FR3125456A1 - Composite material overmolding process - Google Patents

Abstract

The present invention relates to a composite material overmolding method comprising the following steps: providing a composite material part (12) comprising a matrix made of a first polymeric material and reinforcing fibers; providing a second thermoplastic polymer material; a laser source adapted to produce a laser beam (14) is provided and said laser beam (14) is directed against the surface (11) of said part made of composite material (12) so as to ablate said first polymer material from said matrix at said surface, while reinforcing fibers (20) are exposed on said surface; and,- an element (44) is overmoulded in said second polymer material on said ablated surface so as to be able to connect said element (44) and said composite material part (12) together, while said second polymer embeds said fibers bare reinforcements (20). Figure to be published with abstract: Fig. 1

Description

Composite material overmolding process

The present invention relates to a composite material overmolding method.

In particular, the invention aims to improve the mechanical characteristics of an assembly obtained by overmolding an element made of thermoplastic polymer onto a part made of composite material.

Overmolding consists of molding an element on a part that has already been roughed out. Thus, in plastics processing, it is well known to insert metal parts inside an injection mold and then to inject a thermoplastic polymer material at least partially around the metal insert.

Thus, for example, the handles of a tool are overmolded to improve grip comfort, metal parts are overmolded to be able to insulate them from the electric current, and many other parts for various technical reasons.

Usually, when metal parts are overmolded, they are coated at least partially with the polymer material. In this way, the polymer material adheres sufficiently to the metal part after cooling to be integral with it, without risk of subsequent separation.

Also, according to other applications, parts are overmoulded in polymer material themselves, or else in composite material. This involves, for example, making fixing zones on parts made of composite material.

Reference may be made in particular to document FR 3 083 160, which discloses such an example of implementation.

Here too, the overmolded element coats parts of the part and in this case, through an orifice provided for this purpose.

Also, the overmolded element is perfectly secured to the composite material wall without the problem of adhesion arising.

On the other hand, in certain applications where an element is overmoulded on the surface of a composite material part, an adhesion problem arises.

Also, it was imagined to significantly preheat the composite to obtain an intimate mixture between the overmolded polymer and the polymer of the composite. However, this possibility is only offered in the case of composite parts implemented with a thermoplastic polymer matrix. In the case of thermosetting polymers, the polymer no longer softens when heated.

Consequently, there is a need to improve the connection between an overmolded element and a part made of composite material on which it is overmolded.

With the aim of solving this problem, a composite material overmolding process is proposed, characterized in that it comprises the following steps: a part made of composite material is provided comprising a matrix made of a first polymer material and fibers of reinforcement embedded inside said matrix; providing a second polymeric material, said second polymeric material being thermoplastic; a laser source suitable for producing a laser beam is provided and said laser beam is oriented against the surface of said composite material part so as to ablate said first polymeric material from said matrix to said surface, while reinforcing fibers are placed at bare on said surface. And, an element is overmoulded in said second polymer material on said ablated surface so as to be able to connect together said element and said part made of composite material, while said second polymer embeds said exposed reinforcing fibers.

Thus, one characteristic of the invention resides in the treatment of the surface of the composite material by means of a laser beam. Thanks to the laser, one proceeds to the decomposition of the polymer material on the surface of the part and not only to a softening of the material. In this way, the reinforcing fibers of the composite material are exposed and the second thermoplastic polymer material then subsequently coats these fibers. Consequently, when the thermoplastic polymer material cools, and consequently stiffens, the overmolded element is better anchored to the part made of composite material.

In addition, thanks to the laser, it is possible to decompose a thermoset thermosetting polymer material and also expose the reinforcing fibers. There is no other way to ablate such a thermoset polymer material.

According to a particularly advantageous embodiment of the invention, said laser beam is oriented against a surface portion of said composite material part, while a portion of said reinforcing fibers is exposed. And said element is locally overmolded on said surface portion, while said second polymer embeds said portion of exposed reinforcing fibers. Thanks to the laser beam, it is possible to act very locally on the surface of the composite part and very precisely on the area that one wishes to overmold. And therefore, the fibers of the composite are exposed locally. Indeed, the laser beam is easily orientable and focusable on a reduced area, compared to other surface treatment techniques, and in particular to techniques using plasmas.

According to a particular embodiment, said first polymer material is thermoplastic. In other words, the polymer matrix of the composite material is thermoplastic. In this way, a mechanical assembly is produced, a molded element plus a composite part, which assembly is then easily recyclable.

Furthermore, the first polymer material softens in the zone of interaction between the laser beam and the composite, and hence the two thermoplastic polymers of the element and of the part at least partially diffuse into each other and causes better adhesion after cooling.

According to a particularly advantageous implementation characteristic of the invention, said laser source emits electromagnetic radiation in the ultraviolet range. Thanks to such a laser source, the polymer can be ablated relatively selectively with respect to the reinforcing fibers that it impregnates. In other words, the laser radiation essentially interacts with the polymer and does not affect the fibers. Also, ultraviolet radiation interacts with the polymer and leads to its photochemical decomposition.

