Pressure control method and system for low-pressure casting machine

Abstract

The invention discloses a pressure control method for a low-pressure casting machine, which relates to the field of low-pressure casting machines, and comprises the following steps of: setting pressurization time periods corresponding to casting sections, setting target pressure values corresponding to starting time points and ending time points in the pressurization time periods, and generating corresponding target pressure curves; target pressure values corresponding to all time points in the pressurization time period are obtained on the basis of the target pressure curve, in the subsequent casting process, real-time air pressure values in the smelting furnace are collected, the difference value between the real-time air pressure values and the target pressure values at the corresponding time points is obtained, and digital quantity control signals at the next time point are obtained through the difference value, that is, digital quantity control signals at the next time point are obtained. According to the method, the output of the next time point is controlled through the difference value between the real-time air pressure value and the target pressure value at the current time point, so that the opening degree of the pneumatic proportional valve is continuously adjusted, and the actual air pressure value in the whole casting process is close to the corresponding target pressure value as much as possible; therefore, the pressure control precision in the casting process is improved.

Description

Technical Field

[0001] The present invention relates to the field of low-pressure casting machines, and in particular to a pressure control method and system for low-pressure casting machines. Background Art

[0002] In recent years, with the rapid development of lightweight automobiles, low-pressure casting technology has been widely used. The existing low-pressure casting machines control the pressure in the furnace during the casting process by controlling the air path directional valve. However, due to the limitation of the structure of the air path directional valve itself, it can only control the switch of the valve but not the opening size of the valve, which makes the pressure control accuracy low and unstable, affecting the stability of product quality and the yield rate. To solve this problem, the present invention adopts a high-precision pneumatic proportional valve and realizes precise control of the pressure of each casting section by controlling the opening of the pneumatic proportional valve. Summary of the invention

[0003] In order to improve the pressure control accuracy in each casting section, the present invention proposes a pressure control method for a low-pressure casting machine, by setting a pneumatic proportional valve in the low-pressure casting machine and controlling the opening of the pneumatic proportional valve to achieve pressure control of each casting section, the pressure control method includes: S1: Set the pressurization time period corresponding to each casting section, and set the target pressure value corresponding to the start time point and the end time point in each pressurization time period; in adjacent pressurization time periods, the target pressure value corresponding to the end time point of the previous pressurization time period is equal to the target pressure value at the start time point of the next pressurization time period; S2: generating a target pressure curve with the time points in each pressurization time period as the horizontal coordinate and the target pressure values ​​corresponding to the start time point and the end time point in each pressurization time period as the vertical coordinate; S3: obtaining the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve; S4: During the casting process, the real-time air pressure value in the furnace is collected, the difference between the real-time air pressure value and the target pressure value at the corresponding time point is obtained, and the digital control signal at the next time point is obtained through the difference; S5: Convert the digital control signal into a voltage signal, and control the opening of the pneumatic proportional valve through the voltage signal.

[0004] Furthermore, the casting section includes the following consecutive sections: a liquid raising section, a mold filling section, a pressurizing section, a pressure maintaining and solidifying section, and a pressure reducing and cooling section.

[0005] Furthermore, in the step S3, obtaining the target pressure value corresponding to each time point in the pressurization time period includes: S31: Obtain the acceleration corresponding to the pressurization time period, and the formula for obtaining it is: ; Where n is a positive integer, Indicates the target pressure value at the end time point of the nth pressurization time period. It indicates the target pressure value at the end time point of the n-1th pressurization time period or the target pressure value at the start time point of the nth pressurization time period. Indicates the end time point corresponding to the nth pressurization time period, Indicates the end time point corresponding to the n-1th pressurization time period or the start time point corresponding to the nth pressurization time period, Indicates the acceleration corresponding to the nth pressurization time period; S32: Calculate the constant value corresponding to the pressurization time period according to the acceleration corresponding to the pressurization time period, and the calculation formula is: ; In the formula, Indicates the constant value corresponding to the nth pressurization time period; S33: Calculate the target pressure value corresponding to each time point in the pressurization time period by using the acceleration corresponding to the pressurization time period and the constant value. The calculation formula is: ; In the formula, represents any time point within the nth pressurization period, express The target pressure value corresponding to the time point.

