Composite material multi-scale cutting dust grading and time-sharing monitoring and evaluation method

Abstract

The invention belongs to the field of dust monitoring, and provides a grading and time-sharing monitoring and evaluation method for multi-scale cutting dust of a composite material. According to the method, a flow field change condition and dust distribution information in a processing area are obtained based on a one-way coupling analysis method of computational fluid dynamics and a discrete element method, and then graded point distribution of a dust sensor is guided; through the monitoring method of grading point distribution, stable and accurate collection of cutting dust information of different scales is realized, and the monitoring efficiency is improved; real-time automatic monitoring in the machining process is achieved through a time-sharing operation monitoring method; based on a data fusion technology and according to the three dust evaluation indexes, graded and time-sharing scientific evaluation of the multi-scale dust contact level of the workplace is realized.

Description

Technical Field

[0001] The invention belongs to the field of dust monitoring and relates to a multi-scale cutting dust classification and time-sharing monitoring and evaluation method for composite materials. Background Art

[0002] Carbon fiber reinforced resin-based composite materials have the advantages of light weight, high strength, designable performance, and integral manufacturing. They are widely used in high-end equipment manufacturing fields such as aerospace in my country. However, carbon fiber has high strength and hardness. It is easy to break and break into fragments of different sizes under the action of the tool during the cutting process, thus forming multi-scale dust, ranging from micron to millimeter. These dusts are dispersed into the air and are easily inhaled into the respiratory tract by workers, endangering the health of the respiratory system. Studies have shown that dust of different sizes has different effects on the human respiratory system: dust with an aerodynamic diameter of more than 10μm is mostly deposited in the upper respiratory tract (nasal cavity, throat), and long-term inhalation can easily cause rhinitis, pharyngitis, etc.; dust with an aerodynamic diameter of less than 10μm can enter the lower respiratory tract (trachea, bronchi), and long-term inhalation can easily cause asthma, chronic bronchitis, etc.; dust with an aerodynamic diameter of less than 2.5μm can enter the alveoli and even enter the blood circulation system through the alveoli. Long-term inhalation can easily cause lung tissue fibrosis, heart disease, renal failure, etc. It can be seen that due to the multi-scale characteristics of composite material cutting dust, it is particularly important to accurately monitor and scientifically evaluate it.

[0003] In response to the monitoring difficulties of different types of work dust, scholars in many fields such as construction, mining, and blasting have conducted research on related monitoring methods. The patent publication number of Zheng Lina et al. is CN116625896, and the invention name is "A system and method for monitoring the concentration of dust in workplaces". The method collects suspended dust concentration data and deposited dust mass data, generates three-dimensional space full-scale dust concentration distribution data, and obtains real-time record data of the concentration of dust in contact with workers through comprehensive analysis of modules such as personnel information identification processing module, personnel positioning processing module, and personnel motion detection processing module. This method requires the deployment of multiple types of sensors for large open work spaces, but for cutting processing, the working area is small and it is difficult to deploy the multiple types of sensors, so it is not suitable for multi-scale cutting dust monitoring and evaluation of composite materials. The patent publication number of Li Li et al. is CN116519879, and the invention name is "A method and system for automatically monitoring dust from tunnel blasting". The method calculates the optimal layout of monitoring instruments based on the position of the support surface and the explosion energy, and monitors PM2.5 and TSP data. The layout method of the invention is formulated based on the tunnel explosion scene, and does not clearly point out the evaluation method of two scales of dust, so it is not suitable for dust monitoring in the cutting process of the machine tool working area. The patent publication number of Lu Hongyan et al. is CN117411910, and the invention name is "A dust explosion safety monitoring and early warning system based on private cloud". The system uses the Internet of Things technology to achieve real-time status monitoring and fault alarms for various detection parameters in production, but does not propose a clear monitoring and evaluation plan for dust of different scales. Therefore, how to accurately monitor and scientifically evaluate multi-scale cutting dust in the cutting process of composite materials in real time is an important problem that needs to be solved urgently. Summary of the invention

[0004] Based on the above technical problems, the present invention provides a method for monitoring and evaluating the multi-scale cutting dust of composite materials in a graded and time-sharing manner. For the multi-scale dust generated by the cutting of carbon fiber reinforced composite materials, the method can realize the graded point distribution based on the one-way coupling simulation of computational fluid dynamics-discrete element method and the time-sharing monitoring based on system automatic control, and then the graded and time-sharing scientific evaluation of the exposure level of the multi-scale cutting dust of composite materials in the workplace can be carried out according to three evaluation criteria.

[0005] The technical solution of the present invention:

[0006] A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method comprises the following steps:

[0007] S1: One-way coupled simulation based on computational fluid dynamics and discrete element method;

[0008] S2: Carry out dust sensor hierarchical monitoring based on simulation results;

[0009] S3: monitoring system time-sharing operation control;

[0010] S4: Dust sensor data collection and transmission;

[0011] S5: Data fusion processing and graded and time-sharing evaluation of dust information.

[0012] Furthermore, the process of step S1 is specifically as follows:

[0013] S1.1: Establish a digital model of the cutting machine tool;

[0014] S1.2: Construct computational fluid dynamics domain model;

[0015] S1.3: Finite element meshing and mesh optimization of each computational domain;

[0016] S1.4: Import the mesh into the solver and configure the CFD model, materials and boundary conditions;

[0017] S1.5: Set dynamic mesh simulation according to the tool and spindle motion characteristics during cutting;

[0018] S1.6: Particle source modeling and DEM model parameter setting based on the dust characteristics of the cutting process;

[0019] S1.7: Dynamic monitoring settings and demonstration animation configuration of numerical simulation process;

[0020] S1.8: Computational domain initialization and calculation process settings;

[0021] S1.9: Start computational fluid dynamics-discrete element method one-way coupled simulation calculation;

[0022] S1.10: Post-processing of numerical simulation results.

