Variable frequency air extraction control method for mold machining oil mist exhaust gas

Abstract

The present application relates to oil mist exhaust gas extraction control technical field, specifically relates to a kind of mould machining oil mist exhaust gas variable frequency air extraction control method.The method includes: the real-time active current of machine tool spindle motor is collected and the spindle speed is read;Effective rotary radius of tool is read;The cutting line speed is determined using the spindle speed and effective rotary radius, the oil mist particle radius is mapped, the gravity limit settling velocity of oil mist particle is calculated based on Stokes law;Based on real-time active current, the local hot plume rising wind speed is calculated, the local hot plume rising wind speed is subtracted from the gravity limit settling velocity, to obtain net escape velocity;Active current and net escape velocity are combined to construct state machine matrix;When the aerosol suspension escape state caused by low load is identified, control the variable frequency output full load wind pressure to intercept.The present application realizes the effective interception of virulent oil mist under all working conditions, and improves the air cleanliness of precision mould machining workshop.

Description

Technical Field

[0001] This invention relates to the field of oil mist exhaust gas extraction and control technology, specifically to a frequency conversion exhaust gas extraction and control method for oil mist exhaust gas from mold machining. Background Technology

[0002] In modern precision mold manufacturing workshops, such as those producing complex deep-cavity molds using CNC machining, the high-speed rotation of the machine tool spindle and the cutting of the cutting tool cause the high-pressure coolant to undergo centrifugal breakage, forming a large amount of oil mist exhaust gas suspended in the enclosed chamber. To ensure the cleanliness of the workshop air, exhaust fans driven by frequency converters are usually configured for dust extraction. For the frequency conversion control of exhaust fans, existing technologies generally adopt a single linear following logic based on electrical load feedback. For example, Chinese patent application CN102185560A discloses a motor energy-saving frequency conversion control method, which achieves frequency conversion energy-saving control by reducing the reference frequency and fan speed when the equipment is under light load conditions, i.e., when the load current is small. Another example is Chinese patent application CN105450135A, which discloses an automatic energy-saving and flexible torque-boosting VF control method, which automatically adjusts the output of the frequency converter when the load is small by detecting the load current of the motor in real time, thereby achieving energy-saving and environmental protection effects.

[0003] Current technology suggests that the smaller the electrical load of the equipment, the less pollutants are generated, and the frequency conversion speed of the exhaust fan should be actively reduced to save energy. However, in high-speed precision milling scenarios of complex deep cavity molds, tools with small turning radii and shallow cutting depths are usually used. The spindle motor does very little work to overcome cutting resistance, resulting in extremely low real-time active current. Once the controller obtains the extremely low spindle current, the current technology will misjudge that the current state is safe and low-emission, and then send a frequency reduction energy-saving command to the frequency converter, causing the dust collector fan to enter a low-frequency sleep state.

[0004] However, the machine tool spindle rotates at extremely high speeds, and the extreme centrifugal shearing force pulverizes the cutting fluid into submicron-sized aerosols with a gravity settling velocity close to 0. At the same time, the local cutting friction heat at the tool tip heats the surrounding tiny air masses, forming a weak upward-directed local thermal plume. Because the submicron-sized aerosols are relatively light, this weak thermal plume lifts them upward and creates a suspended escape state. At this time, the exhaust fan is kept in a low-frequency dormant state by the control system and cannot output enough downward negative pressure to intercept it. Summary of the Invention

[0005] To address the problem of fine oil mist easily escaping during precision machining in existing technologies, this invention proposes a variable frequency exhaust control method for oil mist exhaust gas from mold machining. This method includes:

[0006] S1. Obtain the real-time active current and spindle speed of the machine tool spindle motor, and read the effective turning radius of the current cutting tool; S2. Calculate the cutting linear velocity based on the spindle speed and the effective turning radius, and then map the oil mist particle radius to calculate the downward gravity-limited settling velocity of the oil mist particles; S3. Based on the real-time active current, calculate the upward local thermal plume rise speed inside the machine tool compartment, subtract the local thermal plume rise speed from the gravity-limited settling velocity to obtain the net escape velocity; S4. Compare the real-time active current with a preset no-load mechanical loss current threshold, and compare the net escape velocity with a preset background disturbance wind speed threshold. When the real-time active current is greater than the no-load mechanical loss current threshold and the net escape velocity is greater than the background disturbance wind speed threshold, it is determined that the machine tool is in an aerosol suspension escape state, and the frequency converter of the exhaust fan is controlled to output the full-load operating frequency for interception.

