Oxygen-flame cutting simulation method

Abstract

The invention discloses an oxygen-flame cutting simulation method which comprises the following steps: establishing a three-dimensional model of a cutting workpiece: independently modeling a slotting area, determining the number of birth and death unit blocks of the slotting area, and setting a slotting as a birth and death unit block model; model importing: importing the three-dimensional model of the cut workpiece into finite element analysis software, and setting parameters, including setting a solver, inserting a life-death unit into the solver, selecting a first block to activate the first block at a first time step delta t and suppress the first block at other time steps, establishing a second block to activate the first two time steps 2 delta t and suppress the other time steps, sequentially establishing all life and death unit blocks; and defining a combined heat source model: simulating a heat source generated by a chemical reaction between cutting oxygen and a cutting workpiece by adopting a cylindrical heat source model, forming the combined heat source model with a Gaussian surface heat source for simulating preheating flame heat release, importing the combined heat source model into finite element analysis software, applying the combined heat source model to the cutting workpiece, and performing oxygen-flame cutting simulation according to life and death unit blocks.

Description

Technical Field

[0001] The invention relates to the technical field of simulation analysis models for metal material cutting processes, and in particular to an oxygen-flame cutting simulation method. Background Art

[0002] Oxy-flame cutting, also known as flame cutting or gas cutting, is a traditional thermal cutting process dating back to the 1870s. Its cutting mechanism involves preheating the workpiece to its ignition point through the combustion of oxygen and fuel gas. High-speed, high-purity cutting oxygen is then introduced, causing a vigorous oxidation reaction on the workpiece, releasing a large amount of oxidation heat that melts the metal. Simultaneously, the high-speed, high-energy cutting oxygen jet blows away the molten metal, forming the kerf. Currently, oxy-flame cutting plays an irreplaceable role in cutting thick plates of low-carbon and low-alloy steel. High-quality cutting thicknesses can exceed 1200mm, and medium- and low-quality cutting thicknesses can exceed 3000mm, far exceeding other thermal cutting methods.

[0003] At present, due to the small number of scholars specializing in flame cutting technology, there are few reports on the research of oxygen-flame cutting mechanism. Moreover, the flame cutting mechanism is completely different from laser cutting, plasma cutting and welding technology. The mapping relationship between heat input and temperature field of metal workpiece during cutting, the size of cutting heat-affected zone and microstructure are difficult to study through advanced numerical simulation technology.

[0004] In welding engineering, numerical simulation has evolved from an auxiliary tool to a core technology for process decision-making, demonstrating significant research value in terms of micro-scale, economic efficiency, and reliability. Heat source models used in existing research are primarily developed for welding simulation and are generally categorized into surface heat source models (suitable for thin plate welding), volume heat source models (such as the double ellipsoid model), combined heat source models (superposition of multiple heat sources), and simplified heat source models (for complex thermal processes). However, due to the fundamentally different mechanisms of flame cutting from other welding and thermal cutting techniques, existing heat source models and simulation methods struggle to accurately simulate the flame cutting process. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides an oxygen-flame cutting simulation method, which is based on the flame cutting mechanism and can truly simulate the oxygen-flame cutting process.

[0006] The present invention provides an oxygen-flame cutting simulation method, comprising the following steps:

[0007] Establish a 3D model of the cut workpiece: Model the kerf area separately, determine the number of birth and death unit blocks in the kerf area, and set the kerf as a birth and death unit block model;

[0008] Model import: Import the 3D model of the cut workpiece into the finite element analysis software and set the parameters. Setting the parameters includes setting the solver, inserting the birth and death unit in the solver, selecting the first block to activate it at the first time step Δt, and suppressing the other time steps, and establishing the second block to activate the first two time steps 2Δt, and suppress the others, and then establish all the birth and death unit blocks in sequence;

[0009] Define the combined heat source model: Use a cylindrical heat source model to simulate the heat source generated by the chemical reaction between cutting oxygen and the cutting workpiece, and combine it with a Gaussian surface heat source that simulates the heat release of the preheating flame to form a combined heat source model. Import it into the finite element analysis software and apply it to the cutting workpiece. Perform oxygen-flame cutting simulation based on the life and death unit block.

[0010] Optionally, setting parameters includes the following steps:

[0011] Define element types and mesh divisions;

[0012] Set the analysis type, initial conditions, and solver: Use transient thermal analysis as the solver analysis type, apply the overall initial temperature, and use the finite element volume method and ANSYS Thermal Solver.

[0013] Set the heat transfer boundary conditions and set the center line of the slit as the adiabatic boundary condition: set the heat exchange mode between the surface of the cut workpiece and the surrounding environment during the heat transfer process to the superposition of natural convection heat transfer and thermal radiation heat transfer;

[0014] Set cutting metal material parameters: set the material's elastic modulus, thermal expansion coefficient, Poisson's ratio and yield strength.

[0015] Optionally, the heat exchange mode after superposition is expressed by a heat exchange coefficient, which is expressed by the following formula:

[0016]

[0017] Where: T is the surface temperature of the workpiece, K; T0 is the ambient temperature, 300K; h conv is the natural convection heat transfer coefficient; σ is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ), ε is the thermal emissivity of the material.

[0018] Optionally, meshing includes mesh refinement of key study areas, including the kerf and its edges, the heat-affected zone, and other locations of the workpiece that require analysis.

[0019] Optionally, the life and death unit settings also include:

[0020] Set the time step: determine the total cutting time T and the time Δt required in each time step, and set the calculation step size for each Δt time;

[0021] Define the preheating flame heat source model: The preheating flame heat source adopts the Gaussian surface moving heat source model.

[0022] Optionally, the Gaussian moving surface heat source model is expressed by heat flux density. The heat flux density of the Gaussian moving surface heat source model is expressed as follows:

[0023]

[0024] Where q (r) is the heat flux density at a distance r from the center of the heat source, in W / m 2 ;η pre is the thermal efficiency of the Gaussian heat source, ranging from 0.2 to 0.35; Q g is the gas flow rate, m 3 / h; H v is the combustion calorific value of the gas, J / m 3 ; r0 represents the characteristic radius of the Gaussian heat source; v0 is the cutting speed, mm / s; Δt is the time required in each time step; x and y are the coordinates of the workpiece surface.

[0025] Optionally, r0 is determined by numerical simulation using Fluent or by experimental method.

[0026] Optionally, the heat generated by the cylindrical heat source on the carrier q(r, x) is expressed by the following formula:

[0027]

[0028] Where: η gen The heat efficiency of the fuel iron-oxygen combustion reaction, η gen =0.25; A gen is the total heat generated by the iron-oxide reaction, J; r1 is the effective radius of the heat source, simplified to the slit width / 2, m; h is the height of the column, that is, the thickness of the metal workpiece, m; r e is the outlet radius of the cutting oxygen channel; D(x) is a unit step function, which means that the effective radius of the heat source r1 is within the radius of the cutting oxygen jet r e When the radius of the cutting oxygen jet is exceeded, the heat generation rate decays exponentially; v0 is the cutting speed, mm / s; x and y are the coordinates of the workpiece surface.