[0023] Furthermore, in step S1.1, establishing a digital model of the cutting machine tool refers to: establishing a digital model of the processing area of ​​the cutting machine tool, which must include the processed parts, tools, spindles, and air sources, among which the moving bodies (such as tools and spindles) need to be modeled independently for further processing in step S1.2.

[0024] Furthermore, in step S1.2, the construction of the computational fluid dynamics calculation domain model refers to: importing the digital model constructed in step S1.1 into the computational fluid dynamics pre-processing software, and preliminarily establishing the computational fluid dynamics fluid domain model by using the volume extraction method; then, by plane stretching modeling on the periphery of the rotating body (such as a tool, a spindle), a cylindrical rotating domain with a diameter 5% to 20% larger than the diameter of the rotating body is constructed to simulate its movement; finally, by volume extraction and Boolean operations, the part of the computational fluid dynamics fluid domain model that overlaps with the rotating domain is removed to obtain the outer flow domain. The outer flow domain and the rotating domain are independent of each other and together constitute the computational fluid dynamics calculation domain model.

[0025] Furthermore, in step S1.3, the finite element meshing and mesh optimization of each computational domain refers to: importing the computational domain model into the finite element meshing tool, selecting the mesh size range according to the size of the computational domain model to draw an unstructured mesh, and encrypting it at key structures such as the tool and the part being cut. The mesh is iteratively optimized for the entire mesh and adjusted for individual meshes to ensure that the mesh distortion is below 0.8 and there is no distorted surface mesh, and the distorted surface mesh includes free, multi-sided, self-intersecting, and self-adjacent. Subsequently, the properties of each surface are defined, the negative pressure gas source is defined as the pressure outlet, the machine tool vent is defined as the pressure inlet, and the machine tool wall and the outer surface of the tool spindle are defined as the wall surface. The regional properties of each computational domain are defined, the outer flow domain and the rotation domain are defined as the fluid region, and the tool spindle region is defined as the physical inhibition region. Finally, a volume mesh is further generated based on the surface mesh and at least 3 boundary layers are added. Through iterative optimization of the entire mesh, the quality of the volume mesh is improved to above 0.25 and there is no negative volume mesh, and the mesh information can be output for subsequent configuration.

[0026] Furthermore, in step S1.4, the importing of the mesh into the solver and the configuration of the CFD model, materials and boundary conditions refers to: importing the volume mesh obtained in step S1.3 into the computational fluid dynamics solver, setting general parameters including temperature, pressure, gravity and selecting the solution mode; calling the appropriate turbulence model according to the cutting conditions, and configuring the model parameters; defining the material properties of the air and tool in the calculation domain; setting the boundary conditions of the flow field inlet, outlet, wall and interfaces of different calculation domains, and the boundary conditions include pressure, air flow rate, backflow, and interface data interaction.

[0027] Furthermore, in step S1.5, setting the dynamic mesh simulation according to the tool and spindle motion characteristics during the cutting process means: for the rotation domain constructed in step S1.2, it is necessary to use a rotating coordinate system, a motion mesh or a mesh reconstruction method, set physical parameters such as the rotation center coordinates, the axis coordinates, the rotation speed, and the translation speed, and give the tool spindle rotation and feed motion in the calculation domain, so as to achieve accurate simulation of the air flow and dust movement distribution under the rotation disturbance during the cutting process.

[0028] Furthermore, in step S1.6, the particle source modeling and DEM model parameter setting based on the dust characteristics of the cutting process refer to: based on the characteristics of the material cutting process, the process of cutting to generate dust is abstracted as a process of incident particles from a particle source of a specific morphology (e.g., for the drilling process, the dust generation process can be abstracted as the incident of several conical particle sources with different vertex angles, and for the milling process, the dust generation process can be abstracted as the incident of a translated point particle source); based on the empirical formula for the dust scale distribution of composite material cutting, the dust scale distribution law under specific cutting parameters is clarified, the parameters are set according to the dust particle diameter grouping to establish a multi-scale particle source model, and the appropriate force model is called according to the particle scale, and the force model includes lift model, drag model, rotational lift model, pressure gradient force model, Brownian force model, turbulent diffusion force model, and collision model; the physical parameters of the dust particles are set according to the cutting material and cutting process, and the physical parameters include density, specific heat, exit velocity, and flow rate.

[0029] Furthermore, the empirical formula for the size distribution of composite material cutting dust is a multivariate nonlinear regression analysis empirical formula constructed based on composite material cutting experiments. The empirical formula assumes that the size distribution of composite material cutting dust conforms to the logarithmic normal distribution law, as shown in the following formula:

[0030]

[0031] Among them, y0 is the offset, which affects the offset of the entire curve along the y-axis direction; x c is the mean of the lognormal distribution, which affects the position of the curve peak along the x-axis; ω is the standard deviation of the lognormal distribution, which affects the overall width of the curve peak; A is the area of ​​the lognormal distribution. When ω is constant, A affects the height of the curve peak.

[0032] The distribution formula contains four parameters: y0, x c , ω, A. When describing the dust size distribution problem, the offset y0 should be taken as 0 by default, x c The values ​​of the three parameters ω, A should be obtained by composite cutting calibration experiment calculation and obey the following formula:

[0033] x c =a0+a1F+a2F 2 +a3F 3 +a4F 4 +a5F 5 +b1S+b2S 2 +b3S 3 +b4S 4

[0034] ω=c0+c1F+c2F 2+c3F 3 +c4F 4 +c5F 5 +d1S+d2S 2 +d3S 3 +d4S 4

[0035] A=e0+e1F+e2F 2 +e3F 3 +e4F 4 +e5F 5 +f1S+f2S 2 +f3S 3 +f4S 4

[0036] Among them, F is the tool feed speed; S is the tool speed; a i 、b i 、c i ,d i 、e i 、f i It is a regression parameter and needs to be determined by calibration experiment. After the regression parameters are determined by calibration experiment, the cutting parameters rotation speed (S) and feed speed (F) can be used as input to calculate the distribution formula of composite cutting dust size under the cutting parameters and clarify the specific distribution law of dust size.