[0007] This invention effectively solves the problem of oil mist leakage during the finishing stage by extracting the escape trend of submicron aerosols caused by high rotation speed under extremely low electrical load conditions of machine tools, and simultaneously identifying high-risk conditions and implementing full-load ventilation interception, thus achieving efficient interception under all working conditions.

[0008] Furthermore, the acquisition of the real-time active current of the machine tool spindle motor includes: acquiring the transient AC current signal of the spindle motor, extracting the active component in the transient AC current signal, and performing smoothing filtering on the active component to obtain the real-time active current.

[0009] This invention effectively removes high-frequency inverter noise and false excitation current in industrial power grids by extracting the active component from transient alternating current and performing smoothing filtering, ensuring the purity of the underlying decision data source and effectively avoiding false alarms caused by complex electromagnetic interference on site.

[0010] Further, the mapping to obtain the oil mist particle radius includes: obtaining a pre-established particle size mapping table, which records multiple cutting line speed ranges and corresponding oil mist particle radii; querying the particle size mapping table according to the cutting line speed, and extracting the matching oil mist particle radius.

[0011] This invention effectively reduces the computing power overhead of the edge controller and improves the real-time response speed of frequency conversion interception commands by pre-establishing a particle size mapping table and performing online queries.

[0012] Furthermore, calculating the downward gravity-limited settling velocity of the oil mist particles includes: obtaining the density difference between the cutting fluid and the ambient air and the aerodynamic viscosity parameters, combining them with the gravitational acceleration, constructing a fluid dynamics resistance model, and calculating the gravity-limited settling velocity.

[0013] Furthermore, the upward local thermal plume rise velocity within the computer bed cabin includes: acquiring a pre-configured thermodynamic calibration table, which contains the correspondence between different current amplitudes and the local air rise velocity within the cabin; retrieving a value matching the real-time active current from the thermodynamic calibration table; and outputting the corresponding local thermal plume rise velocity.

[0014] Furthermore, the variable frequency exhaust control method for oil mist exhaust gas in mold machining also includes: when the machine tool is not cutting and the spindle is running, testing and recording the reference current to maintain operation to generate the no-load mechanical loss current threshold; when the machine tool is stopped and closed, testing and recording the basic micro-wind speed in the chamber to generate the background disturbance wind speed threshold.

[0015] This invention improves the algorithm's anti-disturbance capability by online measurement and generation of no-load current threshold and background wind speed threshold, and by binding the determination dead zone with the mechanical resistance of a specific machine tool and the workshop micro-environment.

[0016] Furthermore, the variable frequency exhaust control method for oil mist exhaust gas in mold machining also includes: when the real-time active current is less than or equal to the no-load mechanical loss current threshold, determining that the machine tool is in a no-load state; issuing a basic standby frequency command to the frequency converter to control the exhaust fan to maintain a basic negative pressure.

[0017] Furthermore, the variable frequency exhaust control method for oil mist exhaust gas in mold machining also includes: when the real-time active current is greater than the no-load mechanical loss current threshold and the net escape velocity is less than or equal to the background disturbance wind speed threshold, the machine tool is determined to be in a gravity-dominated settling state; the output frequency of the inverter and the changing trend of the real-time active current are adjusted synchronously.

[0018] Furthermore, the variable frequency exhaust control method for oil mist exhaust gas in mold machining also includes: monitoring whether the machine tool has exited the aerosol suspension escape state; when the machine tool is identified as exiting the aerosol suspension escape state, a lockout delay mechanism is triggered, and the frequency converter is controlled to maintain the output of the full-load operating frequency within a preset lockout delay time.

