Non-support laser additive manufacturing method for difficult-to-machine overhanging structures of deformable metal materials

Abstract

The present invention discloses a method for unsupported laser additive manufacturing of a difficult-to-machine overhanging structure for easily deformable metal materials. Metal powder is melted by laser to form a metal unsupported overhanging structure. During the process of forming each layer of the metal unsupported overhanging structure by layer-by-layer laser melting of metal powder, when the current formed layer has an overhanging area relative to the previous formed layer, the S1 forming strategy is adopted to form the overhanging area of the current formed layer; when the previous formed layer has an overhanging area, the S2 forming strategy is adopted to form the area where the overhanging areas of the current formed layer and the previous formed layer overlap; the remaining areas are all formed by the S0 forming strategy. Thus, it can be seen that the present invention can reduce powder adhesion, improve the forming quality of the unsupported overhanging structure, and solve the problems of serious surface roughness and severe powder adhesion caused by serious melt infiltration under the action of gravity in the current unsupported overhanging structure.

Description

Technical Field

[0001] The present invention relates to the field of metal additive manufacturing, and particularly to a method for unsupported laser additive manufacturing of difficult-to-machine overhanging structures for deformable metal materials. Background Art

[0002] During the laser powder bed melting process of overhanging structures, due to the poor heat dissipation ability of the unmelted powder particles below the overhanging structures, the overhanging parts will overheat, thus exacerbating the problems of residual stress and warping deformation. Therefore, it is often necessary to introduce support structures. However, the design and addition of support structures require additional post-processing steps, which greatly limit the applicability of complex designs, including the removal of support structures and the surface finishing of parts. This increases the manufacturing time and cost, and there is a potential risk of part damage.

[0003] Unsupported laser additive manufacturing technology realizes a highly customized manufacturing process by minimizing material consumption, reducing support removal time and post-processing workload, thereby effectively reducing manufacturing costs and improving production efficiency. However, during the unsupported laser additive manufacturing process of metal overhanging structures, under the combined action of gravity and capillary force, the molten pool sinks, exacerbating phenomena such as powder adhesion and slagging on the lower surface of the structure, resulting in an increase in surface roughness of the structure, geometric feature distortion, and even warping deformation.

[0004] During the spreading and forming process of the molten pool, the solidification time t of metal droplets s is related to:

[0005]

[0006] In the formula: s is the initial droplet size, k is the thermal conductivity, K sub is the substrate thermal conductivity, T 0 is the initial temperature of the droplet, a is the thermal diffusivity, C is the specific heat capacity, T l is the liquidus temperature, T sub is the substrate temperature.

[0007] When the laser energy input is sufficient, the energy carried by the droplets increases the solidification temperature of the droplets, reduces the solidification time, which is beneficial to reducing slagging caused by the penetration of the melt in the molten pool into the powder voids and reducing the surface roughness.

[0008] Therefore, by reasonably adjusting the process parameters, the solidification time t of the molten pool can be effectively controlled s , thereby optimizing the melting state of the overlapping area and reducing defects such as powder adhesion and slagging. This method based on process parameter adjustment provides an effective improvement strategy for the unsupported laser additive manufacturing of metal overhanging structures. Summary of the Invention

[0009] In the process of laser additive manufacturing of a metal unsupported overhang structure, due to the serious infiltration of the melt under the action of gravity, partial melting of the powder particles occurs, and they adhere to the lower surface of the structure, seriously affecting the forming quality. The present invention provides a method for laser additive manufacturing of a difficult-to-process overhang structure without support for a deformable metal material.