[0006] Furthermore, in the step S4, the digital control signal at the next time point is obtained by the difference, and the acquisition formula is: ; In the formula, Indicates the current time point. Indicates the difference between the real-time pressure value and the target pressure value at the current time point. represents the differential time, represents the integration time, Represents the proportional coefficient of PID control, Indicates the digital control signal at the next time point.

[0007] The present invention also proposes a pressure control system for a low-pressure casting machine, which realizes pressure control of each casting section by arranging a pneumatic proportional valve in the low-pressure casting machine and controlling the opening of the pneumatic proportional valve. The pressure control system includes: A setting module is used to set the pressurization time period corresponding to each casting section, and set the target pressure value corresponding to the start time point and the end time point in each pressurization time period; in adjacent pressurization time periods, the target pressure value corresponding to the end time point of the previous pressurization time period is equal to the target pressure value at the start time point of the next pressurization time period; A curve generating module, used to generate a target pressure curve with the time points in each pressurization time period as the horizontal coordinate and the target pressure values ​​corresponding to the start time point and the end time point in each pressurization time period as the vertical coordinate; A target pressure value acquisition module, used to acquire the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve; A calculation module is used to collect the real-time air pressure value in the furnace during the casting process, obtain the difference between the real-time air pressure value and the target pressure value at the corresponding time point, and obtain the digital control signal at the next time point through the difference; The control module is used to convert the digital control signal into a voltage signal and control the opening of the pneumatic proportional valve through the voltage signal.

[0008] Furthermore, the casting section includes the following consecutive sections: a liquid raising section, a mold filling section, a pressurizing section, a pressure maintaining and solidifying section, and a pressure reducing and cooling section.

[0009] Furthermore, the target pressure value acquisition module specifically includes: The acceleration acquisition unit is used to acquire the acceleration corresponding to the pressurization time period. The acquisition formula is: ; Where n is a positive integer, Indicates the target pressure value at the end time point of the nth pressurization time period. It indicates the target pressure value at the end time point of the n-1th pressurization time period or the target pressure value at the start time point of the nth pressurization time period. Indicates the end time point corresponding to the nth pressurization time period, Indicates the end time point corresponding to the n-1th pressurization time period or the start time point corresponding to the nth pressurization time period, Indicates the acceleration corresponding to the nth pressurization time period; The constant value acquisition unit is used to calculate the constant value corresponding to the pressurization time period according to the acceleration corresponding to the pressurization time period. The calculation formula is: ; In the formula, Indicates the constant value corresponding to the nth pressurization time period; The target pressure value acquisition unit is used to calculate the target pressure value corresponding to each time point in the pressurization time period by using the acceleration corresponding to the pressurization time period and the constant value. The calculation formula is: ; In the formula, represents any time point within the nth pressurization period, express The target pressure value corresponding to the time point.

[0010] Furthermore, in the calculation module, the digital control signal at the next time point is obtained by the difference, and the acquisition formula is: ; In the formula, Indicates the current time point. Indicates the difference between the real-time pressure value and the target pressure value at the current time point. represents the differential time, represents the integration time, Represents the proportional coefficient of PID control, Indicates the digital control signal at the next time point.

[0011] Furthermore, the control module comprises: The analog output unit is used to convert the digital control signal into a voltage signal. The conversion formula is: ; In the formula, Indicates the resolution of the analog output unit. Indicates the digital control signal. Indicates voltage signal.

[0012] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention sets a pressurization time period corresponding to each casting section, sets a target pressure value corresponding to the start time point and the end time point in each pressurization time period, generates a corresponding target pressure curve, and obtains the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve. The present invention calculates the target pressure value corresponding to each time point in advance before casting begins. In the subsequent casting process, the real-time air pressure value in the furnace is collected to obtain the difference between the real-time air pressure value and the target pressure value at the corresponding time point, and obtains the digital control signal at the next time point through the difference. That is to say, the present invention controls the output at the next time point through the difference between the real-time air pressure value and the target pressure value at the current time point, thereby continuously adjusting the opening of the pneumatic proportional valve, so that the actual air pressure value in the entire casting process is as close as possible to the corresponding target pressure value, thereby improving the pressure control accuracy, and solving the problem in the prior art that, due to the limitation of the structure of the air path directional valve itself, only the switch of the valve can be controlled but the opening of the valve cannot be controlled, thereby resulting in low pressure control accuracy; (2) The present invention continuously adjusts the output at the next time point by the difference between the real-time air pressure value at the current time point and the target pressure value, that is, the output is controlled based on the real-time air pressure values ​​at adjacent time points, thereby improving the stability of pressure control. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a flow chart of a pressure control method for a low pressure casting machine; Figure 2 is the target pressure curve; Figure 3 This is a schematic diagram of aluminum liquid suspension; Figure 4 The module diagram of a pressure control system for a low-pressure casting machine.

