FR2834926A1 - Automobile motor cradle has at least one core of synthetic foam, between reinforcement layers, with a bonded elastic elastomer section, shaped in a mold with injected heat-setting resin to give a rigid structure - Google Patents

Abstract

Cradle structure for an automobile motor rigid section(s), with inner core(s) of a synthetic foam between reinforcement layers of composite fibers of glass, carbon or a polymer, stiffened by a heat-setting resin. At least one section of an elastic elastomer, e.g. rubber and/or isoprene, is bonded to the rigid section. Cradle structure for an automobile motor has at least one rigid section, with at least one inner core (34) of a synthetic foam between reinforcement layers (36) of composite fibers of glass, carbon or a polymer, stiffened by a heat-setting resin. At least one section (38) of an elastic elastomer, e.g. rubber and/or isoprene, is bonded to the rigid section. For its production, the inner core is placed within a mold (40), together with the outer reinforcement claddings and the elastomer unit. The resin is injected into the mold, and the elastomer unit is compressed. The molded structure is finally baked.

Description

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"Method of manufacturing a synthetic engine cradle"
The invention relates to a manufacturing method for a structural element.

 The invention relates more particularly to a method of manufacturing a structural element, in particular a motor vehicle cradle, which comprises at least one rigid part comprising at least one internal core of thermosetting synthetic foam covered with an external fiber coating of composite material stiffened by a thermosetting resin, and at least one elastic part formed of an elastomeric material adhering to the rigid part.

 Many examples of manufacturing methods are known for elements of this type.

 A method of manufacturing a complex structural element such as a motor cradle must take into account the many constraints and requirements which must be satisfied by the structural element considered during its use.

 Thus, an engine cradle must perform many functions, such as transmitting to the structure of the vehicle the forces of the suspension, ensuring the recovery of forces from the powertrain, transmitting the forces of the stowage and towing systems, maintaining the piping, cables, fairings, thermal screens and various accessories, and participate in the dissipation of energy resulting from a shock.

 In addition, a motor cradle must also meet the requirements for weight reduction, noise and vibration filtration, economy of the manufacturing process, and resistance to attack from the outside environment.

 For these reasons, a motor cradle must in particular comprise a large number of fastening elements, sound insulation, and structural reinforcement more particularly intended to resist impact and / or fatigue.

 The engine cradles are conventionally made of sheet steel and have many fixing parts

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 such as crimped nuts, “cage” type nuts, stiffening parts such as spacers, or even acoustic filtration parts such as studs made of elastomeric material.

 The most widely used manufacturing process consists in assembling, in particular by welding, two elements made of stamped sheet steel between which the various aforementioned parts are inserted.

 The result is a motor cradle which is relatively heavy and which has a high manufacturing cost.

 To overcome this drawback, the invention provides a method of manufacturing a motor cradle consisting essentially of composite materials.

 More generally, this method is also applicable to any other type of structural element subjected to similar constraints, such as structural elements intended for the aeronautical, naval or space industries.

 To this end, the invention proposes a method of the type described above, characterized in that it successively comprises at least a first step of placing the internal core, the external coating and the elastic part in a mold, a second step of injecting the thermosetting resin, a third step of compressing the elastic part by at least one movable part of the mold, and a fourth step of baking the structural element intended to allow the crosslinking of the synthetic foam thermosetting, thermosetting resin, and elastomeric material.

 According to other characteristics of the process: - the third step is extended throughout the fourth step, - before the first step, the mold is brought to the crosslinking temperature of the thermosetting resin,

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 the fourth baking step is a step of high duration comprising an overall maintenance of the mold at the crosslinking temperature of the thermosetting resin, the fourth baking step is a step of reduced duration comprising an overall maintenance of the mold at the temperature of crosslinking of the thermosetting resin and localized heating of the movable part of the mold to the crosslinking temperature of the elastomeric material of the elastic part, - the method comprises, during the first step, a sub-step of inclusion of at least a first metal insert in the internal core and / or in the external coating, - the method comprises, during the third step, a substep for fixing at least one second metal insert in the elastic part, - the method comprises a fifth step of extracting the structural element from the mold.

 The invention also provides a mold for implementing the method described above, characterized in that the movable part of the mold comprises crimping means intended to allow the fixing of at least one metal insert in the elastic part of the structural element to be manufactured.

