Thermoplastic composite automated placement forming method based on dynamic thermal management

Abstract

The application relates to the technical field of composite material manufacturing, and discloses a thermoplastic composite material automatic laying forming method based on dynamic thermal management, which comprises the following steps: real-time scanning of a laying area, acquisition of surface temperature distribution in the width direction of a prepreg tape and an interface temperature of a laid layer; calculation of a thermal fusion window; generation of a cooperative heating decision when the interface temperature of the laid layer is detected to be lower than the lower limit temperature; laying of the prepreg tape preheated through the partition on the laid layer compensated and heated, real-time monitoring of a fusion interface temperature; dynamic adjustment of a heating power distribution when the fusion interface temperature deviation is greater than a preset critical fusion temperature difference; and starting of an emergency cooling program when the interface temperature change rate is detected to exceed a safety threshold. Through the cooperative heating decision, dynamic closed-loop adjustment and adaptive safety protection, the uniformity of a fusion interface temperature in the width direction and the accurate and stable control of the fusion interface temperature in a time sequence during the laying process are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material manufacturing, in particular to a thermoplastic composite material automatic placement forming method based on dynamic thermal management. BACKGROUND

[0002] Thermoplastic composites play a key role in the lightweight demand of large and complex structural components in the fields of aerospace and automotive manufacturing due to their high fracture toughness, recyclability and rapid forming potential. Automatic placement (AFP) technology is the main process to realize the efficient manufacturing of these components. However, the quality of automatic placement forming of thermoplastic composites directly depends on whether high-quality interface fusion between new and old material layers can be achieved during the placement process. This fusion process is extremely sensitive to temperature and must be accurately controlled between the melting temperature and the degradation temperature of the material.

[0003] Existing thermoplastic composite automatic placement systems usually use hot air heating or overall infrared heating devices. These heating technologies realize the basic feasibility of AFP process, and can provide the basic heat required for melting the matrix to the placement area. By using high-power, constant heating output, these systems can match the high-speed running requirements of automatic placement to a certain extent, realize the rapid stacking of materials and the basic forming of components. In addition, the control logic of such heating systems is relatively simple, usually based on preset constant power or feedback for a single temperature measurement point, easy to deploy and operate.

[0004] However, this constant and uniform heating strategy in the prior art has some shortcomings; first, it cannot solve the "edge effect" of the prepreg tape, that is, uniform heating leads to too low edge temperature (poor fusion) or too high center temperature (material degradation), which cannot achieve temperature uniformity in the width direction. Secondly, its simple control logic cannot cope with complex timing thermal mismatch: when eliminating the "thermal lag" of the substrate, it is easy to cause "temperature overshoot"; when multiple layers are placed, it also cannot compensate for the "thermal accumulation effect", causing heat to accumulate layer by layer. Finally, the existing technology generally lacks the ability to close-loop adjust the actual temperature of the fusion interface to suppress transient disturbances, and its safety mechanism is mostly passive high-temperature cutoff, lacking predictive protection based on temperature change rate, and there is a risk of thermal runaway. SUMMARY

[0005] In view of the shortcomings of the prior art, the present application provides a thermoplastic composite material automatic placement forming method based on dynamic thermal management, which solves the problems of temperature unevenness in the width direction of the prepreg tape (edge effect), thermal lag and overshoot during substrate heating, thermal accumulation during multi-layer placement, and lack of real-time closed-loop adjustment of the fusion interface temperature and predictive thermal runaway protection caused by the use of constant and uniform heating strategy in the prior art.

