Selective laser melting additive manufacturing method for mold with thin-walled fine structure

Abstract

The application provides a kind of selective laser melting additive manufacturing method of thin-walled fine structure mold with cavity, it is related to metal additive manufacturing technical field, including steps: obtaining the three-dimensional model of thin-walled fine structure mold with cavity;According to the three-dimensional model obtained, the mold structure features are identified, and the mold forming area is identified and divided into main body area, two-stage annular transition area and cavity thin-walled fine structure area;According to the process parameters of the corresponding selective laser melting additive manufacturing of the divided mold forming area, the process parameters of the selective laser melting additive manufacturing are set;According to the process parameters of the selective laser melting additive manufacturing set, layer by layer powder laying and partition laser melting are completed, and the scanning forming of main body area, first annular transition area, second annular transition area and cavity thin-walled fine structure area is sequentially completed in the same powder layer, and layer by layer stacking until the part printing is completed.The application can effectively improve the forming quality and overall performance of the fine structure of the mold.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, and specifically to a selective laser melting additive manufacturing method for a thin-walled precision structure mold with a cavity. Background Technology

[0002] Selective laser melting (SLM), a typical metal additive manufacturing technology, uses a high-energy laser beam to selectively melt and deposit metal powder layer by layer, directly manufacturing metal parts with complex shapes and internal structures. It shows good application prospects in fields such as conformal cooling molds and complex flow channel molds.

[0003] Compared to traditional subtractive manufacturing methods, SLM (Surface Mount Molding) offers significant advantages in the manufacture of precision mold structures, including high forming freedom and the ability to integrally form internal structures. It enables the creation of closed cooling channels, microchannels, thin-walled structures, and complex three-dimensional structures that are difficult to achieve using traditional methods. However, in practical engineering applications, existing SLM processes still have limitations in the manufacture of precision mold structures. Problems such as insufficient melting, overheating, dimensional instability, or uneven microstructure and properties frequently occur, limiting the forming quality and reliability of precision mold structures and hindering its further promotion in the field of high-precision molds. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention aims to provide a selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities. By implementing differentiated energy density control strategies for different forming regions of the mold, the method ensures the forming stability of the main mold region while improving the melt pool stability and forming quality of the precision structure and areas with unfavorable forming conditions, thereby achieving high-precision, high-consistency, and high-reliability forming of the precision structure of the mold.

[0005] Specifically, the present invention provides a selective laser melting additive manufacturing method for a thin-walled precision structure mold with a cavity, comprising the following steps: S1. Obtain the three-dimensional model of a thin-walled precision structure mold with a cavity; S2. Based on the obtained 3D model, identify the mold structure features and divide the mold forming area into the main area, two-level annular transition area and cavity thin-wall fine structure area. S3. Set the corresponding process parameters for selective laser melting additive manufacturing based on the divided mold forming areas, specifically including: S31. Determine the reference process parameters for isolated exposed solid structures, including laser power, scanning speed, and scanning spacing, and calculate the reference unit volume energy density ED0. S32. Set the forming process parameters for the main body area of ​​the mold so that the energy density per unit volume of the main body area is 90% to 95% of the reference energy density per unit volume ED0; S33. Set the forming process parameters for the thin-walled fine structure region of the mold cavity, so that the unit volume energy density of the thin-walled fine structure region is 60% to 80% of the energy density of the main region; S34. A two-level annular transition region is set up between the main body area of ​​the mold and the thin-walled fine structure area of ​​the cavity. The laser power decreases linearly along the wall thickness radially, and the scanning speed and scanning spacing increase linearly along the radial direction. The multi-parameter constraint model is satisfied to ensure that the energy density per unit volume decreases monotonically and smoothly, and to eliminate parameter steps and thermal shock at the boundary of the region. S4. Based on the set process parameters for selective laser melting additive manufacturing, the powder spreading and zoned laser melting are completed layer by layer. Within the same powder spreading layer, the main area, the first annular transition area, the second annular transition area, and the cavity thin-wall fine structure area are scanned and formed sequentially. The layers are stacked until the part is printed.

[0006] Furthermore, the S2 medium-sized cavity thin-walled fine structure region includes a suspended lower surface, a thin-walled structure, an inner surface recessed cavity, a micropore / microgroove region, and a region where heat dissipation is restricted.