[0010] To achieve the above technical objectives, the present invention will adopt the following technical solutions:

[0011] A method for laser additive manufacturing of a difficult-to-process overhang structure without support for a deformable metal material, which uses the laser powder bed fusion technology to form a metal unsupported overhang structure. During the process of forming each layer of the metal unsupported overhang structure by laser melting of metal powder layer by layer, when the current formed layer has an overhang area relative to the previous formed layer, the S1 forming strategy is adopted to form the overhang area of the current formed layer; when the previous formed layer has an overhang area, the S2 forming strategy is adopted to form the area where the overhang areas of the current formed layer and the previous formed layer overlap; the remaining areas are all formed by the S0 forming strategy;

[0012] The S0 forming strategy is a fixed-power forming strategy, and the laser power it adopts is the densification laser power P 0 , the densification laser power P 0 which can ensure that the metal powder of the current formed layer is fully melted and densified;

[0013] The S1 forming strategy is a low-power forming strategy, and the laser power it adopts is the low laser power P L , the low laser power P L which can ensure that the metal powder of the current formed layer is partially melted;

[0014] The S2 forming strategy is a high-power forming strategy, and the laser power it adopts is the high laser power P + , the high laser power P + which can ensure that while the metal powder of the current formed layer is completely melted, the metal powder in the third formed area of the previous formed layer is remelted;

[0015] The densification laser power P 0 , the low laser power P L , the high laser power P + satisfy: P L < P 0 < P + .

[0016] Preferably, using laser melting of metal powder to form a metal unsupported overhang structure specifically includes the following steps:

[0017] Step 1. Slice the metal overhang structure:

[0018] Divide the metal overhanging structure into N forming layers, and sequentially label each forming layer from bottom to top as the first forming layer, the second forming layer... the i-th layer... the N-th layer;

[0019] Step Two: Laser additive manufacturing of the metal overhanging structure:

[0020] Form each forming layer by laser melting metal powder layer by layer until the additive manufacturing of the metal overhanging structure is completed, which specifically includes the following steps:

[0021] Step 2.1: Process and form the first forming layer using the S0 forming strategy;

[0022] Step 2.2: Process and form the second forming layer:

[0023] Step 2.2.1: Divide the forming area of the second forming layer into two, corresponding to the first and second forming areas. Among them, the second forming area is set beyond the boundary line of the first forming layer, and it is the overhanging area of the second forming layer relative to the first forming layer;

[0024] Step 2.2.2: Process and form the first forming area of the second forming layer using the S0 forming strategy;

[0025] Step 2.2.3: Process and form the second forming area of the second forming layer using the S1 forming strategy;

[0026] Step 2.3: Process and form the third forming layer:

[0027] Step 2.3.1: Judge whether the width of the third forming layer is larger than that of the second forming layer. When the judgment result shows that the width of the third forming layer is smaller than that of the second forming layer, process and form the third forming layer using the S0 forming strategy; when the judgment result shows that the width of the third forming layer is larger than that of the second forming layer, go to Step 2.3.2;

[0028] Step 2.3.2: Divide the forming area of the third forming layer into three, corresponding to the first to third forming areas; among the three forming areas included in the third forming layer, in the height direction projection, the second forming area can cover the overhanging area of the second forming layer, and the third forming area is set beyond the boundary line of the second forming layer, and it is the overhanging area of the third forming layer relative to the second forming layer;

[0029] Step 2.3.3: Process and form the first forming area of the third forming layer using the S0 forming strategy;

[0030] Step 2.3.4: Process and form the second forming area of the third forming layer using the S2 forming strategy;

[0031] Step 2.3.5: Process the third forming area of the third forming layer using the S1 forming strategy;

[0032] Step 2.4: Process the remaining forming layers in the same way as the third forming layer in Step 2.3 until the Nth forming layer is processed, and the first forming area of the Nth forming layer uses the remelting strategy.

[0033] Preferably, the metal powder is NiTi alloy powder; the densification laser power P 0 has a value range of 125W - 150W; the low laser power P L has a value range of 80W - 100W; the high laser power P + has a value range of 175W - 200W.

[0034] Preferably, the densification laser power P 0 has a value of 125W, the low laser power P L has a value of 80W, and the high laser power P + has a value of 200W.

[0035] Preferably, when the first forming area of the Nth forming layer uses the remelting strategy, the S2 forming strategy is used for air scanning.

[0036] Preferably, for the metal overhang structure, the overhang angle is 20° - 90°.

[0037] Based on the above technical objectives, compared with the prior art, the present invention has the following advantages:

[0038] 1. The laser additive manufacturing method for metal unsupported overhang structures provided by the present invention adopts the "alternating high and low power" forming strategy compared with the traditional fixed laser process parameter forming, solving the problems of rough surface and serious slag hanging of the current unsupported overhang structures.