 According to another characteristic of the mold, the fixed part of the mold comprises at least one cavity for receiving a structural element into which opens at least one channel intended to allow the injection of thermosetting resin.

 The invention also provides a structural element obtained by a method of the type described above, characterized in that it comprises at least a first metal insert forming a spacer and / or fixing point which is arranged in the internal core and / or in the external covering of its rigid part.

 According to another characteristic of the structural element, it comprises at least a second metal insert forming reinforcement and / or spacer and / or point of attachment point which is arranged in its elastic part.

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Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: - Figure 1 is a perspective view of a motor cradle obtained by a conventional manufacturing process; - Figure 2 is a schematic sectional view illustrating a first step of the method corresponding to the establishment of the parts constituting the structural element in the mold; - Figure 3 is a schematic sectional view illustrating an intermediate step of the method corresponding to the closing of the mold; - Figure 4 is a schematic sectional view illustrating a second step of the method corresponding to the injection of a thermosetting resin into the mold; - Figure 5 is a schematic sectional view illustrating a third step of the method corresponding to compression of the elastic part by at least one movable part of the mold and a fourth step of the method corresponding to the baking of the structural element; - Figure 6 is a schematic sectional view illustrating a fifth step of the method corresponding to the release of the structural element.

In the following description, identical reference numerals designate identical parts or having similar functions.

By convention, the terms "lower" and "upper" respectively designate elements or positions oriented respectively downwards and upwards of the figures.

FIG. 1 shows an assembly of a motor cradle 1 0 produced in accordance with a prior state of the art. In known manner, the engine cradle 1 0 comprises a lower part 12 and an upper part 14 which are

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 both produced in the form of stamped sheet steel plates.

 The lower part 12 has bosses 16, arranged opposite bosses (not shown) of the upper part 14 and which are intended to receive spacers 18.

 The lower part 12 has holes 20, arranged opposite the holes 22 (not shown) of the upper part 14 and which are intended to receive elements 24 of elastomeric material, better known by the name of "silent-blocks".

 The upper part 14 also comprises holes 26 in which are received different fixing means such as captive nuts 28, such as nuts of the "cage" type or crimped nuts.

 At least one reinforcing element 30 can be arranged between the lower 12 and upper 14 parts to stiffen the engine cradle 10.

 Once the spacers 18, the elements made of elastomeric material 24, and the reinforcing element 30 are in place, the upper part 14 is assembled to the lower part 12, for example by welding.

 The result of such a manufacturing process is a relatively heavy motor cradle 10 and a high manufacturing cost.

 To remedy these drawbacks, the invention proposes a method of manufacturing a motor cradle 10, and more generally of any structural element 10, using the advantages of composite materials.

 In this configuration, as illustrated in FIG. 6, the structural element 10 to be obtained comprises at least one rigid part 32 comprising at least one internal core 34 of thermosetting synthetic foam covered with an external covering 36 made of fibers of composite material stiffened by a thermosetting resin, and at least one elastic part 38 formed of an elastomeric material adhering to the rigid part.

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 In the preferred embodiment of the invention, the thermosetting synthetic foam of which the internal core is made up 34 is for example a foam based on polyurethane or polyvinyl chloride, the fibers of composite material of which the external coating is made up 36 are for example glass fibers, carbon fibers, or aramid fibers, the elastomeric material of which the elastic part 38 is made comprises natural rubber and / or isoprene, and the thermosetting resin serving to stiffen the element 10 is for example a resin based on polyurethane or polyvinyl chloride.

 In accordance with the invention, as illustrated in FIGS. 2 et seq., The method successively comprises at least a first step of placing in the mold 40 the internal core 34, the external coating 36 and the elastic part 38 , a second step of injecting the thermosetting resin, a third step of compressing the elastic part 38 by at least one movable part of the mold, and a fourth step of baking the structural element 10 intended to allow the crosslinking of synthetic thermosetting foam, thermosetting resin, and elastomeric material.

 As illustrated in FIG. 1, during a first positioning step, there is first of all in the mold 40, the internal core 34, the external coating 36 and the elastic part 38.

