Induction welding method for thermoplastic fiber composite material and method for manufacturing hard-shell hollow structure

Abstract

The invention provides an induction welding method of a thermoplastic fiber composite material and a manufacturing method of a hard shell type hollow structural body, the induction welding method of the thermoplastic fiber composite material comprises the following steps: a first carbon fiber composite material layer, a third thermoplastic resin containing an induction sheet, and a second carbon fiber composite material layer are stacked in sequence to form a lamination layer; preheating the laminated layer before induction welding; and heating the first carbon fiber cloth, the induction sheet and the second carbon fiber cloth until the temperature of the induction sheet exceeds the melting point of the third thermoplastic resin, and heating the first thermoplastic resin between the first carbon fiber cloth and the induction sheet to enable the second carbon fiber cloth to be heated until the temperature of the induction sheet exceeds the melting point of the third thermoplastic resin. And the second thermoplastic resin is positioned between the second carbon fiber cloth and the induction sheet and is respectively in a molten state, so that the first thermoplastic resin and the second thermoplastic resin are respectively jointed with the third thermoplastic resin. According to the method, the joint strength of induction welding with preheating is larger than that of induction welding without preheating.

Description

Technical Field

[0001] The present invention relates to a method for induction welding of a thermoplastic fiber composite material, and more particularly to a method for manufacturing a hard-shell hollow structure using the induction welding method of the thermoplastic fiber composite material. Background Art

[0002] Thermoplastic fiber composite materials such as carbon fiber composites have advantages such as recyclability, good high-temperature performance, and high impact toughness. Therefore, they are widely used in industries such as bicycles and aviation, making them an important direction for cost reduction and high performance.

[0003] Currently, among several commonly used welding technologies for thermoplastic composites, induction welding has many advantages such as low cost, continuous automation, and homogeneous interface welding. Therefore, induction welding is particularly suitable for joining thermoplastic fiber composite components. The principle of this induction welding is: by an induction coil to heat two workpieces (such as carbon fiber composites) to be joined, so that the contact surface between the two workpieces melts, and then the two workpieces are joined to each other.

[0004] As a structural member, carbon fiber composites have a wide range of applications for carbon fiber tubes, which have characteristics such as high strength, low density, and long life. The products have been accepted by many industries, including bicycle frames, automobile anti-collision frames, aircraft ducts, small wing structures, flaps, fins, etc. These components with a hard-shell (monocoque) hollow structure can use impregnated fiber sheets called prepregs, which can usually be cured and formed in a mold under heating and pressure. The hollow part can use an air bag to provide compaction pressure, which often causes wrinkles due to uneven pressure distribution, further leading to resin unevenness and high void areas.

[0005] Therefore, there is a need to provide a method for induction welding of a thermoplastic fiber composite material and a method for manufacturing a hard-shell hollow structure, which can solve the above-mentioned problems. Summary of the Invention

[0006] An object of the present invention is to provide a method for induction welding of a thermoplastic fiber composite material, in which the joint strength of the preheated induction welding is greater than that of the non-preheated induction welding.

[0007] For the above purposes, the present invention provides an induction welding method for a thermoplastic fiber composite material, comprising the following steps: providing a first carbon fiber composite layer, which includes a first thermoplastic resin and at least one first carbon fiber cloth, and the at least one first carbon fiber cloth is located within the first thermoplastic resin; providing a second carbon fiber composite layer, which includes a second thermoplastic resin and at least one second carbon fiber cloth, and the at least one second carbon fiber cloth is located within the second thermoplastic resin; providing an induction sheet and a third thermoplastic resin, wherein the induction sheet is located within the third thermoplastic resin, and the induction sheet is a material that generates heat upon electromagnetic field induction; stacking the first carbon fiber composite layer, the third thermoplastic resin containing the induction sheet, and the second carbon fiber composite layer in sequence to form a stack; preheating the stack before induction welding, wherein a preheating temperature of the preheating is less than or equal to the glass transition temperature of the third thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the third thermoplastic resin; and controlling an induction coil to heat the at least one first carbon fiber cloth, the induction sheet, and the at least one second carbon fiber cloth until the induction sheet is heated to exceed the melting point of the third thermoplastic resin, and enabling the first thermoplastic resin located between the at least one first carbon fiber cloth and the induction sheet and the second thermoplastic resin located between the at least one second carbon fiber cloth and the induction sheet to respectively form a molten state, so that the first and second thermoplastic resins are respectively joined to the third thermoplastic resin to complete the induction welding of the thermoplastic fiber composite material.

