Rainwater and sewage electric well cover prefabricated mold 3D printing production process

Abstract

The application discloses a rain and sewage electric well lid prefabricated mold 3D printing production process, belongs to the prefabricated component mold manufacturing technical field of municipal engineering. The process comprises eight steps of demand analysis and mold three-dimensional modeling, topology optimization and lightweight design, layered slicing and printing path planning, 3D printing forming, post-printing processing, functional coating preparation, mold assembly and debugging and prefabricated well lid trial production. The application adopts additive manufacturing technology to directly form the prefabricated mold, realizes lightweight design through topology optimization, improves cooling efficiency through conformal cooling runner, considers surface precision and printing efficiency through gradient printing strategy, and improves the wear resistance and demolding performance of the mold through functional coating. The application overcomes the defects of long manufacturing cycle, difficulty in manufacturing complex structure and serious material waste of the traditional mold, realizes rapid, accurate, efficient and green manufacturing of the well lid prefabricated mold, and has remarkable industrial practical value and broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of prefabricated component mold manufacturing technology for municipal engineering, and in particular to a 3D printing production process for prefabricated molds for rainwater, sewage and power manhole covers, especially a process method for producing molds for prefabricated rainwater manhole covers, sewage manhole covers and power manhole covers using additive manufacturing technology. Background Technology

[0002] Manhole covers are an indispensable component in municipal infrastructure construction, widely used in urban roads, residential areas, industrial parks, and other locations for sealing the entrances and exits of underground pipelines such as rainwater drainage, sewage transportation, and power cable laying. Based on their usage scenarios, manhole covers are mainly divided into three categories: rainwater manhole covers, sewage manhole covers, and power cable manhole covers, corresponding to the sealing and covering of rainwater inspection wells, sewage inspection wells, and power cable wells, respectively.

[0003] Currently, manhole covers are mainly produced using prefabrication, where concrete, steel fiber reinforced concrete, or composite materials are poured into molds in a factory, cured to the required strength, and then transported to the construction site for installation. Prefabricated manhole covers offer high production efficiency and controllable quality, making them suitable for large-scale engineering projects. However, the molds used in the production of prefabricated manhole covers have long relied on traditional manufacturing processes, resulting in numerous technical bottlenecks.

[0004] Traditional manhole cover prefabrication molds are mainly manufactured using steel or engineering plastics through machining, sheet metal welding, or injection molding. Steel molds use steel plates as the main material, processed through sheet metal techniques such as cutting, bending, welding, and grinding, and employ an inner and outer mold combination structure for demolding. Plastic molds are injection molded using engineering plastics such as polypropylene. These traditional mold manufacturing methods have the following significant drawbacks: First, the manufacturing cycle is long. Traditional steel molds require multiple processes from design to finished product delivery, including material preparation, cutting, bending, welding, grinding, and assembly, with a manufacturing cycle typically lasting several weeks or even months. For the production needs of small batches and multiple varieties of manhole covers, the long manufacturing cycle of traditional molds severely restricts the production response speed.

[0005] Secondly, it is difficult to manufacture complex structures. Traditional mold manufacturing is limited by processing technology, making it difficult to form complex cooling channels, reinforcing rib structures, or fine anti-slip textures inside the mold. In particular, for manhole covers with special patterns, text markings, or irregular shapes, the production of traditional molds is difficult and costly.

[0006] Third, there is significant material waste. The manufacturing of steel molds is a typical subtractive manufacturing process, resulting in substantial material loss during cutting, milling, and grinding. While injection molding of plastic molds has a higher material utilization rate, the machining of the mold cavity still requires numerous machining operations.

[0007] Fourth, mold modification is difficult. Once the mold is manufactured, any design change means rework or even remanufacturing the mold, leading to a sharp increase in development costs and making it difficult to adapt to the rapid iteration and customization needs of manhole cover products.

[0008] Fifth, low cooling efficiency. Traditional molds typically use simple straight-line drilling or external cooling methods for cooling channels, resulting in low cooling efficiency. This leads to prolonged curing time for concrete or composite materials during the prefabrication of manhole covers, limiting production efficiency.

[0009] In recent years, 3D printing technology has begun to be applied in the mold manufacturing field. Also known as additive manufacturing, 3D printing offers advantages over subtractive and equal-material manufacturing, including high efficiency, unique features, and intelligent design and processing. There are studies using 3D printing to create physical models of manhole covers, and reports of directly printing manhole covers using 3D printing. In the mold industry, 3D printing sand mold technology has been used for the rapid manufacturing of casting molds, significantly shortening the trial production cycle for complex, irregularly shaped manhole covers. However, currently, there is no systematic application of 3D printing technology to the entire production process of prefabricated molds for stormwater, sewage, and power manhole covers.

