Selective laser melting forming method for unsupported printing

Abstract

The selective laser melting forming method for unsupported printing comprises the following steps that S1, a powder bed is laid, and a high-energy laser beam in an integrated selective laser melting device is adopted for conducting laser melting forming on a first layer of a to-be-machined component; s2, a powder bed is laid, whether an ith layer of the to-be-machined component has a suspension area or not is judged, and if yes, a preset machining method is adopted for machining, melting and forming; if not, a high-energy laser beam in the integrated selective laser melting device is adopted for conducting laser melting forming on the ith layer of the to-be-machined component; s3, the step S2 is repeated until the integrated selective laser melting device completes laser melting forming of the Nth layer of the to-be-machined component; s4, powder in the unprocessed area and powder in the pre-sintered expansion area L2 are cleaned, and a processed component is obtained; by means of the method, powder on the outer side of the overhanging area can be stabilized, a more stable melting channel is obtained, and therefore the defects of slag adhering, air holes and the like on the overhanging surface are reduced.

Description

Technical Field

[0001] The present invention relates to the field of laser additive manufacturing, and in particular to a laser selective melting forming method for support-free printing. Background Art

[0002] Selective laser melting technology is an additive manufacturing technology that uses a high-energy laser beam to scan the powder layer selectively, melt the powder material, and deposit it layer by layer. It is widely used in aerospace, national defense, automobile manufacturing, biomedicine and other fields. However, in the actual processing process, there are often overhanging areas without bottom support. Since the powder in the overhanging area lacks bottom solid support, it is easy to cause serious surface slag and warping deformation in the overhanging area. There are two main methods for process optimization of the overhanging area: one is to add auxiliary supports to assist heat dissipation and resist thermal deformation, but it will cause many disadvantages such as increased manufacturing time, material waste, and difficulty in removing supports; the other is to use a low-energy density process for sintering to improve the forming quality of the overhanging area, but there are also optimization limits, especially in the forming of low-angle components. The harsh forming conditions make it difficult to achieve support-free printing.

[0003] In general, the existing technology still cannot avoid the use of auxiliary supports when forming low-angle components, and there is an urgent need to develop a new laser selective melting forming process for low-angle support-free printing. Summary of the invention

[0004] In view of this, in order to make up for the problem of the prior art that a large number of auxiliary supports need to be added when manufacturing complex components and to improve the printing quality of the overhanging area, the present invention proposes a laser selective melting forming method for support-free printing.

[0005] The present invention provides a laser selective melting forming method for support-free printing, comprising the following steps:

[0006] S1. Laying a powder bed, using a high-energy laser beam in an integrated laser selective melting device to perform laser melting and forming on the first layer of the component to be processed;

[0007] S2. Lay a powder bed and determine whether there is an overhanging area on the i-th layer of the component to be processed. If so, use a preset processing method to perform melting and forming; if not, use a high-energy laser beam in an integrated laser selective melting device to perform laser melting and forming on the i-th layer of the component to be processed;

[0008] The preset processing method includes: determining the core area L3 and the surface process area L1 of the i-th layer, and setting the expansion area L2;

[0009] The surface process area L1 and the extended area L2 of the i-th layer are pre-sintered by using a flat-top laser in an integrated laser selective melting device;

[0010] The Gaussian laser in the integrated laser selective melting device is used to melt and form the surface process area L1 and the core area L3 after pre-sintering;

[0011] Wherein, 2≤i≤N, N represents the total number of processing layers of the component to be processed;

[0012] S3. Repeat step S2 until the integrated laser selective melting device completes the laser melting of the Nth layer of the component to be processed;

[0013] S4. Clean the powder in the unprocessed area and the powder in the extended area L2 after pre-sintering to obtain a processed component.

[0014] Furthermore, the integrated laser selective melting device comprises: a fiber laser, a beam expander, a beam switcher, a laser galvanometer and a flat-field focusing lens;

[0015] The fiber laser is used to generate a laser beam and transmit it to a beam expander through an optical fiber;

[0016] The beam expander is used to receive the laser beam and adjust the spot size of the laser beam, and transmit the laser beam with the adjusted spot size to the laser galvanometer through the beam switcher;

[0017] The beam switch is used to adjust the profile of the incident laser beam;

[0018] The laser galvanometer is used to control the deflection of the laser beam in the XY plane, so that the laser beam is projected onto the printing plane through the flat-field focusing lens.