[0014] In the figure: 1. furnace; 2. aluminum liquid level in the furnace; 3. compressed gas; 4. riser; 5. suspension liquid level; 6. aluminum liquid. DETAILED DESCRIPTION

[0015] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments. Embodiment 1

[0016] In order to solve the problem in the prior art that, due to the limitation of the structure of the gas path directional valve itself, only the switch of the valve can be controlled but the opening of the valve cannot be controlled, thus resulting in low pressure control accuracy, such as Figure 1 As shown, the present invention proposes a pressure control method for a low-pressure casting machine, by arranging a pneumatic proportional valve in the low-pressure casting machine and controlling the opening of the pneumatic proportional valve, the pressure control of each casting section is realized, and the casting section includes the following consecutive sections: a liquid rising section, a filling section, a pressurizing section, a pressure maintaining solidification section and a decompression cooling section; it should be noted that the filling section includes a filling front end and a crusting section.

[0017] The pressure control method comprises: S1: Set the pressurization time period corresponding to each casting section, and set the target pressure value corresponding to the start time point and the end time point in each pressurization time period; in adjacent pressurization time periods, the target pressure value corresponding to the end time point of the previous pressurization time period is equal to the target pressure value at the start time point of the next pressurization time period; the end time point corresponding to the previous pressurization time period is the start time point of the next pressurization time period; S2: generating a target pressure curve with the time points in each pressurization time period as the horizontal coordinate and the target pressure values ​​corresponding to the start time point and the end time point in each pressurization time period as the vertical coordinate; Specifically, Figure 2 As shown, the target pressure curve can be obtained by connecting two adjacent points into lines. The following is an example of the coordinates of the adjacent points corresponding to the boost section: (T3, P3), T3 represents the starting time point of the boost section, and P3 represents the target pressure value corresponding to the starting time point of the boost section; (T4, P4), T4 represents the end time point of the boost section, and P4 represents the target pressure value corresponding to the end time point of the boost section.

[0018] S3: obtaining the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve; In step S3, obtaining the target pressure value corresponding to each time point in the pressurization time period includes: S31: Obtain the acceleration corresponding to the pressurization time period, and the formula for obtaining it is: ; Where n is a positive integer, Indicates the target pressure value at the end time point of the nth pressurization time period. It indicates the target pressure value at the end time point of the n-1th pressurization time period or the target pressure value at the start time point of the nth pressurization time period. Indicates the end time point corresponding to the nth pressurization time period, Indicates the end time point corresponding to the n-1th pressurization time period or the start time point corresponding to the nth pressurization time period, Indicates the acceleration corresponding to the nth pressurization time period; It should be noted that in the first casting stage, Indicates the starting time point corresponding to the nth pressurization time period, Indicates the target pressure value at the starting time point of the nth pressurization time period.

[0019] S32: Calculate the constant value corresponding to the pressurization time period according to the acceleration corresponding to the pressurization time period, and the calculation formula is: ; In the formula, Indicates the constant value corresponding to the nth pressurization time period; S33: Calculate the target pressure value corresponding to each time point in the pressurization time period by using the acceleration corresponding to the pressurization time period and the constant value. The calculation formula is: ; In the formula, represents any time point within the nth pressurization period, Indicates the target pressure value corresponding to a time point.

