A method for unsupported additive manufacturing of extreme horizontal cantilever structures

Abstract

This invention discloses a supportless additive manufacturing method for extreme horizontal overhanging structures. The horizontal overhanging region is divided into three areas using different laser control strategies: an initial overhanging region, a low-heat-input region, and a high-heat-input region. The initial overhanging region is used to establish a stable initial overhanging structure; the low-heat-input region is used to suppress thermal stress accumulation and warping; and the high-heat-input region is used to improve the strength of the overhanging structure and repair internal defects. This invention achieves warping-free, complete printing of horizontal overhanging structures, significantly improving manufacturing efficiency and the design freedom for complex structures. Furthermore, corresponding energy control strategies for the low-heat-input and high-heat-input regions are provided for the initial overhanging region using different laser energy densities, broadening the process window for supportless printing of overhanging structures.

Description

Technical Field

[0001] This invention belongs to the field of laser additive manufacturing technology, specifically relating to a method for unsupported additive manufacturing of extreme horizontally suspended structures. Background Technology

[0002] Laser powder bed fusion (LPBF), as an advanced metal additive manufacturing technology, can directly form complex structural parts based on 3D model data. This technology is suitable for manufacturing components with thin walls, complex internal flow channels, or lightweight topologies, breaking through the design and forming constraints of traditional subtractive or equal-material manufacturing. However, when forming overhanging structures with small inclination angles or extreme horizontal dimensions, molten metal sag and localized overheating can cause dimensional deviations, surface warping, and even manufacturing failures.

[0003] Currently, the traditional solution to this problem is to design and add a support structure below the overhanging area. However, the support structure not only increases manufacturing costs and post-processing workload, but also restricts the freedom of part geometry design. To reduce reliance on support structures, supportless printing technology has been developed. Existing supportless printing technologies mainly improve the forming quality of overhanging structures by optimizing process parameters and adjusting the scanning path. However, the improvement effect is very limited for overhanging structures with small inclination angles or extreme horizontal overhangs. The core difficulty lies in the stress-deformation competition between accumulated thermal stress and the progressively increasing structural strength in the overhanging area, making it difficult to achieve stable forming with a single process parameter control strategy. Therefore, developing an additive manufacturing method that can achieve highly reliable supportless forming of extreme horizontal overhanging structures is of great significance for releasing design potential and improving manufacturing efficiency. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention employs a supportless additive manufacturing method for extreme horizontal overhanging structures based on process partitioning. By dividing the structure into multiple regions with customized laser power and controlling the heat input, residual stress accumulation is alleviated, thus achieving warp-free printing of horizontal overhanging structures.

[0005] The technical solution adopted in this invention is:

[0006] A method for unsupported additive manufacturing of a horizontally suspended structure includes the following steps:

[0007] Step 1: Based on the forming orientation of the three-dimensional model of the part to be formed on the powder bed of the laser additive manufacturing forming equipment, determine the horizontal overhang area and the solid support area of ​​the part. The horizontal overhang area is the three-dimensional solid formed by depositing multiple layers in a layer-by-layer manner starting from the first deposition layer of the part without solid support corresponding to the overhang structure. The solid support area is all structural parts of the part except for the horizontal overhang area.

[0008] The physical support area is divided into a lower physical support area below the horizontal overhang area and an upper physical support area above the horizontal overhang area.

[0009] The horizontally suspended area is divided from bottom to top along the vertical height direction of the powder bed into an initial suspension area, a low heat input area, and a high heat input area. The initial suspension area is located above the lower solid support area, and the high heat input area is located below the upper solid support area.

[0010] Step 2: Based on the spatial orientation of the part to be formed, lay powder layer by layer from bottom to top. Use laser additive manufacturing equipment to scan the metal powder at the layup positions corresponding to the solid support area and the horizontal overhang area until the forming of all solid support areas and horizontal overhang areas of the additive manufacturing part to be formed is completed.

