A hot press forming step-by-step inflation control method based on dynamic pressure difference feedback

Abstract

The present application belongs to the technical field of hot press forming gas pressure control, and particularly relates to a hot press forming step-by-step inflation control method based on dynamic pressure difference feedback, which comprises the following steps: during the period of filling the preheated mold cavity by the medium-pressure bottle group, the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, the absolute pressure of the mold cavity and the mold thermal equilibrium reference temperature are synchronously obtained; the throttling outlet temperature is determined according to the nitrogen isenthalpic throttling thermophysical property relationship, the thermal recovery coefficient is determined according to the corresponding thermal recovery calibration relationship of the pressure ratio, and the mold cavity transient gas equivalent temperature is formed; the thermal equilibrium equivalent pressure is determined according to the nitrogen state relationship that the same gas mass and effective volume remain unchanged; the dynamic effective pressure difference is formed by subtracting the thermal equilibrium equivalent pressure from the absolute pressure of the medium-pressure bottle group, and the switching from the medium-pressure filling stage to the high-pressure filling stage is executed according to the dynamic effective pressure difference. The present application can reduce the influence of the transient thermal state on the stage switching criterion, and reduce the medium-pressure filling end time deviation and the pressure rebound after the valve is closed.

Description

Technical Field

[0001] This invention relates to the field of gas pressure control technology for hot pressing. More specifically, this invention relates to a step-by-step gas inflation control method for hot pressing based on dynamic differential pressure feedback. Background Technology

[0002] In high-pressure gas filling processes, to improve gas source utilization and reduce the airflow impact caused by a single high-pressure gas source directly filling a low-pressure container, it is known technology to use a group of gas cylinders with different pressure levels to sequentially supply gas to the receiving container. For example, US Patent 6779568B2 discloses a gas distribution system in which a first gas supply cylinder supplies gas to the receiving container using the pressure difference between it and the receiving container. When the pressure difference between the first gas supply cylinder and the receiving container decreases to a selected value, the first gas flow stops, and then the second gas supply cylinder continues to supply gas to the receiving container. Therefore, in multi-stage gas source filling systems, using the current pressure difference between the supply side pressure and the receiving side pressure as the stage switching condition is an existing gas filling control method.

[0003] However, when using pressure as the criterion for determining the gas filling volume or the filling endpoint, changes in gas temperature can affect the gas state represented by the pressure. Chinese patent CN1074110C discloses a gas container filling method, pointing out that the pressure of a certain mass of gas in a fixed volume is affected by temperature. Rapid filling of the gas container causes gas temperature changes, and the flow pressure drop in the filling pipeline also causes a difference between the pressure at the pressure measurement location and the actual pressure inside the container. This technology reduces the impact of temperature changes and flow pressure drop on the accuracy of pressure filling by limiting the flow rate at the beginning of filling, subsequently increasing the flow rate, and decreasing the flow rate near the filling endpoint.

[0004] Besides reducing the impact of temperature changes through increasing the inflation rate, existing technologies have also recognized the significant non-equilibrium thermodynamic behavior of high-pressure real gases during rapid filling. European Patent EP0653585A1 discloses that during rapid filling of a pressure vessel, the gas temperature changes rapidly, and the gas state may deviate significantly from thermal equilibrium, resulting in considerable uncertainty in the pressure values ​​obtained during rapid filling. This document addresses the relationship between pressure, gas mass, temperature, and compressibility factor according to the actual gas state relationship, and points out that the relationship between the pressure and mass of a real gas is not a simple linear one.

[0005] The temperature change of high-pressure gas passing through a throttling structure is also well understood in existing technologies. For example, US Patent 9328868B2 discloses an approximate isenthalpic throttling process of high-pressure gas passing through an filling orifice, and explains, in conjunction with a rapid filling process, that the Joule-Thomson effect causes the gas in the receiving container to experience a temperature drop in the initial stage of filling, and then the gas temperature changes again as filling continues. Therefore, attributing the temperature change of high-pressure gas passing through a throttling structure to the Joule-Thomson effect of real gases, and using isenthalpic relationships to analyze the throttling process, are both fluid thermodynamic laws already recognized in existing technologies.

[0006] The aforementioned existing technologies address the high-pressure gas filling process from aspects such as multi-stage gas source differential pressure switching, filling rate adjustment, actual gas state correction, and throttling temperature changes. However, regarding the control relationships disclosed in the above technical solutions, multi-stage gas source switching still primarily relies on the mechanical pressure states measured at the current moment on the gas supply and receiving sides; the method of reducing temperature influence by adjusting the flow rate mainly reduces pressure measurement errors by altering the filling process itself; the method of calculating mass or pressure according to the actual gas state relationship mainly handles the state conversion of pressure, temperature, mass, and compressibility factor; and the treatment of the Joule-Thomson effect mainly focuses on the local temperature changes of the gas after passing through the throttling structure. The objects of these treatments and the control objectives are not the same.

[0007] In high-pressure nitrogen hot pressing molding equipment, the mold cavity differs significantly from that of a typical room-temperature receiving container: the mold cavity is preheated before filling with nitrogen. After the nitrogen from the medium-pressure cylinder group enters the mold cavity through the throttling structure of the medium-pressure filling valve group, it undergoes a transient temperature change due to the throttling from high to low pressure. Simultaneously, it immediately mixes with the existing gas in the mold cavity and exchanges heat with the high-temperature mold boundary. Therefore, the local gas temperature at the valve port cannot directly represent the overall thermal state of the gas within the entire mold cavity, while the pressure obtained by the mold cavity pressure sensor during rapid filling corresponds to the still-changing transient thermal state.

[0008] When the step-by-step filling system still directly uses the difference between the current pressure of the medium-pressure cylinder group and the current pressure of the mold cavity as the end condition of the medium-pressure stage, if the gas in the mold cavity has not yet completed heat exchange with the preheated mold boundary at the judgment time, the current mold cavity pressure cannot stably correspond to the pressure state formed after the same batch of filled gas has completed subsequent heat exchange. When the current temperature of the gas in the mold cavity is lower than the subsequent thermal equilibrium temperature, the current mold cavity pressure is too low, and the direct pressure difference is correspondingly too large, which prolongs the duration of medium-pressure filling. After the medium-pressure filling ends, the gas already sealed in the mold cavity continues to absorb heat from the preheated mold, and the pressure rises as the thermal state recovers, thus forming a pressure rebound after valve closure, and further compressing the pressure regulation margin of the subsequent high-pressure filling stage.

[0009] Therefore, even though existing technologies have already grasped the relationships between multi-stage differential pressure filling, temperature, actual gas states, and the Joule-Thomson throttling law, it is still necessary to solve the problem that the current mechanical pressure state during the step-by-step filling process of the preheating mold cavity cannot stably correspond to the pressure state after the subsequent heat exchange is completed. Summary of the Invention

[0010] To address the technical problem in the aforementioned high-pressure nitrogen thermoforming step-by-step filling process, where the gas inside the mold cavity is in a continuously changing transient thermal state during the rapid filling of the preheated mold cavity from the medium-pressure cylinder group, the stage switching pressure difference based on the current pressure of the medium-pressure cylinder group and the current pressure of the mold cavity cannot stably reflect the pressure state of the nitrogen already filled after subsequent heat exchange, thus causing deviations at the end of the medium-pressure filling stage and pressure rebound after valve closure, this invention provides a thermoforming step-by-step filling control method based on dynamic pressure difference feedback. This method is applied to a high-pressure nitrogen thermoforming pressurization equipment with a medium-pressure cylinder group, a high-pressure cylinder group, and a preheated mold cavity. The method includes: simultaneously acquiring the absolute pressure of the medium-pressure cylinder group, the absolute temperature of the medium-pressure cylinder group, and the absolute pressure of the mold cavity during the filling of the mold cavity from the medium-pressure cylinder group, and reading the mold thermal balance reference temperature determined before the start of medium-pressure filling; and based on the absolute pressure of the medium-pressure cylinder group, the absolute temperature of the medium-pressure cylinder group, and the absolute pressure of the mold cavity, the method further analyzes the pressure difference between the medium-pressure cylinder group and the preheated mold cavity pressure. The throttling outlet temperature is determined by the isenthalpic throttling thermophysical property relationship of nitrogen between pressures; the pressure ratio is determined by the ratio of the absolute pressure of the mold cavity to the absolute pressure of the medium-pressure cylinder group, and the thermal recovery coefficient is determined based on the thermal recovery calibration relationship formed by the filling calibration data and corresponding to the pressure ratio; the transient gas equivalent temperature of the mold cavity is formed by the throttling outlet temperature, the mold thermal balance reference temperature, and the thermal recovery coefficient; according to the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal balance state, the thermal balance equivalent pressure is determined by the absolute pressure of the mold cavity, the transient gas equivalent temperature of the mold cavity, and the mold thermal balance reference temperature; the dynamic effective pressure difference is formed by subtracting the thermal balance equivalent pressure from the absolute pressure of the medium-pressure cylinder group; when the dynamic effective pressure difference is not greater than the filling completion pressure difference threshold, the outlet valve of the medium-pressure cylinder group is closed to terminate the medium-pressure filling, and the high-pressure cylinder group is switched to continue filling the mold cavity.

