A method for determining the parameter values of laser cutting magnesium alloys based on thermal effect simulation

Abstract

The present invention discloses a method for determining the parameter values of laser cutting of magnesium alloys based on thermal effect simulation, belonging to the technical field of laser cutting of magnesium alloys, and comprising the steps of: S1, obtaining the key parameters affecting the laser cutting of magnesium alloys; S2, mapping the actual key parameters of laser cutting into simulation parameters; S3, fitting the thermal physical property parameters of magnesium alloys, defining and setting the simulation process parameters of laser cutting magnesium alloys; S4, carrying out temperature field simulation and judging the temperature range; S5, outputting the simulation results and analysis results. The present invention proposes a method for determining the parameter values of laser cutting of magnesium alloys based on thermal effect simulation, which can control the processing temperature of magnesium alloy materials that are very sensitive to temperature changes within a suitable range.

Description

Technical Field

[0001] The present invention relates to the technical field of laser cutting of magnesium alloys, and more specifically, to a method for determining laser cutting parameter values of magnesium alloys based on thermal effect simulation. Background Art

[0002] Magnesium alloys have the advantages of low density, light weight, high specific strength and specific stiffness, good electromagnetic shielding performance, etc., and are currently widely used in fields such as electronic communication equipment and aerospace. The wide application of magnesium alloy materials also puts forward requirements for high quality, high precision and high speed in their processing technologies. Laser cutting technology relies on a high-energy laser beam as a heat source to melt the cutting material under the irradiation of the laser, and has advantages such as high processing efficiency, narrow cut width, small heat affected zone and wide application range. It plays an important role especially in the processing of some parts with high precision requirements. Therefore, the application of laser cutting in the processing of magnesium alloy materials is studied.

[0003] Laser cutting, as a complex thermal processing method, is always accompanied by thermal changes such as heat conduction, heat convection and thermal radiation during the cutting process. Different regions of the material obtain different energies at the same time, which causes the temperature of each region to change violently over time. The change of the temperature field will ultimately directly affect the cutting quality. At the same time, magnesium alloys have few outer electrons, relatively large atomic radii and relatively weak metal bond energies, so their melting points and boiling points are relatively low. Improper control of parameters during the thermal processing process is likely to cause the temperature to reach the vaporization temperature, resulting in material volatilization and intense combustion. Magnesium alloys also have characteristics such as chemically active, high thermal conductivity, large thermal expansion coefficient and small surface tension, making them more sensitive to temperature changes during the thermal processing process. Therefore, when using laser cutting for magnesium alloys, more attention needs to be paid to controlling the processing temperature within a suitable range.

[0004] The most fundamental aspect of laser cutting is to control the energy acting on the material. Currently, the main parameters affecting the energy input of laser cutting are mostly determined by experience, lacking a theoretical basis. There is no specific research available for reference in the field of laser cutting of magnesium alloys. It is difficult to obtain the temperature field distribution and change law during the laser cutting process through experiments. The temperature field model of laser cutting can be established by simulation software to solve the temperature field distribution during the cutting process. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for determining laser cutting parameter values of magnesium alloys based on thermal effect simulation, and propose a solution for determining the cutting parameters of laser cutting of magnesium alloys, which can control the processing temperature of magnesium alloy materials that are very sensitive to temperature changes within a suitable range.

[0006] The purpose of the present invention is achieved through the following solutions:

[0007] A method for determining the parameter values of laser cutting of magnesium alloy based on thermal effect simulation, comprising the following steps:

[0008] S1. Obtain the key parameters affecting the laser cutting of magnesium alloy;

[0009] S2. Map the actual key parameters of laser cutting to simulation parameters;

[0010] S3. Fit the thermal physical properties parameters of magnesium alloy, and define and set the simulation process parameters of laser cutting of magnesium alloy;