[0008] Optionally, the induction sheet is selected from one of carbon steel, stainless steel, aluminum alloy, and carbon fiber cloth.

[0009] Optionally, when the induction sheet is a carbon fiber cloth, the preheating temperature is 120 - 190 °C.

[0010] Optionally, the preheating is performed by a preheater, and the preheater includes a hot air gun.

[0011] Optionally, controlling the induction coil to heat the first carbon fiber cloth, the induction sheet, and the second carbon fiber cloth according to a process parameter, and the process parameter is an electromagnetic frequency of 150 - 400 kHz, an induction time of 15 - 120 seconds, an induction current of 18 - 20 amperes, a preheating time of 15 - 120 seconds, a preheating current of 12 - 16 amperes, and a distance between the induction coil and the first carbon fiber composite layer of 1 - 4 mm.

[0012] The present invention further provides a method for manufacturing a hard-shell type hollow structure body, comprising the following steps: providing a first carbon fiber composite layer, which includes a first thermoplastic resin and at least one first carbon fiber cloth, and the at least one first carbon fiber cloth is located within the first thermoplastic resin; hot-pressing the first carbon fiber composite layer to form a first half-shell structure body, and the first half-shell structure body has two first end edges; providing a second carbon fiber composite layer, which includes a second thermoplastic resin and at least one second carbon fiber cloth, and the at least one second carbon fiber cloth is located within the second thermoplastic resin; hot-pressing the second carbon fiber composite layer to form a second half-shell structure body, and the second half-shell structure body has two second end edges; providing a first induction sheet and a third thermoplastic resin, wherein the first induction sheet is located within the third thermoplastic resin, and the first induction sheet is a material that generates heat upon electromagnetic field induction; stacking the first end edge of the first half-shell structure, the third thermoplastic resin containing the first induction sheet, and the second end edge of the second half-shell structure in sequence to form a first stack; performing a first preheating on the first stack, and a preheating temperature of the first preheating is less than or equal to the glass transition temperature of the third thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the third thermoplastic resin; and controlling an induction coil to heat the at least one first carbon fiber cloth located at the first end edge, the first induction sheet, and the at least one second carbon fiber cloth located at the second end edge until the first induction sheet is heated to exceed the melting point of the third thermoplastic resin, and enabling the first thermoplastic resin located between the at least one first carbon fiber cloth and the first induction sheet, and the second thermoplastic resin located between the at least one second carbon fiber cloth and the first induction sheet to respectively form a molten state, so that the first and second thermoplastic resins are respectively joined to the third thermoplastic resin to complete the first induction welding of the end edges of the first and second half-shell structure bodies.

[0013] Optionally, the method further includes the following steps: providing a second induction sheet and a fourth thermoplastic resin, wherein the second induction sheet is located within the fourth thermoplastic resin, and the second induction sheet is a material that generates heat upon electromagnetic field induction; stacking the first edge of the first half-shell structure, the two fourth thermoplastic resins containing the second induction sheet, and the second edge of the second half-shell structure in sequence to form a second stack; performing a second preheating on the second stack, wherein the preheating temperature of the second preheating is less than or equal to the glass transition temperature of the fourth thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the fourth thermoplastic resin; and controlling the induction coil to heat the at least one first carbon fiber cloth at the first edge, the second induction sheet, and the at least one second carbon fiber cloth at the second edge until the second induction sheet is heated to exceed the melting point of the fourth thermoplastic resin, and causing the first thermoplastic resin between the at least one first carbon fiber cloth and the second induction sheet and the second thermoplastic resin between the at least one second carbon fiber cloth and the second induction sheet to respectively form a molten state, so that the first and second thermoplastic resins are respectively joined to the fourth thermoplastic resin to complete the second induction welding of the edges of the first and second half-shell structures, thereby completing a hard-shell hollow structure.

