TWI892299B - Thermoplastic composite induction welding method and monocoque structure manufacturing method - Google Patents

Abstract

An induction welding method for thermoplastic fiber composite materials includes: sequentially stacking a first carbon fiber composite layer, a third thermoplastic resin containing an induction sheet, and a second carbon fiber composite layer to form a lamination; preheating the lamination before an 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 the first thermoplastic resin located between the induction sheet and the second thermoplastic resin located between the induction sheet and the second carbon fiber cloth respectively form a molten state, so that the first and second thermoplastic resins are respectively bonded to the third thermoplastic resins.

Description

Induction welding method of thermoplastic fiber composite material and manufacturing method of hard shell type hollow structure

The present invention relates to a method for induction welding of thermoplastic fiber composite materials, and more particularly to a method for manufacturing a hard-shell hollow structure using the induction welding method of thermoplastic fiber composite materials.

Thermoplastic fiber composites, such as carbon fiber composites, have advantages such as recyclability, excellent 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 low-cost and high-performance.

Among the several welding techniques currently used for thermoplastic composites, induction welding (IW) offers numerous advantages, including low cost, continuous automation, and the ability to weld homogeneous interfaces. Therefore, IW is particularly well-suited for joining thermoplastic fiber composite components. The principle of IW is to heat the two workpieces (e.g., carbon fiber composites) to be joined using an induction coil, causing the contact surfaces between the two workpieces to melt, thereby bonding the two workpieces.

Carbon fiber composites, particularly carbon fiber tubes, have a wide range of applications as structural components. Their high strength, low density, and long lifespan have led to their widespread adoption across numerous industries, including bicycle frames, automotive crash bars, aircraft ducting, small wing structures, flaps, and fins. These components, with their monocoque hollow structures, can be formed by impregnating fiber sheets, known as prepregs, which are typically cured in a mold under heat and pressure. Inflatable bladders can be used to provide compaction pressure within the hollow portion, but this often results in wrinkles due to uneven pressure distribution, which can lead to uneven resin deposition and high-void areas.

Therefore, there is a need to provide an induction welding method for thermoplastic fiber composites and a method for manufacturing a hard shell hollow structure that can solve the aforementioned problems.

An object of the present invention is to provide a method for induction welding of thermoplastic fiber composites, wherein the bonding strength of the induction welding with preheating is greater than the bonding strength of the induction welding without preheating.

In accordance with the above-mentioned object, the present invention provides a method for induction welding of thermoplastic fiber composite materials, comprising the following steps: providing a first carbon fiber composite layer, which comprises 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 comprises a second thermoplastic resin and at least one second carbon fiber cloth; cloth, 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 subjected to an electromagnetic field; stacking the first carbon fiber composite layer, the third thermoplastic resin containing the sensing sheet, and the second carbon fiber composite layer in sequence to form a stack; The stack is preheated 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 a sensing coil is controlled to heat the at least one first carbon fiber cloth, the sensing sheet, and the at least one second carbon fiber cloth until the sensing sheet is heated to a temperature exceeding the third thermoplastic resin. The melting point of the thermoplastic resin is controlled, and the first thermoplastic resin located between the at least one first carbon fiber cloth and the sensing sheet, and the second thermoplastic resin located between the at least one second carbon fiber cloth and the sensing sheet are respectively molten, so that 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.

