A lightweight hydraulic pump shell preparation process based on SLM technology

Abstract

The application relates to the technical field of hydraulic pump additive manufacturing, and discloses a preparation process of a light-weight hydraulic pump shell based on SLM technology, which uniformly selects TC4 metal powder as base material and shell material of the light-weight shell, sets up a recycled powder collecting container in a powder preparation area, establishes a mixing use specification of new powder and recycled powder, realizes efficient recycling and full life cycle traceability of the powder, finally reduces manufacturing cost and waste emission, fills a non-bearing area by adopting a rhombic dodecahedron or a gyroscopic lattice structure, removes low stress material in combination with topological optimization, can reduce the weight of the shell as a whole, directly integrates a hydraulic flow channel in the shell, can effectively avoid the additional requirement of wall thickness of a traditional drilling process, reduces flow channel pressure loss, and effectively improves the power to weight ratio and dynamic response performance of the hydraulic pump.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology for hydraulic pumps, specifically a lightweight hydraulic pump housing fabrication process based on SLM technology. Background Technology

[0002] Hydraulic pumps are high-power-density servo actuation systems that integrate a motor, control valve group, and cylinder, and are widely used in aerospace, robotics, and high-end equipment fields. The housing, as the core load-bearing and hydraulic medium-containing component of the EHA (Electrical Hydraulic Actuator), directly affects the system's power-to-weight ratio, dynamic response, and sealing reliability due to its weight and internal flow channel structure.

[0003] Currently, hydraulic pump housings are mainly made of aluminum alloy, titanium alloy, or stainless steel. The hydraulic flow channels are formed by casting, forging, and CNC machining. However, the traditional manufacturing process has the following shortcomings: (1) The housing is mostly a solid structure. Due to the processing method, it is impossible to perform effective topology optimization or lattice filling in non-load-bearing areas, resulting in a large housing weight and low power density; (2) The hydraulic flow channels must be drilled in a straight line, making it difficult to achieve a smooth transition in three-dimensional bending. The pressure loss at right angle bends is large, and the drilling depth is limited, which restricts the improvement of housing integration; (3) The flow channels and housing are processed separately and then assembled, resulting in many sealing links and a high risk of leakage; (4) The material utilization rate is low (casting + CNC usually less than 70%), especially for difficult-to-machine materials such as titanium alloys, the cost is high.

[0004] In recent years, selective laser melting (SLM) technology, as a metal additive manufacturing method, can directly form complex geometric structures, providing a new approach for the fabrication of lightweight and integrated shells. However, existing SLM processes still face the following challenges when fabricating complex shells containing internal lattices, three-dimensional curved channels, and closed cavities: (1) lack of dedicated process parameter windows and overhanging surface compensation strategies for multiple materials (TC4, Ti6Al4V, 316L), which easily leads to defects such as warping deformation, high porosity, and powder adhesion in the channels; (2) unreasonable support structure design, which is difficult to remove and easily damages functional surfaces; (3) lack of standardized powder recycling, resulting in resource waste and environmental pollution.

[0005] Therefore, there is an urgent need to develop a hydraulic pump housing manufacturing process that can achieve lightweight, high precision, low cost, and environmental friendliness. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a lightweight hydraulic pump housing manufacturing process based on SLM technology. This process offers advantages such as lightweight design, high precision, low cost, and environmental friendliness. It solves the problems of large housing weight, limited flow channel structure, high pressure loss, and low material utilization caused by existing casting and machining processes, as well as the high cost and high scrap rate caused by poor deformation control, difficulty in removing supports, and non-closed-loop powder recycling in conventional SLM processes.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution: a lightweight hydraulic pump housing manufacturing process based on SLM technology, comprising the following steps:

[0010] Step 1, Material Selection: TC4 metal powder is selected as the base material for the lightweight shell, and TC4 metal powder, Ti6Al4V or 316L stainless steel is selected as the high-strength or corrosion-resistant shell material. A recycling powder collection container is set up in the powder preparation area, and a standard for mixing new powder and recycled powder is established.

[0011] Step 2: Lightweight design based on SLM technology: Using ntopology or ANSYS software, topology optimization is used to reduce the weight of the shell in the non-load-bearing or low-stress internal areas, filling it with rhombic dodecahedrons or gyroscope-shaped lattice structures, and designing three-dimensional curved flow channels and closed internal cavities to obtain the CAD model of the shell.

[0012] Step 3: Optimize process parameters: Based on the material determined in Step 1 and the lightweight shell geometry model generated in Step 2, optimize the process parameters to obtain the pre-compensated printing model;

[0013] Step 4: Automatic Support Structure Design: Using Magics or Materialise e-Stage software, automatically add support structures to inclined surfaces, horizontal holes, and suspended curved surfaces with an inclination angle of less than 45° in the model. Import the pre-compensation model output in Step 3, complete the support addition and optimization, and export the complete printable model with support structures.

[0014] Step 5, SLM automated forming process: Import the supported model output from Step 4 into the slicing software that comes with the SLM equipment, set the slicing layer thickness to be the same as in Step 3, generate slicing data, import the slicing data into the SLM forming equipment, and install the substrate after introducing a protective atmosphere. According to the process parameters and scanning strategy set in Step 3, a shell blank with a support structure is obtained on the substrate.

[0015] Step 6, Post-processing: After printing, the substrate is separated by wire electrical discharge machining, the support structure is removed, and then precision CNC machining, internal flow channel abrasive polishing, heat treatment and surface protection treatment are performed in sequence.

[0016] Step 7, Quality Inspection: Through industrial CT non-destructive testing, mechanical property testing, and sealing testing, a closed-loop powder recycling system is completed to achieve green manufacturing and quality traceability.

[0017] Preferably, in step one, the particle size distribution of TC4 powder is 20-60 μm, the particle size distribution of Ti6Al4V or 316L stainless steel powder is 15-53 μm, the sphericity of the powder is ≥95%, the oxygen content is ≤0.2%, and in the powder preparation stage, TC4 metal powder, Ti6Al4V or 316L stainless steel powder are kept at 100-120℃ under vacuum for 2-4 hours.

