Method for electromagnetic welding of fiber-reinforced composite laminates and methods for electromagnetic welding of molded parts thereof.

Abstract

This invention describes a fiber-reinforced composite laminate for a molded component used in electromagnetically welded laminates. The laminate has multiple structural layers, each formed of conductive fibers embedded in a thermoplastic matrix, wherein eddy currents can be induced in the conductive fibers by a conductor generating an electromagnetic field. The structural layers include two adjacent structural layers in a first pair, a second pair, and optionally a third pair. The first pair has an intermediate layer between its structural layers that substantially allows eddy currents to flow between the two structural layers of the first pair. The second pair has an intermediate layer between its structural layers that substantially prevents eddy currents from flowing between the two structural layers of the second pair. The optional third pair has no intermediate layer between the two structural layers of this pair. The laminate is efficiently heated by an electromagnetic field.

Description

Invention Field

[0001] This invention relates to the field of composite materials. In particular, it relates to structures formed from multiple molded components made of electromagnetically welded composite materials. This invention has specific applications in the field of aerospace structures formed by electromagnetically welding multiple composite molded components. Background Technology

[0002] Composite laminates and molded parts are increasingly used in applications that leverage the relatively high specific stiffness and strength of composite materials. Weight reduction is particularly important in the aerospace industry. A commonly used material in this industry is a composite laminate of carbon fiber and a thermosetting matrix polymer. Complex molded parts can be manufactured from such laminates, but once the thermosetting matrix polymer in such parts has cured, its shape is permanent. To achieve complex structures, molded parts often need to be connected to each other or to other parts, such as reinforcements. This is typically achieved mechanically, such as with bolts, or chemically, such as with adhesives.

[0003] In recent years, composite laminates of carbon fiber and thermoplastic matrix polymers have been introduced. These thermoplastic composite laminates can be molded after curing, simply by heating the thermoplastic polymer matrix to above its softening or melting temperature.

[0004] Because carbon fibers are conductive, eddy currents can be induced within them by an electrical conductor that generates an electromagnetic field. These eddy currents heat the carbon fibers, causing the molded parts to heat from the inside. This property provides the possibility of electromagnetically welding the molded parts of the laminate. In this process, the thermoplastic polymer matrix is ​​heated by eddy currents to above its softening or melting temperature, allowing the electromagnetically weldable outer surfaces of each molded part to melt or weld together. Heating areas of the molded part other than the weldable surfaces is generally undesirable, as this could lead to damage to the molded part. Summary of the Invention

[0005] The object of this invention is to provide a method for molding an improved electromagnetically connected fiber-reinforced composite laminate. Another object is to provide a fiber-reinforced composite laminate for use in such an improved method of electromagnetically welded molding. Yet another object relates to a method for manufacturing such a fiber-reinforced composite laminate.

[0006] For these and other purposes, the present invention provides a fiber - reinforced composite laminate for a molded part for electromagnetic welding of the laminate, according to claim 1. The fiber - reinforced composite laminate comprises a plurality of structural layers, each structural layer being formed by conductive fibers embedded in a thermoplastic matrix, wherein eddy currents can be induced in the conductive fibers by an electrical conductor generating an electromagnetic field; wherein the plurality of structural layers comprises a first pair, a second pair and optionally a third pair of two adjacent - positioned structural layers, wherein,

[0007] - The first pair has an intermediate layer located between the two structural layers of the pair, wherein the intermediate layer has an out - of - plane volume resistance R1, and R1 substantially allows eddy currents to flow between the two structural layers of the first pair;

[0008] - The second pair has an intermediate layer located between the two structural layers of the pair, wherein the intermediate layer has an out - of - plane volume resistance R2, and R2 substantially prevents eddy currents from flowing between the two structural layers of the second pair; and

[0009] - The third pair has no intermediate layer between the two structural layers of the pair;

[0010] wherein and, R1 and R2 are defined and 0 < R1 < R2. Preferably, the intermediate layer in each pair is different from the two structural layers in each pair in that the intermediate layer in each pair does not comprise conductive fibers. Thus, each intermediate layer can neither or only to a small extent perform a structural or load - bearing function.

[0011] According to the present invention, when an electrical conductor generating an electromagnetic field is provided in the vicinity of the laminate of the present invention, eddy currents are induced in the conductive fibers, which heat the conductive fibers by Joule heating, which also heats the surrounding thermoplastic matrix polymer.

[0012] Joule heating, also known as resistive heating or ohmic heating, is the process by which an electric current passes through a conductor to generate heat. The heat is proportional to the resistance encountered in the direction of the current flow.

[0013] Since eddy currents are substantially prevented from flowing between the two structural layers of the second pair, the adjacent - positioned structural layers of the second pair are hardly affected by Joule heating. This is possible by providing an intermediate layer with an out - of - plane volume resistance R2 that is relatively high compared to R1 in such a second pair. In the second pair, Joule heating is substantially limited to the eddy currents induced separately in the conductive fibers of each layer, which results in less heat generation. This prevents parts of the laminate containing one or more second pairs from overheating under the influence of the electromagnetic field. Thus, overheating of such second - pair parts can be prevented, which otherwise could be harmful.