[0011] This invention addresses the existing control method in the staged gas source filling process, which directly forms the stage switching pressure difference between the gas supply side pressure and the current receiving side pressure. Instead, it establishes a sequential connection between three continuous but physically different state changes that occur between the medium-pressure cylinder group and the preheating mold cavity.

[0012] First, the throttling outlet temperature is determined based on the actual nitrogen isenthalpic throttling thermophysical property relationship between the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, and the absolute pressure of the mold cavity, so that the temperature state entering the subsequent processing corresponds to the throttling result under the current actual pressure and temperature boundary.

[0013] Secondly, the throttling outlet temperature only reflects the local state of nitrogen after passing through the throttling position. This invention further utilizes the thermal recovery calibration relationship formed by actual filling calibration data to link the throttling outlet temperature, the mold thermal balance reference temperature and the current pressure ratio together to form the transient gas equivalent temperature of the mold cavity, thereby converting the local throttling state of the valve port into a transient thermal state that can correspond to the overall pressure formation process of the mold cavity.

[0014] Furthermore, according to the actual nitrogen state relationship where the gas mass and effective volume of the same mold cavity remain unchanged, the present invention continues to map the current pressure corresponding to the transient gas equivalent temperature of the mold cavity to the thermal equilibrium equivalent pressure corresponding to the completion of thermal recovery of the mold thermal boundary, and then uses the thermal equilibrium equivalent pressure and the absolute pressure of the medium-pressure bottle group to form a dynamic effective pressure difference.

[0015] The aforementioned isenthalpic throttling state determination, thermal recovery calibration, and same-mass thermal equilibrium state mapping are three non-independent additional correction quantities: the isenthalpic throttling relationship can only determine the local state of the valve orifice and cannot represent the overall gas state of the mold cavity alone; the thermal recovery calibration relationship requires the throttling outlet state as the starting point to determine the degree of thermal recovery after entering the mold cavity; and the same-mass state mapping requires the transient gas equivalent temperature of the mold cavity as the current state input to form the subsequent thermal equilibrium pressure. These three technical features are sequentially connected in terms of data and physical relationships, enabling the final dynamic effective pressure difference to directly correspond to the mold side pressure state after the nitrogen has been filled and subsequent heat exchange has been completed. Therefore, during the medium-pressure filling process, even if the current mold cavity pressure is still affected by the transient thermal state, this invention can still perform the medium-pressure stage end judgment based on the pressure level after the subsequent thermal recovery of the nitrogen already filled, thereby reducing the deviation of the medium-pressure filling end time caused by the current mold cavity pressure deviating from the subsequent stable pressure, and reducing the pressure rebound caused by continued thermal recovery after the medium-pressure bottle group outlet valve is closed.

[0016] Preferably, the determination of the mold thermal balance reference temperature includes: before the medium-pressure bottle group fills the mold cavity, the mold heating actuator preheats the mold according to the mold preheating target temperature in the current hot pressing molding process formula, and continuously obtains the mold thermal boundary temperature; a preheating stabilization window is formed by continuous sampling points, and when the difference between the maximum and minimum values ​​of the mold thermal boundary temperature in the preheating stabilization window is not greater than twice the temperature engineering resolution, and the arithmetic mean of the mold thermal boundary temperature in the preheating stabilization window is within the mold preheating temperature range specified in the current hot pressing molding process formula, the arithmetic mean of the mold thermal boundary temperature in the first preheating stabilization window that meets the above conditions is determined as the mold thermal balance reference temperature, and the mold thermal balance reference temperature is kept unchanged during this medium-pressure filling stage.

[0017] This invention establishes a mold thermal balance reference temperature by utilizing the mold thermal boundary temperature that meets stable conditions before the start of medium-pressure filling. This ensures that the mold thermal balance reference temperature corresponds to the actual mold preheating state formed in this production cycle, thereby reducing the deviation caused by changes in the mold preheating state in different production cycles on the subsequent thermal balance pressure mapping benchmark.

[0018] Preferably, determining the throttling outlet temperature based on the nitrogen isenthalpic throttling thermophysical property relationship between the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, and the absolute pressure of the mold cavity includes: pre-establishing nitrogen thermophysical property lookup table data, which at least includes discrete pressure nodes, discrete temperature nodes, and the specific enthalpy and compressibility factor corresponding to each pressure and temperature node; determining the corresponding pre-throttling specific enthalpy in the nitrogen thermophysical property lookup table data based on the absolute pressure and absolute temperature of the medium-pressure bottle group; using the absolute pressure of the mold cavity as the post-throttling pressure, finding a temperature within the temperature range corresponding to the absolute pressure of the mold cavity that makes the nitrogen specific enthalpy equal to the pre-throttling specific enthalpy, and determining this temperature as the throttling outlet temperature; wherein, the throttling outlet temperature satisfies: In the formula, Indicates the current sampling time; For nitrogen gas at absolute pressure and absolute temperature Enthalpy below; This refers to the absolute pressure of the medium-pressure bottle group. This refers to the absolute temperature of the medium-pressure bottle group. This refers to the absolute pressure within the mold cavity; This refers to the outlet temperature of the throttling system.

[0019] This invention determines the enthalpy before throttling by looking up table data of nitrogen thermophysical properties including pressure, temperature, specific enthalpy, and compressibility factor, and determines the throttling outlet temperature based on isoenthalpic conditions under the absolute pressure of the mold cavity. This allows the throttling outlet temperature to change together with the current medium-pressure cylinder group pressure, medium-pressure cylinder group temperature, and mold cavity pressure, thereby reflecting the actual throttling state of high-pressure nitrogen thermophysical properties as pressure and temperature change, and reducing the state deviation caused by linear temperature correction using a fixed Joule-Thomson coefficient over a large pressure variation range.

[0020] Preferably, the formation of the heat recovery calibration relationship includes: determining the effective range of the pressure ratio based on the minimum absolute pressure of the mold cavity allowed to start medium-pressure filling, the maximum absolute pressure allowed for the medium-pressure bottle group, and the minimum pressure difference required to complete medium-pressure filling as specified in the hot-pressing molding process formula; setting multiple pressure ratio calibration nodes within the effective range of the pressure ratio; performing medium-pressure filling calibration at each pressure ratio calibration node to form the heat recovery coefficient corresponding to each pressure ratio calibration node; storing each pressure ratio calibration node and its corresponding heat recovery coefficient in ascending order of pressure ratio, and performing linear interpolation between adjacent pressure ratio calibration nodes, thereby forming the heat recovery calibration relationship.

[0021] This invention sets pressure ratio calibration nodes within the effective range of the pressure ratio and uses the thermal recovery coefficients corresponding to each pressure ratio calibration node to form a thermal recovery calibration relationship. This allows the degree of thermal recovery to change with the relative pressure state between the medium-pressure bottle group and the mold cavity, avoiding the use of a single thermal recovery coefficient to represent the entire medium-pressure filling process and improving the adaptability of the thermal recovery relationship to different filling processes.

[0022] Preferably, the intermediate-pressure filling calibration performed at each pressure ratio calibration node includes: before the start of intermediate-pressure filling in each calibration cycle, maintaining the mold thermal boundary temperature within the mold preheating temperature range specified in the current hot-pressing molding process formula, and determining the mold thermal balance reference temperature for this calibration cycle based on the arithmetic mean of the mold thermal boundary temperatures of continuous sampling points that meet the preheating stability conditions; with the high-pressure filling path, recovery path, and venting path connected to the mold cavity closed, filling the mold cavity from the intermediate-pressure bottle group, and simultaneously obtaining the absolute pressure of the intermediate-pressure bottle group, the absolute temperature of the intermediate-pressure bottle group, and the absolute pressure of the mold cavity to calculate the current pressure ratio; when the current pressure ratio reaches or exceeds the current pressure ratio calibration node for the first time, closing the outlet of the intermediate-pressure bottle group. A valve is used to create a closed gas space between the filling pipeline downstream of the outlet valve of the medium-pressure cylinder group and the mold cavity. The transient pressure of the mold cavity calibration, the absolute pressure of the medium-pressure cylinder group calibration, the absolute temperature of the medium-pressure cylinder group calibration, and the mold thermal balance reference temperature are recorded. The mold thermal boundary temperature is maintained, and the absolute pressure and thermal boundary temperature of the mold cavity are continuously obtained. When two consecutive thermal balance observation windows meet the stability conditions of the mold thermal boundary temperature and the absolute pressure of the mold cavity, and the absolute value of the difference between the arithmetic mean of the absolute pressure of the mold cavity in the two consecutive thermal balance observation windows is not greater than twice the pressure engineering resolution, the arithmetic mean of the absolute pressure of the mold cavity in the latter thermal balance observation window is determined as the mold cavity calibration thermal balance pressure corresponding to the pressure ratio calibration node.

[0023] This invention reduces calibration deviations caused by determining the calibration endpoint based solely on a single time length or a single instantaneous pressure value after sealing the gas space following actual medium-pressure filling, and simultaneously utilizing the stable temperature state of the mold thermal boundary and the stable pressure state of the mold cavity to determine the thermal balance reference state. This allows the thermal recovery calibration endpoint to originate from the pressure recovery process observed under actual mold, actual filling passage, and actual thermal boundary conditions.

