A PID control method for temperature control of carbon fiber composite induction welding

Abstract

This invention belongs to the field of thermoplastic composite material fusion bonding technology, and discloses a PID control method for temperature control in induction welding of carbon fiber composites. This method is a feedback adjustment method based on infrared thermal imaging temperature measurement. It combines the temperature relationship between the welding interface and the welding surface during induction welding of carbon fiber composites with the temperature constraint condition that the welding interface fully melts without overheating and decomposition, establishing a temperature constraint condition for the upper surface of the carbon fiber composite during continuous welding. By introducing PID control of the welding temperature during the welding process, it is possible to achieve accurate monitoring and real-time feedback adjustment of the welding area temperature during continuous induction welding of carbon fiber thermoplastic composites. This avoids insufficient melting of the resin matrix due to excessively low welding area temperature or overheating and decomposition of the resin matrix due to excessively high temperature, ensuring that the welding area temperature remains within a suitable temperature range throughout the entire welding process, thereby improving the quality of continuous induction welding.

Description

Technical Field

[0001] This invention belongs to the field of thermoplastic composite material fusion bonding technology, and relates to a PID control method for induction welding temperature control of carbon fiber composites. Background Technology

[0002] Carbon fiber reinforced polymer matrix composites possess characteristics such as high specific strength, high specific stiffness, customizable performance, and integral manufacturing of components, making them one of the preferred materials for reducing structural weight and improving structural performance. Among them, carbon fiber thermoplastic composites not only have high specific strength, high specific stiffness, and good impact resistance, but also possess unique advantages such as rapid and multiple molding, melt bonding, and easy recycling, making them a preferred material for achieving energy conservation, emission reduction, and green manufacturing in next-generation aerospace equipment.

[0003] Although thermoplastic composites can be molded into large components, aerospace structures not only rely on large-scale skins and panels to withstand aerodynamic loads, but also require numerous internal stringers, frames, and ribs to ensure load-bearing capacity. This results in a large demand for connections between thermoplastic composite components. The industry is leveraging the "heat-melt-cool-solidify" characteristics of thermoplastic composite polymer matrices to develop new heat-based fusion bonding technologies to fully utilize the performance and environmental advantages of thermoplastic composites. Induction welding technology for thermoplastic composites offers advantages such as speed, high connection strength, minimal weight gain, and repeatable welding, making it one of the ideal technologies for achieving high-quality and reliable connections of thermoplastic composite materials.

[0004] In induction welding of thermoplastic composites, the temperature of the welding area directly affects the melting state of the resin matrix at the welding interface. Too low a temperature leads to insufficient melting of the resin matrix, while too high a temperature causes overheating and decomposition. Therefore, to ensure the quality of the connection, it is necessary to monitor the temperature of the welding area during induction welding and maintain it within a suitable range. Some scholars have already conducted research on this issue. Li Peng et al.'s invention patent, CN202311690734, entitled "An Induction Welding End for On-Orbit Bending and Extension Assembly of Thermoplastic Composite Trusses and Its Welding Method," uses a fixed thermocouple to measure the temperature of the welding area, achieving induction welding of thermoplastic composite trusses. However, this method is only suitable for local single-point connections in truss structures, and the temperature measurement method is fixed thermocouple point-area temperature measurement. In continuous induction welding, the welding area is a long surface region, making the fixed thermocouple point-area temperature measurement method no longer applicable.

[0005] Therefore, developing a PID temperature control method and device that can monitor the surface temperature of the welding area and adjust the temperature of the welding area in real time is crucial for ensuring that the temperature of the welding area is within a suitable range during continuous induction welding and improving the quality of continuous induction welding. Summary of the Invention

[0006] To achieve the above objectives, this invention proposes a PID control method for temperature control in induction welding of carbon fiber composites. This method enables precise monitoring and real-time feedback adjustment of the temperature in the welding area during continuous induction welding of carbon fiber thermoplastic composites. It avoids insufficient melting of the resin matrix due to excessively low welding area temperature or overheating and decomposition of the resin matrix due to excessively high temperature, ensuring that the temperature in the welding area remains within a suitable range throughout the welding process, thereby improving the quality of continuous induction welding.