[0006] To achieve the above object, the present application is implemented by the following technical solutions:

[0007] The present application provides a thermoplastic composite automatic placement forming method based on dynamic thermal management, comprising the following steps:

[0008] S1, real-time scanning of the placement area to obtain the surface temperature distribution of the prepreg in the width direction and the interface temperature of the already placed layer;

[0009] S2, based on the surface temperature distribution and the interface temperature of the already placed layer, and in combination with the thermophysical model of the prepreg material, calculating the thermal fusion window, which includes the lower limit temperature required to ensure the activation of molecular chain diffusion and the threshold temperature to prevent material degradation;

[0010] S3, when the interface temperature of the already placed layer is detected to be lower than the lower limit temperature, generating a coordinated heating decision, which includes generating a prepreg partitioned heat flux density function based on the thermophysical model to preheat the prepreg in a partitioned manner, and calculating an already placed layer compensation heat flux based on a thermal hysteresis effect model to compensate for the heating of the interface of the already placed layer;

[0011] S4, placing the prepreg preheated in a partitioned manner onto the already placed layer compensated by heating, real-time monitoring of the fusion interface temperature, and calculating the difference between the fusion interface temperature and the target fusion temperature to obtain the fusion interface temperature deviation, the target fusion temperature being within the thermal fusion window;

[0012] S5, when the fusion interface temperature deviation is greater than the preset critical fusion temperature difference, performing dynamic adjustment of the heating power distribution;

[0013] S6, monitoring the system operating state, when the preset stability conditions are continuously met, reducing the gain coefficient in the thermal hysteresis effect model, and when the interface temperature change rate is detected to exceed the safety threshold, starting an emergency cooling program.

[0014] Preferably, in step S1, the surface temperature distribution of the prepreg in the width direction and the interface temperature of the already placed layer are specifically obtained by:

[0015] acquiring the surface temperature distribution of the prepreg in the width direction by a line scanning infrared thermal imager;

[0016] measuring the interface temperature of the already placed layer by a micro-thermocouple embedded in the placement head.

[0017] Preferably, in step S2, the calculation of the thermal fusion window specifically includes:

[0018] when calculating the lower limit temperature of the thermal fusion window, a historical correction term is introduced;

[0019] The history correction term corrects the base intrinsic molecular chain activation temperature based on an exponentially decaying weighted value of the undercooling temperature deviation of the previous layup layer.

[0020] Preferably, in step S3, the generating the prepreg tape partitioned heat flux density function specifically comprises:

[0021] Calculating the average temperature and the second order spatial derivative of the temperature distribution in the width direction of the prepreg tape;

[0022] Taking the average temperature and the second order spatial derivative as input variables, controlling the heating intensity of the central zone through a thermal conduction compensation coefficient, and controlling the heating intensity of the edge zone through a temperature gradient compensation coefficient, and the temperature gradient compensation coefficient is greater than the thermal conduction compensation coefficient.

[0023] Preferably, in step S3, the generating the cooperative heating decision specifically comprises:

[0024] The temperature gradient compensation coefficient adopted by the prepreg tape partitioned heat flux density function is positively correlated with the laying speed;

[0025] When the laying speed increases, the temperature gradient compensation coefficient increases based on a reference value.

[0026] Preferably, in step S3, the calculating the laid layer compensation heat flux specifically comprises:

[0027] Compensating for the deviation of the laid layer interface temperature from the lower limit temperature by using a quadratic function term;

[0028] Simultaneously introducing a damping term negatively correlated with the interface temperature change rate to suppress temperature overshoot.

[0029] Preferably, in step S4, the calculating the difference between the fusion interface temperature and the target fusion temperature specifically comprises:

[0030] Real-time calculating the temperature deviation of each position of the fusion interface in the width direction;

[0031] And comparing the temperature deviation with the critical fusion temperature difference to identify the supercritical deviation region.

[0032] Preferably, in step S5, the executing the dynamic adjustment of the heating power distribution specifically comprises:

[0033] Real-time calculating the difference between the fusion interface temperature deviation and the critical fusion temperature difference;

[0034] And inversely adjusting the prepreg tape partitioned heat flux density function by a proportional coefficient according to the difference.

[0035] Preferably, in step S6, the starting the emergency cooling program specifically comprises:

[0036] performing a staged cooling strategy;

[0037] a first stage of the staged cooling strategy is to immediately interrupt all heating instructions;

[0038] a second stage of the staged cooling strategy is to calculate a required cooling amount to reduce the laid-up interface temperature below the lower limit temperature.