[0020] S4: During the casting process, the real-time air pressure value in the furnace is collected, the difference between the real-time air pressure value and the target pressure value at the corresponding time point is obtained, and the digital control signal at the next time point is obtained through the difference; In the step S4, the digital control signal at the next time point is obtained by the difference, and the acquisition formula is: ; In the formula, Indicates the current time point. Indicates the difference between the real-time pressure value and the target pressure value at the current time point. represents the differential time, represents the integration time, Represents the proportional coefficient of PID control, Indicates the digital control signal at the next time point.

[0021] S5: Convert the digital control signal into a voltage signal, and control the opening of the pneumatic proportional valve through the voltage signal.

[0022] The present invention sets a pressurization time period corresponding to each casting section, sets a target pressure value corresponding to a start time point and an end time point in each pressurization time period, generates a corresponding target pressure curve, and obtains the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve. The present invention calculates the target pressure value corresponding to each time point in advance before casting begins. In the subsequent casting process, the real-time air pressure value in the furnace is collected to obtain the difference between the real-time air pressure value and the target pressure value at the corresponding time point, and obtains the digital control signal at the next time point through the difference. That is to say, the present invention controls the output at the next time point through the difference between the real-time air pressure value and the target pressure value at the current time point, thereby continuously adjusting the opening of the pneumatic proportional valve, so that the actual air pressure value in the entire casting process is as close as possible to the corresponding target pressure value, thereby improving the pressure control accuracy, and solving the problem in the prior art that, due to the limitation of the structure of the air path directional valve itself, only the switch of the valve can be controlled but the opening of the valve cannot be controlled, thereby resulting in low pressure control accuracy.

[0023] It should be noted that when the low-pressure casting machine performs a pressure relief action after the pressurization is completed, if the pressure is relieved to atmospheric pressure, the aluminum liquid in the riser will drop to the aluminum liquid level in the furnace, thereby affecting the temperature stability in the riser and prolonging the subsequent aluminum liquid rising time. Therefore, after completing a pressurization cycle (a pressurization cycle includes a complete and continuous casting stage pressure control), the present invention Figure 3 As shown, in order to ensure that the suspension liquid level 5 of the aluminum liquid 6 in the riser pipe 4 in the low-pressure casting machine is maintained above the aluminum liquid level 2 in the furnace, the pressure in the furnace 1 is controlled to be maintained at a fixed pressure value during pressure relief. The acquisition of the fixed pressure value includes: As the volume of aluminum liquid in the furnace changes, the fixed pressure value during pressure relief is obtained, and the formula is: ; in, Indicates the weight of a single casting product; Indicates the diameter of the furnace; Indicates the density of aluminum liquid; It indicates the height to which the aluminum liquid in the furnace drops after each production of a casting product or completion of a pressurized cycle; Indicates the height of the suspension surface from the aluminum liquid surface in the furnace under the initial state; Indicates the height of the current suspension surface from the aluminum liquid surface in the furnace. represents the acceleration due to gravity, Indicates the fixed pressure value when unloading; The input amount of the compressed gas 3 in the furnace is controlled based on a fixed pressure value.

[0024] The present invention not only realizes precise control of the pressure of each casting section, but also ensures that the suspended liquid level 5 of the aluminum liquid 6 in the riser tube 4 of the low-pressure casting machine is maintained above the aluminum liquid level 2 in the melting furnace when the pressure is released, thereby improving the temperature stability in the riser tube and reducing the subsequent aluminum liquid rising time. Embodiment 2

