Method for preparing 18Ni300 breathable die steel through selective laser melting forming lattice structure method

Abstract

The invention discloses a method for preparing 18Ni300 breathable die steel through a selective laser melting forming lattice structure method, 18Ni300 alloy is used as a raw material, the advantage that a complex shape can be formed through the selective laser melting technology is utilized, three lattice structure models of BCC, FCC and FBCCZ are designed, optimized selective laser melting forming technological parameters are combined, and the 18Ni300 breathable die steel is prepared. The method comprises the following steps: preparing a 18Ni300 breathable die steel sample with a regular porous structure, and screening out a collaborative optimal process scheme of breathability and mechanical property by combining multi-dimensional performance verification; the performance requirements of different regions are met, and the problem that air permeability and mechanical properties are difficult to be compatible in the prior art is solved.

Description

Technical Field

[0001] This invention mainly relates to the field of selective laser melting, and in particular to a method for preparing 18Ni300 permeable mold steel by selective laser melting forming a lattice structure. Background Technology

[0002] In injection molding production in the automotive, electronics, medical, and packaging industries, poor venting is consistently a critical issue, often leading to defects such as black spots, streaks, and burn marks on molded parts, severely impacting product quality. Currently, the main solutions are adding venting channels to the mold design or using permeable steel embedded in the air-trapping areas of the mold. However, the preparation of traditional permeable steel has limitations: powder metallurgy is only suitable for simple-shaped parts and is difficult to manufacture complex structures; powder injection molding has complex processes and long production cycles; melt foaming methods struggle to control the pore structure, making it impossible to form permeable steel with interconnected small pores, high porosity, and uniform pore size distribution.

[0003] With the rapid development of metal additive manufacturing technology, its application in the manufacturing field has become increasingly widespread. Selective laser melting (SLM) technology, with its advantages of being able to form complex shapes and performing high-precision machining, has brought a new technological path for the preparation of permeable steel. However, the preparation of permeable steel using existing SLM technology still faces problems such as poor controllability of pore structure and difficulty in reconciling air permeability and mechanical properties. For example, permeable steel prepared solely by adjusting SLM process parameters has insufficient internal pore connectivity and a low air permeability coefficient. Therefore, it is necessary to develop a technology for preparing permeable mold steel that can precisely control the pore structure while ensuring excellent air permeability and mechanical properties to meet the requirements of injection molds for complex venting structures. Summary of the Invention

[0004] Based on this, it is necessary to provide a method for preparing 18Ni300 permeable mold steel by laser selective melting forming a lattice structure, which addresses the existing problems.

[0005] In a first aspect, embodiments of this application provide a method for preparing 18Ni300 permeable mold steel using a laser selective melting and forming lattice structure method, characterized in that it includes:

[0006] Step S1: Use Materialise 3-matic software to design lattice structures with different lattice types and unit cell parameters;

[0007] Step S2: Model preprocessing. Export the designed lattice structure model as an STL format, import it into Magics software for slicing, and obtain the geometric data information of each layer.

[0008] Step S3: Selective laser melting and forming. The slice file is uploaded to the equipment control system. After the forming chamber is evacuated, inert argon gas is introduced to prevent the metal powder from oxidizing. The powder chamber moves upward and the horizontal scraper evenly spreads 18Ni300 powder on the substrate. The high-energy laser beam melts the powder according to the slice data and builds up layer by layer until the entire lattice structure sample is completed.

[0009] Step S4: Post-processing process: The sample and substrate are separated by wire cutting. The sample is prepared by metallographic analysis, and then polished with sandpaper and diamond polishing paste. The polished sample is placed in an ultrasonic cleaner and cleaned with anhydrous ethanol to remove residual powder from the surface.

[0010] Preferably, 18Ni300 permeable mold steel can be used alone with one of the three lattice structure models: BCC, FCC, and FBCCZ, or it can be used in combination according to the performance requirements of different areas of the mold.