[0037] Furthermore, in step S1.7, the dynamic monitoring setting and demonstration animation configuration of the numerical simulation process refer to: in order to monitor the operating status of the model constructed in steps S1.1-S1.6 in real time during the calculation process, it is necessary to perform dynamic monitoring settings of key calculation parameters (such as monitoring various residual values, air flow rate near the main axis, and the mass of released particles) to ensure the normal progress of the simulation calculation process; in addition, it is necessary to configure the demonstration animation during the simulation process, set the animation scene, add key grid drawings, cloud maps, particle trajectories, and adjust the output frame rate, so as to visualize the dynamic simulation process of changes in air flow fields and changes in dust movement distribution.

[0038] Furthermore, in step S1.8, the calculation domain initialization and calculation process setting means that before the simulation calculation is performed, the entire calculation domain needs to be initialized, the fluid therein is given an initial state, and the initial motion state of the moving bodies such as the tool and the spindle is also given. It is also necessary to set the iterative calculation process parameters including the number of iterations, the iteration step length, and the convergence condition to prepare for the start of the simulation calculation.

[0039] Furthermore, in step S1.9, the start of computational fluid dynamics-discrete element method one-way coupled simulation calculation refers to calling the computational fluid dynamics model to analyze and calculate fluid motion, and calling the discrete element method model to analyze and calculate dust particle motion, and only considering the force of the fluid on the dust particles, and ignoring the reaction force of the dust particles on the fluid. The above method only involves one-way data transmission from the computational fluid dynamics module to the discrete element method module during the analysis and calculation process, which can improve the calculation efficiency while ensuring the simulation accuracy, and realize accurate and efficient simulation of air flow and dust movement distribution.

[0040] Furthermore, in step S1.10, the post-processing of the numerical simulation results refers to: after the simulation is completed, the key information of the simulation process can be extracted in the finite element analysis post-processing module to visualize the simulation results. The air flow field information in the simulation area is obtained through computational fluid dynamics post-processing, and the air flow trajectory, flow velocity distribution cloud map, and flow velocity vector map are drawn; the dust movement trajectory, movement state and distribution are obtained through discrete element method post-processing, and the dust concentration information in different areas is statistically analyzed, and curves and distribution cloud maps are drawn; the demonstration animation of the simulation process can also be exported according to step S1.7, including the movement demonstration of the tool spindle, the change of air flow field distribution, the particle movement trajectory and the change of the diffusion area. Through the post-processing step of the numerical simulation results, the air flow law in the machine tool and the movement distribution law of the cutting dust are accurately characterized, so as to provide theoretical guidance for the subsequent placement of dust sensors.

[0041] Furthermore, in step S2, the monitoring of dust sensors by graded placement according to the simulation results refers to: according to the flow field change law of the processing area obtained by the simulation analysis in step S1, the dust sensors are arranged in areas with slow air flow, stable flow field and no eddy current, so as to improve the stability of dust sensor sampling and ensure monitoring accuracy. At the same time, the areas where dust of each scale is concentrated are determined according to the simulation analysis results, and dust sensors of corresponding scales are arranged in each area. The use of this graded placement method to monitor multi-scale cutting dust can ensure that dust of each scale is monitored by dust sensors of corresponding scales, which is conducive to improving monitoring accuracy. At the same time, it also avoids the blind and redundant arrangement of dust sensors, which is conducive to improving monitoring efficiency and reducing monitoring costs.

[0042] Furthermore, in step S3, the time-sharing operation control of the monitoring system means that the monitoring system and the processing equipment need to run synchronously to realize the real-time automatic monitoring of multi-scale cutting dust of composite materials during processing. This requires that the monitoring system and the processing equipment are powered at the same time, or the processing equipment sends a power-on signal after starting, and the monitoring system automatically powers on after receiving the signal. On this basis, automatic control software is also required to automatically call relevant programs after the system is powered on, complete the configuration work, and start collecting and processing dust information.

[0043] Furthermore, in step S4, the dust sensor data collection and transmission refers to: using dust sensors for dust of different scales, according to the point arrangement method described in step S2, multi-point hierarchical collection of TSP (dust with an aerodynamic diameter less than 100 μm), PM10 (dust with an aerodynamic diameter less than 10 μm, and so on), PM2.5, PM1.0 dust concentration information in the processing area. Then, the multi-point and multi-scale data in the processing process are summarized and transmitted to the host computer for subsequent processing and analysis.

[0044] Furthermore, in step S5, the data fusion processing and graded time-sharing evaluation of the dust information refers to: the host computer reads the massive data information transmitted by the dust sensor, and the information covers the time variation characteristics of the composite material cutting dust as the processing process changes, the dust spatial variation characteristics in different areas represented by the multi-point dust sensors, and the scale variation characteristics collected by the multi-scale dust sensors. The host computer needs to process the above-mentioned characteristic data in real time and batches based on data fusion technology for subsequent calculation and analysis. The host computer obtains the duration T1, T2…T of each startup working time period of the processing equipment according to the time of the system time-sharing operation. n According to the data information sent back by each dust sensor, the dust concentration information C1, C2…C of different scales in different areas corresponding to each time period is determined. n . The time-weighted average permissible concentration represents the average level of dust concentration during an 8-hour working day, the short-term exposure permissible concentration represents the average level of dust concentration within a shorter period of 15 minutes, and the maximum permissible concentration represents the instantaneous maximum level of dust concentration. The three dust concentration evaluation indicators evaluate the dust concentration exposure level of composite material cutting from the three time scales of long time, short time and instantaneous time respectively. According to the requirements of the three dust concentration evaluation indicators of permissible concentration-time weighted average (PC-TWA, Permissible Concentration-Time Weighted Average), permissible concentration-short term exposure limit (PC-STEL, Permissible Concentration-Short Term Exposure Limit) and maximum allowable concentration (MAC, Maximum Allowable Concentration), the time-weighted average concentration (C-weighted average concentration) of each scale of dust (TSP, PM10, PM2.5, PM1.0, etc.) of composite materials in the processing area is calculated in stages. TWA ), current short-term exposure concentration (C STEL ) and the highest exposure concentration on that day (C MAX ), and then compare and analyze the allowable concentration indicators of the first three items with the calculated exposure concentration indicators of the last three items to evaluate the dust exposure level.