[0039] 2. The present invention provides a laser additive manufacturing method for difficult - to - machine overhang structures without support for easily deformable metal materials, ensuring that under low power, the melt infiltration is relatively light, while under high power, the pre - bonded powder is fully melted, and at the same time, weakening the slag hanging phenomenon under high laser energy input. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flowchart of the laser additive manufacturing method for difficult - to - machine overhang structures without support for easily deformable metal materials described in the present invention;

[0041] Figure 2 is a schematic structural diagram of the metal unsupported overhang structure to be printed and formed in the present invention.

[0042] Figure 3Surface topography diagrams of LPBF-formed NiTi alloy components under different laser powers.

[0043] Figure 4 Surface roughness diagram of Example 1 in the present invention.

[0044] Figure 5 Surface roughness diagram of Comparative Example 1 in the present invention.

[0045] Figure 6 Surface roughness diagram of Example 2 in the present invention.

[0046] Figure 7 Surface roughness diagram of Comparative Example 2 in the present invention.

[0047] Figure 8 Surface roughness diagram of Example 3 in the present invention.

[0048] Figure 9 Surface roughness diagram of Comparative Example 3 in the present invention. Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Unless otherwise specifically stated, the relative arrangements, expressions, and numerical values of the components and steps described in these embodiments do not limit the scope of the present invention. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but should be regarded as part of the specification when appropriate. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0050] When using laser additive manufacturing to form any metal powder, the laser power generally has three characteristic intervals. The first interval is the densification laser power P 0 , and the densification laser power P 0 can ensure that the metal powder of the current forming layer is fully melted and densified; the second interval is the low laser power P L , and the low laser power P L can ensure that the metal powder of the current forming layer is partially melted, making the metal powder form a loose sintered state, while the third interval is the high laser power P +, high laser power P + When the metal powder of the current forming layer can be completely melted, the metal powder of the upper formed layer covered can be remelted.

[0051] Using the existing laser additive manufacturing to form a metal unsupported overhang structure as shown in Figure 3 If in the process of laser additive manufacturing, the densification laser power P 0 is used to form each formed layer of the metal unsupported overhang structure, due to insufficient metallurgical bonding between the upper and lower formed layers, delamination or looseness between the formed layers is likely to occur; if the high laser power P + is directly used to form each formed layer of the metal unsupported overhang structure, high temperature will be generated instantaneously, and the molten metal is likely to flow and deform or collapse, and local overheating makes it difficult for heat to diffuse and conduct in time, easily causing thermal stress concentration, and then resulting in warping deformation.

[0052] Therefore, the present invention develops a method for laser additive manufacturing of unsupported overhang structures of difficult-to-process materials of easily deformable metals. It uses laser melting of metal powder to form a metal unsupported overhang structure. During the process of forming each formed layer of the metal unsupported overhang structure by layer-by-layer laser melting of metal powder, when the current formed layer has an overhang area relative to the upper formed layer, the S1 forming strategy is used to form the overhang area of the current formed layer, so that the metal powder forms a loose bonding state, reducing the infiltration of the melt; when the upper formed layer has an overhang area, the S2 forming strategy is used to form the area where the overhang areas of the current formed layer and the upper formed layer overlap, so as to fully melt the pre-bonded powder sintered in the overhang area of the upper formed layer, and the remaining area is formed by using the S0 forming strategy. The S0 forming strategy is a fixed power forming strategy, and the laser power used is the densification laser power P 0 , the densification laser power P 0 can ensure that the metal powder of the current formed layer is fully melted and densified; the S1 forming strategy is a low power forming strategy, and the laser power used is the low laser power P L , the low laser power P L can ensure that the metal powder of the current formed layer is partially melted; the S2 forming strategy is a high power forming strategy, and the laser power used is the high laser power P + , the high laser power P + can ensure that when the metal powder of the current formed layer is completely melted, the metal powder in the third forming area of the upper formed layer is remelted; the densification laser power P 0 , the low laser power P L , the high laser power P + satisfy: P L < P 0 < P+ 。

[0053] It can be seen that in the present invention, by pre-sintering part of the overhanging area with low power first, the bonding force between metal powders is increased, providing a good bonding interface for subsequent high-power remelting, facilitating interlayer bonding, and enhancing the stability of the overhanging area. Therefore, at low power, the metal powders form a loose sintered state, providing a bonding basis for subsequent high-power scanning; when scanning the next layer, the overhanging area is remelted with high laser power. Since the laser power has exceeded the critical value of the densification laser power, it can ensure that the metal powders of the previous layer are fully melted. This "alternating high and low power" forming strategy not only ensures the stability of the overhanging area but also takes into account the densification quality of other areas.

