FR3111582A1 - Manufacturing process of a thermoplastic material part incorporating heating elements - Google Patents

Abstract

Process for manufacturing a part in thermoplastic material incorporating heating elements A method of manufacturing a part made of thermoplastic material capable of being welded to another part comprises the injection or hot compression of a thermoplastic material (130) in a mold (50) and the demolding of the part made of thermoplastic. The method further includes placing one or more heating elements (120) in the mold (50) prior to introducing the thermoplastic material (130). The heating element(s) (120) are placed in one or more parts of the mold corresponding to one or more assembly surfaces (101) of the part made of thermoplastic material. Figures for the abstract: Fig. 4 and 5.

Description

Process for manufacturing a part in thermoplastic material incorporating heating elements

The present invention relates to the field of parts made of thermoplastic material and, more particularly, to the assembly by welding of such parts.

Thermoplastic materials and in particular composite materials comprising reinforcing fibers, for example carbon fibers and/or glass fibers, dispersed in a thermoplastic polymer matrix have many possible uses, and in particular, in the field of aeronautics.
For the realization of certain structures, it may be necessary to assemble several parts in thermoplastic material such as, for example, for a thrust reverser flap, a stiffened panel, stiffeners, fairing parts, etc.
These composite parts can be assembled by welding, in particular by a technology of the type:

- induction welding,

- resistive welding,

- heat and pressure welding

- ultrasonic welding, laser welding.

Document EP 2 907 651 describes an induction welding process in which an assembly formed by two parts to be welded made of composite material with a thermoplastic matrix and a field absorber or susceptor positioned at the interface between rooms. The magnetic field causes the temperature of the susceptor to rise to a temperature allowing the softening or melting of the thermoplastic resin.
The interposition of a susceptor between the parts to be welded nevertheless has the disadvantage of technically complicating the welding operation by the need to position the susceptor with precision and to maintain it in position between the parts during the welding. Further, the use of a susceptor results in an increase in manufacturing time and cost. Furthermore, the presence of a susceptor at the connection interface between the two parts can adversely affect the mechanical strength of the resulting structure in service.

The main purpose of the present invention is therefore to propose a solution for welding a part made of thermoplastic material which does not have the aforementioned drawbacks.

According to the invention, this object is achieved by means of a process for manufacturing a part made of thermoplastic material capable of being welded to another part, the process comprising the injection or the hot compression of a thermoplastic material in a mold and the demolding of the part made of thermoplastic material, characterized in that it also comprises the placing of one or more heating elements in the mold before the introduction of the thermoplastic material, the heating element(s) being placed in one or more several parts of the mold corresponding to one or more assembly surfaces of the part made of thermoplastic material.

By overmolding or embedding one or more heating elements in one or more parts of the part, the problems associated with the use of an attached susceptor described above are overcome. The integration of one or more heating elements in the thermoplastic material of the part facilitates positioning between the parts to be assembled with good repeatability during mass production. The method of the invention makes it possible to avoid the use of a susceptor which constitutes an additional operation which can be technically or economically penalizing (manual positioning which can be complex, cost and installation of the component). The presence of the susceptor may also impair the behavior of the part in service.

Furthermore, with one or more heating elements overmoulded or embedded in the thermoplastic material of the part, the thermal diffusivity within the latter is controlled. Indeed, it is thus possible to locally heat the thermoplastic material of the part beyond its melting point at the level of the assembly surface(s) of the latter while maintaining in the rest of the material of the part a temperature low enough to ensure its geometric stability and a controlled level of crystallinity.

According to one embodiment of the method according to the invention, the heating element or elements are made of a material capable of heating up under the effect of a magnetic field.

According to another embodiment of the method according to the invention, the heating element or elements are of the resistive type and are made of a material capable of heating up under the effect of an electric current. In this case, the method may further comprise the placement of connectors in the mold before the introduction of the thermoplastic material, said connectors being electrically connected to one or more heating elements.