[0045] Furthermore, the time-weighted average permissible concentration PC-TWA refers to the average permissible exposure concentration for an 8-hour workday or a 40-hour workweek, with time as the weight. The time-weighted average concentration for the day is a monitoring value for the PC-TWA indicator, reflecting the concentration of dust in the air in the workplace. When applying the fixed-point monitoring method to determine the time-weighted average concentration for the day, samples should be collected from a certain workplace and time periods within a working day. The sum of the products of the continuous contact time of each time period and its measured corresponding concentration should be divided by 8 hours to obtain the time-weighted average exposure concentration for a working day. It can be calculated according to the following formula:

[0046]

[0047] Where C TWA It indicates the time-weighted average concentration of the day (8h), in mg / m 3 ; C1, C2…C n Indicates the concentration of dust in the air at each time period; T1, T2…T n It represents the corresponding exposure time of workers under various concentrations, which can be replaced by the working time of each machine tool startup.

[0048] The permissible short-term exposure concentration refers to the weighted average concentration that workers are allowed to be exposed to for a short time (15 minutes) under the premise that the actual measured average exposure concentration of 8h workday and 40h workweek complies with PC-TWA. The current short-term exposure concentration is the monitoring value for the PC-STEL indicator, reflecting the individual exposure level of workers in the workplace in a short period of time. When the fixed-point monitoring method is used to determine the current short-term exposure concentration, samples should be collected at a certain workplace and each time period within 15 minutes. The sum of the products of the continuous contact time of each time period and the corresponding measured concentration is divided by 15 minutes to obtain a time-weighted average exposure concentration in a short period of time. It can be calculated according to the following formula.

[0049]

[0050] Where C STEL It indicates the short-time (15-minute time-weighted average) exposure concentration in mg / m 3 ; C1, C2…C n Indicates the concentration of dust in the air at each time period; T1, T2…T n It represents the corresponding exposure time of workers under various concentrations, which can be replaced by the working time of each machine tool startup.

[0051] The maximum allowable concentration refers to the index value that the dust concentration should not exceed at any time and at any place in a working day. To refer to this index, it is only necessary to screen out the maximum value C of dust concentration at each scale in the collected data. MAX That's it.

[0052] The beneficial effects of the present invention are as follows: in view of the lack of accurate monitoring and scientific evaluation methods for cutting dust during cutting of carbon fiber reinforced composite materials, a hierarchical and time-sharing monitoring and evaluation method for multi-scale cutting dust of composite materials is proposed. The method is based on the method of computational fluid dynamics and discrete element method one-way coupling analysis to obtain the flow field change and dust distribution information in the processing area, and then guide the hierarchical distribution of dust sensors; through the hierarchical distribution monitoring method, stable and accurate collection of cutting dust information of different scales is achieved, thereby improving the monitoring efficiency; through the time-sharing monitoring method, real-time automatic monitoring of the processing process is achieved; based on data fusion technology and three dust evaluation indicators, a hierarchical and time-sharing scientific evaluation of multi-scale dust exposure levels in the workplace is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flow chart of a multi-scale cutting dust classification and time-sharing monitoring and evaluation method for composite materials;

[0054] Figure 2 A simulation analysis flow chart based on one-way coupling of computational fluid dynamics and discrete element method in one embodiment of the present invention;

[0055] Figure 3 A cloud diagram of air flow field distribution near a machine tool wall surface obtained by one-way coupled simulation based on computational fluid dynamics and discrete element method in one embodiment of the present invention;

[0056] Figure 4 This is a flow chart of multi-scale cutting dust classification and time-sharing monitoring and evaluation of composite materials in an embodiment of the present invention.

[0057] Figure 5 This is a screenshot of the multi-scale cutting dust monitoring results of a composite material in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer and enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. It should be noted that the technical solutions claimed to be protected by the present invention include but are not limited to the following embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative work should fall within the scope of protection of the present invention.

[0059] like Figure 1 As shown, a composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method is applied in composite material cutting machine tools. It includes the following steps:

[0060] S1: One-way coupled simulation based on computational fluid dynamics and discrete element method;

[0061] S2: Carry out dust sensor hierarchical monitoring based on simulation results;

[0062] S3: monitoring system time-sharing operation control;

[0063] S4: Dust sensor data collection and transmission;

[0064] S5: Data fusion processing and graded and time-sharing evaluation of dust information.

[0065] Furthermore, the one-way coupling simulation process based on computational fluid dynamics and discrete element method is as follows: Figure 2 As shown, step S1 is specifically as follows: the digital modeling software used in step S1.1 is Autodesk Inventor; the computational fluid dynamics pre-processing software in step S1.2 is SpaceClaim; the rotation domains of the tool and the spindle are specifically set as follows: the tool is a twist drill with a shank diameter of 8 mm, and its rotation domain diameter is set to 9.6 mm; the spindle diameter is 100 mm, and its rotation domain diameter is set to 108 mm; in step S1.3, the finite element meshing tool is Fluentmeshing; a volume mesh is further generated on the basis of the surface mesh and 4 boundary layers are added; in step S1.4, the solver is Ansys Fluent; the gravity is set to -9.81 m / s in the Y-axis direction. 2 , the temperature is set to 273.15K. In step S1.5, the embodiment uses a speed of 3000r / min for composite hole making. The rotating coordinate system method is required to set the moving grid body speed to 3000r / min. In step S1.6, the dust generation process is abstracted as a conical particle source incident process with two different vertex angles of 120° and 60°; the force model is to call the Saffman lift model, Stokes-Cunningham drag criterion, Dennis-et-al rotation drag criterion, set the collision pair and collision model, and call the Brownian force model and turbulent diffusion force model for small-scale dust particles; the physical characteristics of the particles are assigned according to the material properties of the carbon fiber composite material, and the density is set to 1550kg / m 3 , the specific heat is set to 800 J / (g·K), the particle exit velocity is estimated to be 0.94 m / s according to the cutting parameters, and the flow rate is set to 8e-11 kg / s to shorten the calculation time. The number of iterations in step S1.8 is set to 10000 steps, and the iteration step length is set to 0.001 seconds; the finite element post-processing module in step S1.10 is CFD-Post;