[0011] S4. Conduct temperature field simulation and judge the temperature range: Convert the laser cutting simulation heat source model into APDL language, run the APDL language to realize the thermal load loading on the specimen, and the thermal load moves along the set Z-axis direction; Discretize the entire laser cutting simulation process into single sub-steps, solve the temperature field distribution of each sub-step under the action of the heat source, and obtain the temperature field distribution result of the laser cutting process through the solution of each sub-step; In this process, define two element tables Tema and Temb, Tema is used to store the temperatures of all elements, Temb is used to store the temperatures of the elements at the cut seam, select the elements in Tema with temperatures higher than the boiling point temperature to form a new element set Temc, and select the elements in Temb with temperatures lower than the melting point temperature to form a new element set Temd; Judge the number of elements in Temc, if it is greater than 0, directly end the simulation, if it is equal to 0, then judge the number of Temd elements, if it is greater than 0, end the simulation, if it is less than 0, continue the simulation;

[0012] S5. Output the simulation results and analysis results.

[0013] Further, in step S1, the obtaining of the key parameters affecting the laser cutting of magnesium alloy specifically includes the following steps:

[0014] Construct the following relational expression:

[0015] ;

[0016] In the formula, is the laser heat flux density; P is the laser power; f is the laser frequency; r 0 is the laser spot radius; d is the adjacent laser pulse spacing; v is the laser cutting speed;

[0017] From the above relational expression, the key parameters affecting the laser cutting of magnesium alloy are obtained as laser power, cutting speed, defocus amount and laser frequency.

[0018] Further, in step S2, mapping the actual key parameters of laser cutting to simulation parameters specifically includes constructing a laser cutting heat source formula, which represents the heat source formula with laser power, cutting speed, laser frequency, and laser spot radius, and the expression is as follows:

[0019] ;

[0020] In the formula, q ( x,z ) is the heat source distribution function; A is the laser absorption rate of the material; r 0 is the laser spot radius; P is the laser power; f is the laser frequency; v is the cutting speed; x is the position of the heat source on the model X axis; x 0 is the position of the heat source center on the model X axis; z is the position of the heat source on the model Z axis; t is the laser cutting time.

[0021] Further, in step S3, fitting the thermal physical properties of magnesium alloy and defining and setting the key parameters of the laser cutting magnesium alloy simulation process specifically includes the following sub-steps:

[0022] S31, using the Lagrange interpolation method to fit and obtain the values before the boiling point temperature based on the determined thermal physical properties of the magnesium alloy material before 450°C. The expressions of the thermal conductivity, specific heat capacity, thermal expansion coefficient, and convective heat transfer coefficient fitted by the one-dimensional three-node Lagrange polynomial are as follows:

[0023] ;

[0024] In the formula, K ( t ) is the fitting formula of thermal conductivity; C ( t ) is the fitting formula of specific heat capacity; A ( t ) is the fitting formula of thermal expansion coefficient; Con ( t ) is the fitting formula of convective heat transfer coefficient; t is the temperature value;

[0025] S32, defining and setting the simulation process parameters, including: defining the element type and selecting the unit system, setting the obtained thermal physical properties of the material, establishing the model and dividing the grid elements, setting the solution options, setting the parameters in the heat source model, setting the steady-state analysis parameters, and defining the boundary conditions.

[0026] Further, in step S5, the output of the simulation results and analysis results specifically includes: viewing and outputting the temperature and stress change results through the GUI operation method, selecting unit points along the thickness Y-axis direction at the heat source loading position of the specimen to obtain their temperature values, obtaining the temperature distribution along the thickness direction after laser cutting, comparing the temperature value of the lower surface of the specimen with the melting point temperature value of the material, and comparing the highest temperature value during the cutting process with the boiling point temperature value.

[0027] Further, steps S1 to S4 are implemented by writing in APDL language, and step S5 is implemented through GUI operation.