[0014] Optionally, the induction sheet is selected from one of carbon steel, stainless steel, aluminum alloy, and carbon fiber cloth.

[0015] Optionally, when the induction sheet is carbon fiber cloth, the preheating temperature is 120 - 190 °C.

[0016] Optionally, the overlapping form between the first edge and the second edge is a stepped cut profile.

[0017] The thermoplastic fiber composite material of the present invention can be fabricated by the method of laminating and hot-pressing prepreg carbon fiber cloth, and a half-shell structure is fabricated by hot-pressing and forming. After processing the edges of the half-shell structure, it can be joined to another half-shell structure. Then, a material that is easily inductively heated is buried at the interface of two carbon fiber composite layers, and the induction welding process parameters are controlled. With the induction welding equipment, the two carbon fiber composite layers can be continuously welded to complete a hard-shell hollow structure. Furthermore, through two-stage programmed control for preheating and then induction welding, the joint strength of the induction welding with preheating is greater than that of the induction welding without preheating. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flowchart of the steps of the induction welding method of the thermoplastic fiber composite material according to an embodiment of the present invention.

[0019] Figure 2Schematic cross-sectional view of a laminate of a first carbon fiber composite layer, a third thermoplastic resin containing an induction sheet, and a second carbon fiber composite layer according to an embodiment of the present invention.

[0020] Figure 3 Schematic perspective view of an induction welding device according to an embodiment of the present invention.

[0021] Figure 4 Schematic diagram showing the relationship between the shear joint strength, current, preheating temperature T1, and welding temperature T2 according to an embodiment of the present invention.

[0022] Figure 5 Cross-sectional OM image showing a welding current of 20 A and no preheating in Example 1 of the present invention.

[0023] Figure 6 Cross-sectional OM image showing a welding current of 20 A and preheating at 168 °C in Example 3 of the present invention.

[0024] Figure 7 Flowchart of the steps of a manufacturing method of a hard shell type hollow structure according to an embodiment of the present invention.

[0025] Figure 8 Schematic cross-sectional view of the first carbon fiber composite layer according to an embodiment of the present invention.

[0026] Figure 9 Schematic cross-sectional view of the second carbon fiber composite layer and schematic perspective view of the second half-shell structure according to an embodiment of the present invention.

[0027] Figure 10A Schematic cross-sectional view of the first induction sheet and the third thermoplastic resin according to an embodiment of the present invention.

[0028] Figure 10B Schematic cross-sectional view of the second induction sheet and the fourth thermoplastic resin according to an embodiment of the present invention.

[0029] Figure 11 Schematic perspective view of the first half-shell structure, the third thermoplastic resin containing an induction sheet, and the first half-shell structure according to an embodiment of the present invention.

[0030] Figures 12A to 12D Shows four overlapping forms between the first edge and the second edge of the first half-shell structure.

[0031] In the figure:

[0032] 1 First carbon fiber composite layer 1' First half-shell structure

[0033] 11 First thermoplastic resin

[0034] 12 First carbon fiber cloth 13 First edge

[0035] 2 Second carbon fiber composite layer 2' Second half-shell structure

[0036] 21 Second thermoplastic resin 22 Second carbon fiber cloth

[0037] 23 Second edge

[0038] 31 Third thermoplastic resin 32 Inductive sheet

[0039] 32' First inductive sheet

[0040] 33 Fourth thermoplastic resin 34 Second inductive sheet

[0041] 4 Induction welding equipment 40 Induction coil

[0042] 41 Pre-pressing front roller 42 Pre-pressing rear roller

[0043] 43 Welding area 44 Welding direction

[0044] 45 Joint point

[0045] F1 interface F2 interface

[0046] T1 Preheating temperature T2 Welding temperature

[0047] Steps S11 to S16 Steps S21 to S32. Detailed implementation mode

[0048] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0049] The embodiments of the present invention will be described in detail below in conjunction with the drawings. The drawings are mainly simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner. Therefore, only the components related to the present invention are marked in these drawings, and the components shown are not drawn according to the number, shape, size ratio, etc. during implementation. The actual specifications and dimensions during implementation are actually a selective design, and the layout form of its components may be more complex.