[0066] Furthermore, in step S2, the step of carrying out dust sensor hierarchical point monitoring based on the simulation results means: according to the flow field change law of the processing area obtained by the simulation analysis in step S1, the dust sensors are arranged in the areas with slow air flow, stable flow field and no eddy current, so as to improve the sampling stability of the dust sensors and ensure the monitoring accuracy. At the same time, the areas where dust of each scale is concentrated are determined according to the simulation analysis results, and dust sensors of corresponding scales are arranged in each area. Figure 3 As shown in the flow field distribution cloud map, the air flow disturbance in the area near the negative pressure air source is strong, but in the approximately triangular area below the air source, the air velocity is relatively low, which is suitable for the arrangement of dust concentration sensors. Therefore, dust sensors can be arranged 0.5m below the four negative pressure air sources on the right side of the figure (non-working area on the far left), and the distance between the two dust sensors is 1.6m. At the same time, the simulation found that TSP and PM10 dust are almost completely settled within 2m of the processing position. Therefore, the two inner dust sensors need to use TSP, PM10, PM2.5, PM1.0 four-channel dust sensors, while the outermost two only need PM2.5, PM1.0 two-channel dust sensors. Using this hierarchical point distribution method to monitor multi-scale cutting dust can ensure that each scale of dust is monitored by the corresponding scale dust sensor, which is conducive to improving monitoring accuracy. At the same time, it also avoids the blind and redundant arrangement of dust sensors, which is conducive to improving monitoring efficiency and reducing monitoring costs.

[0067] Furthermore, in step S3, the time-sharing operation control of the monitoring system means that the monitoring system and the processing equipment need to run synchronously to realize the real-time automatic monitoring of multi-scale cutting dust of composite materials during processing. The power supply of the monitoring system can be connected to the power supply circuit of the machine tool to ensure that the monitoring system and the machine tool start and stop at the same time, or the signal line is connected from the machine tool, and the machine tool works by sending a signal to the monitoring system to control its automatic operation. On this basis, automatic control software is also required to automatically call the relevant program after the system is powered on or after receiving the machine tool signal, complete the configuration work, and collect and process the dust information.

[0068] Furthermore, in step S4, the sensor data collection and transmission refers to: using dust sensors for dust of different scales, using dust cutters to filter out dust of other scales or determining the dust scale based on light scattering signal intensity, β radiation absorption, etc. According to the point arrangement method described in step S103, multi-point graded collection of TSP (dust with an aerodynamic diameter of less than 100μm), PM10 (dust with an aerodynamic diameter of less than 10μm, and so on), PM2.5 and PM1.0 graded dust concentration information in the processing area. The data is summarized and transmitted to the host computer through the wifi transparent transmission module or the industrial bus transmission module for subsequent processing and analysis.

[0069] Furthermore, in step S5, the data fusion processing and graded time-sharing evaluation of the dust information refers to: the host computer reads the massive data information transmitted by the dust sensor, and the information covers the time variation characteristics of the composite material cutting dust as the processing process changes, the dust space variation characteristics in different areas represented by the multi-point dust sensors, and the scale variation characteristics collected by the multi-scale dust sensors. The host computer needs to process the above-mentioned characteristic data in real time and in batches based on data fusion technology for subsequent calculation and analysis. Figure 4 As shown in the figure, the host computer obtains the duration of each machine tool startup working time period T1, T2…T according to the system time-sharing operation time. n According to the data information sent back by each dust sensor, the dust concentration information C1, C2…C of different scales in different areas corresponding to each time period is determined. n . The time-weighted average permissible concentration represents the average level of dust concentration during an 8-hour working day, the short-term exposure permissible concentration represents the average level of dust concentration within a shorter period of 15 minutes, and the maximum permissible concentration represents the instantaneous maximum level of dust concentration. The three dust concentration evaluation indicators evaluate the dust concentration exposure level of composite material cutting from the three time scales of long time, short time and instantaneous time respectively. According to the requirements of the three dust concentration evaluation indicators of time-weighted average permissible concentration (PC-TWA, Permissible Concentration-Time Weighted Average), short-term exposure permissible concentration (PC-STEL, Permissible Concentration-Short Term Exposure Limit) and maximum permissible concentration (MAC, Maximum Allowable Concentration), the daily time-weighted average concentration (C TWA ), current short-term exposure concentration (C STEL ) and the highest exposure concentration on that day (C MAX ), and then compare and analyze the allowable concentration indicators of the first three items with the calculated exposure concentration indicators of the last three items to evaluate the dust exposure level.

[0070] Furthermore, the time-weighted average permissible concentration PC-TWA refers to the average permissible exposure concentration for an 8-hour workday or a 40-hour workweek, with time as the weight. The time-weighted average concentration for the day is a monitoring value for the PC-TWA indicator, reflecting the concentration of dust in the air in the workplace. When applying the fixed-point monitoring method to determine the time-weighted average concentration for the day, samples should be collected from a certain workplace and time periods within a working day. The sum of the products of the continuous contact time of each time period and its measured corresponding concentration should be divided by 8 hours to obtain the time-weighted average exposure concentration for a working day. It can be calculated according to the following formula:

[0071]

[0072] Where C TWA It indicates the time-weighted average concentration of the day (8h), in mg / m 3 ; C1, C2…C n Indicates the concentration of dust in the air at each time period; T1, T2…T n It represents the corresponding exposure time of workers under various concentrations, which can be replaced by the working time of each machine tool startup.