[0011] Preferably, the method of using the material alone is as follows: For molds with high air permeability requirements, an FCC-type lattice structure is selected, with a cell length of 0.3 mm and a rod diameter of 0.12 mm, resulting in an average relative air permeability coefficient of 751.04 m. 3 ·(h·kPa·m 2 ) -1 Its tensile strength is 161 MPa.

[0012] Preferably, the combined use method is as follows: the FCC, BCC, and FBCCZ type lattice structures uniformly select cell length of 0.3mm and rod diameter of 0.12mm; BCC has strong mechanical properties but low air permeability, FCC has high air permeability but weak mechanical properties, while the hardness and air permeability of FBCCZ are just between BCC and FCC, so that the hard area BCC gradually transitions to the soft area FCC, and the hard area to the soft area is not directly connected, which would cause the overall structure to deform.

[0013] Preferably, the injection mold area is divided into a high venting area, a high load area, and a transition area. The high venting area refers to the part of the mold where air trapping is most severe. The bottom area of ​​the deep cavity is prone to black spots and streaks in the injection molded parts. FCC is preferred in this area. The high load area refers to the part of the mold where the stress is the greatest and the stress time is the longest. The edge area of ​​the cavity is prone to deformation and wear of the parts. BCC is preferred in this area. FBCCZ is used in the transition area, which is the transition part between the high venting area and the high load area.

[0014] Preferably, the proportion of the three types of dot matrix structures is not a fixed value, but should be allocated according to the needs of the injection mold steel. The calculation formula is: proportion of each area = area of ​​each functional area / total effective area of ​​the permeable steel.

[0015] Preferably, the transition layer FBCCZ occupies 5%-15% of the total effective area of ​​the permeable mold steel. For small molds, it is about 5%; for medium molds, it is about 10%; and for large molds, it is about 15%. The ratio of FCC to BCC should not be too high or too low. If the ratio of FCC exceeds 50%, the ratio of BCC should not be less than 30%; if the ratio of BCC exceeds 70%, the ratio of FCC should not be less than 20%.

[0016] Preferably, the material used is 18Ni300 stainless steel spherical powder, and Table 1 shows the chemical composition of the 18Ni300 powder.

[0017]

[0018] The powder spheres have a particle size range of 15-53 μm.

[0019] Preferably, the molding equipment uses an SLM280 laser metal printer with a maximum molding volume of 280mm×280mm×200mm, a maximum laser power of 200W, a laser spot diameter of 100μm, and a maximum substrate preheating temperature of 120℃. Lattice structure models with different aspect ratios L / D are designed using Materialise3-matic software. The core parameters of the single cell include cell length L, rod diameter D, and aspect ratio L / D.

[0020] Compared with the prior art, the present invention has the following advantages: (1) Precise and controllable air permeability and mechanical properties: The optimal mechanical properties scheme has a tensile strength of 305MPa and a micro hardness of 246-277HV. The two schemes meet the performance requirements of different regions respectively, solving the defects of the prior art where air permeability and mechanical properties are difficult to be compatible; (2) Air permeability and mechanical properties far exceed those of the prior art: The average relative coefficient of the optimal air permeability scheme is 289 times that of commercial PM-35 air permeable steel, and the micro hardness of the optimal mechanical properties scheme is 19-47HV higher than that of air permeable steel doped with foaming agent. Moreover, it can directly form complex structures, breaking the shape limitations of the prior art process, and has stronger adaptability; (3) Breaking the limitations of the prior art in preparing air permeable steel: No foaming agent or pore-forming agent is required. By combining the lattice structure with SLM, the complex porous structure is integrated and formed, solving the problems of simple shape in powder metallurgy, disordered pores in melt foaming method, and poor mechanical properties of doped foaming agent. (4) Strong adaptability to application scenarios: The two optimal solutions can be flexibly selected according to the different needs of the mold area, and can also support the collaborative design of partitions to meet the diverse venting needs of injection molds and expand the application range of breathable mold steel. Attached Figure Description

[0021] Exemplary embodiments of the present invention can be more fully understood by referring to the accompanying drawings. The drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain the present invention and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same components or steps.

