A simulation method and device for predicting the effect of SLM laser wavelength on absorption behavior

Abstract

The present invention discloses a simulation method and device for predicting the influence of SLM laser wavelength on absorption behavior, the method comprising the following steps: establishing a mesoscopic three-dimensional powder bed random stacking model; changing light source parameters and optical parameters defining powder properties to simulate laser absorption behavior at different wavelengths; obtaining a GO‑RT model consisting of a powder bed, a substrate, a light source and a spherical analysis surface in Fred software for predicting the influence of laser wavelength on SLM absorption behavior. The present invention takes into account the influence of laser energy and SLM powder layer thickness, which are not easy to accurately measure, on the laser absorption rate and laser‑powder bed interaction in the SLM forming process, and establishes a three-dimensional random stacking model by balancing the computational complexity of numerical simulation and the authenticity of powder layer stacking from a mesoscopic scale; by observing the influence of laser wavelength changes on the laser absorption behavior of the model SLM process, the problem of the influence of laser wavelength on the formability of SLM components, which is not fully considered in existing experiments and simulations, can be predicted to a certain extent.

Description

Technical Field

[0001] The present invention belongs to the technical field of SLM formed metal components, and in particular relates to a simulation method and device for predicting the influence of SLM laser wavelength on absorption behavior. Background Art

[0002] Laser additive manufacturing technology is a rapid prototyping technology that has developed rapidly in recent years. It can form high-density three-dimensional parts through metal powder processing, and only simple heat treatment is required after forming. Selective Laser Melting (SLM) is one of the most promising additive manufacturing technologies, which can produce geometric parts with excellent performance and complex structure. During the SLM process, the laser light source is injected into the forming cavity and enters the system composed of protective gas, metal powder bed and substrate. The powder particles will also have complex interactions with the laser before undergoing the melting and solidification process and forming a solid. In existing studies, it is believed that the SLM laser process parameters are the main factors affecting the subsequent metallurgical behavior. Most of the existing reports tend to improve the forming quality by changing the laser process parameters; the relevant simulations are mostly computational simulations of temperature field and stress field. By adjusting the laser process parameters to affect the temperature field and stress field, the influence of different laser process parameters on the forming quality of the component is analyzed and predicted. However, the change of laser wavelength during laser forming will also directly lead to changes in the laser absorption behavior of the powder bed. In the single-component powder physical model, the laser absorption behavior of the powder bed is often ignored; in the composite powder model, the change of laser wavelength will directly affect the laser absorption behavior and energy conversion efficiency of the micro-area irradiated by the spot, and thus affect the subsequent complex melting behavior. The laser absorption rate and laser-powder bed interaction in the SLM forming process are difficult to measure accurately due to the limitations of the forming laser energy and the SLM powder layer. Therefore, it is necessary to develop a simulation method and device to predict the influence of SLM laser wavelength on absorption behavior. Summary of the invention

[0003] Purpose of the invention: The present invention provides a simulation method and device for predicting the influence of SLM laser wavelength on absorption behavior, which can predict to a certain extent the problem of the influence of laser wavelength on the formability of SLM components that has not been fully considered in existing experiments and simulations.

[0004] Technical solution: The simulation method for predicting the effect of SLM laser wavelength on absorption behavior described in the present invention specifically includes the following steps:

[0005] (1) Based on the observation of composite powder morphology, the computational complexity of numerical simulation and the authenticity of powder layer stacking were balanced. Without considering the overlap and suspension of particles, a mesoscopic random stacking powder bed model was established in MATLAB. The coordinate information of all particles in the calculation domain was obtained and the geometric information was transferred to the unconventional optical software Fred to form a random stacking geometric model of the composite powder bed.