[0050] Figure 1 It is a step flow chart of an induction welding method for a thermoplastic fiber composite material according to an embodiment of the present invention. Figure 2 It is a cross-sectional schematic diagram of a laminate of a first carbon fiber composite layer, a third thermoplastic resin containing an inductive sheet, and a second carbon fiber composite layer according to an embodiment of the present invention. Figure 3 It is a three-dimensional schematic diagram of an induction welding equipment according to an embodiment of the present invention. Please refer to Figure 1, the induction welding method of the thermoplastic fiber composite material includes the following steps:

[0051] Please refer to Figure 2 , in step S11, a first carbon fiber composite layer 1 is provided, which includes a first thermoplastic resin 11 and at least one first carbon fiber cloth 12, and the first carbon fiber cloth 12 is located within the first thermoplastic resin 11. The first carbon fiber composite layer 1 can be made by laminating prepreg carbon fiber cloth. For example, the first carbon fiber composite layer 1 can be made of polysulfone (PSU) carbon fiber composite material, which is a unidirectional (UD) fiber prepreg cloth.

[0052] Please refer to again Figure 2 , in step S12, a second carbon fiber composite layer 2 is provided, which includes a second thermoplastic resin 21 and at least one second carbon fiber cloth 22, and the second carbon fiber cloth 22 is located within the second thermoplastic resin 21. Similarly, the second carbon fiber composite layer 2 can be made by laminating prepreg carbon fiber cloth. For example, the second carbon fiber composite layer 2 can be made of polysulfone (PSU) carbon fiber composite material, which is also a unidirectional (UD) unidirectional fiber prepreg cloth.

[0053] Please refer to again Figure 2 , in step S13, an induction sheet 32 and a third thermoplastic resin 31 are provided, wherein the induction sheet 32 is located within the third thermoplastic resin 31, and the induction sheet 32 is a material that generates heat when induced by an electromagnetic field. The induction sheet 32 can be selected from one of carbon steel, stainless steel, aluminum alloy, and carbon fiber cloth. The third thermoplastic resin 31 can use the same polymer type as the first and second thermoplastic resins 11 and 21, such as polysulfone (PSU). When the induction sheet 32 is a carbon fiber cloth, its fiber arrangement uses a woven arrangement, such as a plain weave (one up and one down interweaving) or a twill weave (two up and two down interweaving) method, not the UD unidirectional. The woven arrangement used can provide a higher temperature at the interface, making it easier for induction welding and the appearance of the component not being easily damaged. In an embodiment of the present invention, when the polysulfone (PSU) is used to impregnate the induction sheet 32, the induction sheet 32 can use carbon fiber with a basis weight of 220 g / m 2 and the carbon fiber uses a 3K tow, and after being woven in a one up and one down plain weave manner, it is impregnated with the polysulfone (PSU) polymer.

[0054] Please refer to again Figure 2 , in step S14, the first carbon fiber composite layer 1, the third thermoplastic resin 31 containing the induction sheet 32, and the second carbon fiber composite layer 2 are stacked in sequence to form a stack.

[0055] In step S15, a preheater (not shown in the figure) is used to preheat the laminate before induction welding, where the preheat temperature (TP) is less than or equal to the glass transition temperature (TG) of the third thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the third thermoplastic resin, i.e., (60%×TG) ≤ TP ≤ TG). The glass transition temperature (TG) refers to the temperature at which a glassy substance can reversibly transform between the glassy state and the high elastic state. When the induction sheet is a carbon fiber cloth, the preheat temperature can be 120 - 190°C. For example, an induction welding device includes the preheater, and the preheater includes a hot air gun for providing preheating before induction welding. The process parameters of the induction welding include: preheat temperature and time.