[0018] Preferably, the recycled powder collection container adopts an anti-static and sealed design and is equipped with a vibrating screening device with a 100-200 mesh screen to remove agglomerated particles or impurities with a particle size >60μm. The mixing and use specifications for new powder and recycled powder are as follows: the proportion of recycled powder added shall not exceed 30%.

[0019] Preferably, the parameter setting process in step two is as follows:

[0020] (1) Topology optimization: ntopology or ANSYS software is used to reduce the volume by 40%-60%;

[0021] (2) Internal lattice structure: Rhombic dodecahedral or gyro-shaped lattice is selected. The rhombic dodecahedral lattice has a unit cell side length of 2-5 mm, a support diameter of 0.3-0.8 mm, and a relative density of 10%-25%. The gyro-shaped lattice adopts a three-period minimal surface structure, with a unit cell size of 3-6 mm and a volume fraction of 12%-20%.

[0022] (3) Functional integrated flow channel: Design a three-dimensional curved flow channel and a closed internal cavity. The minimum curvature radius of the three-dimensional curved flow channel is ≥5mm, the flow channel diameter is designed to be 4-10mm according to the hydraulic power density, and the wall thickness of adjacent flow channels is ≥1.5mm, so as to realize the integration of hydraulic pipeline and shell.

[0023] Preferably, the parameters in step three are optimized as follows:

[0024] (1) For TC4 powder, the laser power range is 280-350W, the scanning speed is 800-1200mm / s, the scanning spacing is 0.10-0.12mm, and the layer thickness is 30-50μm;

[0025] (2) For Ti6Al4V material, the laser power is 200-280W, the scanning speed is 600-1000mm / s, the scanning spacing is 0.08-0.10mm, and the layer thickness is 30-40μm;

[0026] (3) For 316L stainless steel, the laser power is 180-240W, the scanning speed is 700-1100mm / s, the scanning spacing is 0.10-0.12mm, and the layer thickness is 40-60μm;

[0027] (4) And adopt a strip or chessboard scanning strategy, with a strip width of 5-10 mm and adjacent layers rotated by 67°;

[0028] (5) Set an independent volume energy density of 40 to 60 J / mm³ for the region of suspended curved surface with an inclination angle of <45°, and use contour offset compensation, setting the outer contour to offset inward by 0.05 to 0.10 mm and the inner contour to offset outward by 0.05 to 0.10 mm.

[0029] Preferably, the automatic support structure parameter design in step four is as follows:

[0030] (1) For inclined planes with an inclination angle of <45°, a tapered point support is used, with a tip diameter of 0.2 to 0.4 mm, a root diameter of 0.6 to 1.0 mm, and a spacing of 1 to 2 mm;

[0031] (2) The diameter of the horizontal hole is >3mm, and a block support is added below it. The wall thickness is set to 0.3-0.5mm and the tooth gap is 0.5-1.0mm;

[0032] (3) The suspended curved surface adopts tree-shaped or grid-shaped support. The contact surface between the support and the part adopts a sawtooth-shaped break point design. The support structure is automatically generated by the software according to the preset rules, and the support density near the flow channel inlet and the sealing surface is manually adjusted.

[0033] Preferably, after the support is added in step four, the support optimization module of Magics is used to perform collision checks and hollowing out. For block supports with a height > 10mm, hexagonal hollowing is made inside, and the wall thickness is retained at 0.35-0.4mm.

[0034] Preferably, the forming process parameters and monitoring requirements in step five are as follows:

[0035] (1) Use dual lasers and set the spot diameter to 70-100μm; control the oxygen content in the forming chamber to ≤0.1% and use argon gas with a purity of ≥99.999% as a protective atmosphere; the substrate material is the same as the shell material, the substrate thickness is ≥30mm, and the upper surface is ground to a flatness of ≤0.05mm;

[0036] (2) Before printing, the substrate made of TC4 metal powder is preheated to 40-80℃ or the substrate made of Ti6Al4V / 316L is preheated to 100-150℃; the powder spreading squeegee is made of ceramic or hard alloy material, and the thickness of the powder layer is detected by laser sensor after each layer of powder is spread. When the deviation exceeds ±5μm, it is automatically adjusted; after each layer is melted, the temperature of the melt pool is monitored by infrared thermal imaging. When the temperature fluctuation exceeds ±10% of the set value, the laser power is automatically adjusted.

[0037] Preferably, in step six, the post-processing steps are as follows:

[0038] S1.1, Substrate separation: Electrical discharge wire cutting is used, with a cutting speed of 30-50 mm² / min and a cut surface flatness of ≤0.05 mm;

[0039] S1.2, Support Removal: First, use special pliers to remove the main support by ultrasonic vibration at a frequency of 20-40kHz. The remaining contact layer is removed by sandblasting.

[0040] S1.3 Precision CNC machining: Micro-cutting is performed on the assembly surface, threaded holes and sealing grooves, with a single-sided allowance of 0.1-0.3mm, ensuring dimensional tolerance of IT6-IT7 grade and surface roughness Ra≤1.6μm;

[0041] S1.4 Internal flow channel treatment: Abrasive flow polishing is adopted, with abrasive particle size of 100-200 mesh, extrusion pressure of 5-10MPa, and number of cycles of 10-20.

[0042] S1.5 Heat treatment: After holding the TC4 material at 285-300℃ for 2-2.2 hours, stress annealing is carried out under air cooling conditions;

[0043] S1.6 Surface Protection: The aluminum alloy shell is anodized with a film thickness controlled at 10-20μm, and the titanium alloy or stainless steel shell is electroless nickel plated with a film thickness controlled at 5-15μm. Then, an epoxy primer and polyurethane topcoat are sprayed on the outside, with the dry film thickness controlled at 80-120μm.