[0007] Furthermore, the identification conditions for the thin-walled fine structure region of the S2 medium cavity include: For a suspended lower surface, the identification condition is that the suspension angle α < 45°; For thin-walled structures, the identification condition is a wall thickness ≤ 0.50 mm; For concave cavities on the inner surface, the identification criteria are thin-walled areas of concave cavities with a wall thickness ≤ 1.0 mm; For the micropore / microgroove region, the identification condition is that the pore diameter / groove width is ≤0.80mm; For areas with limited heat dissipation, the identification criteria are areas surrounded by local entities or adjacent to or near enclosed areas.

[0008] Furthermore, S32 specifically includes: for the main body area of ​​the mold, simultaneously reducing the laser power, increasing the scanning speed, and increasing the scanning spacing, so that the energy density per unit volume of the main body area reaches 90% to 95% of ED0, in order to reduce the heat accumulation caused by continuous forming and prevent the solid from overheating and cracking.

[0009] Furthermore, S33 specifically includes: for the thin-walled fine structure area of ​​the mold cavity, continue to simultaneously reduce the laser power, increase the scanning speed, and expand the scanning interval, so that the energy density per unit volume of the thin-walled area is 60% to 80% of the energy density of the main area, in order to offset the heat storage and overheating caused by the closed powder environment and avoid the collapse of the thin-walled molten pool and porosity defects.

[0010] Furthermore, the baseline energy density per unit volume ED0 in S31 is calculated using the definition of energy density per unit volume ED, which is defined as follows: ; in: For laser power, For scanning speed, For scanning spacing, The thickness is the layer thickness.

[0011] Furthermore, the multi-parameter constraint model in S34 is as follows: ; ; ; ; in: Instantaneous laser power, Instantaneous scan speed, This refers to the instantaneous scan interval; The slope of the laser power change. The slope of the change in scanning spacing. The slope of the scanning speed change. This represents the change in laser power. The change in scanning speed. This represents the change in scanning spacing. This represents the radial displacement increment.

[0012] Furthermore, the steps in S34 for calculating the two-level transition parameters based on the multi-parameter constraint model include: P1. Determine the process parameters at both ends of the main body region and the thin-walled fine structure region of the cavity as the two endpoints of the linear interpolation; P2. Divide the radial buffer area between the main body and the thin wall of the cavity into two equal segments to form a two-level annular transition zone; P3. Linear interpolation is used to calculate the laser power, scanning speed, and scanning spacing to obtain the intermediate process parameters at the two-stage transition boundary, which are then set as the first-stage transition process parameters and the second-stage transition process parameters, respectively. P4. Control the laser power, scanning speed, and scanning spacing to maintain the same linear change slope throughout the entire process, and substitute them into a multi-parameter constraint model to ensure that the energy density per unit volume decreases monotonically and continuously in the radial direction without local rebound.

[0013] Furthermore, the powder spreading and zoned laser melting process for the single-layer cross-section of the mold in S4 is as follows: W1. Complete the first layer of powdering according to the specified layer thickness; W2. Call the set forming process parameters of the main mold area, and the laser continuously scans the outer main body area in order from the outside to the inside. W3. Call the set first-level transition process parameters, and the laser scans the first annular transition region near the main body in the two-level annular transition region inward. W4. Call the same linear gradient secondary transition process parameters, and the laser scans the second annular transition region inward within the two-stage annular transition region. W5. Call the set forming process parameters for the cavity thin-wall fine structure area, and scan the cavity thin-wall fine structure area inward with the laser.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention targets the main body of a large-area mold, reducing the energy density by 5% to 10% to suppress heat accumulation caused by continuous multi-layer scanning, thus avoiding coarse grains, internal thermal cracks, and warping deformation. For the thin-walled partition wall of the cavity completely covered by loose powder, the energy is further reduced to 60% to 80% based on the main body parameters to eliminate heat storage and overheating in a closed environment, prevent the collapse, overheating, and porosity defects of the thin-walled molten pool, and adopt a two-stage graded energy reduction strategy to correspond to the two extreme heat dissipation environments of open solid and closed thin wall, so as to achieve precise heat control in different zones.