 The mold 40 is formed by two lower parts 42 and upper 44. Each lower part 42 and upper 44 comprises a fixed part 46 and a movable part 48.

 Each fixed part 46 comprises a receiving cavity 50 which is intended to receive the internal core 34 and the external covering 36 which envelops it. This operation can be carried out for example by spreading in the cavity 50 of the lower part 42 an outer coating layer 36, then the inner core 34, then again an outer coating layer 36.

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 Preferably, but not limited to the invention, during an inclusion sub-step, it is possible to arrange, in the assembly consisting of the internal core 34 and / or the external coating 36, a housing 53, in particular cylindrical, which is intended to receive at least a first metal insert 56 forming a spacer and / or fixing point.

 In the assembly consisting of the inner core 34 and / or the outer covering 36, a housing 52 is arranged, for example of substantially cylindrical shape, opening at its two ends, which will be intended to receive the elastic part 38 of the item 10.

 This housing 52 is arranged in the mold 40 substantially opposite two movable parts 48, produced in particular in the form of pistons 48 arranged opposite one another, which will be intended to compress the elastic part 38 to the during a later stage.

Preferably, but without limitation of the invention, the elastic part 38 may include a recess 54, in particular a hole opening at its two ends, which is intended to receive, during a sub-inclusion step, a second metal insert 58 forming reinforcement and / or spacer and / or fixing point. The metal insert 58 is for example substantially shaped in the form of a cylinder
In the preferred embodiment of the invention, the entire mold 40 is, prior to this first step of positioning, brought to the crosslinking temperature of the thermosetting resin which will be injected. As will be seen later, the mold 40 includes heating means making it possible to maintain at least this temperature, which is lower than the crosslinking temperature of the elastomeric material of the elastic part 38.

 Then, as illustrated in FIG. 3, the mold is closed so that the respective edges 60 and 62 of the lower 42 and upper 44 parts are joined.

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 During a second injection step, shown in FIG. 4, thermosetting resin is injected into the mold 40. To this end, the upper part 44 has a channel 64 which is connected to an external injector 66. The thermosetting resin is injected into the channel 64 and spreads in the mold by impregnating the fibers of the external coating 36 and by filling on the one hand the spaces which remain free between on the one hand the housing 52 and the elastic part 38 and on the other hand, the spaces remaining free between the recess 53 and the metal insert 56.

 Then during a third compression step, represented in FIG. 5, the pistons forming the movable parts 48 of the mold 40 are actuated, in order to compress the elastomer material of the elastic part 38 made of elastomer material, this in order to guarantee good adhesion of the elastomer.

 On this occasion, in the case where the elastic part 38 comprises a second metal insert 58, the movable parts 48 of the mold 40 can be used to crimp the metal insert 58 during a fixing step. To this end, the movable parts 48 of the mold 40 may include crimping means (not shown) intended to cooperate with the metal insert 58 to allow its fixing 58 in the elastic part 38.

 In this configuration, the metal insert 58 is shaped in the form of a cylinder of a length greater than that of the elastic part 38, the ends of which are liable to deform so that the movable parts 48 of the mold 40, when compression of the elastic part 38, allow the fixing by crimping of the second metal insert 58 by deforming its ends in the form of flanges enclosing the elastomeric material.

 Then, during a fourth cooking step, the mold 40 is maintained in the position previously described with reference to FIG. 5. The compression is maintained so

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 that the third compression step extends throughout the fourth cooking step.

 As seen above, the mold 40 is initially brought to the crosslinking temperature of the thermosetting resin. Therefore, two variants of the process can be envisaged.

 According to a first alternative embodiment of the method, the mold 40 comprises global means 68 for maintaining the temperature at the crosslinking temperature of the thermosetting resin. These overall means, housed in the fixed part 46 may consist of channels in which oil circulates at the crosslinking temperature of the thermosetting resin, of means by electromagnetic induction, or alternatively, as shown in the figures. , at least one electrical resistance 68 included in the thickness of the fixed part 46.

 In this configuration, the fourth baking step is a step of high duration comprising an overall maintenance of the mold 40 at the crosslinking temperature of the thermosetting resin - approximately 100 ° C. using the overall means 68 for maintaining the temperature. The crosslinking of the elastomeric material of the elastic part 38 occurs after the crosslinking of the thermosetting resin of the rigid part 36, because it takes place at a temperature below its current crosslinking temperature which is of the order of 170 C.