[0073] The permissible short-term exposure concentration refers to the weighted average concentration that workers are allowed to be exposed to for a short time (15 minutes) under the premise that the actual measured average exposure concentration of 8h workday and 40h workweek complies with PC-TWA. The current short-term exposure concentration is the monitoring value for the PC-STEL indicator, reflecting the individual exposure level of workers in the workplace in a short period of time. When the fixed-point monitoring method is used to determine the current short-term exposure concentration, samples should be collected at a certain workplace and each time period within 15 minutes. The sum of the products of the continuous contact time of each time period and the corresponding measured concentration is divided by 15 minutes to obtain a time-weighted average exposure concentration in a short period of time. It can be calculated according to the following formula.

[0074]

[0075] Where C STEL It indicates the short-time (15-minute time-weighted average) exposure concentration in mg / m 3 ; C1, C2…C n Indicates the concentration of dust in the air at each time period; T1, T2…T n It represents the corresponding exposure time of workers under various concentrations, which can be replaced by the working time of each machine tool startup.

[0076] The maximum allowable concentration refers to the index value that the dust concentration should not exceed at any time and at any place in a working day. To refer to this index, it is only necessary to screen out the maximum value C of dust concentration at each scale in the collected data. MAX That's it.

[0077] Taking the monitoring and evaluation results of PM10 dust as an example, PC-TWA is selected as 0.15mg / m 3 , PC-STEL is selected as 0.45mg / m 3 MAC is selected as 0.75 mg / m 3 The machine tool performed three processes on that day: milling, drilling, and edge milling. The milling took 0.5 hours, the drilling took 3 hours, and the edge milling took 0.5 hours. Figure 5 This is the monitoring result of the above three processes.TWA According to statistics, the value of C1=0.117mg / m 3 , C2=0.091mg / m 3 , C3=0.071mg / m 3 , T1 = 0.5h, T2 = 3h, T3 = 0.5h, according to the above method, C TWA ≈0.046mg / m 3 , less than PC-TWA meets the standard; for C STEL According to the calculation, the highest short-term contact concentration occurs in the milling process, which can be taken as C1 = 0.162 mg / m 3 , T1 = 0.25h, according to the above method, C STEL ≈0.162mg / m 3 , less than PC-STEL meets the standard; for C STEL According to the calculation, the highest contact concentration occurs in the milling process, C MAX =3.484mg / m 3 , greater than MAC does not meet the standard. It can be seen that the composite material cutting machine tool has good dust removal performance and can control the dust pollution in the machine tool in a short time, but the staff still need to do a good job of dust protection to avoid the harm caused by instantaneous excessive dust contact.

Claims

1. A method for monitoring and evaluating composite material multi-scale cutting dust classification and time sharing, characterized in that: The steps include: S1: One-way coupled simulation based on computational fluid dynamics and discrete element method; S2: Carry out dust sensor hierarchical monitoring based on simulation results; S3: monitoring system time-sharing operation control; S4: Dust sensor data collection and transmission; S5: Data fusion processing and graded and time-sharing evaluation of dust information.