[0015] 2. This invention employs a two-stage concentric annular buffer zone, dividing the parameter changes from the main body to the thin wall into two smooth straight lines. Laser power decreases linearly, while scanning speed and scanning interval increase synchronously and linearly, eliminating abrupt parameter jumps. The thermal field at the boundary between zones remains continuous and stable, significantly reducing interfacial thermal stress and preventing microcracks at the boundaries. An additional slope inequality constraint strictly ensures that the energy density per unit volume only decreases and does not increase, preventing energy rebound during the process from causing localized tissue inhomogeneity.

[0016] 3. This invention employs a three-parameter coordinated adjustment to stably maintain the quality of the weld bead overlap. Power, scanning speed, and scanning spacing are changed synchronously and gradually, rather than modifying a single parameter. This results in a smooth change in weld bead width and keeps the weld bead overlap rate fluctuation within a very small range. It effectively prevents the weld bead from narrowing sharply near thin-walled areas, thus avoiding insufficient overlap and interlayer porosity, while balancing heat input gradient and metallurgical forming quality.

[0017] 4. This invention divides concentric annular regions within a single-layer XY plane, continuously scanning from the outside inwards within the same layer, forming a single, integrated structure layer by layer in the vertical direction, eliminating the need for segmented printing. Conventional slicing software such as Magics can complete the geometric partitioning and independent parameter configuration without requiring equipment modifications, allowing for direct mass production. The outer contour lines maintain fixed parameters, with gradient changes applied only to the internal filling, resulting in a uniform sidewall surface that avoids striped patterns caused by partitioning, thus ensuring the dimensional accuracy and surface quality of the mold cavity. Attached Figure Description

[0018] Figure 1 This is a flowchart of the selective laser melting additive manufacturing method for a thin-walled precision structure mold with a cavity according to the present invention; Figure 2 This is a schematic diagram of the suspended lower surface structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a thin-walled structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of an inner surface recessed cavity structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the microporous region structure according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the heat dissipation restricted region structure according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a mold core structure including a conformal cooling channel according to an embodiment of the present invention; Figure 8 This is a diagram showing the forming effect of the lower surface of a mold using traditional techniques. Figure 9 This is a diagram showing the forming effect of the lower surface of a mold according to an embodiment of the present invention.

[0019] In the picture: 1. Overhanging lower surface; 2. Thin-walled structure; 3. Inner surface recessed cavity; 4. Microporous region; 5. Heat dissipation restricted region; 6. Main body region; 7. Two-stage annular transition region; 8. Cavity thin-walled fine structure region; 9. Conformal cooling channel. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] like Figure 1 As shown, this invention provides a selective laser melting additive manufacturing method for thin-walled precision-structured molds with cavities, applicable to selective laser melting forming of metal mold materials, including but not limited to mold steel, stainless steel, or high-temperature alloy materials. It includes the following steps: S1. Obtain the three-dimensional model of a thin-walled precision structure mold with a cavity.

[0023] To obtain a 3D model of a thin-walled, fine-structure mold with a cavity, you can use 3D CAD software such as UG, SolidWorks, or Creo. Based on the part drawings, complete the mold structure design and export the 3D model in STL mesh format. Alternatively, you can use a laser scanner to scan the solid mold, collect surface point cloud data, perform noise reduction and encapsulation processing on the point cloud, reconstruct the surface, and generate an STL 3D model of the thin-walled, fine-structure mold with a cavity.

[0024] S2. Based on the obtained three-dimensional model, identify the mold structure features and divide the mold forming area into the main area 6, the two-level annular transition area 7, and the cavity thin-wall fine structure area 8.

[0025] The STL 3D model of the mold was imported into Materialise Magics software. The software analyzed the triangular mesh model and, based on the set identification conditions for the fine structure region of the thin-walled cavity, distinguished between exposed free surfaces and overhanging lower surfaces, as well as the sidewalls of internal closed channels. It also extracted, in batches, closed heat storage regions with poor heat dissipation conditions, providing a geometric basis for subsequent zoned control of the laser process. These fine structure regions of the thin-walled cavity are also thermally unfavorable areas.

[0026] The fine structural regions of the cavity thin-walled structure include the overhanging lower surface 1, the thin-walled structure 2, the inner surface recessed cavity 3, the micropore / microgroove region, and the heat dissipation-restricted region 5. Furthermore, the identification conditions for the fine structural regions of the cavity thin-walled structure include: For the lower overhang surface 1, the identification condition is that the overhang angle α < 45°, such as Figure 2 As shown.

[0027] For thin-walled structure 2, the identification condition is a wall thickness ≤ 0.50 mm, such as... Figure 3 As shown.

