be actuator means that entrain the pusher directly, or actuator means that make it easier to use external means for making the pusher move. For example, the actuator means may comprise a screw which, on being turned, causes the pusher to move. In another example, the actuator means may include a setback enabling a tool to be engaged in order to move the pusher. 
         [0011]    In order to avoid molding material reaching the actuator means and obstructing them or making them unusable, sealing means are provided for isolating the actuator means from the mold cavity that is to receive the molding material. The actuator means are thus protected reliably throughout the molding process, in particular when the blocks are in the assembled position. 
         [0012]    By means of the mold of the invention, unmolding can be performed simply and quickly, thus making it possible to avoid damaging the part and to minimize the residual stresses due to cooling. Furthermore, because of the sealing means, providing actuator means for the pusher has no impact on proper sealing of the mold and the mold cavity. The fabrication of parts of complete shapes, which are difficult to unmold, benefits in particular from this novel type of mold. 
         [0013]    In certain embodiments, the sealing means are placed around the actuator means. The actuator means are thus protected from infiltration of molding material and they remain operational for unmolding. 
         [0014]    In certain embodiments, the sealing means are provided on a surface that does not face the mold cavity. In these embodiments, the sealing means may be provided on a surface of a block that does not face the mold cavity and/or on a surface of the pusher that does not face the mold cavity. In particular, the sealing means may lie between a surface of the pusher and a surface of a block. It is thus possible to provide linear type sealing means (such as a gasket) as opposed to area type sealing means (such as a membrane), thereby diminishing any risk of rupture or leakage past the sealing means. 
         [0015]    In certain embodiments, the actuator means are accessible from a side facing the mold cavity. Consequently, when the blocks are assembled together in the position defining the mold cavity, the actuator means are then inaccessible. This serves in particular to prevent the pusher being set into movement so long as the mold is closed, thereby guaranteeing that the shape of the mold cavity is maintained throughout molding. 
         [0016]    In certain embodiments, the pusher includes a thread and the actuator means comprise a screw engaged in said thread. In such embodiments, the pusher can thus be caused to move in translation by turning the screw. Such actuator means are simple to fabricate and to use. 
         [0017]    In certain embodiments, when the blocks are in the assembled position, a second surface of said pusher is in contact with a second block other than the first block. In these embodiments, this may be done in such a manner that the second block prevents the pusher from moving relative to the first block. Thus, when the blocks are in the assembled position, the pusher can be held in position by the second block. This serves to increase the reliability with which the position of the pusher is controlled. 
         [0018]    In particular, in certain embodiments, the second surface is not parallel to the direction in which the pusher is movable, such that when the blocks of the mold are in the assembled position, the pusher is clamped between the first block and the second block. 
         [0019]    In certain embodiments, the actuator means are accessible via said second surface of the pusher. The actuator means are thus accessible via a surface that is in contact with the second block when the blocks are in the assembled position. The actuator means are thus inaccessible so long as the first and second blocks are in the assembled position. Any untimely movement of the pusher is thus prevented, in particular while molding is taking place. 
         [0020]    In certain embodiments, the sealing means comprise an O-ring configured to be arranged between the pusher and one of the blocks of said plurality. In particular, the O-ring may be arranged between the pusher and the first block or between the pusher and another block, in particular the second block. The use of standard components such as an O-ring makes it possible to reduce the cost of a mold in these embodiments. 
         [0021]    The present description also relates to a method of fabricating a part by injection molding, the method being characterized in that it comprises the following steps:
       providing a mold having a plurality of blocks that, when in an assembled position, define a mold cavity, the mold including at least one pusher, said pusher being housed in a first block of said plurality in a side facing the mold cavity, and presenting a first surface flush with the mold cavity, the mold also including actuator means enabling the pusher to be moved relative to the block in which it is housed, and sealing means isolating the actuator means from the mold cavity;   injecting a material into the mold cavity in order to form the part;   opening the mold cavity by separating at least one block of said plurality and other than the first block from the remainder of the mold; and   actuating the actuator means to cause the pusher to move relative to the first block so that the pusher exerts a force on the part in order to separate the part from the mold.       
