Self-resistance internal heating type 3D printing heating method for fiber reinforced thermoplastic composite material

Abstract

The invention discloses a self-resistance internal heating type 3D printing heating method for a fiber reinforced thermoplastic composite material, belongs to the technical field of additive manufacturing, and particularly relates to a self-resistance internal heating type 3D printing heating method which is characterized in that the conductive characteristic of fibers is utilized, current is supplied to generate Joule heat, the fibers are directly used as a heat source, and the heat is quickly conducted from inside to outside to enable a matrix to be fused and deposited so as to realize printing. Firstly, parameters of the composite material wire are obtained, printing parameters are determined, then the composite material wire is connected into an electrode, circuit detection is carried out, an adjusting mode is selected after no abnormity exists, finally, initial parameters are calculated and output according to the adjusting mode, and the temperature of the composite material wire is adjusted according to the monitored temperature of the composite material wire to reach a set interval. Self-resistance heating of the conductive enhanced phase is used for internal heating, cooperative adjustment of current / voltage and the distance between the electrodes is matched, the device has the advantages of being low in heating power, high in efficiency, fast in response, capable of being suitable for extreme environments such as vacuum and the like, and fast and controllable wire rod melting heating can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology and relates to a self-resistance internal heating method for 3D printing of fiber-reinforced thermoplastic composites. In particular, it relates to a self-resistance internal heating method that uses the Joule effect of conductive fibers to generate heat directly to heat the filament, thereby melting the matrix to achieve 3D printing of composite materials. Background Technology

[0002] Fiber-reinforced thermoplastic composites (referred to as "thermoplastic composites") have been widely used in the manufacturing of key components for high-end equipment in aerospace, transportation, and other fields due to their excellent material properties such as lightweight, high strength, impact resistance, fatigue resistance, and recyclability. 3D printing is an additive manufacturing process that accumulates materials layer by layer from top to bottom, offering advantages such as process flexibility and adaptability. Combining thermoplastic composites with 3D printing technology allows for the construction of load-bearing structures with high strength, high stiffness, and excellent fatigue resistance by depositing filaments layer by layer. This technology breaks through the dependence on molds in traditional processes, supports the direct molding of complex geometries, achieves a material utilization rate of over 90%, and enables rapid personalized customization production through digital models, significantly shortening product development cycles and demonstrating broad application prospects in precision instruments, aerospace structural components, and other fields.

[0003] Currently, most heating methods for thermoplastic composite 3D printing involve heating the print head first using heating rods or resistance wires, and then heating the filament, or using lasers or infrared to heat the filament. In these methods, the heat source is an external structure, and the heat is transferred from the outside to the surface of the filament through layer-by-layer conduction, and then further heated into the interior of the filament. During the printing process, the interlayers where the filaments are in contact are heated first, and then the heat is transferred to the interlayers between the fibers and the matrix inside the filament. Especially when the printing speed is high, the heating is almost instantaneous, which can cause the interlayer interfaces to not be fully heated in time, thus affecting the performance of the sample. In addition, this type of heating method in the printing process also has limitations such as high energy consumption, low heating efficiency, and lag in temperature control.

[0004] To address the above issues, Chinese invention patent CN106827502A proposed a printhead heating device for a 3D printer based on the eddy current effect. By applying alternating current, the heating block generates eddy currents under the eddy current effect, thus heating the filament. This method significantly improves efficiency compared to traditional heating methods. However, heat still needs to be transferred from the heating block to the filament, resulting in considerable energy loss and temperature control lag. Chinese invention patent CN106335182A proposed a high-efficiency heat-insulating end-effector device for a 3D printer, reducing energy loss during printing. However, heat still needs to be conducted layer by layer from the outside in, leading to slow response speed and low heating efficiency in temperature control. Chinese invention patent CN105666876A proposed a method and device for fluid circulation temperature control of the printhead. This method improves the temperature control response speed, but the system's complexity results in high power consumption and unremarkable efficiency.