The present invention further provides a method for manufacturing a hard shell type hollow structure, comprising the following steps: providing a first carbon fiber composite material layer, which comprises 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; hot pressing the first carbon fiber composite material layer to form a first half shell structure, wherein the first half shell structure has two first end edges; providing a second carbon fiber composite material layer, which comprises a second thermoplastic resin and at least one second carbon fiber cloth; fiber cloth, 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, the second half shell structure having two second end edges; a first sensor sheet and a third thermoplastic resin are provided, wherein the first sensor sheet is located in the third thermoplastic resin, and the first sensor sheet is a material that generates heat when subjected to an electromagnetic field; the first end edge of the first half shell structure, the third thermoplastic resin containing the first sensor sheet, and the second half shell structure are hot-pressed to form a second half shell structure; The invention relates to a method for controlling a sensing coil to connect the at least one first carbon fiber cloth at the first end, the first sensing sheet, and the at least one second carbon fiber cloth at the second end. The method comprises the steps of: stacking the first stack of the thermoplastic resin and the second end of the second half shell structure in sequence to form a first stack; performing a first preheating on the first stack, 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; and controlling a sensing coil to connect the at least one first carbon fiber cloth at the first end, the first sensing sheet, and the at least one second carbon fiber cloth at the second end. The cloth is heated 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.

The thermoplastic fiber composite material of the present invention can be manufactured by hot pressing a pre-impregnated carbon fiber layer, and then forming a half shell structure by hot pressing. After the end edge of the half shell structure is processed, it can be joined to the other half shell structure. Then, a material that easily senses heat is embedded in the interface of the two carbon fiber composite layers, and the induction welding process parameters are controlled. In combination with induction welding equipment, the two carbon fiber composite layers can be continuously welded to complete a hard shell hollow structure. Furthermore, preheating is performed through two-stage program control before induction welding. At this time, the bonding strength of the preheated induction welding is greater than the bonding strength of the induction welding without preheating.

In order to make the above-mentioned objects, features and characteristics of the present invention more clearly understood, the relevant embodiments of the present invention are described in detail below with reference to the drawings.

The following is a detailed description of an embodiment of the present invention with reference to the accompanying drawings. The accompanying drawings are primarily simplified schematic diagrams that illustrate the basic structure of the present invention. Therefore, only components relevant to the present invention are labeled in these drawings, and the components shown are not drawn in the same number, shape, or size ratio as in an actual implementation. The specifications and dimensions of the actual implementation are actually a selective design, and the component layout may be more complex.

FIG1 is a flow chart of the steps of an induction welding method for thermoplastic fiber composites according to an embodiment of the present invention. FIG2 is a schematic cross-sectional view of a stack of a first carbon fiber composite layer, a third thermoplastic resin containing a sensing sheet, and a second carbon fiber composite layer according to an embodiment of the present invention. FIG3 is a schematic three-dimensional view of an induction welding apparatus according to an embodiment of the present invention. Referring to FIG1 , the induction welding method for thermoplastic fiber composites includes the following steps:

Referring to Figure 2, in step S11, a first carbon fiber composite layer 1 is provided. The layer comprises a first thermoplastic resin 11 and at least one first carbon fiber cloth 12, with the first carbon fiber cloth 12 disposed within the first thermoplastic resin 11. The first carbon fiber composite layer 1 can be fabricated by laminating pre-impregnated carbon fiber cloths. For example, the first carbon fiber composite layer 1 can be made of polysulfone sulfide (PSU) carbon fiber composite material, which is a unidirectional (UD) fiber pre-impregnated cloth.

Referring again to Figure 2, in step S12, a second carbon fiber composite layer 2 is provided. The layer comprises a second thermoplastic resin 21 and at least one second carbon fiber cloth 22. The second carbon fiber cloth 22 is disposed within the second thermoplastic resin 21. Similarly, the second carbon fiber composite layer 2 can be fabricated by laminating pre-impregnated carbon fiber cloths. For example, the second carbon fiber composite layer 2 can be made of polysulfone sulfide (PSU) carbon fiber composite material, also using unidirectional (UD) fiber pre-impregnation.