[0007] The technical solution of this invention:

[0008] A PID control method for temperature control of induction welding of carbon fiber composites is disclosed. The device used in the PID control method includes an induction welding actuator, a computer, a PLC controller, an induction heating control box, and a carbon fiber composite laminate structure. The induction welding actuator mainly consists of an infrared thermal imager, an induction heating head, a pressure module, and a cooling module.

[0009] The infrared thermal imager is connected to the computer and the computer is connected to the PLC controller via Ethernet. The PLC controller controls the magnitude of the induced current output of the induction heating control box on the induction heating head by outputting an analog current of 4-20mA.

[0010] The PID control method described is a feedback regulation method based on infrared thermal imager temperature measurement. This method combines the temperature relationship between the welding interface and the upper surface of the carbon fiber composite during induction welding with the temperature constraint condition that the welding interface is fully melted without thermal decomposition, establishing the temperature constraint condition for the upper surface of the carbon fiber composite during continuous welding. For the upper surface temperature of the carbon fiber composite during continuous induction welding, an infrared thermal imager is used to collect surface feature temperature data. Based on the temperature information of the induction welding area collected by the infrared thermal imager, the PID temperature control output value is calculated in the computer and sent to the PLC controller. The PLC controller adjusts the output value of the induction heating control box according to the PID temperature output value given by the computer, thereby controlling the output current of the induction heating head on the induction welding actuator, and thus achieving temperature control of the upper surface of the carbon fiber composite.

[0011] The specific steps of the method are as follows:

[0012] The first step is to calibrate the temperature relationship between the welding interface and the upper surface of the carbon fiber composite laminate structure during the motion induction welding process:

[0013] 1) Place an ultra-fine K-type thermocouple on the fusion interface of the carbon fiber composite laminate structure to measure the temperature of the fusion interface. Adjust the distance between the infrared thermal imager and the upper surface of the carbon fiber composite laminate structure in the fusion area and focus the infrared thermal imager to measure the temperature of the upper surface of the carbon fiber composite laminate structure in the fusion area.

[0014] 2) The operating speed of the induction welding actuator is set by the PLC controller so that the continuous induction welding process is carried out at a constant moving speed;

[0015] 3) Set the pressure module of the induction welding actuator to ensure that there is appropriate pressure between the upper and lower plates of the carbon fiber composite laminate structure in the welding area. Set the cooling module of the induction welding actuator to ensure that the temperature of the upper surface of the carbon fiber composite laminate structure in the welding area is lower than the temperature of the welding interface, so as to avoid overheating and decomposition of the upper surface of the carbon fiber composite laminate structure due to excessive temperature.

[0016] 4) Perform continuous induction welding, record the temperature of the upper surface of the carbon fiber composite laminate structure and the welding interface, and obtain the temperature relationship between the welding interface and the upper surface of the carbon fiber composite laminate structure under constant moving speed.

[0017] The second step involves continuous induction welding with PID temperature feedback regulation at the same induction welding actuator moving speed as in the first step.

[0018] 1) Set the target temperature value T on the upper surface of the carbon fiber composite laminate structure in the computer. SP Enable PID control and start the continuous induction welding device;

[0019] 2) The current upper surface temperature T of the carbon fiber composite laminate structure is collected using an infrared thermal imager. PV , calculate the control deviation err(t):

[0020] err(t)=T SP -T PV (t)

[0021] 3) Calculate the integral term err re (t), which represents the magnitude of the accumulated discrete error:

[0022]

[0023] If the magnitude of the accumulated discrete error is greater than the set upper limit CV of the PID control output... high If the accumulated discrete error is less than or equal to the set upper limit of the PID control output, then the magnitude of the accumulated discrete error will be adjusted to the set upper limit of the output; if it is less than or equal to the set upper limit of the PID control output CV, then the upper limit of the output CV will be adjusted to the set upper limit of the output PID control. high If so, no adjustment will be made;

[0024] 4) Calculate the differential term errd (t), which is the difference between the current discrete error and the previous discrete error:

[0025] err d (t) = err(t) - err(t-1)

[0026] 5) The output CV of the PID control is adjusted using proportional gain, integral gain, and derivative gain. The output of the PID control is:

[0027] CV=K p ×err(t)+K i ×err re (t)+K d ×err d (t)

[0028] Among them, K i K is the proportional adjustment coefficient. P K is the integral adjustment coefficient. d These are the differential adjustment coefficients, and the values ​​of each coefficient are obtained through parameter tuning in continuous induction welding experiments;

[0029] If the output CV of the PID control is greater than the set output upper limit CV high Let CV = CV high If the output CV of the PID control is less than the set lower output limit CV... low Let CV = CV low ;

[0030] 6) The PLC controller, acting as a lower-level machine, receives the output signal of the PID control from the computer and converts it into the control signal of the induction heating control box, thereby realizing the real-time adjustment of the magnitude of the induced current on the induction heating head during the continuous induction welding process.