[0039] In one specific embodiment, the second stage of the staged cooling strategy specifically comprises:

[0040] calculating the required cooling amount according to the material heat capacity parameter and the laid-up interface temperature;

[0041] and ensuring that the laid-up interface temperature is reduced below the lower limit temperature within a preset cooling time.

[0042] The present application provides a thermoplastic composite automatic placement forming method based on dynamic thermal management. The following advantages are provided:

[0043] 1. The present application calculates the second-order spatial derivative of the temperature distribution in the width direction of the prepreg tape, and uses the second-order spatial derivative as an input variable to generate a prepreg tape partition heat flux density function, thereby achieving differential control of the heating intensity of the central region and the edge region of the prepreg tape. This method can actively compensate for the edge heat dissipation effect of the prepreg tape, achieve uniformization of the temperature distribution in the width direction of the prepreg tape, and solve the problem of poor fusion caused by excessively low edge temperature.

[0044] 2. The present application introduces a historical correction term when calculating the lower limit temperature of the thermal fusion window, dynamically adjusts the lower limit temperature using the supercooling temperature deviation of the previous placement layer; at the same time, a damping term negatively related to the interface temperature change rate is introduced when calculating the laid-up layer compensation heat flux. This method can adaptively compensate for the thermal accumulation effect of multi-layer placement, and quickly and stably increase the laid-up interface temperature to eliminate thermal hysteresis effect, ensuring the temperature conditions for interlayer fusion.

[0045] 3. The present application performs dynamic adjustment of heating power distribution according to the real-time monitored fusion interface temperature deviation, thereby achieving closed-loop suppression of instantaneous temperature disturbance during placement. At the same time, the emergency cooling program is started by monitoring whether the interface temperature change rate exceeds a safety threshold, which can respond to the trend of thermal runaway in advance, ensuring the safety of the forming process. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The figure is a schematic diagram of the method of the present application. DETAILED DESCRIPTION

[0047] With reference to the drawings accompanying the present application specification, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present application.

[0048] With reference to Figure 1 , Figure 1 is a flowchart of a dynamic thermal management based thermoplastic composite automated placement forming method according to an embodiment of the present application. The present application provides a dynamic thermal management based thermoplastic composite automated placement forming method, which is a closed-loop dynamic thermal management process. The method first performs real-time scanning of the placement area to obtain the surface temperature distribution in the width direction of the prepreg tape and the interface temperature of the already placed layer.

[0049] Based on the obtained surface temperature distribution and the interface temperature of the already placed layer, and in combination with the thermal physical model of the prepreg tape material, a thermal fusion window is calculated. The thermal fusion window defines the lower limit temperature required to ensure molecular chain diffusion activation and the threshold temperature to prevent material degradation.

[0050] When the interface temperature of the already placed layer is detected to be lower than the lower limit temperature, a cooperative heating decision is generated. The cooperative heating decision includes two parallel control actions: one is to generate a prepreg tape partitioned heat flux function based on the thermal physical model to preheat the prepreg tape in partitions; the other is to calculate an already placed layer compensation heat flux based on a thermal hysteresis effect model to compensate for heating of the interface of the already placed layer.

[0051] The prepreg tape subjected to the partitioned preheating is placed on the already placed layer subjected to the compensation heating. During the placement process, the fusion interface temperature is monitored in real time, and the difference between the fusion interface temperature and the target fusion temperature within the thermal fusion window is calculated to obtain a fusion interface temperature deviation.

[0052] The obtained fusion interface temperature deviation is judged. When the fusion interface temperature deviation is greater than a preset critical fusion temperature difference, an action of dynamically adjusting the heating power distribution is performed to correct the heating process in a closed loop.

[0053] Finally, the system operating state is continuously monitored. This step includes an adaptive optimization mechanism and a safety protection mechanism. When the system continuously meets the preset stable conditions, the gain coefficient in the thermal hysteresis effect model is reduced. When the interface temperature change rate is detected to exceed a safety threshold, an emergency cooling program is started.