[0019] This invention effectively eliminates the ping-pong oscillation effect caused by the immediate frequency reduction when the machine tool stops cutting. By controlling the frequency converter to maintain full-load operation, it ensures that the toxic aerosols remaining inside the machine tool are completely extracted before the operator opens the machine tool door, thus ensuring the safety of on-site personnel.

[0020] Furthermore, the locking delay time includes: acquiring the volume data of the machine tool compartment and the volumetric flow rate data of the exhaust fan under full load, and combining them with a preset air exchange rate index to calculate the time required to replace the residual air inside the machine tool compartment, which is used as the locking delay time.

[0021] The present invention has the following technical effects: When the present invention identifies an unloaded or gravity-dominated state with large particles, it saves energy by issuing standby or follow-up frequency reduction commands. However, when it identifies a high-risk suspended escape state, it ignores the low load appearance and outputs full-load wind pressure, thus achieving on-demand ventilation without sacrificing safety for energy saving. Furthermore, it transforms the control of a single electrical index into a multi-dimensional judgment based on electrical, thermodynamic, and fluid dynamics, making the control process transparent and the logical boundaries strict. Attached Figure Description

[0022] Figure 1 This is a flowchart of a variable frequency exhaust control method for oil mist exhaust gas in mold machining, provided by an embodiment of the present invention; Figure 2 This is a comparison diagram of the effects of the prior art provided in the embodiments of the present invention and the present invention. Detailed Implementation

[0023] This invention provides a variable frequency exhaust control method for oil mist exhaust gas from mold machining, referring to... Figure 1 This includes steps S1-S4: S1: Data Acquisition and Preprocessing.

[0024] Specifically, the real-time active current and spindle speed of the machine tool spindle motor are obtained, and the effective turning radius of the current cutting tool is read.

[0025] To avoid communication protocol barriers and data loss risks when acquiring high-frequency data from the machine tool's internal control bus, this embodiment preferably configures a high-frequency Hall current sensor on the three-phase AC output power line of the machine tool's spindle motor. The sampling frequency of this high-frequency Hall current sensor is set to 2000Hz to ensure complete capture of the sudden current surge signal at the moment of cutting contact of the micro-tool. Simultaneously, this embodiment preferably configures an edge computing gateway with independent serial computing capabilities. The edge computing gateway is directly connected to the machine tool's CNC system's host computer network port via an industrial Ethernet communication cable. The communication polling cycle of the edge computing gateway is set to 50ms to read the spindle speed fed back by the spindle encoder and the number of the currently invoked cutting tool in real time.

[0026] Because the power grid environment in industrial workshops is complex, the collected three-phase transient AC current signals contain inverter switching noise and high-frequency harmonics. Therefore, after receiving the three-phase transient AC current signals, the edge computing gateway performs fast Fourier transform processing on them, decomposing the three-phase transient AC current signals into excitation components and torque components. The excitation current component, which is only used to establish the internal magnetic field and does not perform external cutting work, is removed, and the active current amplitude reflecting the work done by the cutting resistance of the tool is extracted. Subsequently, the edge computing gateway performs moving average filtering on the extracted active current amplitude. In this embodiment, the moving average filtering window length is preferably set to 20 consecutive sampling points. By calculating the arithmetic mean of the data from 20 consecutive sampling points, random high-frequency glitches caused by transient fluctuations in the power grid are smoothed out, and finally a clean and smooth real-time active current is obtained.

[0027] It should be noted that before the machine tool equipment is officially put into operation, the effective turning radius of the cutting tools needs to be calibrated offline. The specific steps are as follows: First, a high-precision optical tool setter is used to perform optical profile scanning on all the tools in the machine tool tool magazine one by one; the maximum profile radius of each tool in the rotating state is extracted and recorded; the edge computing gateway establishes a correspondence table between tool number and effective turning radius in its internal non-volatile memory; during the machine tool cutting operation, the edge computing gateway performs address retrieval in the table based on the cutting tool number read in real time, and extracts the corresponding effective turning radius.