[0005] Therefore, in order to solve the problems of high energy loss, low heating efficiency and slow response speed in the current 3D printing process of thermoplastic composite materials, it is urgent to propose a new heating method to achieve energy-saving, efficient and high-quality 3D printing of thermoplastic composite materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a self-resistance internal heating method for 3D printing of fiber-reinforced composite materials. The heating object of this method is a fiber-reinforced composite printing filament, composed of reinforcing fibers and a matrix resin. The method involves connecting the composite filament to an electrode pair. When the electrodes are energized, the fibers inside form a conductive path under the influence of the electric field, generating Joule heating. This achieves internal heating through a "fiber heating—matrix heating" process. The heat generated by the fibers is rapidly conducted from the inside of the filament to the outside, causing the resin matrix to heat up and melt quickly, thus meeting the printing requirements. During the heating process, the output current / voltage and electrode spacing are adjusted based on parameters such as the resistance of the printing filament and real-time temperature monitoring information to regulate the heating temperature, achieving temperature control.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A self-resistance internal heating 3D printing heating method for fiber-reinforced thermoplastic composite materials is disclosed. The processing object is a fiber-reinforced thermoplastic composite filament with a certain degree of conductivity. The heating method first obtains the parameters of the composite filament and determines the printing parameters. Then, the composite filament is connected to electrodes and circuit testing is performed. After confirming no abnormalities, an adjustment mode is selected. Initial parameters are calculated and output according to the selected adjustment mode, and the temperature of the composite filament is adjusted according to the monitored temperature to reach a set range. This invention is based on a traditional 3D printing device. The innovative improvement lies in utilizing the self-resistance heating of the conductive reinforcing phase for internal heating, combined with the coordinated adjustment of current / voltage and electrode spacing, to achieve rapid and controllable filament melting and heating. Specifically, the method includes the following steps: Step 1: Assemble the 3D printing device, which includes at least a filament feeding mechanism, a print head or extrusion module, a DC power supply, a temperature monitoring unit, a control unit, and a motion control unit. Each component can be an existing, mature part. Specifically: The wire feeding mechanism is used to continuously feed fiber-reinforced thermoplastic composite wire into the print head; The printhead or extrusion module is internally equipped with a melting section and a nozzle, and is equipped with a positive electrode and a negative electrode. The two electrodes form an electrical contact with the outer surface of the wire or the conductive reinforcing phase, so that the wire forms an effective passage between the two electrodes. The electrodes are configured with a guiding structure and a clamping structure to ensure stable contact. The DC power supply is used to output current or voltage to the positive and negative electrodes. The temperature monitoring unit is used to collect the temperature T in real time at the melting section of the wire or the location near the nozzle (the temperature can be obtained by thermocouple, infrared temperature measurement or other temperature sensing methods). The control unit is connected to a DC power supply, a temperature monitoring unit, and an electrode spacing adjustment mechanism, and is used to perform circuit detection, mode selection, parameter prediction, and closed-loop adjustment. The motion control unit is used to drive the printhead / platform to move along a preset path and complete layer-by-layer deposition.

[0008] Step 2: Obtain the parameters of the conductive fiber-reinforced thermoplastic composite wire and determine the printing parameters. Specifically: The parameters include the glass transition temperature of the fiber-reinforced thermoplastic composite wire matrix. Melting temperature Decomposition temperature ,diameter ,density Specific heat capacity Fiber volume fraction With resistivity and the distance between the positive and negative electrodes set in the print head or extrusion module ; The printing parameters include printing temperature. Actual temperature With printing speed The printing temperature should generally be higher than the melting temperature of the fiber-reinforced thermoplastic composite filament but lower than the decomposition temperature. Within this range, a suitable value should be determined based on the requirements.

[0009] Based on the above information, the estimated resistance of the composite material wire is obtained. for: (1) in, The buckling parameter is used because the fibers in actual composite wires cannot be guaranteed to be completely straight; they may experience some buckling and torsion, leading to an increase in the resistivity of the composite wire. The value is generally selected between 0.01 and 0.1; Furthermore, due to the contact resistance between the electrode and the composite wire, the contact resistance must also be considered when estimating the resistance of the composite wire. Therefore, the total resistance in the circuit ,in Measurements are taken after the type of composite wire is determined. Combined with other parameters, current, voltage, and electrode spacing can be predicted during subsequent temperature regulation.

[0010] Step 3: Connect the composite material wire to the electrode and perform circuit testing. Specifically: The composite material filament passes sequentially through the guide structure and positive and negative electrodes in the 3D printing device. The clamping force of the clamping structure is adjusted to ensure stable contact. The control unit outputs a low-power detection signal to determine whether the circuit is closed and whether the contact is stable. If the contact is abnormal, it prompts for adjustment. After ensuring that the circuit is closed and conductive, the adjustment mode is selected.

[0011] Step 4: Select the adjustment mode based on the characteristics of the composite material wire used. Specifically: The adjustment modes are divided into two types: current adjustment and voltage adjustment. When the resistance of the printing cable increases after being heated by power, the voltage adjustment mode is selected. When the resistance of the printing cable decreases after being heated by power, the current adjustment mode is selected. This selection method can, to a certain extent, avoid the transient heat shock caused by sudden changes in the cable's state.