[0011] Step 3: After the solid support area and horizontal overhang area of ​​the additive manufacturing part to be formed are processed, the powder is cleaned off the removed part, and then the part is obtained by wire cutting.

[0012] Furthermore, the suspension structure satisfies the geometric conditions that the suspension angle is 0° and the overhang length is not less than 5mm.

[0013] Furthermore, the solid support area described in step 2 is printed using an optimized combination of process parameters, and a constant single-layer thickness is maintained during the deposition process. The optimized combination of process parameters refers to laser power and scanning speed parameters that can prevent incomplete fusion defects and warping deformation in the printing of solid structures without overhang features, such as a laser power of 200W and a scanning speed of 1000mm / s.

[0014] Further, the processing method for the lower solid support area in step 2 is as follows: powder is laid layer by layer on a powder bed, and the metal powder at each layer processing position is scanned layer by layer by a laser with the optimized process parameter combination to complete the processing of the lower solid support area; the processing method for the upper solid support area is as follows: powder is laid layer by layer on a horizontal overhanging area, and the metal powder at each layer processing position is scanned layer by layer by a laser with the optimized process parameter combination to complete the processing of the solid support area above the horizontal overhanging area.

[0015] Furthermore, the processing method for the horizontally overhanging area described in step two includes the following steps:

[0016] Step 1: Based on the positional relationship between the lower solid support area and the initial overhang area, after the lower solid support area is printed, the powder bed is lowered by one layer thickness and metal powder is laid. The metal powder at the current layup position is scanned with a laser to melt and solidify it to form the deposition layer corresponding to the initial overhang area. This step is repeated until the printing of the initial overhang area is completed.

[0017] Step 2: Powder is laid layer by layer above the initial deposition layer in the overhanging region. The metal powder at the current layup position is scanned by a laser with a low energy control strategy, causing it to melt and solidify to form a single-layer cross-section of the low heat input region until the printing of the low heat input region is completed.

[0018] Step 3: Layer by layer, powder is laid on top of the deposition layer in the low heat input region. The metal powder at the current layup location is scanned by a laser with a high energy control strategy, causing it to melt and solidify to form a single-layer cross-section of the high heat input region, until the printing of the high heat input region is completed.

[0019] Furthermore, the laser energy density used in the initial hanging region in step 1 is 75% to 300% of the laser energy density of the optimized process parameter combination.

[0020] Furthermore, the number of deposition layers in the initial overhang region is 1 to 3 layers. When the laser energy density in the initial overhang region is lower than 150% of the laser energy density of the optimized process parameter combination, the number of deposition layers in the overhang region is 1 layer.

[0021] Furthermore, the laser energy density of the low-energy control strategy is lower than the laser energy density of the optimized process parameter combination, and the deposition layer in the low-heat input region forms an unfused region under the laser energy density of the low-energy control strategy. When the laser energy density of the initial overhang region is lower than 150% of the laser energy density of the optimized process parameter combination, the low-heat input region adopts a low-energy progressive power strategy. The low-energy progressive power strategy must simultaneously satisfy the following: the laser power used by the low-energy progressive power strategy is not higher than the forming power of the optimized process parameter combination, its scanning speed is the same as the set value of the optimized process parameter combination, and its laser power gradually increases from the initial deposition layer in the low-heat input region with the increase of the number of deposition layers, and the change value of laser power between adjacent deposition layers in the low-heat input region does not exceed 40% of the difference in laser power between the last layer and the initial deposition layer in the low-heat input region.