[0029] Optional, import into FEA software for oxy-fuel cutting simulation including:

[0030] Select cutting process parameters and import the heat source formula of the combined heat source model into the Mechanical APDL product launcher to calculate the heat source motion trajectory and apply it to the surface and interior of the cut workpiece.

[0031] Optionally, also include:

[0032] Result output and data processing and analysis: After the simulated cutting is completed, simulation cloud maps, curves and characteristic data of any position are output. Based on the output results, the temperature field distribution, cooling rate and heat-affected zone size of the metal workpiece are predicted and quantitatively characterized;

[0033] Result verification.

[0034] The technical solution provided by the embodiment of the present invention has the following advantages compared with the existing technology:

[0035] An oxygen-flame cutting simulation method provided by an embodiment of the present invention targets the flame cutting mechanism and adopts the birth-and-death unit method to establish a combined heat source model of a Gaussian surface heat source and a cylindrical heat source, aiming to accurately simulate the temperature field changes of metal workpieces during the flame cutting process, further explore and study the heat conduction characteristics and cooling rate of flame cutting, and accurately predict and quantitatively analyze the size of the cutting heat-affected zone, providing a theoretical basis for the precise regulation of the flame cutting quality of medium and thick plates and the optimization of cutting process parameters. It can dynamically simulate the flame cutting process, and after experimental and test verification, it has high accuracy and applicability for the heat transfer characteristics, temperature field changes, cooling rate and heat-affected zone prediction and quantitative characterization of metal workpieces during the flame cutting process. The oxygen-flame cutting simulation method provided by the present invention can effectively reduce the number of process tests, shorten the cutting process development cycle, realize the precise regulation of cutting process and quality, and provide a theoretical basis for the development of industrial cutting solutions and digital twin systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A flowchart of an oxygen-flame cutting simulation method provided by an embodiment of the present invention;

[0037] Figure 2 The test point settings provided by the embodiment of the present invention;

[0038] Figure 3 Verification of mesh division and mesh independence provided by the embodiment of the present invention;

[0039] Figure 4 Thermophysical parameter curve of Q345D provided by the embodiment of the present invention;

[0040] Figure 5 A schematic diagram of the birth and death unit technology in the cutting process provided by an embodiment of the present invention;

[0041] Figure 6 The heat flux density distribution model of a Gaussian heat source provided in an embodiment of the present invention, wherein (a) is a Gaussian surface heat source type, (b) is r0 determined by a numerical simulation method, and (c) is r0 determined by an experimental test method;

[0042] Figure 7 The heat flux density distribution model of the Gaussian surface-cylinder combined heat source model provided in the embodiment of the present invention;

[0043] Figure 8 Comparison of the numerical simulation results and experimental verification of point A provided by an embodiment of the present invention, wherein (a) is a numerical simulation temperature cloud map of test point A, (b) is an experimental test of test point A, and (c) is a comparison chart of the numerical simulation and experimental verification results of test point A;

[0044] Figure 9 Grid division provided by the embodiment of the present invention;

[0045] Figure 10 The analysis step settings provided in the embodiment of the present invention;

[0046] Figure 11 Input metal material parameters provided by the embodiment of the present invention;

[0047] Figure 12 The birth and death unit setting provided by the embodiment of the present invention;

[0048] Figure 13 The temperature field cloud map of the metal workpiece and the curve of the test point changing with time provided by the embodiment of the present invention, where (a) is the temperature cloud map of the metal workpiece at different times under the condition of cutting speed of 5mm / s, and (b) is the curve of the temperature change of the test points AF with time;

[0049] Figure 14 The temperature distribution cloud diagram of the MM′ section and the temperature distribution curves at different positions provided by the embodiment of the present invention, where (a) is the temperature cloud diagram of the heat source at the YZ section through the BDE point at t = 15s, (b) is the MM′ section diagram, and (c) is the temperature change curves at Z = -2, -25, and -50mm on the MM′ section;

[0050] Figure 15 The temperature distribution cloud diagrams of the heat source center under different cutting speed conditions provided by the embodiment of the present invention, wherein (a) is the temperature distribution cloud diagram of the heat source center under the cutting speed of 4 mm / s, (b) is the temperature distribution cloud diagram of the heat source center under the cutting speed of 5 mm / s, and (c) is the temperature distribution cloud diagram of the heat source center under the cutting speed of 6 mm / s;

[0051] Figure 16Temperature distribution curves of test points B and F at different cutting speeds provided by the embodiment of the present invention;

[0052] Figure 17 The cross-sectional temperature distribution curves of the upper and lower surfaces of the workpiece at different cutting speeds provided by the embodiment of the present invention;

[0053] Figure 18 The flame cutting experiment verification under different cutting speed conditions provided in the embodiment of the present invention is shown in FIG. 1 , wherein (a) is the experimental scene of cutting 50 mm thick Q345D low alloy steel at cutting speeds of 4 mm / s, 5 mm / s, and 6 mm / s, and (b) is the surface quality morphology of the cutting at different cutting speeds. DETAILED DESCRIPTION

[0054] A specific embodiment of the present invention is described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiment.

[0055] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the technical solutions of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0056] The present invention is described below by means of several specific embodiments. To keep the following description of the embodiments of the present invention clear and concise, detailed descriptions of known functions and components may be omitted. When any component of an embodiment of the present invention appears in more than one drawing, the component may be represented by the same reference numeral in each drawing.

[0057] Existing heat source models and simulation methods are difficult to accurately simulate the flame cutting process. The main problems are as follows:

[0058] Question 1: Existing heat source models, whether they are surface heat sources, volume heat sources, or combined heat sources, calculate the heat input mainly based on current, voltage, power, etc., while the input heat source of flame cutting is divided into two parts, both of which are chemical energy release: one part is the heat release of the preheating flame formed by the mixed combustion of oxygen and gas, and the other part is the heat release of the chemical reaction between high-purity oxygen and the Fe element in low-alloy steel. As we all know, the chemical reaction process is a complex, changeable and dynamic process. Existing heat source models cannot accurately express the flame cutting process, and cannot accurately measure the heat input, molten metal flow removal behavior and dynamic coupling process of heat and mass transfer in the flame cutting process. Therefore, there is no accurate and applicable heat source model and corresponding numerical simulation method for heat transfer in the flame cutting process, temperature field and metal structure changes of metal workpieces, and heat-affected zone prediction.

[0059] Question 2: During the actual cutting process, the slag at the incision is continuously removed as the heat source moves. However, existing studies either adopt preset incisions or weaken the setting methods of incision material properties, which are quite different from actual cutting. They cannot accurately reflect the incision formation, slag removal and heat transfer processes, and are prone to "virtual heat accumulation" problems, resulting in inaccurate temperature gradients at the cutting edge.