[0019] Further, the beam switcher includes a beam shaper and a turntable, the turntable is provided with a through hole, the axis passing through the center of the through hole is parallel to the axis passing through the center of the turntable; the beam shaper is fixedly arranged on the turntable; the beam shaper and the through hole are respectively located on both sides of the axis passing through the center of the turntable, and the distances from the beam shaper and the through hole to the center of the turntable are equal;

[0020] The beam shaper is used to adjust the profile of the incident laser beam, and the through hole is used to pass the laser beam when the profile of the incident laser beam is not adjusted.

[0021] Further, the beam switcher also includes a motor, a motor controller and a photoelectric encoder;

[0022] The power output end of the motor is transmission-connected to one end of the driving rod, the other end of the driving rod is fixedly connected to a photoelectric encoder and the driving rod passes through the center of the turntable;

[0023] The motor controller is used to control the motor, the motor is used to drive the driving rod to rotate, and the photoelectric encoder is used to receive the photoelectric signal and transmit it to the motor controller.

[0024] Further, it also includes industrial computers;

[0025] The industrial computer is used to receive the signal output by the motor controller, and send control signals to the controllers of the fiber laser, the motor controller and the laser galvanometer.

[0026] Further, the surface process area L1 and the core area L3 of the i-th layer are determined by the following steps:

[0027] S21. Determine whether iA is less than or equal to 0. If yes, proceed to step S22; if no, proceed to step S23;

[0028] Among them, A represents the number of downward comparison layers set, A <N;

[0029] S22. The entire processing area of ​​the i-th layer is compared with the entire processing area of ​​the B-th layer, wherein the area of ​​the i-th layer overlapping with the B-th layer is determined as the core area L3, and the area of ​​the i-th layer other than the core area L3 is determined as the surface processing area L1;

[0030] The B layer is determined by the following method:

[0031] Determine whether the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the first layer when B=1. If so, then B=1; if not, then increase layer by layer until the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the m-th layer, then B=m, where m <i;

[0032] S23. Compare the overall processing area of ​​the i-th layer with the overall processing area of ​​the D-th layer, determine the area in the i-th layer that overlaps with the D-th layer as the core area L3, and determine the area in the i-th layer other than the core area L3 as the surface processing area L1;

[0033] The Dth layer is determined by the following method:

[0034] Determine whether the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the first layer when D=iA. If so, D=iA; if not, increase the area layer by layer until the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the n-th layer, then D=n; where n <i。

[0035] Further, the extension area L2 of the i-th layer is determined by the following method:

[0036] The extension area L2 is arranged along the edge of the surface process area L1 of the i-th layer that is not connected to the core area.

[0037] Further, when the component to be processed is formed and the expansion zone L2 of the i-th layer is in a closed structure, the length of the expansion zone L2 of the i-th layer is set to 0; when the component to be processed is formed and the expansion zone L2 of the i-th layer is not in a closed structure, the length of the expansion zone L2 of the i-th layer is set to M times the spot diameter.

[0038] Beneficial effects of the present invention: By pre-sintering the extended area, the present invention can stabilize the powder outside the overhang area and obtain a more stable melt path, thereby reducing defects such as slag and pores on the overhang surface, and can also adjust the heat dissipation performance outside the overhang area, and inhibit warping deformation to a certain extent. The present invention pre-sinters the surface process area through a flat-top laser, which can inhibit metal evaporation and splashing that may occur during the pre-sintering process; the present invention also melts and forms the surface process area and the core area after pre-sintering through a Gaussian laser, which can produce more delicate features and form a dense entity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0040] Figure 1 It is a flow chart of the present invention.

[0041] Figure 2 It is a schematic diagram of the integrated laser selective melting device of the present invention.

[0042] Figure 3 Schematic diagram of flat-top laser pre-sintering.

