A CFD-based nozzle performance evaluation method, computer and readable storage medium

Abstract

The present invention provides a CFD-based nozzle performance evaluation method, a computer, and a readable storage medium, which establishes a three-dimensional model of a nozzle to be evaluated under cutting conditions; imports the three-dimensional model to be evaluated into CFD software, generates a fluid domain model, and performs grid division; divides the inner wall of the nozzle and the inner wall of the cutting slit into boundary layers; sets pressure and flow data in the fluid domain model, simulates and calculates the flow field distribution under cutting conditions; captures preset comparison parameters from the flow field, compares them with relevant parameters of the reference three-dimensional model, and determines the performance of the nozzle to be evaluated; and changes the nozzle structure. The evaluation method not only improves development efficiency and saves development costs, but also helps to optimize and design the nozzle, avoiding the situation where the cutting effect after use cannot meet the requirements. The present invention can also set the pressure size of the boundary condition of the inlet to multiple conditions according to the needs of the simulation conditions, and conducts comprehensive comparisons under different cutting conditions to improve the performance of the nozzle.

Description

Technical Field

[0001] The present invention relates to the technical field of laser cutting nozzles, and in particular to a CFD-based nozzle performance evaluation method, a computer, and a readable storage medium. Background Art

[0002] Laser cutting uses a laser beam to melt metal. The gases released during the cutting process remove the molten metal and some of the heat from the cut. The nozzle is a crucial component in laser cutting, serving as a channel for the laser beam and gases to escape. The nozzle's structural performance impacts laser cutting quality, ensuring optimal processing quality and efficiency.

[0003] In the current laser cutting industry, most of the nozzles used by major laser cutting machine equipment manufacturers are conical nozzles and groove nozzles. The existing practical demand is to change the nozzle structure, optimize the outlet gas flow field, and thus optimize the cutting efficiency.

[0004] Currently, nozzle design typically relies on an experimental approach. This involves designing and calculating different nozzle structures, producing prototypes, and testing them in actual operating conditions to determine if they meet production requirements. This approach is not only inefficient, time-consuming, and expensive, but can also sometimes fail to meet operating requirements and achieve the desired cutting results. Summary of the Invention

[0005] The present invention provides a nozzle performance evaluation method based on CFD, which obtains the nozzle gas flow field condition under actual working conditions through CFD simulation calculation, and then develops a nozzle that meets the working condition requirements, improves development efficiency and saves development costs.

[0006] Methods include:

[0007] Step 1: Create a three-dimensional model of the nozzle to be evaluated under cutting conditions;

[0008] Step 2: Import the 3D model to be evaluated into the CFD software, generate the fluid domain model, and perform meshing;

[0009] Step 3: Divide the inner wall of the nozzle and the inner wall of the cutting slit into boundary layers;

[0010] Step 4: Set pressure and flow data in the fluid domain model and simulate and calculate the flow field distribution under cutting conditions;

[0011] Step 5: Capture preset comparison parameters from the flow field and compare them with relevant parameters of the reference 3D model to determine the performance of the nozzle to be evaluated;

[0012] Step 6: Change the nozzle structure, import the 3D model to be evaluated, and repeat steps 2 to 5 to determine the nozzle performance under different structural forms.

[0013] Preferably, the three-dimensional model to be evaluated established in step 1 is a three-dimensional model based on the gap between the nozzle and the steel plate during laser cutting;

[0014] The parameters of the 3D model to be evaluated include: the proportional nozzle configuration and actual cutting conditions, the distance between the nozzle and the steel plate, the size of the steel plate, the width and depth of the steel plate cutting, and the inclination of the cutting.

[0015] Preferably, in step 1, when establishing the three-dimensional diagram of the nozzle cutting, a closed three-dimensional model of the flow channel of the nozzle cavity is established.

[0016] Preferably, step three further comprises: dividing the inner wall of the nozzle and the inner wall of the cutting slot into boundary layers, and the height of the first boundary layer of the inner wall of the cutting slot is less than 8*10 -7 rice.