[0060] In view of the above problems, an embodiment of the present invention provides an oxygen-flame cutting simulation method, comprising the following steps:

[0061] Establish a 3D model of the cut workpiece: Model the slit area separately, determine the number of birth and death unit blocks in the slit area, and set the slit as a birth and death unit block model;

[0062] Model Import: Import the 3D model of the workpiece to be cut into the finite element analysis software and set parameters. This includes setting up the solver, inserting birth / death cells into the solver, selecting the first block to activate at the first time step Δt and suppressing all other time steps. Create the second block to activate at the first two time steps 2Δt and suppress all other time steps. This is followed by the creation of all birth / death cell blocks. Welding heat sources typically use temperature-triggered birth / death cells, meaning that all cells are "killed" when the temperature exceeds a certain value. This may have little impact on the heat source in additive manufacturing processes such as welding. However, cutting differs from welding in that the material is removed by the cutting oxygen flow during the process, immediately ceasing heat transfer to the surrounding material. This means that upon triggering, the temperature and mass of the cell are immediately forced to "0." Therefore, temperature triggering is not suitable for cutting heat sources. This will cause the front section of the heat source to be "killed" due to its temperature exceeding the melting point. This will manifest in actual cutting as the kerf is formed before the torch reaches the cutting point, resulting in "virtual heat accumulation" and "false heat transfer" in the temperature field. Therefore, the birth / death cell method is key to achieving flame cutting accuracy. The present invention eliminates this "dead" cell.

[0063] Define the combined heat source model: Use a cylindrical heat source model to simulate the heat source generated by the chemical reaction between cutting oxygen and the cutting workpiece, and combine it with a Gaussian surface heat source that simulates the heat release of the preheating flame to form a combined heat source model. Import it into the finite element analysis software and apply it to the cutting workpiece. Perform oxygen-flame cutting simulation based on the life and death unit block.

[0064] An oxygen-flame cutting simulation method provided by an embodiment of the present invention targets the flame cutting mechanism and adopts the birth-and-death unit method to establish a combined heat source model of a Gaussian surface heat source and a cylindrical heat source, aiming to accurately simulate the temperature field changes of metal workpieces during the flame cutting process, further explore and study the heat conduction characteristics and cooling rate of flame cutting, and accurately predict and quantitatively analyze the size of the cutting heat-affected zone, providing a theoretical basis for the precise regulation of the flame cutting quality of medium and thick plates and the optimization of cutting process parameters. It can dynamically simulate the flame cutting process, and after experimental and test verification, it has high accuracy and applicability for the heat transfer characteristics, temperature field changes, cooling rate and heat-affected zone prediction and quantitative characterization of metal workpieces during the flame cutting process. The oxygen-flame cutting simulation method provided by the present invention can effectively reduce the number of process tests, shorten the cutting process development cycle, realize the precise regulation of cutting process and quality, and provide a theoretical basis for the development of industrial cutting solutions and digital twin systems.

[0065] Optionally, setting parameters includes the following steps:

[0066] Define element types and mesh divisions;

[0067] Set the analysis type, initial conditions, and solver: Use transient thermal analysis as the solver analysis type, apply the overall initial temperature, and use the finite element volume method and ANSYS Thermal Solver.

[0068] Set the heat transfer boundary conditions and set the center line of the slit as the adiabatic boundary condition: set the heat exchange mode between the surface of the cut workpiece and the surrounding environment during the heat transfer process to the superposition of natural convection heat transfer and thermal radiation heat transfer, so that analysis can be performed based on the characteristics of flame cutting and material properties;

[0069] Set cutting metal material parameters: set the material's elastic modulus, thermal expansion coefficient, Poisson's ratio and yield strength.

[0070] Optionally, the heat exchange mode after superposition is expressed by a heat exchange coefficient, which is expressed by the following formula:

[0071]

[0072] Where: T is the surface temperature of the workpiece, K; T0 is the ambient temperature, 300K; h convis the natural convection heat transfer coefficient; σ is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ), ε is the thermal emissivity of the material.

[0073] Optionally, meshing includes mesh refinement of key research areas, including the kerf and its edges (both transverse and longitudinal), the heat-affected zone, and other locations of the workpiece that require analysis.

[0074] Optionally, the life and death unit settings also include:

[0075] Set the time step: determine the total cutting time T and the time Δt required in each time step, and set the calculation step for each Δt time; the establishment of the time step is based on the number of birth and death units in the gap to determine the number of time steps, and the time of each time step is determined according to the length of the unit and the moving speed of the heat source, which can realize a series of unit analysis step settings in a more systematic way.

[0076] Define the preheating flame heat source model: The preheating flame heat source adopts the Gaussian surface moving heat source model.

[0077] Optionally, the Gaussian moving surface heat source model is expressed by heat flux density. The heat flux density of the Gaussian moving surface heat source model is expressed as follows:

[0078]

[0079] Where q (r) is the heat flux density at a distance r from the center of the heat source, in W / m 2 ;η pre is the thermal efficiency of the Gaussian heat source, ranging from 0.2 to 0.35; Q g is the gas flow rate, m 3 / h; H v is the combustion calorific value of the gas, J / m 3 ; r0 represents the characteristic radius of the Gaussian heat source, which is determined by numerical simulation or experimental test. The heat source heat within this radius is 95% of the total input heat. This value is related to the oxygen and gas mixture ratio, flow rate and cutting nozzle height. The accuracy of its value directly affects the accuracy of the simulation results; v0 is the cutting speed, mm / s; Δt is the time required in each time step; x and y are the coordinates of the workpiece surface.

[0080] Optionally, r0 is determined by numerical simulation using Fluent or by experimental method.

[0081] Optionally, the heat generated by the cylindrical heat source on the carrier q(r, x) is expressed by the following formula:

[0082]

[0083] Where: η gen The heat efficiency of the fuel iron-oxygen combustion reaction, η gen =0.25; A gen is the total heat generated by the iron-oxide reaction, J; r1 is the effective radius of the heat source, simplified to the slit width / 2, m; h is the height of the column, that is, the thickness of the metal workpiece, m; r e is the outlet radius of the cutting oxygen channel; D(x) is a unit step function, which means that the effective radius of the heat source r1 is within the radius of the cutting oxygen jet r e When the radius of the cutting oxygen jet is exceeded, the heat generation rate remains constant at the peak heat flux. When the radius of the cutting oxygen jet is exceeded, the heat generation rate decays exponentially. v0 is the cutting speed in mm / s; x and y are the coordinates of the workpiece surface. Based on the flame cutting mechanism, a unit step function D(x) was introduced to more accurately simulate flame cutting of a cylindrical heat source, making the simulation process closer to the actual cutting process.

[0084] Optional, import into FEA software for oxy-fuel cutting simulation including:

[0085] Select cutting process parameters and import the heat source formula of the combined heat source model into the Mechanical APDL product launcher to calculate the heat source motion trajectory and apply it to the surface and interior of the cut workpiece.

[0086] Optionally, also include:

[0087] Result output and data processing and analysis: After the simulated cutting is completed, simulation cloud maps, curves and characteristic data of any position are output. Based on the output results, the temperature field distribution, cooling rate and heat-affected zone size of the metal workpiece are predicted and quantitatively characterized;

[0088] Result verification.