2. The method for multi-scale cutting dust classification and time-sharing monitoring and evaluation of composite materials according to claim 1 is characterized in that: The specific process of step S1 is: S1.1: Establish a digital model of the cutting machine tool; S1.2: Construct computational fluid dynamics domain model; S1.3: Finite element meshing and mesh optimization of each computational domain; S1.4: Import the mesh into the solver and configure the CFD model, materials and boundary conditions; S1.5: Set dynamic mesh simulation according to the tool and spindle motion characteristics during cutting; S1.6: Particle source modeling and DEM model parameter setting based on dust characteristics of the cutting process; S1.7: Dynamic monitoring settings and demonstration animation configuration of numerical simulation process; S1.8: Computational domain initialization and calculation process settings; S1.9: Start computational fluid dynamics-discrete element method one-way coupled simulation calculation; S1.10: Post-processing of numerical simulation results; In step S1.1, the establishment of a digital model of the cutting machine tool refers to: establishing a digital model of the machining area of ​​the cutting machine tool, which must include the machined parts, tools, spindles, and gas sources, wherein the moving body must be independently modeled for further processing in step S1.2; In step S1.2, the construction of the computational fluid dynamics calculation domain model refers to: importing the digital model constructed in step S1.1 into the computational fluid dynamics pre-processing software, and preliminarily establishing the computational fluid dynamics fluid domain model by using the volume extraction method; then constructing a cylindrical rotation domain with a diameter 5% to 20% larger than the diameter of the rotating body by plane stretching modeling on the periphery of the rotating body, so as to simulate its movement; finally, by volume extraction and Boolean operation, removing the part of the computational fluid dynamics fluid domain model that overlaps with the rotation domain to obtain the outer flow domain; the outer flow domain and the rotation domain are independent of each other and together constitute the computational fluid dynamics calculation domain model; In step S1.3, the finite element meshing and mesh optimization of each computational domain refer to: importing the computational domain model into the finite element meshing tool, selecting the mesh size range according to the size of the computational domain model to draw an unstructured mesh, and encrypting it at key structures such as the tool and the part being cut; iteratively optimizing the overall mesh and adjusting individual meshes to ensure that the mesh distortion is below 0.8 and there is no distorted surface mesh, and the distorted surface mesh includes free, polygonal, self-intersecting, and self-adjacent meshes; then defining the properties of each surface, defining the negative pressure gas source as the pressure outlet, the machine tool vent as the pressure inlet, and the machine tool wall and the outer surface of the tool spindle as the wall; defining the regional properties of each computational domain, defining the outer flow domain and the rotation domain as the fluid region, and defining the tool spindle region as the physical inhibition region; finally, further generating a volume mesh based on the surface mesh and adding at least 3 boundary layers, and through iterative optimization of the overall mesh, improving the quality of the volume mesh to above 0.25 and ensuring that there is no negative volume mesh, and then outputting the mesh information for subsequent configuration; In step S1.4, the step of importing the mesh into the solver and configuring the CFD model, materials and boundary conditions refers to: importing the volume mesh obtained in step S1.3 into the computational fluid dynamics solver, setting general parameters including temperature, pressure, gravity and selecting the solution mode; calling the appropriate turbulence model according to the cutting conditions and configuring the model parameters; defining the material properties of the air and tool in the calculation domain; setting the boundary conditions of the flow field inlet, outlet, wall and the interface of different calculation domains, and the boundary conditions include pressure, air velocity, backflow and the interaction relationship of interface data; In step S1.5, the dynamic mesh simulation is set according to the motion characteristics of the tool and the spindle during the cutting process. It means that for the rotation domain constructed in step S1.2, a rotation coordinate system, a motion mesh or a mesh reconstruction method is used to set physical parameters such as the rotation center coordinates, the rotation axis coordinates, the rotation speed, and the translation speed, and the tool spindle rotation and feed motion are given in the calculation domain to achieve accurate simulation of the air flow and dust movement distribution under the rotation disturbance during the cutting process; In step S1.6, the particle source modeling and DEM model parameter setting based on the dust characteristics of the cutting process refer to: based on the characteristics of the material cutting process, the process of cutting to generate dust is abstracted as the process of incident particles of a particle source with a specific morphology; based on the empirical formula for the dust scale distribution of composite material cutting, the dust scale distribution law under specific cutting parameters is clarified, and the parameters are set according to the dust particle diameter grouping to establish a multi-scale particle source model, and the appropriate force model is called according to the particle scale, and the force model includes lift model, drag model, rotation lift model, pressure gradient force model, Brownian force model, turbulent diffusion force model, and collision model; the physical parameters of the dust particles are set according to the cutting material and cutting process, and the physical parameters include density, specific heat, exit velocity, and flow rate; Furthermore, in step S1.7, the dynamic monitoring setting and demonstration animation configuration of the numerical simulation process refer to: in order to monitor the running status of the model built in steps S1.1-S1.6 in real time during the calculation process, it is necessary to perform dynamic monitoring settings of key calculation parameters to ensure that the simulation calculation process proceeds normally; in addition, it is necessary to configure the demonstration animation during the simulation process, set the animation scene, add key grid drawings, cloud maps, particle trajectories, and adjust the output frame rate, so as to visualize the dynamic simulation process of the changes in the air flow field and the changes in the dust movement distribution; In step S1.8, the calculation domain initialization and calculation process setting refer to: before the simulation calculation is performed, the entire calculation domain needs to be initialized, the fluid therein needs to be given an initial state, and the initial motion state of the moving bodies such as the tool and the spindle also needs to be given; iterative calculation process parameters including the number of iteration steps, iteration step length, and convergence conditions need to be set to prepare for the start of simulation calculation; In step S1.9, the starting of the computational fluid dynamics-discrete element method one-way coupled simulation calculation refers to calling the computational fluid dynamics model to analyze and calculate the fluid motion, and calling the discrete element method model to analyze and calculate the dust particle motion, wherein only the force of the fluid on the dust particles is considered, and the reaction force of the dust particles on the fluid is ignored; In step S1.10, the post-processing of the numerical simulation results refers to: after the simulation is completed, the key information of the simulation process can be extracted in the finite element analysis post-processing module to visualize the simulation results; the air flow field information in the simulation area can be obtained through computational fluid dynamics post-processing, and the air flow trajectory, flow velocity distribution cloud map, and flow velocity vector map can be drawn; the dust movement trajectory, movement state and distribution can be obtained through discrete element method post-processing, and the dust concentration information in different areas can be statistically analyzed to draw curves and distribution cloud maps; It is also possible to export the demonstration animation of the simulation process according to step S1.7, including the movement demonstration of the tool spindle, the change of the air flow field distribution, the particle movement trajectory and the change of the diffusion area; through the post-processing step of the numerical simulation results, the air flow law in the machine tool and the movement distribution law of the cutting dust are accurately characterized, so as to provide theoretical guidance for the subsequent placement of dust sensors.

3. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to claim 2, characterized in that: The empirical formula for the size distribution of composite material cutting dust is a multivariate nonlinear regression analysis empirical formula constructed based on composite material cutting experiments; the empirical formula assumes that the size distribution of composite material cutting dust conforms to the logarithmic normal distribution law, as shown in the following formula: Among them, y0 is the offset, which affects the offset of the entire curve along the y-axis direction; x c is the mean of the lognormal distribution, which affects the position of the curve peak along the x-axis; ω is the standard deviation of the lognormal distribution, which affects the overall width of the curve peak; A is the area of ​​the lognormal distribution. When ω is constant, A affects the height of the curve peak; The distribution formula contains four parameters: y0, x c ,ω,A; when describing the dust size distribution problem, the offset y0 should be taken as 0 by default, x c The values ​​of the three parameters ω, A should be obtained by composite cutting calibration experiment calculation and obey the following formula: <h2 style=";text-align:left;direction:ltr">x<h2 style=";text-align:left;direction:ltr"> c <h2 style=";text-align:left;direction:ltr"> =a0+a1F+a2F<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +a3F<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> +a4F<h2 style=";text-align:left;direction:ltr"> 4 <h2 style=";text-align:left;direction:ltr"> +a5F<h2 style=";text-align:left;direction:ltr"> 5 <h2 style=";text-align:left;direction:ltr"> +b1S+b2S<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b3S<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> +b4S<h2 style=";text-align:left;direction:ltr"> 4 ω=c0+c1F+c2F 2 +c3F 3 +c4F 4 +c5F 5 +d1S+d2S 2 +d3S 3 +d4S 4 A=e0+e1F+e2F 2 +e3F 3 +e4F 4 +e5F 5 +f1S+f2S 2 +f3S 3 +f4S 4 Among them, F is the tool feed speed; S is the tool speed; a i 、b i 、c i d i 、e i 、f i It is a regression parameter and needs to be determined by a calibration experiment. After the regression parameters are determined by the calibration experiment, the cutting parameter rotation speed S and feed speed F can be used as input to calculate the distribution formula of composite material cutting dust size under the cutting parameters and clarify the specific distribution law of dust size.

4. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claims 1 to 3, characterized in that: In step S2, the monitoring of dust sensors in a graded manner based on the simulation results refers to: according to the flow field change law of the processing area obtained by the simulation analysis in step S1, the dust sensors are arranged in areas with slow air flow rate, stable flow field and no eddy current, so as to improve the stability of dust sensor sampling and ensure monitoring accuracy; at the same time, according to the simulation analysis results, the areas where dust of various scales is concentrated are determined, and dust sensors of corresponding scales are arranged in each area; using this graded distribution method to monitor multi-scale cutting dust can ensure that dust of each scale is monitored by dust sensors of corresponding scales, which is beneficial to improving monitoring accuracy, while also avoiding blind and redundant arrangement of dust sensors, which is beneficial to improving monitoring efficiency and reducing monitoring costs.

5. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claims 1 to 3, characterized in that: In step S3, the time-sharing operation control of the monitoring system means that the monitoring system and the processing equipment need to run synchronously to realize real-time automatic monitoring of multi-scale cutting dust of composite materials during processing; this requires that the monitoring system and the processing equipment are powered on at the same time, or the processing equipment sends a power-on signal after startup, and the monitoring system automatically powers on after receiving the signal; on this basis, automatic control software is also required to automatically call relevant programs after the system is powered on, complete the configuration work, and start collecting and processing dust information.

6. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claims 1 to 3, characterized in that: In step S4, the dust sensor data collection and transmission refers to: using dust sensors for dust of different scales, according to the point layout method described in step S2, multi-point hierarchical collection of TSP, PM10, PM2.5, PM1.0 dust concentration information in the processing area, TSP, PM10, PM2.5, PM1.0 refer to dust with aerodynamic diameters less than 100μm, 10μm, 2.5μm, and 1.0μm; then summarizing the multi-point and multi-scale data in the processing process and transmitting them to the host computer for subsequent processing and analysis.

7. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claims 1 to 3, characterized in that: In step S5, the data fusion processing and hierarchical time-sharing evaluation of the dust information refers to: the host computer reads the massive data information transmitted by the dust sensor, and the information covers the time variation characteristics of the composite material cutting dust as the processing process changes, the dust space variation characteristics in different areas represented by the multi-point dust sensor, and the scale variation characteristics collected by the multi-scale dust sensor; The host computer needs to process the above-mentioned characteristic data in real time and in batches based on data fusion technology for subsequent calculation and analysis; the host computer obtains the duration of each startup working period of the processing equipment T1, T2…T according to the time of system time-sharing operation. n According to the data information sent back by each dust sensor, the dust concentration information C1, C2…C of different scales in different areas corresponding to each time period is determined. n The time-weighted average permissible concentration represents the average dust concentration level within an 8-hour working day, the short-term contact permissible concentration represents the average dust concentration level within a shorter period of 15 minutes, and the maximum permissible concentration represents the instantaneous maximum dust concentration level; the three dust concentration evaluation indicators evaluate the composite material cutting dust concentration exposure level from the three time scales of long time, short time and instantaneous time respectively; according to the requirements of the three dust concentration evaluation indicators of time-weighted average permissible concentration PC-TWA, short-term contact permissible concentration PC-STEL and maximum permissible concentration MAC, the daily time-weighted average concentration C of the composite material dust at each scale in the processing area is calculated in stages. TWA 、Current short-term exposure concentration C STEL and the highest exposure concentration on that day, C MAX , and then compare and analyze the first three allowable concentration indicators with the calculated last three contact concentration indicators to evaluate the dust exposure level.

8. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claim 7, characterized in that: The time-weighted average permissible concentration PC-TWA refers to the average permissible exposure concentration for an 8-hour workday or a 40-hour workweek, with time as the weight. The time-weighted average concentration for the day is the monitoring value for the PC-TWA index, reflecting the concentration of dust in the air of the workplace. When the fixed-point monitoring method is used to determine the time-weighted average concentration for the day, samples should be collected from a certain workplace and each time period within a working day. The sum of the products of the continuous exposure time of each time period and the measured corresponding concentration is divided by 8 hours to obtain the time-weighted average exposure concentration for a working day. It can be calculated according to the following formula: Where C TWA It indicates the 8-hour time-weighted average concentration of the day, in mg / m 3 ; C1, C2…C n Indicates the concentration of dust in the air at each time period; T1, T2…T n It represents the corresponding exposure time of workers under various concentrations, which can be replaced by the working time of each machine tool startup.

9. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claim 7, characterized in that: The short-term exposure permissible concentration refers to the weighted average concentration that workers are allowed to be exposed to for a short time, provided that the actual measured average exposure concentration for an 8-hour workday or a 40-hour workweek complies with the PC-TWA. The current short-term exposure concentration is the monitoring value for the PC-STEL index, reflecting the individual exposure level of workers in the workplace in a short period of time. When the fixed-point monitoring method is used to determine the current short-term exposure concentration, samples should be collected at a certain workplace and at each time period within 15 minutes, and the sum of the products of the continuous exposure time of each time period and the corresponding measured concentration divided by 15 minutes is used to obtain a time-weighted average exposure concentration in a short period of time. It can be calculated according to the following formula: Where C STEL Indicates short-term exposure concentration in mg / m 3 ; C1, C2…C n Indicates the concentration of dust in the air at each time period; T1, T2…T n It represents the corresponding exposure time of workers under various concentrations, which can be replaced by the working time of each machine tool startup.

10. A composite material multi-scale cutting dust classification and time-sharing monitoring and evaluation method according to any one of claim 7, characterized in that: The maximum allowable concentration refers to the index value that the dust concentration should not exceed at any time and at any place in a working day. To refer to this index, it is only necessary to screen out the maximum value C of dust concentration at each scale in the collected data. MAX That's it.

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