[0025] like Figure 4 As shown, the present invention also proposes a pressure control system for a low-pressure casting machine, which realizes pressure control of each casting section by arranging a pneumatic proportional valve in the low-pressure casting machine and controlling the opening of the pneumatic proportional valve. The casting section includes: a liquid raising section, a mold filling section, a pressurizing section, a pressure maintaining solidification section and a decompression cooling section in sequence; the pressure control system includes: A setting module is used to set the pressurization time period corresponding to each casting section, and set the target pressure value corresponding to the start time point and the end time point in each pressurization time period; in adjacent pressurization time periods, the target pressure value corresponding to the end time point of the previous pressurization time period is equal to the target pressure value at the start time point of the next pressurization time period; A curve generating module, used to generate a target pressure curve with the time points in each pressurization time period as the horizontal coordinate and the target pressure values ​​corresponding to the start time point and the end time point in each pressurization time period as the vertical coordinate; A target pressure value acquisition module, used to acquire the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve; The target pressure value acquisition module specifically includes: The acceleration acquisition unit is used to acquire the acceleration corresponding to the pressurization time period. The acquisition formula is: ; Where n is a positive integer, Indicates the target pressure value at the end time point of the nth pressurization time period. It indicates the target pressure value at the end time point of the n-1th pressurization time period or the target pressure value at the start time point of the nth pressurization time period. Indicates the end time point corresponding to the nth pressurization time period, Indicates the end time point corresponding to the n-1th pressurization time period or the start time point corresponding to the nth pressurization time period, Indicates the acceleration corresponding to the nth pressurization time period; The constant value acquisition unit is used to calculate the constant value corresponding to the pressurization time period according to the acceleration corresponding to the pressurization time period. The calculation formula is: ; In the formula, Indicates the constant value corresponding to the nth pressurization time period; The target pressure value acquisition unit is used to calculate the target pressure value corresponding to each time point in the pressurization time period by using the acceleration corresponding to the pressurization time period and the constant value. The calculation formula is: ; In the formula, represents any time point within the nth pressurization period, express The target pressure value corresponding to the time point.

[0026] A calculation module is used to collect the real-time air pressure value in the furnace during the casting process, obtain the difference between the real-time air pressure value and the target pressure value at the corresponding time point, and obtain the digital control signal at the next time point through the difference; In the calculation module, the digital control signal at the next time point is obtained by the difference, and the acquisition formula is: ; In the formula, Indicates the current time point. Indicates the difference between the real-time pressure value and the target pressure value at the current time point. represents the differential time, represents the integration time, Represents the proportional coefficient of PID control, Indicates the digital control signal at the next time point.

[0027] The control module is used to convert the digital control signal into a voltage signal and control the opening of the pneumatic proportional valve through the voltage signal.

[0028] The control module comprises: The analog output unit is used to convert the digital control signal into a voltage signal. The conversion formula is: ; In the formula, Indicates the resolution of the analog output unit. Indicates the digital control signal. Indicates voltage signal.

[0029] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0030] In addition, in the present invention, descriptions such as "first", "second", "one", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0031] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A pressure control method for a low pressure casting machine, characterized in that: By setting a pneumatic proportional valve in the low-pressure casting machine and controlling the opening of the pneumatic proportional valve, the pressure control of each casting section is achieved. The pressure control method includes: S1: Set the pressurization time period corresponding to each casting section, and set the target pressure value corresponding to the start time point and the end time point in each pressurization time period; in adjacent pressurization time periods, the target pressure value corresponding to the end time point of the previous pressurization time period is equal to the target pressure value at the start time point of the next pressurization time period; S2: generating a target pressure curve with the time points in each pressurization time period as the horizontal coordinate and the target pressure values ​​corresponding to the start time point and the end time point in each pressurization time period as the vertical coordinate; S3: obtaining the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve; S4: During the casting process, the real-time air pressure value in the furnace is collected, the difference between the real-time air pressure value and the target pressure value at the corresponding time point is obtained, and the digital control signal at the next time point is obtained through the difference; S5: Convert the digital control signal into a voltage signal, and control the opening of the pneumatic proportional valve through the voltage signal.

2. A pressure control method for a low pressure casting machine according to claim 1, characterized in that: The casting section includes the following consecutive sections: a liquid raising section, a mold filling section, a pressurizing section, a pressure maintaining and solidifying section, and a pressure reducing and cooling section.

3. A pressure control method for a low pressure casting machine according to claim 2, characterized in that: In step S3, obtaining the target pressure value corresponding to each time point in the pressurization time period includes: S31: Obtain the acceleration corresponding to the pressurization time period, and the formula for obtaining it is: ; Where n is a positive integer, Indicates the target pressure value at the end time point of the nth pressurization time period. It indicates the target pressure value at the end time point of the n-1th pressurization time period or the target pressure value at the start time point of the nth pressurization time period. Indicates the end time point corresponding to the nth pressurization time period, Indicates the end time point corresponding to the n-1th pressurization time period or the start time point corresponding to the nth pressurization time period, Indicates the acceleration corresponding to the nth pressurization time period; S32: Calculate the constant value corresponding to the pressurization time period according to the acceleration corresponding to the pressurization time period, and the calculation formula is: ; In the formula, Indicates the constant value corresponding to the nth pressurization time period; S33: Calculate the target pressure value corresponding to each time point in the pressurization time period by using the acceleration corresponding to the pressurization time period and the constant value. The calculation formula is: ; In the formula, represents any time point within the nth pressurization period, express The target pressure value corresponding to the time point.