[0043] Figure 4 Schematic diagram of Gaussian laser selective melting. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the accompanying drawings:

[0045] The present invention provides a laser selective melting forming method for support-free printing, comprising the following steps:

[0046] S1. Laying a powder bed, using a high-energy laser beam in an integrated laser selective melting device to perform laser melting and forming on the first layer of the component to be processed;

[0047] S2. Lay a powder bed and determine whether there is an overhanging area on the i-th layer of the component to be processed. If so, use a preset processing method to perform melting and forming; if not, use a high-energy laser beam in an integrated laser selective melting device to perform laser melting and forming on the i-th layer of the component to be processed;

[0048] The preset processing method includes: determining the core area L3 and the surface process area L1 of the i-th layer, and setting the expansion area L2;

[0049] The surface process area L1 and the extended area L2 of the i-th layer are pre-sintered by using a flat-top laser in an integrated laser selective melting device;

[0050] The Gaussian laser in the integrated laser selective melting device is used to melt and form the surface process area L1 and the core area L3 after pre-sintering;

[0051] Wherein, 2≤i≤N, N represents the total number of processing layers of the component to be processed;

[0052] S3. Repeat step S2 until the integrated laser selective melting device completes the laser melting of the Nth layer of the component to be processed;

[0053] S4. Clean the powder in the unprocessed area and the powder in the extended area L2 after pre-sintering to obtain a processed component.

[0054] The method described in the present application is preferably used for low-angle components to be processed. Through the above method, surface slag and warping deformation in the overhanging area can be effectively suppressed, the printing quality of the overhanging area can be improved, and the problem that the prior art requires a large amount of auxiliary support when manufacturing low-angle components can be solved.

[0055] Selective laser melting (SLM) technology is an additive manufacturing technology that uses a high-energy laser beam to melt metal powder layer by layer. The designed three-dimensional model is sliced ​​into two-dimensional sections of a certain thickness, and the metal powder is melted layer by layer according to these sections to build parts. In the SLM process, each layer of powder is evenly laid on the building platform, and then the laser beam accurately scans and melts the powder particles of this layer according to the CAD data. Because there is a certain contact area between the powder particles, they can bond together at high temperature to form an integral structure.

[0056] In this embodiment, the integrated laser selective melting device includes: a fiber laser, a beam expander, a beam switcher, a laser galvanometer and a flat field focusing lens (f-theta field mirror), such as Figure 2 As shown;

[0057] The fiber laser is used to generate a laser beam and transmit it to a beam expander through an optical fiber;

[0058] The beam expander is used to receive the laser beam and adjust the spot size of the laser beam, and transmit the laser beam with the adjusted spot size to the laser galvanometer through the beam switcher;

[0059] The beam switch is used to adjust the profile of the incident laser beam; in the present application, it is mainly used to adjust the Gaussian laser to a flat-top laser;

[0060] The laser galvanometer is used to control the deflection of the laser beam in the XY plane (this is a prior art and will not be described here in detail), so that the laser beam is projected onto the printing plane through the flat-field focusing lens. Through the above device, it is convenient and quick to realize arbitrary switching between Gaussian laser and flat-top laser through the beam switcher.

[0061] In this embodiment, the beam switcher includes a beam shaper and a turntable, the turntable is provided with a through hole, the axis passing through the center of the through hole is parallel to the axis passing through the center of the turntable; the beam shaper is fixedly arranged on the turntable; the beam shaper and the through hole are respectively located on both sides of the axis passing through the center of the turntable, and the distances from the beam shaper (center of the circle) and the through hole (center of the circle) to the center of the turntable are equal; it is ensured that the laser beam can smoothly pass through the beam shaper or the through hole;

[0062] The beam shaper is used to adjust the profile of the incident laser beam. The beam shaper can use an aspherical mirror, a diffractive optical element, or other element that can adjust the Gaussian laser to a flat-top laser. The through hole is used to pass the laser beam when the profile of the incident laser beam is not adjusted. When the incident laser beam does not need to be adjusted, the above device rotates the turntable to adjust the position of the through hole and the beam shaper; the laser beam is transmitted to the laser galvanometer through the through hole; when the incident laser beam needs to be adjusted, the turntable is rotated to transmit the laser beam to the laser galvanometer through the beam shaper. At this time, the Gaussian laser has been adjusted to a flat-top laser through the beam shaper; under the same laser power input conditions, the energy density of the flat-top laser is lower than that of the Gaussian laser, which reduces the possibility of evaporation and is conducive to controlling the powder bed to form a bonding state; the above device can achieve the change of the energy density of the laser beam under the same laser power input conditions.

[0063] In this embodiment, the beam switcher further includes a motor, a motor controller and a photoelectric encoder;

[0064] The power output end of the motor is transmission-connected with one end of the driving rod. The connection method between the driving rod and the motor is the existing technology, for example, the driving rod is transmission-connected with the rotating gear in the motor, and the connection method is not limited here; the other end of the driving rod is fixedly connected with a photoelectric encoder and the driving rod passes through the center of the turntable; the positions of the motor and the photoelectric encoder on the driving rod should keep the driving rod balanced;

[0065] The motor controller is used to control the motor, the motor is used to drive the driving rod to rotate, the driving rod drives the turntable to rotate, and the photoelectric encoder is used to receive the photoelectric signal and transmit it to the motor controller.