[0024] Preferably, the formation of the thermal recovery coefficient corresponding to each pressure ratio calibration node includes: determining the calibration throttling outlet temperature according to the nitrogen isenthalpic throttling thermophysical property relationship based on the calibration absolute pressure of the medium-pressure cylinder group, the calibration absolute temperature of the medium-pressure cylinder group, and the calibration transient pressure of the mold cavity; calculating the calibration transient gas equivalent temperature of the mold cavity based on the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the closing time of the outlet valve of the medium-pressure cylinder group and the thermal balance reference state characterized by the calibration thermal balance pressure of the mold cavity and the thermal balance reference temperature of the mold cavity; and determining the calibration value of the thermal recovery coefficient based on the calibration transient gas equivalent temperature of the mold cavity, the calibration throttling outlet temperature, and the thermal balance reference temperature of the mold cavity, wherein the calibration value of the thermal recovery coefficient satisfies: In the formula, This is the calibration value for the thermal recovery coefficient; Calibrate the transient gas equivalent temperature for the mold cavity; To calibrate the throttling outlet temperature; The reference temperature for mold thermal equilibrium is used; the arithmetic mean of the thermal recovery coefficient calibration values ​​formed by multiple effective calibration cycles at the same pressure ratio calibration node is taken, and the arithmetic mean is determined as the thermal recovery coefficient corresponding to the pressure ratio calibration node.

[0025] This invention calculates the equivalent temperature of transient gas in the mold cavity by back-calculating the actual nitrogen state relationship with the same mass and effective volume. Then, it forms the thermal recovery coefficient calibration value by using the equivalent temperature of transient gas in the mold cavity, the calibration throttling outlet temperature, and the mold thermal balance reference temperature. This allows the thermal recovery coefficient to be back-calculated from two detectable states before and after actual filling. Furthermore, averaging multiple effective calibration cycles at the same pressure ratio calibration node can reduce the impact of single pressure or temperature acquisition fluctuations on the thermal recovery coefficient of that calibration node.

[0026] Preferably, the determination of the equivalent pressure for thermal equilibrium based on the nitrogen state relationship where the same gas mass and the same effective volume remain constant between the current transient state and the thermal equilibrium state satisfies: In the formula, Indicates the current sampling time; This refers to the absolute pressure within the mold cavity; The equivalent temperature of the transient gas in the mold cavity; Equivalent pressure for thermal equilibrium; This is the reference temperature for mold thermal balance. For nitrogen gas at absolute pressure and absolute temperature The compression factor is below.

[0027] This invention introduces a nitrogen compressibility factor into the calculation of thermal equilibrium equivalent pressure, so that the pressure mapping between the current transient state and the thermal equilibrium state is carried out according to the relationship of the actual gas state under high pressure, thereby reducing the systematic deviation of nitrogen from the ideal gas state in the tens of megapascal pressure range on the thermal equilibrium equivalent pressure.

[0028] Preferably, the equivalent thermal equilibrium pressure is determined through a pre-formed thermal equilibrium pressure conversion lookup table, including: forming a three-dimensional input node combination with the absolute pressure node of the mold cavity, the equivalent temperature node of the transient gas in the mold cavity, and the reference temperature node of the mold thermal equilibrium; for each three-dimensional input node combination, determining the corresponding equivalent thermal equilibrium pressure offline according to the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal equilibrium state, and writing the equivalent thermal equilibrium pressure into the thermal equilibrium pressure conversion lookup table; during medium-pressure filling, using the current absolute pressure of the mold cavity, the current equivalent temperature of the transient gas in the mold cavity, and the reference temperature of the mold thermal equilibrium as inputs, determining the adjacent grids surrounding the current input state in the thermal equilibrium pressure conversion lookup table, and performing trilinear interpolation on the equivalent thermal equilibrium pressure corresponding to the adjacent grids to form the equivalent thermal equilibrium pressure at the current sampling time.

[0029] This invention pre-forms thermal balance pressure conversion lookup table data with the absolute pressure of the mold cavity, the equivalent temperature of the transient gas in the mold cavity, and the thermal balance reference temperature of the mold as inputs, and directly forms the equivalent thermal balance pressure during the production process using trilinear interpolation. This transforms the implicit state solution that originally included the compressibility factor into a deterministic lookup table calculation process, reducing the burden of online iterative calculation for PLC and the impact of iterative convergence state on the real-time control cycle.

[0030] Preferably, after switching to the high-pressure cylinder group to continue filling the mold cavity, the method further includes: pre-establishing a high-pressure stage thermal recovery calibration relationship for the high-pressure cylinder group and the high-pressure filling path; obtaining the absolute pressure, absolute temperature, and absolute pressure of the high-pressure cylinder group and the mold cavity during high-pressure filling; determining the high-pressure stage throttling outlet temperature based on the nitrogen isenthalpic throttling thermophysical property relationship between the absolute pressure, absolute temperature, and absolute pressure of the high-pressure cylinder group and the mold cavity; forming the high-pressure stage transient gas equivalent temperature of the mold cavity based on the high-pressure stage thermal recovery calibration relationship; and determining the high-pressure stage thermal equilibrium equivalent pressure according to the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal equilibrium state; and terminating the high-pressure filling of the mold cavity by the high-pressure cylinder group when the high-pressure stage thermal equilibrium equivalent pressure reaches the hot-pressing molding target pressure specified in the current hot-pressing molding process formula.

[0031] This invention establishes a high-pressure stage thermal recovery calibration relationship independently during the high-pressure charging stage and forms an equivalent pressure for high-pressure stage thermal balance according to the actual pressure and temperature state of the high-pressure cylinder group. This ensures that the high-pressure charging end conditions can also correspond to the pressure state after the nitrogen has been charged and completed subsequent heat exchange, thereby reducing the end-point pressure deviation caused by the transient thermal state affecting the high-pressure charging endpoint.

[0032] Preferably, the high-pressure nitrogen thermoforming pressurization equipment includes a first mold cavity and a second mold cavity; the corresponding absolute pressure and mold thermal balance reference temperature are obtained for the first mold cavity and the second mold cavity respectively, and corresponding thermal recovery calibration relationships are established respectively; when the first mold cavity is filled with medium pressure, the dynamic effective pressure difference corresponding to the first mold cavity is formed according to the absolute pressure, mold thermal balance reference temperature and thermal recovery calibration relationship corresponding to the first mold cavity; when the second mold cavity is filled with medium pressure, the dynamic effective pressure difference corresponding to the second mold cavity is formed according to the absolute pressure, mold thermal balance reference temperature and thermal recovery calibration relationship corresponding to the second mold cavity; and the medium pressure filling stage switching of the corresponding mold cavity is performed according to the dynamic effective pressure difference of each mold cavity.

[0033] This invention establishes corresponding mold thermal balance reference temperatures and thermal recovery calibration relationships for the first mold cavity and the second mold cavity respectively, and forms corresponding dynamic effective pressure differences, so that the stage switching feedback of the two mold cavities corresponds to their respective actual thermal boundaries and filling states, thereby reducing the misuse of cross parameters caused by differences in the structure, temperature state or filling state of different mold cavities.

[0034] The beneficial effects of this invention are as follows:

[0035] This invention uses the actual high-pressure nitrogen throttling, mold thermal recovery, and changes in the state of the same mass of gas occurring in the preheated mold cavity as a continuous physical basis. It transforms the judgment object of the medium-pressure filling stage from the current transient mechanical pressure of the mold cavity to the pressure state corresponding to the completion of subsequent heat exchange with the nitrogen already filled. This establishes a correspondence between the stage switching feedback quantity and the actual mold-side pressure state that will be formed after the medium-pressure filling is completed. Based on this, through subordinate technical features such as determining the mold preheating state, looking up actual nitrogen thermophysical properties, calibrating the filling process, correcting the actual gas state, and calculating the controller table, the certainty and engineering feasibility of the reference temperature, throttling state, thermal recovery relationship, and thermal balance pressure calculation are improved. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart illustrating a step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention discloses a step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback, applied to a high-pressure nitrogen thermoforming pressurization equipment. See also... Figure 1 This is a flowchart of a step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback, provided by an embodiment of the present invention. Figure 1 As shown, Figure 1 The steps S1 to S6 shown constitute the online control main chain for the medium-pressure filling stage in a production cycle.

[0039] To ensure that every online calculation during production has a known source, before executing step S1 for the first time, the control object configuration, nitrogen thermophysical property data establishment, and thermal recovery calibration relationship establishment must be completed. Only after these preparatory processes are completed can the step-by-step gas filling program enter the automatic production state. The specific preparatory processes are as follows:

[0040] 1. Determine the controlled object and testing conditions.

[0041] The high-pressure nitrogen thermoforming pressurization equipment in this embodiment includes a medium-pressure cylinder group, a high-pressure cylinder group, a mold cavity, a mold heating actuator, a medium-pressure cylinder group outlet valve, a mold cavity filling main valve, a high-pressure main outlet valve, a high-pressure low-speed outlet valve, a medium-pressure recovery valve, a low-pressure recovery valve, a vent valve, a pressure detection channel, a temperature detection channel, and a PLC. The PLC receives the detection results from the medium-pressure cylinder group pressure detection channel, the medium-pressure cylinder group temperature detection channel, the mold cavity pressure detection channel, and the mold cavity temperature detection channel, and outputs control signals to the aforementioned valves and the mold heating actuator, respectively. The medium-pressure cylinder group outlet valve and the mold cavity filling main valve together constitute a medium-pressure filling valve group and establish a medium-pressure filling path. The high-pressure main outlet valve, the high-pressure low-speed outlet valve, and the mold cavity filling main valve together constitute a high-pressure filling valve group and establish a high-pressure filling path. The medium-pressure recovery valve, the low-pressure recovery valve, and the vent valve remain closed during filling.