Referring again to Figure 2 , in step S13, a sensor sheet 32 and a third thermoplastic resin 31 are provided. The sensor sheet 32 is located within the third thermoplastic resin 31 and is a material that generates heat when induced by an electromagnetic field. The sensor sheet 32 can be made from one of carbon steel, stainless steel, aluminum alloy, and carbon fiber cloth. The third thermoplastic resin 31 can be made from the same polymer as the first and second thermoplastic resins 11 and 21, such as polysulfone sulfide (PSU). When the sensor sheet 32 is a carbon fiber cloth, its fibers are arranged in a woven pattern, such as a plain weave (one-up, one-down interlaced) or a diagonal weave (two-up, two-down interlaced), rather than a unidirectional UD weave. This weave arrangement provides a higher interface temperature, facilitating inductive welding and minimizing damage to the component's appearance. In one embodiment of the present invention, when the sensor sheet 32 is pre-impregnated with polysulfide (PSU), the sensor sheet 32 may be made of carbon fiber with a basis weight of 220 g/ ^m² . The carbon fiber is 3K tow, woven in a plain weave pattern, and then pre-impregnated with polysulfide (PSU) polymer.

Referring to FIG. 2 again, in step S14, the first carbon fiber composite layer 1, the third thermoplastic resin 31 containing the sensor sheet 32, and the second carbon fiber composite layer 2 are stacked in sequence to form a stack.

In step S15, a preheater (not shown) is used to preheat the laminate before induction welding, wherein 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. The glass transition temperature (TG) refers to the temperature at which a glassy material reversibly transitions between a glassy state and a highly elastic state. When the sensor sheet is a carbon fiber cloth, the preheating temperature can be 120-190°C. For example, an induction welding apparatus includes a preheater, which includes a hot air gun for preheating before induction welding. The process parameters of the induction welding include: preheating temperature and time.

Referring again to FIG. 2 , in step S16, a sensing coil is controlled to heat the first carbon fiber cloth 12, the sensing sheet 32, and the second carbon fiber cloth 22 until the temperature of the sensing sheet 32 exceeds the melting point of the third thermoplastic resin 31. This causes the first thermoplastic resin 11 between the first carbon fiber cloth 12 and the sensing sheet 32, and the second thermoplastic resin 21 between the second carbon fiber cloth 22 and the sensing sheet 32, to melt. This allows the first and second thermoplastic resins 11 and 21 to bond with the third thermoplastic resin 31, respectively, completing the induction welding of the thermoplastic fiber composite. In one embodiment of the present invention, the inductive sheet 32 is more susceptible to electromagnetic field induction during step S16 than the first carbon fiber cloth 12 and the second carbon fiber cloth 22, thereby generating more heat energy. For example, when the inductive sheet 32 is a carbon fiber cloth, the inductive sheet 32 can have different configuration conditions (e.g., a higher basis weight, a weave method that is more susceptible to magnetism, other methods that enhance magnetic heating performance, or any combination of such methods) to generate more heat energy than the first carbon fiber cloth 12 and the second carbon fiber cloth 22. For example, referring to FIG3 , the inductive welding device 4 further includes: the inductive coil 40, a front pressure roller 41, and a rear pressure roller 42. The induction coil 40, the front pressure roller 41, and the rear pressure roller 42 simultaneously move in a welding direction 44. The area below the movement forms a welding area 43, and the position below the induction coil 40 corresponds to the joint 45. The welding speed can be 50-200 mm/min. Furthermore, the induction welding equipment 4 may further include an induction host, an air cooling device, an XY motion mechanism, and other components to perform induction welding. The induction welding process parameters further include: the distance between the stacked layers of the thermoplastic fiber composite and the induction coil, the clamping pressure of the front and rear pressure rollers, the preheating current, preheating time, induction frequency, induction current, induction time, and air cooling pressure. The implementation parameters for controlling induction welding in one embodiment of the present invention are shown in Tables 1 and 2 below: Material combination Molecular types of the first to third thermoplastic resins Basis weight of the first and second carbon fiber cloths (g/m ² ) Content of the first and second carbon fiber cloths (%) General categories of sensor sheets (carbon fiber cloth) Basis weight of sensor sheet (carbon fiber cloth) (g/m ² ) Polysulphide (PSU) 130 50 3k plain weave 220 Table 1 Process parameters and conditions Air cooling pressure (kg/cm ² ) Electromagnetic frequency (kHz) Inductive current (A) Induction time (sec) Preheating current (A) Warm-up time (sec) Clamping pressure (Kgf) Distance between the stack and the sensing coil (mm) 5~7.5 150~400 18~20 15~ 120 12~16 15~ 120 10 1~4 Table 2