[0054] Specifically, when using laser melting of metal powders to form a metal unsupported overhanging structure, as Figure 1 shown, the following steps are included:

[0055] Step 1: Slice the metal overhanging structure:

[0056] Divide the metal overhanging structure into N forming layers, and sequentially label each forming layer from bottom to top as the 1st forming layer, the 2nd forming layer... the i-th layer... the N-th layer, where N is a positive integer and i ∈ N.

[0057] The forming area of each layer is denoted as l i (i = 1, 2,... N).

[0058] Step 2: Laser additive manufacturing of the metal overhanging structure:

[0059] Layer by layer, laser melt the metal powders to form each forming layer until the additive manufacturing of the metal overhanging structure is completed. Specifically, the following steps are included:

[0060] Step 2.1: Process and form the 1st forming layer using the S0 forming strategy;

[0061] Step 2.2: Process and form the 2nd forming layer:

[0062] Step 2.2.1: Divide the forming area of the 2nd forming layer into two, corresponding to the first and second forming areas; among the two forming areas included in the 2nd forming layer, in the height direction projection, the first forming area can overlap with the first forming layer, and the second forming area is set beyond the boundary profile of the first forming layer; thus, it can be seen that relative to the 1st forming layer, the second forming area of the 2nd forming layer is the overhanging area of the 2nd forming layer relative to the 1st forming layer.

[0063] Step 2.2.2: Process and form the first forming area of the 2nd forming layer using the S0 forming strategy;

[0064] Step 2.2.3: Process the second forming area of the second forming layer using the S1 forming strategy;

[0065] Step 2.3: Process and form the third forming layer:

[0066] Step 2.3.1: Determine whether the width of the third forming layer is larger than that of the second forming layer. When the determination result shows that the width of the third forming layer is smaller than that of the second forming layer, process and form the third forming layer using the S0 forming strategy; when the determination result shows that the width of the third forming layer is larger than that of the second forming layer, go to Step 2.3.2.

[0067] Step 2.3.2: Divide the forming area of the third forming layer into three, corresponding to the first to third forming areas; among the three forming areas included in the third forming layer, in the height direction projection, the first forming area can overlap with the second forming layer and the first forming layer respectively, the second forming area can overlap with the second forming layer, and the third forming area is set beyond the boundary line of the second forming layer; thus, it can be seen that the second forming area of the third forming layer covers the overhanging area of the second forming layer, and the third forming area of the third forming layer is the overhanging area of the third forming layer relative to the second forming layer;

[0068] Step 2.3.3: Process the first forming area of the third forming layer using the S0 forming strategy;

[0069] Step 2.3.4: Process the second forming area of the third forming layer using the S2 forming strategy;

[0070] Step 2.3.5: Process the third forming area of the third forming layer using the S1 forming strategy;

[0071] Step 2.4: Process and form the remaining forming layers in the same way as processing and forming the third forming layer in Step 2.3 until the Nth forming layer is processed, and the first forming area of the Nth forming layer uses the remelting strategy.

[0072] Thus, it can be seen that when i ≥ 3, before processing and forming the current forming layer, it is necessary to determine whether there is an overhanging area for the current forming layer relative to the upper forming layer. When there is no overhanging area, process and form the current forming layer using the S0 forming strategy, otherwise go to Step 2.3.2.

[0073] Based on the above technical route, for NiTi alloy powder, the surface topography maps of LPBF forming under different laser powers shown in Table 1 below are as Figure 1 shown.