4. A pressure control method for a low pressure casting machine according to claim 2, characterized in that: In the step S4, the digital control signal at the next time point is obtained by the difference, and the acquisition formula is: ； In the formula, Indicates the current time point. Indicates the difference between the real-time pressure value and the target pressure value at the current time point. represents the differential time, represents the integration time, Represents the proportional coefficient of PID control, Indicates the digital control signal at the next time point.

5. A pressure control system for a low pressure casting machine, characterized in that: By setting a pneumatic proportional valve in the low-pressure casting machine and controlling the opening of the pneumatic proportional valve, the pressure control of each casting section is achieved. The pressure control system includes: A setting module is used to set the pressurization time period corresponding to each casting section, and set the target pressure value corresponding to the start time point and the end time point in each pressurization time period; in adjacent pressurization time periods, the target pressure value corresponding to the end time point of the previous pressurization time period is equal to the target pressure value at the start time point of the next pressurization time period; A curve generating module, used to generate a target pressure curve with the time points in each pressurization time period as the horizontal coordinate and the target pressure values ​​corresponding to the start time point and the end time point in each pressurization time period as the vertical coordinate; A target pressure value acquisition module, used to acquire the target pressure value corresponding to each time point in the pressurization time period based on the target pressure curve; A calculation module is used to collect the real-time air pressure value in the furnace during the casting process, obtain the difference between the real-time air pressure value and the target pressure value at the corresponding time point, and obtain the digital control signal at the next time point through the difference; The control module is used to convert the digital control signal into a voltage signal and control the opening of the pneumatic proportional valve through the voltage signal.

6. A pressure control system for a low pressure casting machine according to claim 5, characterized in that: The casting section includes the following consecutive sections: a liquid raising section, a mold filling section, a pressurizing section, a pressure maintaining and solidifying section, and a pressure reducing and cooling section.

7. A pressure control system for a low pressure casting machine according to claim 6, characterized in that: The target pressure value acquisition module specifically includes: The acceleration acquisition unit is used to acquire the acceleration corresponding to the pressurization time period. The acquisition formula is: ; Where n is a positive integer, Indicates the target pressure value at the end time point of the nth pressurization time period. It indicates the target pressure value at the end time point of the n-1th pressurization time period or the target pressure value at the start time point of the nth pressurization time period. Indicates the end time point corresponding to the nth pressurization time period, Indicates the end time point corresponding to the n-1th pressurization time period or the start time point corresponding to the nth pressurization time period, Indicates the acceleration corresponding to the nth pressurization time period; The constant value acquisition unit is used to calculate the constant value corresponding to the pressurization time period according to the acceleration corresponding to the pressurization time period. The calculation formula is: ; In the formula, Indicates the constant value corresponding to the nth pressurization time period; The target pressure value acquisition unit is used to calculate the target pressure value corresponding to each time point in the pressurization time period by using the acceleration corresponding to the pressurization time period and the constant value. The calculation formula is: ; In the formula, represents any time point within the nth pressurization period, express The target pressure value corresponding to the time point.

8. A pressure control system for a low pressure casting machine according to claim 6, characterized in that: In the calculation module, the digital control signal at the next time point is obtained by the difference, and the acquisition formula is: ; In the formula, Indicates the current time point. Indicates the difference between the real-time pressure value and the target pressure value at the current time point. represents the differential time, represents the integration time, Represents the proportional coefficient of PID control, Indicates the digital control signal at the next time point.

9. A pressure control system for a low pressure casting machine according to claim 5, characterized in that: The control module comprises: The analog output unit is used to convert the digital control signal into a voltage signal. The conversion formula is: ; In the formula, Indicates the resolution of the analog output unit. Indicates the digital control signal. Indicates voltage signal.

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