[0044] Preferably, in step seven, the testing standards and recycling requirements are as follows:

[0045] S2.1 Industrial CT inspection: Check the unobstructed flow of internal channels, the integrity of the lattice structure, and the presence of unfused holes or cracks. Defects larger than 0.1mm are considered unqualified.

[0046] S2.2 Mechanical property testing: Print 3 horizontal and 3 vertical test bars of the same batch in the furnace and test tensile strength, yield strength, elongation after fracture and Vickers hardness.

[0047] S2.3 Sealing test: Pressurize the hydraulic flow channel to 1.5 times the working pressure and hold the pressure for 25-30 minutes. A leakage rate of ≤0.1mL / min is acceptable.

[0048] S2.4 Powder recycling closed loop: Collect unmelted powder and metal dust generated during post-processing grinding in the printing chamber, pass them through a 200-mesh sieve, mix them with new powder and recycled powder at a ratio of 7:3, and return them to step one after testing for qualified oxygen content and particle size distribution for use in the next batch of production;

[0049] S2.5 Quality Traceability: Each shell is assigned a unique code, which records the material batch number, process parameters, and test data to achieve full-process traceability.

[0050] Compared with the prior art, the present invention provides a lightweight hydraulic pump housing manufacturing process based on SLM technology, which has the following advantages:

[0051] 1. This invention achieves the beneficial effects of reducing shell weight and increasing power density through topology optimization, internal lattice filling, and three-dimensional curved flow channel integration. Specifically, by using rhombic dodecahedrons or gyroscope-shaped lattice structures to fill non-load-bearing areas, combined with topology optimization to remove low-stress materials, the overall weight of the shell can be reduced. At the same time, the hydraulic flow channels are directly integrated into the shell to avoid the additional wall thickness requirements of traditional drilling processes, and the flow channel pressure loss is reduced, thereby effectively improving the power-to-weight ratio and dynamic response performance of the hydraulic pump.

[0052] 2. This invention achieves the beneficial effects of high-precision forming of complex internal structures and reduction of printing defects by using multiple material parameter windows, thermo-mechanical coupling simulation and reverse compensation strategies. Specifically, optimized parameter windows for laser power, scanning speed and layer thickness are established for three materials: TC4, Ti6Al4V and 316L. Independent volume energy density and contour offset compensation are set for the suspended curved surface. Combined with layer-by-layer thermo-mechanical simulation and reverse displacement compensation, the forming quality of lattice structures, closed flow channels and suspended curved surfaces is improved.

[0053] 3. This invention achieves the beneficial effects of green manufacturing, cost reduction and quality control through closed-loop powder recycling and full-process quality traceability. In particular, by establishing a standard for the mixed use of new powder and recycled powder, and through CT detection, mechanical testing, sealing testing and recording of the number of times each batch of recycled powder is used, the efficient recycling of powder and full life cycle traceability are achieved, ultimately reducing manufacturing costs and waste emissions. Attached Figure Description

[0054] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0056] Please see Figure 1 A lightweight hydraulic pump housing manufacturing process based on SLM technology includes the following steps:

[0057] Step 1, Material Selection: TC4 (Ti-6Al-4V titanium alloy) metal powder is selected as the matrix material for the lightweight shell. TC4 (Ti-6Al-4V titanium alloy) metal powder, Ti6Al4V (titanium alloy), or 316L stainless steel are selected as the high-strength or corrosion-resistant shell material. A recycled powder collection container is set up in the powder preparation area, and a standard for mixing new powder and recycled powder is established (this standard will be implemented in the recycling closed loop in Step 7).

[0058] Step 2: Lightweight Design Based on SLM Technology: Using ntopology or ANSYS software, topology optimization is employed to reduce the weight of the shell in non-load-bearing or low-stress internal regions. This involves filling the shell with rhombic dodecahedrons or gyroscope-shaped lattice structures and designing three-dimensional curved flow channels and closed internal cavities. The flow channels are required to have smooth transitions and no right-angle bends. Through integrated structural-functional lightweight design, a CAD model of the shell (including external contours, internal lattice structures, and curved flow channels) is obtained. This model will serve as the input for the next step of process simulation.

[0059] Step 3: Optimize process parameters: Based on the material determined in Step 1 (TC4, Ti6Al4V or 316L stainless steel) and the lightweight shell geometry model generated in Step 2 (including features such as lattice structure, three-dimensional curved flow channel and suspended curved surface), optimize the process parameters to obtain the pre-compensated printing model.

[0060] Step 4: Automatic Support Structure Design: Using Magics or Materialise e-Stage software, automatically add support structures to inclined surfaces with an angle less than 45°, horizontal holes, and overhanging curved surfaces in the model. Import the pre-compensated model output from Step 3, complete the support addition and optimization, and export the complete printable model with support structures in .slc or .cli format suitable for slicing preparation. This model will be directly used for slicing and SLM forming in Step 5.

[0061] Step 5. SLM automated forming process: Import the supported model output from Step 4 into the slicing software supporting the SLM device, set the slicing layer thickness consistent with that in Step 3 to generate slicing data, import the slicing data into the SLM forming device, install the substrate after introducing a protective atmosphere, and layer by layer spread powder and melt it according to the process parameters and scanning strategy set in Step 3 to directly form the closed flow channel, overhanging curved surface and internal lattice structure, thereby obtaining a shell blank with a support structure (the substrate and the part are integrated) on the substrate;

[0062] Step 6. Post-processing: After printing, separate the substrate by wire electrical discharge machining, remove most of the support structure (i.e., the support structure designed in Step 4), and successively carry out precision CNC machining, abrasive flow polishing of the internal flow channel, heat treatment and surface protection treatment to meet the requirements of assembly accuracy and sealing performance;

[0063] Step 7. Quality inspection: Through industrial CT non-destructive inspection, mechanical property testing and sealing performance testing, ensure that the internal quality and external accuracy of the shell meet the use requirements. At the same time, complete the powder recycling closed loop to achieve green manufacturing and quality traceability.