[0014] For welding to be performed, the electromagnetic field must heat other parts of the laminate so that the thermoplastic matrix polymer in those parts reaches a temperature exceeding the softening or melting temperature of the matrix polymer. For this purpose, a third pair of adjacent structural layers can be used. The third pair of adjacent structural layers will be heated by so-called join heating caused by direct fiber-to-fiber contact and / or dielectric hysteresis. Essentially, eddy currents are allowed to flow between the two structural layers of the third pair, which are virtually directly connected to each other, without the intervention of an intermediate layer with a relatively high defined out-of-plane volume resistivity R2. Joule losses in the third pair are moderate because the out-of-plane current flows against the relatively low surface resistivity ρ3 (in Ohm·m). 2 ) Flow. The measured surface resistivity ρ3 value is typically less than 10. -3 Ohm.m 2 For example, 0.20 × 10 -4 Up to 5×10 -4 Ohm.m 2 .

[0015] The inventors have realized that Joule heating in laminates can be increased under the same electromagnetic field strength. To this end, according to one aspect of the invention, the first pair has an intermediate layer located between the two structural layers of the pair, wherein the intermediate layer has an out-of-plane volume resistivity R1, which substantially allows eddy currents to flow between the two structural layers of the first pair. A sufficiently large out-of-plane volume resistivity R1 is chosen so that Joule heating in the first pair is higher than in a laminate comprising only the second and third pairs of structural layers. On the other hand, the volume resistivity R1 is less than R2 to allow eddy currents to flow between the structural layers of the first pair. In other words, the first pair allows for optimization of the laminate in terms of heating efficiency. The second pair of the laminate remains relatively cool to prevent damage, while the first pair is heated more efficiently than in the prior art known in the art, which in fact relies on using only the third pair, i.e., a laminate with multiple structural layers directly connected to each other.

[0016] Without any theoretical constraints, the out-of-plane volume resistivity R1 of the intermediate layer of the first pair is optimized to increase Joule heating and essentially allow eddy currents to flow between the two structural layers of the first pair. This optimization can be achieved by selecting factors that influence the out-of-plane volume resistivity R1. This resistance is given by the following equation:

[0017] R1=ρ1.t / A (1)

[0018] In this text, ρ1 is the volume resistivity of the material of the intermediate layer (in Ohm.m), 't' is the average thickness of the intermediate layer, and 'A' is the area through which the current flows. The area 'A' in the laminate is approximately equal to the surface area of the laminate. Therefore, the out-of-plane volume resistance R1 may be affected by the choice of the intermediate layer material (resistivity) and / or the average thickness 't' of the intermediate layer. The upper limit of R2 can be determined by providing a laminate with a second pair and observing the heat generated by the electromagnetic field in such a laminate.

[0019] It should be noted that all values of (volume and surface) resistivity and resistance are measured at room temperature (i.e., a temperature of 25°C).

[0020] Note that the surface resistance R3 between the structural layers of the third pair is equal to ρ3 / A, and the total resistance between the two layers in the first pair is equal to the volume resistance R1 + 2 times the surface resistance R3. In fact, there are two interfaces between each structural layer and the intermediate layer. Since R1 is usually much larger than R3, the contribution of R3 can be neglected.

[0021] In the laminate provided by the improved embodiment of the present invention, 0.1R2 < R1 < 0.9R2, more preferably 0.2R2 < R1 < 0.8R 2, Even more preferably 0.3R2 < R1 < 0.7R2, and most preferably 0.4R2 < R1 < 0.6R2.

[0022] Another embodiment of the laminate according to the present invention has an outer surface that can be electromagnetic welded, and the first pair is located in the laminate in the out-of-plane direction of the laminate on the weldable outer side of the laminate. This promotes the heating of the weldable outer surface.

[0023] Another embodiment of the laminate according to the present invention has an outer surface that can be electromagnetic welded, and one of the second pair or the third pair is located in the laminate on the outer side opposite to the weldable outer side or on the inner side of the laminate. This prevents overheating of the outer side opposite to the weldable outer side or the inner side of the laminate. This embodiment also reduces the need to use a heat sink to reduce the heating of parts of the laminate other than the weldable outer surface.

[0024] It is advantageous to provide a laminate according to an embodiment, wherein the intermediate layer of at least the second pair includes non-conductive fibers, such as in the form of thickness-calibrated gauze or mesh. In a laminate provided according to another preferred embodiment, the intermediate layer of at least the first pair includes non-conductive fibers, such as in the form of thickness-calibrated gauze or mesh. The above embodiments allow for better control of the volume resistances R1 and / or R2. In fact, when these laminates are molded into a molded product, the average thickness of the intermediate layer of the first pair and / or the second pair is less likely to change. In fact, non-conductive fibers are not easily compressed and can provide some protection against the extrusion of softened polymers. This is particularly relevant for the intermediate layer of the first pair, considering that R1 < R2, the intermediate layer of the first pair is actually heated to a higher temperature than the intermediate layer of the second pair.

[0025] In the context of the present application, non-conductive fibers are less conductive than, for example, carbon fibers or graphite fibers. Suitable examples are glass fibers, natural fibers such as jute, and organic fibers such as polyethylene and aramid fibers.

[0026] It has further been confirmed that heating under the action of an electromagnetic field can be further promoted by providing a laminate according to an embodiment, in which the conductive fibers in at least one of the structural layers of the first pair, the second pair, and / or the third pair are locally interrupted in at least one of the adjacent structural layers. A significant increase in heat is observed at the local interruption.

[0027] In a laminate provided according to another useful embodiment, the conductive fibers in two of the structural layers of the first pair, the second pair, and / or optionally the third pair are locally interrupted along a line in one structural layer of the pair and along another line in another adjacent layer of the pair, where the two lines intersect each other.

