FR2841818A1 - Moulding procedure for thermosetting composition materials uses moving pistons to create perforations before polymerisation - Google Patents

Abstract

The procedure, using a mould (1) with an inner cavity (20), consists of delivering a thermosetting composition material (21) to the cavity and forming one or more perforations in it before it is polymerised in the mould. The perforations are made by at least one, and preferably two pistons (7a, 7b), moving together and holding the removed portion of the composition material between them as they maintain a constant distance apart. After polymerisation the removed portion is returned to its original position before the mould is opened by separating the matrix (2a) and die (2b).

Description

The present invention relates to a method, a mold and a device for

  manufacture of a molded part in composite material. The molding of a part by compression, injection5 compression or injection of a composite material resulting from the mixture of a thermosetting material and reinforcing fibers or the like is known, the composite material possibly, for example, being in the form of '' a sheet molding compound (Sheet Mold Compound or SMC), a bulk molding compound (Bulk Mold Compound or BMC) or a suitable molding compound (Adapted Mold Compound or AMC). The latter may, for example, contain about% by mass of long glass fibers, that is to say of a

length of about 25 mm.

  A first known way of providing the part with openings or through holes consists in using a mold such that the parts which come out of the mold are already perforated. However, due for example to their positions on the part, certain holes cannot be obtained in this way. This is also the case when the part is produced from a sheet molding compound (SMC). In addition, the portion of the mold which corresponds to a hole in the molded part passes through the closed volume delimited by the closed mold and therefore forms an obstacle which the composite material must bypass during molding. This makes it difficult to implement a molding technique where a vacuum inside the mold is provided to improve the flow of the material to be molded and the surface condition of the molded part. In addition, this leads to a particular and often unfavorable orientation of the fibers of the composite material and to the appearance of bonding surfaces. In the sense in which it is understood here, a bonding surface is a meeting surface of two fronts of material progressing in opposite directions. A second known way of providing holes or openings in a part molded of composite material consists in drilling, either by machining or by punching, this part after it has been molded and then removed from the mold. This second way of operating, unlike the first, can almost always be used. However, it is long and dusty. It therefore has the disadvantage of resulting in an overcharge. It is also noisy and generates microcracks in the room, these microcracks being the result of constraints which

appear during drilling.

  The invention, which intends to remedy the aforementioned drawback, therefore aims at least to reduce the cost of a

  part both molded in composite material and perforated.

  To this end, the subject of the invention is a method of manufacturing a molded part made of composite material, using a mold defining an interior volume, this method comprising the steps in which: (a) the mold with thermosetting composite material and the part is molded in this mold, (b) the composite material is polymerized in the mold, characterized in that between steps (a) and (b) (c) cleaning is carried out minus one pass through the

  composite material contained by the mold.

  It is therefore a question of drilling the part while the material

  composite which constitutes it is in the visco-elastic state.

  According to other advantageous characteristics of this manufacturing process: - step (c) is carried out by causing at least one piston to enter the interior volume of the mold; - Step (c) is carried out by removing at least part of the molded part; - Step (c) is carried out by pushing said part outside the interior volume of the mold; - step (c) is carried out by simultaneously sliding, in the same direction, said piston and another piston which form part of the mold, are disposed opposite, respectively in a punch and a die of the mold, and maintain said part between them; - during step (c), the distance between the two pistons is not reduced - during step (c), the distance between the two pistons is kept constant; - After step (b) and before the part is removed from the mold, this part is deburred by bringing the two pistons back to a position that these two pistons occupied during step (a); - Before step (c), the closed volume is not completely filled and step (c) is carried out by moving, using at least said piston, the composite material from one region to the inside the mold to another region inside the mold; - in step (a), a movable matrix is moved from the mold to a fixed punch of the mold and the composite material is made to flow by crushing it between the punch and the

moving matrix.

  The invention also relates to a mold for shaping a part made of composite material, the closed mold defining an interior volume, characterized in that it comprises: - at least first and second passages which are in line with the one from the other and open opposite, in said interior volume, - as well as at least a first and a second piston respectively mounted to slide in the first

and the second pass.