[0054] With reference to Figure 1The first step of the method of the embodiment of the present application is to scan the laying area in real time to obtain the surface temperature distribution of the prepreg in the width direction and the interface temperature of the laid layer.

[0055] In a specific embodiment, the temperature state of two key thermal zones in the laying process is synchronously obtained by two different types of sensing devices.

[0056] The surface temperature distribution of the prepreg in the width direction is specifically obtained by a line scanning infrared thermal imager installed on the automatic laying head. The optical axis of the line scanning infrared thermal imager is perpendicular to the surface of the prepreg, and the scanning line is arranged in the width direction of the prepreg (i.e. perpendicular to the laying motion direction). The thermal imager continuously collects the temperature of the upper surface of the prepreg entering the compression roller fusion zone in a non-contact manner, thereby obtaining a one-dimensional temperature data array, denoted as the surface temperature distribution of the prepreg in the width direction , wherein is the coordinate in the width direction of the prepreg. The distribution data can quantitatively represent the phenomenon that the temperature of the edge of the prepreg is lower than the temperature of the center due to the edge heat dissipation effect.

[0057] The interface temperature of the laid layer is specifically obtained by a micro-thermocouple embedded in the laying head. The micro-thermocouple has a low heat capacity characteristic to ensure the immediacy of the measurement response. The measurement probe is installed in front of the compression roller and is in elastic contact with the surface of the laid layer (i.e. the substrate on which the next layer of prepreg is about to be laid). The micro-thermocouple performs real-time contact temperature measurement on the surface of the laid layer on the laying path, thereby obtaining a scalar temperature value, denoted as the interface temperature of the laid layer . The is a key parameter representing the thermal hysteresis effect of the laid layer.

[0058] In this step, the control system performs time stamp synchronization processing on the data obtained by the line scanning infrared thermal imager and the data obtained by the micro-thermocouple, to ensure the consistency of the two groups of data in the time reference, and uses the synchronized real-time temperature data as the input for subsequent calculation.

[0059] Referring to Figure 1 , the second step of the method of the embodiment of the present application is to calculate the thermal fusion window based on the surface temperature distribution and the interface temperature of the laid layer, and in combination with the thermal physical model of the prepreg material.

[0060] The thermal fusion window is defined as , wherein is the lower limit temperature, is the threshold temperature.

[0061] The threshold temperature This is the maximum permissible temperature set to prevent thermal degradation of the prepreg tape material during heating. The value is calibrated based on the thermophysical model of the prepreg material (e.g., the material degradation initiation temperature determined by thermogravimetric analysis (TGA)) and is typically used as a fixed upper limit constraint during the laying process.

[0062] The lower limit temperature This is the minimum process temperature required to ensure sufficient molecular chain diffusion and interfacial wetting between the prepreg tape matrix and the laid-up matrix. In one embodiment of the invention, this lower limit temperature is set to compensate for the heat accumulation effect during multilayer layup. The calculation is dynamically adjusted.

[0063] Specifically, a historical correction term is introduced when calculating the lower limit temperature of the thermal fusion window. This lower limit temperature... The calculation is based on the activation temperature of the intrinsic molecular chains of a matrix. Make corrections, the aforementioned The glass transition temperature of a material is determined based on a material thermophysical model (e.g., by differential scanning calorimetry, DSC). or melting temperature The calibrated reference temperature. The specific calculation formula can be expressed as:

[0064]

[0065] In the formula, The dynamic lower limit temperature calculated in the current step; This is the activation temperature of the inherent molecular chains of the matrix; This is a historical correction item.

[0066] The historical correction item The historical correction term is calculated based on the exponentially decaying weighted value of the supercooled temperature deviation of the preceding layers. Its purpose is to incorporate unreleased heat or heat deficit from previous layers into the current thermal management model. The specific calculation formula can be expressed as:

[0067]

[0068] In the formula, This is the historical temperature influence coefficient, used to calibrate the overall impact of historical heat accumulation on the current lower limit temperature; The total number of preceding layers included in the calculation; For the first The supercooling temperature deviation of each preceding layer is measured and stored when the kk-th layer is laid. It is defined as the difference between the actual fusion interface temperature of that layer and its target lower limit temperature at that time. For the first The exponential decay weight of each preceding layer.