[0042] In this embodiment, the temperature detection element of the mold cavity temperature detection channel is fixedly set at a fixed temperature measurement position adjacent to the mold cavity and capable of continuously reflecting the temperature of the mold body. The mold cavity temperature detection channel detects the mold thermal boundary temperature, not the local temperature of the cold flow jet at the valve port. The mold heating actuator maintains heating control according to the mold preheating target temperature given in the current hot pressing process formula during both the preheating stage and the intermediate pressure filling stage, so that the mold thermal boundary remains within the same process temperature band during one intermediate pressure filling.

[0043] The pressure and temperature detection channels are periodically updated by the same analog quantity acquisition task, which has a predetermined sampling period. Before entering the thermodynamic calculations in this embodiment, each detection channel is converted into an engineering quantity, with pressure engineering quantities uniformly converted to absolute pressure and temperature engineering quantities uniformly converted to Kelvin temperature. When the field pressure transmitter outputs gauge pressure, the PLC adds the gauge pressure to the field atmospheric absolute pressure during the engineering quantity conversion stage to form the absolute pressure; subsequent steps do not use the gauge pressure. The engineering quantity resolution of each pressure and temperature detection channel is determined by the corresponding channel's engineering quantity range and digital acquisition range, and is written into the PLC parameter area during equipment commissioning, denoted as the pressure engineering quantity resolution and temperature engineering quantity resolution, respectively.

[0044] 2. Establish a lookup table for the thermophysical properties of nitrogen.

[0045] Before the first automated production run, the equipment commissioning personnel first establish nitrogen thermophysical property lookup table data. This lookup table data is generated using the same version of the nitrogen thermophysical property base data, which at least provides discrete pressure nodes, discrete temperature nodes, and the specific enthalpy and compressibility factor corresponding to each pressure and temperature node. The pressure range of the nitrogen thermophysical property lookup table data covers the absolute pressures that can occur in the medium-pressure cylinder group, high-pressure cylinder group, and mold cavity under permissible operating conditions. The temperature range covers the temperature ranges that can occur at the gas source temperature, throttle outlet temperature, transient gas equivalent temperature in the mold cavity, and mold thermal equilibrium reference temperature. After generation, the nitrogen thermophysical property lookup table data, data version number, lower pressure limit, upper pressure limit, lower temperature limit, and upper temperature limit are written into the non-volatile storage area of ​​the PLC.

[0046] The PLC uses a fixed adjacent node interpolation rule for looking up nitrogen thermophysical properties. For a given absolute pressure and absolute temperature, the PLC determines two adjacent pressure nodes that are not greater than or less than the absolute pressure, and two adjacent temperature nodes that are not greater than or less than the absolute temperature. It then performs bilinear interpolation based on the four surrounding nodes to form the corresponding specific enthalpy or compressibility factor. When a given state falls on a data node, the value of that node is read directly. If the given pressure or temperature exceeds the valid range of the nitrogen thermophysical property lookup data, the lookup is marked as invalid.

[0047] 3. Establish a lookup table for thermal balance pressure conversion.

[0048] To ensure a unique real-time acquisition rule for the thermal equilibrium equivalent pressure within the PLC, during the equipment commissioning phase, thermal equilibrium pressure conversion lookup data was also generated offline based on the same version of nitrogen thermophysical property lookup data. For each set of mold cavity absolute pressure nodes, mold cavity transient gas equivalent temperature nodes, and mold thermal equilibrium reference temperature nodes, the mold cavity transient gas equivalent temperature node was denoted as... First, the compressibility factor under the current state is obtained based on the absolute pressure of the mold cavity and the equivalent temperature of the transient gas in the mold cavity. Then, the candidate thermal equilibrium states are calculated in ascending order of pressure at the pressure nodes of the nitrogen thermophysical property lookup table. and corresponding to the current state Comparison. When the target value first falls between the corresponding values ​​of two adjacent candidate pressure nodes, linear interpolation is performed between these two adjacent candidate pressure nodes to obtain the thermal equilibrium equivalent pressure corresponding to the three input nodes in this group, and this is written into the thermal equilibrium pressure conversion lookup table data. During production, the PLC determines adjacent grids according to the absolute pressure of the mold cavity, the equivalent temperature of the transient gas in the mold cavity, and the thermal equilibrium reference temperature of the mold, and performs trilinear interpolation to directly form the thermal equilibrium equivalent pressure. If two candidate pressure nodes surrounding the target value cannot be found during offline table creation, the three input nodes in this group are marked as having no effective thermal equilibrium equivalent pressure, and automatic stage switching is not allowed in this area during production.

[0049] 4. Determine the thermal recovery calibration range and calibration nodes.

[0050] Before the first automated production, a thermal recovery calibration relationship was established for each type of mold actually used, its corresponding mold cavity, medium-pressure filling passage, and mold preheating process formula. Each set of thermal recovery calibration relationships corresponds one-to-one with the mold number, mold cavity number, medium-pressure filling valve group number, nitrogen thermophysical property lookup data version number, and mold preheating process formula number. If any of the above numbers changes, the original thermal recovery calibration relationship becomes invalid, and the PLC will not allow the invalid thermal recovery calibration relationship to be called to perform automatic medium-pressure filling stage switching.

[0051] When establishing the heat recovery calibration relationship, the effective range of the pressure ratio allowed by the process formulation is first determined. The pressure ratio is defined as the ratio of the absolute pressure of the mold cavity to the absolute pressure of the medium-pressure bottle group. The lower limit of the effective range of the pressure ratio is formed by dividing the lowest absolute pressure of the mold cavity allowed to start medium-pressure filling by the highest absolute pressure allowed by the medium-pressure bottle group; the upper limit of the effective range of the pressure ratio is formed by subtracting the minimum pressure difference at the completion of medium-pressure filling in the process formulation from the highest absolute pressure allowed by the medium-pressure bottle group, and then dividing by the highest absolute pressure allowed by the medium-pressure bottle group. The PLC establishes nine pressure ratio calibration nodes within the effective range of the pressure ratio. The first pressure ratio calibration node is equal to the lower limit of the effective range of the pressure ratio, the ninth pressure ratio calibration node is equal to the upper limit of the effective range of the pressure ratio, and the remaining seven pressure ratio calibration nodes are arranged at equal pressure ratio intervals.

[0052] 5. Determine the thermal recovery calibration cycle and thermal equilibrium state.

[0053] Each pressure ratio calibration node performs three effective calibration cycles in the same order. When a calibration cycle begins, the PLC closes the high-pressure main outlet valve, high-pressure low-speed outlet valve, medium-pressure recovery valve, low-pressure recovery valve, and vent valve. The mold heating actuator maintains the mold thermal boundary temperature within the temperature range of the current mold preheating process formula. The PLC opens the vent valve to reduce the absolute pressure of the mold cavity to the medium-pressure filling allowable start-up pressure given in the current process formula. After reaching the medium-pressure filling allowable start-up pressure, the PLC closes the vent valve and uses ten consecutive sampling points to form a calibration preheating stability window. When the difference between the maximum and minimum values ​​of the mold thermal boundary temperature within the calibration preheating stability window is no greater than twice the temperature engineering resolution, and the arithmetic mean of the mold thermal boundary temperature within the calibration preheating stability window is within the mold preheating temperature range specified in the current process formula, the PLC determines the arithmetic mean as the mold thermal balance reference temperature for this calibration cycle. After the mold thermal balance reference temperature is formed, the PLC opens the mold cavity filling main valve and the medium-pressure bottle group outlet valve to allow nitrogen from the medium-pressure bottle group to enter the mold cavity.

[0054] During the calibration filling process, the PLC synchronously latches the absolute pressure and temperature of the medium-pressure cylinder group, the absolute pressure of the mold cavity, and the thermal boundary temperature of the mold in each analog sampling cycle, and calculates the current pressure ratio. When the current pressure ratio reaches or exceeds the current pressure ratio calibration node for the first time, the PLC immediately closes the outlet valve of the medium-pressure cylinder group, while keeping the main filling valve of the mold cavity open. The high-pressure main outlet valve, high-pressure low-speed outlet valve, medium-pressure recovery valve, low-pressure recovery valve, and vent valve remain closed. Thus, the filling pipeline from the outlet valve of the medium-pressure cylinder group to the mold cavity and the mold cavity together form a closed gas space, and no new nitrogen mass enters after the seal.