[0074] Table 1 LPBF-formed NiTi alloy powder under different laser powers

[0075]

[0076] It can be found that when the laser power is 125W - 150W, there are fewer pores inside the LPBF-formed NiTi alloy, and it has the best forming quality. Therefore, the densification process window for laser additive manufacturing of NiTi alloy is 125 - 150W. When the laser power is 80W - 100W, the laser input energy is severely insufficient, resulting in incomplete melting of the metal powder. The formed molten pool has poor fluidity and spreading ability, making it difficult to achieve good interlayer bonding. Therefore, a large number of unfused hole defects are generated inside the NiTi alloy formed by LPBF at low laser power. When the laser power exceeds 175W, the high laser energy input exacerbates the evaporation of the liquid metal. The solubility of these evaporated metal gases in the molten pool increases significantly. During the rapid solidification process, these gases cannot escape completely but are quickly frozen inside the metal matrix, also forming a large number of pore defects. Therefore, to obtain a dense NiTi alloy, the laser power must be maintained within the range of 125 - 150W to ensure complete melting of the powder and reduce the formation of pores.

[0077] For the powder pre-bonded metal overhang structure non-support metal additive manufacturing method of the present invention, at low power, the metal powder is made to form a loose sintered state, and then the same area of the next forming layer is scanned with high power to fully melt the pre-sintered powder. Therefore, for the overhang area of the NiTi alloy component, the low laser power is selected as 80W - 100W. At this time, the laser input energy is insufficient, causing partial melting of the metal powder into an adhesive state. When scanning the same area of the next forming layer, high laser energy input is then used to ensure full melting of the metal powder in the previous layer. When the high laser power is selected as 175W - 200W, it has exceeded the densification laser power of 125W, and the laser energy is sufficient to fully melt the metal powder in the previous layer. For the non-overhang area, the laser power is selected as 125W - 150W to ensure high densification.

[0078] The technical solution of the present invention will be described in detail below in combination with each embodiment and comparative example.

[0079] Example 1

[0080] As Figure 2 shown in the schematic diagram of the metal non-support overhang structure with an overhang angle of 60°. The specific structural parameters are shown in the following table. The material used to form this overhang structure is NiTi alloy, and it is formed using a laser powder bed melting equipment. The forming parameters are: laser power 80 - 200W, scanning speed 1400mm / s, scanning spacing 60μm, and scanning layer thickness 30μm.

[0081] Table 2 Structural parameters of Example 1

[0082]

[0083] The forming process specifically includes the following steps:

[0084] Step 1: Import the STL model of the metal unsupported overhang structure with a 60° overhang angle into 3D printing slicing software, and slice it with a thickness of 30 μm per layer, for a total of 200 layers.

[0085] Step 2: Layer 1: Use S0 for forming, set the laser power to 125 W, and keep other process parameters unchanged.

[0086] Step 3: Layer 2: Use S1 for forming in the part exceeding the area of Layer 1, set the laser power to 80 W; use S0 for forming in the remaining area, set the laser power to 125 W, and keep other process parameters unchanged.

[0087] Step 4: Layer 3: Use S1 for forming in the part exceeding the area of Layer 2, set the laser power to 80 W; use S2 for forming in the area same as the 80 W forming part of Layer 2, set the laser power to 200 W; use S0 for forming in the remaining area, set the laser power to 125 W, and keep other process parameters unchanged.

[0088] Step 5: Layer 4: Use S1 for forming in the part exceeding the area of Layer 3, set the laser power to 80 W; use S2 for forming in the area same as the 80 W forming part of Layer 3, set the laser power to 200 W; use S0 for forming in the remaining area, set the laser power to 125 W, and keep other process parameters unchanged.

[0089] Step 6: Layers 5 to 200: Perform cyclic scanning in the form of "use S1 for forming in the part exceeding the area of Layer N - 1, set the laser power to 80 W; use S2 for forming in the area same as the 80 W forming part of Layer N - 1, set the laser power to 200 W; use S0 for forming in the remaining area, set the laser power to 125 W", and keep other process parameters unchanged.

[0090] Step 7: Layer 200 is scanned with a high power of 200 W, and keep other process parameters unchanged.