  According to other advantageous characteristics of this mold, when the mold is closed, the first piston is

  able to enter the second passage.

  In addition, the subject of the invention is a device for manufacturing a part made of composite material, characterized in that it comprises a mold as defined above, as well as means for driving the first and second pistons, and in that when the mold is closed, said drive means are able to move the first piston at least to that of the two ends of the second passage which opens inside said volume

inside.

  The invention will be clearly understood on reading the

  description which follows, given only as

  example and made with reference to the accompanying drawings, in which: - Figures 1 to 5 are schematic views, in vertical section, of a device, according to the invention, for manufacturing a molded piece of material composite and illustrate the successive stages of a process, also according to the invention, for manufacturing such a part, and FIGS. 6 and 7 are schematic views, in vertical section, of a portion of a conforming mold to the invention and illustrate two stages of a method, according to an alternative embodiment of the invention, of manufacturing

  of a molded piece of composite material.

  In Figures 1 to 5, a compression molding device comprises a mold 1 in two main parts, which are a movable die 2a and a fixed punch 2b. The die 2a is carried by the mobile plate 3a of a press with vertical movement, known per se and not shown. It is fixed to this movable plate 3a by means of a plate 4a and separation blocks a. The punch 2b is carried by the fixed plate 3b of the press, by being fixed to this plate 3b via

  of a plate 4b and of separation blocks 5b.

  In what follows, the references designating elements carried by the fixed plate 3b are constructed by replacing, by the letter "b", the letter "a" which is at the end of the references identifying the elements

  similar as carried by the movable plate 3a.

  The matrix 2a is pierced with several cylindrical passages or of suitable vertical shape 6a, only one of which is visible in FIGS. 1 to 5 and the respective cross sections of which have the same shape as the cross sections of the passages to be formed through the part to be produced . A piston 7a is slidably mounted in each passage 6a, the side wall of which is coated with a wear jacket 8a. Each of the pistons 7a is located at the end of one of several rods 9a, which couple these pistons 7a to a vertically movable plate 10a. Stops lla, fixed on the top of the die 2a and stops 12a, fixed on the underside of the plate 4a, limit the travel of the movable plate lOa downwards and upwards, as drive means, formed by hydraulic cylinders 13a installed on either side of the matrix

  2a, are able to move vertically.

  The cylinder 14a of each hydraulic cylinder 13a is fixed to the matrix 2a, while the piston 15a of each

  hydraulic cylinder 13a is coupled to the movable plate 10a.

  Each hydraulic cylinder 13a has two chambers 16a and 17a of variable volume, which its piston 15a separates from one another. The supply of each of these chambers 16a and

  17a is controlled by a pilot operated non-return valve 18a.

  Unlike each chamber 17a, of large cross section, each chamber 16a, of small cross section, is crossed by the coupling rod of the piston 15a which partially delimits it. The upper face of the punch 2b carries support wedges 19 for the die 2a. For the rest, what the fixed plate 3b carries is generally similar to what the

the movable plate 3a.

  In Figure 2, the mold 1 is closed. The die 2a, including the pistons 7a, and the punch 2b, including the pistons 7b, jointly delimit an interior and closed volume 20, which has the shape of the part to be produced and in which the passages 6a and 6b, closed by the pistons 7a and 7b, open opposite. Each passage 6a is in the axis of a passage 6b and each piston 7a is directed towards

a piston 7b and vice versa.

  A process, in accordance with the invention, for manufacturing a piece of composite material using the device shown in FIGS. 1 to 5 can begin as soon as the mold 1 is open and the movable plate 10b resting on the stops 12b, pistons 7b are flush with the surface

upper of punch 2b.

  The first step of this process, which includes a compression molding phase, consists in depositing a blank of composite material 21, not polymerized, on the punch 2b, after which we are in the configuration illustrated in FIG. 1, the draft that may arise

  in the form of a sheet molding compound (SMC).