[0028] The beneficial effects of the present invention include:

[0029] The present invention particularly aims at the laser cutting of magnesium alloys. Combining its material characteristics, a solution for determining the laser cutting parameter values is proposed, which can control the laser cutting temperature of magnesium alloy materials that are very sensitive to temperature changes within a suitable range. Further, by using the Lagrange interpolation method to fit the multi-term expression of the thermal physical properties parameters based on the known thermal physical properties parameter values of magnesium alloys, the thermal physical properties parameter values of magnesium alloys are obtained, improving the simulation accuracy. In the simulation process, adding the step of obtaining the temperature values at each unit point in real time and ending the simulation in a timely manner when the range is exceeded not only makes the cutting parameters preliminarily determined by the simulation be appropriate values but also omits meaningless simulation results. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is the flowchart of the steps of the method in the embodiment of the present invention;

[0032] Figure 2 It is the schematic diagram of laser cutting in the embodiment of the present invention;

[0033] Figure 3a It is the schematic diagram of the geometric model of the magnesium alloy plate in the embodiment of the present invention;

[0034] Figure 3b It is the schematic diagram of the unit model of the magnesium alloy plate after division in the embodiment of the present invention;

[0035] Figure 4 It is the temperature distribution nephogram during the cutting process of the magnesium alloy plate in the embodiment of the present invention. Detailed Embodiments

[0036] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or extended, replaced in any way.

[0037] In view of the problems in the background, the inventors of this application, after creative thinking, believe that:

[0038] Facing the actual problems encountered in laser cutting of magnesium alloys, parameters affecting cutting energy should be obtained according to laser cutting theory to verify the laser cutting processing experience theoretically. At the same time, the characteristics of magnesium alloys need to be specifically considered, and an adaptive theory on how to control the processing temperature within a suitable range should be proposed for this material.

[0039] Laser cutting is a complex metallurgical process involving knowledge such as the interaction between laser and material and the theory of material melting. The distribution and variation law of its transient temperature field are also very complex. After creative thinking, the present invention is based on establishing a temperature field model for laser cutting to solve the variation law of the temperature field during the cutting process of magnesium alloys, and uses the proposed adaptive cutting theory for magnesium alloys to further obtain reasonable values of laser cutting parameters.

[0040] Specifically, based on thermal effect simulation analysis, the inventive concept takes into account the main parameters affecting laser cutting obtained through laser cutting theory analysis, and then relates the actual processing parameters to the simulation parameters by deriving the heat source formula, enabling the main parameters to be adjusted in actual processing to be set in the simulation as well. In the temperature field simulation, the thermal physical properties of the material have a great influence on the simulation results. Specifically, the material characteristics of magnesium alloy are considered. However, there are very few simulation studies on the hot processing of magnesium alloy materials, and most of them focus on surface modification. The energy input required for surface modification is relatively low. Therefore, the thermal physical properties of magnesium alloy materials are generally only analyzed up to about 500 °C, lacking thermal physical property parameters in the high-temperature range (before the boiling point temperature). Therefore, the present invention fits the multi-term expression of thermal physical properties by Lagrange interpolation method to obtain the thermal physical property values of magnesium alloy, improving the accuracy of the simulation results and thus affecting the accuracy of the cutting parameters determined by the simulation. During the laser cutting of magnesium alloy, it is necessary to control the temperature above the melting point temperature and below the boiling point temperature. Since the melting point and boiling point temperatures of magnesium alloy are both relatively low and not very different, precise processing parameters are required for laser cutting of magnesium alloy to control the reasonable energy input. Therefore, in the simulation process of the present invention, a step of obtaining the temperature values at each unit point in real time and ending the simulation in a timely manner when the range is exceeded is added. This not only makes the cutting parameters preliminarily determined by the simulation appropriate values, but also omits meaningless simulation results, reducing the experimental difficulty and experimental cost. At the same time, the simulation process combines APDL and GUI operations, giving full play to the respective advantages of these two methods. The temperature field simulation is carried out by using APDL command stream to define and set the process parameters of laser cutting magnesium alloy. The APDL command stream supports parametric design, facilitating the creation of complex models, and the modeling process is easier to operate and modify. The analysis of the simulation results adopts the GUI operation mode, making it more convenient to select unit nodes during the analysis process and easier to output the result graph.