[0056] Please refer to Figure 2 , in step S16, an induction coil is controlled to heat the first carbon fiber cloth 12, the induction sheet 32, and the second carbon fiber cloth 22 until the induction sheet 32 is heated to exceed the melting point of the third thermoplastic resin 31, and the first thermoplastic resin 11 between the first carbon fiber cloth 12 and the induction sheet 32, and the second thermoplastic resin 21 between the second carbon fiber cloth 22 and the induction sheet 32 are respectively formed in a molten state, so that the first and second thermoplastic resins 11, 21 are respectively joined to the third thermoplastic resin 31 to complete the induction welding of the thermoplastic fiber composite material. In an embodiment of the present invention, compared with the first carbon fiber cloth 12 and the second carbon fiber cloth 22, the induction sheet 32 is more susceptible to electromagnetic field induction and generates more heat energy at step S16. For example, when the induction sheet 32 is a carbon fiber cloth, the induction sheet 32 can have different configuration conditions (for example: a higher basis weight, a more magnetic-sensitive weaving method, other methods to improve the magnetic-sensitive heating performance, or any combination of the methods) to generate more heat energy than the first carbon fiber cloth 12 and the second carbon fiber cloth 22. For example, please refer to Figure 3, the induction welding device 4 further includes: the induction coil 40, the pre-pressing front roller 41 and the pre-pressing rear roller 42. The induction coil 40, the pre-pressing front roller 41 and the pre-pressing rear roller 42 move simultaneously along the welding direction 44, and the area below their movement forms a welding area 43, and the position below the induction coil 40 is the joint point 45. At this time, the welding speed can be 50-200 mm / min. Furthermore, the induction welding device 4 can further include: an induction main machine, an air cooling device, an XY moving mechanism, etc. to perform induction welding. The process parameters of the induction welding further include: the distance between the laminate of the thermoplastic fiber composite material and the induction coil, the clamping pressure of the pre-pressing front roller and the pre-pressing rear roller, the preheating current, the preheating time, the induction frequency, the induction current, the induction time, and the air cooling wind pressure, etc. The implementation parameters for controlling the induction welding in an embodiment of the present invention are as shown in Table 1 and Table 2 below:

[0057]

[0058] Table 1

[0059]

[0060] Table 2

[0061] In an embodiment of the present invention, the induction welding device can be configured as follows: First, an induction machine working head and an induction coil. An adjustment mechanism for the X-axis and Z-axis is provided below the induction machine working head, which can finely adjust the distance between the induction coil and the laminate of the thermoplastic fiber composite material to provide the required temperature for induction welding. The output power of the induction machine working head can be adjusted. Second, a motor is provided to provide the moving function in the Y-axis direction, and its moving speed can be controlled to provide the welding time. Third, another motor is provided to provide the downward pressure in the Z-axis direction, which contacts the laminate of the thermoplastic fiber composite material as the pre-pressing front roller and the pre-pressing rear roller, and its downward pressure can be controlled to provide the welding pressure. Fourth, an adjustable-position compressed air nozzle is provided, which is aligned with the welding area and the wind pressure can be adjusted to cool the surface of the laminate of the thermoplastic fiber composite material.

[0062] Figure 4 It is a schematic diagram showing the relationship between the shear joint strength, current, preheating temperature T1 and welding temperature T2 in an embodiment of the present invention. Please refer to Figure 4, in Example 1, there is no preheating, and the preheating temperature T1 is the room temperature of 25°C; a welding current of 20A provides a welding temperature T2 of approximately 272°C, and the bonding strength of the induction welding of the first and second carbon fiber composite layers is 9.3 MPa. In Examples 2, 3, and 4, the welding current is fixed at 20A, providing welding temperatures T2 of approximately 220°C, 242°C, and 256°C respectively; after preheating through a two-stage programmed control and then performing induction welding, the preheating temperatures in Examples 2, 3, and 4 are set at approximately 120°C, 168°C, and 189°C respectively. The bonding strength of the induction welding after preheating at 120°C is 13.9 MPa, the bonding strength of the induction welding after preheating at 168°C is 14.6 MPa, and the bonding strength of the induction welding after preheating at 189°C is 13.1 MPa, indicating that excessive preheating makes the polymer at the carbon fiber composite interface prone to cracking, increasing pores and resulting in a decrease in the bonding strength. Figure 5 Showing the cross-sectional OM image of the welding current of 20A and no preheating in Example 1 of the present invention. Please refer to Figure 5 , an interface F1 of incomplete welding appears in this OM image. Figure 6 Showing the cross-sectional OM image of the welding current of 20A and preheating at 168°C in Example 3 of the present invention. Please refer to Figure 6 , an interface F2 of good welded joint appears in this OM image.