[0017] Preferably, in step three, the nozzle inlet convergence section angle of the three-dimensional model to be evaluated is set to 60°, with a smooth transition section in the middle, the length of the divergence section is 4.5 mm, and the divergence angle is 10°.

[0018] Preferably, step 4 further includes configuring the maximum skness value of the CFD software grid to be below 0.85, setting multiple inlet pressure flow boundaries, and setting the outlet pressure to 0;

[0019] The pressure values ​​of multiple inlets are simulated and calculated, and the shear stress of the slit wall, the gas flow rate entering the slit, the velocity of the nozzle outlet gas and the change of turbulence intensity over time are calculated.

[0020] Preferably, the preset comparison parameters captured from the flow field include: shear stress of the slit wall, gas flow rate of the slit, velocity at the nozzle outlet and turbulence intensity.

[0021] Preferably, the KW-sst turbulence model is used as the flow field equation for the closed cutting fluid domain;

[0022] The gas is nitrogen or oxygen.

[0023] The present invention also provides a computer for implementing a CFD-based nozzle performance evaluation method, comprising:

[0024] a memory for storing a computer program and a CFD-based nozzle performance evaluation method;

[0025] The processor is configured to execute the computer program and the CFD-based nozzle performance evaluation method to implement the steps of the CFD-based nozzle performance evaluation method.

[0026] The present invention also provides a readable storage medium having a CFD-based nozzle performance evaluation method, wherein a computer program is stored on the readable storage medium, and the computer program is executed by a processor to implement the steps of the CFD-based nozzle performance evaluation method.

[0027] It can be seen from the above technical solutions that the present invention has the following advantages:

[0028] The CFD-based nozzle performance evaluation method provided by the present invention can conduct a rapid quantitative evaluation of the nozzle performance before processing or design, which not only improves development efficiency and saves development costs, but also helps to optimize and design the nozzle, avoiding the situation where the nozzle is blindly designed and tested, and the cutting effect cannot meet the expected demand level.

[0029] The CFD-based nozzle performance evaluation method provided by the present invention can be completed using drawings in the early stage of development, avoiding the need in the prior art to manufacture and test the nozzle in order to test the cutting performance of the nozzle, which causes waste of manpower and material resources and prolongs the R&D cycle. Therefore, this method greatly improves development efficiency and saves costs.

[0030] The present invention sets the nozzle inlet convergence section angle of the three-dimensional model to be evaluated to 60°, with a smooth transition section in the middle, a diffusion section length of 4.5 mm, and a diffusion angle of 10°. Compared with the existing nozzles, the shear stress of the gas on the wall and the gas flow entering the cutting seam can be increased, and the shear stress distribution is more even, and the cutting surface is delicate and smooth.

[0031] The present invention can also set the pressure of the boundary condition of the inlet to a variety of situations according to the needs of the simulated working conditions, and conduct comprehensive comparisons under different cutting working conditions to improve the performance of the nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for the description. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 The flow chart of the nozzle performance evaluation method based on CFD is shown in Figure 2.

[0034] Figure 2 This is a cross-sectional view of a nozzle after cutting in the prior art;

[0035] Figure 3 This is a cross-sectional view of a nozzle after cutting in the prior art;

[0036] Figure 4This is a physical picture of the nozzle cut section used after evaluation by the nozzle performance evaluation method;

[0037] Figure 5 This is a cross-sectional view of a nozzle that has been evaluated using the nozzle performance evaluation method. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] The units and algorithmic steps of each example described in the embodiments disclosed in the CFD-based nozzle performance evaluation method provided by this invention can be implemented using electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the above description generally describes the components and steps of each example according to their functionality. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Professionals may use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0040] In the CFD-based nozzle performance evaluation method provided by the present invention, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is merely a logical functional division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interface, device or unit, or it can be an electrical, mechanical or other form of connection.