[0028] In a laminate provided according to yet another useful embodiment, the conductive fibers in two of the structural layers of the first pair, the second pair, and / or optionally the third pair are locally interrupted along a line in one structural layer of the pair and along another line in another adjacent layer of the pair, where the two lines coincide with each other.

[0029] In a laminate provided according to a particularly useful embodiment, the conductive fibers in the first pair and / or the third pair are locally interrupted because efficient heating is particularly required in these pairs.

[0030] Conductive fibers can exist in the structural layers in any form known in the art. For example, conductive fibers can be applied in the form of a fabric in which fibers travel in a straight direction along the main fiber direction, and undulating transverse fibers travel in a direction substantially perpendicular to the main fiber direction. Alternatively, conductive fibers can be applied in the form of a disordered mat in which fibers travel randomly on the plane of the mat. Other forms may include three-dimensional structures, such as woven structures. Yet another form may include multiple unidirectionally oriented fibers traveling parallel to each other in the fiber direction. In a laminate provided in a preferred embodiment, the conductive fibers in the structural layers are unidirectionally oriented. The same is true for optional non-conductive fibers that may be present in the intermediate layers of the pair.

[0031] When using unidirectional fibers, the laminated article according to the preferred embodiment is characterized in that at least a first pair includes structural layers with unidirectional fiber directions that differ between one structural layer and another. Particularly preferred is that, in the first pair, the unidirectional fiber direction in one structural layer travels substantially perpendicular to the unidirectional fiber direction in the other structural layer of the pair.

[0032] Each structural layer is formed by embedding conductive fibers into a thermoplastic matrix. Materials particularly suitable for constructing laminates include structural layers in semi-finished form, also known in the art as prepregs. When heated above the softening or melting temperature of the polymer, the thermoplastic polymer can be easily bonded between layers or to the reinforcing fibers of the layers by melting. Prepregs can be stacked to form laminates.

[0033] The material of the intermediate layer can be any material suitable for this purpose. For example, suitable materials used in the intermediate layer can be rubber, thermosetting and / or thermoplastic polymers, or combinations thereof. It is advantageous when the material of the intermediate layer in a pair of structural layers is the same as or similar to the thermoplastic matrix polymer used in the pair of structural layers.

[0034] Examples of particularly suitable thermoplastic polymers include polyolefins such as polyethylene or polypropylene, polyamides and / or heat-resistant polymers such as polyetherimide, polyetherketone and polyphenylene sulfide, etc.

[0035] The intermediate layer of the first and / or second pair of structural layers can be a separate layer inserted between two structural layers to form the pair. However, in the laminated articles according to the preferred embodiment, the structural layers have a thickness (e.g., in the prepreg) and a matrix polymer-rich region that extends a portion of that thickness on one or both sides of one or both layers. The intermediate layer of the first and / or second pair can then be formed from the polymer-rich region of at least one of the adjacent structural layers of the pair, and inserting a separate intermediate layer between the structural layers is not necessary.

[0036] Based on this structural layer, there are several possibilities regarding the optimal combination of prepregs. First, the matrix polymer-rich regions may exist on both sides, at the top, or at the bottom of the structural layer. A structural layer with a matrix polymer-rich region on only one side can be combined with another structural layer having a matrix polymer-rich region on only one side in three ways: by placing the matrix polymer-rich regions opposite each other; by placing the matrix polymer-rich region of one structural layer opposite the non-matrix polymer-rich region of the second structural layer; or by placing two non-matrix polymer-rich regions opposite each other. Due to the different thicknesses of the resulting intermediate layers, a second, first, and third pair can be obtained accordingly.

[0037] In practice, in one embodiment of the laminated article, the intermediate layers of the first pair and / or the second pair are formed from polymer-rich regions of at least one of the adjacent structural layers of the pair. In another embodiment of the laminated article, the intermediate layers of the second pair are formed from matrix polymer-rich regions of both adjacent structural layers of the pair.

[0038] The first pair of intermediate layers according to the invention has an out-of-plane volume resistivity R1, while the second pair of intermediate layers according to the invention has an out-of-plane volume resistivity R2, wherein R1 is selected such that eddy currents are substantially allowed to flow between the two structural layers of the first pair, and wherein R2 is selected such that eddy currents are substantially prevented from flowing between the two structural layers of the second pair.

[0039] One way to influence the out-of-plane volume resistivity R of the interlayer is to change the thickness of the interlayer. Therefore, in one embodiment, the laminate is characterized in that the average thickness t1 of the interlayers in the first pair is less than the average thickness t2 of the interlayers in the second pair. The third pair exhibits an average thickness of 0 because such a third pair has no interlayer between its structural layers.

[0040] In a laminated material provided according to one embodiment, the intermediate layer of the first pair comprises a thermoplastic polymer and has an average thickness of 0.05 to 15 mm, more preferably 0.07 to 12 mm.

[0041] In another embodiment of the laminated article, the intermediate layer of the second pair comprises a thermoplastic polymer and has an average thickness greater than 0.20 mm.

[0042] It should be noted that the average thickness shown is the thickness after processing, that is, the thickness of the laminate after it has been formed, optionally compacted, and cured.

[0043] The intermediate layer may be continuous over the entire planar area of ​​the laminate, but may also cover only a portion of that planar area. The same applies to the contact area between two adjacent structural layers. In fact, in the laminate provided according to an embodiment of the invention, each pair of adjacent structural layers has a contact area, and the matrix polymer-rich region extends only a portion of that contact area.