[0022] Furthermore, the laser energy density of the high-energy control strategy is not less than the laser energy density of the optimized process parameter combination, and the laser energy density of the high-energy control strategy does not exceed 200% of the laser energy density of the optimized process parameter combination. When the laser energy density of the initial overhang region is lower than 150% of the energy density of the optimized process parameter combination, the high-heat input region adopts the high-energy progressive power strategy. The high-energy progressive power strategy must simultaneously satisfy the following: the laser power used by the high-energy progressive power strategy is not lower than the forming power of the optimized process parameter combination, its scanning speed is the same as the set value of the optimized process parameter combination, and its laser power gradually increases from the initial deposition layer of the high-heat input region with the increase of the number of deposition layers. The change value of laser power between adjacent layers in the high-heat input region does not exceed 30% of the difference in laser power between the last layer and the initial deposition layer in the high-heat input region. The difference between the laser energy density of the initial layer in the high-heat input region and the laser energy density of the last layer in the low-heat input region does not exceed 50% of the laser energy density in the optimized process parameter combination.

[0023] Furthermore, the laser energy density of the optimized process parameter combination, the laser energy density used in the initial overhang region, the laser energy density of the low-energy control strategy, and the laser energy density of the high-energy control strategy are all calculated according to E=P / (v·h·d), where E is the corresponding laser energy density, P is the laser power, v is the scanning speed, h is the scanning spacing, and d is the layer thickness.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This invention divides the horizontally suspended area into three customized laser energy density regions: an initial suspension region, a low heat input region, and a high heat input region. In the low heat input region, the power is lower than the optimized parameters to suppress the accumulation of thermal stress, while in the high heat input region, the high power is increased layer by layer to enhance the structural strength. This balances the competition between thermal stress and structural strength, and achieves warp-free and complete printing of horizontally suspended structures.

[0026] 2. This invention provides energy control schemes for low-heat-input and high-heat-input regions corresponding to different initial hanging regions with varying energy densities. These schemes adaptively adjust the power progression amplitude and range of subsequent regions based on the fusion state of the initial layer, thereby effectively expanding the adaptability of the supportless printing process to different hanging conditions.

[0027] 3. This invention precisely controls the laser energy density, suppressing thermal stress accumulation in low heat input areas while progressively increasing density layer by layer. In high heat input areas, it utilizes remelting to repair interlayer non-fusion defects. This synergistic effect of partitioning enables the horizontal overhanging area to achieve structural self-support during the printing process, eliminating the need for the support structures required by traditional methods. This avoids support design, printing, and removal processes, significantly improving manufacturing efficiency and the design freedom of complex structures.

[0028] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the part to be formed in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the process partitioning of the part to be formed in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of laser melting forming in a horizontally suspended region in an embodiment of the present invention;

[0032] Figure 4 This is an industrial camera image of the printing process of the overhanging area of ​​the part to be formed in an embodiment of the present invention;

[0033] Figure 5 This is a comparison image of the printing results of the parts to be formed in an embodiment of the present invention.

[0034] The attached diagrams are labeled as follows: 1. Solid support area; 2. Horizontal overhang area; 201. Initial overhang area; 202. Low heat input area; 203. High heat input area; 3. Scraper; 4. Powder bed. Detailed Implementation

[0035] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0036] A method for unsupported additive manufacturing of a horizontally suspended structure, comprising:

[0037] See Figures 1-5 This embodiment uses the laser selective melting process of an octagonal horizontally suspended structural part as an example to describe in detail the process of an unsupported additive manufacturing method for an extreme horizontally suspended structure according to the present invention. The material of the octagonal horizontally suspended structural part is AlCoCrFeNi. 2.1 High-entropy alloy with a horizontal overhang of 20 mm; this example uses a powder bed additive manufacturing system with a 1064 nm wavelength fiber laser as the laser source.