[0012] Step 5: Calculate and output the initial values ​​of current / voltage and electrode spacing based on the composite material wire information. Specifically: Step 5.1: After determining the adjustment mode in step 4, when the current adjustment mode is selected, the heat generated by heating the composite material wire... for: (2) in, For current; The total resistance in the circuit; For the quality of composite material wire in the heating section; This refers to the power-on time; Specific heat capacity.

[0013] Based on this, the control unit calculates and outputs the initial output current according to the acquired information of the composite material wire. The specific calculation formula is as follows: (3) If the current value obtained after the above calculation exceeds the current value that the power supply can output, it proves that the current electrode spacing is not suitable. Therefore, in the current... Electrode spacing when selecting limit values The calculation and output are as follows: (4) The system outputs the above parameters (the parameters mentioned here include the output current). Spacing between electrodes Afterwards, the temperature of the composite material wire will reach or be close to the set temperature range. In subsequent steps, the parameters will be fine-tuned to ensure that the temperature remains stable within the set range.

[0014] Furthermore, the current in step 5.1 The limit value is selected as the maximum current that the selected power supply can output.

[0015] Step 5.2, after determining the adjustment mode in step 4, when the voltage adjustment mode is selected, the heat generated by heating the composite material wire... for: (5) in, Voltage; Based on this, the control unit calculates and outputs the initial output voltage according to the acquired information of the composite material wire. The specific calculation formula is as follows: (6) If the voltage value obtained after the above calculation exceeds the output voltage value of the power supply, it proves that the current electrode spacing is inappropriate. Therefore, in terms of voltage... Electrode spacing when selecting limit values The calculation and output are as follows: (7) The system outputs the above parameters (the parameters mentioned here include the output voltage). Spacing between electrodes Afterwards, the temperature of the composite material wire will reach or be close to the set temperature range. In subsequent steps, the parameters will be fine-tuned to ensure that the temperature remains stable within the set range.

[0016] Furthermore, in step 5.2, the voltage The limit value is selected as the maximum voltage that the selected power supply can output.

[0017] Step 6: Adjust the output parameters in real time based on the monitored temperature of the composite material wire. Specifically: If the temperature of the composite wire reaches near the set range but still deviates after the output parameters (current / voltage and electrode spacing) in step 5, then a small-range adjustment of the output parameters is performed: When the current regulation mode is selected, the temperature monitoring unit acquires the temperature of the composite material filament in real time, and the control unit adjusts the error. First, while keeping the electrode spacing constant, the current is adjusted preferentially to stabilize the temperature of the composite material filament within the target range. When the temperature of the composite material filament is too high, the output current is reduced, and vice versa. When the power output reaches the safe upper limit, or when the resistance of the composite material filament fluctuates and current regulation alone cannot maintain the target temperature, the second-level regulation is activated: by increasing or decreasing the electrode spacing, the effective energizing length is changed, thereby changing the resistance to control the temperature. When the temperature of the composite material filament is too high, the electrode spacing is reduced, and vice versa. Combined with the predicted output of current and electrode spacing in step 5, this constitutes a predictive-correction dual-stage control and a two-level collaborative regulation mode to ensure that the composite material filament is heated to the preset temperature range, ultimately achieving full melting of the matrix material for high-quality 3D printing, and finally obtaining the printed sample.

[0018] When the voltage regulation mode is selected, the temperature monitoring unit acquires the temperature of the composite material filament in real time, and the control unit adjusts the error. First, while keeping the electrode spacing constant, the voltage is adjusted preferentially to stabilize the temperature of the composite material filament within the target range. If the temperature of the composite material filament is too high, the output voltage is reduced, and vice versa. When the power output reaches the safe upper limit, or when the resistance of the composite material filament fluctuates and voltage regulation alone cannot maintain the target temperature, the second-level regulation is activated: by increasing or decreasing the electrode spacing, the effective energizing length is changed, thereby changing the resistance to control the temperature. If the temperature of the composite material filament is too high, the electrode spacing is increased, and vice versa. Combined with the predicted output of voltage and electrode spacing in step 5, this constitutes a predictive-correction dual-stage control and a two-level collaborative regulation mode to ensure that the composite material filament is heated to the preset temperature range, ultimately achieving full melting of the matrix material for high-quality 3D printing, and finally obtaining the printed sample.

[0019] Furthermore, in step 6, if the temperature of the composite material wire reaches near the set range but still deviates, this means that the actual temperature deviates from the set temperature range within ±15℃. If it exceeds this range, the output parameters (current, voltage, electrode spacing) are recalculated. If it still cannot be reached after multiple calculations, the wire parameters are reconfirmed and recalculated.