[0066] In this embodiment, an industrial computer is also included;

[0067] The industrial computer is used to receive the signal output by the motor controller, and send control signals to the controllers of the fiber laser, the motor controller and the laser galvanometer;

[0068] The industrial computer determines the position of the turntable according to the photoelectric signal transmitted by the motor controller, that is, determines whether the through hole and the beam shaper have reached the specified position. The industrial computer controls the motor driver according to the request of the laser type. The motor driver further drives the motor to work. The motor drives the turntable to rotate through the driving rod, thereby changing the position of the through hole and the beam shaper. When the Gaussian laser passes through the beam shaper, the beam shaper adjusts the Gaussian laser to a flat-top laser, thereby realizing the switching between the Gaussian laser and the flat-top laser. Through the above device, the switching between the Gaussian laser and the flat-top laser can be realized simply and quickly, and the energy density of the laser can be changed without changing the input power.

[0069] In this embodiment, in step S1, a powder bed is laid and a high-energy laser beam in an integrated laser selective melting device is used to perform laser melting on the first layer of the component to be processed; the high-energy laser beam in this application refers to a Gaussian laser beam or a flat-top laser beam; the first layer of the component to be processed is laser melted using conventional operations, that is, a Gaussian laser beam, a flat-top laser beam, or a combination of the two is arbitrarily selected to perform laser melting on the first layer, because the bonding force between the powder particles of the first layer provides sufficient stability; no additional measures are required for processing.

[0070] In this embodiment, in step S2, a powder bed is laid, and it is determined whether the i-th layer of the component to be processed has an overhanging area. If so, a preset processing method is used to perform processing and melting forming; if not, a high-energy laser beam in an integrated laser selective melting device is used to perform laser melting forming on the i-th layer of the component to be processed;

[0071] The overhang area is the area without support compared to the previous layer, e.g. Figure 3 As shown, L0 is the overhanging area; the overhanging area is prone to serious surface slag and warping deformation. The existing method is to add auxiliary support to the overhanging area, but adding auxiliary support not only consumes materials but is also difficult to remove.

[0072] The preset processing method includes: determining the core area L3 and the surface process area L1 of the i-th layer, and setting the expansion area L2; Figure 3 As shown (the surface process area L1 in this application refers to Figure 3 The lower surface process area L1);

[0073] The surface process area L1 and the extended area L2 of the i-th layer are pre-sintered by using a flat-top laser in an integrated laser selective melting device;

[0074] The Gaussian laser in the integrated selective laser melting device is used to melt and form the surface process area L1 and the core area L3 after pre-sintering;

[0075] Where 2 ≤ i ≤ N, and N represents the total number of processing layers of the component to be processed;

[0076] The surface process area L1 and the core area L3 of the i-th layer are determined through the following steps:

[0077] S21. Determine whether i - A is less than or equal to 0. If so, proceed to step S22; if not, proceed to step S23;

[0078] Where A represents the set number of layers for downward comparison, and A < N;

[0079] S22. When i - A is less than or equal to 0, compare the overall processing area of the i-th layer with the overall processing area of the B-th layer. The area of the i-th layer that coincides with the B-th layer is determined as the core area L3, and the area of the i-th layer other than the core area L3 is determined as the surface process area L1;

[0080] The B-th layer is determined through the following method:

[0081] Determine whether the overall processing area of the i-th layer is greater than the overall processing area of the first layer when B = 1. If so, B = 1; if not, increment layer by layer until the overall processing area of the i-th layer is greater than the overall processing area of the m-th layer, then B = m, where m < i; that is, when the overall processing area of the i-th layer is less than or equal to the overall processing area of the first layer, compare the i-th layer with the overall processing area of the second layer until the overall processing area of the determined comparison layer is less than that of the i-th layer; where the overall processing area refers to a two-dimensional cross-section with a certain thickness formed by slicing the three-dimensional model.

