Method for determining laser cutting magnesium alloy parameter value based on thermal action simulation

Abstract

The invention discloses a method for determining laser cutting magnesium alloy parameter values based on thermal action simulation, which belongs to the technical field of magnesium alloy laser cutting and comprises the following steps: S1, acquiring key parameters influencing laser cutting of magnesium alloy; s2, the laser cutting actual key parameters are mapped into simulation parameters; s3, fitting thermophysical parameters of the magnesium alloy, and defining and setting simulation process parameters of the magnesium alloy cut by the laser; s4, temperature field simulation is carried out, and a temperature interval is judged; and S5, outputting a simulation result and an analysis result. The invention provides the method for determining the parameter value of the laser cutting magnesium alloy based on thermal action simulation, and the processing temperature of the magnesium alloy material which is very sensitive to the temperature change influence can be controlled in a proper range.

Description

Technical Field

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

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

[0003] Laser cutting is a complex thermal processing method. The cutting process is always accompanied by thermal changes such as heat conduction, heat convection and heat radiation. The different energy obtained by different regions of the material at the same time makes the temperature of each region change dramatically over time. The temperature field change will eventually directly affect the cutting quality. At the same time, magnesium alloy has few electrons outside the nucleus, large atomic radius and relatively weak metal bond energy, so its melting point and boiling point are low. Improper parameter control during the thermal processing process can easily cause the temperature to reach the vaporization temperature, causing the material to volatilize and burn violently. Magnesium alloy also has the characteristics of active chemical properties, high thermal conductivity, large thermal expansion coefficient and small surface tension, which makes it more sensitive to temperature changes during the thermal processing process. Therefore, when using laser cutting of magnesium alloy, it is more important to control the processing temperature within an appropriate range.

[0004] The most fundamental aspect of laser cutting is to control the energy acting on the material. Currently, the main parameters that affect the energy input of laser cutting are mostly determined by experience and lack theoretical basis. There is no specific research available for reference in the field of magnesium alloy laser cutting. The temperature field distribution and change law of the laser cutting process are difficult to obtain through experiments. The temperature field model of laser cutting can be established through 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 shortcomings of the prior art and provide a method for determining the parameter values ​​of laser cutting of magnesium alloy based on thermal action simulation, and proposes a solution for determining the cutting parameters of laser cutting of magnesium alloy, which can control the processing temperature of magnesium alloy materials that are very sensitive to temperature changes within an appropriate range.

[0006] The object of the present invention is achieved through the following solutions: A method for determining parameter values ​​of laser cutting magnesium alloy based on thermal action simulation comprises the following steps: 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.

[0007] Further, in step S1, the key parameters affecting the laser cutting of magnesium alloy are obtained, specifically including 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.

[0008] Furthermore, 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; r0 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.

[0009] Furthermore, 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.

[0010] Furthermore, 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 of the cutting process with the boiling point temperature value.

[0011] Furthermore, steps S1 to S4 are implemented by using APDL language, and step S5 is implemented by GUI operation.

[0012] The beneficial effects of the present invention include: The present invention is particularly aimed at magnesium alloy laser cutting. In combination with its material properties, a solution for determining its 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 an appropriate range. Furthermore, the thermophysical parameter polynomial expressions are fitted based on the known thermophysical parameter values ​​of the magnesium alloy through the Lagrange interpolation method to obtain the thermophysical parameter values ​​of the magnesium alloy, thereby improving the simulation accuracy. In the simulation process, the step of obtaining the temperature value at each unit point in real time and terminating the simulation in time when it exceeds the range is added, which not only makes the cutting parameters preliminarily determined by the simulation appropriate values, but also omits meaningless simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

[0014] Figure 1 is a flowchart of the steps of the method according to the embodiment of the present invention; Figure 2 This is a schematic diagram of laser cutting according to an embodiment of the present invention; Figure 3a Schematic diagram of the geometric model of the magnesium alloy plate in the embodiment of the present invention; Figure 3b Schematic diagram of a unit model after the magnesium alloy plate is divided in an embodiment of the present invention; Figure 4 This is a cloud diagram of temperature distribution during the magnesium alloy plate cutting process in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] 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 expanded or replaced in any manner.

[0016] In view of the problems in the background, the inventor of the present application believes after creative thinking that: In the face of the actual problems encountered in magnesium alloy laser cutting, the parameters that affect the cutting energy should be derived based on laser cutting theory, so that the laser cutting processing experience can be theoretically verified. At the same time, the characteristics of magnesium alloys need to be considered specifically, and an adaptability theory on how to control the processing temperature within an appropriate range for this material should be proposed.