[0069] The exponential decay weight To ensure that more recent layups have a higher weight in the current calculation, the formula can be expressed as:

[0070]

[0071] In the formula, This is the time decay coefficient, used to control the decay rate of historical effects; The current moment; For the first The moment when the preceding layer is completed; For the first The exponential decay weight of each preceding layer.

[0072] The final output is the lower limit temperature obtained through dynamic calculation. and the threshold temperature obtained by calibration The thermal fusion window formed by the two This will serve as a process constraint and target benchmark.

[0073] Reference Figure 1 The third step of the method in this embodiment of the invention is to generate a collaborative heating decision when the temperature of the laid layer interface is detected to be lower than the lower limit temperature.

[0074] This step involves obtaining the interface temperature of the laid layers. The calculated lower limit temperature Triggered when the temperature is deemed too low. This collaborative heating decision aims to simultaneously correct for spatial temperature inhomogeneity and temporal thermal hysteresis. Specifically, the decision comprises two parallel parts: generating the heat flux density function for each prepreg zone and calculating the compensated heat flux for the laid layers.

[0075] The first part describes generating a prepreg zone heat flux density function based on the thermophysical model to preheat the prepreg zone, the purpose of which is to compensate for the uneven temperature in the width direction of the prepreg zone caused by the edge heat dissipation effect.

[0076] In one specific embodiment, the prepreg zone heat flux density function The generation first requires calculating the surface temperature distribution along the width direction of the prepreg. Two characteristic quantities: the average temperature in the width direction of the prepreg belt and the second spatial derivative of the temperature distribution. .

[0077] The second spatial derivative The concave degree of the temperature profile is characterized, which is much larger in the edge region of the prepreg tape than in the central region, for quantifying the severity of the edge heat dissipation effect.

[0078] The average temperature is calculated as an input variable for calculating . . The calculation formula of the average temperature .

[0079]

[0080] In the formula, is the required preheating heat flux density applied at the position of the prepreg tape in the width direction ; is the target preheating temperature of the prepreg tape, which can be set according to the heat fusion window ; is a heat conduction compensation coefficient for controlling the overall heating intensity of the central region of the prepreg tape to adjust ; is a temperature gradient compensation coefficient for controlling the compensation heating intensity of the edge region of the prepreg tape; is the second-order spatial derivative.

[0081] According to the embodiment, the temperature gradient compensation coefficient is greater than the heat conduction compensation coefficient to ensure the application of compensation heat flux in the edge region of the temperature concave.

[0082] In another preferred embodiment, the temperature gradient compensation coefficient is positively correlated with the laying speed . This is because when the laying speed increases, the time of the prepreg tape exposed to the environment is shortened, and the edge heat dissipation effect is relatively intensified. The calculation formula of the average temperature .

[0083]

[0084] In the formula, is the reference value of the temperature gradient compensation coefficient; is the current laying speed; is a speed coupling coefficient for calibrating the influence degree of the laying speed on the edge heat dissipation effect; is the temperature gradient compensation coefficient.

[0085] This calculation method ensures that when the laying speed increases, the temperature gradient compensation coefficient increases on the basis of the reference value , thereby applying stronger edge compensation heating.

[0086] The second part is to calculate the prepreg compensation heat flow based on the thermal hysteresis effect model to compensate the prepreg interface for heating, so as to make the supercooled prepreg interface temperature Rapidly rise to the lower limit temperature Horizontal.