[0044] In another embodiment of the laminated component, adjacent structural layers each have a contact width and a length, and a matrix polymer-rich region extends a portion of the contact width or length.

[0045] It is also possible to provide an intermediate layer on the reinforcing fibers of the structural layer. For example, such reinforcing fibers can be coated with a shell or sheath of a polymer with suitable resistance.

[0046] To influence the out-of-plane volume resistivity R1 of the first pair of intermediate layers, the intermediate layers can be made of a conductive material. In a useful embodiment of the laminate, the first pair of intermediate layers comprises conductive particles, such as metal particles, embedded in a thermoplastic polymer. Other additives, such as ferromagnetic particles, may also be used.

[0047] Volume resistivity is also affected by the volume resistivity of the material used to manufacture the intermediate layer. The volume resistivity of the material is measured using standard test methods as described in ASTM D257. In short, a standard-sized sample is placed between two electrodes. A voltage is then applied for a period of time (60 seconds) and the resistance is measured. The volume resistivity is then calculated according to formula (1) above. All values ​​of resistivity and resistance (volume and surface) are measured at a temperature of 25°C. For minor deviations, corrections are made according to the instructions in ASTM D257.

[0048] In a laminated component provided according to an embodiment of the present invention, the material of the intermediate layer of the first pair and / or the second pair of adjacent structural layers has a content of 10. 15 Ohm.cm to 20×10 15 Volume resistivity in Ohm.cm.

[0049] The resistance that any material provides to an electric current is a combined effect of volume resistivity and surface resistivity, which always act in parallel. Volume resistivity is the resistance that leaks as current flows through the bulk of the material, while surface resistivity involves the resistance that leaks along the surface of the material or the interface between two materials. The surface resistivity of electrically insulating materials is several orders of magnitude smaller than their volume resistivity.

[0050] According to another aspect of the present invention, a method for manufacturing a molded part of the composite laminate of the present invention is provided. The method includes the following steps:

[0051] - providing a plurality of structural layers, each structural layer including conductive fibers embedded in a thermoplastic matrix;

[0052] - providing an intermediate layer having an out-of-plane volume resistance R1 between two adjacent structural layers to form a first pair, wherein eddy currents are substantially allowed to flow between the two structural layers of the first pair;

[0053] - providing an intermediate layer having an out-of-plane volume resistance R2 between two adjacent structural layers to form a second pair, wherein eddy currents are substantially blocked from flowing between the two structural layers of the second pair, where R1 and R2 are defined and 0 < R1 < R2, and wherein the intermediate layer in each pair is different from the two structural layers in each pair in that the intermediate layer in each pair does not include conductive fibers;

[0054] - optionally providing two adjacent structural layers opposite each other to form an optional third pair;

[0055] - stacking the structural layers and the intermediate layers to form a stack of one or more of the first pair, the second pair, and the optional third pair;

[0056] - forming the thus obtained stack by heating the stack and applying pressure to form a molded part of a composite laminate; and

[0057] - curing the molded part by cooling.

[0058] In an exemplary embodiment of a method for manufacturing a molded part, a laminate has an electromagnetically weldable outer surface, and a first pair is located in the laminate on the weldable outer side of the laminate in an out-of-plane direction; wherein the laminate has an electromagnetically weldable outer surface, and one pair of a second or third pair is located in the laminate on the outer side opposite to the weldable outer side or on the inner side of the laminate; wherein conductive fibers in at least one of the first, second, and / or optional third pairs of structural layers are partially interrupted in at least one of adjacent structural layers; wherein the first, second, and / or... The conductive fibers in two of the structural layers of the optional third pair are partially interrupted along a line in one structural layer of the pair and along another line in the other adjacent layer of the pair, wherein the two lines intersect each other; wherein the conductive fibers in two of the structural layers of the first pair, second pair, and / or optional third pair are partially interrupted along a line in one structural layer of the pair and along another line in the other adjacent layer of the pair, wherein the two lines coincide with each other; wherein the conductive fibers in the first pair and / or optional third pair are partially interrupted; wherein the conductive fibers in the structural layers are unidirectionally oriented, and Furthermore, multiple structural layers are stacked such that at least the first pair includes structural layers with unidirectional fiber orientations differing between one and the other structural layers in the first pair; wherein the structural layers have a thickness and a matrix polymer-rich region, the matrix polymer-rich region extending a portion of the thickness on one or both sides of some layers, and wherein the intermediate layer of the first pair and / or the second pair is formed by a polymer-rich region of at least one of the adjacent structural layers of the pair; wherein the intermediate layer of the second pair is formed by the matrix polymer-rich regions of the two adjacent structural layers of the pair; wherein each of the adjacent structural layers has a contact region, and the matrix polymer-rich region extends a portion of the contact region; wherein each of the adjacent structural layers has a contact width and a length, and the matrix polymer-rich region extends a portion of the contact width or length; wherein the intermediate layer of the first pair includes conductive particles embedded in a thermoplastic matrix to adjust the out-of-plane volume resistivity R1, substantially allowing eddy currents to flow between the two structural layers of the first pair; wherein the matrix thermoplastic polymer of the first pair and / or the second pair of structural layers and / or intermediate layers includes a semi-crystalline polyaryletherketone thermoplastic polymer; and wherein the material of the intermediate layer of the first pair and / or the second pair of adjacent structural layers has a material conforming to ASTM standards. The 10 measured by D257 15 Ohm.cm to 20×10 15 Volume resistivity in Ohm.cm.