[0028] Simultaneously, offline experimental calibration of the no-load mechanical loss current threshold is required. The specific steps are as follows: First, control the machine tool spindle to be in a no-load operation state without clamping any workpiece and without any cutting contact; control the machine tool spindle to accelerate from zero speed to the highest spindle speed allowed by the machine tool in a stepwise manner, and maintain stable operation for 3 minutes at each speed step; during operation, the high-frequency Hall current sensor continuously collects the average current maintained by the spindle motor overcoming internal bearing friction and external air resistance; the microprocessor of the edge computing gateway extracts the maximum value of the average current at all test speeds; in order to prevent false triggering caused by voltage fluctuations in the workshop's natural power grid, this embodiment preferably multiplies the maximum value by an additional safety tolerance factor of 105%, and the final calculated result is the no-load mechanical loss current threshold.

[0029] S2: Calculation of gravity-limited settlement velocity.

[0030] Specifically, based on the spindle speed and effective gyration radius, the cutting linear velocity is calculated, which is then mapped to obtain the oil mist particle radius, and the downward gravity-limited settling velocity of the oil mist particles is calculated.

[0031] First, the spindle speed and effective turning radius obtained by S1 are called. The edge computing gateway multiplies the spindle speed with the effective turning radius and twice the value of pi. After completing the engineering unit conversion, the cutting speed under the current working condition is obtained. This cutting speed determines the magnitude of the centrifugal shear force on the cutting fluid at the cutting tip.

[0032] Subsequently, the corresponding oil mist particle radius is obtained based on the cutting linear velocity mapping. In this embodiment, the oil mist particle radius is preferably extracted using a preset particle size mapping table, which is calibrated through a standardized offline experiment. The specific steps are as follows: a high-precision explosion-proof laser particle size analyzer is configured in a machine tool sealed calibration chamber. The machine tool is controlled to run idle under standard exhaust conditions without cutting heat interference, and at the same time, the cooling pump is started to spray standard cutting fluid. The machine tool spindle performs stepped operation, and at each linear velocity gradient, the laser particle size analyzer continuously collects the sortopy value of suspended droplets in the air inside the chamber. The average diameter is determined by three independent repeated tests, after which larger errors are removed. The arithmetic mean of the remaining valid data is taken as the average oil mist particle radius. Through the above experimental steps, the correspondence between different cutting speed ranges and the average oil mist particle radius can be obtained. A particle size mapping table is generated and stored in the non-volatile memory of the edge computing gateway. During the actual operation and control of the machine tool, the edge computing gateway directly performs retrieval and linear interpolation in the particle size mapping table based on the cutting speed calculated in real time, accurately mapping the oil mist particle radius that matches the current cutting state.

[0033] After obtaining the radius of the oil mist particles, the gravitational settling velocity of the oil mist particles is calculated based on Stokes' law in classical fluid dynamics. First, the edge computing gateway extracts the radius of the oil mist particles and squares it. In this embodiment, the gravitational acceleration is preferably set to 9.81 m / s². 2 The system multiplies the square of the oil mist particle radius, the gravitational acceleration parameter, and the pre-input density difference between the cutting fluid and ambient air to obtain the numerator of the fluid dynamics. Simultaneously, it obtains the pre-stored aerodynamic viscosity constant under the current constant temperature environment of the workshop, multiplies this aerodynamic viscosity constant by the inherent constant coefficient of the Stokes equation (which is 18), to obtain the denominator of the drag. Finally, the edge computing gateway divides the numerator of the fluid dynamics by the denominator of the drag to obtain the gravitational limit settling velocity, which is vertically downward.

[0034] S3: Local thermal plume updraft speed mapping and net escape velocity calculation.

[0035] Specifically, based on the real-time active current, the upward wind speed of the local thermal plume inside the computer bed cabin is calculated. The net escape velocity is obtained by subtracting the upward wind speed of the local thermal plume from the gravity-limited settling velocity.