[0089] Two specific embodiments are provided below:

[0090] like Figure 1 As shown in Example 1, a numerical simulation study was conducted on the cutting of 20mm thick Q345D low alloy steel plate using a 307-5# cutting nozzle (cutting oxygen channel diameter 1.8mm).

[0091] 1. Model Establishment: Based on the target workpiece dimensions, use 3D modeling software (such as UG, SW, CATIA, or PRO / E) to create a workpiece model. Model the kerf area separately according to the actual cutting position, width, and trajectory. Design and calculate the number of birth and death cells used in the kerf area (25 in this example, with the kerf set as a 150mm × 4mm × 20mm cube. The kerf cross-section is divided into 25 segments, each 6mm long, for a total of 3840 grid cells). Configure the kerf to be either equally divided or unequally divided. The kerf width of 4mm in this example is the average value obtained from multiple test measurements. Different cutting nozzles using different process parameters will produce different kerf widths when cutting workpieces of varying thicknesses. Modeling should be based on the actual kerf width measurements.

[0092] 2. Model import: Import the 3D model into the finite element analysis software ANSYS-Mechanical in parasolid x_t format.

[0093] 3. Define the element type: Select the eight-node hexahedral Solid70 body element and the surface element surf152.

[0094] 4. Grid division: In order to improve the grid quality and calculation accuracy as much as possible, structural grid division is adopted, and the grid is refined in key research areas, such as the slit and its edge, heat-affected zone, thickness direction, etc. In this example, in order to eliminate the influence of the number of grids on the calculation results, the number of grids is set to 24300, 34500, 45965, 60480, 72562 and 88200 respectively, and grid independence verification is carried out. The KA-2A melting thermocouple patch (type k) is used to measure the temperature of the AF temperature measuring point on the steel plate, and its range is -30-1800℃. Figure 2 and Figure 3 As shown in the figure, when the number of grids increases to more than 60480, the maximum temperature values ​​of points A and F are basically stable. When the number of grids is 60480, 72562, and 882006, respectively, the deviation of the maximum temperature results of points A and F does not exceed 5%. Therefore, a grid with a number of 60480, that is, the grid unit size at the refined position is about 0.5mm×0.5mm×0.5mm, is adopted. The numerical simulation results are basically consistent with the actual results. The experimental measurement is to verify the influence of the grid on the numerical simulation results and determine the minimum size of the grid.

[0095] 5. Set the analysis type, initial conditions, and solver: Use transient thermal analysis as the solver analysis type, apply an overall initial temperature (300K in this example), and use the finite element volume method and ANSYS Thermal Solver.

[0096] 6. Set the heat transfer boundary conditions and set the center line of the slit as the adiabatic boundary condition: set the heat exchange between the surface of the cut workpiece and the surrounding environment during the heat transfer process to the superposition of natural convection heat transfer and thermal radiation heat transfer. The superposition heat transfer coefficient can be expressed as:

[0097] q conv+rad =h conv (T-T0)+σε(T 4 -T0 4 ) (1)

[0098] Where: T is the surface temperature of the workpiece, K; T0 is the ambient temperature, 300K; h conv is the natural convection heat transfer coefficient; σ is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ) ; ε is the thermal emissivity of the material, and the rough steel surface is taken as 0.6-0.8.

[0099] 7. Input cutting metal material parameters: Since the thermal conductivity and specific heat capacity of metal steel plates at different temperatures are different, it will directly affect the simulation results of heat conduction and loss during the cutting process. In this example, the thermal physical curve of Q345D material is as follows: Figure 4 As shown; set the elastic modulus, thermal expansion coefficient, Poisson's ratio and yield strength of the material.

[0100] 8. Birth and death unit setting: insert the birth and death unit in the solver, select the first block to activate it in the first time step Δt, suppress the other time steps, establish the second block to activate the first two time steps 2Δt, suppress the others, and establish 25 blocks in sequence; the present invention uses birth and death unit technology to simulate the movement of the heat source model and the change of molten metal removal over time during the cutting process. When the heat source passes through this place, these units are invalidated in the calculation to calculate the change of the grid boundary over time. When the unit dies, the mass, specific heat and temperature will be set to be excluded from the simulation to simulate the removal of molten metal during the cutting process and its influence on heat conduction. The birth and death unit technology in the cutting process is as follows: Figure 5 shown.

[0101] 9. Set the time step: According to the cutting characteristics of the flame cutting nozzle and the steel plate, select the cutting speed and cutting distance to calculate the total time T and the time Δt required in each time step, and set the calculation step of each Δt time.

[0102] 10. Define the preheating flame heat source model: The preheating flame heat source adopts the Gaussian surface moving heat source model, such as Figure 6 As shown, its expression is as follows:

[0103] q (r) =q0exp(-kr2 ) (2)

[0104] in

[0105]

[0106] but:

[0107]

[0108] Where: q (r) is the heat flux density at a distance r from the center of the heat source, W / m 2 ;q0 is the maximum heat flux, W / m 2 ; is the attenuation coefficient; η pre is the thermal efficiency of the Gaussian heat source, ranging from 0.2 to 0.35; Q g is the gas flow rate, m 3 / h; H v is the combustion calorific value of the gas, J / m 3 ; r0 represents the characteristic radius of the Gaussian heat source, which is determined by numerical simulation or experimental test. The heat source heat within this radius accounts for 95% of the total input heat; the exponential term exp(-kr 2 ) describes the decay rate of heat flux density with r; r is the radial distance from the center of the heat source, m; v0 is the cutting speed, mm / s; x and y are the coordinates of the workpiece surface; x0 and y0 are the position parameters of the moving heat source. In this example, the heat source moves parallel to the x-axis, so there is no velocity component on the y-axis.

[0109] In formula (4), the unknown parameter Q g is the gas flow rate during preheating, which can be read from a flow meter using the theoretical flow rate of a commercial cutting nozzle or by experimental method; r0 is the characteristic radius of the heat source acting on the upper surface of the metal workpiece by the preheating flame. This value is related to the height of the cutting nozzle from the upper surface of the workpiece and the cutting nozzle characteristics. It can be determined by numerical simulation using Fluent or by experimental method, such as Figure 6 As shown in (b) and (c).

[0110] 11. Define the combined heat source model: Use the cylindrical heat source model to simulate the heat source generated by the chemical reaction between cutting oxygen and iron, and combine it with the Gaussian surface heat source to form a combined heat source model, such as Figure 7 shown.