[0041] The CFD-based nozzle performance evaluation method provided by the present invention uses CFD software to perform simulation calculations and evaluations. CFD software (Computational Fluid Dynamics), also known as computational fluid dynamics, or CFD for short, uses computers as tools and applies various discrete mathematical methods to perform numerical experiments, calculations, and simulation analyses on various fluid mechanics problems to solve the problems faced in nozzle design. Figure 1 As shown, the method specifically includes:

[0042] S101, establishing a three-dimensional model of the nozzle to be evaluated under cutting conditions;

[0043] The established 3D model to be evaluated is based on the 3D model between the nozzle and the steel plate during laser cutting.

[0044] The 3D model parameters to be evaluated include the nozzle configuration proportional to the actual cutting conditions, the distance between the nozzle and the steel plate, the steel plate dimensions, the kerf width and depth, and the kerf inclination. The vaporization zone above the kerf coincides with the nozzle axis, while the lower melting zone corresponds to the kerf inclination, which is approximately 3°-6°.

[0045] For the nozzle, when establishing the three-dimensional diagram of the nozzle cutting, a closed three-dimensional model of the flow channel in the nozzle cavity is established.

[0046] The present invention is based on restoring the state of the region sensitive to cutting when establishing the three-dimensional model to be evaluated.

[0047] As an embodiment, the radius of the computational fluid domain is about 50-100 mm, the slit width can be selected to be 1-2 mm, the nozzle height can be 0.5-1 mm, the nozzle diameter is 3.5-4 mm, and the cutting-insensitive area can be appropriately simplified.

[0048] When establishing a three-dimensional diagram of nozzle cutting, the present invention removes components that do not affect flow channel generation and are not in direct contact with the fluid medium and small components that do not affect the calculation results, and only establishes a three-dimensional model of the flow channel closure in the nozzle cavity. Only the fluid part can be considered to avoid affecting the measurement, and the grid quality and calculation efficiency can also be improved, simplifying the analysis process.

[0049] S102, importing the three-dimensional model to be evaluated into CFD software, generating a fluid domain model, and performing meshing;

[0050] When dividing the grid, configure the number of grids inside the nozzle and the number of grids in the slit. Add an appropriate boundary layer inside the nozzle. The grid in the slit should be at least 30 to 40 layers. According to the cutting situation, and based on the comparison between the calculation results and the actual working conditions, the height of the boundary layer grid of the first layer is less than 8*10 -7 m, can meet the requirements, the mesh between the nozzle and the steel plate is encrypted. In the fluid domain size, the number of meshes is greater than 3 million, and the skness of the CFD software is less than 0.9.

[0051] This invention uses the KW-SST turbulence model as the flow field equation for the closed cutting fluid domain; a compressible solver can be used. Nitrogen or oxygen is selected as the gas. The gas inlet is defined as a pressure inlet, and parameters are set based on actual conditions. For example, the nozzle inlet pressure is defined as 1 MPa based on typical site requirements.

[0052] S103, dividing the inner wall of the nozzle and the inner wall of the cutting slit into boundary layers;

[0053] S104, setting pressure and flow data in the fluid domain model, and simulating and calculating the flow field distribution under the cutting condition;

[0054] When using CFD software to evaluate the nozzle performance, the present invention sets the gas as a compressible fluid, selects transient calculation, and uses a time step of less than 0.0001s. The discrete reconstruction format of the gradient term, divergence term, and Laplace term uses the second-order GaussLinear series format. The Euler format is recommended for the time derivative term, and the calculation step is 1000 steps.

[0055] According to the evaluation results, the residual error of CFD software can be set to less than 10 -3 If the calculation does not converge, the second-order linear Gaussian discretization format can be changed to a first-order upwind format, and the calculation step size and relaxation factor can be appropriately reduced.

[0056] S105 , capturing preset comparison parameters from the flow field, comparing them with relevant parameters of the reference three-dimensional model, and determining the performance of the nozzle to be evaluated.

[0057] S106 , changing the nozzle structure, importing the three-dimensional model to be evaluated, and repeating S102 to S105 to determine the nozzle performance under different structural forms.

