Ship sample plate laser cutting numerical simulation method

Abstract

The invention discloses a marine sample plate laser cutting numerical simulation method, which comprises the following steps of: establishing a finite element model based on structure size parameters of a sample plate and the position of a laser cutting area, and performing grid division; thermal physical performance parameters and thermal boundary conditions including specific heat, heat conduction coefficients and the like are set, the environment temperature is defined, and boundary flux is accurately expressed through a formula; a laser cutting heat source model is constructed, and a DFLUX subprogram is modified to adjust technological parameters such as laser power and cutting speed; the established model is used for heat transfer analysis, and a transient temperature field in the laser cutting process is obtained; mechanical property parameters and boundary conditions are set, and preparation is made for stress analysis; carrying out secondary development on the VUSDFLD subprogram, and deleting or retaining the unit according to a comparison result of the transient temperature and the ignition point value; and carrying out stress-strain analysis by taking the transient temperature as a load, and evaluating the shape and the stress distribution condition of the cut seam. According to the invention, high-precision simulation and effect evaluation of the laser cutting process are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of shipbuilding, and particularly to a numerical simulation method for the laser cutting process of marine templates. Background Art

[0002] A sample box is a three-dimensional frame structure used to inspect the curvature of the ship's outer plate, which is made of fixed curved templates. For outer plates with particularly complex line types that are difficult to develop by geometric drawing methods, such as shaft sleeve plates, bulbous bow plates, and bow and stern column plates, it is particularly necessary to nail sample boxes. With the transformation of the modern shipbuilding mode towards digitalization and automation, this trend has gradually penetrated into all fields of shipbuilding production. Therefore, traditional tools that highly rely on manual operations, such as triangular templates and flexible splines, have significantly fallen behind and are incompatible with the modern digital and green shipbuilding mode, and need to be innovated.

[0003] Laser cutting technology has shown great advantages in the processing of templates, including high-precision cutting, fast operation, pollution-free, the ability to process complex graphics, neat cut edges, and time and labor savings. However, when using laser cutting for wooden boards, our understanding of the thermophysical behavior of wooden boards and their mechanical response mechanisms is not deep enough. To improve this situation, it is urgent to develop corresponding numerical simulation methods to predict the laser cutting process of wooden boards and further explore their physical nature. Summary of the Invention

[0004] The present invention proposes a numerical simulation method for laser cutting of marine templates, which can predict the laser cutting process of templates.

[0005] According to one aspect of the embodiment, a numerical simulation method for laser cutting of marine templates is proposed, including: Step 1, establishing a finite element model of the ship template, performing mesh division, and dividing the ship template into several elements; Step 2, setting the thermophysical property parameters related to the template temperature, as well as the thermal boundary conditions on the surface of the finite element model, and defining the ambient temperature; Step 3, based on the thermophysical property parameters and thermal boundary conditions set in Step 2, through secondary development of the DFLUX subroutine, configuring a heat source model describing the laser cutting process and its heat flux density distribution equation, and setting the process parameters of laser cutting; Step 4, based on the finite element model in Step 1 and the DFLUX subroutine in Step 3, solving the non-linear heat transfer equation to obtain the transient temperature during the laser cutting process of the template; Step 5, setting the mechanical property parameters related to the template temperature, and defining the mechanical boundary conditions of the finite element model; Step 6, based on the mechanical property parameters and mechanical boundary conditions set in Step 5, configuring the VUSDFLD subroutine as: comparing the transient temperature of the element with the ignition point value of the template, if the transient temperature is not lower than the ignition point value, deleting the element to simulate the process of the material being cut and removed; if the transient temperature is lower than the ignition point value, retaining the element to reflect the uncut area; Step 7, taking the transient temperature in Step 4 as the thermal load input, and combining the element deletion logic of the VUSDFLD subroutine, calculating the cut seam morphology and residual stress and strain distribution after laser cutting, for evaluating the cutting accuracy and process effect.