In one embodiment of the present invention, the induction welding equipment can be configured as follows: First, an induction head and an induction coil. The induction head is equipped with an X-axis and Z-axis adjustment mechanism, which can fine-tune the distance between the induction coil and the thermoplastic fiber composite material stack to provide the required temperature for induction welding. The induction head can adjust the output power. Second, a motor is provided to provide a Y-axis movement function, and its movement rate can be controlled to provide welding time. Third, another motor is provided to provide a downward pressure in the Z-axis direction, and the front and rear downward pressure rollers in contact with the thermoplastic fiber composite material stack can control their downward pressure force to provide welding pressure. Fourth, a compressed air nozzle with adjustable position is installed, aimed at the welding area, and the air pressure can be adjusted to cool the surface of the thermoplastic fiber composite laminate.

Figure 4 is a diagram showing the relationship between shear bond strength, current, preheating temperature T1, and welding temperature T2 for one embodiment of the present invention. Referring to Figure 4, in Example 1, no preheating was performed, and the preheating temperature T1 was room temperature (25°C). A welding current of 20A provided a welding temperature T2 of approximately 272°C. The induction weld strength between the first and second carbon fiber composite layers was 9.3 MPa. In Examples 2, 3, and 4, a fixed welding current of 20A was used to provide welding temperatures T2 of approximately 220°C, 242°C, and 256°C. Induction welding was performed after preheating using a two-stage program control. In Examples 2, 3, and 4, the preheating temperatures were set to approximately 120°C, 168°C, and 189°C, respectively. The joint strength of the induction weld after preheating at 120°C was 13.9 MPa, the joint strength after preheating at 168°C was 14.6 MPa, and the joint strength after preheating at 189°C was 13.1 MPa. This indicates that excessive preheating easily decomposes the polymer at the carbon fiber composite interface, increasing pores and resulting in a decrease in joint strength. Figure 5 shows a cross-sectional OM image of Example 1 of the present invention with a welding current of 20A and no preheating. Referring to Figure 5 , this OM image shows an incompletely welded interface F1. Figure 6 shows a cross-sectional OM image of Example 3 of the present invention with a welding current of 20A and preheating at 168°C. Referring to Figure 6 , this OM image shows a well-welded interface F2.

Figure 7 is a step flow chart of a method for manufacturing a hard shell hollow structure according to an embodiment of the present invention. Figure 8 is a schematic cross-sectional view of a first carbon fiber composite layer and a three-dimensional schematic view of a first half shell structure according to an embodiment of the present invention. Figure 9 is a schematic cross-sectional view of a second carbon fiber composite layer and a three-dimensional schematic view of a second half shell structure according to an embodiment of the present invention. Figure 10A is a schematic cross-sectional view of a first sensor sheet and a third thermoplastic resin according to an embodiment of the present invention. Figure 10B is a schematic cross-sectional view of a second sensor sheet and a fourth thermoplastic resin according to an embodiment of the present invention. Figure 11 is a three-dimensional schematic view of a first half shell structure, a third thermoplastic resin containing a sensor 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:

Referring to Figure 8 , in step S21, a first carbon fiber composite layer 1 is provided, comprising a first thermoplastic resin 11 and at least one first carbon fiber cloth 12. The first carbon fiber cloth 12 is disposed within the first thermoplastic resin 11. In step S22, the first carbon fiber composite layer 1 is hot-pressed to form a first half-shell structure 1′ having two first end edges 13.