[0063] Figure 7 It is a flowchart of the steps of the manufacturing method of the hard-shell hollow structure according to an embodiment of the present invention. Figure 8 It is a schematic cross-sectional view of the first carbon fiber composite layer and a three-dimensional schematic view of the first half-shell structure according to an embodiment of the present invention. Figure 9 It is a schematic cross-sectional view of the second carbon fiber composite layer and a three-dimensional schematic view of the second half-shell structure according to an embodiment of the present invention. Figure 10A It is a schematic cross-sectional view of the first induction sheet and the third thermoplastic resin according to an embodiment of the present invention. Figure 10B It is a schematic cross-sectional view of the second induction sheet and the fourth thermoplastic resin according to an embodiment of the present invention. Figure 11 It is a three-dimensional schematic view of the first half-shell structure, the third thermoplastic resin containing the induction sheet, and the first half-shell structure according to an embodiment of the present invention. The manufacturing method of the hard-shell hollow structure includes the following steps:

[0064] Please refer to Figure 8 , in step S21, a first carbon fiber composite layer 1 is provided, which includes a first thermoplastic resin 11 and at least one first carbon fiber cloth 12, and the first carbon fiber cloth 12 is located within the first thermoplastic resin 11. In step S22, the first carbon fiber composite layer 1 is hot-pressed and formed into a first half-shell structure 1', and the first half-shell structure 1' has two first end edges 13.

[0065] Please refer toFigure 9 In step S23, a second carbon fiber composite layer 2 is provided, which includes a second thermoplastic resin 21 and at least one second carbon fiber cloth 22, and the second carbon fiber cloth 22 is located within the second thermoplastic resin 21. In step S24, the second carbon fiber composite layer 2 is hot-pressed and formed into a second half-shell structure 2', and the second half-shell structure 2' has two second end edges 23.

[0066] Please refer to Figure 10A In step S25, a first induction sheet 32' and a third thermoplastic resin 31 are provided, wherein the first induction sheet 32' is located within the third thermoplastic resin 31, and the first induction sheet 32' is a material that generates heat upon electromagnetic field induction. The first induction sheet 32' can be selected from one of carbon steel, stainless steel, aluminum alloy, and carbon fiber cloth. The third thermoplastic resin 31 can use the same polymer type as the first and second thermoplastic resins 11 and 21, such as polysulfone (PSU).

[0067] Please refer to Figure 11 In step S26, the first end edge 13 of the first half-shell structure 1', the third thermoplastic resin 31 containing the first induction sheet 32', and the second end edge 23 of the second half-shell structure 2' are stacked in sequence to form a first stack. Please refer to Figures 12A to 12D which shows four overlapping forms between the first end edge 13 of the first half-shell structure 1' and the second end edge 23 of the second half-shell structure 2'. Preferably, Figure 12B shows a cross-section of the overlapping form between the first end edge 13 and the second end edge 23 as a stepped cut. After induction welding, the welding area is the smoothest without unevenness.

[0068] In step S27, the first stack is preheated with a preheater (not shown in the figure). The required preheating temperature is less than or equal to the glass transition temperature (TG) of the third thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the third thermoplastic resin.

[0069] Please refer to again Figure 8 、 Figure 9 and Figure 11, in step S28, control an induction coil to heat the first carbon fiber cloth 12, the first induction sheet 32', and the second carbon fiber cloth 22 located at the second edge 23 of the first edge 13 until the temperature of the first induction sheet 32' rises above the melting point of the third thermoplastic resin 31, and the first thermoplastic resin 11 between the first carbon fiber cloth 12 and the first induction sheet 32', and the second thermoplastic resin 21 between the second carbon fiber cloth 22 and the first induction sheet 32' respectively form a molten state, so that the first and second thermoplastic resins 11, 21 are respectively joined to the third thermoplastic resin 31 to complete the first induction welding of the edges of the first and second half-shell structures 1', 2'.

[0070] Please refer to Figure 10B , in step S29, provide a second induction sheet 34 and a fourth thermoplastic resin 33, wherein the second induction sheet 34 is located within the fourth thermoplastic resin 33, and the second induction sheet 34 is a material that generates heat when induced by an electromagnetic field. The material of the second induction sheet 34 may be the same as or different from the material of the first induction sheet 32'.