[0036] First, based on the real-time active current obtained by S1, the rising velocity of the local thermal plume within the machine tool's sealed chamber is mapped. In this embodiment, the rising velocity of the local thermal plume is extracted using a preset thermodynamic calibration table, which is calibrated through an offline experiment. The specific steps are as follows: In a controlled, standard constant-temperature machine tool sealed chamber, all external airflow interference sources such as dust removal and exhaust are cut off. To maintain consistency with the actual machining exhaust conditions of the machine tool, the cooling pump is started to spray standard cutting fluid, and the spindle motor is controlled to run continuously under load current steps, thereby reproducing the different cutting friction heat generation power and the state of the cutting fluid in the high-temperature zone at the tool tip during machining. Simultaneously, three high-precision thermal anemometers are deployed in an array at the exhaust throat directly above the machining area of ​​the machine tool tool tip. Thermal equilibrium is achieved in the local thermal field induced by each load current step. After reaching the equilibrium state, the thermal anemometer continuously collects the rising air velocity generated by the local air thermal expansion and the vaporization of the cutting fluid. It should be noted that the above-mentioned thermal equilibrium state is that within a set time window, the fluctuation range of the wind speed data collected by the thermal anemometer is less than the preset small tolerance, which indicates that the local gas-liquid two-phase thermal plume flow field has reached dynamic stability. In this embodiment, it is preferred that within 60 seconds, the absolute value of the first derivative of the data collected by the three thermal anemometers is less than 0.05 m / s. The arithmetic mean of the wind speed data collected by the three thermal anemometers at the same time is calculated to achieve spatial flow field smoothing. After three independent repeated measurements and calculation of the arithmetic mean, the correspondence between the active current of the spindle motor and the local air rising wind velocity in the machine tool cabin is established, a thermodynamic calibration table is generated, and it is stored in the non-volatile memory of the edge computing gateway.

[0037] In machine tool cutting operation control, the edge computing gateway extracts the smoothed real-time active current, uses this real-time active current to search and compare in the thermodynamic calibration table, and combines linear interpolation algorithm to calculate and output the local thermal plume rising wind speed corresponding to the current working condition and in the vertical upward direction.

[0038] Subsequently, the edge computing gateway extracts the updraft velocity of the local thermal plume, which is vertically upward, and subtracts it from the gravitational limit settling velocity obtained from S2, thus obtaining the net escape velocity. The specific calculation logic is as follows: taking the vertically upward direction as the positive direction in space, the absolute value of the updraft velocity of the local thermal plume is taken as the positive term, and the absolute value of the gravitational limit settling velocity is taken as the negative term. The positive term and the negative term are algebraically added together, which is essentially a subtraction operation on the physical vector. The final algebraic calculation result is the net escape velocity. When the value of the net escape velocity is greater than zero, it physically indicates that the upward thermal lifting force is greater than the gravitational constraint of the particles themselves, indicating that the submicron aerosol has the aerodynamic conditions to suspend upward and escape from the machine tool compartment.

[0039] S4: Multidimensional state machine matrix determination and asymmetric instruction execution.

[0040] Specifically, the real-time active current is compared with the preset no-load mechanical loss current threshold, and the net escape velocity is compared with the preset background disturbance wind speed threshold. When the real-time active current is greater than the no-load mechanical loss current threshold and the net escape velocity is greater than the background disturbance wind speed threshold, the machine tool is determined to be in an aerosol suspension escape state, and the frequency converter of the exhaust fan is controlled to output the full-load operating frequency to intercept it.

[0041] To effectively define and accurately transition between control states, the edge computing gateway, in addition to calling the no-load mechanical loss current threshold determined by S1, also needs to call the workshop background disturbance wind speed threshold. This workshop background disturbance wind speed threshold is calibrated through an offline field experiment. The specific steps are as follows: with the machine tool stopped and the protective door completely sealed, a high-precision thermal anemometer probe is placed in the core area of ​​the machine tool's internal compartment to continuously collect the wind speed at the air outlet of the constant temperature and humidity air conditioner in the workshop, obtaining a micro-wind speed sequence. The microprocessor of the edge computing gateway calculates the arithmetic mean of this sequence, and adds twice the standard deviation value to the arithmetic mean to construct the upper bound of the 95% confidence interval, which is the workshop background disturbance wind speed threshold.