 According to a second alternative embodiment of the method, the mold 40 comprises the overall means 68 for maintaining the temperature at the crosslinking temperature of the thermosetting resin and it further comprises means 70 for localized heating of the movable part 48 of the mold at the crosslinking temperature of the elastomeric material. These localized means, housed in each movable part 48, can consist of channels in which oil circulates at the crosslinking temperature of the elastomeric material, means

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 by electromagnetic induction, or as shown in the figures, at least one electrical resistance 70 included in the movable part 48.

 In this configuration, the fourth baking step is a step of reduced duration comprising overall maintenance of the mold 40 at the crosslinking temperature of the thermosetting resin and localized heating of the movable part 48 of the mold 40 at the crosslinking temperature of the material elastomer of the elastic part 38.

 In this case, the crosslinking of the elastomeric material of the elastic part 38 occurs at the same time as the crosslinking of the thermosetting resin of the rigid part 36.

 Finally, as illustrated in FIG. 6, the method includes a fifth step of extracting the structural element 10 from the mold 40.

 The invention therefore provides an innovative process for obtaining a structural element 10, in particular a motor cradle, light, resistant, and of reduced cost.

Claims (12)

1. Method for manufacturing a structural element (10), in particular a motor vehicle cradle, which comprises at least: - a rigid part (32) comprising at least one internal core (34) of thermosetting synthetic foam covered with '' an outer covering (36) made of fibers of composite material stiffened by a thermosetting resin, - at least one elastic part (38) formed of an elastomeric material adhering to the rigid part (32), characterized in that it successively comprises at least a first step of placing the inner core (34), the outer covering (36) and the elastic part (38) in a mold (40), a second step of injecting the thermosetting resin, a third stage of compression of the elastic part (38) by at least one movable part (48) of the mold (40), and a fourth stage of baking of the structural element (10) intended to allow the crosslinking of the foam synthetic th hermoset, thermosetting resin, and elastomeric material.  2. Method according to the preceding claim, characterized in that the third step extends throughout the fourth step.  3. Method according to any one of the preceding claims, characterized in that, before the first step, the mold (40) is brought to the crosslinking temperature of the thermosetting resin.  4. Method according to the preceding claim, characterized in that the fourth cooking step is a step of high duration comprising an overall maintenance of the mold (40) at the crosslinking temperature of the thermosetting resin.  5. Method according to claim 3, characterized in that the fourth cooking step is a step of reduced duration comprising an overall maintenance of the mold (40) at the temperature of <Desc / Clms Page number 12>  crosslinking of the thermosetting resin and localized heating of the movable part (48) of the mold to the crosslinking temperature of the elastomeric material of the elastic part (38).  6. Method according to any one of the preceding claims, characterized in that it comprises, during the first step, a sub-step of inclusion of at least one first metal insert (56) in the core ( 34) internal and / or in the coating (36) external.  7. Method according to any one of the preceding claims, characterized in that it comprises, during the third step, a substep for fixing at least one second metal insert (58) in the elastic part (38 ).  8. Method according to any one of the preceding claims, characterized in that it comprises a fifth step of extracting the structural element (10) from the mold (40).  9. Mold (40) for implementing a method according to any one of claims 7 or 8, characterized in that the movable part (46) of the mold comprises crimping means intended to allow the fixing of at least one metal insert (58) in the elastic part (38) of the structural element (10) to be manufactured.  10. Mold (40) for implementing a method according to the preceding claim, characterized in that a fixed part (46) of the mold comprises at least one cavity (50) for receiving an element (10) structure in which opens at least one channel (64) intended to allow the injection of thermosetting resin.  11. element (10) of structure obtained according to a method according to any one of claims 6 to 8, characterized in that it comprises at least a first metallic insert (56) forming a spacer and / or fixing point which is arranged in the inner core (34) and / or in the outer covering (36) of its rigid part (32). <Desc / Clms Page number 13>  12. element (10) of structure obtained according to a method according to the preceding claim, characterized in that it comprises at least a second metal insert (58) forming reinforcement and / or spacer and / or fixing point which is arranged in its elastic part (38).