[0082] A is set according to requirements. Preferably, A is set to 3. When A = 3, as Figure 3 shown, the second layer to the third layer belong to the case where i - A is less than or equal to 0, that is, both the second layer and the third layer are compared with the first layer to determine the core area and the surface process area;

[0083] S23. Compare the overall processing area of the i-th layer with the overall processing area of the D-th layer. The area of the i-th layer that coincides with the D-th layer is determined as the core area L3, and the area of the i-th layer other than the core area L3 is determined as the surface process area L1;

[0084] The D-th layer is determined through the following method:

[0085] Determine whether the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the first layer when D=iA. If so, D=iA; if not, increase the area layer by layer until the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the n-th layer, then D=n; where n <i;

[0086] When A is equal to 3, the Nth layer is compared with the N-3th layer, such as Figure 3 As shown, the overlapping part is the core area, and the part other than the core area is the surface process area, and the surface process area includes the overhang area, and the overhang area is located on the side of the surface process area that is not in contact with the core area. Through the above method, it is possible to ensure that the unsupported overhang area is determined, so that the overhang area (surface process area) is pre-sintered.

[0087] In this embodiment, the extended area L2 of the i-th layer is determined by the following method:

[0088] The extension area L2 is arranged along the edge of the surface process area L1 of the i-th layer that is not connected to the core area.

[0089] Since each layer of the component to be processed is obtained by slicing the three-dimensional model, whether the expansion area of ​​the current layer will be in the closed structure can also be determined in advance; when the component to be processed is formed, when the expansion area L2 of the i-th layer is in the closed structure, the length of the expansion area L2 of the i-th layer is set to 0; because if the expansion area is set in the closed structure, the metal powder inside cannot be cleaned after the component is formed, so the length of the expansion area in the closed structure is set to 0; when the component to be processed is formed, when the expansion area L2 of the i-th layer is not in the closed structure, the length of the expansion area L2 of the i-th layer is set to M times the spot diameter, M is set according to demand, and M is preferably 2 or 3; when the expansion area is set too long or too short, its adhesion cannot be guaranteed, and the powder at the edge of the overhanging area cannot be stabilized;

[0090] This application first uses a flat-top laser to pre-sinter the surface process area and the expansion area, such as Figure 3As shown in the figure, the gray part is the area for pre-sintering. Because the flat-top laser has a more uniform energy distribution than the Gaussian laser, it can suppress the metal evaporation and splashing that may occur during the pre-sintering process, and the splashing phenomenon will cause the erosion and instability of the powder bed. In addition, the flat-top spot diameter after beam shaping is usually larger than the initial Gaussian spot diameter, which means that under the same laser power input conditions, the energy density of the flat-top laser is lower than that of the Gaussian laser, which reduces the possibility of evaporation and is beneficial to control the powder bed to form a bonding state. Pre-sintering the area outside the overhang area can stabilize the powder at the edge of the overhang area and obtain a more stable melt path, thereby reducing defects such as slag and pores on the overhang surface. At the same time, pre-sintering the extension area also adjusts the heat dissipation performance of the outer side of the overhang area, suppressing warping deformation to a certain extent. Subsequently, the Gaussian laser is used to completely melt the pre-sintered area and the core area to form a dense entity, such as Figure 4 As shown; the black part is the Gaussian laser melting part; since the aforementioned pre-sintering process has solidified the powder bed to a certain extent, using Gaussian laser to completely melt the powder in the overhanging area will not cause serious spattering. At the same time, the spot diameter of Gaussian laser is usually smaller, which is more conducive to manufacturing more delicate features.

[0091] In this embodiment, in step S3, step S2 is repeated until the integrated selective laser melting device completes the laser melting forming of the Nth layer of the component to be processed; that is, the laser melting forming is performed on the component to be processed layer by layer.

[0092] In this embodiment, in step S4, the powder in the unprocessed area and the powder in the extended area L2 after pre-sintering are cleaned to obtain a processed component.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A laser selective melting forming method for support-free printing, characterized in that: The following steps are involved: S1. Laying a powder bed, using a high-energy laser beam in an integrated laser selective melting device to perform laser melting and forming on the first layer of the component to be processed; S2. Laying a powder bed and determining whether there is an overhanging area in the i-th layer of the component to be processed. If so, a preset processing method is used for processing and melting; If not, the i-th layer of the component to be processed is laser melted and formed by using a high-energy laser beam in an integrated laser selective melting device; The preset processing method includes: determining the core area L3 and the surface process area L1 of the i-th layer, and setting the expansion area L2; The flat-top laser in the integrated laser selective melting device is used to pre-sinter the surface process area L1 and the extension area L2 of the i-th layer; The Gaussian laser in the integrated laser selective melting device is used to melt and form the surface process area L1 and the core area L3 after pre-sintering; Wherein, 2≤i≤N, N represents the total number of processing layers of the component to be processed; S3. Repeat step S2 until the integrated laser selective melting device completes the laser melting of the Nth layer of the component to be processed; S4. Clean the powder in the unprocessed area and the powder in the extended area L2 after pre-sintering to obtain a processed component.