[0041] The specific implementation process of the present invention is as follows:

[0042] Currently, with the development of computer technology, numerical simulation technology provides a new way to study the laser cutting temperature field process. In the preferred embodiment of the present invention, it aims to establish a laser cutting magnesium alloy temperature field model based on simulation, and determine the parameters of laser cutting magnesium alloy by analyzing the temperature field distribution. Specifically, a method for determining the parameter values of laser cutting magnesium alloy based on thermal action simulation is disclosed. The simulation process can be implemented by writing based on the APDL language, and the simulation result analysis is implemented based on GUI operation, making the whole simulation have the respective advantages of the APDL language and GUI operation at the same time. In the technical concept, based on the known thermal physical property parameter values of magnesium alloy, a multi-term expression of thermal physical property parameters is fitted by the Lagrange interpolation method to obtain the thermal physical property parameter values of magnesium alloy, which is used to improve the accuracy of the simulation results and further affect the accuracy of the cutting parameters determined by the simulation. In the simulation process, adding the step of obtaining the temperature values at each unit point in real time and ending the simulation in time when it exceeds the range not only makes the cutting parameters preliminarily determined by the simulation be appropriate values, but also omits meaningless simulation results. The whole process is as Figure 1 shown, and specifically includes the following steps:

[0043] Step S1, obtain the main parameters affecting laser cutting of magnesium alloy;

[0044] Step S2, map the actual key parameters of laser cutting to simulation parameters;

[0045] Step S3, fit the thermal physical property parameters of magnesium alloy, and define and set the parameters of the laser cutting simulation process;

[0046] Step S4, carry out temperature field simulation and judge the temperature range;

[0047] Step S5, output the simulation results and analyze the results.

[0048] In a further embodiment of the present invention, the following steps are further included:

[0049] Step 1: Obtain the main parameters affecting laser cutting of magnesium alloy; Laser realizes cutting processing mainly relying on the input energy. The laser energy, laser heat flux density, laser power, and laser frequency can be expressed by the following formulas:

[0050] ;

[0051] ;

[0052] ;

[0053] ;

[0054] In the formulas, is the laser heat flux density; E is the laser energy per unit time;K is the energy concentration coefficient; P is the laser power; f is the laser frequency; r 0 is the laser spot radius; d is the adjacent pulse spacing; v is the laser cutting speed. It can be seen from the above formula that the laser energy density is directly determined by the laser power and the laser frequency. The absorption of magnesium alloy materials by laser is lower than that of general metal materials, so magnesium alloys require high-power processing. And the laser cutting speed indirectly affects the cutting quality through the cutting pulse spacing, manifested in that too small a spacing will cause over-cutting, and too large a spacing will cause the specimen to not be cut through. The defocus amount is related to the laser spot radius. The larger the spot diameter, the larger the defocus amount. Therefore, through analysis, the main parameters affecting the quality of laser cutting of magnesium alloy obtained in the present invention are laser power, cutting speed, laser frequency and defocus amount.

[0055] Step 2: Map the actual key parameters of laser cutting to simulation parameters; The simulation heat source of laser cutting adopts a Gaussian heat source, and the heat source model is as Figure 2 shown. The Gaussian heat source formula is expressed by power, cutting speed and laser frequency as:

[0056] ;

[0057] ;

[0058] In the formula, q ( x,z ) is the heat source distribution function; r 0 is the laser spot radius; f is the laser power; v is the cutting speed; x is the position of the heat source on the X axis of the model; x 0 is the position of the heat source center on the X axis of the model; z is the position of the heat source on the Z axis of the model; t is the laser cutting time; A is the laser absorption rate of the material, which is mainly related to the material resistivity and the laser incident wavelength . It can be seen from the above formula that the power, cutting speed, laser frequency and defocus amount of the actual laser cutting parameters can be related to the simulation parameters.

[0059] Step 3: Fitting the thermal physical properties of magnesium alloy, including thermal analysis parameters and stress analysis parameters. In the process of laser cutting magnesium alloy, there are changes in the physical state of the material, and it is necessary to consider the variation of the thermal physical properties of the material with temperature. Due to its own characteristics, there are few studies on the thermal processing simulation of magnesium alloy, and it is difficult to obtain all its thermal physical properties. In the example, the material is AZ31B magnesium alloy, and some of its known thermal physical properties are shown in Table 1 below:

[0060] Table 1

[0061]

[0062] Substitute the above discrete point values into the formula of Lagrange interpolation method to obtain the fitting expressions of thermal conductivity, specific heat capacity, coefficient of thermal expansion and convective heat transfer coefficient as follows:

[0063] ;

[0064] In the formula, K ( t ) is the fitting formula of thermal conductivity; C ( t ) is the fitting formula of specific heat capacity; A ( t ) is the fitting formula of coefficient of thermal expansion; Con ( t ) is the fitting formula of convective heat transfer coefficient; t is the temperature value.