[0028] For the inner surface recessed cavity 3, the identification condition is that the wall thickness is less than the conventional solid wall thickness, that is, the thin-walled area of ​​the recessed cavity with a wall thickness ≤ 1.0 mm. In SLM mold selective laser melting forming, the conventional wall thickness of the solid structure is generally greater than 1.5 mm; when the wall thickness of the cavity is reduced to 1.0 mm or less, coupled with the poor heat dissipation conditions of the closed cavity, overheating, warping and cracking are very likely to occur. Therefore, a wall thickness ≤ 1.0 mm is used as the thin-walled judgment condition, such as... Figure 4 As shown.

[0029] For microporous region 4, the identification condition is that the pore size is ≤0.80mm, such as Figure 5 As shown. For the microgroove region, the identification condition is that the groove width is ≤0.80mm.

[0030] For region 5, where heat dissipation is restricted, the identification criteria are a locally enclosed or adjacent / nearly enclosed area, such as... Figure 6 As shown.

[0031] like Figure 7 As shown, taking a mold core containing a conformal cooling channel 9 as an example, the inner wall of the cooling channel has micropores and a thin-walled fine structure.

[0032] S3. Set the corresponding process parameters for selective laser melting additive manufacturing according to the divided mold forming areas.

[0033] Additive manufacturing (selective laser melting, SLM) equipment is a complete set of equipment that melts metal powder layer by layer to achieve near-net-shape forming of parts. Its full name is powder bed laser melting additive manufacturing equipment, which is an integrated machine composed of an optical system, a powder spreading and forming system, an atmosphere protection system, and an electrical control system.

[0034] In this embodiment of the invention, the core heat source component of its optical system is a 500W single-mode fiber laser, and the laser output power can be continuously adjusted within the range of 25 to 500W. The laser spot diameter in this embodiment is 50μm, the layer thickness is 30μm, and the scanning spacing is 0.09mm; the layer thickness remains constant in this solution.

[0035] Based on the defined mold forming area, set the process parameters for selective laser melting additive manufacturing, including: S31. Determine the reference process parameters used for isolated exposed solid structures and calculate the reference unit volume energy density ED0.

[0036] The isolated exposed solid structure is an independent exposed structure with excellent heat dissipation, weak heat accumulation, and no powder coating on all sides. This structure has a small forming area, a short continuous scanning stroke, weak heat accumulation, and excellent heat dissipation.

[0037] First, the standard forming parameters for the isolated, exposed solid structure are determined. This structure has a small scanning range, good heat dissipation, and almost no heat accumulation during continuous scanning. As an embodiment of the present invention, the standard parameters are: laser power 176W, scanning speed 1244mm / s, scanning spacing 0.09mm, and energy density per unit volume 51.89J / mm². 3 .

[0038] S32. For the main body area of ​​the mold that is continuously scanned over a large area, the laser power is simultaneously reduced, the scanning speed is increased, and the scanning interval is increased so that the energy density per unit volume of the main body area reaches 90% to 95% of E0, thereby reducing the heat accumulation caused by continuous forming and preventing the solid from overheating and cracking.

[0039] For the main body area of ​​the mold, the energy density per unit volume is set to be 5% to 10% lower than that of the baseline forming process to suppress the heat accumulation caused by large-area continuous scanning.

[0040] In the main body area of ​​the mold, the first process parameter is set, reducing the unit volume energy density by 5% to 10%. Laser melting and forming of the main body area is then performed. Taking CX material with a layer thickness of 30µm as an example, the unit volume energy density is set to 30J / mm². 3 ~50J / mm 3 between.

[0041] The main body of the mold is a large, continuous forming area, and scanning layer by layer will generate significant heat accumulation. Therefore, the energy density per unit volume of the main body area is reduced by 5% to 10% compared to the baseline forming parameters to avoid overheating of the solid body, which can lead to grain coarsening, internal thermal cracking, and part warping. At the same time, the heat input baseline of the main body area is lowered in advance to reduce the energy difference between the main body area and the thin-walled area of ​​the cavity's fine structure, making the parameter changes in the subsequent gradient transition range smoother and further reducing the thermal shock at the partition interface. The reduction in energy density per unit volume can be achieved by adjusting the laser power, scanning speed, and scanning spacing.