2. The laser selective melting forming method for support-free printing according to claim 1, characterized in that: The integrated laser selective melting device comprises: a fiber laser, a beam expander, a beam switcher, a laser galvanometer and a flat-field focusing lens; The fiber laser is used to generate a laser beam and transmit it to a beam expander through an optical fiber; The beam expander is used to receive the laser beam and adjust the spot size of the laser beam, and transmit the laser beam with the adjusted spot size to the laser galvanometer through the beam switcher; The beam switch is used to adjust the profile of the incident laser beam; The laser galvanometer is used to control the deflection of the laser beam in the XY plane, so that the laser beam is projected onto the printing plane through the flat-field focusing lens.

3. The laser selective melting forming method for support-free printing according to claim 2, characterized in that: The beam switcher comprises a beam shaper and a turntable, wherein a through hole is provided on the turntable, and the axis passing through the center of the through hole is parallel to the axis passing through the center of the turntable; the beam shaper is fixedly arranged on the turntable; the beam shaper and the through hole are respectively located on both sides of the axis passing through the center of the turntable, and the distances from the beam shaper and the through hole to the center of the turntable are equal; The beam shaper is used to adjust the profile of the incident laser beam, and the through hole is used to pass the laser beam when the profile of the incident laser beam is not adjusted.

4. The laser selective melting forming method for support-free printing according to claim 3, characterized in that: The beam switcher also includes a motor, a motor controller and a photoelectric encoder; The power output end of the motor is transmission-connected to one end of the driving rod, the other end of the driving rod is fixedly connected to a photoelectric encoder and the driving rod passes through the center of the turntable; The motor controller is used to control the motor, the motor is used to drive the driving rod to rotate, and the photoelectric encoder is used to receive the photoelectric signal and transmit it to the motor controller.

5. The laser selective melting forming method for support-free printing according to claim 4, characterized in that: It also includes industrial computers; The industrial computer is used to receive the signal output by the motor controller, and send control signals to the controllers of the fiber laser, the motor controller and the laser galvanometer.

6. The laser selective melting forming method for support-free printing according to any one of claim 1 or claim 5, characterized in that: The surface process area L1 and the core area L3 of the i-th layer are determined by the following steps: S21. Determine whether iA is less than or equal to 0. If yes, proceed to step S22; if no, proceed to step S23; Among them, A represents the number of downward comparison layers set, A <N; S22. The entire processing area of ​​the i-th layer is compared with the entire processing area of ​​the B-th layer, wherein the area of ​​the i-th layer overlapping with the B-th layer is determined as the core area L3, and the area of ​​the i-th layer other than the core area L3 is determined as the surface processing area L1; The B layer is determined by the following method: Determine whether the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the first layer when B=1. If so, then B=1; if not, then increase layer by layer until the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the m-th layer, then B=m, where m <i; S23. Compare the overall processing area of ​​the i-th layer with the overall processing area of ​​the D-th layer, determine the area in the i-th layer that overlaps with the D-th layer as the core area L3, and determine the area in the i-th layer other than the core area L3 as the surface processing area L1; The Dth layer is determined by the following method: Determine whether the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the first layer when D=iA. If so, D=iA; if not, increase the area layer by layer until the overall processing area of ​​the i-th layer is greater than the overall processing area of ​​the n-th layer, then D=n; where n <i。 7. The laser selective melting forming method for support-free printing according to claim 6, characterized in that: The extended area L2 of the i-th layer is determined by the following method: The extension area L2 is arranged along the edge of the surface process area L1 of the i-th layer that is not connected to the core area.

8. The laser selective melting forming method for support-free printing according to claim 7, characterized in that: When the component to be processed is formed and the expansion zone L2 of the i-th layer is in a closed structure, the length of the expansion zone L2 of the i-th layer is set to 0; when the component to be processed is formed and the expansion zone L2 of the i-th layer is not in a closed structure, the length of the expansion zone L2 of the i-th layer is set to M times the spot diameter.

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