To do this, for example, an excimer laser is used.

Other types of laser can be implemented depending on the types of polymer materials of the composite and the fibers it includes.

Preferably, an injection mold is provided having a housing for inserting said part made of composite material and for overmolding said element on said ablated surface. The injection mould, or tooling, comprises two parts adapted to be applied against each other. And one of the parts has the housing in which the composite material part is inserted when the two parts are separated from each other. Then, the two parts are applied against each other to form a sealed chamber including the composite material part. Then the thermoplastic polymer can be injected in the viscous state into said chamber to form the overmolded element.

Advantageously, said injection mold has heating members to supply thermal energy to said composite material part. Heating the part made of composite material makes it possible, in certain circumstances, to soften the polymer material of the matrix in addition and thus promote the adhesion of the second viscous and hot polymer material. In addition, thanks to the heating of the composite material, and consequently of the bare fibers, the second polymer material drowns them all the better.

According to a particularly advantageous but non-limiting embodiment, said injection mold has deformation members in order to be able to at least partially deform said part made of composite material. Such members make it possible to shape the composite material part more precisely during overmolding when necessary. Such a possibility is obviously only possible when the polymer material of the matrix of the composite material is thermoplastic.

Other particularities and advantages of the invention will become apparent on reading the description given below of particular embodiments of the invention, given by way of indication but not limitation, with reference to the appended drawings in which:
is a partial schematic perspective view of a part made of composite material treated according to the process in accordance with the invention in a first phase;
is a schematic partial perspective view of the part shown in the at the end of the first phase;
is a schematic partial cross-sectional view of the part shown in the engaged inside a device making it possible to implement the method according to the invention through a second phase;
is a partial schematic view of the product obtained at the end of the second phase; And,
is a view of a flowchart of the method according to the invention.

There partially shows one end 10 of a flat part made of composite material 12. The flat part 12 has an upper surface 11 opposite a lower surface 13.

Thus, according to a first step 15, in accordance with the method according to the invention, said flat part 12 is provided.

The composite material here is made of a thermosetting polyester matrix inside which is embedded a three-dimensional textile made of aramid fibers. The polyester used here is thus an unsaturated polyester. Other types of composites can be implemented, with an epoxy or vinyl ester polymer matrix, while the fibers are glass or carbon fibers.

The composite is usually hot formed, then cools to stiffness as the matrix polymer crosslinks.

Also, the illustrates, above the end 10 of the flat part 12, a laser beam 14 focused by a lens 16 inside a rectangular zone 18 of the end 10 of the part 12.

The laser beam 14 is obtained by a laser source associating an optical amplifier with an optical cavity. The laser here is a laser using a solid medium, an aluminum and yttrium garnet: YAG. This laser emits electromagnetic radiation in the ultraviolet.

Other types of laser, gas, excimer lasers emit in the ultraviolet and can be implemented.

Thus, the laser beam 14 is oriented in a direction substantially normal to the upper surface 11 of the flat part 12 and, in accordance with a second step 17 of implementing the method according to the invention, it is driven in translation step by step, according to the mutually perpendicular components X, Y, so as to cover the entire upper surface 11 defined by the rectangular area 18.

The interaction between the laser beam 14 and the polymer material of the composite 12 leads to photochemical decomposition of the material and its ablation. In other words, the laser beam 14 breaks the molecular bonds of the polymer material.

The material is then denatured and ejected in the form of gas and molecular fragments. This ablation of the polymer takes place over a variable thickness depending on the exposure time of the material to the beam 14.

Thus, as illustrated in the , after the laser beam 14 has scanned the entire upper surface 11 corresponding to the rectangular zone 18 of the end 10 of the flat part 12, the thermosetting polyester has been ablated and the intersecting fibers 20 are exposed.

Thanks to the laser used here, the polymer material has been denatured and ejected locally without affecting the fibers of the rectangular zone 18, over a small thickness. Therefore, the flat part 12 has a hollow 23 in the rectangular zone 18, inside which the intersecting fibers 20 extend.

We will now refer to the showing in cross section, an injection mold 22 comprising a lower part 25 having a housing 24, and above an upper part 26.

The housing 24 is of rectangular parallelepipedic shape and it has a bottom 27 and dimensions identical to those of the flat part 12, and this, except for the functional clearance, so as to be able to accommodate it inside.

Also, the flat piece 12 is fitted inside the housing 24, the lower surface 13 bearing against the bottom 27 so that the rectangular zone 18 of the upper surface 11 appears opposite the upper part 26 of the injection mold 22. The upper part 26 is movable in vertical translation along a sufficiently large amplitude to be able to carry the flat part 12 inside the housing 24.

According to a variant embodiment, the lower part 25 is equipped with heating elements extended around the housing 24 so as to be able to supply thermal energy to the flat part 12.