[0020] Furthermore, in step 6, the safe upper limit of the power supply output is the maximum current and voltage values ​​that the power supply itself can output.

[0021] Furthermore, the fiber-reinforced thermoplastic composite wire is selected from wire containing conductive fillers such as continuous / short-cut carbon fibers and graphite.

[0022] This invention heats the wire by directly utilizing the self-resistive internal heat generated by energizing conductive fibers, unlike traditional heating methods that rely on external heat sources such as heating rods or lasers. Compared to these methods, the advantages of this invention are: (1) This invention connects the composite material wire to the positive and negative electrodes so that the composite material wire itself generates Joule heat that directly acts on the matrix, causing the matrix to melt rapidly and achieve deposition molding, thus avoiding the large amount of heat loss and lag caused by the layer-by-layer conduction of heat in the traditional heating method. (2) The composite material wire itself, which is the object of processing in this invention, serves as a heat source, has high heating efficiency, and can achieve a temperature response speed that is significantly faster than that of traditional external heating methods; (3) The heating and monitoring objects of the present invention are the composite material wires themselves, which can achieve more accurate temperature control.

[0023] In summary, this invention can solve the problems of high heating energy consumption, low efficiency, and lag in temperature control caused by the reliance on external heat sources for layer-by-layer heat transfer during the melting of the resin matrix in the existing thermoplastic composite 3D printing process. It can achieve effective and high-quality heating of composite material filaments for subsequent molding in scenarios such as high melting point materials and special environments (such as vacuum environments). Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the wire heating principle and temperature distribution trend of the present invention; Figure 2 This is a flowchart illustrating the heating method implemented in this invention; Figure 3 This is a schematic diagram illustrating the implementation process of an embodiment of the present invention; Figure 4 This is a comparison of the heating efficiency of the present invention with that of the traditional method in Embodiment 1 of the present invention.

[0025] In the figure: 1 Composite material filament; 2 Fiber feeding mechanism; 3 Guiding structure; 4 Print head or extrusion module; 5 Temperature monitoring unit; 6 Electrode and clamping structure; 7 DC power supply; 8 Printed sample. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the examples and descriptions in the present invention are only used to explain the invention and are not intended to limit the invention in any way.

[0027] This invention utilizes the inherent electrical conductivity of fibers, applying an electric current to generate Joule heating, directly using the fibers as a heat source. Heat is rapidly conducted from the inside out, melting and depositing the substrate to achieve printing. During the heating process, a two-stage temperature control system combined with a predictive-correction dual-stage control mode is employed. The initial output current / voltage and electrode spacing are calculated, and then, based on the real-time temperature, the current and voltage are fine-tuned first. When the current / voltage reaches its limit, the electrode spacing is adjusted to bring the wire temperature to a preset range. Specific implementation examples are given below: Example 1 This embodiment provides a basic implementation method for a self-resistance internal heating 3D printing heating method for continuous carbon fiber reinforced PA-based composite material filament 1. The specific steps are as follows: Step 1: Assemble the 3D printing device, which includes at least a filament feeding mechanism (2), a print head or extrusion module (4), a DC power supply (7), a temperature monitoring unit (5), a control unit, and a motion control unit. Each component can be an existing, mature part. Specifically: The wire feeding mechanism 2 is used to continuously feed the fiber-reinforced thermoplastic composite wire 1 into the print head; The printhead or extrusion module 4 is internally equipped with a melting section and a nozzle, and is equipped with a positive electrode and a negative electrode. The two electrodes form an electrical contact with the outer surface of the composite wire 1 or the conductive reinforcing phase, so that the composite wire 1 forms an effective passage between the two electrodes. The electrodes are equipped with a guide structure 3 and a clamping structure 6 to ensure stable contact. The DC power supply 7 is used to output current or voltage to the positive and negative electrodes; The temperature monitoring unit 5 is used to collect the temperature T of the melting section of wire 1 or the location near the nozzle in real time (the temperature can be obtained by thermocouple, infrared temperature measurement or other temperature sensing methods). The control unit is connected to the DC power supply 7, the temperature monitoring unit 5, and the electrode spacing adjustment mechanism, and is used to perform circuit detection, mode selection, parameter prediction, and closed-loop adjustment. The motion control unit is used to drive the print head / platform to move along a preset path and complete layer-by-layer deposition. Step 2: Obtain the parameters of the continuous carbon fiber reinforced PA-based composite filament 1 and determine the printing parameters. Specifically: The parameters include the glass transition temperature of the fiber-reinforced thermoplastic composite wire matrix 1. Melting temperature Decomposition temperature ,diameter ,density Specific heat capacity Fiber volume fraction =50% and resistivity and the distance between the positive and negative electrodes inside the printhead Initial distance selection ; The printing parameters include printing temperature. Actual temperature With printing speed The printing temperature should generally be higher than the melting temperature of the fiber-reinforced thermoplastic composite filament 1 but lower than its decomposition temperature. Within this range, a suitable value should be determined based on requirements. For the selected filament 1, the printing temperature is set at 270℃. The actual temperature... The initial room temperature was set to 25℃, and the printing speed was set to 5mm / s.