[0022] Figure 1 A schematic diagram of the morphology of 18Ni300 powder;

[0023] Figure 2 This is a design drawing of a lattice structure;

[0024] Figure 3 Light microscopic images of the XOY surface morphology of a BCC-type lattice structure specimen.

[0025] Figure 4 Light microscopic images of the XOY surface morphology of an FCC-type lattice structure sample;

[0026] Figure 5 A light microscope image of the XOY surface morphology of an FBCCZ type lattice structure specimen.

[0027] Figure 6 Electron microscopy images of the XOY surface morphology of a BCC-type lattice structure sample;

[0028] Figure 7 Electron microscopy images of the XOY surface morphology of an FCC-type lattice structure sample;

[0029] Figure 8 Electron microscopy images of the XOY surface morphology of the FBCCZ type lattice structure sample;

[0030] Figure 9 The graph shows the relationship between the density of samples with different lattice structures and the rod diameter.

[0031] Figure 10 The image shows the microstructure of the XOY surface of a BCC-type lattice sample with a density of 91.82%.

[0032] Figure 11 The image shows the microstructure of the XOY plane of a FCC-type lattice sample with a density of 87.16%.

[0033] Figure 12 The image shows the microstructure morphology of the XOY surface of the FBCCZ sample with a density of 70.73%.

[0034] Figure 13 The graph shows the relationship between the microhardness of samples with different unit cell types and the rod diameter.

[0035] Figure 14 Stress-strain curves for tensile specimens of three unit cell types;

[0036] Figure 15 Fracture morphology of a tensile specimen with a BCC lattice structure;

[0037] Figure 16 Fracture morphology of an FCC-type lattice structure tensile specimen;

[0038] Figure 17 Fracture morphology of tensile specimen with FBCCZ lattice structure.

[0039] Figure 18 This is a schematic diagram of the device used to test the air permeability of the sample. Detailed Implementation

[0040] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0041] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0042] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] This application provides a method for preparing 18Ni300 permeable mold steel by laser selective melting forming a lattice structure, which will be described below with reference to the accompanying drawings.

[0045] Material selection, matrix material: The material used in this solution is commercially available 18Ni300 stainless steel spherical powder. Table 1 shows the chemical composition of the 18Ni300 powder. Figure 1 This is a morphology diagram of 18Ni300 powder. This powder exhibits good sphericity, excellent flowability, high bulk density, and a particle size range of 15-53 μm, which is beneficial for achieving good molding results in processes such as 3D printing.

[0046]

[0047] Molding equipment: The SLM280 laser metal printer is used, with a maximum molding volume of 280mm×280mm×200mm, a maximum laser power of 200W, a laser spot diameter of 100μm, and a maximum substrate preheating temperature of 120℃, which can realize high-precision dot matrix structure molding.

[0048] Lattice Structure Parameter Design: This scheme selects three lattice types: BCC, FCC, and FBCCZ. Among them, the BCC and FCC structures are both centrally symmetric, anisotropic, simple in structure, and their failure modes are easily observed. To improve support, the FBCCZ structure adds support columns to the BCC and FCC structures, which can enhance the structural support and stability. The lattice structure model is shown below. Figure 2 As shown.

[0049] Lattice structure models with different aspect ratios (L / D) were designed using Materialise3-matic software. The core parameters of the unit cell include cell length (L), rod diameter (D), and aspect ratio (L / D), as shown in Table 2.