[0031] The PID control output provided by the computer has an upper output limit CV set during output. high With output lower limit CV low This is to ensure the safety of the continuous induction welding process; through the conversion of the PLC controller, the range of the induced current of the induction heating head is 55A to 205A.

[0032] The beneficial effects of this invention are as follows: This invention uses PID control to adjust the magnitude of the induction current on the induction heating head in real time, enabling real-time feedback adjustment of the welding interface temperature during continuous induction welding of carbon fiber composites. This keeps the welding interface temperature stable near the set value, improving the induction welding quality of carbon fiber composites. Furthermore, this invention can obtain the PID control value of the carbon fiber composite surface temperature at different continuous induction welding speeds by testing the temperature relationship between the welding interface and the upper surface of the composite at different induction welding actuator movement speeds. This allows for corresponding adjustments to the magnitude of the induction current, achieving high-quality and efficient continuous induction welding of carbon fiber composites. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a PID control device for controlling the induction welding temperature of carbon fiber composites, according to an embodiment of the present invention.

[0034] Figure 2 This is a flowchart of a PID control method for controlling the induction welding temperature of carbon fiber composites, according to an embodiment of the present invention.

[0035] In the diagram: 1-Induction heating head, 2-Infrared thermal imager, 3-Pressure module, 4-Cooling module, 5-Carbon fiber composite laminate structure, 6-Induction welding actuator, 7-Computer, 8-PLC controller, 9-Induction heating control box. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0037] This embodiment discloses a PID control method for temperature control in induction welding of carbon fiber composites. This embodiment takes the PID temperature regulation control in the continuous induction welding process of carbon fiber / polyetheretherketone composite laminates as an example, referring to... Figure 1 A PID control device for temperature control of induction welding of carbon fiber composites is disclosed. The device includes an induction welding actuator 6, a computer 7, a PLC controller 8, an induction heating control box 9, and a carbon fiber composite laminate structure 5. The induction welding actuator 6 consists of an infrared thermal imager 2, an induction heating head 1, a pressure module 3, and a cooling module 4.

[0038] The infrared thermal imager 2 is connected to the computer 7, and the computer 7 is connected to the PLC controller 8 via Ethernet. The PLC controller 8 controls the magnitude of the induced current output of the induction heating control box 9 on the induction heating head 1 by outputting an analog current of 4-20mA.

[0039] The PID control method for induction welding temperature control is a feedback adjustment method based on infrared thermal imager temperature measurement. This method combines the temperature relationship between the welding interface and the welding surface during induction welding of carbon fiber composites with the temperature constraint condition that the welding interface fully melts without thermal decomposition, establishing a temperature constraint condition for the upper surface of the carbon fiber composite during continuous welding. For the upper surface temperature of the carbon fiber composite during continuous induction welding, an infrared thermal imager 2 is used to collect surface feature temperature data. Based on the temperature information of the induction welding area collected by the infrared thermal imager 2, the PID temperature control output value is calculated in the computer 7 and sent to the PLC controller 8. The PLC controller 8 adjusts the output value of the induction heating control box 9 according to the PID temperature output value given by the computer 7, thereby controlling the output current of the induction heating head 1 on the induction welding actuator 6, and thus achieving temperature control of the upper surface of the carbon fiber composite. The specific steps of the method are as follows:

[0040] The first step is to calibrate the temperature relationship between the welding interface and the upper surface of the carbon fiber composite laminate structure during the induction welding process. The specific steps are as follows:

[0041] 1) Five ultra-fine K-type thermocouples are laid at equal intervals on the fusion interface of the carbon fiber composite laminate structure to measure the temperature of the fusion interface of the carbon fiber composite laminate structure. The distance between the infrared thermal imager 2 and the upper surface of the carbon fiber composite laminate structure in the fusion area is adjusted and the infrared thermal imager 2 is focused to measure the temperature of the upper surface of the carbon fiber composite laminate structure in the fusion area.

