A method for compensating residual stress of an SLM formed part based on an applied static magnetic field

Abstract

The application discloses an SLM formed part residual stress compensation method based on an applied static magnetic field, and belongs to the field of additive manufacturing. The method applies a static magnetic field which is from top to bottom and perpendicular to the direction of a substrate in a printing bin. The method reduces the residual stress of an SLM formed part by means of the Lorentz force and the thermoelectric magnetic force generated between the static magnetic field and an SLM molten pool. A single-layer single-path selective SLM simulation model is established by using Comsol Multiphysics. In the process of using the model, a probe is used to select a certain point processing position. The temperature change, the residual stress change and the volume strain before and after the magnetic field is increased are observed and compared, so that the feasibility of the method is verified.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing, specifically relating to a method for compensating residual stress in SLM-molded parts based on an external static magnetic field. Background Technology

[0002] Selective laser melting (SLM) is an advanced metal additive manufacturing method that uses a laser to melt metal powder layer by layer to create complex metal parts. During this process, rapid solidification and heat transfer, along with differences in the coefficient of thermal expansion in different regions, can lead to residual stress within the formed part. This residual stress can affect the part's dimensional stability, mechanical properties, and deformation behavior, and may even negatively impact its service life and safety. Therefore, finding an effective compensation method to reduce residual stress within the formed part has become a research hotspot for scholars both domestically and internationally. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for compensating residual stress in SLM molded parts based on an external static magnetic field, so as to reduce the residual stress inside the molded parts.

[0004] The technical solution to achieve the objective of this invention is: a method for compensating residual stress in SLM-formed parts based on an externally applied static magnetic field, comprising the following steps:

[0005] Step 1: Apply an external static magnetic field;

[0006] The molded part is placed on the SLM processing platform. During the SLM processing, a static magnetic field is applied from top to bottom and perpendicular to the substrate direction through a static magnetic field generator. The strength of the magnetic field is controlled to precisely control the compensation of residual stress.

[0007] Step 2: Use a static magnetic field to reduce the residual stress in the SLM-formed part;

[0008] An interaction occurs between a current-carrying fluid and a static magnetic field, and a Lorentz force is generated between the static magnetic field and the SLM molten pool:

[0009] F E =J u ×B

[0010] In the formula: FE is the Lorentz force, Ju is the current density, and B is the magnetic induction intensity;

[0011] Lorentz force acts on the fluid, affecting its flow, changing the heat and mass transfer process of the molten pool, and affecting the solidification and forming of the molten pool, thereby reducing the residual stress of the SLM formed parts.

[0012] Furthermore, the applied static magnetic field generates the Hartmann effect and Seebeck effect during the SLM forming process, which in turn induces current in the molten pool. The current-carrying mass in the molten pool interacts with the magnetic field to generate an induced current, which can be represented as:

[0013] J u =σu×B

[0014]

[0015] In the formula: Ju is the induced current density, σ is the conductivity, u is the melt flow velocity, B is the magnetic induction intensity, FE is the Lorentz force, and D is the width of the molten pool;

[0016] In the SLM forming process, the electrical conductivity between the liquid and solid phases of the molten pool metal is significantly different, resulting in a thermoelectric current that moves from the liquid phase to the solid phase. The interaction between the static magnetic field and the thermoelectric current generates a thermoelectric force, which, under a certain magnetic field strength, can be expressed as:

[0017] F∝σSGB

[0018] In the formula: F is the thermo-magnetic force, σ is the conductivity of the melt, S is the absolute electric potential energy, G is the temperature gradient, and B is the magnetic field strength.

[0019] Thermo-magnetic forces will drive localized flow in the molten pool, thereby affecting the microstructure and properties of the SLM at the location being processed.

[0020] Step 3: Verify the correctness of the method of compensating for residual stress in SLM-formed parts by applying an external static magnetic field through finite element simulation analysis;

[0021] An SLM simulation model was established, and the changes in temperature, residual stress, and volumetric strain before and after the addition of the magnetic field were compared to verify the feasibility of the method.

[0022] The beneficial effects of this invention are:

[0023] The residual stress compensation method for SLM molded parts based on an external static magnetic field can effectively reduce the residual stress of the molded parts and improve the accuracy of the molded parts. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the external static magnetic field applied in this invention;

[0025] Figure 2 This is a schematic diagram of the single-layer, single-channel temperature of the present invention;

[0026] Figure 3 This is a temperature comparison diagram before and after applying an external static magnetic field to a single layer of the present invention.