[0050]

[0051] SLM process parameter optimization

[0052] The processing layer thickness h = 0.05 mm and the scanning interval d = 0.05 mm were fixed. Using the controlled single variable method, laser power P was set to 100 W, 120 W, 140 W, 160 W, 180 W, and 200 W, and scanning speed V to 400 mm / s, 600 mm / s, 800 mm / s, 1000 mm / s, 1200 mm / s, 1400 mm / s, 1600 mm / s, and 1800 mm / s. Laser power P and scanning speed V were freely combined, and after multiple parameter optimizations, experimental verification showed that when laser power P = 200 W and scanning speed V = 600 mm / s, the formed lattice structure sample had the highest density and the fewest porosity defects. Therefore, this parameter was selected to prepare 12 groups of lattice structure 18Ni300 permeable mold steel samples (Table 2).

[0053] Molding and post-processing process

[0054] (1) Model preprocessing: Export the designed lattice structure model as STL format, import it into Magics software for slicing, set the slice layer thickness to 0.05mm, and obtain the geometric data information of each layer.

[0055] (2) SLM molding: The slice file is uploaded to the printer equipment control system. After the molding chamber is evacuated, inert argon gas is introduced to prevent the metal powder from oxidizing. The powder chamber moves upward by 0.05 mm, and the horizontal scraper spreads the 18Ni300 powder evenly on the substrate. The high-energy laser beam melts the powder according to the slice data and builds up layer by layer until the entire lattice structure sample is completed.

[0056] (3) Post-processing: The sample and the substrate were separated by wire cutting; the sample was prepared by metallography, and then polished with 180#-2000# sandpaper in sequence, and then polished with diamond polishing paste; the polished sample was placed in an ultrasonic cleaner and cleaned with anhydrous ethanol for 10 minutes to remove residual powder on the surface and restore the pores.

[0057] Performance testing and characterization

[0058] To determine the optimal forming process, it is necessary to verify the structural rationality and performance advantages of the proposed lattice structure. The following performance characterization tests were conducted:

[0059] Pore ​​feature characterization

[0060] (1) Pore morphology analysis

[0061] The surface and internal pore morphology of 12 groups of samples were observed using a DM2500 Leica optical microscope and a Zeiss Sigma 500 field emission scanning electron microscope, respectively. Significant differences in pore morphology were observed among samples with different unit cell types, such as... Figure 3 , Figure 4 , Figure 5 Light microscopic images of the XOY surface morphology of three lattice structure samples and Figure 6 , Figure 7 , Figure 8 The images show electron microscope (EM) images of the XOY surface morphology of three types of lattice structure samples.

[0062] Under an optical microscope, BCC-type samples show irregular macropores formed by the pores merging together, indicating that the liquid phase did not completely fill the interparticle voids. Under an electron microscope, the pore size initially decreases, then increases, and then decreases again with increasing rod diameter; unmelted powder is present in smaller diameter samples, while pore size decreases with larger diameter samples. Under an optical microscope, the number of pores in FCC-type samples initially increases and then decreases with increasing rod diameter, with different pore morphologies for different diameters; under an electron microscope, the pore size initially decreases and then increases, with unmelted powder present in the pores of some diameter samples, and spheroidization also occurs. Under an optical microscope, the pore size in FBCCZ-type samples continuously increases with increasing rod diameter; under an electron microscope, the pore size initially decreases and then increases, with new macropores merging together in larger diameter samples.

[0063] (2) Density characterization

[0064] Based on Archimedes' principle, the density of 12 groups of samples was tested using the wax sealing method. The density of paraffin wax was 0.89 g / cm³. 3 The procedure involves first measuring the mass of the sample in air (m1) before sealing with paraffin wax, then sealing the sample with paraffin wax, and subsequently measuring the mass of the sample in air (m2) and in pure water (m3) after sealing with paraffin wax. Then, the mass is calculated according to the formula... Calculate density and porosity Each group of samples was measured three times and the average value was taken.