[0010] Therefore, there is an urgent need to develop a prefabrication process for rainwater, sewage, and power manhole covers that can overcome the defects of traditional mold manufacturing, achieve rapid response, manufacture complex structures, have high material utilization, and have excellent cooling efficiency. Summary of the Invention

[0011] This invention addresses the technical problems of existing prefabricated molds for rainwater, sewage, and power manhole covers, such as long manufacturing cycles, difficulty in manufacturing complex structures, serious material waste, difficulty in modification, and low cooling efficiency. It provides a 3D printing production process for prefabricated molds for rainwater, sewage, and power manhole covers, aiming to achieve rapid, precise, efficient, and green manufacturing of manhole cover prefabricated molds.

[0012] The above-mentioned objective of this invention is achieved through the following technical solutions: This invention provides a 3D printing production process for prefabricated molds for stormwater and sewage power manhole covers, comprising the following steps: Step 1: Based on the usage scenario, load-bearing capacity, specifications, and appearance requirements of the stormwater, sewage, and power manhole covers, determine the design parameters of the prefabricated mold. These parameters include mold type, mold size, cavity structure, draft angle, parting line position, and cooling channel layout. Use 3D modeling software to create a 3D solid model of the prefabricated mold. This model includes the 3D geometric information of the upper mold assembly, lower mold assembly, cavity, cooling channels, gating system, and ejection mechanism. Step 2: Perform finite element analysis and topology optimization on the 3D solid model established in Step 1. Based on the stress distribution, temperature field distribution, and thermal stress distribution of the mold in actual use, remove low-stress redundant materials from the model to form a lightweight structure while ensuring the strength and stiffness of the mold structure, thus obtaining the optimized 3D mold model. The topology optimization takes minimizing the mold mass as the objective function and uses the constraint that the maximum stress of the mold does not exceed the allowable stress of the material and the maximum deformation does not exceed the preset deformation threshold. Step 3: The optimized 3D mold model obtained in Step 2 is sliced ​​along the height direction according to a preset layer thickness, converting the 3D model into a series of 2D contour information; based on the contour information of each layer and combined with the process parameters of the 3D printing equipment, the scanning path and printing strategy for 3D printing are planned, and 3D printing control code is generated; the preset layer thickness is 0.02mm to 0.2mm. Step 4: Import the 3D printing control code generated in Step 3 into the 3D printing equipment, and use additive manufacturing to deposit the molding material layer by layer to print the blank of the pre-made mold; the 3D printing equipment is one of selective laser melting equipment, selective laser sintering equipment, electron beam melting equipment, or binder jet molding equipment; the molding material is one or a combination of mold steel powder, stainless steel powder, nickel-based alloy powder, cobalt-chromium alloy powder, or ceramic powder; Step 5: Remove the pre-made mold blank obtained in Step 4 from the 3D printing equipment and perform powder cleaning to remove unsintered powder remaining on the surface and inside of the blank. Then, perform heat treatment on the blank, which includes stress-relieving annealing and / or solution aging treatment to eliminate thermal stress and microstructure defects generated during the printing process. After heat treatment, perform surface finishing, which includes one or more combinations of grinding, polishing, sandblasting or CNC milling, so that the surface roughness of the mold cavity reaches Ra≤0.8μm and the dimensional accuracy of the mold reaches within ±0.05mm. Step Six: Prepare a functional coating on the mold cavity surface and the inner wall of the cooling channel after the treatment in Step Five; the functional coating is one or more of the following: wear-resistant coating, anti-corrosion coating, release coating, or thermally conductive coating; the preparation method of the functional coating is one of physical vapor deposition, chemical vapor deposition, thermal spraying, electroplating, or electroless plating. Step 7: Assemble the upper and lower mold components processed in Step 6, install the ejection mechanism, gating system, and cooling system interfaces, and assemble them into a complete precast mold; perform mold closing and demolding debugging, and cooling system sealing test on the assembled precast mold to ensure that the mold components move smoothly and that the fitting accuracy meets the design requirements; Step 8: Using the precast mold assembled in Step 7, precast rainwater, sewage, and power manhole covers are produced. Concrete, steel fiber concrete, or composite material is poured into the mold cavity, compacted by vibration, cured, and then demolded to obtain the precast manhole cover. The precast manhole cover is then subjected to quality inspection, and the mold is fine-tuned and optimized based on the inspection results.

[0013] According to one embodiment of the present invention, the prefabricated mold is a modular mold, including a mold base, a mold cover plate, and replaceable cavity inserts; The mold base and mold cover are integrally formed by 3D printing. The cavity insert is an independent component that can be detachably installed between the mold base and the mold cover. Different specifications of cavity inserts correspond to manhole cover products of different specifications and patterns.

[0014] According to one embodiment of the present invention, the cooling channel is a conformal cooling channel, and the direction of the conformal cooling channel is adapted to the surface contour of the mold cavity, so that the wall thickness of the cooling channel at each point is basically consistent with the distance from the surface of the mold cavity. The cross-sectional shape of the conformal cooling channel is one of circular, elliptical, rectangular or D-shaped, and the equivalent diameter of the conformal cooling channel is 4 mm to 12 mm.