[0111] The choice of cylindrical heat source depends on the thickness h of the workpiece, the volume V of the cutting oxygen flow loading body, and the cutting simulation process. Since during flame cutting, in addition to the iron-oxygen reaction that generates heat, sufficient oxygen is also required to blow away the molten metal. Therefore, it can be assumed that the amount of oxygen participating in the iron-oxygen reaction is sufficient, indicating that as the reaction heat source continues to progress to the lower layer, the heat flux peak is assumed to remain unchanged in the thickness direction to conform to the characteristics of the actual flame cutting process; however, since the oxygen purity is highest at the center of the cutting oxygen flow and gradually decreases toward the outside, the reaction heat generation rate of the cylindrical heat source loading body can be expressed as

[0112]

[0113] Where: A gen is the total heat generated by the iron-oxide reaction, J; η gen The heat efficiency of the fuel iron-oxygen combustion reaction, η gen =0.25; r1 is the effective radius of the heat source, which is simplified to the radius of the loading body (slit width / 2), m; h is the height of the column, that is, the thickness of the metal workpiece, m; r e is the outlet radius of the cutting oxygen channel; D(x) is a unit step function, which means that the effective radius of the heat source r1 is within the radius of the cutting oxygen jet r e When the heat generation rate remains constant at the peak heat flux, it decays exponentially when the radius of the cutting oxygen jet is exceeded. v0 is the cutting speed in mm / s; x and y are the coordinates of the workpiece surface; x0 and y0 are the position parameters of the moving heat source; the body heat source and the surface heat source move parallel to the x-axis, so there is no velocity component on the y-axis.

[0114] In formula (5), A gen is the total heat generated by the iron-oxygen reaction, which can be calculated based on the heat values ​​generated when the iron-oxygen combustion reaction produces different oxides in formula (6).

[0115]

[0116] There are two methods for determining combustion products. Method 1 is an experimental test method. This involves cutting a 20 mm thick Q345D steel plate and analyzing the composition and mass fraction of the slag produced by cutting using X-ray diffraction (XRD). For Example 1, the composition of 1 g of the slag product is as follows (by mass fraction): Fe accounts for 16.5%, Fe₃O₄ accounts for 52.5%, and Fe₂O₃ accounts for 31.0%. Based on the calorific value of different oxides produced by the iron-oxygen combustion reaction in formula (6), the heat generated per unit mass of slag can be calculated, as shown in Table 1.

[0117] Table 1 The heat generated per unit mass (1g) of slag (A gen , kJ)

[0118]

[0119] According to the heat generation in Table 1, the mass of Fe element required to react to produce 1g of slag is 0.786g. The density of iron is ρ = 7.86g / cm 3 It can be seen that 0.1cm 3 The heat released by the combustion of Fe element is 4.275kJ, so the heat generation rate per unit volume of iron is Then use formula (7) to calculate the total heat generation A gen .

[0120]

[0121] Where: is the heat generation rate per unit volume of slag, kJ / m 3 ; V is the total volume of the heat source carrier.

[0122] Method 2 uses empirical values ​​from reference books for estimation. However, because slag composition is significantly affected by cutting speed, cutting oxygen channel diameter, metal material composition, and workpiece thickness, and heat-affected zone size prediction and quantitative characterization require accurate heat input values, Method 1 is more accurate.

[0123] 12. Heat source application and solution analysis: Utilize the characteristics of the flame cutting nozzle and the steel plate, select process parameters such as cutting speed, and use the heat source formula. Import the expression into the Mechanical APDL product launcher to calculate the heat source motion trajectory command, apply it to the surface and interior of the steel plate, define the temperature at the time point, and view the temperature field and other characteristics of the steel plate.

[0124] 13. Result output and data processing and analysis: Enter the post-processing mode, view and output the required data, or export the data to third-party software (such as Tecplot, etc.) to view the simulation cloud map, curve graph and characteristic data at any position. Based on the output results, the temperature field distribution, cooling rate, heat-affected zone size, etc. of the metal workpiece can be predicted and quantitatively characterized.

[0125] 14. Result verification: The post-processing results are exported as a simulation cloud diagram of test point A. Figure 8 (a) and the temperature variation curve of the specimen, and experimental verification using thermocouples Figure 8 (b) in the figure compares the numerical simulation results of test point A with the actual experimental results. Figure 8(c) in the figure shows that the simulation results are in perfect agreement with the experimental curves, with the maximum temperature difference between the simulation and the experimental results being only 5.9%, validating the accuracy and applicability of this heat source model for simulating the heat transfer characteristics of flame cutting on metal workpieces. The experimental temperature is slightly lower than the simulation temperature due to the heat conduction from the cutting platform at the bottom of the experimental steel plate, while the kerf area is set as an adiabatic boundary in the simulation. This can be adjusted based on actual conditions. Indirect heat conduction temperature measurements were used to verify the accuracy of the heat source model and simulation results.

[0126] Example 2 - To further illustrate the applicability of the combined numerical model and modeling simulation method proposed in the present invention to the prediction and quantitative characterization of the heat-affected zone, etc., a 307-5# cutting nozzle (cutting oxygen channel diameter 1.8 mm) is used, the metal workpiece material is Q345D low alloy steel plate, the cutting thickness is 50 mm, and the cutting process parameters are the recommended parameters: the cutting oxygen pressure is maintained at 0.7 MPa (gauge pressure), the preheating oxygen inlet pressure is maintained at 0.35 MPa (gauge pressure), and the propane inlet pressure is maintained at 0.05 MPa (gauge pressure). The gas flow Q is recorded using a self-developed pressure-flow test bench. g .

[0127] Step 1: Physical Model Establishment: Based on the target workpiece dimensions, a workpiece model with dimensions of 150mm × 80mm × 50mm was established. The kerf width was measured through multiple tests, averaging 4.8mm. The kerf area was loaded with 25 life / death unit blocks, each measuring 4.8mm × 6mm × 50mm. To accurately determine heat transfer characteristics, cooling rates, and quantitatively analyze heat-affected zone (HAZ) dimensions, the model's input conditions must be realistic and accurate. For example, the size of the load in this step represents the average kerf width for the process parameters. While this approach is more complex and cumbersome than traditional estimation or unification methods, it is an effective method for ensuring subsequent HAZ dimensions and cooling rate curves.

[0128] Step 2: Model import: Import the 3D model into the finite element analysis software ANSYS-Mechanical in parasolid x_t format.

[0129] Step 3: Define the element type: select the eight-node hexahedral Solid70 body element and the surface element surf152.

[0130] Step 4: Meshing: Use hexahedral meshing to refine the meshes of the slit, the area adjacent to the slit (area A) and the study area (area B, D, E, and F). The total number of meshes is 184,300, and the minimum mesh unit size at the refinement point is approximately 0.48 mm × 0.5 mm × 0.5 mm. Each loading body has a total of 12,000 mesh units. Figure 9 Meshing needs to be performed based on the characteristics of flame cutting and the desired results in subsequent post-processing. The minimum mesh size of 0.5 mm × 0.5 mm × 0.5 mm is an experimentally verified mesh size that does not interfere with the heat transfer characteristics of the metal and does not cause virtual heat accumulation.

[0131] Step 5: Set the transient thermal analysis type, apply the overall initial temperature to 300K, use the finite element volume method and the ANSYS Thermal Solver solver. Set 25 time steps Δt = 1.2s, and each time step is divided into 10 substeps on average; set the 26th time step ΔT = 30s, and divide it into 30 substeps on average, as the cooling time of the metal workpiece, such as Figure 10 As shown. The time step is converted based on the flame cutting speed, kerf length, and cutting nozzle model (cutting oxygen channel diameter), which can simulate the heat conduction situation during the entire cutting period. The time step setting in this invention is divided according to the flame cutting mechanism and characteristics (the intensity of the chemical reaction); each time step is further divided into several sub-steps, which is actually an iteration at a smaller time increment. This is based on the solver (ANSYS Thermal Solver) to solve the nonlinear equation system and achieve convergence. This setting method has been verified by experiments and can extract the temperature field results at any time. The 26th time step is to obtain the cooling rate curve. The 30s time step is divided into 30 sub-steps. The sub-step length of 1s is sufficiently accurate for the slow cooling process.