[0065] The density results of the 12 groups of samples are shown in Table 3. The density of the three lattice structure samples varies with the rod diameter, respectively. Figure 9 Subfigures (a)-(c) show that the main reasons for the density variation are the pore structure determined by the rod diameter, the effect of the molten pool on the powder, and the differences in pore size and powder melting caused by different cell types. For the BCC type, the density exhibits a "decreasing then increasing then decreasing" trend with increasing rod diameter; the highest density (91.82%) is achieved with a rod diameter of 0.12 mm, and the density fluctuates by 12.59% as the rod diameter increases from 0.10 mm to 0.13 mm. For the FCC type, the density exhibits a "increasing then decreasing" trend with increasing rod diameter; the highest density (87.16%) is achieved with a rod diameter of 0.12 mm, and the density fluctuates by 13.13% as the rod diameter increases from 0.10 mm to 0.13 mm. For the FBCCZ type, the density decreases rapidly with increasing rod diameter; the highest density (88.33%) is achieved with a rod diameter of 0.10 mm, and the density decreases by 20.45% as the rod diameter increases from 0.10 mm to 0.13 mm.

[0066]

[0067] 6.2 Microstructural Characterization

[0068] To investigate the influence of different cell types on the microstructure of 18Ni300 permeable mold steel samples with lattice structure, the metallographically prepared samples were etched with 10% nitric acid alcohol solution for 88-95 s, and the microstructure was then observed using a Zeiss Sigma 500 field emission scanning electron microscope.

[0069] like Figure 10 , Figure 11 , Figure 12 This shows the microstructure morphology of the XOY plane of three different unit cell types of lattice structure samples with a diameter of 0.12 mm after chemical corrosion. For example... Figure 10 (a) The sample surface shows a few pores and fine cracks; magnified observation Figure 10(b) There is no clear boundary between hexagonal cell tissue and banded tissue, and they can evolve into each other. For example... Figure 11 (a) The surface of the sample has only a few pores; magnified observation Figure 11 (b) The transition from cellular tissue to elongated cells is natural and smooth, without a clear boundary. For example... Figure 12 (b) It exhibits a typical subgrain structure, which is small in size. The hexagonal honeycomb structure is due to the fact that during selective laser melting, the energy input to the center of the melt channel is higher than that to the sides, and the energy decreases over time and dissipates to the sides, which promotes the formation of the cellular structure. Figure 12 (b) The size of the cellular structure is significantly smaller than that of the cellular structure. Figure 11 The cellular structure in (b) is due to the rapid solidification of the molten powder during the laser selective melting process, which affects the formation of secondary dendrite arms and leads to the formation of cellular structures of different shapes.

[0070] 6.3 Characterization of Mechanical Properties

[0071] 6.3.1 Microhardness Test

[0072] The HVS-30A Vickers hardness tester was used, with a load of 4.903 N and a holding time of 10 s. Seven test points were randomly selected for each sample, and the average value was taken after removing the maximum and minimum values.

[0073] like Figure 13 This is a graph showing the relationship between the microhardness of samples with different unit cell types and the rod diameter. Figure 13 (a) The BCC type shows a trend of "increase first and then decrease"; Figure 13 (b) The FCC type shows a trend of "first decreasing, then increasing, and then decreasing again"; Figure 13 (c) The FBCCZ type shows a "gradually decreasing" trend. The microhardness test error is related to the porosity distribution: more pores tend to result in a larger indentation area and increased error; fewer pores result in smaller error and more accurate hardness. The BCC type has the largest overall hardness error due to the different stress conditions after the unit cell is formed; the FBCCZ type has a smoother hardness fluctuation, reflecting the supporting effect of the Z pillars on the unit cell.

[0074] 6.3.2 Tensile properties

[0075] In accordance with the GB / T228-2002 standard, this test was conducted using an M6.104-L / EM6.304-L electronic universal testing machine. After the test, the yield strength, tensile strength, and elongation after fracture were recorded.