According to a particular characteristic of the method of the invention, the heating element or elements are made from a mesh, a mesh or a wire made of an electrically and thermally conductive material. The electrically and thermally conductive material may in particular be chosen from one of the following materials: copper, brass, bronze, steel, nickel alloy, titanium and continuous carbon fibers. In the case where the heating element(s) made from a grid or a mesh, the grid or the mesh preferably has a mesh size greater than 1 mm so as to facilitate the passage of the softened or molten thermoplastic material . This promotes the junctions between the polymer chains of the assembled parts, which reinforces the connection by welding.

According to another particular characteristic of the method of the invention, the thermoplastic material comprises a single resin or a resin filled with short fibers.

According to another embodiment of the method according to the invention, the mold has a plurality of cavities forming a network of ribs, the heating element or elements being placed in the bottom of the cavities so as to be present at a top of the ribs of the piece of thermoplastic material.

The invention also relates to a method for manufacturing a structure comprising at least a first part made of thermoplastic material and a second part, the method comprising the manufacture of a first part made of thermoplastic material according to the method for manufacturing a part made of thermoplastic material of the invention, the docking of the assembly surface(s) of the first part with a second part and the heating of the heating element(s) present in the first part so as to weld said first part to the second piece.

According to one embodiment of the method for manufacturing a structure according to the invention, the first part made of thermoplastic material comprises a network of ribs, the heating element(s) being present at a top of the ribs of the part made of thermoplastic material and in which the second part corresponds to a skin made of composite material with continuous fibers, the top of the ribs comprising the heating element(s) being in contact with the skin made of composite material during the heating of the heating element(s) so as to weld the first piece to said skin.

There is a schematic perspective view of a part made of thermoplastic material according to one embodiment of the invention,

There is a schematic exploded perspective view showing the positioning of a mesh in a mold,

There is a schematic perspective view showing the closing of the mold of the ,

There is a schematic sectional view of the mold of the when closed showing the injection of a thermoplastic material into the mould,

There is another schematic sectional view of the mold of the once closed and after injection of a thermoplastic material,

There is a schematic perspective view of a part made of thermoplastic material according to another embodiment of the invention,

There is a schematic sectional view showing the docking of the part of the with a composite skin,

There is a schematic sectional view showing the production of a structure by welding the two parts of the .

There represents a part made of thermoplastic material 100 in accordance with one embodiment of the invention. The part made of thermoplastic material 100 here comprises a network of ribs 110 crossing each other perpendicularly. In accordance with the invention, the part 100 further comprises a heating element constituted here by a grid or trellis 120 molded into the thermoplastic material 130 of the part. In the example described here, the mesh 120 is present at the level of a vertex 111 of the ribs 110 which defines the assembly surface 101 of the part 100, that is to say the part of the part 100 intended to be welded with another part.

As illustrated on the , the manufacture of the part in thermoplastic material 100 comprises first of all the placement of the mesh 120 in the bottom 52 of the molding cavity 51 of an injection mold 50, the bottom 52 corresponding to the location at which the top 111 of the ribs 110 is formed. The mold 50 can include, if necessary, means for holding the mesh 120 in position at the determined location (not shown in the figure). ), in particular means making it possible to adjust the height position of the mesh in the mold in order to adjust the depth of the mesh relative to the assembly surface.

Once the grid 120 has been put in place, the mold 50 is closed with a lid 53 which comprises blocks 55 making it possible to divide the molding cavity 51 into a plurality of cavities 56 forming a network of ribs (FIGS. 3 and 5).

Once the mold 50 is closed, a thermoplastic material 130 is injected under pressure and hot into the mold via an injection port 54 as shown in Figures 4 and 5.

After injection and cooling of the mold, the part made of thermoplastic material 100 comprising the network of ribs 110 and the mesh 120 overmoulded in the thermoplastic material 130 at the level of the top 111 of the ribs ( ). When part 100 is subjected to a magnetic field, mesh 120 heats up so as to locally melt the thermoplastic material. Part 100 is thus able to be assembled by inductive welding to another part.