  Then, while the hydraulic jacks 13a apply the movable plate lOa against the stops lla and the pistons 7a are therefore flush with the bottom surface of the matrix 2a, the part is molded by moving this matrix 2a downwards, in the direction of the fixed punch 2b, so that the composite material 21 is crushed and creeps inside the interior volume 20. The movement of the die 2a is stopped when the latter is close to the support shims 19, that is to say say at a distance of the order of 0.2 to 0.3 mm from these support wedges 19. The configuration of the assembly is then that which is illustrated in FIG. 2: the mold 1 is closed and the volume is closed and filled with composite material 21. In the case of injection-compression or injection, there is

  contact between the support wedges 19 and the matrix 2a.

  As soon as a timer between 0 and 12 seconds, preferably of the order of 5 seconds, has been counted down by a timer, from the stop of the matrix 2a, the hydraulic jacks 13a and 13b simultaneously drive the plates movable lOa and lob upwards, so that the composite material 21 is perforated by being sheared in the pasty state, and more precisely in the visco-elastic state, its parts 22 held in sandwich between the pistons 7a and 7b being removed by being moved outside the enclosed volume 20. The hydraulic cylinders 13a and 13b are dimensioned in such a way that the movable plate loa moves slightly faster than the movable plate 10b, that is to say in such a way that the differences between the pistons 7a, on the one hand, and the pistons 7b, on the other hand, are not reduced, but on the contrary increased during the shearing of the material

composite 21.

  The movable plate lob stops against the stops llb,

  after each piston 7b has entered a passage 6a.

  The plate 10a is stopped by the stops 12a. The assembly is then in the position illustrated in FIG. 3 and the

  composite material 21 is polymerized by baking.

  Then, the resulting part 23 is deburred by displacement of the pistons 7a and 7b downwards, to their initial position, after which the assembly is at the

position illustrated in figure 4.

  Finally, the movable plate 3a is moved upwards and the mold 1 is opened, after which the molded part 23 is detached from the punch 2b by a battery of ejection pistons, known per se and not shown. The removal of the removed parts 22 takes place during the conventional blowing and cleaning operation of the mold 1, as

shown in figure 5.

  At the outlet of the mold 1, the part 23 of composite material is pierced with passages which result from the withdrawal of the parts 22, so that these passages do not have to be provided after molding, by machining or by punching. This results in savings and a gain of

  time, in accordance with the object of the invention.

  When we want to clean the pistons 7a and 7b, we dismount the stops 11a and 11b, then, the mold 1 being open, we release these pistons 7a and 7b by pushing them

using rods 9a and 9b.

  During the stop phases, the matrix 2a rests on the

support shims 19.

  A method according to an alternative embodiment of the invention begins in the same way as the method described above, until the mold 1 is closed. At the end of this closure, the closed volume 20 is not

  completely full, as can be seen in Figure 6.

  The step following the closing of the mold 1 begins as soon as a time delay of 0.1 to 0.2 seconds has been counted from the stop of the matrix 2a. It consists in moving the pistons 7a in the direction of the pistons 7b, as well as the pistons 7b in the direction of the pistons 7a. It leads to the punching of the composite material 21 in the viscoelastic or liquid state, and ends when each piston 7a and a piston 7b are in the position illustrated in FIG. 7 and are only separated by a small distance. , of the order of 0.7 mm, due to the presence of reinforcing fibers between them. This step also leads to the composite material 21 occupying the entire enclosed volume 20, owing to the fact that the penetration of the pistons 7a and 7b, which drive out the composite material, results in

  a reduction in the volume to be filled.

  Then, the composite material 21 is polymerized and the method according to an alternative embodiment of the invention is

  ends like the one described above.

  This method according to an alternative embodiment of the invention has the advantage of leading to a reduction in the composite material consumed. It goes without saying that it cannot be implemented by the device shown in FIGS. 1 to 5 without this device being modified in such a way that the pistons 7a can penetrate inside the closed volume 20 and that the pistons 7b is stopped before reaching the passages lOa. As a variant, the passages 6a and the pistons 7a can be omitted, the pistons 7b being able to pass through the entire enclosed volume 20. It goes without saying that the passages 6b and the pistons 7b can be omitted instead of the

passages 6a and pistons 7a.

  The invention is not limited to the embodiments described above. In particular, the press which receives the mold 1 may not have a vertical movement, but by

example with horizontal movement.