[0076] (1) Tensile strength

[0077] To investigate the effects of different lattice structure parameters and laser processing parameters on the tensile properties of 18Ni300 permeable die steel, 12 groups of samples were tested. However, during the testing process, the 0.13mm diameter sample was discarded because the software simulation revealed no pores, indicating that the lattice structure could not be prepared as expected. Additionally, 6 groups of samples fractured during polishing and could not complete the tensile test, indicating that the laser processing technology still has defects that need optimization. Ultimately, only 3 groups of samples successfully completed the tensile test, and the results are shown in Table 4.

[0078] The test results are as follows Figure 14 The stress-strain curves are shown for three unit cell types of specimens with a rod diameter of 0.12 mm. The BCC type specimen exhibits the highest tensile strength and elongation, at 305 MPa and 0.81%, respectively; the FCC type specimen has the lowest tensile strength at 161 MPa; and the FBCCZ type has the lowest elongation at 0.34%. This demonstrates that, for the same rod diameter, the BCC type lattice structure specimen exhibits superior tensile properties compared to the FCC and FBCCZ type lattice structure specimens.

[0079]

[0080] (2) Fracture morphology

[0081] The fracture morphology of three unit cell types of samples was observed using scanning electron microscopy. The fracture morphologies are shown in the figures below. Figure 15 , Figure 16 , Figure 17 As shown.

[0082] observe Figure 15 , Figure 16 , Figure 17 Numerous large and regularly distributed dense pores were found on the fracture surface. These pores are the main source of crack formation and also negatively affect the bonding strength of the structural interfaces, thus leading to a decrease in the overall material integrity. Observing the sub-images of the three figures reveals their differences: Figure 15 (d) The fracture surface of the BCC type specimen has a dimple structure, which was not observed in the FCC and FBCCZ types. This microstructure gives the BCC type specimen excellent tensile properties. Figure 15 (a) The fracture surface of the BCC type specimen has no large, neat holes. Figure 16 (a) FCC type specimen and Figure 17 (a) The fracture surface of the FBCCZ type specimen has neat large holes, which also indicates that large holes will reduce the interfacial bonding strength of the material.

[0083] 6.4 Characterization of air permeability

[0084] Using a self-made air permeability testing device, such as Figure 18As shown, after the post-treatment of the six groups of samples that meet the requirements of the air permeability test is completed, they are put into the air permeability device and sealed. Compressed gas is then introduced, and the gas flow rate (Q) and the pressure difference (Δp) between the two ends of the sample are recorded respectively. The relative air permeability coefficient K is then calculated according to Darcy's law K=Q / (A·Δp), where A is the effective area of ​​the sample. Each group is tested three times and the average value is taken.

[0085] The test results are shown in Table 5. As the rod diameter increases, the relative permeability coefficients of all three unit cell types of samples show an increasing trend. The FCC type exhibits the largest increase in relative permeability coefficient, reaching a maximum of 826.07 m when the rod diameter is 0.12 mm. 3 ·(h·kPa·m 2 ) -1 The BCC type rod diameter reaches its minimum relative air permeability of 3.76m when it is 0.10mm. 3 ·(h·kPa·m 2 ) -1 This is because the FCC dot matrix structure model has larger through holes on both sides, and the pores left by the melt channel during printing are also larger, making it easier for gas to penetrate the through holes; while the BCC type has smaller pores in the melt channel during printing, making it difficult for gas to penetrate the through holes; therefore, the FCC type has the highest gas permeability coefficient, and the BCC type has the lowest.

[0086]

[0087] Optimal Solution: Based on the above performance test and characterization results, and considering the shortcomings of existing technologies in preparing permeable mold steel, this solution identifies two optimal process schemes: one with optimal permeability and the other with optimal mechanical properties. For both schemes, the SLM process parameters are: processing thickness h = 0.05 mm, scanning spacing d = 0.05 mm, laser power P = 200 W, and scanning speed V = 600 mm / s.

