Method and system for predicting residual stress of additive manufacturing part after heat treatment

Abstract

The invention discloses a residual stress prediction method and system for an additive manufacturing part after heat treatment, and belongs to the field of additive manufacturing, and the method comprises the steps: obtaining the original residual stress distribution in a large-size additive manufacturing block through a finite element method based on inherent strain; then, comparing the distribution of the residual stress in the AM part obtained by the finite element method with the residual stress result in the AM equipment printing part, and verifying the accuracy of the distribution of the residual stress in the block obtained by the finite element method; in a subsequent heat treatment model, hyperbolic sine function creep model parameters of the material at different heat treatment temperatures are defined, and the creep parameters are obtained through creep experiments at the corresponding temperatures; and comparing the residual stress distribution of the block obtained by heat treatment simulation with the residual stress distribution result measured by the experiment to verify the effectiveness of the method. Accurate prediction of the residual stress distribution of the AM part in the full heat treatment temperature range can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a method and system for predicting residual stress of an additively manufactured part after heat treatment. Background Art

[0002] Additive manufacturing (AM) technology can directly produce parts with high precision and complex shapes based on the three-dimensional model of the object. This method not only reduces material waste, but also significantly reduces the cost and time of manufacturing complex structures. Austenitic stainless steel (AUSS) has excellent corrosion resistance and mechanical properties and has been widely used in industry. Thanks to this, AM-made AUSS parts not only have complex geometric shapes that cannot be achieved by traditional manufacturing methods, but also can improve the overall performance of the parts by optimizing process parameters. In industry, AM parts can be used to manufacture key components such as corrosion-resistant pipes, valves and pumps; in the biomedical field, AUSS is used to manufacture orthopedic implants and surgical instruments; in the aerospace field, AM technology is used to produce lightweight and high-strength structural components such as turbine blades and fuel nozzles.

[0003] However, the rapid heating and cooling during the AM manufacturing process will cause huge residual stress in the parts, especially the tensile residual stress near the surface (>500MPa). The existence of large tensile residual stress will significantly affect the service performance of AM parts, especially fatigue performance, and seriously affect the life and reliability of the equipment.

[0004] Post-heat treatment is usually used to reduce the overall residual stress level of AM parts. In the article "Influence of laser shock peening on the residual stresses in additively manufactured 316L by Laser Powder Bed Fusion: A combined experimental–numerical study", Sandmann et al. heat treated AM AUSS samples at 700°C and found that the surface tensile residual stress was released by about 40%. Heat treatment can effectively reduce the residual stress level of AM parts, but there are significant differences in the degree of residual stress release under different heat treatment temperature and time conditions. In addition, since a large number of experiments are required to establish the relationship between the degree of residual stress release and the heat treatment temperature and time, it is necessary to use the finite element method to predict the residual stress distribution results under various heat treatment temperatures and times. In the article "Simulation of Annealing Process on AISI 316L Stainless Steel Fabricated Via Laser Powder Bed Fusion Using Finite Element Method With Creep", Qing et al. used a creep model based on the time / strain hardening equation to predict the residual stress distribution in AM AUSS after heat treatment. However, this time / strain hardening equation is not applicable to the situation where the residual stress decreases rapidly during the heat treatment of AM parts. In addition, this method is only applicable to the working conditions of 650℃ and 750℃ mentioned in the article, and there is no direct measurement of the residual stress value as a verification of the validity of the model. Therefore, it is urgent to design a new residual stress prediction technology for heat treatment of additively manufactured parts to achieve the prediction of residual stress distribution results of AM AUSS parts after heat treatment in the full heat treatment temperature range. Summary of the invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a residual stress prediction technology for additively manufactured parts after heat treatment based on the finite element method, aiming to use a creep model based on the hyperbolic sine function to achieve accurate prediction of the residual stress distribution results of AM AUSS parts after heat treatment in the full heat treatment temperature range.

[0006] In order to achieve the above technical objectives, the present application provides a method for predicting residual stress of an additively manufactured part after heat treatment, comprising the following steps:

[0007] Based on the additive manufacturing AM parts, the initial model is constructed by the finite element method based on inherent strain to obtain the original residual stress distribution of the AM parts;

[0008] Based on the initial model, a hyperbolic sine function creep model was constructed according to the creep parameters at different heat treatment temperatures fitted by an exponential function. Thermal boundary conditions were applied to simulate the heat treatment conditions and obtain the residual stress distribution results after heat treatment.