[0059] According to another aspect of the present invention, a method is provided for electromagnetically welding a molded component of a laminated part of the present invention. The method includes the following steps:

[0060] - To make the weldable outer surfaces of the molded parts come into contact with each other to define the contact surface;

[0061] - Provide an inductor that generates an electromagnetic field under alternating current and heats the conductive fibers in the molded part, such that the matrix polymer of the second pair of structural layers of each molded part remains above its melting temperature.

[0062] - To keep the base polymer of the first pair and optionally the third pair of structural layers of each molded component below its melting temperature; and

[0063] -Optionally press the molded parts together.

[0064] This method enables the rapid and efficient achievement of high-quality welded connections between molded components, resulting in products with exceptionally good mechanical load-bearing capacity. Heat is efficiently generated in the first pair of structural layers, keeping the temperature of the thermoplastic matrix above its softening or melting temperature, while heating of the second pair of structural layers is inhibited, keeping the temperature of the thermoplastic matrix in the second pair below its softening or melting temperature. Since the inductor is not necessarily in contact with the molded component, the possibility of mechanical damage is minimized, which is particularly important for advanced applications such as aerospace.

[0065] In one embodiment of the method, the inductor moves along a line relative to the contact surface of the molded part, such that conductive fibers are heated in a predetermined portion of the contact surface. This further improves efficiency. The inductor can be connected by moving across the contact surface, for example, using a robotic arm or via linear guides.

[0066] The type of inductor can be selected depending on the situation. For example, it can be helical. The method can also use an inductor that includes a linear inductance section. The linear inductance section generates an electromagnetic field that is generally cylindrical, at least in the welding direction. By positioning the inductor so that the inductance section runs substantially parallel to the mold wall, the contact surfaces between the molded parts can be heated in a highly selective manner, thereby achieving a precision welded connection.

[0067] Depending on the materials used, the appropriate power and frequency of the electromagnetic field can be determined. The frequency, in particular, determines the penetrating power of the electromagnetic field; the power of the inductor determines the strength of the fluctuating electromagnetic field and thus the degree of heat generated in the conductive fibers.

[0068] For application in the method according to the invention, the inductor is connected to an alternator, wherein the alternator is electrically connected to the inductor via an electrical connection device. The usable frequency is typically 0.1 to 10 MHz. A frequency of 0.1 to 0.5 MHz is preferred, and a frequency of 0.15 to 0.4 MHz is more preferred. At this preferred frequency, an optimal balance is achieved between the electromagnetic field's penetration power and the heating rate.

[0069] The embodiments of the invention described in this patent application can be combined in any possible combination of these embodiments, and each embodiment can form the subject matter of a divisional patent application. Attached Figure Description

[0070] The invention will now be described with reference to the following figures, but is not limited thereto. In the figures:

[0071] Figure 1 This illustration schematically shows a method for connecting two molded components by electromagnetic welding according to an embodiment of the present invention;

[0072] Figure 2 A perspective view of a laminate according to an embodiment of the present invention is shown schematically;

[0073] Figure 3 A perspective view of a laminate according to another embodiment of the present invention is shown schematically;

[0074] Figure 4 The schematic diagram illustrates a structural layer pair that can be used in a laminated component according to yet another embodiment of the invention;

[0075] Figure 5 Schematic illustration Figure 4 The heating curves of the pair are shown below;

[0076] Figure 6 The schematic diagram illustrates components of a laminate according to yet another embodiment of the present invention;

[0077] Figure 7A A perspective view of a single layer of conductive fiber, which is a component of a laminate according to another embodiment of the present invention, is shown schematically.

[0078] Figure 7B Schematic illustration Figure 7A The cross-section of the single layer shown;

[0079] Figure 8 A perspective view of two conductive fiber monolayers, which are components of a laminate according to another embodiment of the present invention, is schematically shown; and

[0080] Figure 9 Finally, a welding apparatus that can be used in a method according to an embodiment of the present invention is shown. Detailed Implementation

[0081] Figure 1A linear inductor 1 is shown, which generates a circular electromagnetic field 2 by applying an alternating current at a frequency suitable for electromagnetic welding at appropriate power. A first molded component or laminate 3 and a second molded component or laminate 4 are in contact with each other along the contact surface of the electromagnetic field 2. The molded components are made of thermoplastic resin reinforced with carbon fibers. Under the influence of the electromagnetic field 2, the carbon fibers locally generate heat, thereby heating the thermoplastic polymer to above its melting point temperature, at least at the contact surface 5. By pressing with a pressure device (not shown), it is possible to bond the thermoplastic molded components (3, 4) that are thus thermally activated at the contact surface 5, wherein the bond at the contact surface 5 becomes permanent after the molded components (3, 4) cool to below the softening or melting temperature of the thermoplastic polymer. The figure further shows a temperature diagram at the contact surface 5 during heating, where the relative temperature T is plotted relative to the position of the contact surface 5. A third direction 6 defines the direction of movement of the inductor coil 1 during the welding process. The temperature diagram shows that a constant-intensity electromagnetic field 2 may cause irregular heating in the contact surface 5, where the temperature is observed to vary more or less parabolically. The temperature diagram also shows the variation in direction 6, which corresponds to the direction of movement of the inductor coil 1, i.e., the welding direction A. This variation in heating may further lead to thermal degradation of parts of the molded components (3, 4) due to localized overheating and / or incomplete bonding. This is generally undesirable, and the laminated parts and methods according to the invention provide a solution to this and other problems.