[0006] The present invention has the following advantages: 1. The present invention accurately reproduces the heat conduction, stress and strain, and cut seam morphology evolution process during the laser cutting process of marine templates; 2. For templates of different materials and thicknesses, the present invention can simulate the cut seam morphology under different laser cutting process parameters, and then form a process database; 3. The present invention can greatly reduce the number of laser cutting tests for marine templates and save costs. Description of the Drawings

[0007] Figure 1 is a flow chart of the numerical simulation method for laser cutting of the marine template sample box.

[0008] Figure 2 is the finite element model of the ship template.

[0009] Figure 3 is the transient temperature during the laser cutting process.

[0010] Figure 4 is the cut seam morphology after template cutting. Detailed Embodiments

[0011] In the present invention, a finite element model for laser cutting of ship templates is constructed, a finite element model of the laser cutting heat source is established, and thermal analysis is carried out with the aid of the secondary developed DFLUX subroutine. Then, taking the results of the thermal analysis as the load for mechanical analysis, mechanical analysis is carried out through the secondary developed VUSDFLD subroutine, thereby accurately reproducing the transient temperature distribution and the evolution process of the cut seam during the laser cutting process of ship templates. The specific process is as Figure 1 shown below.

[0012] Step 1: Establish a finite element model

[0013] Based on the structural dimension parameters of the ship template (including plate length, plate width, and plate thickness), the position of the laser cutting processing area, and the type of heat transfer analysis element, a finite element model is established. The cutting processing area refers to the specific position and path of the cut seam during the laser cutting process. Mesh division is performed on the entire model, and the template is divided into multiple elements and nodes. In particular, a fine mesh is used in the laser processing area to improve accuracy, while a coarser mesh is used in the areas far from the processing area to save computing resources and improve efficiency. The finite element model constructed in this way can more accurately simulate the thermophysical behavior and mechanical response during the laser cutting process.

[0014] Step 2: Set thermophysical property parameters

[0015] Set the thermophysical property parameters related to the template temperature, including specific heat, thermal conductivity, density, etc. In addition, the heat radiation and convection coefficients on the model surface also need to be set as the thermal boundary conditions of the finite element model, and the ambient temperature is defined. Specifically, these thermal boundary conditions should reflect the boundary fluxes generated by heat convection and heat radiation during the laser cutting process. The boundary flux expression is as follows:

[0016] q = q 对流 + q 辐射 = h 散热 (T - T0) + εσ[(T + 273) 4 - (T0 + 273) 4 ;

[0017] In the formula, q is the boundary flux; q 对流 and q 辐射 respectively represent heat convection and heat radiation, with the unit of W / mm 2 ; h 散热 represents the heat dissipation coefficient, with the unit of W / (mm 2 × °C); T0 represents the ambient temperature, with the unit of °C; ε is the emissivity, ε ∈ (0 - 1); σ is the Stefan - Boltzmann constant, with a value of 5.67E - 14 W / (mm 2 × K 4 ).

[0018] Step 3: Construct a laser cutting heat source model

[0019] Construct a heat source model that accurately describes the laser cutting process and its heat flux density distribution equation, and set process parameters such as laser power and cutting speed by modifying the DFLUX subroutine. The heat source model used in laser cutting is a frustum of a cone, and its energy density expression is as follows:

[0020]

[0021] In the formula, Q(x, y, z, t) represents the energy distribution of the heat source model at the node coordinates (x, y, z) in the finite element model; a, b, and c respectively represent the shape parameters of the heat source model, with the unit of mm; η is the thermal efficiency; v represents the moving speed of the cutting heat source, with the unit of mm / s; Q represents the laser power.

[0022] The DFLUX subroutine usually refers to a user-defined subroutine used in finite element analysis (FEA) software to define non-uniform heat flux. It allows users to customize the specific parameters and distribution of the input heat source according to their own needs, rather than using the software's default settings. This is particularly useful for simulating complex heating processes, such as laser cutting and welding, because the heat input in these processes is usually highly localized and time-varying.