The thermoplastic material used to form the part can be of different types. By way of non-limiting examples, the part according to the invention can be made with one of the following thermoplastic materials: PAEK (PolyArylEtherCetone), PEEK (PolyEtherEtherCetone), PEKK (PolyEtherCetoneCetone), PEI (polyetherimide), TPU or PU (Thermoplastic Polyurethane ), PESU or PPS (phenylene polysulphide). The thermoplastic material can be in the form of a single resin or a resin filled in particular with short fibers which can be carbon, glass, aramid, etc

The part can also be produced by compression molding of a composite material reinforced with discontinuous long fibers of the BMC (Bulk Molding Compound), SMC (Sheet Molding Compound) or DLF (Discontinuous Long Fibers) type.

The size of the fibers is typically between 0.1 mm and 1 mm for the short fibers and between 1 mm and 50 mm for the long fibers.

The heating element(s) molded into the thermoplastic material of the part can be made of a material capable of heating up under the effect of a magnetic field and/or an electric current. By way of non-limiting examples, the heating element(s) can be made from one of the following materials: copper, brass, bronze, steel, nickel alloy, titanium and continuous carbon fibers.

The heating element(s) can be made from a grid or mesh as described above or from a wire made of an electrically and thermally conductive material.

There represents a part made of thermoplastic material 200 in accordance with another embodiment of the invention. Part 200, which also includes a network of perpendicularly crossing ribs 210, differs from part 100 described above in that the heating element here consists of a conductive wire 220 overmoulded in the thermoplastic material 230 of the part. The conductive wire 220 extends over the entire top 211 of the ribs 210 which corresponds to the assembly surface 201 of the part 200, that is to say the part of the part 200 intended to be welded with a another room. Conductive wire 220 is a resistive element which heats up when an electric current passes through it. To this end, the part 200 further comprises two electrical connectors 240 and 250 electrically connected to the conductive wire 220. The connectors 240 and 250 are partially molded in the thermoplastic material with the conductive wire 220. The connectors 240 and 250 are intended to be connected to a current generator (not shown on the ) in order to cause a current to flow in the conductive wire 220. The conductive wire 220 heats up under the effect of the current which circulates so as to locally melt the thermoplastic material. Part 200 is thus able to be assembled by resistive welding to another part.

In the case of resistive-type welding, the wire or wires overmolded in a thermoplastic part preferably have a diameter or cross-section of between 10 μm and 2 mm. They are preferably but not exclusively made with one of the following materials: copper, bronze, brass and steel.

In the case where the heating element or elements are made from a grid or trellis, the latter preferably has a mesh size greater than 1 mm. Indeed, if the mesh or mesh is present at the top of the part, for example at the top of the ribs, and the meshes are too tight, the molten or softened thermoplastic material may have difficulty migrating to the interface with the other room. This can prevent the polymer chains of the two parts from intermingling, resulting in a good weld.

We will now describe a method for manufacturing a structure in accordance with one embodiment of the invention between the part made of thermoplastic material 100 described previously and a skin 300. The method begins, as illustrated in the , by docking the assembly surface 101 of the part 100 comprising the mesh 120 with a surface 301 of the skin 300 in a determined position. In the example described here, the skin 300 is made of a composite material comprising a fibrous reinforcement with continuous fibers densified by a thermoplastic matrix. The skin 300 can in particular be produced by stamping, thermocompression, automatic placement of AFP fibers, etc.

Once the parts 100 and 300 have been positioned relative to each other while maintaining the assembly surface 101 of the part 100 in contact with the assembly surface 301 of the part 300, the operation of welding as shown in the . The assembly thus formed is subjected to a magnetic field C60 created by an inductor 60.