[0091] After steps 1 to 7, the surface roughness of the metal unsupported overhang structure obtained in this embodiment can be referred to in the appendix Figure 4 .

[0092] To further illustrate the effects of the present invention, a comparative example is also set in the present invention.

[0093] Comparative Example 1

[0094] Compared with Example 1, the difference in this comparative example is that each forming layer of the entire overhanging structure is formed using S0, with a fixed laser power of 125 W, and other process parameters remain unchanged.

[0095] The forming process specifically includes the following steps:

[0096] Step 1: Import the STL model of the metal unsupported overhanging structure with an overhang angle of 60° into 3D printing slicing software, and slice it with a thickness of 30 μm per layer, for a total of 200 layers.

[0097] Step 2: Set the laser power of each layer to 125 W, and keep other process parameters unchanged.

[0098] After steps 1 to 2, the surface roughness of the metal unsupported overhanging structure obtained in this comparative example can be referred to in the appendix Figure 5 .

[0099] Example 2

[0100] A metal unsupported overhanging structure with an overhang angle of 45°. The specific structural parameters are shown in the following table. The material used to form this overhanging structure is NiTi alloy, and it is formed using a laser powder bed fusion device. The forming parameters are: laser power 80 - 200 W, scanning speed 1400 mm / s, scanning spacing 60 μm, and scanning layer thickness 30 μm.

[0101] Table 3 Structural parameters of Example 2

[0102]

[0103] The forming process specifically includes the following steps:

[0104] Step 1: Import the STL model of the metal unsupported overhanging structure with an overhang angle of 45° into 3D printing slicing software, and slice it with a thickness of 30 μm per layer, for a total of 200 layers.

[0105] Step 2: Layer 1: Use S0 forming, set the laser power to 125 W, and keep other process parameters unchanged.

[0106] Step 3: Layer 2: For the part exceeding the area of Layer 1, use S1 forming and set the laser power to 80 W; for the remaining area, use S0 forming and set the laser power to 125 W. Keep other process parameters unchanged.

[0107] Step 4: Layer 3: For the part exceeding the area of Layer 2, use S1 forming and set the laser power to 80 W; for the area same as the 80 W forming part of Layer 2, use S2 forming and set the laser power to 200 W; for the remaining area, use S0 forming and set the laser power to 125 W. Keep other process parameters unchanged.

[0108] Step 5, the 4th layer: The part exceeding the area of the 3rd layer is formed by S1 with a laser power of 80 W; the same area as the 80 W forming part of the 3rd layer is formed by S2 with a laser power of 200 W; the remaining area is formed by S0 with a laser power of 125 W, and other process parameters remain unchanged.

[0109] Step 6, the 5th layer to the 200th layer: Perform cyclic scanning in the form of "the part of the Nth layer exceeding the area of the N - 1th layer is formed by S1 with a laser power of 80 W; the same area as the 80 W forming part of the N - 1th layer is formed by S2 with a laser power of 200 W; the remaining area is formed by S0 with a laser power of 125 W", and other process parameters remain unchanged.

[0110] Step 7, the 200th layer is scanned empty at a high power of 200 W, and other process parameters remain unchanged.

[0111] After steps 1 to 7, the surface roughness of the metal unsupported overhang structure obtained in this embodiment can be referred to in the appendix Figure 6 .

[0112] To further illustrate the effects of the present invention, a comparative example is also set in the present invention.

[0113] Comparative Example 2

[0114] Compared with Example 2, the difference is that each forming layer of the entire overhang structure is formed by S0 with a fixed laser power of 125 W, and other process parameters remain unchanged.

[0115] The forming process specifically includes the following steps:

[0116] Step 1, import the STL model of the metal unsupported overhang structure with an overhang angle of 60° into 3D printing slicing software, and slice it with a thickness of 30 μm per layer, for a total of 200 layers.

[0117] Step 2, the laser power of each layer is set to 125 W, and other process parameters remain unchanged.

[0118] After the above forming process, the surface roughness of the metal unsupported overhang structure obtained in this comparative example can be referred to in the appendix Figure 7 .