[0055] During the same sampling cycle when the outlet valve of the medium-pressure bottle group is closed, the PLC records the transient pressure of the mold cavity calibration, the absolute pressure of the medium-pressure bottle group calibration, the absolute temperature of the medium-pressure bottle group calibration, and the mold thermal balance reference temperature. Subsequently, the PLC continues to operate the mold heating actuator to keep the mold thermal boundary temperature within the temperature range specified in the current process formula, and continuously collects the absolute pressure of the mold cavity and the mold thermal boundary temperature. The PLC uses ten consecutive sampling points to form a thermal balance observation window. When the difference between the maximum and minimum values ​​of the mold thermal boundary temperature within the same thermal balance observation window is no greater than twice the temperature engineering resolution, the difference between the maximum and minimum values ​​of the absolute pressure of the mold cavity is no greater than twice the pressure engineering resolution, and the arithmetic mean of the mold thermal boundary temperature within the thermal balance observation window remains within the mold preheating temperature range specified in the current process formula, the PLC determines this thermal balance observation window as the first stable window.

[0056] After obtaining the first stable window, ten consecutive sampling points immediately following the first stable window are collected to form the second stable window. Only when the second stable window simultaneously meets the aforementioned temperature fluctuation and pressure fluctuation conditions, and the absolute value of the difference between the arithmetic mean of the absolute pressure in the mold cavity of the first and second stable windows is not greater than twice the pressure engineering resolution, will the PLC determine the arithmetic mean of the absolute pressure in the mold cavity of the second stable window as the calibration thermal equilibrium pressure of the mold cavity in this calibration cycle relative to that pressure point. If the second window following the first stable window does not meet the above conditions, the PLC continues to move the window backward according to the sampling time until two consecutive stable windows that meet the conditions are obtained; the calibration thermal equilibrium pressure of the mold cavity is not formed until two consecutive stable windows are obtained.

[0057] The above calibration endpoint utilizes both the mold thermal boundary temperature and the mold cavity absolute pressure. The physical relationship is as follows: after the outlet valve of the medium-pressure cylinder group is closed, the gas mass in the enclosed gas space no longer increases, the geometry of the mold and filling pipeline remains unchanged, and the effective gas volume remains constant. When the mold thermal boundary remains within the current process temperature range, the gas continuing to gain heat from the mold thermal boundary will manifest as a continued change in the mold cavity absolute pressure. When the mold thermal boundary temperature remains stable and the mold cavity absolute pressure shows no discernible change in two consecutive observation windows, it indicates that there is no longer any observable change in thermal recovery pressure at the current detection resolution. Therefore, this state is taken as the thermal balance reference state under the current process conditions. If the mold thermal boundary temperature remains stable while the mold cavity absolute pressure continuously decreases by more than twice the pressure engineering resolution between consecutive windows, then this calibration cycle is considered an invalid seal, and the data from this cycle is not used to form the thermal recovery coefficient.

[0058] 6. Establish the thermal recovery coefficient and thermal recovery calibration relationship.

[0059] For the calibration cycle that obtains the effective mold cavity calibration thermal equilibrium pressure, the PLC calculates the throttling outlet temperature corresponding to the calibration node according to the isenthalpic throttling rule in step S2 described later, based on the intermediate-pressure bottle group calibration absolute pressure, intermediate-pressure bottle group calibration absolute temperature, and mold cavity calibration transient pressure. Then, based on the actual nitrogen state relationship where the same gas mass and the same effective volume remain constant between the instant the intermediate-pressure bottle group outlet valve closes and the thermal equilibrium reference state characterized by the mold cavity calibration thermal equilibrium pressure and the mold thermal equilibrium reference temperature of this calibration cycle, the equivalent temperature of the mold cavity calibration transient gas is calculated. The equivalent temperature of the mold cavity calibration transient gas satisfies:

[0060]

[0061] In the formula, The transient pressure in the mold cavity is calibrated at the moment the outlet valve of the medium-pressure bottle group is closed; The thermal equilibrium pressure of the mold cavity formed in this calibration cycle is calibrated; This is the reference temperature for the mold thermal balance during this calibration cycle; The transient gas equivalent temperature is calibrated for the mold cavity to be inversely calculated; This indicates that nitrogen gas is at absolute pressure and absolute temperature The compression factor is below.

[0062] When back-calculating the transient gas equivalent temperature for mold cavity calibration, the PLC calculates the left-hand side of the above equation from low to high based on discrete temperature nodes from the nitrogen thermophysical property lookup table data between the throttling outlet temperature and the mold thermal equilibrium reference temperature, and compares it with the target value on the right-hand side. When the target value lies between the corresponding values ​​of two adjacent temperature nodes, linear interpolation is performed between these two adjacent temperature nodes to form a unique transient gas equivalent temperature for mold cavity calibration. If no two adjacent temperature nodes surrounding the target value are found, the current calibration cycle is invalid.

[0063] After obtaining the equivalent temperature of the transient gas in the mold cavity, the calibration value of the thermal recovery coefficient for this calibration cycle is calculated according to the following formula:

[0064]

[0065] In the formula, This is the calibration value for the thermal recovery coefficient during this calibration cycle; This is the throttling outlet temperature corresponding to the calibration node for this pressure ratio. When the temperature engineering resolution is no greater than twice that of the standard temperature measurement, there is a lack of a resolvable temperature span between the throttling outlet state and the thermal equilibrium reference state, rendering this calibration cycle invalid; when or If the calibration cycle fails to pass the tests for sealing effectiveness, back-calculation effectiveness of the equation of state, and physical range of the thermal recovery coefficient, it is considered a valid calibration cycle.

[0066] After obtaining three valid calibration cycles for the same pressure ratio calibration node, the PLC calculates the arithmetic mean of the three thermal recovery coefficient calibration values ​​and uses this arithmetic mean as the thermal recovery coefficient of that pressure ratio calibration node. If three valid calibration cycles are not obtained, the pressure ratio calibration node remains in an incomplete state, and the entire set of thermal recovery calibration relationships cannot enter the effective production state; after ruling out abnormalities in sensors, valve seals, or mold preheating, calibration restarts from the incomplete pressure ratio calibration node. After all nine pressure ratio calibration nodes are completed, the PLC stores the nine pressure ratio calibration nodes and their corresponding thermal recovery coefficients in ascending order of pressure ratio. Linear interpolation is used between adjacent pressure ratio calibration nodes, thereby forming a unique thermal recovery calibration relationship corresponding to the current mold, the current mold cavity, the current medium-pressure filling passage, and the current mold preheating process formula.

[0067] After completing the above preparations, the PLC will set the version status of the nitrogen thermophysical property lookup data, the thermal equilibrium pressure conversion lookup data, and the thermal recovery calibration relationship to valid before the automatic production program can proceed. Figure 1 Steps S1 to S6 are shown below:

[0068] S1. During the medium-pressure filling stage, simultaneously obtain the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, the absolute pressure of the mold cavity, and the reference temperature of the mold thermal balance.

[0069] After the workpiece enters the mold, the mold closing actuator completes the mold closing, and the mold heating actuator preheats the mold according to the mold preheating target temperature in the current hot pressing molding process formula. The PLC continuously reads the mold cavity temperature detection channel and still uses ten continuous sampling points to form a preheating stability window.

[0070] When the difference between the maximum and minimum values ​​of the mold thermal boundary temperature within the preheating stabilization window is no greater than twice the temperature engineering resolution, and the arithmetic mean of the mold thermal boundary temperature within the preheating stabilization window is within the mold preheating temperature range specified in the current process formula, the PLC determines the arithmetic mean of the mold thermal boundary temperature within the first preheating stabilization window that meets the above conditions as the sole mold thermal balance reference temperature for this medium-pressure filling stage. .

[0071] After the mold reaches thermal equilibrium reference temperature, the PLC closes the high-pressure main outlet valve, the high-pressure low-speed outlet valve, the medium-pressure recovery valve, the low-pressure recovery valve, and the vent valve, and opens the mold cavity filling main valve and the medium-pressure bottle group outlet valve. Under the pressure difference between the medium-pressure bottle group and the mold cavity, the nitrogen in the medium-pressure bottle group enters the mold cavity through the medium-pressure filling passage, thus starting the medium-pressure equal pressure filling.

[0072] During the medium-pressure equalization filling process, the PLC synchronously acquires the absolute pressure of the medium-pressure cylinder group according to a pre-defined control sampling cycle. Absolute temperature of medium-pressure bottle group absolute pressure of mold cavity and mold thermal boundary temperature The four detection quantities share the same sampling period number.

[0073] S2. Determine the throttling outlet temperature based on the isenthalpic throttling thermophysical property relationship of nitrogen.

[0074] Nitrogen gas in the medium-pressure cylinder group enters the lower-pressure mold cavity through the outlet valve of the medium-pressure cylinder group and the main throttling section in the filling pipeline. The main throttling section is the minimum flow section in the current medium-pressure filling passage that mainly restricts the gas mass flow rate and whose effective flow area is determined by the valve opening and closing state.

[0075] In this embodiment, during the medium-pressure filling process after the outlet valve of the medium-pressure cylinder group is fully opened, the short throttling process from upstream to downstream of the main throttling section is treated as an isenthalpic throttling process with no shaft work, negligible energy storage change in the throttling section, and negligible heat exchange with the outside environment during the throttling period relative to the gas passage time. Therefore, the nitrogen specific enthalpy before and after throttling satisfies:

[0076]

[0077] In the formula, This indicates that nitrogen gas is at absolute pressure and absolute temperature Enthalpy below; The throttling outlet temperature at the current sampling moment; This represents the absolute pressure of the medium-pressure bottle group at the current sampling time. This represents the absolute temperature of the medium-pressure bottle group at the current sampling time. This represents the absolute pressure of the mold cavity at the current sampling moment.