Under the effect of the magnetic field, the mesh 120 present at the level of the assembly surface 101 heats up so as to locally melt the thermoplastic material of the part 100 as close as possible to the assembly interface between the two parts and weld them together. Preferably, a pressure P between is applied to two parts during welding.

A structure 500 is then obtained comprising a skin 300 secured to a network of ribs corresponding to the part 100. The junction portions between the ribs 110 of the part 100 and the skin 300 have beads 112 resulting from the softening or fusion thermoplastic material at the assembly interface. The beads 112 make it possible to reinforce the welded connection between the part 100 and the skin 300. The structure 500 can in particular constitute all or part of a thrust reverser flap, of a stiffened panel, of a fuselage part or of fairing, of a structure of the sandwich type in particular for acoustic treatments, etc.

The part made of plastic material according to the invention may comprise several heating elements. Several identical or different heating elements can be placed in the same place in the room in order to increase the local heating temperature if necessary. Several identical or different heating elements can also be placed at different places in the part in order to form several assembly surfaces in the part and allow, for example, the welding of the part with several other parts.

By overmolding or embedding one or more heating elements in one or more parts of the part, the thermal diffusivity in the latter is controlled. It is thus possible to locally heat the thermoplastic material of the part beyond its melting point at the assembly surface(s) of the latter while maintaining a sufficiently low temperature in the rest of the material of the part. to ensure its geometric stability and a controlled level of crystallinity.

Claims (12)

Method of manufacturing a part made of thermoplastic material (100) capable of being welded to another part, the method comprising the injection or hot compression of a thermoplastic material (130) in a mold (50) and the demolding of the part made of thermoplastic material (100), characterized in that it further comprises the placement of one or more heating elements (120) in the mold (50) before the introduction of the thermoplastic material (130), the the heating elements (120) being placed in one or more parts of the mold corresponding to one or more assembly surfaces (101) of the part made of thermoplastic material (100). Process according to Claim 1, in which the heating element(s) (120) are made of a material capable of being heated under the effect of a magnetic field (C ₆₀ ). Method according to claim 1, in which the heating element(s) of the resistive type, the said heating element(s) (220) being made of a material capable of being heated under the effect of an electric current. A method according to claim 3, comprising placing connectors (240, 250) in the mold prior to introduction of the thermoplastic material (230), said connectors being electrically connected to one or more heating elements (220). A method as claimed in any one of claims 1 to 4, wherein the at least one heating element (120) is made from a mesh or mesh. A method according to claim 5, wherein the mesh or netting has a mesh size greater than 1mm. A method according to any of claims 1 to 4, wherein the at least one heating element (220) is made from a wire of electrically and thermally conductive material. Process according to Claim 7, in which the electrically and thermally conductive material is chosen from one of the following materials: copper, brass, bronze, steel, nickel alloy, titanium and continuous carbon fibres. A method according to any of claims 1 to 8, wherein the thermoplastic material (130, 230) comprises a resin or a resin filled with short fibers. Method according to any one of claims 1 to 9, in which the mold has a plurality of cavities (56) forming a network of ribs, the heating element(s) (120) being placed in the bottom of the cavities so as to be present at a vertex (111) of the ribs (110) of the part made of thermoplastic material (100). Method of manufacturing a structure (500) comprising at least a first part made of thermoplastic material and a second part, the method comprising the manufacture of a first part made of thermoplastic material (100) according to the method as defined in claims 1 to 9, the docking of the assembly surface(s) (101) of the first part with a second part (300) and the heating of the heating element(s) (120) present in the first part so as to weld said first piece to second piece. Method according to claim 11, in which the first part of thermoplastic material (100) comprises a network of ribs (110), the heating element(s) (120) being present at an apex (111) of the ribs (110) of the part made of thermoplastic material and in which the second part (300) corresponds to a skin made of composite material with continuous fibers, the tops of the ribs (111) comprising the heating element(s) (120) being in contact with the skin made of composite material during the heating of the heating element(s) so as to weld the first part (100) to the said skin.