[0065] Defining and setting the parameters of the laser cutting simulation process mainly include setting the model unit system to Mpa, mm - c - mW - mg - sec - mJ, setting the simulation name as The laser cutting, defining the thermal analysis element type as Solid70, setting the thermal physical properties of the magnesium alloy material varying with temperature. First, use the mptemp command to set the temperature points, and then set the corresponding thermal physical properties of the material at each temperature point respectively, including material density mpdata, dens, material thermal conductivity mpdata, kxx, material specific heat capacity mpdata, c, coefficient of thermal expansion mpdata, alpx, and convective heat transfer coefficient *dim, conve. Use the rectng command to establish the geometric model of the magnesium alloy plate. In this example, the length of the magnesium alloy plate is 60mm, the width is 40mm, and the thickness is 1mm. The established geometric model is as shown in Figure 3a ; Use the esize command to determine the size of the mesh elements, and then use the vmesh command to divide the geometric model into mesh elements. The sizes of the mesh elements in the three regions are set to 0.2mm, 0.5mm and 2mm respectively. The divided element model is as shown in Figure 3bAs shown. Set the parameters in the heat source model. Finally, set the solution analysis type to transient thermal-structural analysis, the solution method to the full Newton-Raphson method, set the heat source movement step size and thermal efficiency, and perform a steady-state analysis.

[0066] Step 4: Apply the thermal load and perform cyclic solution to simulate the temperature field. Convert the laser cutting simulation heat source model into APDL language. The APDL command stream expression of the heat source model is: qr = ((0.8607 * P) / (3.14 * (r^2) * f)) * exp((-3 * (((x - 20)^2) + ((z - vt)^2))) / (r^2)). Run the APDL language to load the thermal load on the specimen, and the thermal load moves along the set Z-axis direction. Discretize the entire laser cutting simulation process into individual sub-steps (*do, i, 1, 60), solve the temperature field distribution of each sub-step under the action of the heat source, and obtain the temperature field distribution result of the laser cutting process through the solution of each sub-step. Define (etable) two element tables Tema and Temb in this process. Tema is used to store the temperatures of all elements, and Temb stores the temperatures of the elements at the cut seam. Select the elements in Tema with temperatures higher than the boiling point temperature to form a new element set Temc, and select the elements in Temb with temperatures lower than the melting point temperature to form a new element set Temd. Judge the number of elements in Temc and Temd (if-else command). If the number does not meet the requirements, directly end the simulation ( / Post1). If it meets the requirements, continue the simulation.

[0067] Step 5: Output the results. Enter the post-processing mode using the GUI operation method, click General Postproc → Plot Results → Contour Plot → Nodal Solu to view the temperature change contour map during the magnesium alloy cutting process. Figure 4 It is the temperature distribution contour map at the 20th second during the laser cutting of magnesium alloy. Select the element points along the thickness (Y-axis) direction of the specimen to obtain the temperature values. It can be seen that the temperature decreases from top to bottom along the thickness. The temperature value at the lower surface of the specimen is 678 °C, which is greater than the melting point temperature of AZ31B magnesium alloy, 650 °C. The specimen can be cut through under this parameter. The highest temperature is 1041 °C, which is less than the boiling point temperature of magnesium alloy, 1107 °C.

[0068] The units involved in the embodiments of the present invention can be implemented in software, and the described units can be set in the processor. Among them, the names of these units do not constitute a limitation to the unit itself in some cases.