[0027] Figure 4 This is a schematic diagram of the single-layer, single-channel residual stress of the present invention;

[0028] Figure 5 This is a comparison diagram of residual stress before and after applying an external static magnetic field to a single layer of the present invention;

[0029] Figure 6 This is a schematic diagram of single-layer, single-channel volumetric strain of the present invention;

[0030] Figure 7 This is a comparison diagram of volumetric strain before and after applying a static magnetic field to a single layer of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0032] Example

[0033] In practice, the specific implementation steps of this invention are as follows:

[0034] A single-layer, single-channel SLM simulation model was established using Comsol Multiphysics. A static magnetic field perpendicular to the substrate direction and extending from top to bottom was applied in the printing chamber. The main parameters are as follows: laser absorptivity of 0.6, scanning speed of 600 mm / s, laser power of 100 W, spot radius of 60 μm, powder thickness of 40 μm, and background magnetic field strength of 1000 A / m. A schematic diagram of the applied static magnetic field is shown below. Figure 1 As shown, a Gaussian heat source is used as the heat source model. Figure 2 This is a schematic diagram of a single-layer, single-channel temperature. During model usage, a probe is used to select a specific processing location, and the temperature comparison at that point before and after the magnetic field is applied is shown below. Figure 3 As shown.

[0035] The temperature comparison graph of the probe point before and after the addition of the magnetic field shows that at 0.00066 seconds, the peak temperature of the probe point without a static magnetic field is 3745.69 K, while the peak temperature of the probe point after the addition of the static magnetic field is 3051.60 K, a decrease of 696.09 K. Then the temperature gradually tends to reach equilibrium. During this period, the temperature after the magnetic field is added is lower than the temperature without the magnetic field.

[0036] Using a probe, select the same machining location and observe the effect of the applied static magnetic field on the residual stress. Figure 4 This is a schematic diagram of residual stress in a single layer and a single channel. The comparison of residual stress at this point before and after the addition of the magnetic field is shown in the figure. Figure 5 As shown.

[0037] The comparison of residual stress at the point before and after the addition of the magnetic field in the model shows that at 0.04 seconds, the residual stress at the probe point without a magnetic field is 701.559 MPa, while the residual stress at the probe point after the addition of the static magnetic field is 584.196 MPa, a decrease of 117.363 MPa. Then the residual stress tends to reach equilibrium. During this period, the residual stress after the addition of the static magnetic field is less than the residual stress without the addition of the static magnetic field.

[0038] Using a probe, select the same processing location and observe the effect of an applied static magnetic field on volumetric strain. Figure 6 This is a schematic diagram of single-layer, single-channel volumetric strain. The comparison of volumetric strain at this point before and after the addition of the magnetic field is shown in the figure. Figure 7 As shown.

[0039] The comparison of volumetric strain at the point before and after the addition of the static magnetic field shows that at 0.00066 seconds, the peak volumetric strain at the probe point without the static magnetic field was 20.8717%, while the peak volumetric strain at the probe point after the static magnetic field was added was 16.7138%, a reduction of 4.6979%. After that, the volumetric strain tended to reach equilibrium. During this period, the volumetric strain after the static magnetic field was added was slightly smaller than the volumetric strain without the static magnetic field.

[0040] The above embodiments are merely illustrative examples of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for compensating residual stress in SLM-formed parts based on an applied static magnetic field, characterized in that, Includes the following steps: Step 1: Apply an external static magnetic field; The molded part is placed on the SLM processing platform. During the SLM processing, a static magnetic field is applied from top to bottom and perpendicular to the substrate direction through a static magnetic field generator. The strength of the magnetic field is controlled to precisely control the compensation of residual stress. Step 2: Use a static magnetic field to reduce the residual stress in the SLM-formed part; An interaction occurs between a current-carrying fluid and a static magnetic field, and a Lorentz force is generated between the static magnetic field and the SLM molten pool: In the formula: F E For Lorentz force, J u Let B be the current density and B be the magnetic flux density. Lorentz force acts on the fluid, affecting its flow, changing the heat and mass transfer process of the molten pool, and affecting the solidification and forming of the molten pool, thereby reducing the residual stress of the SLM formed parts. Furthermore, the applied static magnetic field generates the Hartmann effect and Seebeck effect during the SLM forming process, which in turn induces current in the molten pool. The current-carrying mass in the molten pool interacts with the magnetic field to generate an induced current, which can be represented as: In the formula: σ is the electrical conductivity, u is the melt flow velocity, and D is the width of the molten pool; In the SLM forming process, the electrical conductivity between the liquid and solid phases of the molten pool metal is significantly different, resulting in a thermocurrent that moves from the liquid phase to the solid phase. The interaction between the static magnetic field and the thermocurrent generates a thermoelectric force, which, under a certain magnetic field strength, can be expressed as: In the formula: F is the thermo-magnetic force, S is the absolute electric potential energy, and G is the temperature gradient; Thermo-magnetic forces will drive localized flow in the molten pool, thereby affecting the microstructure and properties of the SLM at the location being processed. Step 3: Verify the correctness of the method of compensating for residual stress in SLM-formed parts by applying an external static magnetic field through finite element simulation analysis; An SLM simulation model was established, and the changes in temperature, residual stress, and volumetric strain before and after the addition of the magnetic field were compared to verify the feasibility of the method.

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