[0064] Specifically, in Step 1, the particle size distribution of the TC4 powder is 20 - 60 μm, the particle size distribution of the Ti6Al4V or 316L stainless steel powder is 15 - 53 μm, the powder sphericity ≥ 95%, the oxygen content ≤ 0.2%. The oxygen content is measured by the inert gas pulse infrared thermal conductivity method (oxygen-nitrogen-hydrogen analyzer, such as LECO ONH836). And in the powder preparation stage, keep the TC4 metal powder, Ti6Al4V or 316L stainless steel powder at 100 - 120 °C under vacuum conditions for 2 - 4 hours to remove the moisture and gas in the powder and prevent the generation of pore defects during the printing process.

[0065] Specifically, the recycled powder collection container is designed with anti-static and sealed properties, and is equipped with a vibrating screening device with a 100 - 200 mesh sieve to screen out agglomerated particles or impurities with a particle size > 60 μm. The mixing specification of new powder and recycled powder is: the addition ratio of recycled powder does not exceed 30% (mass fraction). Before mixing each batch, detect the fluidity (Hall flowmeter, ≤ 40 s / 50 g) and oxygen content (≤ 0.25%) of the recycled powder. After mixing, mix it with a three-dimensional mixer at 15 - 20 r / min for 1.5 - 2 h to ensure uniform composition. This specification is achieved by recording the number of times of using recycled powder in each batch (not exceeding 5 times) for closed-loop control in Step 7.

[0066] The advantages are: by clearly defining and accurately detecting key indicators such as particle size, sphericity, and oxygen content of different material powders, combined with vacuum preheating and pretreatment, defects such as poor powder flowability, impurities, and gas content leading to forming pores and incomplete fusion can be effectively avoided; by using antistatic sealed recycling containers and vibrating screening devices, along with scientific mixing specifications for new and recycled powders, efficient recycling and reuse of powders can be achieved, while reducing production costs.

[0067] Specifically, the parameter setting process in step two is as follows:

[0068] (1) Topology optimization: Using ntopology software or ANSYS (using Abacus or ANSYS software), with the goal of reducing the volume by 40%-60%, the main force transmission path is retained and the material in the low stress area is removed;

[0069] (2) Internal lattice structure: Rhombic dodecahedral or gyro-shaped lattice is selected. The rhombic dodecahedral lattice has a unit cell side length of 2-5 mm, a pillar diameter of 0.3-0.8 mm, and a relative density of 10%-25%. The gyro-shaped lattice adopts a three-period minimal surface (TPMS) structure with a unit cell size of 3-6 mm and a volume fraction of 12%-20%.

[0070] (3) Functional integrated flow channel: Design a three-dimensional curved flow channel (smooth transition, no right angle bend) and a closed internal cavity. The minimum curvature radius of the three-dimensional curved flow channel is ≥5mm, the flow channel diameter is designed to be 4-10mm according to the hydraulic power density, and the wall thickness of adjacent flow channels is ≥1.5mm. This realizes the integration of hydraulic pipeline and shell, avoiding the straight line limitation of traditional drilling.

[0071] The advantages are: by precisely removing low-stress redundant materials through topology optimization and combining it with lattice structure filling with specific parameters, a weight reduction of 40%-60% can be achieved while ensuring the load-bearing stiffness and mechanical properties of the shell, thus meeting the lightweight requirements of hydraulic pumps; through the precise control of the minimum radius of curvature, flow channel diameter and adjacent wall thickness in the smooth transition design of the three-dimensional curved flow channel, it can not only effectively avoid the straight line limitation of traditional drilling and realize the integrated integration of hydraulic pipelines and shell, but also reduce fluid resistance. At the same time, the closed internal cavity can adapt to the functional requirements of sealing and heat preservation, ultimately realizing the integrated design of structure and function, and improving the integration and practicality of the shell.

[0072] Specifically, parameter optimization in step three:

[0073] (1) For TC4 powder, the laser power range is 280-350W, the scanning speed is 800-1200mm / s, the scanning spacing is 0.10-0.12mm, and the layer thickness is 30-50μm;

[0074] (2) For Ti6Al4V material, the laser power is 200-280W, the scanning speed is 600-1000mm / s, the scanning spacing is 0.08-0.10mm, and the layer thickness is 30-40μm;

[0075] (3) For 316L stainless steel, the laser power is 180-240W, the scanning speed is 700-1100mm / s, the scanning spacing is 0.10-0.12mm, and the layer thickness is 40-60μm;

[0076] (4) And adopt a strip or chessboard scanning strategy, with a strip width of 5-10 mm and adjacent layers rotated by 67°;

[0077] (5) Set an independent volume energy density of 40 to 60 J / mm³ for the region of the suspended curved surface with an inclination angle of <45°, and use contour offset compensation, setting the outer contour to offset inward by 0.05 to 0.10 mm and the inner contour to offset outward by 0.05 to 0.10 mm;

[0078] Based on the above parameters, printing experiments were conducted on single-pass, single-layer, and block specimens. The parameter windows were verified using a metallographic microscope (porosity <0.5%) and a universal testing machine (tensile strength reaching over 95% of the casting). The thermo-mechanical coupling field of the shell was simulated layer by layer using ANSYS Additive or Materialise Magics Simulation modules to predict deformation and stress distribution, generating a pre-compensated model (STL format). The pre-compensation strategy was as follows: a reverse displacement compensation factor (1.0–1.2 times) was applied to areas with deformation >0.1 mm, and size amplification compensation (magnification factor 1.005–1.015) was applied to pore features with shrinkage >0.05 mm. The compensated model needed to be simulated again for verification, with the maximum deformation controlled within ±0.05 mm.

[0079] The advantages are: by customizing different process parameters such as laser power, scanning speed and layer thickness for different materials, the powder of different materials can be fully melted, which ultimately improves the shell forming density (porosity <0.5%) and mechanical properties (tensile strength reaches more than 95% of the casting).