[0042] 2) The operating speed of the induction welding actuator 6 is set to 1 mm / s by the PLC controller 8, so that the continuous induction welding process is carried out at a constant moving speed;

[0043] 3) Set the pressure module 3 of the induction welding actuator 6 to 0.5MPa so that there is appropriate pressure between the upper and lower plates of the carbon fiber composite laminate structure in the welding area. Set the cooling module 4 of the induction welding actuator 6 to 70L / min for the compressed air flow rate used for cooling so that the temperature of the upper surface of the carbon fiber composite laminate structure in the welding area is lower than the temperature of the welding interface, thus avoiding overheating and decomposition of the upper surface of the carbon fiber composite laminate structure due to excessive temperature.

[0044] 4) Perform continuous induction welding, record the temperature of the upper surface of the carbon fiber composite laminate structure and the welding interface, and obtain the temperature relationship between the welding interface and the upper surface of the carbon fiber composite laminate structure under constant moving speed.

[0045] The second step involves performing continuous induction welding with PID temperature feedback regulation at the same moving speed as in the first step using the induction welding actuator 6. The specific steps are as follows:

[0046] 1) Set the target temperature value T on the upper surface of the carbon fiber composite laminate structure 5 in computer 7. SP Enable PID control and start the continuous induction welding device;

[0047] 2) The current upper surface temperature T of the carbon fiber composite laminate structure 5 is collected by infrared thermal imager 2. PV , calculate the control deviation err(t):

[0048] err(t)=T SP -T PV (t)

[0049] 3) Calculate the integral term err re (t), which represents the magnitude of the accumulated discrete error:

[0050]

[0051] If the magnitude of the accumulated discrete error is greater than the set upper limit CV of the PID control output... high If the accumulated discrete error is less than or equal to the set upper limit of the PID control output, then the magnitude of the accumulated discrete error will be adjusted to the set upper limit of the output; if it is less than or equal to the set upper limit of the PID control output CV, then the upper limit of the output CV will be adjusted to the set upper limit of the output PID control. high If so, no adjustment will be made;

[0052] 4) Calculate the differential term err d (t), which is the difference between the current discrete error and the previous discrete error:

[0053] err d (t) = err(t) - err(t-1)

[0054] 5) The output CV of the PID control is adjusted using proportional gain, integral gain, and derivative gain. The output of the PID control is:

[0055] CV=K p ×err(t)+K i ×err re (t)+K d ×err d (t)

[0056] Among them, K i K is the proportional adjustment coefficient. P K is the integral adjustment coefficient. d These are the differential adjustment coefficients, and the values ​​of each coefficient are obtained through parameter tuning in continuous induction welding experiments;

[0057] If the output CV of the PID control is greater than the set output upper limit CV high Let CV = CV highIf the output CV of the PID control is less than the set lower output limit CV... low Let CV = CV low .

[0058] 6) The PLC controller 8, acting as a lower-level machine, receives the output signal of the PID control from the computer 7 and converts it into the control signal of the induction heating control box 9, so as to realize the real-time adjustment of the magnitude of the induced current on the induction heating head 1 during the continuous induction welding process.

[0059] The PID control output provided by the computer 7 has an upper output limit CV set during output. high With output lower limit CV low This is to ensure the safety of the continuous induction welding process; through the conversion of the PLC controller 8, the magnitude of the induced current of the induction heating head 1 is in the range of 55A to 205A.