[0038] The corresponding forming method flow is as follows:

[0039] Step 1: Based on the forming orientation of the 3D model of the part to be formed on the powder bed 4 of the laser additive manufacturing forming equipment, determine the horizontal overhang region 2 and the solid support region 1 of the part. The horizontal overhang region 2 is a 3D solid formed by depositing 10 to 20 layers in a layer-by-layer manner, starting from the first deposition layer with a corresponding unsupported part of the overhang structure. The overhang structure satisfies the geometric conditions of an overhang angle of 0° and an overhang length of not less than 5mm. The solid support region 1 is all the structural parts of the part except for the horizontal overhang region 2. According to the positional relationship between the solid support region 1 and the horizontal overhang region 2, the solid support region 1 is divided into a lower solid support region 101 below the horizontal overhang region 2 and an upper solid support region 102 above the horizontal overhang region 2.

[0040] The model of the part to be formed in this embodiment is as follows: Figure 1 As shown, the solid region within the dashed line, representing 12 layers of deposition, is defined as horizontal overhang region 2, with its overhang bottom surface forming a 0° angle with the horizontal plane. The other solid structural regions of the part model to be processed, excluding horizontal overhang region 2, are defined as solid support region 1.

[0041] The horizontally suspended region 2 is divided from bottom to top along the vertical height direction of the powder bed into an initial suspended region 201, a low heat input region 202, and a high heat input region 203.

[0042] The region division method in this embodiment is as follows: Figure 2 As shown, the horizontally suspended region 2 is divided vertically into an initial suspended region 201, a low heat input region 202, and a high heat input region 203.

[0043] The overhanging initial region 201 is used to form a structural substrate that supports the subsequent material deposition behavior.

[0044] The low heat input region 202 is used to reduce the overall heat input to suppress the accumulation of residual stress and prevent the overhanging structure from warping.

[0045] The high heat input region 203 is used to enhance energy input to improve the deformation resistance of the overhanging structure, while simultaneously remelting the deposited areas to repair incomplete fusion defects.

[0046] Step 2: Based on the spatial orientation of the part to be formed, powder is laid layer by layer from bottom to top. Using laser additive manufacturing equipment, the metal powder at the corresponding layup positions in the solid support area 1 and the horizontal overhang area 2 is scanned until the forming of all solid support areas 1 and horizontal overhang areas 2 of the additively manufactured part is completed. In this embodiment, the processing flow for the three divided areas of solid support area 1 and horizontal overhang area 2 is as follows:

[0047] Step 2.1: Spread powder layer by layer on the powder bed 4 with a scraper 3, and use laser scanning with optimized process parameter combination to scan the metal powder at each layer processing position to complete the processing of the lower solid support area 101 below the horizontal overhang area 2.

[0048] In this embodiment, the optimized process parameter combination is set as follows: laser power of 200W, scanning speed of 1000mm / s, single forming layer thickness of 30μm, interlayer rotation angle of 90°, scanning spacing of 0.07mm, and scanning path of bidirectional serpentine scanning.

[0049] The solid support area and the horizontal overhang area are printed with the same single forming layer thickness, and the thickness of the single forming layer is 30-60μm.

[0050] Step 2.2: Based on the positional relationship between the lower solid support area 101 and the initial hanging area 201, after the lower solid support area 101 is printed, the powder bed 4 descends by one layer thickness and lays metal powder. The metal powder at the current layup processing position is scanned with a laser to melt and solidify it to form the deposition layer corresponding to the initial hanging area 201. This step is repeated until the printing of the initial hanging area 201 is completed.

[0051] The number of deposition layers in the initial overhang region is 1 to 3. When the laser energy density in the initial overhang region is less than 150% of the laser energy density of the optimized process parameter combination, the number of deposition layers in the overhang region is 1.

[0052] In this embodiment, the process parameters of the initial overhang region 201 are set as follows: laser power of 300W, scanning speed of 1000mm / s, and laser energy density of 300% of the energy density of the optimized process parameter combination. The number of deposition layers in the initial overhang region 201 is 3.

[0053] In this example, the surface morphology features of the initial overhang region 201 correspond to Figure 4 Layers #1 to #3 were used. The results showed that the overhang surface cracked under thermal stress. At the same time, the extremely high laser energy density effectively improved the strength of the overhang structure, so that the warping deformation of the third layer was controlled within a limited range and did not affect the subsequent powder spreading process.