[0006] (2) In order to eliminate the uncertainty of the change of random stacking mode of powders on the numerical simulation of laser absorption behavior, different light source wavelengths and particle physical optical parameters are defined in the same particle stacking model to construct multiple geometric models with different laser wavelengths but the same particle arrangement, enhancement phase distribution and particle physical properties;

[0007] (3) Referring to the experimental method of measuring laser absorptivity using an integrating sphere, a spherical laser energy analysis surface was established outside the model, and line tracing was used to observe the complex interaction between the laser and the powder bed.

[0008] Furthermore, the step (1) comprises the following steps:

[0009] (11) randomly generating the coordinates of the center of a circle within the determined powder bed domain, particle size range, and particle quantity and ratio;

[0010] (12) Make logical judgments on whether overlap occurs, whether the particle size is within the particle size range, or whether the particle size exceeds the geometric domain;

[0011] (13) If “yes”, store all geometric information in the database; if “no”, jump to step (11);

[0012] (14) The geometric information data was imported into the Fred software to obtain the GO-RT model powder bed particle entity, which was used to predict the effect of laser wavelength change on laser absorption behavior during the SLM forming process.

[0013] Furthermore, the implementation process of step (2) is as follows:

[0014] When the laser beam irradiates the powder layer at a certain angle θ0, the s-polarized absorption rate (α s ) and p-polarized absorptivity (α p ) can be obtained from the Fresnel formula:

[0015]

[0016]

[0017] Where n is the complex refractive index of the material; the absorption of the incident laser by the powder particles is the sum of the s-polarized and p-polarized absorption vectors; for different materials in different wavelength models, the complex refractive index is defined to represent the attenuation characteristics between light and the metal medium, which is used as the inherent optical property of different materials in different models:

[0018] n=n0+ik

[0019] Among them, n0 represents the refractive index, which is determined by the propagation speed of light in the medium; k represents the extinction coefficient, which depends on the energy attenuation caused by the light beam penetrating the medium material; i is the imaginary unit, i 2= -1;

[0020] At the same time, the energy distribution characteristics of laser irradiation are considered: the laser light source is 10 6 The laser beam is composed of a beam of light, and the laser energy is given to each beam according to the coordinate information in the spot of each beam. On the basis of simplifying the global laser power W to 1, the overall laser power satisfies the Gaussian characteristic distribution:

[0021]

[0022] Where ω0 is Gaussian distribution in 1 / e 2 The power at the radius; in the Gaussian light source of different laser wavelength models, a specific energy value is defined for each beam according to its position in the spot and its interaction with the composite powder bed particles is tracked.

[0023] Furthermore, the implementation process of step (3) is as follows:

[0024] A phase field consisting of three parts is established on the basis of the existing powder bed entity: composite powder bed, substrate and protective atmosphere; a spherical analysis surface including the composite powder bed, light source and substrate is established outside the model according to the principle of integrating sphere method; by recording the escape energy E0 of the powder bed system and according to the formula:

[0025]

[0026] Among them, A is the laser absorption rate of the powder bed, E is the input energy, and E0 is the output energy. At the same time, the number of light rays in the laser-powder bed interaction is directly recorded to measure the strength of the laser-powder bed interaction at different wavelengths to a certain extent.

[0027] Based on the same inventive concept, the present invention proposes a simulation device for predicting the influence of SLM laser wavelength on absorption behavior, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded into the processor, the simulation method for predicting the influence of SLM laser wavelength on absorption behavior is implemented.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: 1. Taking into account the influence of factors such as the difference in powder particle size of the powder layer material and the gap between particles on the multiple reflection of the laser, the powder is not regarded as a continuous uniform medium and the complexity of numerical simulation calculation and the authenticity of the powder layer stacking are balanced. Starting from the mesoscopic scale, a random stacking geometric model is established; this model is close to the actual SLM powder laying situation and provides a basis for simulating the interaction and absorption behavior of the laser-powder bed; 2. A method combining the definition of the complex refractive index of the material with the change of the laser light source parameters is used to establish multiple models to study the effect of wavelength on SLM formation when the powder particles are arranged consistently. The influence of random powder stacking mode changes on SLM formability is eliminated to a certain extent, which eliminates the uncertainty of the influence of random powder stacking mode changes on numerical simulation of laser absorption behavior; 3. Through the numerical simulation of laser absorption behavior, SLM laser traces at different powder bed positions can be observed and the laser absorption rate and the number of laser rays can be obtained; the overall and single-phase irradiation situation diagrams can be obtained to further reveal the mechanism of the influence of wavelength change on SLM formability; the irradiation situation distribution diagram of any single particle can be obtained, and the influence of wavelength change on SLM formability can be further discussed based on the simulation results; the irradiation situation distribution diagram in the depth direction can be obtained to study the influence of wavelength change on laser penetration in the SLM forming process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart of the simulation method for predicting the effect of SLM laser wavelength on absorption behavior;