[0119] Example 3

[0120] A metal unsupported overhang structure with an overhang angle of 30°, and the specific structural parameters are shown in the following table. The material used to form this overhang structure is NiTi alloy, and it is formed by a laser powder bed fusion device. The forming parameters are: laser power 80 - 200 W, scanning speed 1400 mm / s, scanning spacing 60 μm, and scanning layer thickness 30 μm..

[0121] Table 4 Structural parameters of Example 3

[0122]

[0123] The forming process specifically includes the following steps:

[0124] Step 1: Import the STL model of the metal unsupported overhang structure with a 60° overhang angle into 3D printing slicing software, and slice it with a thickness of 30 μm per layer, for a total of 200 layers.

[0125] Step 2: Layer 1: Use S0 for forming, set the laser power to 125 W, and keep other process parameters unchanged.

[0126] Step 3: Layer 2: Use S1 for forming in the part exceeding the area of Layer 1, set the laser power to 80 W; use S0 for forming in the remaining area, set the laser power to 125 W, and keep other process parameters unchanged.

[0127] Step 4: Layer 3: Use S1 for forming in the part exceeding the area of Layer 2, set the laser power to 80 W; use S2 for forming in the area same as the 80-W forming part of Layer 2, set the laser power to 200 W; use S0 for forming in the remaining area, set the laser power to 125 W, and keep other process parameters unchanged.

[0128] Step 5: Layer 4: Use S1 for forming in the part exceeding the area of Layer 3, set the laser power to 80 W; use S2 for forming in the area same as the 80-W forming part of Layer 3, set the laser power to 200 W; use S0 for forming in the remaining area, set the laser power to 125 W, and keep other process parameters unchanged.

[0129] Step 6: Layers 5 to 200: Perform cyclic scanning in the form of "use S1 for forming in the part exceeding the area of Layer N - 1, set the laser power to 80 W; use S2 for forming in the area same as the 80-W forming part of Layer N - 1, set the laser power to 200 W; use S0 for forming in the remaining area, set the laser power to 125 W", and keep other process parameters unchanged.

[0130] Step 7: Layer 200 is scanned empty at a high power of 200 W, and keep other process parameters unchanged.

[0131] After steps 1 to 7, the surface roughness of the metal unsupported overhang structure obtained in this embodiment can be referred to in the appendix Figure 8 .

[0132] To further illustrate the effects of the present invention, a comparative example is also set in the present invention.

[0133] Comparative Example 3

[0134] Compared with Example 3, the difference is that in each forming layer of the entire overhang structure, S0 forming is adopted, the fixed laser power is 125W, and other process parameters remain unchanged.

[0135] The forming process specifically includes the following steps:

[0136] Step 1: Import the STL model of the metal unsupported overhang structure with an overhang angle of 60° into 3D printing slicing software, and slice it with a thickness of 30μm per layer, for a total of 200 layers.

[0137] Step 2: Set the laser power of each layer to 125W, and keep other process parameters unchanged.

[0138] After the above forming process, the surface roughness of the metal unsupported overhang structure obtained in this comparative example can be referred to in the appendix Figure 9 .

[0139] The methods for characterizing the forming quality of the metal unsupported overhang structures in Examples 1 to 3 and Comparative Examples 1 to 3 are as follows:

[0140] Use a laser confocal scanning microscope to test the surface roughness of the metal unsupported overhang structure fabricated by laser additive manufacturing.

[0141] Table 5 Test results of the overhang surface roughness of Examples 1 to 3 and Comparative Examples 1 to 3

[0142]

[0143] As can be seen from Table 5, compared with Comparative Example 1, the surface roughness of the unsupported overhang structure in Example 1 decreased by 39.9%.

[0144] As can be seen from Table 5, compared with Comparative Example 2, the surface roughness of the unsupported overhang structure in Example 2 decreased by 31.4%.

[0145] As can be seen from Table 5, compared with Comparative Example 3, the surface roughness of the unsupported overhang structure in Example 3 decreased by 27.1%.

[0146] From the above results, it can be seen that the overhang surface quality of the metal overhang structure unsupported metal additive manufacturing method based on powder pre-bonding in Examples 1 to 3 of the present invention has been significantly improved.