[0009] Preferably, in the process of obtaining the original residual stress distribution, the residual stress distribution obtained by the finite element method is compared with the residual stress distribution result in the AM part printed by the AM equipment to verify the accuracy of the residual stress distribution in the block obtained by the finite element method.

[0010] Preferably, in the process of obtaining the residual stress distribution, the residual stress distribution is obtained by X-ray diffraction.

[0011] Preferably, in the process of obtaining creep parameters, creep coefficient, stress coefficient and stress exponent are used as creep parameters.

[0012] Preferably, in the process of constructing the hyperbolic sine function creep model, the hyperbolic sine function creep model is expressed as:

[0013]

[0014] In the formula, A represents the creep coefficient, B represents the stress coefficient, and sinh represents the hyperbolic sine term. represents the stress term, n represents the stress exponent, ΔH represents the activation energy, R represents the gas constant, θ represents the current temperature, Z represents the base temperature, exp() represents the exponential term, represents the creep strain rate.

[0015] The present invention discloses a system for predicting residual stress of an additively manufactured part after heat treatment, comprising:

[0016] The finite element analysis module is used to construct an initial model based on the additive manufacturing AM parts through the finite element method based on inherent strain to obtain the original residual stress distribution of the AM parts;

[0017] The prediction module is used to construct a hyperbolic sine function creep model based on the initial model and the creep parameters at different heat treatment temperatures fitted by an exponential function, and to apply thermal boundary conditions to simulate the heat treatment conditions and obtain the residual stress distribution results after heat treatment.

[0018] Preferably, the system also compares the residual stress distribution obtained by the finite element method with the residual stress distribution results in the AM parts printed by the AM equipment to verify the accuracy of the residual stress distribution in the block obtained by the finite element method.

[0019] Preferably, the system obtains the residual stress distribution by X-ray diffraction.

[0020] Preferably, the creep parameters include a creep coefficient, a stress coefficient and a stress exponent.

[0021] Preferably, the hyperbolic sine function creep model is expressed as:

[0022]

[0023] In the formula, A represents the creep coefficient, B represents the stress coefficient, and sinh represents the hyperbolic sine term. represents the stress term, n represents the stress exponent, ΔH represents the activation energy, R represents the gas constant, θ represents the current temperature, Z represents the base temperature, exp() represents the exponential term, represents the creep strain rate.

[0024] The present invention discloses the following technical effects:

[0025] (1) The method for predicting residual stress after heat treatment based on the hyperbolic sine function creep model established by the present invention can accurately calculate the rapid change of residual stress in AM parts after heat treatment with high accuracy, and the error with the experimentally measured surface residual stress is within 10%.

[0026] (2) The creep parameter model with a full temperature range established by the present invention can predict the residual stress distribution results in AM parts at higher heat treatment temperatures, especially at 900°C, and can accurately describe the effects of heat treatment time and temperature on residual stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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 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 work.

[0028] Figure 1 is a flow chart of the method described in the present invention;

[0029] Figure 2 A residual stress distribution cloud diagram of the AM part calculated by finite element method in step 1 provided in an example of the present invention;

[0030] Figure 3 The residual stress results in the AM parts obtained by the step 2 experiment provided in the example of the present invention;

[0031] Figure 4Creep parameters within the entire heat treatment temperature range in step 3 provided for the present invention example.

[0032] Figure 5 A cloud diagram of residual stress distribution in an AM part after heat treatment (at 750° C. for 6 hours) calculated by finite element method in step 5 of the present invention;

[0033] Figure 6 The maximum residual stress on the surface of the AM part after heat treatment (at 750°C for 6 hours) calculated by finite element in step 5 of the present invention is compared with the maximum residual stress on the surface measured by experiment;

[0034] Figure 7 The maximum residual stress on the surface of the AM part after heat treatment (at 850°C for 2 hours and at 900°C for 1 hour) calculated by finite element in step 5 of the example provided in the present invention is compared with the maximum residual stress on the surface measured experimentally. DETAILED DESCRIPTION

[0035] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0036] like Figure 1 As shown, the present invention provides a method for predicting residual stress of an additively manufactured part after heat treatment, using a hyperbolic sine function creep model to construct a method for predicting residual stress distribution results of an AM AUSS part after heat treatment in the full heat treatment temperature range, comprising the following steps:

[0037] Step 1: Using the inherent strain-based finite element method, an AM AUSS piece with a size of 10 mm × 10 mm × 10 mm was established using ABAQUS finite element modeling software, and the residual stress distribution results in the AM AUSS block were obtained;

[0038] Step 2: Compare the residual stress distribution results in the block obtained by the finite element method in step 1 with the residual stress distribution results in the AM AUSS block prepared by the AM equipment to verify the accuracy of the residual stress distribution results in the block obtained by the finite element method; among them, the experimental measurement method of the residual stress distribution is the X-ray diffraction method.

[0039] Step 3: Use exponential function to fit the creep parameters at different heat treatment temperatures and establish the creep parameters for the entire heat treatment temperature range. The creep parameters that need to be defined include creep coefficient, stress coefficient and stress exponent. The creep parameters are obtained from creep experiments at the corresponding heat temperatures.

[0040] Step 4: Based on steps 1 and 3, add the hyperbolic sine function creep model material parameters of the full thermal temperature range to the subsequent heat treatment model.

[0041] Step 5: Apply thermal boundary conditions to the model, simulate heat treatment conditions, and obtain residual stress distribution results after heat treatment. Compare the predicted residual stress results with the experimentally measured residual stress results to verify the accuracy of the hyperbolic sine function creep model in predicting the residual stress distribution results in AM parts within the full heat treatment temperature range.

[0042] Embodiment: The present invention provides a method for accurately predicting the residual stress distribution in an additively manufactured part after heat treatment using the technical solution of the present invention. The AM part in this embodiment has a size of 10 mm × 10 mm × 10 mm and is made of 316L austenitic stainless steel.

[0043] In this embodiment, the present invention provides a method for predicting residual stress of an additively manufactured part after heat treatment, such as Figure 1 As shown, the following steps are included:

[0044] Step 1: The original residual stress distribution in the AM316L AUSS block is obtained by using the finite element method based on inherent strain using ABAQUS finite element modeling software. Figure 2 ;

[0045] Step 2: Compare the residual stress distribution in the block obtained by the finite element method in step 1 with the residual stress distribution results in the AM 316L block printed by the AM equipment to verify the accuracy of the residual stress distribution in the block obtained by the finite element method. (1) Use computer CAD software to model a sample model with a size of 10mm*10mm*10mm, then slice the model into layers with a thickness of 30μm per layer, set the rotation between layers to 66.7°, and use special software for additive manufacturing to plan the scanning path. Then use the SLM-125HL additive manufacturing equipment to prepare 316L austenitic stainless steel samples. Among them, the set additive manufacturing printing parameters are: laser power of 200W, scanning speed of 800mm / s, layer thickness of 30μm, and scanning spacing of 120μm. (2) The residual stress measurement equipment is the PROTO-iXRD X-ray diffractometer, and the measurement position is the middle position of the sample surface. The residual stress results are shown in Figure 3 .

[0046] Step 3: Based on step 1, add material parameters based on the hyperbolic sine function creep model to the model. The creep parameters are obtained from the creep experiment at the corresponding temperature, such as Figure 4 As shown, the hyperbolic sine function creep model is:

[0047]

[0048] Among them, A represents the creep coefficient, B represents the stress coefficient, sinh represents the hyperbolic sine term, represents the stress term, n represents the stress exponent, ΔH represents the activation energy, R represents the gas constant, θ represents the current temperature, Z represents the base temperature, exp() represents the exponential term, represents the creep strain rate.

[0049] Step 4: Apply a thermal boundary condition of 750°C to the model for 6 hours to simulate the heat treatment condition and obtain the residual stress distribution results after heat treatment, see Figure 5 The simulation results are compared with the experimental residual stress results to verify the accuracy of the hyperbolic sine function creep model in predicting the stress in AM 316L parts. The results are compared in Figure 6 .

[0050] Step 6: Use the established creep parameter model to predict the residual stress distribution results in the AM block at 850℃-2h and 900℃-1h. Compare the predicted residual stress results with the experimental results, see Figure 7 , verifying the accuracy of the hyperbolic sine function creep model in predicting the residual stress distribution in L-PBF 316L blocks after high temperature heat treatment.