Claims

1. A method for determining the parameter values ​​of laser cutting magnesium alloy based on thermal simulation, characterized in that: The steps include: S1, obtain the key parameters affecting laser cutting of magnesium alloy; S2, mapping actual key parameters of laser cutting into simulation parameters; S3, fitting the thermophysical property parameters of magnesium alloy, defining and setting the simulation process parameters of laser cutting magnesium alloy; S4, conduct temperature field simulation and determine the temperature range: convert the laser cutting simulation heat source model into APDL language, run APDL language to load the heat load on the specimen, and move the heat load along the set Z-axis direction; discretize the entire laser cutting simulation process into a single sub-step, solve the temperature field distribution of each sub-step under the action of the heat source, and obtain the temperature field distribution result of the laser cutting process through the solution of each sub-step; define two unit tables Tema and Temb in this process, Tema is used to store all unit temperatures, and Temb is used to store the unit temperature at the slit, select the units in Tema with a temperature higher than the boiling point to form a new unit set Temc, and select the units in Temb with a temperature lower than the melting point to form a new unit set Temd; determine the number of units in Temc, if it is greater than 0, end the simulation directly, if it is equal to 0, determine the number of Temd units, if it is greater than 0, end the simulation, if it is less than 0, continue the simulation; S5, output simulation results and analysis results.

2. The method for determining the parameter values ​​of laser cutting magnesium alloy based on thermal action simulation according to claim 1 is characterized in that: In step S1, the key parameters affecting laser cutting of magnesium alloy are obtained, which specifically includes the following steps: Construct the following relational expression: ； In the formula, is the laser heat flux density; P is the laser power; f is the laser frequency; r 0 is the laser spot radius; d is the spacing between adjacent laser pulses; v is the laser cutting speed; From the relationship expression, it can be concluded that the key parameters affecting laser cutting of magnesium alloy are laser power, cutting speed, defocusing amount and laser frequency.

3. The method for determining the parameter values ​​of laser cutting magnesium alloy based on thermal simulation according to claim 1, characterized in that: In step S2, the actual key parameters of laser cutting are mapped to simulation parameters, specifically including constructing a heat source formula for laser cutting, where the heat source formula is represented by laser power, cutting speed, laser frequency and laser spot radius, and the expression is as follows: ； In the formula, q ( x,z ) is the heat source distribution function; A is the laser absorptivity of the material; r 0 is the laser spot radius; P is the laser power; f is the laser frequency; v is the cutting speed; x For heat sources in the model X Axis position; x 0 is the center of the heat source in the model X Axis position; z For heat sources in the model Z Axis position; t Laser cutting time.

4. The method for determining the parameter values ​​of laser cutting magnesium alloy based on thermal action simulation according to claim 1, characterized in that: In step S3, fitting the thermophysical property parameters of magnesium alloy and defining and setting the key parameters of the laser cutting magnesium alloy simulation process specifically include the following sub-steps: S31, the Lagrangian interpolation method is used to fit the thermophysical parameters of the magnesium alloy material determined before 450°C to obtain the value before the boiling point temperature. The expressions of thermal conductivity, specific heat capacity, thermal expansion coefficient and convection heat transfer coefficient fitted by one-dimensional three-node Lagrangian polynomial are as follows: ； In the formula, K ( t ) is the thermal conductivity fitting formula; C ( t ) is the specific heat capacity fitting formula; A ( t ) is the thermal expansion coefficient fitting formula; Con ( t ) is the fitting formula of convective heat transfer coefficient; t is the temperature value; S32, define and set simulation process parameters, including: define unit type and select unit system, set obtained material thermal property parameters, establish model and divide grid units, set solution options, set various parameters in heat source model, set steady-state analysis parameters and define boundary conditions.

5. The method for determining the parameter values ​​of laser cutting magnesium alloy based on thermal action simulation according to claim 1, characterized in that: In step S5, the output simulation results and analysis results specifically include: viewing and outputting temperature and stress change results through GUI operation, selecting unit points along the Y-axis direction of the thickness at the heat source loading point of the specimen to calculate their temperature values, obtaining the temperature distribution along the thickness direction after laser cutting, comparing the temperature value of the lower surface of the specimen with the melting point temperature value of the material, and the highest temperature value and boiling point temperature value of the cutting process.

6. The method for determining the parameter values ​​of laser cutting magnesium alloy based on thermal action simulation according to claim 1, characterized in that: Steps S1 to S4 are implemented using APDL language, and step S5 is implemented through GUI operation.

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