[0082] refer to Figure 2 A schematic perspective view of a laminated plate 10 according to an embodiment of the present invention is shown. Figure 1 As shown, the fiber-reinforced composite laminate 10 can be advantageously used for electromagnetic welding of molded parts of the laminate. The laminate 10 includes six structural layers, three of which (11a, 11b, 11c) have conductive fibers embedded in a thermoplastic PEEK matrix such that the fibers extend unidirectionally parallel to the longitudinal direction 15 of the laminate 10 (as shown by arrow 110). In the laminate 10, the other three structural layers (12a, 12b, 12c) have conductive fibers embedded in a thermoplastic matrix such that the fibers extend unidirectionally in the transverse direction 16 of the laminate 10 (as shown by arrow 120). Therefore, the fibers of layers 11 (11a, 11b, 11c) and 12 (12a, 12b, 12c) are at a 90-degree angle to each other. Through an electrical conductor 1 (e.g., ... Figure 1 The electric conductor 1 shown generates electromagnetic field 2, which induces eddy currents in the conductive fiber.

[0083] Layers (11, 12) are stacked directly or through intermediate layers (13, 14) and structural layers (11, 12) in the following stacking order:

[0084] The first pair 17c has an intermediate layer 14 located between the two structural layers (11c, 12c) of the pair 17c. The intermediate layer 14 is made of a PEEK polymer having a given electrical volumetric resistivity and has an average thickness 140 that results in an out-of-plane electrical volume resistance R1, which substantially allows eddy currents to flow between the two structural layers (11c, 12c) of the first pair 17c.

[0085] The laminate 10 further includes a second pair 17b, each formed by an intermediate layer (13a, 13b, 13c) sandwiched between two adjacently positioned structural layers. For example, the intermediate layer 13a is located between the structural layers 12a and 11b, the intermediate layer 13b is located between the structural layers 11b and 12b, and the intermediate layer 13c is located between the structural layers 12b and 11c. Note that in this definition, a structural layer can be part of different pairs of layers. In fact, for example, the structural layer 11b is part of two second pairs 17b. In the illustrated embodiment, the intermediate layers (13a, 13b, 13c) are also made of a PEEK polymer having a given electrical volumetric resistivity and all have an average thickness 130 that results in an out-of-plane electrical volume resistance R2, which substantially prevents eddy currents from flowing between the structural layers (12a, 11b, 12b, 11c) contacting the intermediate layers (13a, 13b, 13c) of the second pair 17b. The resistances R1 and R2 are defined and 0 < R1 < R2. In the illustrated embodiment, 0.4R2 < R1 < 0.6R2, which is achieved by selecting the average thickness 140 to be in the range of 0.4 to 0.6 of the average thickness 130.

[0086] As shown, the laminate may further include a third pair 17a of structural layers. The third pair 17a is located on the top surface of the laminate 10, and there is no intermediate layer between the two structural layers (11a, 12a) of the pair 17a. In other words, the layers (11a, 12a) are directly bonded to each other.

[0087] As shown, the laminate 10 has an outer surface that can be electromagnetically welded, and the outer surface corresponds to the bottom surface 150. As shown, the first pair 17c is located in the laminate 10 in the out-of-plane direction 18 of the laminate 10, near the weldable outer surface 150 of the laminate 10. The second pair 17b is located inside the laminate 10, further away from the bottom surface 150. The third pair 17a is located on the top surface 160 of the laminate 10.

[0088] The molded laminate 10 can be electromagnetically welded or bonded to another molded component 40. Although not shown in detail, the molded component 40 may also include a laminate as described above. As Figure 1As shown, components (3, 4) are replaced by a laminated component 10 and a molded component 40, respectively. Under the influence of the electromagnetic field 2, the carbon fibers locally generate heat, thereby heating the thermoplastic PEEK polymer to above its melting temperature, at least at the bottom surface 150. By pressing with a pressure device (not shown), it is possible to bond the thus thermally activated thermoplastic molded components (10, 40) at the bottom surface 150, wherein the bond at the contact surface 5 becomes permanent after the molded components (10, 40) cool to below the softening or melting temperature of the thermoplastic PEEK polymer. The presence of a second pair of 17b in the laminated component 10 substantially prevents these pairs of 17b from being heated above the softening or melting temperature of the thermoplastic PEEK polymer. This prevents overheating of these second pairs of 17b. On the other hand, the presence of a first pair of 17c in the laminated component 10 promotes the heating of these pairs of 17c to above the softening or melting temperature of the thermoplastic PEEK polymer and utilizes the electromagnetic field strength more efficiently than known. The third pair 17a is also heated, but more gently than the first pair 17c. To prevent the first pair 17c from overheating, a heat sink (not shown) can be applied to the top surface 160 of the laminate 10.

[0089] Please note that, if necessary, another intermediate layer with out-of-plane volume resistance R1 may be located between the bottom surface 150 and the top surface of the molded part 40.

[0090] Figure 3 A perspective view of a laminate according to another embodiment of the invention is schematically shown, wherein intermediate layers (13, 14) extend longitudinally 15 along a portion of the length of the laminate 10. Note that the reference numerals used are... Figure 2 Same characteristics. Also note that the laminate shown is in an uncured state with exaggerated layer thickness. Upon curing, layers 12a, 11b, 12b, and 11c will press against each other along the transverse side 170 of the laminate. In the illustrated embodiment, the intermediate layers (13, 14) extend at least longitudinally 15 to the molded part 40 welded to the laminate 10.