[0080] Specifically, step four involves the automatic design of support structure parameters:

[0081] (1) For inclined planes with an inclination angle of <45°, a tapered point support is used, with a tip diameter of 0.2 to 0.4 mm, a root diameter of 0.6 to 1.0 mm, and a spacing of 1 to 2 mm;

[0082] (2) The diameter of the horizontal hole is >3mm, and a block support is added below it. The wall thickness is set to 0.3-0.5mm and the tooth gap is 0.5-1.0mm;

[0083] (3) The suspended curved surface adopts tree-shaped or grid-shaped support. The contact surface between the support and the part adopts a sawtooth-shaped break point design, which is convenient for post-processing removal. After the support structure is automatically generated by the software according to the preset rules, the support density of key areas (such as the flow channel inlet and near the sealing surface) is manually adjusted to avoid damage to the functional surface.

[0084] The advantages are: by designing different support types and parameters for different types of suspended structures (sloping surfaces, horizontal holes, suspended curved surfaces), the stability of the support is ensured, thereby effectively preventing the collapse and deformation of the suspended parts during the forming process, and ultimately ensuring the integrity of the forming of the fine structure.

[0085] Specifically, after adding the supports in step four, use Magics' support optimization module to perform collision checks and cutout processing (for block supports with a height > 10mm, make hexagonal cutouts inside, retaining a wall thickness of 0.35-0.4mm) to reduce support volume and powder residue. Export the file in .slc (slice outline format) or .cli (universal layer interface format), with layer thickness information consistent with step three. The exported file needs to be checked for integrity (no missing layers, no outline intersections), and metadata such as the volume, weight, and estimated printing time of the support structure should be saved.

[0086] The advantages are: by checking for collisions and hollowing out the supports, the volume of the supports and the amount of powder residue can be greatly reduced, thereby reducing material waste and post-processing workload. At the same time, the integrity verification of the exported files and the storage of metadata provide a reliable basis for subsequent slicing, forming and quality traceability, ultimately improving the standardization and traceability of the process.

[0087] Specifically, the forming process parameters and monitoring requirements in step five are as follows: a dual-laser (single-mode fiber laser, wavelength 1070nm) or four-laser SLM equipment is selected, with a spot diameter of 70-100μm; the oxygen content in the forming chamber is controlled at ≤0.1%, and high-purity argon (purity ≥99.999%) is used as the protective atmosphere; the substrate material is consistent with the shell material (TC4, Ti6Al4V or 316L stainless steel), the substrate thickness is ≥30mm, and the upper surface is ground to a flatness of ≤0.05mm; Before printing, the substrate is preheated to 40-80℃ (TC4) or 100-150℃ (Ti6Al4V / 316L). The powder spreading blade is made of ceramic or hard alloy. After each layer of powder is spread, a laser sensor is used to detect the thickness of the powder layer. If the deviation exceeds ±5μm, the system will automatically adjust. After each layer melts, infrared thermal imaging is used to monitor the temperature of the molten pool. If the temperature fluctuation exceeds ±10% of the set value, the laser power will be automatically adjusted. Throughout the printing process, the equipment records oxygen content, pressure, temperature and images of each layer in real time for quality traceability.

[0088] The advantages are: by ensuring consistency between the substrate and shell materials, precise control of flatness, and targeted preheating temperature settings, the temperature difference between the substrate and shell is reduced, thereby lowering residual stress and forming deformation; by real-time monitoring and automatic adjustment of powder layer thickness and molten pool temperature, the stability of the forming quality of each layer is ensured, thus avoiding abnormal defects such as incomplete fusion and spheroidization; by recording all parameters in real time during the printing process, complete data support is provided for subsequent quality traceability and process optimization, ultimately improving the controllability and reliability of the shell forming process.

[0089] Specifically, in step six, the post-processing steps are as follows:

[0090] S1.1, Substrate separation: Electrical discharge wire cutting is used, with a cutting speed of 30-50 mm² / min and a cut surface flatness of ≤0.05 mm;

[0091] S1.2, Support Removal: First, use special pliers and ultrasonic vibration (frequency 20-40kHz) to remove the main support. The remaining contact layer is removed by manual grinding or sandblasting (pressure 0.3-0.5MPa, abrasive particle size 100-200).

[0092] S1.3 Precision CNC machining: Micro-cutting is performed on key parts such as assembly surfaces, threaded holes, and sealing grooves, with a single-sided allowance of 0.1-0.3mm, ensuring dimensional tolerance of IT6-IT7 grade and surface roughness Ra≤1.6μm;

[0093] S1.4 Internal flow channel treatment: Abrasive flow polishing is adopted with an abrasive particle size of 100-200 mesh, an extrusion pressure of 5-10 MPa, and 10-20 cycles to reduce the surface roughness of the inner flow channel to Ra≤0.8μm and reduce pressure loss by 20%-30%;

[0094] S1.5 Heat treatment: TC4 material is subjected to stress annealing (holding at 285-300℃ for 2-2.2 hours, then air cooling) or T6 solution aging (solution at 530-535℃ for 1.8-2 hours + aging at 160℃ for 5-6 hours) to eliminate residual stress and improve tensile strength to ≥490MPa.

[0095] S1.6 Surface Protection: The aluminum alloy shell is anodized (film thickness 10-20μm), and the titanium alloy or stainless steel shell is chemically nickel plated (film thickness 5-15μm). Then, an epoxy primer and polyurethane topcoat are sprayed on the outside, and the dry film thickness is controlled at 80-120μm. The double protection improves corrosion resistance and sealing surface hardness.

[0096] The advantages are: through precise control of wire EDM (cutting speed, surface flatness), the shell is ensured to be free from deformation and damage during the separation of the substrate, thus ensuring the dimensional accuracy of the shell; through the support removal method combining ultrasonic vibration and sandblasting, the main support and residual contact layer can be quickly removed, while avoiding damage to the shell surface and internal fine structure.

[0097] Specifically, the testing standards and recycling requirements in step seven are as follows:

[0098] S2.1 Industrial CT inspection: Scanning resolution ≤0.1mm, check the unobstructed flow of internal channels, the integrity of the lattice structure and the presence of unfused holes or cracks. Defect size >0.1mm is considered unqualified.