[0030] Figure 2 This is a mesoscopic scale powder bed model diagram;

[0031] Figure 3 Schematic diagram for powder property definition;

[0032] Figure 4 It is a mesoscopic scale model consisting of substrate, light source, powder bed and spherical analysis surface;

[0033] Figure 5 It is a schematic diagram of laser line tracking;

[0034] Figure 6 is the variation of absorption rate and number of rays with laser wavelength;

[0035] Figure 7 This is the overall irradiation situation of the powder bed and the enlargement of some areas;

[0036] Figure 8 This is the irradiation diagram of Ni and Fe particles;

[0037] Fig. 9 For the irradiation of a single particle;

[0038] Fig.10 This is the irradiation situation in the depth direction of the powder bed. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0040] The present invention provides a simulation method for predicting the effect of SLM laser wavelength on absorption behavior, which mainly involves the following three steps: first, establishing a mesoscopic three-dimensional powder bed random stacking model; then, changing the light source parameters and the optical parameters that define the powder properties to simulate the laser absorption behavior at different wavelengths; then, obtaining the GO-RT model consisting of the powder bed, substrate, light source and spherical analysis surface in the Fred software to predict the effect of wavelength on laser absorption behavior. Figure 1 As shown, the specific steps include:

[0041] Step 1: Based on the observation of the composite powder morphology, the computational complexity of numerical simulation and the authenticity of powder layer stacking are balanced. Without considering the overlap and suspension of particles, a mesoscopic random stacking powder bed model is established in MATLAB, as shown in Figure 2 As shown, the coordinate information of all particles in the calculation domain is obtained and the geometric information is transmitted to the unconventional optical software Fred to form a random stacking geometric model of the composite powder bed.

[0042] A three-element random stacking powder model of W-Ni-Fe particles is established at the mesoscopic scale. 1) The coordinates of the center of a circle are randomly generated in the domain based on the powder bed domain, particle size range, and the number and proportion of particles. 2) Logical judgments are made on whether overlap occurs, whether it is within the particle size range, or whether it exceeds the geometric domain. 3) If yes, all geometric information is stored in the database. If no, 1 is continued. 4) The geometric information data is imported into the Fred software to obtain the GO-RT model powder bed particle entity used to predict the effect of laser wavelength change on laser absorption behavior during the SLM forming process.

[0043] Step 2: To eliminate the uncertainty of the effect of random powder stacking on the numerical simulation of laser absorption behavior, different light source wavelengths are defined in the same particle stacking model and physical properties of different materials are defined, such as Figure 3 As shown in Figure 1, multiple geometric models with different laser wavelengths but the same particle arrangement, enhanced phase distribution, and particle properties are constructed, such as Figure 4 shown.