[0028] Furthermore, based on the above information, the estimated resistance of composite material wire 1 is obtained. for: in, The buckling parameter is used because the fibers in the actual composite wire 1 cannot be guaranteed to be completely straight; they may exhibit some buckling and torsion, leading to an increase in the resistance of the composite wire 1. The value is generally selected between 0.01 and 0.1. For the composite material wire 1 in this embodiment, k=0.05 is selected. Meanwhile, due to the contact resistance between the electrode and the composite wire 1, the contact resistance must also be considered when estimating the resistance of the composite wire 1. Therefore, the total resistance in the circuit ,in After determining the type of composite wire, a measurement was taken, which showed an Ω of approximately 10Ω. Therefore, R = 15.7Ω. Combined with other parameters, the output parameters can be predicted during subsequent temperature adjustment.

[0029] Step 3: Connect composite wire 1 to the electrode and perform circuit testing. Specifically: The composite material wire 1 passes through the guide structure 3 and the positive and negative electrodes in sequence. The clamping force of the clamping structure 6 is adjusted to ensure stable contact. The control unit outputs a low-power detection signal to determine whether the circuit is closed and whether the contact is stable. If the contact is abnormal, it prompts for adjustment. After ensuring that the circuit is closed and conductive, the adjustment mode is selected.

[0030] Step 4: Select the adjustment mode based on the characteristics of the composite material wire 1 used. Specifically: The adjustment modes are divided into two types: current adjustment and voltage adjustment. When the resistance of the printing filament 1 increases after being heated by electricity, the voltage adjustment mode is selected. When the resistance of the printing filament 1 decreases after being heated by electricity, the current adjustment mode is selected. Since the resistance of the continuous carbon fiber reinforced PA-based composite material filament 1 decreases after being heated by electricity, the current adjustment mode is selected in this embodiment.

[0031] Step 5: Calculate and output the initial values ​​of current / voltage and electrode spacing based on the information of composite wire 1. Specifically: The heat generated by heating composite wire 1 for: in, For current; The mass of the composite material wire in the heating section; This refers to the power-on time.

[0032] Based on this, the control unit calculates and outputs the initial output current according to the information obtained from the composite material wire 1. The specific calculation formula is as follows: If the current value obtained after the above calculation If the current exceeds the output current of power supply 7, it proves that the current electrode spacing is inappropriate. Therefore, in this embodiment, the current... Electrode spacing when selecting limit values The calculation and output are as follows: The system outputs the above parameters (in this embodiment, the parameters include the output current). Spacing between electrodes Afterwards, the temperature of composite material wire 1 will reach or be close to the set temperature range. In subsequent steps, the parameters will be fine-tuned to ensure that the temperature remains stable within the set range.

[0033] Step 6: Adjust the output parameters in real time based on the monitored temperature of composite material wire 1. Specifically: In this embodiment, a current regulation mode is selected. The temperature monitoring unit 5 acquires the temperature of the filament 1 in real time, and the control unit adjusts the error. First, while keeping the electrode spacing constant, the current is adjusted first to stabilize the temperature of the filament 1 within the target range. When the temperature of the filament 1 is too high, the output current is reduced, and vice versa. When the output of the power supply 7 reaches the safe upper / lower limit, or when the resistance of the filament 1 fluctuates and the current regulation alone cannot maintain the target temperature, the second-level regulation is initiated: the effective energizing length is changed by increasing or decreasing the electrode spacing, thereby changing the resistance and achieving temperature control. When the temperature of the filament 1 is too high, the electrode spacing is reduced, and vice versa. Combined with the predicted output of current and electrode spacing in step 4, a prediction-correction dual-stage control and a two-level collaborative regulation mode are formed to ensure that the filament 1 is heated to the preset temperature range, ultimately achieving full melting of the matrix material to achieve high-quality 3D printing, and finally obtaining the printed sample 8.

[0034] Example 2 This embodiment provides a basic implementation method for a self-resistance internal heating 3D printing heating method for steel fiber reinforced PA-based composite material filament 1. The specific steps are as follows: Step 1: Assemble the 3D printing device, as in Example 1.