[0091] like Figure 4 As shown, one embodiment of the laminated part may be constructed from fiber-reinforced prepreg 20 as structural layers (11, 12). Each prepreg 20 has a thickness 21 and a matrix polymer-rich region 22, the matrix polymer-rich region 22 being located on one side of the prepreg 20 (i.e., Figure 4A portion 23 of thickness extends from the top surface of the prepreg 20 shown in the left-hand diagram. Fiber-reinforced regions 25 comprise reinforcing fibers of the prepreg 20 embedded in the matrix polymer. Polymer-rich regions 22 are substantially free of reinforcing fibers. Fiber-reinforced regions 25 extend to the bottom of the prepreg 20, and this bottom is referred to as the polymer-deficient region 26. These prepregs 20 are used to stack multiple such prepregs 20 on top of each other in a specific stacking order to construct a laminate 10. Figure 4 The right-hand diagram illustrates an example of a stack of two prepregs 20. A first stack 24a of the two prepregs 20 includes prepregs 20 such that a polymer-rich region 22 of one prepreg 20 contacts a polymer-deficient region 26 of the second prepreg 20 to form an intermediate layer of thickness 23. A second stack 24b of the two prepregs 20 includes prepregs 20 such that a polymer-rich region 22 of one prepreg 20 contacts a polymer-rich region 22 of the second prepreg 20 to form an intermediate layer of twice the thickness 23. A third stack 24c of the two prepregs 20 includes prepregs 20 such that a polymer-deficient region 26 of one prepreg 20 contacts a polymer-deficient region 26 of the second prepreg 20. This forms a third pair of structural layers 17a (11a, 12a), in which the intermediate layer is missing. Based on the obtained volume resistivity (or, the obtained thickness), stack 24a can form a first pair having an intermediate layer 22 located between the two structural prepregs 20, wherein the intermediate layer has an out-of-plane volume resistivity R1, which substantially allows eddy currents to flow between the two structural layers of the first pair. Based on the obtained volume resistivity (or, the obtained thickness), stack 24b can form a second pair having an intermediate layer formed by two polymer-rich regions 22 located between the two structural prepregs 20, wherein the intermediate layer has an out-of-plane volume resistivity R2, which substantially prevents eddy currents from flowing between the two structural layers of the second pair.

[0092] refer to Figure 5 An example is shown Figure 4 The heating curves for the pair are shown. In this figure, the temperature 50 (°C) reached in the pair is shown as a function of the current 51 (A) through the inductor. The upper curve 52a represents the result obtained by stack 24a, while the lower curve 52b represents the result obtained by stack 24b. The result obtained by stack 24c lies between these two extreme values ​​(curve 52c). Clearly, the current required to heat stack 24a is less than that required to heat stack 24b. Alternatively, for the same current value 51a (or electromagnetic field strength), stack 24a will be heated above the softening or melting temperature of the matrix polymer, while stack 24b can remain below its softening or melting temperature, a temperature difference of approximately 30°C.

[0093] Another embodiment of the laminate 10 of the present invention is as follows: Figure 6As shown. Note that only the two structural layers (11c, 12c) of 17c are shown (see attached figures). Figure 2 (Consistent), wherein 17c further includes an intermediate layer 14, which is shown as a transparent layer. In this embodiment, the conductive fibers (60, 61) in the two structural layers (11c, 12c) of the first pair of 17c are partially interrupted along a line 55 parallel to the longitudinal direction 15 of the laminate. In the lower structural layer 12c of the pair, fiber 61 extends in the transverse direction 16 of the laminate and along another line 56 parallel to the transverse direction 16 of the laminate. In the upper structural layer 11c of the pair, fiber 60 extends in the longitudinal direction 15 of the laminate. As shown, the two lines (55, 56) intersect each other in region B, and it is demonstrated that the interruption of the conductive fibers greatly enhances the heating inside and around region B. To achieve the same effect, it is also possible to interrupt the fibers on a portion of the thickness of the two structural layers (11c, 12c).

[0094] The similar principles illustrated above can be applied to a smaller level, namely the level of a single layer of 7 fibers (60, 61). [Reference] Figure 7A and according to Figure 7B A cross-sectional view along line C-C' shows numerous fibers 60 coated or surrounded by polymer layers or sheets 63. The polymer layers or sheets 63 may have an out-of-plane volume resistivity R1, which essentially allows eddy currents to flow between two structural monolayers 7 stacked on top of each other. Alternatively, the polymer layers or sheets 63 may have an out-of-plane volume resistivity R2, which essentially prevents eddy currents from flowing between the structural monolayers 7 stacked on top of each other. Although Figure 7B Multiple fibers 60 are shown coated or surrounded by a polymer layer or sheet 63, but such a coating or sheet 63 can also be applied around a single fiber (with multiple filaments) or a bundle of fibers.

[0095] refer to Figure 8 In this embodiment, the conductive fibers (60, 61) in two adjacent monolayers 7 (7a, 7b) are partially interrupted along a line 65 parallel to the longitudinal direction 15 of the laminate. In the lower monolayer 7b of this pair, fiber 61 extends in the transverse direction 16 of the laminate and along another line 66 parallel to the transverse direction 16 of the laminate. In the upper monolayer 7a of this pair, fiber 60 extends along the longitudinal direction 15 of the laminate. As shown, the two lines (65, 66) intersect each other at region B', and it is demonstrated that the interruption of the conductive fibers (60, 61) greatly enhances the heating inside and around region B'.