[0058] The present invention can compare the nozzle flow field of the three-dimensional model to be evaluated with the nozzle flow field of the reference three-dimensional model. The quality of the nozzle to be evaluated is judged based on parameters such as whether the size of the wall shear stress affects the cutting speed; whether the distribution balance of the shear stress affects the quality of the cut surface, whether the cut surface is delicate and smooth, the depth of the cut lines, and whether there is slag at the bottom of the cut surface. In addition, the present invention also evaluates the gas flow rate entering the cutting seam; since the turbulence intensity at the nozzle outlet also directly affects the quality of the cut surface, when performing the comparison, the quality of the nozzle to be evaluated can also be judged based on the turbulence intensity at the nozzle outlet. Through the comprehensive comparison of multiple parameters, the nozzle can be comprehensively evaluated.

[0059] Furthermore, the present invention evaluates nozzle performance based on the shear stress exerted by the gas on the slit wall and the gas flow rate entering the slit. These factors also significantly impact cutting efficiency. Other parameters influencing cutting efficiency include the turbulence intensity of the gas at the nozzle outlet, the gas velocity distribution along the nozzle axis, and the amplitude of velocity fluctuations. Furthermore, the inlet boundary pressure can be set to various levels to simulate the desired conditions, allowing for comprehensive comparison of nozzle performance under different cutting conditions.

[0060] The gas's slag removal capacity is determined by statistically analyzing gas parameters during cutting. This means the required gas flow rate in critical areas is determined based on the shear stress on the kerf wall and the gas flow rate entering the kerf. This is because greater shear stress and greater gas flow rate facilitate the removal of molten metal, ensuring the quality of the cut kerf.

[0061] Specifically, the present invention configures the maximum skness value of the CFD software grid to below 0.85, sets multiple inlet pressure and flow boundaries, and sets the outlet pressure to 0; simulates and calculates the pressure values ​​of multiple inlets, and calculates the shear stress of the slit wall, the gas flow entering the slit, the velocity of the nozzle outlet gas, and the change in turbulence intensity over time.

[0062] Because shear stress directly affects cutting performance, the present invention calculates the average shear stress on the slit wall. The nozzle performance is judged by comparing the average shear stress distribution. If the average shear stress distribution is relatively even, the cut surface will be smooth and stable when the same cutting parameters are used. If the average shear stress distribution is uneven, the cut surface will easily develop rough lines, affecting the cutting quality.

[0063] Furthermore, the present invention also measures the stability of the gas flow rate entering the slit at each time step. The flow rate influences cutting speed. If the flow rate fluctuates over time, it will affect the quality of the cut surface. Therefore, the slit gas flow rate and stability must be maintained at each time step during the cutting process.

[0064] According to the above evaluation method, when designing the nozzle, evaluation calculations can be performed first, and then processing and manufacturing can be carried out after the expected simulation analysis is completed.

[0065] The CFD-based nozzle performance evaluation method provided by the present invention can evaluate the cutting ability of the nozzle under a given air pressure, improve the development and design efficiency of the nozzle, and ensure the quality of the nozzle design. In actual development projects, the nozzle designed according to the evaluation method has significantly improved the cutting speed and cutting surface quality during the stainless steel cutting process.

[0066] As an application example of the present invention, the designed nozzle uses high-pressure nitrogen to cut stainless steel. The outlet Mach number of this embodiment is designed to be 2, the stainless steel plate thickness is 10mm, 12mm, and 14mm, the grade is 316L, and the laser power is 12000W. During cutting, the nozzle is adjusted to the fastest cutting speed. The fastest cutting speed is shown in the table below. It can be seen that the optimized nozzle increases the cutting speed by approximately 10%. The cutting surface image is as follows: Figures 2 to 5 As shown, it can be seen that the quality of the cutting surface has been greatly improved.

[0067] Nozzle fastest cutting speed comparison table

[0068] Nozzle model\plate thickness 10mm 12mm 14mm Optimized nozzle 8.3m / s 5.0m / s 4.2m / s Current nozzle 7.2m / s 4.5m / s 3.7m / s

[0069] Based on the above-mentioned nozzle performance evaluation method, the present invention also provides a computer for implementing the CFD-based nozzle performance evaluation method, including: a memory for storing a computer program and the CFD-based nozzle performance evaluation method; a processor for executing the computer program and the CFD-based nozzle performance evaluation method to implement the steps of the CFD-based nozzle performance evaluation method.