[0035] Step 2: Obtain the parameters of conductive fiber-reinforced thermoplastic composite wire 1 and determine the printing parameters. Specifically: The parameters include the glass transition temperature of the fiber-reinforced thermoplastic composite wire matrix 1. Melting temperature Decomposition temperature ,diameter ,density Specific heat capacity Fiber volume fraction =15% and resistivity and the distance between the positive and negative electrodes inside the printhead Initial distance selection ; The printing parameters include printing temperature. Actual temperature With printing speed The printing temperature should generally be higher than the melting temperature of the fiber-reinforced thermoplastic composite filament 1 but lower than its decomposition temperature. Within this range, a suitable value should be determined based on requirements. For the selected filament 1, the printing temperature is set at 270℃. The actual temperature... The initial room temperature was set to 25℃, and the printing speed was set to 5mm / s.

[0036] Furthermore, based on the above information, the estimated resistance of composite material wire 1 is obtained. for: in, The buckling parameter is used because the fibers in the actual composite wire 1 cannot be guaranteed to be completely straight; they may exhibit some buckling and torsion, leading to an increase in the resistance of the composite wire 1. The value is generally selected between 0.01 and 0.1. For the composite material wire 1 in this embodiment, k=0.05 is selected. Meanwhile, due to the contact resistance between the electrode and the composite wire 1, the contact resistance must also be considered when estimating the resistance of the composite wire 1. Therefore, the total resistance in the circuit ,in After determining the type of composite wire, a measurement was taken, which showed an Ω of approximately 5Ω. Therefore, R = 63.21Ω. Combined with other parameters, the output parameters can be predicted during subsequent temperature adjustment.

[0037] Step 3: Connect composite wire 1 to the electrode and perform circuit testing. Specifically: The composite material wire 1 passes through the guide structure 3 and the positive and negative electrodes in sequence. The clamping force of the clamping structure 6 is adjusted to ensure stable contact. The control unit outputs a low-power detection signal to determine whether the circuit is closed and whether the contact is stable. If the contact is abnormal, it prompts for adjustment. After ensuring that the circuit is closed and conductive, the adjustment mode is selected.

[0038] Step 4: Select the adjustment mode based on the characteristics of the composite material wire 1 used. Specifically: The adjustment mode is divided into two types: current adjustment and voltage adjustment. When the resistance of the printing cable 1 increases after being heated by power, the voltage adjustment mode is selected. When the resistance of the printing cable 1 decreases after being heated by power, the current adjustment mode is selected. This selection method can, to a certain extent, avoid the transient heat shock caused by the sudden change in the state of the cable 1.

[0039] The fourth step is to calculate and output the initial values ​​of current / voltage and electrode spacing based on the information of composite wire 1. Specifically: The heat generated by heating composite wire 1 for: in, Voltage; Based on this, the control unit calculates and outputs the initial output voltage according to the information obtained from the composite material wire 1. The specific calculation formula is as follows: If the voltage value obtained after the above calculation The voltage exceeding the output value of power supply 7 indicates that the current electrode spacing is inappropriate. Therefore, the voltage... Electrode spacing when selecting limit values The calculation and output are as follows: The system outputs the above parameters (in this embodiment, the parameters include the output voltage). Spacing between electrodes Afterwards, the temperature of composite material wire 1 will reach or be close to the set temperature range. In subsequent steps, the parameters will be fine-tuned to ensure that the temperature remains stable within the set range.

[0040] Step 6: Adjust the output parameters in real time based on the monitored temperature of composite material wire 1. Specifically: In this embodiment, when the voltage regulation mode is selected, the temperature monitoring unit 5 acquires the temperature of the filament 1 in real time, and the control unit adjusts the error. First, while keeping the electrode spacing constant, the voltage is adjusted first to stabilize the temperature of the filament 1 within the target range. When the temperature of the filament 1 is too high, the output voltage is reduced, and vice versa. When the output of the power supply 7 reaches the safe upper / lower limit, or when the resistance of the filament 1 fluctuates and voltage regulation alone cannot maintain the target temperature, the second-level regulation is initiated: the effective energizing length is changed by increasing or decreasing the electrode spacing, thereby changing the resistance and achieving temperature control. When the temperature of the filament 1 is too high, the electrode spacing is increased, and vice versa. Combined with the predicted output of parameters such as voltage and electrode spacing in step 4, a prediction-correction dual-stage control and a two-level collaborative regulation mode are formed to ensure that the filament 1 is heated to the preset range, ultimately achieving full melting of the matrix material to achieve high-quality 3D printing, and finally obtaining the printed sample 8.