[0023] Step 4: Conduct heat transfer analysis

[0024] Use the finite element model established in Step 1 to conduct heat transfer analysis of the template laser cutting, read the DFLUX subroutine code in Step 3 and submit the calculation to obtain the transient temperature field during the template laser cutting process. The temperature field refers to the temperature distribution of each node in the finite element model during the laser cutting heating process, and the temperature value of each node in the finite element model at a certain moment is obtained by solving the non-linear heat transfer equation. The solving process is as follows:

[0025]

[0026] In the formula, T represents the temperature; k represents the thermal conductivity of the ship template, with the unit of J / mm×s×℃; Q(x, y, z, t) represents the heat generation rate at the node coordinates (x, y, z) in the finite element model at time t, with the unit of W / mm 3 ; ρ represents the density of the ship template, with the unit of g / mm 3 ; C 比热 represents the specific heat capacity of the ship template, with the unit of J / g×℃; x, y, z are the node coordinates in the finite element model, with the unit of mm; t is the time, with the unit of seconds.

[0027] Step 5: Set mechanical property parameters

[0028] Set mechanical property parameters related to the template temperature, such as Young's modulus, yield strength, coefficient of linear expansion, etc., and determine the mechanical boundary conditions of the finite element model. For example, the mechanical boundary condition means setting 3-node 6-degree-of-freedom to constrain the rigid body displacement of the finite element model. The element type is set to stress analysis type and it is determined that the element can be deleted.

[0029] Step 6: Secondary development of the VUSDFLD subroutine

[0030] Perform secondary development on the VUSDFLD subroutine. By comparing the transient temperature with the ignition point value of the template, if the transient temperature is not lower than the ignition point value, delete the element; if the transient temperature is lower than the ignition point value, retain the element.

[0031] The VUSDFLD subroutine is a user-defined subroutine used in finite element analysis (FEA). It allows users to customize the input material properties or state variables according to specific requirements. Specifically, in processes involving highly localized and time-varying heat input such as laser cutting and welding, VUSDFLD can be used to dynamically update the state variables of each element in the model, such as mechanical property parameters related to temperature.

[0032] Step 7: Stress and strain analysis

[0033] Using the transient temperature in Step 4 as the load, read the VUSDFLD subroutine code in Step 6 and submit the calculation to obtain the slot morphology and stress-strain distribution after laser cutting of the template. The slot morphology after laser cutting of the template includes the upper and lower slot widths and the cutting surface flatness, which are used to evaluate the accuracy of laser cutting the template.

[0034] A specific case is provided below

[0035] I. Establish a finite element model for laser cutting of a ship template

[0036] Taking 5-mm-thick pine wood as an example, according to the structural dimensions and laser cutting trajectory, select an appropriate element type to establish a finite element model. For example, solid elements are selected, with the number of elements being 175,421 and the number of nodes being 199,064. To balance calculation accuracy and efficiency, fine mesh division is used in the laser action area, while coarser mesh division is used in areas far from the laser action area, as Figure 2 shown.

[0037] II. Setting of material parameters and thermal boundary conditions

[0038] Assign the temperature-dependent performance parameters of pine wood to the finite element model established in Step 1, including density, thermal conductivity, specific heat, elastic modulus, and linear expansion coefficient, etc. Set the thermal boundary conditions of the finite element model: During the laser cutting process, the heat convection generated by the temperature difference between the sample surface and the surrounding fluid and the electromagnetic radiation energy emitted to the environment will both cause energy loss. Therefore, the boundary flux q (W / mm 2 ) generated by heat convection and thermal radiation is usually used as the boundary condition of the sample surface during thermal analysis. Among them, convective heat dissipation follows Newton's cooling law, while radiative heat dissipation follows the Stefan-Boltzmann law.