[0078] PLC first and As input, the enthalpy before throttling is generated by bilinear interpolation of adjacent nodes based on the nitrogen thermophysical property lookup data. ; then with As the pressure after throttling, the specific enthalpy is found from low to high at the temperature node corresponding to this pressure. When the PLC is initially located between the specific enthalpy of two adjacent temperature nodes, it performs linear interpolation between those two adjacent temperature nodes and determines the interpolated temperature as... .

[0079] like , or Exceeding the valid range of nitrogen thermophysical property lookup data, or in There is no encirclement within the corresponding temperature range If two adjacent specific enthalpy values ​​are not found, the current nitrogen thermophysical property query is invalid; the PLC immediately closes the outlet valve of the medium-pressure cylinder group and the main filling valve of the mold cavity, locks the current automatic cycle, and does not perform boundary extrapolation.

[0080] After adopting the above isenthalpy lookup table, the throttling outlet temperature is determined by the current absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, and the absolute pressure of the mold cavity. This process uses the relationship between the actual nitrogen specific enthalpy and the changes in pressure and temperature to determine the current throttling state.

[0081] S3. Determine the thermal recovery coefficient based on the pressure ratio and thermal recovery calibration relationship, and form the equivalent temperature of transient gas in the mold cavity.

[0082] The throttling outlet temperature only corresponds to the local thermal state of nitrogen gas just after it crosses the main throttling section. As nitrogen continues to flow into the preheated mold cavity, it mixes with the existing nitrogen in the mold cavity and absorbs heat from the mold's thermal boundary. Therefore, if... Using the temperature of the entire mold cavity gas directly as the temperature would incorrectly extend the localized throttling temperature drop to all the gas in the mold cavity. To establish a calibrated bridging relationship between the local pressure at the valve orifice and the overall pressure state of the mold cavity, the PLC first calculates the pressure ratio using the following formula:

[0083]

[0084] In the formula, The pressure ratio at the current sampling time; This represents the absolute pressure of the medium-pressure bottle group at the current sampling time. This represents the absolute pressure of the mold cavity at the current sampling moment.

[0085] PLC Comparison Effective range of pressure ratio relative to current thermal recovery calibration: When the pressure ratio is within the effective range, the PLC determines it to be less than or equal to... The most recent pressure ratio is greater than or equal to the calibration node. The most recent pressure ratio calibration node is used, and linear interpolation is performed between the thermal recovery coefficients corresponding to the two pressure ratio calibration nodes to form the current thermal recovery coefficient. ; The pressure ratio is equal to the thermal recovery coefficient of the node when it is calibrated. When the result exceeds the effective range, the PLC immediately closes the outlet valve of the medium-pressure bottle group and the main filling valve of the mold cavity, locks the current automatic cycle, and does not use the extrapolation result from the out-of-range.

[0086] Subsequently, the PLC calculates the equivalent temperature of the transient gas in the mold cavity according to the following formula:

[0087]

[0088] In the formula, The equivalent temperature of the transient gas in the mold cavity at the current sampling moment; This represents the current thermal recovery coefficient; This is the mold thermal balance reference temperature that has been determined and remains unchanged during this medium-pressure filling stage.

[0089] when hour, equal ;when hour, equal ;when hour, lie in and Between. The transient gas equivalent temperature of the mold cavity represents the equivalent temperature used to map the current overall gas state of the mold cavity to the subsequent thermal equilibrium reference state under the current absolute pressure of the mold cavity.

[0090] S4. Determine the thermal equilibrium equivalent pressure based on the actual nitrogen state relationship for the same gas mass and the same effective volume.

[0091] The PLC constructs a stop-gas-replenishment state at the current sampling moment, solely for state mapping: from the current sampling moment, no new nitrogen mass enters the mold cavity, while the mold remains closed, and the geometric state of the enclosed gas space between the mold cavity and the outlet valve of the medium-pressure cylinder group remains unchanged. This stop-gas-replenishment state does not output a closing command to the valve; its function is only to map the same mass of nitrogen that has already entered the mold cavity and the connected enclosed space from the current transient gas equivalent temperature to the mold thermal equilibrium reference temperature.

[0092] For the same mass of nitrogen and the same effective volume, the actual gas state relations satisfy:

[0093]

[0094] In the formula, This represents the thermal equilibrium equivalent pressure at the current sampling moment; This indicates that nitrogen gas is at absolute pressure and absolute temperature The compression factor is below; This is the mold thermal balance reference temperature that has been determined and remains unchanged during this medium-pressure filling stage; The equivalent temperature of the transient gas in the mold cavity at the current sampling moment; This represents the absolute pressure of the mold cavity at the current sampling moment.

[0095] PLC , and As three inputs, trilinear interpolation is performed from the existing thermal equilibrium pressure conversion lookup table data to form a unique... If any of the three inputs exceeds the valid range of the heat balance pressure conversion lookup table data, or if the grid in question is marked as having no valid heat balance equivalent pressure, the PLC will immediately close the outlet valve of the medium-pressure bottle group and the main filling valve of the mold cavity, locking the current automatic cycle.

[0096] Thermal equilibrium equivalent pressure This indicates that the mass of nitrogen gas currently entering the mold cavity and the connected enclosed space remains constant, and is distributed within the same effective volume by... Continue to recover to The corresponding mold side pressure. When the gas is still in a relatively low thermal state relative to the mold thermal boundary, Higher than This allows the thermal recovery pressure, which would only gradually appear after the outlet valve of the medium-pressure cylinder group is actually closed, to be mapped into the medium-pressure filling period in advance.

[0097] S5. Form a dynamic effective differential pressure and compare it with the differential pressure threshold after filling.

[0098] The PLC calculates the dynamic effective pressure difference according to the following formula:

[0099]

[0100] In the formula, This represents the dynamic effective pressure difference at the current sampling moment; This represents the absolute pressure of the medium-pressure bottle group at the current sampling time. This represents the equivalent thermal equilibrium pressure at the current sampling moment.

[0101] The current hot pressing process formula already provides the differential pressure parameter for completing the medium-pressure filling. The PLC uses this parameter as the threshold for the differential pressure during filling. The pressure difference threshold for completion of filling is the allowable pressure difference between the medium-pressure bottle group and the mold side at the end of the medium-pressure equalization stage, rather than a sensor threshold specifically set for the instantaneous reading of a certain pressure sensor.

[0102] This step is only executed after all valid results have been obtained in steps S1 to S4 within each online sampling cycle. At this time, the PLC maintains the opening of the outlet valve of the medium-pressure bottle group and the main filling valve of the mold cavity, and enters the next sampling cycle. The next sampling cycle only re-executes the four detection quantity latching, throttling outlet temperature calculation, pressure ratio calculation, thermal recovery coefficient interpolation, mold cavity transient gas equivalent temperature calculation, thermal balance equivalent pressure calculation and dynamic effective pressure difference comparison. It does not re-execute the mold preheating stability judgment, nor does it re-form the mold thermal balance reference temperature.

[0103] when First time satisfied At that time, the PLC immediately ends the medium-pressure equalization filling state and enters step S6.

[0104] Since the determination uses thermal equilibrium equivalent pressure, when the current mechanical pressure in the mold cavity is still low due to the transient low temperature, the PLC can stop replenishing gas from the medium-pressure cylinder group when the subsequent thermal recovery pressure of the currently filled nitrogen has met the final state requirements of the medium-pressure stage, thereby reducing the need to wait... The excess mass produced by the continued increase.

[0105] S6. Determine the switch from the medium-pressure filling stage to the high-pressure filling stage, and complete the current hot pressing molding cycle of pressing, holding and depressurizing.

[0106] When the switching conditions are met for the first time in step S5, the PLC first closes the outlet valve of the medium-pressure bottle group, while keeping the main filling valve of the mold cavity open, the main outlet valve of the high-pressure gas and the low-speed outlet valve of the high-pressure gas remain closed, and starts a 1-second stage interval timer. During this 1-second stage interval, the medium-pressure bottle group is isolated from the mold cavity, so no more gas mass from the medium-pressure bottle group will be added to the mold cavity; the main filling valve of the mold cavity remains open, so that subsequent high-pressure filling still uses the same mold cavity filling path, and it is not necessary to switch the main valve of the mold cavity side between the medium-pressure stage and the high-pressure stage.

[0107] After the 1-second interval timer ends, the PLC keeps the medium-pressure bottle group outlet valve closed and the mold cavity filling main valve open, while simultaneously opening the high-pressure main exhaust valve and the high-pressure low-speed exhaust valve to continue pressurizing the mold cavity from the high-pressure bottle group. The PLC reads the target hot-pressing pressure given in the current hot-pressing process formula. When the absolute pressure in the mold cavity meets the requirements... At this time, the PLC closes the high-pressure main exhaust valve, while keeping the high-pressure low-speed exhaust valve and the mold cavity filling main valve open, allowing the high-pressure filling to transition from the high-flow stage to the low-speed final pressure replenishment stage; when the absolute pressure of the mold cavity meets the requirements... When the high-pressure low-speed exhaust valve and the mold cavity filling main valve are closed by the PLC, the high-pressure filling is completed.