[0087] In one specific embodiment, the calculation of the prepreg compensation heat flow When the deviation of the prepreg interface temperature from the lower limit temperature is compensated by a quadratic function term, a damping term is introduced which is negatively related to the interface temperature change rate to suppress temperature overshoot. The calculation formula can be expressed as:

[0088]

[0089] In the formula, is the required prepreg compensation heat flow; is the quadratic term gain coefficient; is the deviation of the prepreg interface temperature from the lower limit temperature. The quadratic function term of the deviation , can apply an increased compensation heat flow when the deviation is large, achieving a rapid nonlinear temperature rise response. is the damping coefficient; is the interface temperature change rate, which is obtained by differentiating the time series data of . The damping term is negatively related to the interface temperature change rate. When is positive and has a large value (i.e. the temperature rises too fast), the damping term is negative, thereby reducing the total compensation heat flow , effectively suppressing from temperature overshoot when is close to

[0090] This step finally outputs the prepreg partition heat flux density function and the prepreg compensation heat flow , and sends these two calculation results as control instructions to the corresponding heating execution units (such as partition infrared heating array and hot air heater).

[0091] Referring to Figure 1 , the fourth step of the method of the embodiment is to lay the prepreg preheated by the partition on the prepreg that has been compensated by heating, to monitor the fusion interface temperature in real time, and to calculate the difference between the fusion interface temperature and the target fusion temperature to obtain the fusion interface temperature deviation, the target fusion temperature being within the thermal fusion window.

[0092] In one specific embodiment, this step first performs a physical laying action: applying pressure to the pre-impregnated tape, which has been preheated (controlled by ) in zones, and the already-laid layer, which has been preheated (controlled by ) in compensation, under the pressure roller of the laying head, so that the two are fused at the interface in a heated state.

[0093] At the same time as laying fusion, this step performs real-time monitoring. This monitoring is achieved by a non-contact temperature sensor (for example, an infrared thermal imager or a pyrometer array) arranged on the rear side of the pressure roller. This sensor collects the temperature field of the interface just after fusion in the width direction in real time, denoted as , where is the width direction coordinate, is the time.

[0094] The target fusion temperature is a pre-set process parameter value, and the value of is within the calculated thermal fusion window .

[0095] After obtaining the real-time fusion interface temperature , this step calculates the difference between the fusion interface temperature and the target fusion temperature, obtaining the fusion interface temperature deviation .

[0096] The calculation of the difference between the fusion interface temperature and the target fusion temperature specifically includes.

[0097] The temperature deviation of the fusion interface at each position in the width direction is calculated in real time. The calculation formula is:

[0098]

[0099] In the formula, is the fusion interface temperature deviation at time, position; is the real-time fusion interface temperature monitored at time, position; is the target fusion temperature.

[0100] The temperature deviation is compared with a pre-set critical fusion temperature difference . The is the upper limit value of the fusion interface temperature deviation allowed by the process.

[0101] The purpose of this comparison is to identify the supercritical deviation region. The supercritical deviation region is defined as all width coordinates that satisfy the condition . a set of positions.

[0102] the calculated fusion interface temperature deviation for all positions in the width direction and the identified supercritical deviation region (if any) as the basis for dynamically adjusting the heating power distribution.

[0103] Referring to Figure 1 , the fifth step of the method of the embodiment of the present application is to perform dynamic adjustment of the heating power distribution when the fusion interface temperature deviation is greater than the preset critical fusion temperature difference.

[0104] In a specific embodiment, the performance of dynamic adjustment of the heating power distribution specifically includes:

[0105] For each xx position in the supercritical deviation region identified in step S4, the fusion interface temperature deviation is calculated in real time, and the difference between the fusion interface temperature deviation and the critical fusion temperature difference is calculated. The difference is denoted as the supercritical temperature difference , and the calculation formula is:

[0106]

[0107] In the formula, is the supercritical temperature difference at the xx position at the time t, is the fusion interface temperature deviation measured at the xx position at the time t, and the value is always positive; is the preset critical fusion temperature difference. According to the difference , the proportionality coefficient is inversely adjusted to the prepreg partition heat flux density function. This adjustment is achieved by calculating a heat flow adjustment amount , and the adjustment amount is only applied to the region of