[0070] The present invention may store CFD in a readable storage medium, wherein the readable storage medium stores a computer program, and the computer program is executed by a processor to implement the steps of the nozzle performance evaluation method based on CFD.

[0071] The computer system for implementing the CFD-based nozzle performance evaluation method provided by the present invention incorporates the elements and algorithmic steps of each example described in the embodiments disclosed herein and can be implemented using electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been generally described above by function. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the present invention.

[0072] Those skilled in the art will appreciate that various aspects of the CFD-based nozzle performance evaluation method provided herein can be implemented as a system, method, or program product. Therefore, various aspects of the present disclosure can be implemented in the following forms: a complete hardware implementation, a complete software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, which may be collectively referred to herein as "circuits," "modules," or "systems."

[0073] The readable storage medium stores a program product for implementing the CFD-based nozzle performance evaluation method provided by the present invention. In some possible implementations, various aspects of the present disclosure may also be implemented in the form of a program product, which includes program code. When the program product is executed on a terminal device, the program code is used to cause the terminal device to execute the steps according to various exemplary embodiments of the present disclosure described in the "Exemplary Methods" section above.

[0074] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nozzle performance evaluation method based on CFD, characterized in that: Methods include: Step 1: Create a three-dimensional model of the nozzle to be evaluated under cutting conditions; When establishing the three-dimensional diagram of the nozzle cutting, a closed three-dimensional model of the flow channel in the nozzle cavity is established; The established 3D model to be evaluated is based on the 3D model between the nozzle and the steel plate during laser cutting; The parameters of the 3D model to be evaluated include: the proportional nozzle configuration and actual cutting conditions, the distance between the nozzle and the steel plate, the size of the steel plate, the width and depth of the steel plate kerf, and the inclination of the kerf; Step 2: Import the 3D model to be evaluated into the CFD software, generate the fluid domain model, and perform meshing; Step 3: Divide the inner wall of the nozzle and the inner wall of the cutting slit into boundary layers; The nozzle inlet convergence section of the 3D model to be evaluated is set at an angle of 60°, with a smooth transition section in the middle, a divergence section of 4.5 mm in length, and a divergence angle of 10°; The boundary layer of the nozzle inner wall and the cutting slot inner wall is divided, and the height of the first boundary layer of the cutting slot inner wall is less than 8*10 -7 rice; Step 4: Set pressure and flow data in the fluid domain model and simulate and calculate the flow field distribution under cutting conditions; Set the maximum skness value of the CFD software mesh to below 0.85, set multiple inlet pressure and flow boundaries, and set the outlet pressure to 0; Simulate and calculate the pressure values ​​of multiple inlets, and calculate the shear stress of the slit wall, the gas flow rate entering the slit, the velocity of the nozzle outlet gas, and the change of turbulence intensity over time; Step 5: Capture preset comparison parameters from the flow field and compare them with relevant parameters of the reference 3D model to determine the performance of the nozzle to be evaluated; Step 6: Change the nozzle structure, import the 3D model to be evaluated, and repeat steps 2 to 5 to determine the nozzle performance under different structural forms; Use the KW-sst turbulence model as the flow field equation for the closed cutting fluid domain; The gas is nitrogen or oxygen.

2. The nozzle performance evaluation method based on CFD according to claim 1, characterized in that: The preset comparison parameters captured from the flow field include: the shear stress of the slit wall, the gas flow rate of the slit, the velocity at the nozzle outlet and the turbulence intensity.

3. A computer for implementing a CFD-based nozzle performance evaluation method, characterized in that: include: a memory for storing a computer program and a CFD-based nozzle performance evaluation method; A processor is used to execute the computer program and the CFD-based nozzle performance evaluation method to implement the steps of the CFD-based nozzle performance evaluation method as described in any one of claims 1 to 2.

4. A readable storage medium having a CFD-based nozzle performance evaluation method, characterized in that: The readable storage medium stores a computer program, which is executed by a processor to implement the steps of the nozzle performance evaluation method based on CFD according to any one of claims 1 to 2.

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