Claims

1. A method for unsupported laser additive manufacturing of difficult-to-process overhanging structures of easily deformable metal materials, using laser powder bed fusion technology to form metal unsupported overhanging structures, characterized in that: In the process of forming each forming layer of the metal unsupported overhang structure by laser melting metal powder layer by layer, a high-low power alternating forming strategy is adopted: when the current forming layer has an overhang area relative to the previous forming layer, the overhang area of ​​the current forming layer is formed by the S1 forming strategy; when the previous forming layer has an overhang area, the S2 forming strategy is used to form the overlapping area of ​​the overhang area of ​​the current forming layer and the previous forming layer; The remaining areas are formed using the S0 forming strategy; The S0 forming strategy is a fixed power forming strategy, and the laser power used is the densification laser power P0, which can ensure that the metal powder of the current forming layer is fully melted and densified; The S1 forming strategy is a low power forming strategy, and the laser power used is low laser power P L , low laser power P L It can ensure that the metal powder of the current forming layer is partially melted to form pre-bonded powder, so as to increase the bonding force between the metal powders, make the metal powders form a loose bonding state, and reduce the infiltration of the melt; The S2 forming strategy is a high-power forming strategy, and the laser power used is a high laser power P + , high laser power P + When the metal powder of the current forming layer is completely melted, the pre-bonded powder formed by sintering the overhanging area of ​​the previous forming layer is re-melted to fully melt the pre-bonded powder; Densification laser power P0, low laser power P L , high laser power P + Satisfaction: P L < P0< P + ; The metal powder is NiTi alloy powder; the value of the densification laser power P0 is 125 W-150 W; the low laser power P L The value of is 80W-100W; the high laser power P + The value is 175W-200W.

2. The unsupported laser additive manufacturing method for difficult-to-process overhanging structures of easily deformable metal materials according to claim 1, characterized in that: The laser powder bed fusion technology is used to form a metal unsupported overhang structure, which specifically includes the following steps: Step 1: Slice the metal overhang structure: Divide the metal suspension structure into N The shaping layers are sequentially recorded from bottom to top as the first shaping layer, the second shaping layer, and so on. i Layer... N layer; Step 2: Laser additive manufacturing of metal overhanging structure: Laser melting metal powder layer by layer to form each forming layer until the additive manufacturing of the metal overhang structure is completed, specifically including the following steps: Step 2.1, using the S0 forming strategy to process and form the first forming layer; Step 2.2: Processing and forming the second forming layer: Step 2.2.1, dividing the forming area of ​​the second forming layer into two, corresponding to the first and second forming areas, wherein the second forming area is arranged beyond the boundary line of the first forming layer, and is the overhanging area of ​​the second forming layer relative to the first forming layer; the remaining area is the first forming area; Step 2.2.2, using the S0 forming strategy to process the first forming area of ​​the second forming layer; Step 2.2.3, using the S1 forming strategy to process the second forming area of ​​the second forming layer; Step 2.3: Processing and forming the third forming layer: The forming area of ​​the third forming layer is divided into three, corresponding to the first to third forming areas; among the three forming areas included in the third forming layer, in the projection in the height direction, the second forming area is the area overlapping with the overhanging area of ​​the second forming layer, and the third forming area is set beyond the boundary line of the second forming layer, which is the overhanging area of ​​the third forming layer relative to the second forming layer; the remaining area is the first forming area; The first forming area of ​​the third forming layer is processed by adopting the S0 forming strategy; The second forming area of ​​the third forming layer is processed by adopting the S2 forming strategy; The third forming area of ​​the third forming layer is processed by adopting the S1 forming strategy; Step 2.4, forming the remaining shaping layers in the same manner as the third shaping layer in step 2.3, until the Nth shaping layer is formed.

3. The unsupported laser additive manufacturing method for difficult-to-process overhanging structures of easily deformable metal materials according to claim 2, characterized in that: The densification laser power P0 is 125 W, and the low laser power P L The value is 80W, the high laser power P + The value is 200W.

4. The method for unsupported laser additive manufacturing of difficult-to-process overhanging structures of easily deformable metal materials according to claim 1, characterized in that: The metal unsupported overhanging structure has an overhanging angle of 20°-90°.

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