[0042] During machine tool operation, the microprocessor of the edge computing gateway performs matrix comparison in each communication cycle, comparing the real-time active current with the no-load mechanical loss current threshold, and simultaneously comparing the net escape velocity with the workshop background disturbance wind speed threshold. Based on the comparison results, it enters one of the following three control states and sends physical control commands downstream: When the microprocessor determines that the real-time active current is less than or equal to the no-load mechanical loss current threshold, it triggers the first state, namely the no-load insulation state, and controls the machine tool to perform mechanical actions such as rapid positioning. The tool and the workpiece do not make cutting contact, and there is no source of cutting fluid atomization in the chamber. The edge computing gateway sends the basic standby frequency command to the frequency converter of the exhaust fan, thereby controlling the exhaust fan to maintain the basic speed and only maintaining the basic negative pressure in the exhaust duct to prevent external airflow backflow. When the microprocessor determines that the real-time active current is greater than the no-load mechanical loss current threshold and the net escape velocity is less than or equal to the background disturbance wind speed threshold of the workshop, it triggers the second state, namely the gravity-dominated settling state. At this time, the machine tool is in the roughing stage. The oil droplets generated by the machine tool cutting have a large mass. The settling velocity generated by their own gravitational potential energy is greater than the upward lifting force of the local thermal plume. The edge computing gateway generates a following frequency command that is linearly mapped to the magnitude of the real-time active current and sends it to the frequency converter, thereby smoothly and energy-efficiently extracting the conventional hot air mass generated by cutting. When the microprocessor determines that the real-time active current is greater than the no-load mechanical loss current threshold and that the net escape velocity is greater than the background disturbance wind speed threshold in the workshop, it triggers the third state, namely the high-risk state of suspension escape. At this time, the machine tool spindle speed is high and the depth of cut is small. The machine tool is in the fine surface polishing stage and the active current is low. However, under the extreme centrifugal shearing action, the gravity settling velocity of the aerosol is small. The edge computing gateway cuts off all frequency reduction energy-saving control loops based on the low load appearance. The microprocessor skips levels and writes the limit full-load operating frequency instruction into the control register of the frequency converter. The frequency converter drives the exhaust fan to output a full-load physical high negative pressure flow field. Relying on the directional suction force to destroy the upward weak thermal plume structure, it sucks in the suspended and diffused highly toxic aerosol.

[0043] In addition, to prevent the frequency reduction caused by the decrease in active current when the machine tool stops processing, which could lead to the leakage of residual aerosols, this embodiment preferably configures an asymmetric timing cleanup and latching mechanism in the control logic. When the state machine judgment logic of the edge computing gateway switches from the high-risk third state to the safe first state, the interrupt latch inside the microprocessor prevents the inverter from immediately executing the frequency reduction instruction, and at the same time activates the internal countdown timer to control the inverter to continue operating at the extreme full-load operating frequency for a latching delay time.

[0044] For the lockout delay time, first read the sealed volume of the machine tool processing chamber and the volumetric flow rate of the centrifugal exhaust fan under extreme full-frequency operation conditions; combined with industrial-grade air cleanliness standards, set the air exchange rate index to 1.5 times; the microprocessor multiplies the sealed volume by the air exchange rate index, and then divides the product by the volumetric flow rate to finally obtain the time required to clean the residual suspended aerosols in the chamber. This time is used as the lockout delay time. Only when the countdown timer is cleared will the interrupt latch release the frequency reduction permission, allowing the frequency converter to gradually reduce the operating frequency.

[0045] Figure 2 This is a comparison diagram of the effects of the prior art and the present invention provided in the embodiments of the present invention. It can be seen that in the high-speed low-load precision machining stage, the active current drops significantly. The prior art is limited by the low load phenomenon and incorrectly issues a frequency reduction command, causing the exhaust fan speed to drop sharply. However, the present invention, through the state machine matrix, successfully identifies the hidden aerosol suspension escape state in this stage, cuts off the conventional frequency reduction energy-saving circuit, outputs the full-load operating frequency, and controls the aerosol escape concentration near the safety bottom line.