[0132] Step 6: Set the heat transfer boundary conditions, set the center line of the slit as the adiabatic boundary condition, set the heat exchange between the surface of the cut workpiece and the surrounding environment to the superposition of natural convection heat transfer and thermal radiation heat transfer, and set the superposition heat transfer coefficient to

[0133]

[0134] Where: T is the surface temperature of the workpiece, K; T0 is the ambient temperature, 300K; h conv is the natural convection heat transfer coefficient; σ is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ) ; ε is the thermal emissivity of the material, and the rough steel surface is taken as 0.6-0.8.

[0135] Step 7: Input the cutting metal material parameters: density, specific heat capacity, thermal conductivity, thermal expansion coefficient, elastic modulus, Poisson's ratio and yield strength, such as Figure 11 shown.

[0136] Step 8: Set up the life and death unit: Based on the actual length of the workpiece 150mm and the cutting speed 5mm / s, calculate the total cutting time T = 30s, which is evenly divided into 25 time steps Δt = 1.2s. Select the first block and activate it at the first time step Δt (kill the unit) while suppressing other time steps. Select the second block and activate it at the second time step 2Δt; activate all time steps in turn, establish the second block to activate the first two time steps 2Δt, and suppress other blocks; follow this method to establish the life and death units of 25 blocks in turn, as shown in the following example: Figure 12 shown.

[0137] Step 9: Add another time step ΔT = 30s as the cooling time of the metal workpiece. This step is the key to calculating the cooling rate and heat-affected zone of the flame-cut metal workpiece.

[0138] Step 10: Define the preheating flame heat source model: Import and define the preheating flame heat source using the Gaussian surface moving heat source model, as shown below:

[0139] q (r) =q0exp(-kr 2 ) (2)

[0140] in

[0141]

[0142] but:

[0143]

[0144] Where: q (r) is the heat flux density at a distance r from the center of the heat source, W / m 2 ;q0 is the maximum heat flux, W / m 2 ; is the attenuation coefficient; η pre is the thermal efficiency of the Gaussian heat source, ranging from 0.2 to 0.35; Q g is the gas flow rate, m 3 / h; H v is the combustion calorific value of the gas, J / m 3 ; r0 represents the characteristic radius of the Gaussian heat source, which is determined by numerical simulation or experimental test. The heat source heat within this radius accounts for 95% of the total input heat; the exponential term exp(-kr 2 ) describes the decay rate of heat flux with r; r is the radial distance from the center of the heat source, in meters; v0 is the cutting speed (in this example, v0 = 4, 5, and 6 mm / s); x and y are the coordinates of the workpiece surface; x0 and y0 are the position parameters of the mobile heat source. Based on the characteristics of flame cutting, a movable Gaussian surface heat source model that matches reality was created.

[0145] Name the heat source "GAUSSIAN HEAT SOURCE", edit the expression or import it into APDL-Parameters for automatic editing, and enter the code into the software ANSYS-Mechanical-Transient Thermal-Commands.

[0146] Step 11: Define the heat source model of the ferrite reaction body, cylindrical heat source, workpiece thickness h = 50mm, cutting oxygen flow loading body volume V = πr1 2 h.

[0147]

[0148] Where: A gen The total heat generated by the iron-oxygen reaction is obtained by examining the composition of the iron-oxygen reaction product and calculating the calorific value A. gen =61560J;η gen The heat efficiency of the fuel iron-oxygen combustion reaction, η gen =0.25; r1 = 0.0024m; h is the height of the column, i.e. the thickness of the metal workpiece, m; r e is the outlet radius of the cutting oxygen channel; D(x) is a unit step function, which means the effective radius of the heat source r1 is the radius of the cutting oxygen jet r e =0.0009m, the heat generation rate remains constant at the peak heat flux. When the radius of the cutting oxygen jet is exceeded, the heat generation rate decays exponentially. The total heat generation is determined by examining the composition of the iron-oxygen reaction combustion products or by estimating theoretical values. The body heat source is a heat source model created based on the cutting mechanism.

[0149] Name the heat source "BODY HEAT SOURCE";

[0150] Step 12: Heat source application and solution analysis: Using the characteristics of the flame cutting nozzle and the steel plate, select the cutting speed and other process parameters, and use the heat source formula to import the expression into the Mechanical APDL product launcher to calculate the heat source motion trajectory command, and apply it to the surface and inside of the steel plate; define the time point and check the temperature field characteristics of the metal workpiece. The accuracy of the temperature field is the key to subsequent process control, cooling rate analysis and heat affected zone prediction.

[0151] Step 13: Result Output and Data Processing and Analysis: Enter post-processing mode and view and output the required data, or export the data to third-party software (such as Tecplot) for viewing simulation cloud diagrams, curves, and feature data at any location. Based on the output results, the temperature field distribution, cooling rate, and heat-affected zone size of the metal workpiece can be predicted and quantitatively characterized. Analyzing the cooling rate and heat-affected zone size during flame cutting of metal workpieces can significantly reduce material utilization, improve flame cutting quality, and provide microscopic control over the evolution and transformation of metal structures.

[0152] Step 14: Check the temperature field of each point on the surface of the metal workpiece over time: For example, Figure 13 Figure a shows the temperature cloud of the metal workpiece at different times under a cutting speed of 5 mm / s. This dynamically and intuitively displays the cutting kerf formation process. The temperature changes steadily as the cutting heat source moves, with the maximum temperature of the metal workpiece located at the center of the heat source's path, approximately 2200°C. As the heat source rapidly moves along the cutting direction, the workpiece temperature behind the heat source gradually decreases. This is because as the heat source moves forward, the rearward region no longer receives heat input, and heat is dissipated through conduction, convection, and radiation, causing the temperature to continue to drop. The temperature of the metal workpiece can be displayed at any position, along any line, or across any cross-section. Points AF in the figure are test points selected to verify the accuracy of the numerical simulation. Figure 13 b is the temperature variation curve of test point AF over time. Experimental verification was carried out on each test point based on thermocouples. The results show that the numerical simulation results of each point are completely consistent with the experimental results. Among them, the difference between the numerical simulation and experimental results of point F is the largest because it is located at the center of the heat source. Figure 13 Figure b shows a comparison curve between the numerical simulation and experimental test results at point F. The maximum temperature at point F in the numerical simulation is 2192°C, and the temperature at this point increases the fastest. However, after reaching its maximum temperature, it immediately drops to 0°C. This is because when the heat source moves to the death unit, the unit is "deactivated" and the temperature is forcibly set to 0°C. The experimentally measured maximum temperature at point F is 2088°C, with an error of only 4.74%, highly consistent with the simulation value. After reaching its maximum temperature, the temperature drops rapidly to the ambient temperature. This is because the thermocouple still needs to automatically cool down after the molten metal is blown away. Numerical simulation can accurately analyze and predict the temperature values ​​at each point, and the accuracy and reliability have been verified by experiments.