[0099] S2.2 Mechanical property testing: Print test bars of the same batch (3 in the horizontal direction and 3 in the vertical direction) in the furnace and test tensile strength (target ≥490MPa), yield strength (target ≥250MPa), and elongation after fracture (target ≥8%); perform Vickers hardness testing on key areas (TC4 target ≥120HV).

[0100] S2.3 Sealing test: Pressurize the hydraulic flow channel to 1.5 times the working pressure (typical working pressure is 28MPa, test pressure is 42MPa), hold the pressure for 25-30 minutes, and the leakage rate ≤0.1mL / min is qualified;

[0101] S2.4 Powder recycling closed loop: Collect unmelted powder and metal dust generated during post-processing and polishing in the printing chamber, pass them through a 200-mesh sieve, mix them with new powder and recycled powder at a ratio of 7:3, and return them to step one after testing for qualified oxygen content and particle size distribution for the next batch of production;

[0102] S2.5 Quality Traceability: Each shell is assigned a unique code, which records the material batch number, process parameters, and test data to achieve full-process traceability.

[0103] The advantages are: high-resolution industrial CT non-destructive testing can comprehensively identify defects inside the shell, ensuring unobstructed flow channels and integrity of the lattice structure, and preventing internal defects from affecting the shell's performance; mechanical property testing of furnace test bars and hardness testing of key areas ensure that the shell's mechanical properties meet the standards, ultimately satisfying the load-bearing requirements of the hydraulic pump.

[0104] According to the above-described preparation process of the present invention, combined with different materials and parameters, the following examples, comparative examples, and performance test results are given in detail below:

[0105] Example 1

[0106] This embodiment is basically the same as the preparation process of the present invention, except that: in step one, Ti6Al4V powder (particle size distribution 15-53μm, D50=32μm, sphericity 97%, oxygen content 0.12%) is used; in step two, the lattice structure adopts a gyro-shaped TPMS lattice (unit cell size 4mm, volume fraction 15%); in step three, the Ti6Al4V process parameters are: laser power 240W, scanning speed 800mm / s, scanning spacing 0.09mm, and layer thickness 35μm; in step six, the heat treatment adopts stress-relief annealing (holding at 650℃ for 2h, furnace cooling), and the surface protection adopts chemical nickel plating (film thickness 10μm). The resulting shell has a tensile strength of 950MPa, a yield strength of 860MPa, an elongation after fracture of 12%, and a weight reduction of 52%.

[0107] Example 2

[0108] This embodiment is basically the same as Embodiment 1, except that: Step 1 uses 316L stainless steel powder (particle size distribution 15-53μm, D50=35μm, sphericity 95%, oxygen content 0.18%); Step 3 uses a rhombic dodecahedron lattice structure (unit cell side length 4mm, pillar diameter 0.6mm, relative density 20%); Step 3 316L process parameters: laser power 210W, scanning speed 900mm / s, scanning spacing 0.11mm, layer thickness 50μm; Step 6 heat treatment uses solution treatment (1050℃ for 1h, water quenching), surface protection uses passivation treatment, and the resulting shell has a tensile strength of 520MPa, a yield strength of 240MPa, an elongation after fracture of 28%, and a weight reduction of 48%.

[0109] Comparative Example 1 (Traditional Machining Process)

[0110] The hydraulic pump housing is manufactured using traditional casting and machining processes. The housing is a solid structure, and the hydraulic flow channels are machined through drilling (straight flow channels with right-angle bends). The material is cast TC4. The process flow is: sand casting → heat treatment → CNC rough machining → drilling → CNC finish machining → surface treatment.

[0111] The results show that: the shell weight of Comparative Example 1 is 52% heavier than that of Example 1 (no lightweighting was achieved), the flow channel pressure drop is 35% higher than that of Example 1 (due to right-angle bends), and it is impossible to manufacture internal lattice structures and three-dimensional curved flow channels. The power density is significantly lower than that of the present invention.

[0112] Comparative Example 2 (SLM process but without process parameter optimization and pre-compensation)

[0113] The SLM process was used, but the process parameter optimization and pre-compensation in step three were not performed. The CAD model from step two was used directly for printing, with general parameters (laser power 280W, scanning speed 800mm / s). No independent energy density was set for the suspended curved surface, and no thermo-mechanical coupling simulation and reverse compensation were performed.

[0114] The results showed that the shell printed in Comparative Example 2 had obvious warping deformation (maximum deformation of 0.35 mm), the internal lattice structure collapsed, the flow channel had serious powder adhesion, the porosity was 2.5%, and some dimensions were still out of tolerance after post-processing (assembly surface flatness of 0.12 mm). The leakage rate in the sealing test was 0.25 mL / min (unqualified), and the scrap rate reached 40%.

[0115] Comparative Example 3 (without using powder recovery closed loop)

[0116] The same SLM process as in Example 1 was used, but the powder recycling closed loop was not implemented (the recycled powder mixing specifications in step one and the recycling closed loop in step seven). New powder was used for each batch, and waste powder was not recycled.

[0117] The results showed that the shell quality of Comparative Example 3 was comparable to that of Example 1, but the material utilization rate was only 45% (about 55% of the powder in each batch was not melted and was discarded). The material cost of a single shell was 68% higher than that of Example 1, and a large amount of metal powder waste was generated, which did not meet the requirements of green manufacturing.