[0042] Energy density per unit volume (ED) is defined as: ; In the formula: For laser power, For scanning speed, For scanning spacing, The thickness is the layer thickness.

[0043] Maintain scan spacing Thick powder layer Unchanged; decrease in molecule Increase the denominator The two work together to precisely reduce total heat input.

[0044] In the main forming area, the laser power is reduced, the scanning speed is increased, and the scanning interval is enlarged, resulting in a 5%–10% reduction in the energy density per unit volume compared to the baseline forming parameters, thus alleviating heat accumulation caused by continuous scanning over a large area. As an embodiment of the invention, the first process parameters include: laser power 170W; scanning speed 1300mm / s; scanning interval 0.12mm; and energy density per unit volume 48J / mm². 3 .

[0045] S33. For the thin-walled partition wall of the cavity with fine structure surrounded by powder, continue to reduce the laser power, increase the scanning speed and expand the scanning distance simultaneously, so that the energy density per unit volume of the thin-walled area is 60% to 80% of the energy density of the main area, so as to offset the heat storage and overheating caused by the closed powder environment and avoid the collapse of the thin-walled molten pool and porosity defects.

[0046] For thin-walled, fine-structured cavities, the energy density per unit volume is reduced by 20% to 40% from that in the main forming area to suppress overheating of the molten pool in a closed powder environment.

[0047] In the case of a thin-walled fine structure with relatively unfavorable forming conditions, a second process parameter is set. By reducing the laser power, increasing the scanning speed, and expanding the scanning interval, the energy density per unit volume is further reduced by 20% to 40% based on the first process parameter. This makes the energy density per unit volume in the area with relatively unfavorable forming conditions 60-80% of that in the main area. This counteracts the heat storage phenomenon caused by powder insulation, avoids the collapse of the thin-walled molten pool, porosity, and overheating, and achieves stable forming of the fine structure.

[0048] As an embodiment of the present invention, the second process parameters include: laser power 130W, scanning speed 1450mm / s, scanning spacing 0.09mm, and energy density per unit volume 33J / mm². 3 .

[0049] S34. Two-stage annular transition regions are set between the main body region and the fine structure of the thin-walled cavity; the laser power decreases linearly along the wall thickness radially, and the scanning speed and scanning spacing increase linearly along the radial direction, while satisfying the multi-parameter constraint model to ensure that the energy density per unit volume decreases monotonically and smoothly, eliminating parameter steps and thermal shocks at the region boundary.

[0050] Within the two-stage annular transition region, the laser power decreases linearly, while the scanning speed and scanning interval increase linearly, satisfying a multi-parameter constraint model: ; ; ; ; in: Instantaneous laser power, Instantaneous scan speed, This refers to the instantaneous scan interval; The slope of the laser power change. The slope of the change in scanning spacing. The slope of the scanning speed change; This represents the change in laser power. The change in scanning speed. This represents the change in scanning spacing. The radial displacement increment is represented by the total difference between the starting and ending points. Under the constraints, the energy density per unit volume decreases monotonically and gradually, and the overlap rate of the melt channel remains constant throughout the process.

[0051] The physical meaning of the multi-parameter constraint model is that the rate of power growth must be less than the rate of energy dilution caused by the combined increase of velocity and spacing in order to ensure that the energy density continues to decrease gradually and that there is no local energy rebound.

[0052] The steps for calculating the two-level transition parameters based on the multi-parameter constraint model include: P1. Determine the process parameters at both ends of the main body region and the cavity thin-walled fine structure region as the two endpoints of the linear interpolation. The process parameters specifically refer to the laser power, scanning speed and scanning spacing.

[0053] P2. Divide the radial buffer area between the main body and the thin wall of the cavity into two equal segments to form a two-level annular transition zone.

[0054] P3. Linear interpolation is used to calculate the laser power, scanning speed, and scanning spacing to obtain the intermediate process parameters at the two-stage transition boundary, which are then set as the first-stage transition process parameters and the second-stage transition process parameters, respectively.

[0055] P4. Control the three parameters to maintain the same linear change slope throughout the process, and substitute them into the multi-parameter constraint model to ensure that the energy density per unit volume decreases monotonically and continuously in the radial direction without local rebound.

[0056] The laser power, scanning speed, and scanning spacing are synchronously and linearly varied to maintain a constant fusion overlap rate, achieve a continuous and gradual change in energy density per unit volume, and suppress the generation of thermal stress cracks at the partition interface.