[0041] The embodiments described above are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A self-resistance internal heating method for 3D printing of fiber-reinforced thermoplastic composite materials, wherein the 3D printing heating method is based on a traditional 3D printing device, and the processing object is a conductive fiber-reinforced thermoplastic composite filament, characterized in that... The heating method utilizes the self-resistance heating of the conductive reinforcing phase for internal heating, combined with the coordinated adjustment of current / voltage and electrode spacing, to achieve rapid and controllable wire melting and heating. First, the composite material wire parameters are acquired and printing parameters are determined. Then, the composite material wire is connected to the electrodes and the circuit is tested. After confirming there are no abnormalities, the adjustment mode is selected. Finally, the initial parameters are calculated and output according to the selected adjustment mode, and the temperature of the composite material wire is adjusted according to the monitored temperature to bring the composite material wire temperature to the set range. Specifically, the method includes the following steps: Step 1: Assemble the 3D printing device, including a filament feeding mechanism, a print head or extrusion module, a DC power supply, a temperature monitoring unit, a control unit, and a motion control unit; Step 2: Obtain the parameters of the conductive fiber-reinforced thermoplastic composite wire and determine the printing parameters; Step 3: Connect the composite material wire to the electrode and perform circuit testing; The composite material filament passes sequentially through the guide structure and positive and negative electrodes in the 3D printing device. The clamping force of the clamping structure is adjusted to ensure stable contact. The control unit outputs a low-power detection signal to determine whether the circuit is closed and whether the contact is stable. If the contact is abnormal, it prompts for adjustment. After ensuring that the circuit is closed and conductive, the adjustment mode is selected. Step 4: Select the adjustment mode according to the characteristics of the composite material wire used, including both current adjustment and voltage adjustment; Step 5: Calculate and output the initial values ​​of current / voltage and electrode spacing based on the composite material wire information; Step 6: Adjust the output parameters in real time based on the monitored temperature of the composite material wire; specifically: If the temperature of the composite material filament reaches near the set range after the output parameters in step 5, but still deviates, the output parameters are adjusted within a small range to achieve full melting of the matrix material and thus achieve high-quality 3D printing, resulting in a printed sample.

2. A self-resistive internal heating 3D printing method of fiber reinforced thermoplastic composites according to claim 1, characterized in that, In step 1, specifically: The wire feeding mechanism is used to continuously feed fiber-reinforced thermoplastic composite wire into the print head; The printhead or extrusion module is internally equipped with a melting section and a nozzle, and is equipped with a positive electrode and a negative electrode. The two electrodes form an electrical contact with the outer surface of the wire or the conductive reinforcing phase, so that the wire forms an effective passage between the two electrodes. The electrodes are configured with a guiding structure and a clamping structure to ensure stable contact. The DC power supply is used to output current or voltage to the positive and negative electrodes. The temperature monitoring unit is used to collect the temperature T in real time at the melting section of the wire or the location near the nozzle. The control unit is connected to a DC power supply, a temperature monitoring unit, and an electrode spacing adjustment mechanism, and is used to perform circuit detection, mode selection, parameter prediction, and closed-loop adjustment. The motion control unit is used to drive the printhead / platform to move along a preset path and complete layer-by-layer deposition.

3. A self-resistive internal heating method for 3D printing of fiber reinforced thermoplastic composites according to claim 2, characterized in that, Step 2 specifically involves: The parameters include the glass transition temperature of the fiber-reinforced thermoplastic composite wire matrix. Melting temperature Decomposition temperature ,diameter ,density Specific heat capacity Fiber volume fraction With resistivity and the distance between the positive and negative electrodes set in the print head or extrusion module ; The printing parameters include printing temperature. Actual temperature With printing speed The printing temperature should generally be higher than the melting temperature of the fiber-reinforced thermoplastic composite filament but lower than the decomposition temperature. Within this range, a suitable value should be determined according to the requirements. Estimated resistance of composite wires for: （1） in, For buckling parameters; The total resistance in the circuit ,in This represents the contact resistance, which is measured after the type of composite wire is determined.

4. The self-resistive internal heating 3D printing method of fiber reinforced thermoplastic composites according to claim 3, characterized in that, The bending parameter The value is selected to be between 0.01 and 0.

1.

5. The self-resistive internal heating 3D printing method of fiber reinforced thermoplastic composites according to claim 3, characterized in that, In step 4, when the resistance of the printing cable increases after being heated by electricity, the voltage adjustment mode is selected; when the resistance of the printing cable decreases after being heated by electricity, the current adjustment mode is selected.

6. A self-resistive internal heating 3D printing method of fiber reinforced thermoplastic composites according to claim 5, characterized in that, Step 5 specifically involves: Step 5.