Also, it will be observed that the upper surface 11 of the flat part 12 is flush with the housing 24 and in the joint plane 28 defined by the upper face 30 of the lower part 25 of the mold 22.

Conversely, the upper part 26 of the injection mold 22 has a lower face 32 in which is made a molding cavity 34. Also, an injection channel 36 opens into this molding cavity 34.

Here on the , the molding cavity 34 has a rectangular parallelepipedal shape and it is centered on the housing 24. More precisely, it comes here opposite the rectangular zone 18 of the flat part 12.

According to a third step 38 in accordance with the invention, a thermoplastic polymer is provided, and in this case a thermoplastic polyester. In this way, this thermoplastic polyester will have a greater affinity with the thermosetting polyester of the flat piece 12. And consequently, it will adhere to it much better.

Thus, according to a fourth step 40, this thermoplastic polyester is conveyed in the hot and viscous state through the injection channel 36 of the upper part 26 of the injection mold 22, after the injection mold 22 has been lowered according to the arrow F, its lower face 32 bears against the upper face 30 of the lower part 25.

Thus, the lower face 32 also comes to rest against the upper surface 11, partially, around the rectangular zone 18 of the flat part 12. In this way, the molding cavity 34 forms a sealed chamber facing the digging 23 .

The thermoplastic polyester is then injected inside the molding cavity 34 and it thus spreads in the sealed chamber to extend into the hollow 23 and impregnate the exposed fibers 20.

According to the aforementioned embodiment aimed at supplying thermal energy to the flat part 12, the viscous and hot thermoplastic polyester then exhibits better adhesion to the polymer of the part 12. It will be observed that this adhesion is further accentuated when the polymer of the composite part is a thermoplastic polymer. In this case, the two polymers can diffuse into each other at their interface.

The upper part 26 of the injection mold 22 is then held against the lower part 25, during a cooling phase of the thermoplastic polyester. At the end of this phase, the polymer is then rigid.

Preferably, the upper part 26 of the injection mold 22 is equipped with a cooling circuit in order to be able to accelerate the cooling of the polymer material and thus its stiffening.

Thus, in a final step 42, the upper part 26 of the injection mold 22 is raised, while the flat part 12, surmounted by an additional element 44 is removed from the lower part 25 of the mold 22

It is thus represented on the .

The additional element 44 is then perfectly secured to the flat part 12 thanks to the extension of the exposed fibers 20 in the additional element 44. In other words, the additional element 44 and the flat part 12 are firmly linked together and more resistant to separation than would be an element overmolded on a composite part using a traditional method without surface treatment with a laser.

The additional element 44, molded here on the flat part 12, is an example of implementation for illustrative purposes.

Of course, the method according to the invention can be adapted to connect together any element made of thermoplastic material to a part made of composite material, whatever its shape.

In addition, other polymeric materials can be implemented, including thermoplastic materials for the composite material.

Also, when the composite part has a thermoplastic matrix, the injection mold can be equipped with deformation members to be able to at least partially deform the part made of composite material during overmoulding. This possibility is also offered by the aforementioned heating elements of the lower part 25.

Claims (8)

Composite material overmolding process characterized in that it comprises the following steps:
- a composite material part (12) comprising a matrix made of a first polymeric material and reinforcing fibers embedded inside said matrix is provided;
- a second polymer material is provided, said second polymer material being thermoplastic;
- a laser source adapted to produce a laser beam (14) is provided and said laser beam (14) is oriented against the surface (11) of said part made of composite material (12) so as to ablate said first polymer material from said matrix at said surface, while reinforcing fibers (20) are exposed at said surface; And,
- an element (44) is overmoulded in said second polymer material on said ablated surface so as to be able to connect together said element (44) and said composite material part (12), while said second polymer embeds said reinforcing fibers exposed (20). Overmolding process according to Claim 1, characterized in that the said laser beam (14) is oriented against a portion (18) of the surface (11) of the said part made of composite material (12), while a portion of the said fibers of reinforcement is exposed, and in that said element (44) is locally overmolded on said surface portion, while said second polymer embeds said portion of exposed reinforcing fibers. Overmolding process according to Claim 1 or 2, characterized in that the said first polymeric material is thermoplastic. Overmolding process according to Claim 1 or 2, characterized in that the said first polymeric material is thermoset. Overmolding process according to any one of Claims 1 to 4, characterized in that the said laser source emits electromagnetic radiation in the ultraviolet range. Overmolding process according to any one of Claims 1 to 4, characterized in that an injection mold (22) is provided having a housing (24) for inserting the said part made of composite material (12) and for overmolding the said element (44) on said ablated surface. Overmolding process according to Claim 6, characterized in that the said injection mold (22) has heating elements for supplying thermal energy to the said part made of composite material (12). Overmolding process according to Claims 3 and 6 or 7, characterized in that the said injection mold has deformation members in order to be able to at least partially deform the said part made of composite material.