 
         [0026]    By means of such a method, the part can be unmolded in particularly simple and quick manner, thereby serving to diminish residual stresses in the molded part and to accelerate the fabrication process using such a mold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The invention and its advantages can be better understood on reading the detailed description of embodiments of the invention given as non-limiting examples. The device refers to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a perspective view of a first block in which a pusher is housed; 
           [0029]      FIG. 2  is a diagrammatic section of the mold in the embodiment of  FIG. 1 ; and 
           [0030]      FIG. 3  is a plan view of the first block of  FIG. 1 , also containing a molded part. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]      FIG. 1  is a perspective view of a first block  11  of a mold  10 . In the present embodiment, the mold  10  is designed for injecting molding a turbine engine blade out of composite material. In this example, the mold  10  has two blocks  11  and  13 , but it could have more. Since systems for assembling mold blocks are well known to the person skilled in the art, such a system is not described in the present description. When in the assembled position, the blocks  11  and  13  forming the mold  10  define a mold cavity  14  having the shape of the part that is to be molded (ignoring any scrap), i.e. the shape of a blade in this example. 
         [0032]    A groove  17  is provided around the mold cavity  14  for receiving a gasket  17   a . The gasket  17   a  is to be located between the first block  11  and the second block  13 . The gasket  17   a  provides sealing for the mold cavity  14  when the first block  11  and the second block  13  are assembled together. 
         [0033]    A housing  20  is provided in the first block  11  and a pusher  21  is placed therein. The pusher  21  is of a shape that is complementary to the shape of the housing  20 . The pusher  21  is housed in a side facing the mold cavity  14 , i.e. the pusher  21  possesses a first surface S 1  inside the mold cavity  14 . In addition, the first surface S 1  is flush with the mold cavity  14 . 
         [0034]    The pusher  21  is movably mounted in the first block  11 . More precisely, the pusher  21  is movable between a retracted position in which the pusher  21  is fully received in the housing  20  and flush with the mold cavity  14 , and a partially extended position in which the pusher  21  projects relative to the mold cavity  14 . For driving the pusher  21 , a screw  25  is provided in a hole  22  in the pusher  21 , the hole  22  having tapping  23 . The hole  22  also includes a countersink (or spot face)  22   a  arranged beside the cavity  14  and receiving the head of the screw  25 . As described in greater detail below, moving the screw  25  in rotation enables the pusher  21  to be moved away from and towards the first block  11 , and in particular enables the pusher  21  to be moved in translation along the direction of the screw  25  between the retracted position and the partially-extended position. 
         [0035]    In order to mold a part, and in particular a turbine engine blade, the first and second blocks  11  and  13  of the mold  10  are assembled together, and then molding material is injected via at least one injection orifice (not shown) of the mold  10 . Particularly when injection molding a turbine engine blade, it is possible before closing the mold  10  prior to injection to insert a preform in the mold cavity  14 , in particular a woven preform. At the end of injection, the still-closed mold  10  is as shown in  FIG. 2 , which is a fragmentary view in section of the mold  10 . 
         [0036]    In  FIG. 2 , the first block  11  and the second block  13  are assembled together and they define the mold cavity  14 , which is now filled by the molded part  15 . As mentioned above, the gasket  17   a  housed in the groove  17  provides sealing means for sealing the mold cavity  14  at the junction between the various blocks  11 ,  13  of the mold  10 . 
         [0037]    The pusher  21  is housed in the first block  11  so that the first surface S 1  of the pusher  21  faces the mold cavity  14 , i.e. in such a manner that the first surface S 1  is in direct contact with the molded part  15 . The first surface S 1  is for exerting a force on the part  15  in order to separate the part  15  from the first block  11  when the pusher  21  is driven. 
         [0038]    The pusher  21  is also housed in the first block  11  in such a manner that in the assembled position the pusher  21  has a second surface S 2  in contact with a block of the mold  10  that is other than the first block  11 . As can be seen in  FIG. 2 , in the present example, the second surface S 2  is in contact with the second block  13 . The second surface S 2  is to prevent any movement of the pusher  21  so long as the second block  13  is assembled with the first block  11 . 