[0088] Optimal breathability

[0089] Its core parameters are: FCC type lattice structure, cell length 0.3mm, and rod diameter 0.12mm. The average relative permeability coefficient of the permeable steel prepared with these core parameters is the highest across all test groups. A comparison with the average relative permeability coefficient of permeable mold steel prepared using existing technologies is shown in Table 6. Table 6 shows that permeable mold steel prepared with these core parameters can quickly expel trapped gas from the mold cavity, solving venting defects such as black spots and streaks in injection molded parts.

[0090] The FCC-type lattice structure model has larger through holes on both sides. The pores left by the melt channel during the printing process are larger and more uniformly distributed. Compared with the disordered "honeycomb" pores of the doped foaming agent, the pore structure of this scheme is regular, and the gas flow is more stable and easier to penetrate the through holes.

[0091] The microhardness of this design is 253-265 HV, higher than the highest 229.6 HV achieved by ventilated steel prepared with doped foaming agents. The tensile strength is 161 MPa, which meets the structural requirements of non-heavy-load, high-ventilation areas of the mold, while also preventing mold damage due to insufficient strength of the ventilated structure.

[0092]

[0093] Optimal mechanical properties

[0094] Its core parameters are: FCC-type lattice structure, cell length 0.3mm, rod diameter 0.12mm. Its average relative air permeability is 30.11m. 3 ·(h·kPa·m 2 ) -1 Although it is lower than FCC type, it is much higher than commercial PM-35 breathable steel, which can meet the air venting needs of injection molds in the edge area and avoids the excessive pursuit of breathability while ignoring mechanical properties.

[0095] The density of the permeable mold steel prepared with these core parameters reached 91.82%, the highest among all test groups. Its microhardness ranged from 246 to 277 HV, with an average of 262 HV, higher than that of the FCC and FBCCZ types. The tensile strength was 305 MPa, and the elongation after fracture was 0.8%, which also prevented deformation or breakage of the permeable structure during injection molding, meeting the structural requirements of non-high-venting, heavy-load areas of the mold.

[0096] The optimal ventilation performance solution is suitable for non-heavy-load, high-ventilation areas, while also avoiding insufficient structural strength; the optimal mechanical performance solution is suitable for non-heavy-load, high-ventilation areas, while also meeting the ventilation requirements of the mold edge area.

[0097] The two approaches can be designed collaboratively in different areas. Within the same mold, the optimal air permeability scheme can be used for deep cavities and areas with severe air trapping, while the optimal mechanical performance scheme can be used for cavity edges and heavy-load areas. This ensures both efficient venting of the mold and the strength of the air-permeable structure, breaking the limitations of using only air-permeable steel.

[0098] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0099] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0100] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0101] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0102] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0103] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application.

Claims

1. A method for preparing 18Ni300 permeable mold steel by laser selective melting forming a lattice structure, characterized in that, include: Step S1: Use Materialise 3-matic software to design lattice structures with different lattice types and unit cell parameters; Step S2: Model preprocessing. Export the designed lattice structure model as an STL format, import it into Magics software for slicing, and obtain the geometric data information of each layer. Step S3: Selective laser melting and forming. The slice file is uploaded to the equipment control system. After the forming chamber is evacuated, inert argon gas is introduced to prevent the metal powder from oxidizing. The powder chamber moves upward and the horizontal scraper evenly spreads 18Ni300 powder on the substrate. The high-energy laser beam melts the powder according to the slice data and builds up layer by layer until the entire lattice structure sample is completed. Step S4: Post-processing process: The sample and substrate are separated by wire cutting. The sample is prepared by metallographic analysis, and then polished with sandpaper and diamond polishing paste. The polished sample is placed in an ultrasonic cleaner and cleaned with anhydrous ethanol to remove residual powder from the surface.