[0108] After the high-pressure filling is completed, the PLC starts the pressure holding timer. In a specific process of this embodiment, the pressure holding time is 10 seconds. During the pressure holding period, the outlet valve of the medium-pressure bottle group, the main high-pressure outlet valve, the low-speed high-pressure outlet valve, the medium-pressure recovery valve, the low-pressure recovery valve, and the vent valve are all kept closed, and the mold remains closed.

[0109] After the pressure holding timer ends, the PLC performs gas recovery according to the recovery sequence given in the current process formula: first, the medium-pressure recovery valve is opened, allowing the gas in the mold cavity to enter the medium-pressure bottle group through the existing cooling and filtration channels; when the difference between the absolute pressure of the mold cavity and the absolute pressure of the medium-pressure bottle group is not greater than the pressure difference parameter for the completion of medium-pressure recovery in the current process formula, the medium-pressure recovery valve is closed; then, the low-pressure recovery valve is opened, allowing the gas in the mold cavity to enter the low-pressure bottle group; when the absolute pressure of the mold cavity is not greater than the pressure parameter for the end of low-pressure recovery in the current process formula, the low-pressure recovery valve is closed.

[0110] After low-pressure recovery is complete, the PLC opens the vent valve to further reduce the residual pressure in the mold cavity. The aforementioned pressure engineering quantity conversion stage already used the absolute atmospheric pressure at the site. When the absolute pressure of the mold cavity meets the requirements At that time, the PLC closes the vent valve, in which This is the pressure engineering resolution of the mold cavity pressure detection channel. Only after this condition is met will the PLC release the mold opening pressure interlock and allow the mold closing actuator to perform mold opening.

[0111] Thus, a complete production cycle with a defined inlet and a defined outlet is formed, from workpiece mold closing, mold preheating, medium-pressure dynamic effective differential pressure control, high-pressure replenishment, pressure holding, medium-pressure recovery, low-pressure recovery to final release and mold opening.

[0112] Within any medium-pressure online calculation cycle of the aforementioned production cycle, if any of the following occurs: invalid pressure or temperature measurement, invalid nitrogen thermophysical property lookup, pressure ratio exceeding the effective range of the thermal recovery calibration relationship, mold thermal boundary temperature deviating from the mold preheating temperature zone of the current process formula, or no valid result for the thermal balance pressure conversion lookup table or a mismatch in the calibration relationship version, the PLC will execute the same safety exit action: immediately close the medium-pressure cylinder group outlet valve and the mold cavity filling main valve, keep the high-pressure main outlet valve and the high-pressure low-speed outlet valve closed, stop automatic stage switching, and lock the current production cycle. After the fault is locked, filling will not automatically resume; after troubleshooting the corresponding fault and re-completing the mold pressure safety confirmation, the operator will restart a new production cycle. This avoids the situation where, after an out-of-range interpolation failure, medium-pressure filling continues while waiting for parameters to recover automatically.

[0113] In a specific set of equipment, the working pressure of the medium-pressure bottle group is 30MPa to 35MPa, the volume of the medium-pressure bottle group is 400L, and the average standard volumetric flow rate of the medium-pressure bottle group during flat-pressure filling into the mold cavity is 1Nm³ / s to 1.5Nm³ / s; the pressure difference parameter for the completion of medium-pressure filling in the current process formula is 2MPa. The working pressure of the high-pressure bottle group is 80MPa to 90MPa, and the volume is 48L; taking the hot-pressing target pressure of 70MPa as an example, the medium-pressure flat-pressure filling ends when the dynamic effective pressure difference is no greater than 2MPa for the first time, and then high-pressure filling is entered according to the above 1s stage interval. After high-pressure replenishment is completed, the pressure is held for 10s, and then medium-pressure recovery, low-pressure recovery, and release mold opening are performed. The above parameters are used to illustrate the equipment scale and existing process position in this embodiment, and do not change the technical relationship of steps S1 to S6.

[0114] In this embodiment, the high-pressure cylinder assembly is equipped with a high-pressure cylinder assembly pressure detection channel and a high-pressure cylinder assembly temperature detection channel. The PLC obtains the absolute pressure and absolute temperature of the high-pressure cylinder assembly through the pressure detection channel and the temperature detection channel, respectively. During high-pressure filling, the mold heating actuator continues to maintain the mold thermal boundary temperature according to the current hot-pressing molding process formula, and continues to use the mold thermal balance reference temperature determined before the start of medium-pressure filling in this production cycle.

[0115] In another embodiment, after the medium-pressure filling stage completes the switch to the high-pressure filling stage according to the aforementioned steps, the high-pressure filling stage uses the high-pressure stage thermal equilibrium equivalent pressure as the high-pressure filling end feedback quantity. In this embodiment, before the high-pressure filling begins, a high-pressure stage thermal recovery calibration relationship is independently established for the high-pressure cylinder group and the corresponding high-pressure filling path. During high-pressure filling, the absolute pressure and absolute temperature of the medium-pressure cylinder group in step S2 are replaced with the absolute pressure and absolute temperature of the high-pressure cylinder group, respectively. The high-pressure stage thermal equilibrium equivalent pressure is formed according to the same isenthalpic throttling, thermal recovery calibration, and same mass state mapping rules. When the high-pressure stage thermal equilibrium equivalent pressure reaches the hot-pressing molding target pressure in the current hot-pressing molding process formula, the high-pressure filling of the high-pressure cylinder group into the mold cavity is terminated. This embodiment is independent of the aforementioned ordinary embodiment, and the operator does not temporarily select two high-pressure end rules in the same main implementation path.

[0116] For a high-pressure nitrogen thermoforming pressurization equipment with a north mold cavity and a south mold cavity, in another embodiment, independent mold numbers, mold cavity numbers, mold cavity pressure detection channels, mold cavity temperature detection channels, medium-pressure filling valve group numbers, and thermal recovery calibration relationships are established for the north mold cavity and the south mold cavity, respectively. The dynamic effective pressure difference of the north mold cavity is formed only using the absolute pressure of the mold cavity, the mold thermal balance reference temperature, and the thermal recovery calibration relationship corresponding to the north mold cavity, and the dynamic effective pressure difference of the south mold cavity is formed only using the data corresponding to the south mold cavity; the thermal recovery coefficients and calibration versions of the two mold cavities are not cross-referenced.

[0117] When changing the mold, altering the mold cavity geometry, changing the outlet valve of the medium-pressure cylinder group or the main throttling device in the medium-pressure filling passage, changing the mold thermal boundary temperature detection position, changing the temperature zone of the mold preheating process formula, or changing the version of the nitrogen thermophysical property lookup data, the PLC sets the thermal recovery calibration relationship corresponding to the original object combination to an invalid state. Before recompiling the nine pressure ratio calibration nodes for the corresponding object combination, the PLC will not allow that object combination to enter automatic medium-pressure dynamic effective differential pressure control. Modifying only the display text or HMI layout that is not involved in the above calculations and physical boundaries will not change the effective state of the thermal recovery calibration relationship.

[0118] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A step-by-step inflation control method for thermoforming based on dynamic differential pressure feedback, applied to a high-pressure nitrogen thermoforming pressurization equipment with a medium-pressure bottle group, a high-pressure bottle group, and a preheated mold cavity, characterized in that, include: During the filling of the mold cavity by the medium-pressure bottle group, the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, and the absolute pressure of the mold cavity are obtained simultaneously, and the mold thermal balance reference temperature that was determined before the start of medium-pressure filling is read. The throttling outlet temperature is determined based on the nitrogen isenthalpic throttling thermophysical property relationship between the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, and the absolute pressure of the mold cavity. The ratio of the absolute pressure of the mold cavity to the absolute pressure of the medium-pressure bottle group is determined as the pressure ratio, and the thermal recovery coefficient is determined based on the thermal recovery calibration relationship formed by the filling calibration data and corresponding to the pressure ratio. The transient gas equivalent temperature of the mold cavity is formed by the throttling outlet temperature, the mold thermal balance reference temperature and the thermal recovery coefficient. Based on the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal equilibrium state, the thermal equilibrium equivalent pressure is determined by the absolute pressure of the mold cavity, the equivalent temperature of the transient gas in the mold cavity, and the thermal equilibrium reference temperature of the mold. The dynamic effective pressure difference is formed by subtracting the thermal equilibrium equivalent pressure from the absolute pressure of the medium-pressure bottle group. When the dynamic effective pressure difference is not greater than the filling completion pressure difference threshold, the outlet valve of the medium-pressure bottle group is closed to terminate the medium-pressure filling, and the high-pressure bottle group is switched to continue filling the mold cavity.

2. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 1, characterized in that, The determination of the mold thermal balance reference temperature includes: Before the medium-pressure bottle group fills the mold cavity, the mold heating actuator preheats the mold according to the mold preheating target temperature in the current hot pressing process formula, and continuously obtains the mold thermal boundary temperature. A preheating stabilization window is constructed using continuous sampling points. When the difference between the maximum and minimum values ​​of the mold thermal boundary temperature within the preheating stabilization window is no greater than twice the temperature engineering resolution, and the arithmetic mean of the mold thermal boundary temperature within the preheating stabilization window is within the mold preheating temperature range specified in the current hot pressing molding process formula, the arithmetic mean of the mold thermal boundary temperature within the first preheating stabilization window that meets the above conditions is determined as the mold thermal balance reference temperature, and the mold thermal balance reference temperature is kept unchanged during this medium-pressure filling stage.

3. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 1, characterized in that, The throttling outlet temperature is determined based on the nitrogen isenthalpic throttling thermophysical property relationship between the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group, and the absolute pressure of the mold cavity, including: A lookup table of nitrogen thermal properties is pre-established, which includes at least discrete pressure nodes, discrete temperature nodes, and the specific enthalpy and compressibility factor corresponding to each pressure and temperature node. Based on the absolute pressure and absolute temperature of the medium-pressure cylinder group, determine the corresponding enthalpy before throttling from the nitrogen thermophysical property lookup table data; Using the absolute pressure of the mold cavity as the pressure after throttling, find the temperature within the temperature range corresponding to the absolute pressure of the mold cavity that makes the specific enthalpy of nitrogen equal to the specific enthalpy before throttling, and determine the temperature as the throttling outlet temperature. Wherein, the throttling outlet temperature satisfies: ； In the formula, Indicates the current sampling time; For nitrogen gas at absolute pressure and absolute temperature Enthalpy below; This refers to the absolute pressure of the medium-pressure bottle group. This refers to the absolute temperature of the medium-pressure bottle group. This refers to the absolute pressure within the mold cavity. This refers to the outlet temperature of the throttling system.

4. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 2, characterized in that, The formation of the thermal recovery calibration relationship includes: The effective range of the pressure ratio is determined based on the minimum absolute pressure of the mold cavity that allows the start of medium-pressure filling, the maximum absolute pressure that allows the medium-pressure bottle group, and the minimum pressure difference required to complete medium-pressure filling as specified in the hot pressing process formula. Multiple pressure ratio calibration nodes are set within the effective range of the pressure ratio; Medium-pressure charging calibration was performed at each pressure ratio calibration node to generate the thermal recovery coefficient corresponding to each pressure ratio calibration node; The pressure ratio calibration nodes and their corresponding thermal recovery coefficients are stored in ascending order of pressure ratio, and linear interpolation is performed between adjacent pressure ratio calibration nodes to form the thermal recovery calibration relationship.

5. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 4, characterized in that, The intermediate pressure filling calibration performed at each pressure ratio calibration node includes: before the start of intermediate pressure filling in each calibration cycle, keeping the mold thermal boundary temperature within the mold preheating temperature range specified in the current hot pressing molding process formula, and determining the mold thermal balance reference temperature for this calibration cycle based on the arithmetic average of the mold thermal boundary temperatures of continuous sampling points that meet the preheating stability conditions. With the high-pressure filling passage, recovery passage and venting passage connected to the mold cavity closed, the medium-pressure bottle group fills the mold cavity, and the absolute pressure of the medium-pressure bottle group, the absolute temperature of the medium-pressure bottle group and the absolute pressure of the mold cavity are obtained simultaneously to calculate the current pressure ratio. When the current pressure ratio reaches or exceeds the current pressure ratio calibration node for the first time, the outlet valve of the medium-pressure bottle group is closed, so that the filling pipeline downstream of the outlet valve of the medium-pressure bottle group forms a closed gas space with the mold cavity, and the calibrated transient pressure of the mold cavity, the calibrated absolute pressure of the medium-pressure bottle group, the calibrated absolute temperature of the medium-pressure bottle group and the thermal balance reference temperature of the mold are recorded. Continue to maintain the mold thermal boundary temperature and continuously obtain the absolute pressure and thermal boundary temperature of the mold cavity. When two consecutive thermal balance observation windows meet the stability conditions of the mold thermal boundary temperature and absolute pressure of the mold cavity, and the absolute value of the difference between the arithmetic mean of the absolute pressure of the mold cavity in the two consecutive thermal balance observation windows is not greater than twice the pressure engineering resolution, the arithmetic mean of the absolute pressure of the mold cavity in the latter thermal balance observation window is determined as the mold cavity calibration thermal balance pressure corresponding to the pressure ratio calibration node.

6. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 5, characterized in that, The formation of the thermal recovery coefficient corresponding to each pressure ratio calibration node includes: The calibrated throttling outlet temperature is determined based on the calibrated absolute pressure of the medium-pressure bottle group, the calibrated absolute temperature of the medium-pressure bottle group, and the calibrated transient pressure of the mold cavity, according to the isenthalpic throttling thermophysical property relationship of nitrogen. Based on the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the closing time of the outlet valve of the medium-pressure cylinder group and the thermal balance reference state characterized by the calibrated thermal balance pressure of the mold cavity and the thermal balance reference temperature of the mold, the equivalent temperature of the calibrated transient gas in the mold cavity is calculated by back-calculating the calibrated transient gas temperature in the mold cavity from the calibrated transient pressure of the mold cavity, the calibrated thermal balance pressure of the mold cavity, and the thermal balance reference temperature of the mold. The thermal recovery coefficient calibration value is determined based on the calibrated transient gas equivalent temperature of the mold cavity, the calibrated throttling outlet temperature, and the mold thermal balance reference temperature. The thermal recovery coefficient calibration value satisfies the following: ; In the formula, This is the calibration value for the thermal recovery coefficient; Calibrate the transient gas equivalent temperature for the mold cavity; To calibrate the throttling outlet temperature; This is the reference temperature for mold thermal balance. The arithmetic mean of the thermal recovery coefficient calibration values ​​formed by multiple effective calibration cycles for the same pressure ratio calibration node is taken, and the arithmetic mean is determined as the thermal recovery coefficient corresponding to the pressure ratio calibration node.

7. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 1, characterized in that, The equivalent pressure for thermal equilibrium is determined according to the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal equilibrium state, satisfying: ； In the formula, Indicates the current sampling time; This refers to the absolute pressure within the mold cavity. The equivalent temperature of the transient gas in the mold cavity; Equivalent pressure for thermal equilibrium; This is the reference temperature for mold thermal balance. For nitrogen gas at absolute pressure and absolute temperature The compression factor is below.

8. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 7, characterized in that, The equivalent thermal equilibrium pressure is determined through a pre-formed thermal equilibrium pressure conversion lookup table, including: A three-dimensional input node combination is formed by the absolute pressure node of the mold cavity, the equivalent temperature node of the transient gas in the mold cavity, and the thermal balance reference temperature node of the mold. For each combination of three-dimensional input nodes, the corresponding equivalent thermal equilibrium pressure is determined offline according to the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal equilibrium state, and the equivalent thermal equilibrium pressure is written into the thermal equilibrium pressure conversion lookup table data. During medium-pressure filling, the current absolute pressure of the mold cavity, the current transient gas equivalent temperature of the mold cavity, and the mold thermal balance reference temperature are used as inputs. The adjacent grids surrounding the current input state are determined from the thermal balance pressure conversion lookup table data, and trilinear interpolation is performed on the thermal balance equivalent pressures corresponding to the adjacent grids to form the thermal balance equivalent pressure at the current sampling time.

9. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 1, characterized in that, After switching to the high-pressure cylinder group to continue filling the mold cavity, the process further includes: A high-pressure stage thermal recovery calibration relationship is pre-established for the high-pressure cylinder group and high-pressure filling passage; During high-pressure filling, the absolute pressure of the high-pressure cylinder group, the absolute temperature of the high-pressure cylinder group, and the absolute pressure of the mold cavity are obtained. The throttling outlet temperature of the high-pressure stage is determined based on the nitrogen isenthalpic throttling thermophysical property relationship between the absolute pressure of the high-pressure cylinder group, the absolute temperature of the high-pressure cylinder group, and the absolute pressure of the mold cavity. The equivalent temperature of transient gas in the mold cavity during the high-pressure stage is determined based on the thermal recovery calibration relationship of the high-pressure stage, and the equivalent pressure of thermal equilibrium during the high-pressure stage is determined according to the nitrogen state relationship where the same gas mass and the same effective volume remain unchanged between the current transient state and the thermal equilibrium state. When the equivalent pressure of thermal balance in the high-pressure stage reaches the target pressure for hot pressing as specified in the current hot pressing process formula, the high-pressure injection of the high-pressure bottle group into the mold cavity is terminated.

10. The step-by-step inflation control method for hot pressing molding based on dynamic differential pressure feedback according to claim 1, characterized in that, The high-pressure nitrogen thermoforming booster equipment includes a first mold cavity and a second mold cavity; For the first mold cavity and the second mold cavity, respectively, the corresponding absolute pressure and mold thermal balance reference temperature of the mold cavity are obtained, and the corresponding thermal recovery calibration relationship is established respectively. During medium-pressure filling of the first mold cavity, the dynamic effective pressure difference corresponding to the first mold cavity is formed based on the absolute pressure of the mold cavity, the mold thermal balance reference temperature, and the thermal recovery calibration relationship of the first mold cavity. During medium-pressure filling of the second mold cavity, the dynamic effective pressure difference corresponding to the second mold cavity is formed based on the absolute pressure of the mold cavity, the mold thermal balance reference temperature, and the thermal recovery calibration relationship. The medium-pressure filling stage of each mold cavity is switched according to the dynamic effective pressure difference of each mold cavity.

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