[0057] In this embodiment, the first annular transition region near the main body has the following characteristics: laser power 157W, scanning speed 1350mm / s, scanning spacing 0.11mm, and energy density per unit volume 43J / mm². 3 .

[0058] Second annular transition region: laser power 143W, scanning speed 1400mm / s, scanning spacing 0.10mm, energy density per unit volume 38J / mm². 3 .

[0059] From the main solid area to the cavity thin-walled fine structure area, the laser power decreases linearly and the scanning speed increases linearly. The parameters satisfy the multi-parameter constraint model, achieving a smooth and continuous transition of thermal input.

[0060] S4. Based on the set process parameters for selective laser melting additive manufacturing, the powder spreading and zoned laser melting are completed layer by layer. Within the same powder spreading layer, the main area, the first annular transition area, the second annular transition area, and the cavity thin-wall fine structure area are scanned and formed sequentially. The layers are stacked until the part is printed.

[0061] The powder spreading and zoned laser melting process for a single-layer cross-section of the mold is as follows: W1. Apply one layer of powder according to the specified thickness.

[0062] W2. Call the set forming process parameters of the main body area of ​​the mold, and the laser continuously scans from the outside to the inside, scanning the outer main body area entity.

[0063] W3. Call the forming process parameters of the first-level annular gradient transition zone set, and the laser scans the first-level annular gradient region near the main body in the two-level annular transition region.

[0064] W4. Call the forming process parameters of the second-level annular gradient region with the same linear gradient, and scan the second-level annular transition region inward with the laser.

[0065] W5. Call the set forming process parameters for the cavity thin-wall fine structure area, and scan the cavity thin-wall fine structure area inward with the laser.

[0066] The present invention sets a parameter gradient transition zone between the main body region and the thin-walled fine structure of the cavity, so that the energy density per unit volume decreases layer by layer, thereby reducing the concentration of thermal stress.

[0067] The forming results show that after adopting the method of the present invention, the consistency of fine structure dimensions is good, the forming quality of the lower surface is significantly improved, the lower surface collapse height is reduced from 180μm to 63μm, a reduction of 65%, and the surface roughness Ra is reduced from 22.3μm to 10.1μm. No obvious powder adhesion or edge collapse phenomenon is observed. Figure 8The image shows the forming result of a traditional process using uniform process parameters, such as... Figure 9 The figure shows the forming results using the process parameters of the method of the present invention. A comparison between the traditional process and the method of the present invention is shown in Table 1 below: Table 1: Comparison of Traditional Processes and the Method of the Invention (Detailed Table)

[0068] This invention effectively improves the forming stability and dimensional accuracy of fine structures and the lower surface by implementing zoned energy density control in different forming areas of the mold; it improves the molten pool behavior in areas with unfavorable forming conditions by adopting a low energy density strategy, reducing the probability of collapse, fusion, and internal defects; reasonable control of energy density in the main area helps to reduce heat accumulation and residual stress, and improve the overall structural reliability of the mold; the method of this invention is applicable to a variety of complex and fine structural forms, and has good engineering applicability and promotion value.

[0069] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A selective laser melting additive manufacturing method for a thin-walled precision structure mold with a cavity, characterized in that, It includes the following steps: S1. Obtain the three-dimensional model of a thin-walled precision structure mold with a cavity; S2. Based on the obtained 3D model, identify the mold structure features and divide the mold forming area into the main area, two-level annular transition area and cavity thin-wall fine structure area. S3. Set the corresponding process parameters for selective laser melting additive manufacturing based on the divided mold forming areas, specifically including: S31. Determine the reference process parameters for isolated exposed solid structures, including laser power, scanning speed, and scanning spacing, and calculate the reference unit volume energy density ED0. S32. Set the forming process parameters for the main body area of ​​the mold so that the energy density per unit volume of the main body area is 90% to 95% of the reference energy density per unit volume ED0; S33. Set the forming process parameters for the thin-walled fine structure region of the mold cavity, so that the unit volume energy density of the thin-walled fine structure region is 60% to 80% of the energy density of the main region; S34. A two-level annular transition region is set up between the main body area of ​​the mold and the thin-walled fine structure area of ​​the cavity. The laser power decreases linearly along the wall thickness radially, and the scanning speed and scanning spacing increase linearly along the radial direction. The multi-parameter constraint model is satisfied to ensure that the energy density per unit volume decreases monotonically and smoothly, and to eliminate parameter steps and thermal shock at the boundary of the region. S4. Based on the set process parameters for selective laser melting additive manufacturing, the powder spreading and zoned laser melting are completed layer by layer. Within the same powder spreading layer, the main area, the first annular transition area, the second annular transition area, and the cavity thin-wall fine structure area are scanned and formed sequentially. The layers are stacked until the part is printed.

2. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 1, characterized in that, The S2 medium-sized cavity thin-walled fine structure region includes the overhanging lower surface, thin-walled structure, inner surface recessed cavity, micropore / microgroove region, and heat dissipation restricted region.

3. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 2, characterized in that, The identification criteria for the S2 medium-sized cavity thin-walled fine structure region include: For a suspended lower surface, the identification condition is that the suspension angle α < 45°; For thin-walled structures, the identification condition is a wall thickness ≤ 0.50 mm; For concave cavities on the inner surface, the identification criteria are thin-walled areas of concave cavities with a wall thickness ≤ 1.0 mm; For the micropore / microgroove region, the identification condition is that the pore diameter / groove width is ≤0.80mm; For areas with limited heat dissipation, the identification criteria are areas surrounded by local entities or adjacent to or near enclosed areas.

4. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 1, characterized in that, S32 specifically includes: for the main body area of ​​the mold, simultaneously reducing the laser power, increasing the scanning speed, and increasing the scanning spacing, so that the energy density per unit volume of the main body area reaches 90% to 95% of ED0, in order to reduce the heat accumulation caused by continuous forming and prevent the solid from overheating and cracking.

5. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 1, characterized in that, S33 specifically includes: for the thin-walled fine structure area of ​​the mold cavity, continue to simultaneously reduce the laser power, increase the scanning speed, and expand the scanning interval, so that the energy density per unit volume of the thin-walled area is 60% to 80% of the energy density of the main area, in order to offset the heat storage and overheating caused by the closed powder environment and avoid the collapse of the thin-walled molten pool and porosity defects.

6. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 1, characterized in that, In S31, the baseline energy density per unit volume ED0 is calculated using the definition of energy density per unit volume ED, which is: ； in: For laser power, For scanning speed, For scanning spacing, The thickness is the layer thickness.

7. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 1, characterized in that, The multi-parameter constrained model in S34 is as follows: ； ； ； ； in: Instantaneous laser power, Instantaneous scan speed, This refers to the instantaneous scan interval; The slope of the laser power change. The slope of the change in scanning spacing. The slope of the scanning speed change. This represents the change in laser power. The change in scanning speed. This represents the change in scanning spacing. This represents the radial displacement increment.

8. The selective laser melting additive manufacturing method for thin-walled precision structure molds with cavities according to claim 7, characterized in that, The steps in S34 for calculating the two-level transition parameters based on the multi-parameter constraint model include: P1. Determine the process parameters at both ends of the main body region and the thin-walled fine structure region of the cavity as the two endpoints of the linear interpolation; P2. Divide the radial buffer area between the main body and the thin wall of the cavity into two equal segments to form a two-level annular transition zone; P3. Linear interpolation is used to calculate the laser power, scanning speed, and scanning spacing to obtain the intermediate process parameters at the two-stage transition boundary, which are then set as the first-stage transition process parameters and the second-stage transition process parameters, respectively. P4. Control the laser power, scanning speed, and scanning spacing to maintain the same linear change slope throughout the entire process, and substitute them into a multi-parameter constraint model to ensure that the energy density per unit volume decreases monotonically and continuously in the radial direction without local rebound.

9. The selective laser melting additive manufacturing method for a thin-walled precision structure mold with a cavity according to claim 8, characterized in that, The powder spreading and zoned laser melting process for a single-layer cross-section of the mold in S4 is as follows: W1. Complete the first layer of powdering according to the specified layer thickness; W2. Call the set forming process parameters of the main mold area, and the laser continuously scans the outer main body area in order from the outside to the inside. W3. Call the set first-level transition process parameters, and the laser scans the first annular transition region near the main body in the two-level annular transition region inward. W4. Call the same linear gradient secondary transition process parameters, and the laser scans the second annular transition region inward within the two-stage annular transition region. W5. Call the set forming process parameters for the cavity thin-wall fine structure area, and scan the cavity thin-wall fine structure area inward with the laser.

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