Claims

1. A variable frequency extraction control method for mold machining oil mist exhaust gas, characterized by, include: S1, acquire the real-time active current and spindle speed of the machine tool spindle motor, and read the effective turning radius of the current cutting tool; S2, calculate the cutting line speed based on the spindle speed and the effective turning radius, and then map the oil mist particle radius to calculate the downward gravity limit settling velocity of the oil mist particles; S3. Based on the real-time active current, the upward wind speed of the local thermal plume inside the computer bed cabin is calculated. The net escape velocity is obtained by subtracting the upward wind speed of the local thermal plume from the gravity-limited settling velocity. S4, compare the real-time active current with the preset no-load mechanical loss current threshold, and compare the net escape velocity with the preset background disturbance wind speed threshold. When the real-time active current is greater than the no-load mechanical loss current threshold and the net escape velocity is greater than the background disturbance wind speed threshold, determine that the machine tool is in an aerosol suspension escape state, and control the frequency converter of the exhaust fan to output the full-load operating frequency to intercept it.

2. The variable frequency air extraction control method of oil mist exhaust gas of a mold machining according to claim 1, characterized by, The process of obtaining the real-time active current of the machine tool spindle motor includes: acquiring the transient AC current signal of the spindle motor, extracting the active component from the transient AC current signal, and performing smoothing filtering on the active component to obtain the real-time active current.

3. The variable frequency air extraction control method of oil mist exhaust gas of a mold machining according to claim 1, characterized by, The mapping to obtain the oil mist particle radius includes: obtaining a pre-established particle size mapping table, which records multiple cutting line speed ranges and corresponding oil mist particle radii; and querying the particle size mapping table according to the cutting line speed to extract the matching oil mist particle radius.

4. The variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 1, characterized in that, Calculating the downward gravity-limited settling velocity of the oil mist particles includes: obtaining the density difference between the cutting fluid and ambient air and the aerodynamic viscosity parameters, combining them with the gravitational acceleration, constructing a fluid dynamic resistance model, and calculating the gravity-limited settling velocity.

5. The variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 1, characterized in that, The upward local thermal plume rise velocity within the computer bed cabin includes: acquiring a pre-configured thermodynamic calibration table, which contains the correspondence between different current amplitudes and the local air rise velocity within the cabin; retrieving a value matching the real-time active current from the thermodynamic calibration table; and outputting the corresponding local thermal plume rise velocity.

6. The variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 1, characterized in that, The method further includes: testing and recording the reference current for maintaining operation when the machine tool is not cutting and the spindle is running, and generating the no-load mechanical loss current threshold; testing and recording the basic micro-wind speed inside the cabin when the machine tool is stopped and closed, and generating the background disturbance wind speed threshold.

7. The variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 1, characterized in that, The method further includes: determining that the machine tool is in an unloaded state when the real-time active current is less than or equal to the no-load mechanical loss current threshold; issuing a basic standby frequency command to the frequency converter to control the exhaust fan to maintain basic negative pressure.

8. The variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 1, characterized in that, The method further includes: when the real-time active current is greater than the no-load mechanical loss current threshold and the net escape velocity is less than or equal to the background disturbance wind speed threshold, determining that the machine tool is in a gravity-dominated settlement state; and synchronously adjusting the output frequency of the inverter and the changing trend of the real-time active current.

9. The variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 1, characterized in that, The method further includes: monitoring whether the machine tool exits the aerosol suspension escape state; when the machine tool exits the aerosol suspension escape state, triggering a lockout delay mechanism, and controlling the frequency converter to maintain the output of the full-load operating frequency within a preset lockout delay time.

10. A variable frequency exhaust control method for oil mist exhaust gas in mold machining according to claim 9, characterized in that, The locking delay time includes: acquiring the volume data of the machine tool compartment and the volumetric flow rate data of the exhaust fan under full load, and combining it with a preset air exchange rate index to calculate the time required to replace the residual air inside the machine tool compartment, which is used as the locking delay time.

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