[0044] When the laser beam irradiates the powder layer at a certain angle θ0, the s-polarized absorption rate (α s ) and p-polarized absorptivity (α p ) can be obtained from the Fresnel formula:

[0045]

[0046]

[0047] Where n is the complex refractive index of the material. Usually, the absorption of the incident laser by the powder particles is the sum of the s-polarized absorption vectors and the p-polarized absorption vectors. For different materials in different wavelength models, the complex refractive index is defined to represent the attenuation characteristics between light and the metal medium, which is used as the inherent optical property of different materials in different models:

[0048] n=n0+ik

[0049] Among them, n0 represents the refractive index, which is usually determined by the propagation speed of light in the medium; k represents the extinction coefficient, which depends on the energy attenuation caused by the light beam penetrating the medium material; i is the imaginary unit, i 2 = -1. In order to increase the accuracy of numerical simulation of laser absorption behavior, in addition to defining the complex refractive index, this model also considers the characteristics of laser irradiation energy distribution. The laser source consists of 10 6 The laser beam is composed of a beam of light, and the laser energy is given to each beam according to the coordinate information in the spot of each beam. On the basis of simplifying the global laser power W to 1, the overall laser power satisfies the Gaussian characteristic distribution:

[0050]

[0051] Where ω0 is Gaussian distribution in 1 / e 2 Power at radius. Define specific energy values ​​for each beam according to its position in the spot in a Gaussian source with different laser wavelength models and track its interaction with the composite powder bed particles.

[0052] Step 3: Predict the wavelength effect of SLM laser absorption behavior based on the GO-RT model.

[0053] Referring to the experimental method of measuring laser absorptivity with an integrating sphere, a spherical laser energy analysis surface was established outside the model, and line tracking was used to observe the complex interaction between the laser and the powder bed, such as Figure 5 Taking the infrared band as an example, the influence of laser wavelength on laser absorption behavior is studied, the number of light rays N and the escape energy E0 of the random stacked powder bed system are recorded, and the powder bed laser absorption rate A is calculated according to the formula.

[0054] A phase field consisting of three parts is established on the basis of the existing powder bed entity: composite powder bed, substrate and protective atmosphere. At the same time, a spherical analysis surface including the composite powder bed, light source and substrate is established outside the model according to the principle of integrating sphere method. By recording the escape energy E0 of the powder bed system and according to the formula:

[0055]

[0056] Calculate the laser absorption rate A, where E is the input energy and E0 is the output energy; at the same time, directly record the number of rays and the absorption rate in the laser-powder bed interaction, such as Figure 6As shown in , it can measure the strength of laser-powder bed interaction at different wavelengths to a certain extent. Figure 7 , Figure 8 The overall and single-phase irradiation diagrams further reveal the mechanism of the influence of wavelength change on SLM formability; the irradiation distribution diagram of any single particle can be obtained, such as Fig. 9 As shown, the effect of wavelength variation on SLM formability is further discussed based on the simulation results; the distribution diagram of irradiation in the depth direction can be obtained, such as Fig.10 As shown, it is used to study the effect of wavelength change on laser penetration in the SLM forming process.

[0057] Based on the same inventive concept, the present invention proposes a simulation device for predicting the influence of SLM laser wavelength on absorption behavior, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded into the processor, the simulation method for predicting the influence of SLM laser wavelength on absorption behavior is implemented.

[0058] Through the above description, relevant technicians in the field of additive manufacturing can clearly understand that the present invention can be implemented in the following ways: software and necessary general hardware platforms. Moreover, the implementation scheme of the present invention can reflect its contribution to the prior art in the form of software products. The obtained software products can be stored in storage media such as ROM / RAM, magnetic disks, optical disks, etc., and finally control computer devices (which can be personal computers, servers, or network devices, etc.) through relevant instructions to execute the methods described in the embodiments of the present invention or some parts of the embodiments.