         [0039]    As mentioned above, in order to avoid molding material reaching the actuator means of the pusher  21 , which it might obstruct and make unusable, sealing means are provided for isolating the actuator means  23 ,  25  from the mold cavity  14  that receives the molding material. The molding material could, a priori, penetrate into all of the interstices between the various portions of the mold  10 ; for example, when injecting epoxy resin as the molding material, the resin penetrates into all interstices of a size greater than or equal to 0.2 millimeters (mm). 
         [0040]    Specifically, the pusher  21  is provided with a groove  27  surrounding the hole  22  on its side facing the second block  13 . Specifically, the groove  27  surrounds the countersink  22   a . An O-ring  27   a  is placed in the groove  27  to provide sealing between the mold cavity  14  and the hole  22  at the junction between the pusher  21  and the second block  13 . In addition, the first block  11  is provided with a groove  19  surrounding the tapped hole  22  on its side facing the pusher  21 . An O-ring  19   a  is placed in the groove  19  to provide sealing between the mold cavity  14  and the tapped hole  22 , at the junction between the pusher  21  and the first block  11 . As a result, the tapped and countersunk hole  22  is isolated at both of its ends from the mold cavity, thereby ensuring the integrity of the tapping  23  and of the screw  25 . In addition, it can be seen that the sealing means  19 ,  27  are provided in respective surfaces that do not face the mold cavity  14 . 
         [0041]    As can be seen in  FIG. 2 , the means for actuating the pusher  21 , in particular the head of the screw  25 , are accessible via the first surface S 2 . Thus, so long as the second block  13  is in contact with the second surface S 2 , the actuator means are not accessible. 
         [0042]    In order to unmold the part  15 , after the part  15  has cooled sufficiently, the mold  10  is opened by separating the second block  13  from the first block  11 . The mold  10  and the part  15  are then in the configuration shown in  FIG. 3 . Because of the differential cooling between the blocks  11 ,  13  and the part  15 , the part  15  is blocked in position in the first block  11 . Since the second block  13  has been withdrawn, the second surface S 2  and thus the actuator means, and in particular the head of the screw  25 , are accessible once more. 
         [0043]    In order to separate the part  15  from the first block  11 , the screw  25  is turned (manually or automatically). Since movement in translation of the screw  25  is stopped by the first block  11  (see  FIG. 2 ), turning the screw  25  acts via the tapping  23  to drive the pusher  21  in translation away from the first block  11 , i.e. in a direction that exerts a force on the part  15 . The pusher  21  thus makes it possible via the first surface S 1  providing contact between the pusher  21  and the part  15  to exert thrust on the part  15 . The screw  25  is thus turned until the part  15  becomes detached from the first block  11 . The greater the area of the first surface S 1 , the smaller the amount of force that needs to be applied, thus making it possible to reduce any risk of marking the part  15 . 
         [0044]    With reference to the embodiment described, experience shows that the root of a blade is particularly difficult to unmold, which is why the mold  10  has a single pusher  21  placed close to the root of the blade  15 . Nevertheless, it is clear that the number and the locations of the pushers can be adapted by the person skilled in the art, while nevertheless taking into consideration the need for each extra pusher in a mold block to have sealing means, e.g. O-rings, and that such sealing means constitute a potential source of failure in the molding process. It is also preferable for the number and positions of the pushers to be optimized in order to minimize the stresses induced on the part by the unmolding operation. 
         [0045]    The use of a mold of the invention is not incompatible with other means for unmolding or for providing assistance in unmolding, e.g. applying a coating to the mold for reducing adhesion between the molded part and the walls of the cavity-forming blocks of the mold. 
         [0046]    The actuator means are not limited to the configuration shown in  FIG. 2 . Numerous known means enable the pusher to be moved in a manner equivalent to that described, whether or not those means make use of a screw or a threaded rod co-operating with a tapped hole. 
         [0047]    Although the present invention is described with reference to specific embodiments, modifications may be provided to those embodiments without going beyond the general scope of the invention as defined by the claims. In particular, the individual characteristics of the various embodiments shown and/or mentioned may be combined in additional embodiments. Consequently, the description and the drawings should be considered in an illustrative sense rather than in a restrictive sense.