[0054] Step 2.3: Layer by layer powder is laid above the deposition layer in the initial overhang region 201. The metal powder at the current layup position is scanned by a laser with a low energy control strategy, so that it melts and solidifies to form a single-layer cross-section of the low heat input region 202, until the printing of the low heat input region 202 is completed.

[0055] Preferably, the laser energy density of the low-energy control strategy is lower than the laser energy density of the optimized process parameter combination, and the deposited layer in the low-heat input region forms an unfused region under the laser energy density of the low-energy control strategy. When the laser energy density of the initial overhang region is lower than 150% of the laser energy density of the optimized process parameter combination, the low-heat input region adopts a low-energy progressive power strategy. The low-energy progressive power strategy must simultaneously satisfy the following: the laser power used by the low-energy progressive power strategy is not higher than the forming power of the optimized process parameter combination, its scanning speed is the same as the set value of the optimized process parameter combination, and its laser power gradually increases from the initial deposited layer in the low-heat input region with the increase of the number of deposited layers. Furthermore, the change in laser power between adjacent deposited layers in the low-heat input region does not exceed 40% of the difference in laser power between the last layer and the initial deposited layer in the low-heat input region, so as to avoid the melt pool depth exceeding the thickness of the deposited layer and causing interlayer breakdown, thus preventing damage to the overhang surface.

[0056] In this embodiment, the process parameters of the low heat input region 202 are set as follows: laser power of 100W, scanning speed of 1000mm / s, and number of deposition layers of 6.

[0057] In this example, the surface morphology features of the initial overhang region 201 correspond to Figure 4 Layers #1 to #3 were used. The results showed that the overhang surface cracked under thermal stress. At the same time, the extremely high laser energy density effectively improved the strength of the overhang structure, so that the warping deformation of the third layer was controlled within a limited range and did not affect the subsequent powder spreading process.

[0058] Step 2.4: Layer by layer powder is laid on top of the deposition layer in the low heat input region 202. The metal powder at the current layup position is scanned by a laser with a high energy control strategy, so that it melts and solidifies to form a single-layer cross-section of the high heat input region 203, until the printing of the high heat input region 203 is completed.

[0059] Preferably, the laser energy density of the high-energy control strategy is not less than the laser energy density of the optimized process parameter combination, and the laser energy density of the high-energy control strategy does not exceed 200% of the laser energy density of the optimized process parameter combination. When the laser energy density of the initial overhang region is less than 150% of the energy density of the optimized process parameter combination, the high-heat input region adopts the high-energy progressive power strategy. The high-energy progressive power strategy must simultaneously satisfy the following: the laser power used by the high-energy progressive power strategy is not less than the forming power of the optimized process parameter combination. The scanning speed is the same as the set value of the optimized process parameter combination, and its laser power gradually increases from the starting deposition layer in the high heat input region with the increase of the number of deposition layers. The change value of laser power between adjacent layers in the high heat input region does not exceed 30% of the difference in laser power between the last layer and the starting deposition layer in the high heat input region. The difference in laser energy density between the starting layer in the high heat input region and the last layer in the low heat input region does not exceed 50% of the laser energy density in the optimized process parameter combination, so as to avoid the melt pool depth exceeding the thickness of the deposited layer and causing interlayer breakdown, and to prevent damage to the overhang surface or severe spheroidization.

[0060] In this embodiment, the process parameters of the high heat input region 203 are set as follows: laser power 300W, scanning speed 800mm / s, and number of deposition layers 6.

[0061] In this embodiment, the surface morphology features of the initial layer of the high heat input region 203 correspond to Figure 4 Layer #10 in the process. The results show that due to the excessive difference in laser energy density between the starting layer in the high heat input region and the ending layer in the low heat input region, which exceeds 50% of the laser energy density in the optimized process parameter combination, obvious spheroidization occurs on the surface of the overhanging surface.