[0039] III. Develop the DFLUX subroutine and simulate the cutting temperature field

[0040] In the thermal analysis stage, select the element type suitable for heat transfer analysis, and use a frustum-shaped heat source model with a uniform energy density distribution to simulate the laser heat source. By secondary development of the DFLUX subroutine, solve the non-linear heat transfer equation to obtain the temperature values of each node at a specific moment, and then simulate the laser cutting temperature field. The transient temperature distribution of the sample during laser cutting is as Figure 3 shown.

[0041] IV. Set the constraint conditions and element analysis type

[0042] Set the force boundary conditions of the finite element model. Usually, the rigid body displacement of the finite element model is restricted by constraining the six degrees of freedom of three nodes. Specifically, three of the four corners of the upper surface of the finite element model are constrained: the displacements of the lower left corner node in the X-axis, Y-axis, and Z-axis directions are all constrained; the displacements of the upper right corner node in the X-axis and Z-axis directions are all constrained; the displacement of the upper left corner node in the Z-direction is constrained. The element type is set to a form suitable for stress analysis, and it is confirmed that the element can be deleted.

[0043] V. Develop the VUSDFLD subroutine and simulate the evolution of the cut seam morphology

[0044] Taking whether the maximum temperature exceeds the ignition point of pine wood (250 °C) as the criterion, read the transient temperature data of the elements and nodes of the finite element model in Step 3, develop the VUSDFLD subroutine, consider the temperature-dependent mechanical property parameters, and simulate the stress field and the cut seam morphology during the laser cutting process. The cut seam morphology of the sample during laser cutting is as Figure 4 shown.

[0045] The finite element analysis software implementing the present invention can be ABAQUS or ANSYS.

Claims

1. A numerical simulation method for laser cutting of marine sample, characterized in that: Include: Step 1, establish a finite element model of the ship sample, and perform mesh division to divide the ship sample into several units; Step 2, setting the thermophysical performance parameters related to the sample temperature, as well as the thermal boundary conditions of the finite element model surface, and defining the ambient temperature; Step 3, based on the thermophysical performance parameters and thermal boundary conditions set in step 2, the heat source model describing the laser cutting process and its heat flux density distribution equation are configured through secondary development of the DFLUX subroutine, and the process parameters of the laser cutting are set; Step 4, based on the finite element model of step 1 and the DFLUX subroutine of step 3, solve the nonlinear heat transfer equation to obtain the transient temperature of the sample during the laser cutting process; Step 5, setting mechanical property parameters related to the sample temperature and defining the mechanical boundary conditions of the finite element model; Step 6, based on the mechanical property parameters and mechanical boundary conditions set in step 5, configure the VUSDFLD subroutine to: compare the unit transient temperature with the ignition point value of the sample; if the transient temperature is not lower than the ignition point value, delete the unit to simulate the process of material being cut and removed; if the transient temperature is lower than the ignition point value, retain the unit to reflect the uncut area; Step 7, using the transient temperature in step 4 as the heat load input, combined with the unit deletion logic of the VUSDFLD subroutine, calculates the slit morphology and residual stress and strain distribution after laser cutting to evaluate the cutting accuracy and process effect.

2. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: A finite element model was established based on the structural size parameters of the ship sample, the location of the laser cutting processing area and the type of heat transfer analysis unit.

3. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: Thermophysical performance parameters, including specific heat, thermal conductivity and density.

4. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: The boundary flux generated by thermal convection and thermal radiation during laser cutting is taken as the thermal boundary condition.

5. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: The heat source model adopts a truncated cone model.

6. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: The process parameters of laser cutting include laser power, cutting speed and thermal efficiency.

7. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: Mechanical properties parameters include Young's modulus, yield strength and linear expansion coefficient.

8. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: Mechanical boundary conditions constrain the rigid body displacements of the finite element model.

9. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: The slit morphology of the sample after laser cutting includes the slit width on the upper and lower sides and the cutting surface contour.

10. The method for numerical simulation of laser cutting of marine sample according to claim 1, characterized in that: A fine grid is used in the laser processing area, and a coarser grid is used in the non-processing area.

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