[0108] . The calculation formula can be expressed as:

[0109]

[0110] In the formula, is the heat flow adjustment amount required to be applied to the xx position at the time t, is the proportionality coefficient, which is a preset calibration value; is the supercritical temperature difference at the xx position at the time t, and the value is always positive. ​​​​​​

[0111] The control system will calculate the updated heat flux function superimposed to the reference prepreg zonal heat flux function generated in step S3 to obtain the updated heat flux function :

[0112]

[0113] wherein, is the updated heat flux function; is the reference prepreg zonal heat flux function; is the heat flux adjustment amount required to be applied at time, position.

[0114] Finally, the control system converts the updated heat flux function into specific power control instructions (e.g. PWM duty cycle adjustment) for the prepreg zonal preheating device (e.g. the heating unit corresponding to position xx in the zonal infrared heating array), thereby implementing a closed-loop correction of the fusion interface temperature, which is reduced and tends to approach the target fusion temperature .

[0115] Referring to Figure 1 , the sixth step of the method of the embodiment of the present application monitors the system operating state. When the preset stability condition is continuously met, the gain coefficient in the thermal hysteresis effect model is reduced. When the interface temperature change rate exceeds the safety threshold, an emergency cooling program is started.

[0116] This step includes two parallel and continuously executed monitoring branches: an adaptive optimization branch and a safety protection branch.

[0117] When the control system confirms that the preset stability condition is continuously met, the action of "reducing the gain coefficient in the thermal hysteresis effect model" is performed. Specifically, the system reduces the quadratic gain coefficient used in step S3 to calculate the laid layer compensation heat flux . The update rule of this gain coefficient can be expressed as:

[0118]

[0119] wherein, is the updated gain coefficient; is the gain coefficient before update; is a preset decay factor. The purpose of this action is to reduce the response strength of the compensation heating control loop after the system has reached a thermal equilibrium steady state, in order to reduce the possibility of overshoot or oscillation of the control system.

[0120] The emergency cooling procedure is implemented by executing a staged cooling strategy:

[0121] The first stage of the staged cooling strategy is to immediately interrupt all heating instructions. This action specifically includes setting the pre-preg zonal heat flux function and the already-laid-up compensating heat flux to zero. In physical terms, this means immediately cutting off the power supply to all zonal pre-heating devices and compensating heating devices.

[0122] The second stage of the staged cooling strategy is to calculate the required cooling amount to reduce the already-laid-up interface temperature below the lower limit temperature. This action is performed immediately after the first stage of interrupting heating. The control system activates an active cooling device (e.g., an array of high-pressure cold gas nozzles) to forcibly cool the already-laid-up interface region.

[0123] The specific implementation of the second stage includes calculating the required cooling amount based on the material heat capacity parameter and the already-laid-up interface temperature. The required cooling amount defined as the cooling power or the amount of heat required to be removed per unit time, can be calculated as follows:

[0124]

[0125] wherein, is the cooling power required to activate the active cooling device; is the estimated mass of the material to be cooled, which can be estimated based on the ply thickness, density, and cooling area; is the specific heat capacity parameter of the pre-preg material (provided by the thermal physics model); is the instantaneously detected already-laid-up interface temperature when the safety protection mechanism is triggered; is the current dynamic lower limit temperature calculated in step S2; is the pre-set cooling time.

[0126] This formula ensures that the applied cooling power can forcibly reduce the temperature of the region to be cooled from to the lower limit temperature within the pre-set cooling time below, thereby preventing the occurrence of thermal runaway.