[0062] Step 2.5: Apply powder layer by layer on the horizontal overhanging area 2 using a scraper 3, and use laser scanning with optimized process parameter combinations to scan the metal powder at each layer processing position to complete the processing of the upper solid support area 102 above the horizontal overhanging area 2.

[0063] In this embodiment, the surface morphology features of the upper solid support region 102 correspond to Figure 4 Layers #13 to #40 were used. The results showed that the spheroidized protrusions on the overhanging surface were gradually covered by subsequent deposited material, and the top surface eventually returned to a smooth state.

[0064] In this embodiment, the scraper 3 is damaged during the printing process due to the influence of other samples, resulting in localized protrusions on the upper surface of the part to be formed, such as... Figure 4 As shown in floors #9 to #40.

[0065] Step 3: After the solid support area 1 and horizontal overhang area 2 of the additive manufacturing part to be formed are processed, the powder of the removed part is cleaned off, and then the part is obtained by wire cutting.

[0066] In this embodiment, the printing result of the part to be formed is as follows: Figure 5 As shown. Using fixed process parameters (such as...) Figure 5 The first figure shows parts processed using fixed process parameters of 200W laser power and 1000mm / s scanning speed; the second figure shows parts processed using fixed process parameters of 300W laser power and 1000mm / s scanning speed, where the overhanging surfaces of the parts failed to form due to severe warping; while the third figure shows parts printed using the supportless additive manufacturing method of this invention, which are formed completely, with no obvious warping or deformation on the overhanging surfaces except for areas affected by damage to the scraper.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for unsupported additive manufacturing of an extreme horizontally suspended structure, characterized in that, Includes the following steps: Step 1: Based on the forming orientation of the three-dimensional model of the part to be formed on the powder bed of the laser additive manufacturing forming equipment, determine the horizontal overhang area and the solid support area of ​​the part. The horizontal overhang area is the three-dimensional solid formed by depositing multiple layers in a layer-by-layer manner starting from the first deposition layer of the part without solid support corresponding to the overhang structure. The solid support area is all structural parts of the part except for the horizontal overhang area. The physical support area is divided into a lower physical support area below the horizontal overhang area and an upper physical support area above the horizontal overhang area. The horizontally suspended area is divided from bottom to top along the vertical height direction of the powder bed into an initial suspension area, a low heat input area, and a high heat input area. The initial suspension area is located above the lower solid support area, and the high heat input area is located below the upper solid support area. Step 2: Based on the spatial orientation of the part to be formed, lay powder layer by layer from bottom to top. Use laser additive manufacturing equipment to scan the metal powder at the layup positions corresponding to the solid support area and the horizontal overhang area until the forming of all solid support areas and horizontal overhang areas of the additive manufacturing part to be formed is completed. Step 3: After the solid support area and horizontal overhang area of ​​the additive manufacturing part to be formed are processed, the powder is cleaned off the removed part, and then the part is obtained by wire cutting.

2. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 1, characterized in that, The suspension structure meets the geometric conditions of a suspension angle of 0° and an overhang length of not less than 5mm.

3. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 1 or 2, characterized in that, In step 2, the solid support area is printed using an optimized combination of process parameters, and a constant single-layer thickness is maintained during the deposition process. The optimized combination of process parameters consists of laser power and scanning speed parameters that can prevent incomplete fusion defects and warping deformation in the printing of solid structures without overhang features.

4. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 3, characterized in that, The processing method for the lower solid support area in step 2 is as follows: powder is laid layer by layer on a powder bed, and the metal powder at each layer processing position is scanned layer by layer by a laser with the optimized process parameter combination to complete the processing of the lower solid support area; the processing method for the upper solid support area is as follows: powder is laid layer by layer on a horizontal overhanging area, and the metal powder at each layer processing position is scanned layer by layer by a laser with the optimized process parameter combination to complete the processing of the solid support area above the horizontal overhanging area.

5. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 3, characterized in that, The processing method for the horizontally overhanging area described in step two includes the following steps: Step 1: Based on the positional relationship between the lower solid support area and the initial overhang area, after the lower solid support area is printed, the powder bed is lowered by one layer thickness and metal powder is laid. The metal powder at the current layup position is scanned with a laser to melt and solidify it to form the deposition layer corresponding to the initial overhang area. This step is repeated until the printing of the initial overhang area is completed. Step 2: Powder is laid layer by layer above the initial deposition layer in the overhanging region. The metal powder at the current layup position is scanned by a laser with a low energy control strategy, causing it to melt and solidify to form a single-layer cross-section of the low heat input region until the printing of the low heat input region is completed. Step 3: Layer by layer, powder is laid on top of the deposition layer in the low heat input region. The metal powder at the current layup location is scanned by a laser with a high energy control strategy, causing it to melt and solidify to form a single-layer cross-section of the high heat input region, until the printing of the high heat input region is completed.

6. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 5, characterized in that, The laser energy density used in the initial hanging region in step 1 is 75% to 300% of the laser energy density of the optimized process parameter combination.

7. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 6, characterized in that, The number of deposition layers in the initial overhang region is 1 to 3. When the laser energy density in the initial overhang region is less than 150% of the laser energy density of the optimized process parameter combination, the number of deposition layers in the overhang region is 1.

8. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 6, characterized in that, The laser energy density of the low-energy control strategy is lower than that of the optimized process parameter combination, and the deposition layer in the low-heat input region forms an unfused region under the laser energy density of the low-energy control strategy. When the laser energy density of the initial overhang region is lower than 150% of the laser energy density of the optimized process parameter combination, the low-heat input region adopts a low-energy progressive power strategy. The low-energy progressive power strategy must simultaneously satisfy the following: the laser power used by the low-energy progressive power strategy is not higher than the forming power of the optimized process parameter combination, its scanning speed is the same as the set value of the optimized process parameter combination, and its laser power gradually increases from the initial deposition layer in the low-heat input region with the increase of the number of deposition layers. Furthermore, the change in laser power between adjacent deposition layers in the low-heat input region does not exceed 40% of the difference in laser power between the last layer and the initial deposition layer in the low-heat input region.

9. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 6, characterized in that, The laser energy density of the high-energy control strategy is not less than the laser energy density of the optimized process parameter combination, and the laser energy density of the high-energy control strategy does not exceed 200% of the laser energy density of the optimized process parameter combination. When the laser energy density of the initial hanging region is less than 150% of the energy density of the optimized process parameter combination, the high-heat input region adopts the high-energy progressive power strategy. The high-energy progressive power strategy must simultaneously satisfy the following: the laser power used by the high-energy progressive power strategy is not less than the forming power of the optimized process parameter combination, its scanning speed is the same as the set value of the optimized process parameter combination, and its laser power gradually increases from the initial deposition layer of the high-heat input region with the increase of the number of deposition layers. The change value of laser power between adjacent layers in the high-heat input region does not exceed 30% of the difference in laser power between the last layer and the initial deposition layer in the high-heat input region. The difference between the laser energy density of the initial layer in the high-heat input region and the laser energy density of the last layer in the low-heat input region does not exceed 50% of the laser energy density in the optimized process parameter combination.

10. The method for unsupported additive manufacturing of a horizontally suspended structure according to claim 6, characterized in that, The laser energy density of the optimized process parameter combination, the laser energy density used in the initial hanging region, the laser energy density of the low-energy control strategy, and the laser energy density of the high-energy control strategy are all calculated according to E=P / (v·h·d), where E is the corresponding laser energy density, P is the laser power, v is the scanning speed, h is the scanning spacing, and d is the layer thickness.

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