[0153] Step 15: Check the temperature field of any cross section of the cut workpiece at a certain moment: Figure 14 a is the temperature cloud of the heat source at t=15s through the BDE point on the YZ section, from the MM′ section Figure 14As can be seen from b, the highest temperature appears on the upper surface of the workpiece, which is about 2200℃; while the highest temperature on the bottom surface of the workpiece is about 1755℃. The upper and lower surface temperatures are much higher than the melting point of the material, 1500℃. Based on this derived result, it can be judged whether the cutting conditions are met. Under this process parameter, the lower surface temperature is much higher than the melting point of the metal, indicating that the heat input is too large. Based on this result, the cutting speed or cutting workpiece thickness in actual cutting can be adjusted to improve cutting quality and reduce energy loss. In addition, Figure 14 b also shows that the temperature difference between the upper and lower surfaces of the workpiece is 445°C, which is much lower than the average temperature of the heat source. This shows that in flame cutting, the preheating flame only provides a small amount of heat energy, about 20% of the total heat, while the heat generated by the iron-oxygen reaction is the main factor that maintains the continuous cutting. It can be seen that the heat source model proposed in this invention can accurately analyze the proportion of heat input in the preheating flame when cutting different process parameters, thicknesses, and materials, so as to control the cutting quality according to the upper and lower surface temperatures of the cutting. The temperature distribution at any depth on any cross section can also be extracted from the simulation results. Figure 14 c shows the temperature change curves at Z = -2, -25, and -50 mm on the MM′ section. The results show that the temperature values ​​at different cutting depths on the section gradually decrease from the upper surface to the lower surface of the workpiece, indicating that heat is also dissipated through conduction, convection, and radiation in the thickness direction of the workpiece, resulting in a continuous drop in temperature, so that there is a certain temperature difference in the workpiece at different thicknesses, and the greater the thickness of the workpiece, the greater the temperature difference; it can be seen from the above simulation results that the heat source model proposed in the present invention can output the temperature change of any point, line, section, and any moment of the cutting workpiece.

[0154] Step 16: Check the effect of cutting speed on temperature field, cooling rate, etc.: By setting the heat source moving speed v = 4mm / s, 5mm / s and 6mm / s (set in the above step 8), and calculating T and Δt at the same time, the temperature cloud map under the conditions of cutting speed of 4mm / s, 5mm / s and 6mm / s can be compared. Taking the cloud map of the workpiece surface as an example, the simulation results under each cutting speed are imported into the third-party software Tecplot for observation, and measured with a ruler, such as Figure 15 As shown in the figure, as the heat source movement speed increases, the length of the heat source center area decreases, reaching 3.25mm, 1.96mm, and 1.59mm, respectively; and the maximum temperature at the heat source center decreases, reaching 2200°C, 2129°C, and 2065°C, respectively. This indicates that the heat source movement speed is negatively correlated with the heat input per unit length. As the heat source movement speed increases, the heat input per unit length of the workpiece decreases, shortening the time the heat source acts locally. This causes the high-temperature area to shrink due to insufficient heat input and shortened diffusion time. The peak temperature also decreases due to insufficient heat input and shortened heating time.

[0155] Step 17: Calculate the cooling rate of the material: Figure 16 The temperature distribution curves for test points B and F at different cutting speeds show that the maximum temperature at these points decreases with increasing cutting speed, consistent with the temperature contour map at the center of the heat source. The temperature curves for test point B at different cutting speeds show that the maximum temperature at point B gradually decreases with increasing cutting speed. When the speed increases to 6 mm / s, the maximum temperature at point B is below the melting point of the material, indicating that the metal at this location has not melted and the metal structure remains in the solid phase transition range.

[0156] In the field of welding engineering, Δt is generally used. 8 / 5 The cooling behavior of carbon steel and low alloy steel in the critical temperature range (800℃ to 500℃) is quantitatively characterized by calculating the time Δt consumed by the metal material to cool from 800℃ to 500℃. 8 / 5 , to determine the actual cooling rate V in this temperature range 8 / 5 ,Right now

[0157]

[0158] Where: V 8 / 5 is the cooling rate, °C / s; Δt 8 / 5 is the cooling time from 800℃ to 500℃, ℃.

[0159] It can be seen from the derived data and the above formula that when the cutting speed v = 4mm, 5mm, and 6mm, the cooling rate is approximately 45℃ / s, 81℃ / s, and 131℃ / s, respectively. That is, the greater the cutting speed, the greater the cooling rate of the workpiece; under the above cutting speed, the cooling rate of the metal at test point B is greater than the CCR threshold of the material (Q345D) (critical cooling rate 30℃ / s). From the calculation results, it can be seen that the cooling rate at 3mm away from the kerf is greater than the critical cooling rate of the material. The metal structure at this location is prone to martensitic transformation, as well as local hardness increase, stress concentration, and the risk of cold cracks. In actual cutting, preheating can be used to prevent this risk. It can be seen that the heat source model and simulation method proposed in the present invention can quantify the cooling rate of the metal workpiece under the cutting process, providing a theoretical basis for the optimization of cutting process parameters.

[0160] Step 18: Predict and quantify the heat-affected zone of the cut workpiece: derive the cross-sectional temperature changes of the upper and lower surfaces of the workpiece when the cutting speed v = 4mm / s, 5mm / s, and 6mm / s, such as Figure 17As shown in the figure, the higher the cutting speed, the lower the peak temperature of the upper and lower surfaces of the workpiece. When the cutting speed v = 6mm / s, the maximum temperature of the lower surface of the workpiece is about 1750℃, which is much higher than the melting point of the material, indicating that the cutting conditions can still be met at this speed. The temperature of the metal workpiece gradually diffuses symmetrically from the center of the heat source to the far end. In welding engineering, the SCHAZ line (727℃) is generally used to represent the boundary of the heat affected zone. The distance from the intersection of the SCHAZ line and the temperature curve to the edge of the kerf is the width of the heat affected zone under this process condition. Figure 17 It can be seen that when the cutting speed v = 6mm / s, the width of the heat-affected zone is the smallest, with the width of the heat-affected zone on the upper surface being approximately 2.9mm and that on the lower surface being approximately 1.2mm. This example shows that the heat source model and simulation method proposed in this invention can effectively and accurately predict the size of the heat-affected zone of the incision.