Claims

1. A method of automated placement forming of thermoplastic composites based on dynamic thermal management, characterized in that, The method comprises the following steps: S1, real-time scanning of the laying area to obtain the surface temperature distribution of the prepreg in the width direction and the interface temperature of the laid layer; S2, based on the surface temperature distribution and the interface temperature of the laid layer, and in combination with the thermal physical model of the prepreg material, calculating a thermal fusion window, the thermal fusion window comprising a lower limit temperature required to ensure molecular chain diffusion activation and a threshold temperature to prevent material degradation; S3, when the interface temperature of the laid layer is detected to be lower than the lower limit temperature, generating a coordinated heating decision, the coordinated heating decision comprising generating a prepreg partitioned heat flux density function based on the thermal physical model to preheat the prepreg by partition, and calculating a laid layer compensation heat flux based on a thermal hysteresis effect model to compensate for heating of the interface of the laid layer; S4, laying the prepreg preheated by partition onto the laid layer compensated by heating, real-time monitoring of the fusion interface temperature, and calculating the difference between the fusion interface temperature and the target fusion temperature to obtain a fusion interface temperature deviation, the target fusion temperature being within the thermal fusion window; S5, when the fusion interface temperature deviation is greater than a preset critical fusion temperature difference, performing dynamic adjustment of the heating power distribution; S6, monitoring the system operating state, when the preset stable conditions are continuously met, reducing the gain coefficient in the thermal hysteresis effect model, and when the interface temperature change rate is detected to exceed a safety threshold, starting an emergency cooling program.

2. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S1, the surface temperature distribution of the prepreg in the width direction and the interface temperature of the laid layer are specifically obtained as follows: The surface temperature distribution of the prepreg in the width direction is collected by a line scanning infrared thermal imager; The interface temperature of the laid layer is measured by a micro-thermocouple embedded in the laying head.

3. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S2, the calculation of the thermal fusion window specifically comprises: When calculating the lower limit temperature of the thermal fusion window, a historical correction term is introduced; The historical correction term is based on the exponentially decaying weighted value of the supercooling temperature deviation of the previous laying layer, and corrects the base intrinsic molecular chain activation temperature.

4. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S3, the generation of the coordinated heating decision specifically comprises: The temperature gradient compensation coefficient adopted by the prepreg partitioned heat flux density function is positively correlated with the laying speed; When the laying speed increases, the temperature gradient compensation coefficient increases based on the reference value.

5. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S3, the generation of the prepreg partitioned heat flux density function specifically comprises: The average temperature and the second-order spatial derivative of the temperature distribution in the width direction of the prepreg are calculated; The average temperature and the second-order spatial derivative are used as input variables, the heating intensity of the central region is controlled by a thermal conduction compensation coefficient, and the heating intensity of the edge region is controlled by a temperature gradient compensation coefficient, and the temperature gradient compensation coefficient is greater than the thermal conduction compensation coefficient.

6. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S3, the calculation of the laid layer compensation heat flux specifically comprises: A quadratic function term is used to compensate for the deviation of the interface temperature of the laid layer from the lower limit temperature; At the same time, a damping term negatively correlated with the interface temperature change rate is introduced to suppress temperature overshoot.

7. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S4, the calculation of the difference between the fusion interface temperature and the target fusion temperature specifically comprises: calculating the temperature deviation of each position of the fusion interface in the width direction in real time; comparing the temperature deviation with the critical fusion temperature difference to identify a supercritical deviation region.

8. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S5, the executing dynamic adjustment of the heating power distribution specifically includes: calculating the difference between the temperature deviation of the fusion interface and the critical fusion temperature difference in real time; and inversely adjusting the pre-impregnated tape partition heat flux density function according to the difference by a proportional coefficient.

9. The dynamic thermal management based thermoplastic composite automated placement forming method of claim 1, wherein, In step S6, the starting emergency cooling program specifically includes: executing a staged cooling strategy; the first stage of the staged cooling strategy is to immediately interrupt all heating instructions; the second stage of the staged cooling strategy is to calculate the required cooling amount to reduce the laid layer interface temperature below the lower limit temperature.

10. The dynamic thermal management based thermoplastic composite automated placement molding method of claim 9, wherein, The second stage of the staged cooling strategy specifically includes: calculating the required cooling amount according to the material heat capacity parameter and the laid layer interface temperature; and ensuring that the laid layer interface temperature is reduced below the lower limit temperature within a preset cooling time.

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