Claims

1. A simulation method for predicting the effect of SLM laser wavelength on absorption behavior, characterized in that: The following steps are involved: (1) Based on the observation of the composite powder morphology, the computational complexity of numerical simulation and the authenticity of powder layer stacking were balanced. Without considering the overlap and suspension of particles, a mesoscopic random stacking powder bed model was established in MATLAB. The coordinate information of all particles in the calculation domain was obtained and the geometric information was transferred to the unconventional optical software Fred to form a random stacking geometric model of the composite powder bed. (2) In order to eliminate the uncertainty of the change in the random stacking mode of powders on the numerical simulation of laser absorption behavior, different light source wavelengths and particle physical optical parameters are defined in the same particle stacking model to construct multiple geometric models with different laser wavelengths but the same particle arrangement, enhancement phase distribution and particle properties. This can obtain a mesoscopic GO-RT model for predicting the effect of SLM laser wavelength on absorption behavior. (3) Based on the GO-RT model, referring to the experimental method of measuring laser absorptivity with an integrating sphere, a spherical laser energy analysis surface was established outside the model, and line tracing was used to observe the complex interaction between the laser and the powder bed to predict the effect of different laser wavelengths on the SLM formability. Specifically, through the numerical simulation of laser absorption behavior, the SLM laser line traces at different powder bed positions were observed and the laser absorptivity and the number of laser rays were obtained, the overall and single-phase irradiation diagrams were obtained, the irradiation distribution diagrams of any single particle were obtained, and the irradiation distribution diagrams in the depth direction were obtained. At the same time, the overall and single-phase irradiation diagrams were used to reveal the mechanism of the influence of laser wavelength changes on SLM formability. The irradiation distribution diagrams of any single particle were used to discuss the influence of laser wavelength changes on SLM formability. The irradiation distribution diagrams in the depth direction were used to study the influence of laser wavelength changes on laser penetration in the SLM forming process. The step (1) comprises the following steps: (11) Randomly generate the coordinates of the center of a circle within the determined powder bed domain, particle size range, and particle quantity and ratio; (12) Make logical judgments on whether overlap occurs, whether the particle size is within the particle size range, or whether the particle size exceeds the geometric domain. (13) If "yes", store all geometric information in the database; if "no", jump to step (11); (14) Import the geometric information data into Fred software to obtain the powder bed solid model; The implementation process of step (2) is as follows: When the laser beam is at an angle θ 0 irradiates the powder layer, the s-polarized absorption rate α s and p-polarized absorptivity α p From the Fresnel formula we get: ； ； in, n is the complex refractive index of the material; the absorption of the incident laser by the powder particles is the sum of the s-pole and p-pole polarized absorption vectors; for different materials in different wavelength models, the complex refractive index is defined to represent the attenuation characteristics between light and the metal medium, which is used as the inherent optical property of different materials in different models: ； in, n 0 represents the refractive index, which is determined by the speed of light in the medium; k represents the extinction coefficient, which depends on the energy attenuation caused by the light beam penetrating the dielectric material; i is an imaginary unit, i 2 =-1; At the same time, the energy distribution characteristics of laser irradiation are considered: the laser light source is 10 6 The laser power is determined by the coordinate information of each beam spot. W Simplify it to 1 to make it satisfy the Gaussian characteristic distribution as a whole: ； in, ω 0 is Gaussian distribution at 1 / e 2 The power at the radius; in the Gaussian light source of different laser wavelength models, the energy value is defined according to the position of each beam in the spot and its interaction with the composite powder bed particles is tracked.

2. The simulation method for predicting the effect of SLM laser wavelength on absorption behavior according to claim 1, characterized in that: The implementation process of step (3) is as follows: A phase field consisting of three parts is established on the basis of the existing powder bed entity: composite powder bed, substrate and protective atmosphere; a spherical analysis surface including the composite powder bed, light source and substrate is established outside the model according to the principle of integrating sphere method; the energy escaped from the powder bed system is recorded E 0 and according to the formula: ； in, A is the laser absorptivity of the powder bed, E is the input energy, E 0 is the output energy; at the same time, the number of light rays in the laser-powder bed interaction is directly recorded to measure the strength of the laser-powder bed interaction at different wavelengths.

3. A simulation device for predicting the effect of SLM laser wavelength on absorption behavior, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the computer program is loaded into a processor, the simulation method for predicting the influence of SLM laser wavelength on absorption behavior according to claim 1 or 2 is implemented.

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