Referring to Figure 9, in step S23, a second carbon fiber composite layer 2 is provided. The layer includes a second thermoplastic resin 21 and at least one second carbon fiber cloth 22. The second carbon fiber cloth 22 is disposed within the second thermoplastic resin 21. In step S24, the second carbon fiber composite layer 2 is hot-pressed to form a second half-shell structure 2'. The second half-shell structure 2' has two second end edges 23.

Referring to Figure 10A , in step S25, a first sensor sheet 32' and a third thermoplastic resin 31 are provided. The first sensor sheet 32' is located within the third thermoplastic resin 31 and is made of a material that generates heat when induced by an electromagnetic field. The first sensor sheet 32' can be selected from carbon steel, stainless steel, aluminum alloy, and carbon fiber cloth. The third thermoplastic resin 31 can be made of the same polymer as the first and second thermoplastic resins 11 and 21, such as polysulfone sulfide (PSU).

Referring 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 sensor sheet 32', and the second end edge 23 of the second half shell structure 2' are stacked in sequence to form a first stack. Referring to Figures 12A through 12D , four different overlap configurations are shown 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 stepped cross-section of the overlap between the first end edge 13 and the second end edge 23. After induction welding, the welded area is smoothest and free of unevenness.

In step S27, the first laminate is preheated using a preheater (not shown). 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.

Referring again to FIG8, FIG9 and FIG11, in step S28, a sensing coil is controlled to heat the first carbon fiber cloth 12 located at the first end 13, the first sensing sheet 32', and the second carbon fiber cloth 22 located at the second end 23 until the first sensing sheet 32' is heated to a temperature exceeding the melting point of the third thermoplastic resin 31, and the first carbon fiber cloth 12 and the first sensing sheet 32' are heated to a temperature exceeding the melting point of the third thermoplastic resin 31. The first thermoplastic resin 11 between the first and second sensing sheets 32', and the second thermoplastic resin 21 between the second carbon fiber cloth 22 and the first sensing sheet 32', are respectively molten, and the first and second thermoplastic resins 11, 21 are respectively bonded to the third thermoplastic resin 31 to complete the first induction welding of the end edges of the first and second half shell structures 1', 2'.

Referring to Figure 10B , in step S29, a second sensor sheet 34 and a fourth thermoplastic resin 33 are provided. The second sensor sheet 34 is located within the fourth thermoplastic resin 33 and is made of a material that generates heat when induced by an electromagnetic field. The material of the second sensor sheet 34 may be the same as or different from the material of the first sensor sheet 32′.

Referring to FIG. 11 , in step S30, the first end 13 of the first half shell structure 1′, the two fourth thermoplastic resins 33 containing the second sensor sheet 34, and the second end 23 of the second half shell structure 2′ are stacked in sequence to form a second stack.

In step S31, the second laminate is preheated by 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.

Referring again to FIG8, FIG9 and FIG11, in step S32, the sensing coil is controlled to heat the first carbon fiber cloth 11 located at the first end 13, the second sensing sheet 34, and the second carbon fiber cloth 21 located at the second end 23 until the temperature of the second sensing sheet 34 is raised to a temperature exceeding the melting point of the fourth thermoplastic resin 33, and the carbon fiber cloth 12 located between the first carbon fiber cloth 12 and the second sensing sheet 34 is heated. The first thermoplastic resin 11 and the second thermoplastic resin 21 located between the second carbon fiber cloth 22 and the second sensor sheet 34 are each molten, allowing the first and second thermoplastic resins 11, 21 to be bonded to the fourth thermoplastic resin 33, respectively, to complete the second induction welding of the end edges of the first and second half-shell structures 1', 2', thereby completing a hard shell hollow structure.

The thermoplastic fiber composite material of the present invention can be manufactured by hot pressing a pre-impregnated carbon fiber layer, and then forming a half shell structure by hot pressing. After the end edge of the half shell structure is processed, it can be joined to the other half shell structure. Then, a material that easily senses heat is embedded in the interface of the two carbon fiber composite layers, and the induction welding process parameters are controlled. In combination with induction welding equipment, the two carbon fiber composite layers can be continuously welded to complete a hard shell hollow structure. Furthermore, preheating is performed through two-stage program control before induction welding. At this time, the bonding strength of the preheated induction welding is greater than the bonding strength of the induction welding without preheating.