[0060] In this embodiment, it should be noted that the proportional, integral, and derivative adjustment coefficients can be determined through experimental investigation. The adjustment coefficients will affect the output of the PID control and the temperature of the welding area.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A PID control method for controlling the induction welding temperature of carbon fiber composites, characterized in that, The device used in this PID control method includes an induction welding actuator, a computer, a PLC controller, an induction heating control box, and a carbon fiber composite laminate structure; the induction welding actuator mainly consists of an infrared thermal imager, an induction heating head, a pressure module, and a cooling module. The infrared thermal imager is connected to the computer and the computer to the PLC controller via Ethernet. The PLC controller controls the magnitude of the induced current output of the induction heating control box on the induction heating head by outputting an analog current of 4-20mA. The PID control method described is a feedback regulation method based on infrared thermal imager temperature measurement. This method combines the temperature relationship between the welding interface and the upper surface of the carbon fiber composite during induction welding with the temperature constraint condition that the welding interface is fully melted without thermal decomposition, to establish the temperature constraint condition of the upper surface of the carbon fiber composite during continuous welding. For the upper surface temperature of the carbon fiber composite during continuous induction welding, an infrared thermal imager is used to collect the surface feature temperature. Based on the temperature information of the induction welding area collected by the infrared thermal imager, the PID temperature control output value is calculated in the computer and sent to the PLC controller. The PLC controller adjusts the output value of the induction heating control box according to the PID temperature output value given by the computer, thereby controlling the output current of the induction heating head on the induction welding actuator, and thus achieving temperature control of the upper surface of the carbon fiber composite. The specific steps are as follows: The first step is to calibrate the temperature relationship between the welding interface and the upper surface of the carbon fiber composite laminate structure during the motion induction welding process: 1) Place an ultra-fine K-type thermocouple on the fusion interface of the carbon fiber composite laminate structure to measure the temperature of the fusion interface. Adjust the distance between the infrared thermal imager and the upper surface of the carbon fiber composite laminate structure in the fusion area and focus the infrared thermal imager to measure the temperature of the upper surface of the carbon fiber composite laminate structure in the fusion area. 2) The operating speed of the induction welding actuator is set by the PLC controller so that the continuous induction welding process is carried out at a constant moving speed; 3) Set the pressure module of the induction welding actuator to ensure that there is appropriate pressure between the upper and lower plates of the carbon fiber composite laminate structure in the welding area. Set the cooling module of the induction welding actuator to ensure that the temperature of the upper surface of the carbon fiber composite laminate structure in the welding area is lower than the temperature of the welding interface, so as to avoid overheating and decomposition of the upper surface of the carbon fiber composite laminate structure due to excessive temperature. 4) Perform continuous induction welding, record the temperature of the upper surface of the carbon fiber composite laminate structure and the welding interface, and obtain the temperature relationship between the welding interface and the upper surface of the carbon fiber composite laminate structure under constant moving speed. The second step involves continuous induction welding with PID temperature feedback regulation at the same induction welding actuator moving speed as in the first step. 1) Set the target temperature value T on the upper surface of the carbon fiber composite laminate structure in the computer. SP Enable PID control and start the continuous induction welding device; 2) The current upper surface temperature T of the carbon fiber composite laminate structure is collected using an infrared thermal imager. PV , calculate the control deviation err(t): err(t)=T SP -T PV (t) 3) Calculate the integral term err re (t), which represents the magnitude of the accumulated discrete error: If the magnitude of the accumulated discrete error is greater than the set upper limit CV of the PID control output... high Then the magnitude of the accumulated discrete error will be adjusted to the set upper limit of the output; If the output CV is less than or equal to the set upper limit of the PID control... high If so, no adjustment will be made; 4) Calculate the differential term err d (t), which is the difference between the current discrete error and the previous discrete error: err d (t)=err(t)-err(t-1) 5) The output CV of the PID control is adjusted using proportional gain, integral gain, and derivative gain. The output of the PID control is: CV=K p ×err(t)+K i ×err re (t)+K d ×err d (t) Among them, K i K is the proportional adjustment coefficient. P K is the integral adjustment coefficient. d These are the differential adjustment coefficients, and the values ​​of each coefficient are obtained through parameter tuning in continuous induction welding experiments; If the output CV of the PID control is greater than the set output upper limit CV high Let CV = CV high If the output CV of the PID control is less than the set lower output limit CV... low Let CV = CV low ; 6) The PLC controller, acting as a lower-level machine, receives the output signal of the PID control from the computer and converts it into the control signal of the induction heating control box, thereby realizing the real-time adjustment of the magnitude of the induced current on the induction heating head during the continuous induction welding process. The PID control output provided by the computer has an upper output limit CV set during output. high With output lower limit CV low This is to ensure the safety of the continuous induction welding process; through the conversion of the PLC controller, the range of the induction current of the induction heating head is 55A to 205A.

Images