[0071] Please refer to again Figure 11 , in step S30, stack the first edge 13 of the first half-shell structure 1', the two fourth thermoplastic resins 33 containing the second induction sheet 34, and the second edge 23 of the second half-shell structure 2' in sequence to form a second stack.

[0072] In step S31, preheat the second stack with the preheater, and the required preheating temperature is less than or equal to the glass transition temperature (TG) of the fourth thermoplastic resin and greater than or equal to 60% of the glass transition temperature TG of the fourth thermoplastic resin.

[0073] Please refer to again Figure 8 , Figure 9 and Figure 11, in step S32, control the induction coil to heat the first carbon fiber cloth 11, the second induction sheet 34 located at the first edge 13, and the second carbon fiber cloth 21 located at the second edge 23 until the temperature of the second induction sheet 34 rises above the melting point of the fourth thermoplastic resin 33, and cause the first thermoplastic resin 11 between the first carbon fiber cloth 12 and the second induction sheet 34, and the second thermoplastic resin 21 between the second carbon fiber cloth 22 and the second induction sheet 34 to form a molten state respectively, so that the first and second thermoplastic resins 11, 21 are respectively joined to the fourth thermoplastic resin 33 to complete the second induction welding of the edges of the first and second half-shell structures 1', 2', and further complete a hard-shell hollow structure.

[0074] The thermoplastic fiber composite material of the present invention can be made by the method of laminating and hot pressing prepreg carbon fiber cloth, and a half-shell structure is made by hot pressing and forming. After processing the edges of the half-shell structure, it can be joined to another half-shell structure. Then, a material that is easy to induce heat is buried at the interface of two carbon fiber composite layers, and the induction welding process parameters are controlled. With the induction welding equipment, the two carbon fiber composite layers can be continuously welded to complete a hard-shell hollow structure. Furthermore, through two-stage programmed control for preheating and then induction welding, at this time, the joint strength of the induction welding with preheating is greater than that of the induction welding without preheating.

[0075] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

1. A method for induction welding of thermoplastic fiber composite materials, characterized in that: The following steps are involved: Providing a first carbon fiber composite layer, which includes a first thermoplastic resin and at least one first carbon fiber cloth, wherein the at least one first carbon fiber cloth is located in the first thermoplastic resin; Providing a second carbon fiber composite layer, which includes a second thermoplastic resin and at least one second carbon fiber cloth, wherein the at least one second carbon fiber cloth is located in the second thermoplastic resin; Providing a sensing sheet and a third thermoplastic resin, wherein the sensing sheet is located in the third thermoplastic resin, and the sensing sheet is a material that generates heat when induced by an electromagnetic field; The first carbon fiber composite layer, the third thermoplastic resin containing the induction sheet, and the second carbon fiber composite layer are stacked in sequence to form a stack; Preheating the laminate before induction welding, wherein a preheating temperature of the preheating is less than or equal to the glass transition temperature of the third thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the third thermoplastic resin; and An induction coil is controlled to heat the at least one first carbon fiber cloth, the induction sheet, and the at least one second carbon fiber cloth until the temperature of the induction sheet rises to a temperature exceeding the melting point of the third thermoplastic resin, and the first thermoplastic resin between the at least one first carbon fiber cloth and the induction sheet, and the second thermoplastic resin between the at least one second carbon fiber cloth and the induction sheet are molten, respectively, and the first and second thermoplastic resins are respectively bonded to the third thermoplastic resin to complete the induction welding of the thermoplastic fiber composite material.

2. The induction welding method of thermoplastic composite material according to claim 1, characterized in that: The sensor sheet is selected from one of carbon steel, stainless steel, aluminum alloy and carbon fiber cloth.

3. The induction welding method of thermoplastic composite material according to claim 2, characterized in that: When the induction sheet is made of carbon fiber cloth, the preheating temperature is 120-190°C.

4. The induction welding method of thermoplastic composite material according to claim 3, characterized in that: The preheating is performed by a preheater, and the preheater includes a hot air gun.