[0118] The performance comparison between the embodiments of the present invention and the comparative examples is shown in Table 1 below:

[0119] Table 1

[0120] index Example 1 (Ti6Al4V) Example 2 (316L) Comparative Example 1 (Conventional Machining - Ti6Al4V) Comparative Example 2 (Unoptimized SLM-Ti6Al4V) Comparative Example 3 (Unrecovered powder - Ti6Al4V) Weight loss percentage (%) 52 48 0 50 52 Tensile strength (MPa) 950 520 895 780 948 Yield strength (MPa) 860 240 800 710 855 Elongation after fracture (%) 12 28 10 8.5 11.8 Flow channel pressure loss reduction (%) 30 25 0 12 30 Maximum deformation (mm) 0.03 0.05 0.02 (after CNC) 0.42 0.03 Porosity (%) 0.2 0.4 <0.1 (casting) 3.2 0.2 Leakage rate (mL / min) 0.04 0.08 0.09 0.35 0.04 Material utilization rate (%) 95 94 70 95 48 Relative cost per unit 0.60 0.50 1.00 0.55 1.72

[0121] From Table 1, we can obtain:

[0122] (1) The present invention’s Example 1 (Ti6Al4V) and Example 2 (316L) are superior to Comparative Example 1 (conventional machining, 0% weight reduction, 0% reduction in flow channel pressure loss) in terms of weight reduction ratio (48%~52%), flow channel pressure loss reduction (25%~30%) and material utilization rate (94%~95%). This shows that excellent lightweighting effect and hydraulic performance improvement can be achieved by lattice filling, topology optimization and three-dimensional curved flow channel integration.

[0123] (2) The mechanical properties (tensile strength 950MPa, elongation 12%) and forming accuracy (maximum deformation 0.03mm, porosity 0.2%) of Example 1 of the present invention are far superior to those of Comparative Example 2 (without process parameter optimization and pre-compensation, tensile strength 780MPa, maximum deformation 0.42mm, porosity 3.2%), indicating that the multi-material parameter window, suspended surface energy density control and thermo-mechanical coupling pre-compensation strategy in step three significantly improve the forming quality of complex internal structures.

[0124] (3) The leakage rate (0.04 mL / min) and sealing performance of Example 1 of the present invention meet the requirements of aviation hydraulic system, while the leakage rate (0.35 mL / min) of Comparative Example 2 is unqualified, which can further verify the necessity of process parameter optimization.

[0125] (4) Although the shell quality of Comparative Example 3 is comparable to that of Example 1, the material utilization rate is only 48% and the relative cost per unit is as high as 1.72, indicating that the closed-loop powder recycling in Step 1 and Step 7 of this invention (the proportion of recycled powder added is ≤30%, and the flowability and oxygen content are detected before mixing) has significant advantages in green manufacturing and cost control.

[0126] In summary, this invention achieves the following technical effects through integrated structural-functional lightweight design, multi-material process parameter optimization and pre-compensation, automatic support structure design, strict process monitoring, systematic post-processing, and closed-loop quality inspection and powder recycling throughout the entire process: a 40%–60% reduction in shell weight, a 20%–30% reduction in flow channel pressure loss, a material utilization rate ≥94%, forming accuracy within ±0.05mm, porosity <0.5%, and leakage rate ≤0.1mL / min. Examples 1 (Ti6Al4V) and 2 (316L) respectively verified the applicability of this process to high-strength titanium alloys and corrosion-resistant stainless steel materials. The comparative examples further demonstrate the process optimization and green manufacturing advantages of this invention. The process of this invention significantly improves the power density, reliability, and economy of hydraulic pumps.

[0127] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lightweight hydraulic pump housing manufacturing process based on SLM technology, characterized in that, Includes the following steps: Step 1, Material Selection: TC4 metal powder is selected as the base material for the lightweight shell, and TC4 metal powder, Ti6Al4V or 316L stainless steel is selected as the high-strength or corrosion-resistant shell material. A recycling powder collection container is set up in the powder preparation area, and a standard for mixing new powder and recycled powder is established. Step 2: Lightweight design based on SLM technology: Using ntopology or ANSYS software, topology optimization is used to reduce the weight of the shell in the non-load-bearing or low-stress internal areas, filling it with rhombic dodecahedrons or gyroscope-shaped lattice structures, and designing three-dimensional curved flow channels and closed internal cavities to obtain the CAD model of the shell. Step 3: Optimize process parameters: Based on the material determined in Step 1 and the lightweight shell geometry model generated in Step 2, optimize the process parameters to obtain the pre-compensated printing model; Step 4: Automatic Support Structure Design: Using Magics or Materialise e-Stage software, automatically add support structures to inclined surfaces, horizontal holes, and suspended curved surfaces with an inclination angle of less than 45° in the model. Import the pre-compensation model output in Step 3, complete the support addition and optimization, and export the complete printable model with support structures. Step 5, SLM automated forming process: Import the supported model output from Step 4 into the slicing software that comes with the SLM equipment, set the slicing layer thickness to be the same as in Step 3, generate slicing data, import the slicing data into the SLM forming equipment, and install the substrate after introducing a protective atmosphere. According to the process parameters and scanning strategy set in Step 3, a shell blank with a support structure is obtained on the substrate. Step 6, Post-processing: After printing, the substrate is separated by wire electrical discharge machining, the support structure is removed, and then precision CNC machining, internal flow channel abrasive polishing, heat treatment and surface protection treatment are performed in sequence. Step 7, Quality Inspection: Through industrial CT non-destructive testing, mechanical property testing, and sealing testing, a closed-loop powder recycling system is completed to achieve green manufacturing and quality traceability.

2. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, In step one, the particle size distribution of TC4 powder is 20-60 μm, and the particle size distribution of Ti6Al4V or 316L stainless steel powder is 15-53 μm. The sphericity of the powder is ≥95%, and the oxygen content is ≤0.2%. In the powder preparation stage, TC4 metal powder, Ti6Al4V or 316L stainless steel powder are kept at 100-120℃ under vacuum for 2-4 hours.

3. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, The recycled powder collection container adopts an anti-static and sealed design and is equipped with a vibrating sieving device with a 100-200 mesh screen to remove agglomerated particles or impurities with a particle size >60μm. The mixing and use specifications for new powder and recycled powder are as follows: the proportion of recycled powder added shall not exceed 30%.

4. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, The parameter setting process in step two is as follows: (1) Topology optimization: ntopology or ANSYS software is used to reduce the volume by 40%-60%; (2) Internal lattice structure: Rhombic dodecahedral or gyro-shaped lattice is selected. The rhombic dodecahedral lattice has a unit cell side length of 2-5 mm, a support diameter of 0.3-0.8 mm, and a relative density of 10%-25%. The gyro-shaped lattice adopts a three-period minimal surface structure, with a unit cell size of 3-6 mm and a volume fraction of 12%-20%. (3) Functional integrated flow channel: Design a three-dimensional curved flow channel and a closed internal cavity. The minimum curvature radius of the three-dimensional curved flow channel is ≥5mm, the flow channel diameter is designed to be 4-10mm according to the hydraulic power density, and the wall thickness of adjacent flow channels is ≥1.5mm, so as to realize the integration of hydraulic pipeline and shell.

5. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, Parameter optimization in step three: (1) For TC4 powder, the laser power range is 280-350W, the scanning speed is 800-1200mm / s, the scanning spacing is 0.10-0.12mm, and the layer thickness is 30-50μm; (2) For Ti6Al4V material, the laser power is 200-280W, the scanning speed is 600-1000mm / s, the scanning spacing is 0.08-0.10mm, and the layer thickness is 30-40μm; (3) For 316L stainless steel, the laser power is 180-240W, the scanning speed is 700-1100mm / s, the scanning spacing is 0.10-0.12mm, and the layer thickness is 40-60μm; (4) And adopt a strip or chessboard scanning strategy, with a strip width of 5-10 mm and adjacent layers rotated by 67°; (5) Set an independent volume energy density of 40 to 60 J / mm³ for the region of suspended curved surface with an inclination angle of <45°, and use contour offset compensation, setting the outer contour to offset inward by 0.05 to 0.10 mm and the inner contour to offset outward by 0.05 to 0.10 mm.

6. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, The automatic support structure parameter design in step four: (1) For inclined planes with an inclination angle of <45°, a tapered point support is used, with a tip diameter of 0.2 to 0.4 mm, a root diameter of 0.6 to 1.0 mm, and a spacing of 1 to 2 mm; (2) The diameter of the horizontal hole is >3mm, and a block support is added below it. The wall thickness is set to 0.3-0.5mm and the tooth gap is 0.5-1.0mm; (3) The suspended curved surface adopts tree-shaped or grid-shaped support. The contact surface between the support and the part adopts a sawtooth-shaped break point design. The support structure is automatically generated by the software according to the preset rules, and the support density near the flow channel inlet and the sealing surface is manually adjusted.

7. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 5, characterized in that, After the support is added in step four, use Magics' support optimization module to perform collision checks and hollowing out. For block supports with a height > 10mm, make hexagonal hollowing out inside, and retain a wall thickness of 0.35-0.4mm.

8. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, The forming process parameters and monitoring requirements in step five are as follows: (1) Use dual lasers and set the spot diameter to 70-100μm; control the oxygen content in the forming chamber to ≤0.1% and use argon gas with a purity of ≥99.999% as a protective atmosphere; the substrate material is the same as the shell material, the substrate thickness is ≥30mm, and the upper surface is ground to a flatness of ≤0.05mm; (2) Before printing, the substrate made of TC4 metal powder is preheated to 40-80℃ or the substrate made of Ti6Al4V / 316L is preheated to 100-150℃; the powder spreading squeegee is made of ceramic or hard alloy material, and the thickness of the powder layer is detected by laser sensor after each layer of powder is spread. When the deviation exceeds ±5μm, it is automatically adjusted; after each layer is melted, the temperature of the melt pool is monitored by infrared thermal imaging. When the temperature fluctuation exceeds ±10% of the set value, the laser power is automatically adjusted.

9. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, In step six, the post-processing steps are as follows: S1.1, Substrate separation: Electrical discharge wire cutting is used, with a cutting speed of 30-50 mm² / min and a cut surface flatness of ≤0.05 mm; S1.2, Support Removal: First, use special pliers to remove the main support by ultrasonic vibration at a frequency of 20-40kHz. The remaining contact layer is removed by sandblasting. S1.3 Precision CNC machining: Micro-cutting is performed on the assembly surface, threaded holes and sealing grooves, with a single-sided allowance of 0.1-0.3mm, ensuring dimensional tolerance of IT6-IT7 grade and surface roughness Ra≤1.6μm; S1.4 Internal flow channel treatment: Abrasive flow polishing is adopted, with abrasive particle size of 100-200 mesh, extrusion pressure of 5-10MPa, and number of cycles of 10-20. S1.5 Heat treatment: After holding the TC4 material at 285-300℃ for 2-2.2 hours, stress annealing is carried out under air cooling conditions; S1.6 Surface Protection: The aluminum alloy shell is anodized with a film thickness controlled at 10-20μm, and the titanium alloy or stainless steel shell is electroless nickel plated with a film thickness controlled at 5-15μm. Then, an epoxy primer and polyurethane topcoat are sprayed on the outside, with the dry film thickness controlled at 80-120μm.

10. The lightweight hydraulic pump housing manufacturing process based on SLM technology according to claim 1, characterized in that, In step seven, the testing standards and recycling requirements are as follows: S2.1 Industrial CT inspection: Check the unobstructed flow of internal channels, the integrity of the lattice structure, and the presence of unfused holes or cracks. Defects larger than 0.1mm are considered unqualified. S2.2 Mechanical property testing: Print 3 horizontal and 3 vertical test bars of the same batch in the furnace and test tensile strength, yield strength, elongation after fracture and Vickers hardness. S2.3 Sealing test: Pressurize the hydraulic flow channel to 1.5 times the working pressure and hold the pressure for 25-30 minutes. A leakage rate of ≤0.1mL / min is acceptable. S2.4 Powder recycling closed loop: Collect unmelted powder and metal dust generated during post-processing grinding in the printing chamber, pass them through a 200-mesh sieve, mix them with new powder and recycled powder at a ratio of 7:3, and return them to step one after testing for qualified oxygen content and particle size distribution for use in the next batch of production; S2.5 Quality Traceability: Each shell is assigned a unique code, which records the material batch number, process parameters, and test data to achieve full-process traceability.

Images