[0051] In summary, the residual stress prediction technology for additively manufactured parts after heat treatment provided by the present invention first obtains the original residual stress distribution in the block of large-scale additively manufactured (AM) austenitic stainless steel (AUSS) by the finite element method based on inherent strain; then, the distribution of residual stress in the AM parts obtained by the finite element method is compared with the residual stress results in the AM equipment printout to verify the accuracy of the residual stress distribution in the block obtained by the finite element method; in the subsequent heat treatment model, the hyperbolic sine function creep model parameters of the material at different heat treatment temperatures (600-900°C) are defined, and the creep parameters are obtained by the creep experiment at the corresponding temperature; then, the residual stress distribution of the block obtained by the heat treatment simulation is compared with the residual stress distribution results measured experimentally to verify the effectiveness of the method. The method of the present invention can achieve accurate prediction of the residual stress distribution of AM parts in the full heat treatment temperature range (especially high temperature heat treatment, >750°C).

[0052] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0053] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0054] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for predicting residual stress of additively manufactured parts after heat treatment, characterized in that: The following steps are involved: Based on the additive manufacturing AM parts, the initial model is constructed by the finite element method based on inherent strain to obtain the original residual stress distribution of the AM parts; Based on the initial model, a hyperbolic sine function creep model is constructed according to the creep parameters at different heat treatment temperatures fitted by an exponential function, and thermal boundary conditions are applied to simulate the heat treatment conditions to obtain the residual stress distribution results after heat treatment.

2. A method for predicting residual stress after heat treatment of additively manufactured parts according to claim 1, characterized in that: In the process of obtaining the original residual stress distribution, the residual stress distribution obtained by the finite element method is compared with the residual stress distribution results in the AM parts printed by the AM equipment to verify the accuracy of the residual stress distribution in the block obtained by the finite element method.

3. A method for predicting residual stress after heat treatment of additively manufactured parts according to claim 2, characterized in that: In the process of obtaining the residual stress distribution, the residual stress distribution is obtained by X-ray diffraction.

4. The method for predicting residual stress after heat treatment of additively manufactured parts according to claim 3, characterized in that: In the process of obtaining creep parameters, creep coefficient, stress coefficient and stress exponent are used as creep parameters.

5. A method for predicting residual stress after heat treatment of additively manufactured parts according to claim 4, characterized in that: In the process of constructing the hyperbolic sine function creep model, the hyperbolic sine function creep model is expressed as: In the formula, A represents the creep coefficient, B represents the stress coefficient, and sinh represents the hyperbolic sine term. represents the stress term, n represents the stress exponent, ΔH represents the activation energy, R represents the gas constant, θ represents the current temperature, Z represents the base temperature, exp() represents the exponential term, represents the creep strain rate.

6. A residual stress prediction system for additively manufactured parts after heat treatment based on finite element method, characterized in that: include: The finite element analysis module is used to construct an initial model based on the additive manufacturing AM parts through the finite element method based on inherent strain to obtain the original residual stress distribution of the AM parts; The prediction module is used to construct a hyperbolic sine function creep model based on the initial model and the creep parameters at different heat treatment temperatures fitted by an exponential function, and to apply thermal boundary conditions to simulate the heat treatment conditions to obtain the residual stress distribution results after heat treatment.

7. According to claim 6, a system for predicting residual stress after heat treatment of additively manufactured parts based on finite element method, characterized in that: The system also compares the residual stress distribution obtained by the finite element method with the residual stress distribution results in the AM parts printed by the AM equipment to verify the accuracy of the residual stress distribution in the block obtained by the finite element method.

8. According to claim 7, a system for predicting residual stress after heat treatment of additively manufactured parts based on finite element method, characterized in that: The system obtains the residual stress distribution through X-ray diffraction.

9. The residual stress prediction system for additively manufactured parts after heat treatment based on the finite element method according to claim 8, characterized in that: The creep parameters include creep coefficient, stress coefficient and stress exponent.

10. The residual stress prediction system for additively manufactured parts after heat treatment based on the finite element method according to claim 9, characterized in that: The hyperbolic sine function creep model is expressed as: In the formula, A represents the creep coefficient, B represents the stress coefficient, and sinh represents the hyperbolic sine term. represents the stress term, n represents the stress exponent, ΔH represents the activation energy, R represents the gas constant, θ represents the current temperature, Z represents the base temperature, exp() represents the exponential term, represents the creep strain rate.

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