[0017] As a complex metallurgical process involving knowledge such as the interaction between laser and material and material melting theory, the distribution and changing law of the transient temperature field of laser cutting are also very complex. After creative thinking, the present invention establishes a temperature field model for laser cutting to solve the changing law of the temperature field during the cutting process of magnesium alloy, and uses the proposed magnesium alloy adaptive cutting theory to obtain reasonable values ​​of laser cutting parameters.

[0018] Specifically, the present invention is based on the simulation analysis of thermal effects, and after considering the main parameters affecting laser cutting according to the theoretical analysis of laser cutting, the actual processing parameters are linked to the simulation parameters by deriving the heat source formula, so that the main parameters that need to be adjusted in the actual processing can also be set in the simulation. The material thermophysical parameters in the temperature field simulation have a great influence on the simulation results, which specifically takes into account the material properties of magnesium alloys. However, there are very few existing simulation studies on the thermal processing of magnesium alloy materials, and most of them focus on surface modification. The energy required for surface modification is relatively low, so the thermophysical parameters of magnesium alloy materials are generally only analyzed to about 500°C, lacking thermophysical parameters in the high temperature range (before the boiling point). Therefore, the present invention fits the polynomial expression of thermophysical parameters by the Lagrange interpolation method, obtains the thermophysical parameter values ​​of magnesium alloys, improves the accuracy of the simulation results, and thus affects the accuracy of the cutting parameters determined by the simulation. In the process of laser cutting magnesium alloy, the temperature must be controlled to be higher than the melting point and lower than the boiling point. The melting point and boiling point of magnesium alloy are both low and not much different, so laser cutting of magnesium alloy requires precise processing parameters to control reasonable energy input. Therefore, the present invention adds the step of obtaining the temperature value of each unit point in real time during the simulation process, and terminating the simulation in time when it exceeds the range. This not only makes the cutting parameters preliminarily determined by the simulation appropriate values, but also omits meaningless simulation results, reduces the difficulty of the experiment and reduces the experimental cost. At the same time, the simulation process is a combination of APDL and GUI operations, which greatly brings out the respective advantages of these two methods. The APDL command stream is used to define and set the laser cutting magnesium alloy process parameters for temperature field simulation. The APDL command stream supports parametric design, which is convenient for creating complex models and makes the modeling process easier to operate and modify. The simulation result analysis adopts the GUI operation mode, which makes it easier to select unit nodes in the analysis process and output result graphs.

[0019] The specific implementation process of the present invention is as follows: With the development of computer technology, numerical simulation technology has provided a new way to study the temperature field process of laser cutting. In the preferred embodiment scheme, the present invention aims to establish a temperature field model for laser cutting of magnesium alloy based on simulation, and determine the parameters of laser cutting of magnesium alloy by analyzing the temperature field distribution. Specifically, a method for determining the parameter values ​​of laser cutting of magnesium alloy based on thermal action simulation is disclosed. The simulation process can be implemented based on the APDL language, and the analysis of the simulation results is implemented based on GUI operation, so that the entire simulation has the respective advantages of APDL language and GUI operation. In the technical concept, the Lagrange interpolation method is used to fit the polynomial expressions of thermophysical parameters based on the known thermophysical parameter values ​​of magnesium alloy to obtain the thermophysical parameter values ​​of magnesium alloy, which are used to improve the accuracy of the simulation results and thus affect the accuracy of the cutting parameters determined by the simulation. In the simulation process, the step of obtaining the temperature value at each unit point in real time and terminating the simulation in time if it exceeds the range is added, so that the cutting parameters preliminarily determined by the simulation are appropriate values, and meaningless simulation results are omitted. The whole process is as follows Figure 1 As shown, the specific steps include: Step S1, obtaining the main parameters affecting laser cutting of magnesium alloy; Step S2, mapping actual key parameters of laser cutting into simulation parameters; Step S3, fitting the thermophysical property parameters of magnesium alloy, defining and setting the laser cutting simulation process parameters; Step S4, conducting temperature field simulation to determine the temperature range; Step S5, output simulation results and analyze the results.

[0020] In a further implementation of the embodiment of the present invention, the following steps are further included: Step 1: Obtain the main parameters that affect laser cutting of magnesium alloy; Laser cutting mainly depends on the input energy. Laser energy, laser heat flux, laser power and laser frequency can be expressed by the following formula: ; ; ; ; In the formula, is the laser heat flux density; E is the laser energy per unit time; K is the energy concentration factor; P is the laser power; f is the laser frequency; r 0 is the laser spot radius; d is the interval between adjacent pulses; vis 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. Magnesium alloy materials absorb lasers less than general metal materials, so magnesium alloys require high-power processing. The laser cutting speed indirectly affects the cutting quality through the cutting pulse spacing, which is manifested in that a small spacing will cause overcutting, and a large 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 greater the defocus amount. Therefore, the present invention can analyze and obtain the main parameters that affect the quality of laser cutting of magnesium alloys, which are laser power, cutting speed, laser frequency and defocus amount.