1. Heat generated by heating the composite wire when the current regulation mode is selected is: （2） in, For current; The total resistance in the circuit; For the quality of composite material wire in the heating section; This refers to the power-on time; Specific heat capacity; The initial output current is calculated and output based on the information obtained from the composite material wire. The formula is as follows: （3） If the current value calculated by formula (3) exceeds the current value that the power supply can output, it proves that the current electrode spacing is not suitable. Electrode spacing when selecting limit values The calculation and output are as follows: （4） After the system outputs the above parameters, the temperature of the composite material wire will reach or be close to the set temperature range. Subsequent parameter fine-tuning will then be performed to ensure the temperature remains stable within the set range. These parameters include the output current. Spacing between electrodes ; Step 5.2, when the voltage regulation mode is selected, the heat generated by heating the composite wire is: （5） wherein V is a voltage; Based on this, the control unit calculates and outputs the initial output voltage according to the acquired information of the composite material wire. The specific calculation formula is as follows: （6） If the voltage value calculated by formula (6) exceeds the output voltage value of the power supply, it proves that the current electrode spacing is not suitable, and then the voltage... Electrode spacing when selecting limit values The calculation and output are as follows: （7） After the system outputs the above parameters, the temperature of the composite material wire will reach or be close to the set temperature range. Subsequent parameter fine-tuning will then be performed to ensure the temperature remains stable within the set range. These parameters include the output voltage. Spacing between electrodes .

7. A self-resistive internal heating 3D printing method of fiber reinforced thermoplastic composites according to claim 6, characterized in that, In step 5: The current in step 5.1 The limit value is selected as the maximum current value that the selected power supply can output. In step 5.2, the voltage The limit value is selected as the maximum voltage that the selected power supply can output.

8. The self-resistive internal heating 3D printing method of a fiber reinforced thermoplastic composite according to claim 7, characterized in that, Step 6 specifically involves: When the current regulation mode is selected, the temperature monitoring unit acquires the temperature of the composite wire in real time, and the control unit adjusts the error. First, while keeping the electrode spacing constant, the current is adjusted first to stabilize the temperature of the composite wire within the target range. When the temperature of the composite wire is too high, the output current is reduced, and vice versa. When the power output reaches the safe upper limit, or when the resistance of the composite wire fluctuates and current regulation alone cannot maintain the target temperature, the second-level regulation is activated: the effective energizing length is changed by increasing or decreasing the electrode spacing, thereby changing the resistance and achieving temperature control. When the temperature of the composite wire is too high, the electrode spacing is reduced, and vice versa. Combined with the predicted output of current and electrode spacing in step 5, a prediction-correction dual-stage control and two-level collaborative regulation mode are formed to ensure that the composite wire is heated to the preset temperature range, and finally the matrix material is fully melted to achieve high-quality 3D printing, resulting in a printed sample. When the voltage regulation mode is selected, the temperature monitoring unit acquires the temperature of the composite wire in real time, and the control unit adjusts the error. First, while keeping the electrode spacing constant, the voltage is adjusted first to stabilize the temperature of the composite wire within the target range. When the temperature of the composite wire is too high, the output voltage is reduced, and vice versa. When the power output reaches the safe upper limit, or when the resistance of the composite wire fluctuates and voltage regulation alone cannot maintain the target temperature, the second-level regulation is activated: the effective energizing length is changed by increasing or decreasing the electrode spacing, thereby changing the resistance and achieving temperature control. When the temperature of the composite wire is too high, the electrode spacing is increased, and vice versa. Combined with the predicted output of voltage and electrode spacing in step 5, a prediction-correction dual-stage control and two-level collaborative regulation mode are formed to ensure that the composite wire is heated to the preset temperature range, and finally the matrix material is fully melted to achieve high-quality 3D printing, resulting in a printed sample.

9. The self-resistive internal heating 3D printing method of a fiber reinforced thermoplastic composite according to claim 8, characterized in that, In step 6: The temperature of the composite material wire reaches near the set range but still deviates. Here, it means that the actual temperature deviates from the set temperature range within ±15℃. If it exceeds this range, the output parameters are recalculated. If it still cannot be reached after multiple calculations, the wire parameters are reconfirmed and recalculated. The output parameters include current, voltage, and electrode spacing. The safe upper limit of the power supply output is the maximum current and voltage value that the power supply itself can output.

10. The self-resistive internal heating 3D printing method of a fiber reinforced thermoplastic composite according to claim 9, characterized in that, The fiber-reinforced thermoplastic composite wire is selected from wire containing continuous / short-cut carbon fibers, graphite, or other conductive fillers.

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