2. The method according to claim 1, characterized in that, 18Ni300 permeable mold steel can be used alone in one of the three lattice structure models: BCC, FCC, and FBCCZ, or it can be used in combination according to the performance requirements of different areas of the mold.

3. The method according to claim 2, characterized in that, The method of using it alone is as follows: For molds with high air permeability requirements, an FCC type lattice structure is selected, with a cell length of 0.3 mm and a rod diameter of 0.12 mm, and its average relative air permeability coefficient is [missing value]. Its tensile strength is 161 MPa.

4. The method according to claim 2, characterized in that, The combined usage method is as follows: the FCC, BCC, and FBCCZ type lattice structures are uniformly selected with a cell length of 0.3mm and a rod diameter of 0.12mm; BCC has strong mechanical properties but low air permeability, FCC has high air permeability but weak mechanical properties, while the hardness and air permeability of FBCCZ are just between BCC and FCC, so that the hard area BCC gradually transitions to the soft area FCC, and the hard area is not directly connected to the soft area, which would cause the overall structure to deform.

5. The method according to claim 4, characterized in that, The injection mold area is divided into a high venting area, a high load area, and a transition area. The high venting area refers to the part of the mold where air trapping is most severe. The bottom area of ​​the deep cavity is prone to black spots and streaks in the injection molded parts. FCC is preferred in this area. The high load area refers to the part of the mold where the stress is the greatest and the stress time is the longest. The edge area of ​​the cavity is prone to deformation and wear of the parts. BCC is preferred in this area. FBCCZ is used in the transition area, which is the transition part between the high venting area and the high load area.

6. The method according to claim 5, characterized in that, The proportion of the three types of dot matrix structures is not a fixed value. It should be allocated according to the needs of the injection mold steel. The calculation formula is: proportion of each area = area of ​​each functional area / total effective area of ​​the permeable steel.

7. The method according to claim 6, characterized in that, For the transition layer FBCCZ, its area should be 5%-15% of the total effective area of ​​the permeable mold steel. For small molds, take about 5%; for medium molds, take about 10%; for large molds, take about 15%. The ratio of FCC and BCC should not be too high or too low. If the ratio of FCC exceeds 50%, the ratio of BCC should not be less than 30%; if the ratio of BCC exceeds 70%, the ratio of FCC should not be less than 20%.

8. The method according to claim 1, characterized in that, The material used is 18Ni300 stainless steel spherical powder. Table 1 shows the chemical composition of the 18Ni300 powder. ； The powder spheres have a particle size range of 15-53 μm.

9. The method according to claim 8, characterized in that, The molding equipment uses an SLM280 laser metal printer with a maximum molding volume of 280mm×280mm×200mm, a maximum laser power of 200W, a laser spot diameter of 100μm, and a maximum substrate preheating temperature of 120℃. Lattice structure models with different aspect ratios L / D are designed using Materialise3-matic software. The core parameters of the single cell include cell length L, rod diameter D, and aspect ratio L / D.

10. An apparatus for implementing the method of preparing 18Ni300 permeable mold steel by laser selective melting forming lattice structure as described in claim 1, characterized in that, include: The model preprocessing module exports the designed lattice structure model into STL format, imports it into Magics software for slicing, and obtains geometric data information for each layer. The laser selective melting and forming module uploads the slice file to the equipment control system. After the forming chamber is evacuated, inert argon gas is introduced to prevent the metal powder from oxidizing. The powder hopper moves upward and the horizontal scraper evenly spreads 18Ni300 powder on the substrate. The high-energy laser beam melts the powder according to the slice data and builds it up layer by layer until the entire lattice structure sample is completed. The post-processing module uses wire cutting to separate the sample from the substrate, performs metallographic preparation on the sample, grinds it with sandpaper, and then polishes it with diamond polishing paste. The polished sample is then placed in an ultrasonic cleaner and cleaned with anhydrous ethanol to remove residual powder from the surface.

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