[0021] Step 2: Map the actual key parameters of laser cutting to simulation parameters; the simulation heat source of laser cutting adopts Gaussian heat source, and the heat source model is as follows: Figure 2 The Gaussian heat source formula is expressed by power, cutting speed and laser frequency as follows: ; ; 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 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 is the laser cutting time; A is the laser absorption rate of the material, which is mainly related to the resistivity of the material and laser incident wavelength The above formula can be used to link the actual laser cutting parameters of power, cutting speed, laser frequency and defocus with the simulation parameters.

[0022] Step 3: Fitting the thermophysical parameters of magnesium alloy includes thermal analysis parameters and stress analysis parameters. The laser cutting process of magnesium alloy changes the physical state of the material, and it is necessary to consider the change of the thermophysical parameters of the material with temperature. Due to its own characteristics, there are few thermal processing simulation studies on magnesium alloy, and it is difficult to obtain all its thermophysical parameters. The material in the example is AZ31B magnesium alloy, and some of its known thermophysical parameters are shown in Table 1 below: Table 1

[0023] Substituting the above discrete point values ​​into the formula of Lagrange interpolation method, the fitting expressions of thermal conductivity, specific heat capacity, thermal expansion coefficient and convection heat transfer coefficient 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.

[0024] The definition and setting of laser cutting simulation process parameters mainly include setting the model unit system to MPa, mm-c-mW-mg-sec-mJ, setting the simulation name The laser cutting, defining the thermal analysis unit type to Solid70, and setting the thermal physical parameters of the magnesium alloy material that change with temperature. First, use the mptemp command to set the temperature point, and then set the corresponding thermal physical parameters of the material at each temperature point, including material density mpdata, dens, material thermal conductivity coefficient mpdata, kxx, material specific heat capacity mpdata, c, thermal expansion coefficient mpdata, alpx, and convection 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 60 mm, the width is 40 mm, and the thickness is 1 mm. The established geometric model is as follows: Figure 3a As shown in the figure, the esize command is used to determine the size of the grid unit, and then the vmesh command is used to divide the geometric model into grid units. The sizes of the grid units in the three regions are set to 0.2mm, 0.5mm and 2mm respectively. The divided unit model is as follows Figure 3b Set the parameters in the heat source model, and finally set the solution analysis type to transient thermal-structural analysis, the solution method to full Newton-Raphson method, set the heat source moving step size and thermal efficiency, and perform steady-state analysis.

[0025] Step 4: Apply thermal load and solve cyclically to simulate temperature field. Convert the heat source model of laser cutting simulation into APDL language. The APDL command flow 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 APDL language to load the thermal load on the specimen. The thermal load moves along the set Z-axis direction. Discretize the entire laser cutting simulation process into a single sub-step (*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. In this process, two unit tables Tema and Temb are defined (etable). Tema is used to store all unit temperatures, and Temb stores the unit temperatures at the slits. Units with temperatures higher than the boiling point in Tema are selected to form a new unit set Temc, and units with temperatures lower than the melting point in Temb are selected to form a new unit set Temd. The number of units in Temc and Temd is determined (if-else command). If the number does not meet the requirements, the simulation is terminated directly ( / Post1). If it meets the requirements, the simulation continues.

[0026] Step 5: Output the results. Use the GUI to enter the post-processing mode. Click General Postproc→Plot Results→Contour Plot→Nodal Solu to view the temperature change cloud map during magnesium alloy cutting. Figure 4 This is the temperature distribution cloud diagram at 20s in the simulation process of laser cutting of magnesium alloy. Unit points are selected along the thickness (Y-axis) direction of the specimen to obtain the temperature value. It can be seen that the temperature decreases from top to bottom along the thickness. The temperature value of the lower surface of the specimen is 678℃, which is greater than the melting point of AZ31B magnesium alloy of 650℃. The specimen can be cut through under this parameter. The highest temperature is 1041℃, which is less than the boiling point of magnesium alloy of 1107℃.

[0027] The units involved in the embodiments of the present invention may be implemented by software, and the units described may be arranged in a processor. The names of these units do not constitute limitations on the units themselves in certain circumstances.

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; 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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