5. The induction welding method of thermoplastic composite material according to claim 1, characterized in that: The induction coil is controlled to heat the first carbon fiber cloth, the induction sheet and the second carbon fiber cloth according to a process parameter, wherein the process parameter is an electromagnetic frequency of 150 to 400 kHz, an induction time of 15 to 120 seconds, an induction current of 18 to 20 amperes, a preheating time of 15 to 120 seconds, a preheating current of 12 to 16 amperes, and a distance between the induction coil and the first carbon fiber composite layer of 1 to 4 mm.

6. A method for manufacturing a hard shell hollow structure, characterized in that: The following steps are involved: Providing a first carbon fiber composite layer, which includes a first thermoplastic resin and at least one first carbon fiber cloth, wherein the at least one first carbon fiber cloth is located in the first thermoplastic resin; The first carbon fiber composite material layer is hot-pressed to form a first half-shell structure having two first end edges; Providing a second carbon fiber composite layer, which includes a second thermoplastic resin and at least one second carbon fiber cloth, wherein the at least one second carbon fiber cloth is located in the second thermoplastic resin; The second carbon fiber composite material layer is hot-pressed to form a second half-shell structure having two second end edges; A first induction sheet and a third thermoplastic resin are provided, wherein the first induction sheet is located in the third thermoplastic resin, and the first induction sheet is a material that generates heat when subjected to electromagnetic field induction; The first end edge of the first half shell structure, the third thermoplastic resin containing the first sensing sheet, and the second end edge of the second half shell structure are stacked in sequence to form a first stack; Performing a first preheating on the first laminate, wherein a preheating temperature of the first preheating is less than or equal to the glass transition temperature of the third thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the third thermoplastic resin; as well as An induction coil is controlled to heat the at least one first carbon fiber cloth located at the first end edge, the first sensing sheet, and the at least one second carbon fiber cloth located at the second end edge until the temperature of the first sensing sheet rises to a temperature exceeding the melting point of the third thermoplastic resin, and the first thermoplastic resin located between the at least one first carbon fiber cloth and the first sensing sheet, and the second thermoplastic resin located between the at least one second carbon fiber cloth and the first sensing sheet are respectively molten, and the first and second thermoplastic resins are respectively bonded to the third thermoplastic resin to complete the first induction welding of the end edges of the first and second half-shell structures.

7. The method for manufacturing a hard shell type hollow structure according to claim 6, characterized in that: The method further comprises the following steps: providing a second induction sheet and a fourth thermoplastic resin, wherein the second induction sheet is located in the fourth thermoplastic resin, and the second induction sheet is a material that generates heat by electromagnetic field induction; The first end edge of the first half shell structure, the two fourth thermoplastic resins containing the second sensing sheets, and the second end edge of the second half shell structure are stacked in sequence to form a second stack; Performing a second preheating on the second laminate, wherein a preheating temperature of the second preheating is less than or equal to the glass transition temperature of the fourth thermoplastic resin and greater than or equal to 60% of the glass transition temperature of the fourth thermoplastic resin; and The induction coil is controlled to heat the at least one first carbon fiber cloth, the second induction sheet, and the at least one second carbon fiber cloth at the second end edge until the temperature of the second induction sheet rises to a temperature exceeding the melting point of the fourth thermoplastic resin, and the first thermoplastic resin between the at least one first carbon fiber cloth and the second induction sheet, and the second thermoplastic resin between the at least one second carbon fiber cloth and the second induction sheet are molten respectively, and the first and second thermoplastic resins are respectively bonded to the fourth thermoplastic resin to complete the second induction welding of the end edges of the first and second half-shell structures, thereby completing a hard shell type hollow structure.

8. The method for manufacturing a hard shell type hollow structure according to claim 7, characterized in that: The sensor sheet is selected from one of carbon steel, stainless steel, aluminum alloy and carbon fiber cloth.

9. The method for manufacturing a hard shell type hollow structure according to claim 8, characterized in that: When the induction sheet is made of carbon fiber cloth, the preheating temperature is 120-190°C.

10. The method for manufacturing a hard shell type hollow structure according to claim 9, characterized in that: The overlapped shape between the first end edge and the second end edge is a stepped cut cross section.

Images