[0096] Figure 9Finally, a welding apparatus 30 with a connecting inductor 31 is shown. The inductor 31 can be guided along a welding path pre-programmed by a six-axis industrial robot 32 to achieve the desired weld. In this case, molded parts according to an embodiment of the invention can be fixed for welding and pressed together in a mold 33 manufactured for this purpose. The mold 33 may be provided with a groove 34 through which the inductor 15 can be moved close to the molded part for welding. To generate an electromagnetic field, the inductor 15 can be connected to an alternator 35 arranged on the robot 32. The strength of the electromagnetic field can be varied along the welding path to at least partially compensate for any temperature variations that may occur on the contact surface of the molded parts along the welding path.

Claims

1. A fiber-reinforced composite laminate for a molded part for electromagnetic welding of laminates, the laminate comprising a plurality of structural layers, each structural layer being formed of conductive fibers embedded in a thermoplastic matrix, wherein eddy currents can be induced in the conductive fibers by a conductor generating an electromagnetic field; wherein the plurality of structural layers includes a first pair, a second pair, and optionally a third pair of two adjacently positioned structural layers, wherein, - the first pair has an intermediate layer located between the two structural layers of the pair, wherein the intermediate layer has an out-of-plane volume resistance R1, and R1 allows eddy currents to flow between the two structural layers of the first pair; - the second pair has an intermediate layer located between the two structural layers of the pair, wherein the intermediate layer has an out-of-plane volume resistance R2, and R2 prevents eddy currents from flowing between the two structural layers of the second pair; and - the optional third pair has no intermediate layer between the two structural layers of the pair; wherein and, R1 and R2 are defined and 0 < R1 < R2, the intermediate layer in each first pair and second pair is different from the two structural layers in each first pair and second pair in that the intermediate layer in each first pair and second pair does not include conductive fibers; and the condition R1 < R2 is achieved by having ρ1.t1 < ρ2.t2, where ρ1 is the volume resistivity of the material of the intermediate layer in the first pair, t1 is the average thickness of the intermediate layer in the first pair, ρ2 is the volume resistivity of the material of the intermediate layer of the second pair, and t2 is the average thickness of the intermediate layer of the second pair.

2. The laminated component according to claim 1, wherein, The laminate has an electromagnetic-weldable outer surface, and the first pair is located in the laminate in the out-of-plane direction of the laminate on the weldable outer side of the laminate.

3. The laminated component according to claim 1 or 2, wherein, The laminate has an electromagnetic-weldable outer surface, and one of the second pair or the third pair is located in the laminate on the outer side opposite to the weldable outer side or inside the laminate.

4. The laminated component according to claim 1 or 2, wherein, At least the intermediate layer in the second pair includes non-conductive fibers.

5. The laminated component according to claim 1 or 2, wherein, The conductive fibers in at least one of the structural layers of the first pair, second pair, and / or third pair are locally interrupted in at least one of the adjacent structural layers.

6. The laminated component according to claim 5, wherein, The conductive fibers in two of the structural layers of the first pair, second pair, and / or third pair are locally interrupted along a line in one structural layer of the pair and along another line in another adjacent layer of the pair, where the two lines intersect each other.

7. The laminated component according to claim 5, wherein, The conductive fibers in the first pair and / or the third pair are locally interrupted.

8. The laminated component according to claim 1 or 2, wherein, The conductive fibers in the structural layers are unidirectionally oriented.

9. The laminated part according to claim 1 or 2, wherein, The intermediate layer of the first pair includes a thermoplastic polymer and has an average thickness of 0.05 to 0.15 mm, and the intermediate layer of the second pair includes a thermoplastic polymer and has an average thickness greater than 0.20 mm.

10. The laminated part according to claim 1 or 2, wherein, The structural layers have a thickness and a matrix polymer-rich region that extends a portion of the thickness on one or both sides of some of the structural layers.

11. The laminated part according to claim 10, wherein, The intermediate layer of the first pair and / or the second pair is formed by the matrix polymer-rich region of at least one of the adjacent structural layers of the pair.

12. The laminated component according to claim 1 or 2, wherein, The intermediate layer of the first pair includes conductive particles embedded in a thermoplastic polymer to modulate the out-of-plane volume resistivity R1, allowing eddy currents to flow between the two structural layers of the first pair.

13. The laminated component according to claim 1 or 2, wherein, The material of the intermediate layer of the first pair and / or second pair of adjacent structural layers has a 10 as measured by ASTM D257. 15 Ohm.cm to 20×10 15 Volume resistivity in Ohm.cm.

14. A method for electromagnetic welding a molded part of a laminated part according to any one of claims 1 to 13, comprising the following steps: - To bring the weldable outer surfaces of the molded components into contact with each other to define a contact surface; - An inductor is provided that generates an electromagnetic field under alternating current and heats the conductive fibers in the molded component, such that the matrix polymer of the second pair of structural layers in each molded component remains above its melting temperature; and - Keep the matrix polymer of the first pair and optionally the third pair of structural layers of each molded component below its melting temperature; as well as -Optionally, the molded parts are pressed together.

15. The method according to claim 14, wherein, The inductor moves along a line relative to the contact surface of the molded component, such that the conductive fibers are heated in a predetermined portion of the contact surface.

16. The method according to claim 14 or 15, wherein, The inductor includes a linear induction section that generates an electromagnetic field that is at least cylindrical in the welding direction.

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