The foregoing merely describes preferred embodiments or examples of the technical means employed by this invention to solve the problem, and is not intended to limit the scope of implementation of this patent. In other words, all equivalent variations and modifications consistent with the scope of this patent application or based on the scope of this patent are covered by this patent.

1: First carbon fiber composite layer 1': First shell half 11: First thermoplastic resin 12: First carbon fiber cloth 13: First end edge 2: Second carbon fiber composite layer 2': Second shell half 21: Second thermoplastic resin 22: Second carbon fiber cloth 23: Second end edge 31: Third thermoplastic resin 32: Sensor sheet 32': First sensor sheet 33: Fourth thermoplastic resin 34: Second sensor sheet 4: Inductive welding equipment 40: Inductive coil 41: Front pressure roller 42: Rear pressure roller 43: Welding area 44: Welding direction 45: Joint F1: Interface F2: Interface T1: Preheating Temperature T2: Soldering Temperature S11-S16: Steps S21-S32: Steps

Figure 1 is a flow chart of the steps of an induction welding method for thermoplastic fiber composites according to an embodiment of the present invention. Figure 2 is a schematic cross-sectional view of a stack of a first carbon fiber composite layer, a third thermoplastic resin containing a sensing sheet, and a second carbon fiber composite layer according to an embodiment of the present invention. Figure 3 is a schematic perspective view of an induction welding apparatus according to an embodiment of the present invention. Figure 4 is a schematic diagram showing the relationship between shear bond strength, current, preheating temperature T1, and welding temperature T2 according to an embodiment of the present invention. Figure 5 shows a cross-sectional OM image of Example 1 of the present invention at a welding current of 20A and without preheating. Figure 6 shows a cross-sectional OM image of Example 3 of the present invention at a welding current of 20A and preheating to 168°C. Figure 7 is a flow chart of the steps of a method for manufacturing a hardshell hollow structure according to an embodiment of the present invention. Figure 8 is a schematic cross-sectional view of the first carbon fiber composite layer according to an embodiment of the present invention. Figure 9 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 is a schematic cross-sectional view of the first sensor sheet and the third thermoplastic resin according to an embodiment of the present invention. Figure 10B is a schematic cross-sectional view of the second sensor sheet and the fourth thermoplastic resin according to an embodiment of the present invention. Figure 11 is a schematic perspective view of a first half shell structure, a third thermoplastic resin containing a sensor sheet, and the first half shell structure according to one embodiment of the present invention. Figures 12A-12D illustrate four different types of overlaps between the first end edge of the first half shell structure and the second end edge of the first half shell structure.

S11~S16: Steps

Claims (10)