[0161] Step 19: Experimental verification of numerical simulation results: Based on the above 307-5# propane cutting nozzle and cutting process parameters, a cutting test was conducted on a 50mm thick Q345D low carbon steel plate using cutting speeds of 4mm / s, 5mm / s and 6mm / s (see Figure 18 (a)). The results show that as the cutting speed increases, the cutting surface quality gradually improves. Figure 18 (b) It can be seen that when v = 4mm / s, the upper surface of the workpiece exhibits melt collapse, and there is a small amount of dross on the lower surface. The verticality and surface roughness are poor, indicating that the heat input is too high under this process, resulting in excessive melting of the parent material. When v = 5mm / s, the collapse disappears, and a small amount of dross is observed on the lower surface of the workpiece. Combined with the cutting, there is no obvious drag, indicating that the cutting speed is still too low, and the molten metal is too much and accumulates at the bottom due to lack of timely blowing. When v = 6mm / s, the cut section is flat and smooth, with no melt collapse or dross. This indicates that at this speed, the cutting oxygen jet and the production rate of the molten metal are in dynamic equilibrium, the amount of slag is small and completely blown away, and only a thin slag layer that is easily detached remains on the surface. The experimental results are completely consistent with the conclusion of the numerical simulation results that the heat source movement speed is negatively correlated with the heat input.

[0162] In summary, the oxygen-flame cutting simulation method proposed in the present invention can accurately simulate the temperature field of each point, line, and cross-section of the cut workpiece, calculate the cooling rate under different processes, and accurately predict and quantify the cutting heat-affected zone. This provides a theoretical basis for further improving cutting quality and optimizing cutting process parameters, and solves the problem of being unable to predict and accurately control cutting quality during flame cutting. The numerical simulation complexity of oxygen-flame cutting is much greater than that of welding or laser cutting. Its core difficulty lies in the turbulent combustion of the preheating flame, the multi-stage exothermic oxidation reaction of the iron-oxygen reaction, and the slag dynamics of slag removal. Existing heat source models do not conform to the mechanism of oxygen-flame cutting and the dynamic removal behavior of molten metal. The oxygen-flame cutting simulation method proposed in the present invention is based on the flame cutting mechanism and uses the life-death unit method to dynamically simulate the flame cutting process. After experimental and test verification, it has high accuracy and applicability for the heat transfer characteristics, temperature field changes, cooling rate, and heat-affected zone prediction and quantitative characterization of metal workpieces during flame cutting. The heat source model proposed in this invention can effectively reduce the number of process tests, shorten the cutting process development cycle, and achieve precise control of the cutting process and quality, providing a theoretical basis for the development of industrial cutting solutions and digital twin systems.

[0163] The above inventions are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. An oxygen-flame cutting simulation method, characterized in that: The following steps are involved: Establish a 3D model of the cut workpiece: Model the slit area separately, determine the number of birth and death unit blocks in the slit area, and set the slit as a birth and death unit block model; Model import: import the three-dimensional model of the cut workpiece into the finite element analysis software and set parameters, including setting the solver, inserting birth and death units into the solver, selecting the first block to activate it at the first time step Δt and suppressing other time steps, establishing the second block to activate the first two time steps 2Δt and suppressing others, and establishing all birth and death unit blocks in sequence; Define the combined heat source model: Use a cylindrical heat source model to simulate the heat source generated by the chemical reaction between cutting oxygen and the cutting workpiece, and combine it with a Gaussian surface heat source that simulates the heat release of the preheating flame to form a combined heat source model. Import it into the finite element analysis software and apply it to the cutting workpiece. Perform oxygen-flame cutting simulation based on the life and death unit block.

2. The oxygen-flame cutting simulation method according to claim 1, characterized in that: The parameter setting includes the following steps: Define element types and mesh divisions; Set the analysis type, initial conditions, and solver: Use transient thermal analysis as the solver analysis type, apply the overall initial temperature, and use the finite element volume method and ANSYS Thermal Solver. Set the heat transfer boundary conditions and set the center line of the slit as the adiabatic boundary condition: set the heat exchange mode between the surface of the cut workpiece and the surrounding environment during the heat transfer process to the superposition of natural convection heat transfer and thermal radiation heat transfer; Set cutting metal material parameters: set the material's elastic modulus, thermal expansion coefficient, Poisson's ratio and yield strength.

3. The oxygen-flame cutting simulation method according to claim 2, characterized in that: The heat exchange mode after superposition is expressed by the heat exchange coefficient, which is expressed by the following formula: Where: T is the surface temperature of the workpiece, K; T0 is the ambient temperature, 300K; h conv is the natural convection heat transfer coefficient; σ is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ), ε is the thermal emissivity of the material.

4. The oxygen-flame cutting simulation method according to claim 2, wherein: The grid division includes performing grid refinement processing on key research areas, and the key research areas include: the cutting seam and its edge, the heat-affected zone and other positions of the workpiece that need to be analyzed.

5. The oxygen-flame cutting simulation method according to claim 1, characterized in that: The life and death unit setting also includes: Set the time step: determine the total cutting time T and the time Δt required in each time step, and set the calculation step size for each Δt time; Define the preheating flame heat source model: The preheating flame heat source adopts the Gaussian surface moving heat source model.

6. The oxygen-flame cutting simulation method according to claim 5, characterized in that: The Gaussian surface moving heat source model is expressed by heat flux density. The heat flux density of the Gaussian surface moving heat source model is expressed as follows: Where q (r) is the heat flux density at a distance r from the center of the heat source, in W / m 2 ; η pre is the thermal efficiency of the Gaussian heat source, ranging from 0.2 to 0.35; Q g is the gas flow rate, m 3 / h; H v is the combustion calorific value of the gas, J / m 3 ; r0 represents the characteristic radius of the Gaussian heat source; v0 is the cutting speed, mm / s; Δt is the time required in each time step; x and y are the coordinates of the workpiece surface.

7. The oxygen-flame cutting simulation method according to claim 6, characterized in that: The r0 is determined by numerical simulation using Fluent or by experimental method.

8. The oxygen-flame cutting simulation method according to claim 1, characterized in that: The heat generated by the cylindrical heat source to the load q (r, x) is expressed by the following formula: Where: η gen The heat efficiency of the fuel iron-oxygen combustion reaction, η gen =0.25; A gen is the total heat generated by the iron-oxide reaction, J; r1 is the effective radius of the heat source, simplified to the slit width / 2, m; h is the height of the column, that is, the thickness of the metal workpiece, m; r e is the outlet radius of the cutting oxygen channel; D(x) is a unit step function, which means that the effective radius of the heat source r1 is within the radius of the cutting oxygen jet r e When the radius of the cutting oxygen jet is exceeded, the heat generation rate decays exponentially; v0 is the cutting speed, mm / s; x and y are the coordinates of the workpiece surface.

9. The oxygen-flame cutting simulation method according to claim 1, wherein: The oxygen-flame cutting simulation by importing the finite element analysis software includes: Select cutting process parameters, and import the heat source formula of the combined heat source model into the Mechanical APDL product launcher to calculate the heat source motion trajectory, which is applied to the surface and interior of the cut workpiece.

10. The oxygen-flame cutting simulation method according to claim 1, characterized in that: Also includes: Result output and data processing and analysis: After the simulated cutting is completed, simulation cloud maps, curves and characteristic data of any position are output. Based on the output results, the temperature field distribution, cooling rate and heat-affected zone size of the metal workpiece are predicted and quantitatively characterized; Result verification.

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