  In addition, the molding of the composite material can be done not by compression but by compression injection or injection molding, injection compression molding being distinguished from compression molding in that it is not a blank which is deposited on the punch. 2b but a mass of composite material deposited by a

injection unit.

  In addition, each of the movable plates 10a and lob can cause only one piston 7a or 7b, in the case where one wishes to provide only one passage through the

molded part 23.

  The method according to the invention has the advantage of being able to be easily implemented for producing large parts from sheet molding compounds (SMC). It also has the advantage of being compatible with a molding technique involving

  a vacuum inside the mold (vacuum molding).

  Among the other advantages of the invention, it will be noted that, during molding, the flowing or flowing composite material does not encounter any obstacle to be circumvented, which results in a reduction in the number, or even a elimination, when times gluing planes inside the molded part and regions of this part where the reinforcing fibers have a

particular orientation.

  In addition, due to the good surface condition of the entire part after polymerization, the method according to the invention may include a step, which follows this polymerization and precedes the opening of the mold, in which the visible surface is covered. of the molded part, by injecting, under high pressure, a coating primer

  called IMC (In Mold Coating), in the closed mold.

Claims (13)

  1. Method for manufacturing a molded part made of composite material, using a mold (1) delimiting an interior volume (20), this method comprising the steps in which (a) the mold (1) is supplied with thermosetting composite material (21) and the part is molded in this mold (1), (b) the composite material (21) is polymerized in the mold (1), characterized in that between steps (a ) and (b) (c) cleaning at least one passage through the   composite material (21) contained by the mold (1).   2. Method according to claim 1, characterized in that step (c) is carried out by causing at least one   piston (7b) in the interior volume (20) of the mold (1).   3. Method according to claim 1 or 2, characterized in that step (c) is carried out by removing at least one part (22) of the molded part.   4. Method according to claim 3, characterized in that step (c) is carried out by pushing said part (22)   outside the interior volume (20) of the mold (1).   5. Method according to claims 2 and 4,   characterized in that step (c) is carried out by simultaneously sliding, in the same direction, said piston (7b) and at least one other piston (7a) which are part of the mold (1), are arranged in screws -visible, respectively in a punch (2b) and a matrix (2a) of   mold (1), and hold between them said part (22).   6. Method according to claim 5, characterized in that during step (c), the distance between the two pistons (7a, 7b) is not diminished.   7. Method according to claim 6, characterized in that during step (c), the distance between the two pistons (7a, 7b) is kept constant.   8. Method according to any one of claims 5   7, characterized in that after step (b) and before the part is removed from the mold, this part is deburred by bringing the two pistons (7a, 7b) into a position that these two   pistons (7a, 7b) occupied during step (a).   9. Method according to claim 2, characterized in that before step (c), the closed volume (20) is not completely filled and in that step (c) is carried out by moving, to using at least said piston (7b), composite material (21) from a region inside the mold   (1) to another region inside the mold (1).   10. Method according to any one of the claims   previous, characterized in that in step (a), a movable matrix (2a) is moved from the mold (1) to a fixed punch (2b) of the mold (1) and the composite material (21) is made to flow crushing it between the punch (2b) and the moving matrix (2a).   11. Conformation mold of a part made of composite material, the closed mold defining an interior volume (20), characterized in that it comprises - at least first and second passages (6a, 6b) which are in the extension l 'from each other and open opposite, in said interior volume (20), - as well as at least a first (7a) and a second piston (7b) respectively mounted to slide   in the first (6a) and the second passage (6b).   12. Mold according to claim 11, characterized in that when the mold (1) is closed, the first piston (7b)   is able to enter the second passage (6a).   13. Device for manufacturing a part made of composite material, characterized in that it comprises a mold (1) according to claim 11 or 12, as well as means (9a, 1Qa, lob, 13a, 13b) for driving first and second pistons (7a, 7b), and in that when the mold (1) is closed, said drive means (9a, lOa, lOb, 13a, 13b) are able to move the first piston (7b) at least up to that of the two ends of the second passage (6a)   which opens inside said interior volume (20).