A method for induction welding of thermoplastic fiber composites comprises the following steps: Providing a first carbon fiber composite layer comprising a first thermoplastic resin and at least one first carbon fiber cloth, wherein the at least one first carbon fiber cloth is disposed within the first thermoplastic resin; Providing a second carbon fiber composite layer comprising a second thermoplastic resin and at least one second carbon fiber cloth, wherein the at least one second carbon fiber cloth is disposed within the second thermoplastic resin; Providing an inductive sheet and a third thermoplastic resin, wherein the inductive sheet is disposed within the third thermoplastic resin and is a material that generates heat when subjected to an electromagnetic field; The first carbon fiber composite layer, the third thermoplastic resin containing the sensor sheet, and the second carbon fiber composite layer are sequentially stacked to form a laminate; Preheating the laminate prior to induction welding, wherein the preheating time is 15 to 120 seconds, wherein a preheating temperature 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 A sensing coil is controlled to heat the at least one first carbon fiber cloth, the sensing sheet, and the at least one second carbon fiber cloth until the temperature of the sensing sheet rises to a temperature exceeding the melting point of the third thermoplastic resin. This causes the first thermoplastic resin between the at least one first carbon fiber cloth and the sensing sheet, and the second thermoplastic resin between the at least one second carbon fiber cloth and the sensing sheet, to melt. The first and second thermoplastic resins are then bonded to the third thermoplastic resin, thereby completing induction welding of the thermoplastic fiber composite. The induction welding temperature is a welding temperature that is greater than the preheating temperature. The induction welding method for thermoplastic composites as described in claim 1, wherein the sensing sheet is selected from one of carbon steel, stainless steel, aluminum alloy and carbon fiber cloth. The induction welding method of thermoplastic composite materials as described in claim 2, wherein when the sensing sheet is carbon fiber cloth, the preheating temperature is 120~190℃. The induction welding method of thermoplastic composite materials as described in claim 3, wherein the preheating is performed using a preheater, and the preheater includes a hot air gun. The induction welding method of thermoplastic composite materials as described in claim 1, wherein 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, the process parameter being an electromagnetic frequency of 150-400 kHz, an induction time of 15-120 seconds, an induction current of 18-20 amperes, 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. A method for manufacturing a hardshell hollow structure comprises the following steps: Providing a first carbon fiber composite layer comprising a first thermoplastic resin and at least one first carbon fiber cloth, wherein the at least one first carbon fiber cloth is disposed within the first thermoplastic resin; Hot-pressing the first carbon fiber composite layer to form a first half-shell structure, wherein the first half-shell structure has two first end edges; Providing a second carbon fiber composite layer comprising a second thermoplastic resin and at least one second carbon fiber cloth, wherein the at least one second carbon fiber cloth is disposed within the second thermoplastic resin; The second carbon fiber composite layer is hot-pressed to form a second half-shell structure having two second end edges. A first sensing sheet and a third thermoplastic resin are provided, wherein the first sensing sheet is located within the third thermoplastic resin and is a material that generates heat when induced by an electromagnetic field. 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 sequentially stacked to form a first stack. Performing a first preheating on the first laminate, wherein the first preheating time is 15 to 120 seconds, 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 A sensing 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 is raised 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. The first and second thermoplastic resins are respectively bonded to the third thermoplastic resin to complete a first induction welding of the end edges of the first and second half shell structures. At this time, the temperature of the first induction welding is a welding temperature, wherein the welding temperature is greater than the preheating temperature. The method for manufacturing a hard-shell hollow structure as described in claim 6 further includes the following steps: Providing a second sensing sheet and a fourth thermoplastic resin, wherein the second sensing sheet is located within the fourth thermoplastic resin and is a material that generates heat when induced by an electromagnetic field; Laying the first end edge of the first half shell structure, the two fourth thermoplastic resins containing the second sensing sheet, and the second end edge of the second half shell structure in sequence to form a second stack; Performing a second preheating on the second stack, 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 sensing coil is controlled to heat the at least one first carbon fiber cloth at the first end, the second sensing sheet, and the at least one second carbon fiber cloth at the second end until the temperature of the second sensing sheet exceeds the melting point of the fourth thermoplastic resin. This causes the first thermoplastic resin between the at least one first carbon fiber cloth and the second sensing sheet, and the second thermoplastic resin between the at least one second carbon fiber cloth and the second sensing sheet, to melt. The first and second thermoplastic resins are then bonded to the fourth thermoplastic resin, completing a second induction welding of the end edges of the first and second half-shell structures, thereby forming a hard-shell hollow structure. The method for manufacturing a hard shell hollow structure as described in claim 7, wherein the sensing sheet is selected from one of carbon steel, stainless steel, aluminum alloy and carbon fiber cloth. In the method for manufacturing a hard-shell hollow structure as described in claim 8, when the sensor sheet is carbon fiber cloth, the preheating temperature is 120-190°C. A method for manufacturing a hard-shell hollow structure as described in claim 9, wherein the overlap between the first end edge and the second end edge is a stepped cross-section.