[0015] According to one embodiment of the present invention, in the 3D printing process of step four, a gradient printing strategy is adopted, that is, the outer surface layer of the mold is printed with fine powder and low layer thickness for high precision, and the inner core layer of the mold is printed with coarse powder and high layer thickness for rapid printing. The outermost layer has a printing thickness of 0.02 mm to 0.05 mm, and the inner core layer has a printing thickness of 0.08 mm to 0.2 mm.

[0016] According to one embodiment of the present invention, the heat treatment in step five is a step-by-step heat treatment, including: a first heat treatment stage, stress-relief annealing is performed by holding at a temperature of 400°C to 600°C for 1 to 3 hours; In the second heat treatment stage, solution treatment is carried out by holding the temperature at 800℃ to 1050℃ for 0.5 hours to 2 hours. The third heat treatment stage involves aging at 500℃ to 700℃ for 2 to 6 hours.

[0017] According to one embodiment of the present invention, the functional coating in step six is ​​a composite coating, which includes a transition layer, a functional layer and a surface layer from the inside out. The transition layer is made of titanium, chromium, or nickel; the functional layer is made of titanium nitride, chromium nitride, aluminum titanium nitride, diamond-like carbon, or tungsten carbide; and the surface layer is made of polytetrafluoroethylene, molybdenum disulfide, or graphene.

[0018] According to one embodiment of the present invention, the topology optimization in step two adopts a two-way progressive structural optimization method or a variable density method, with the optimization objective being to minimize the strain energy or flexibility of the mold, and the constraint being that the volume fraction does not exceed 60% to 80% of the original volume, and iterative optimization is used to obtain a lightweight structure.

[0019] According to one embodiment of the present invention, in the trial production of the precast manhole cover in step eight, the castable material is filled into the mold cavity using a vibration molding process or a compression molding process. The vibration molding process has a vibration frequency of 30Hz to 80Hz, an amplitude of 0.5mm to 2mm, and a vibration time of 30 seconds to 120 seconds. The pressing pressure of the compression molding process is 5MPa to 30MPa, and the holding time is 10 seconds to 60 seconds.

[0020] According to one embodiment of the present invention, the 3D printing equipment is a selective laser melting device, the forming material is mold steel powder, the particle size distribution of the mold steel powder is 15μm to 53μm, the laser power of the selective laser melting device is 200W to 1000W, the scanning speed is 200mm / s to 2000mm / s, and the scanning spacing is 0.05mm to 0.15mm.

[0021] According to one embodiment of the present invention, the inner wall of the cavity of the prefabricated mold is provided with an anti-slip texture molding structure, a text logo molding structure, or a pattern decoration molding structure. The anti-slip texture molding structure, text logo molding structure, or pattern decoration molding structure is integrally modeled with the mold cavity in the three-dimensional modeling of the mold in step one, and integrally printed with the mold body in the 3D printing molding in step four.

[0022] In summary, compared with the prior art, the present invention includes at least one of the following beneficial technical effects: The manufacturing cycle is significantly shortened. This invention uses 3D printing additive manufacturing technology to directly form prefabricated molds, eliminating the need for multiple complex processes in traditional manufacturing. The process from a 3D model to a mold blank can be completed in hours to days, which is significantly more efficient than the manufacturing cycle of traditional steel molds, which can take weeks to months.

[0023] It can manufacture complex and intricate structures. This invention uses 3D printing technology to build up layers one by one, which can create complex cavity structures, conformal cooling channels, fine anti-slip textures and text patterns that are difficult to achieve with traditional processes, without being limited by draft angle and tool accessibility.

[0024] High material utilization and environmentally friendly. This invention uses additive manufacturing, achieving a material utilization rate of over 90%, far exceeding the 50% to 70% of traditional subtractive manufacturing. This significantly reduces material waste and aligns with the concept of green manufacturing.

[0025] The design is flexible and iterative. This invention allows for rapid changes to the mold design simply by modifying the 3D model data, without the need to remake tooling fixtures, making it particularly suitable for small-batch, multi-variety, and customized manhole cover production needs.

[0026] Excellent cooling efficiency. This invention uses 3D printing technology to create conformal cooling channels, so that the direction of the cooling channels matches the surface contour of the mold cavity. The cooling efficiency is increased by more than 40% compared with traditional straight-line drilling cooling channels, effectively shortening the curing time in the prefabrication process of manhole covers.

[0027] The mold has a long service life. This invention achieves lightweight design through topology optimization, reducing stress concentration; it balances high precision of the outer surface layer with high efficiency of the inner core layer through a gradient printing strategy; and it improves the wear resistance, corrosion resistance, and demolding performance of the cavity surface through functional coatings, thus comprehensively extending the mold's service life.

[0028] The products exhibit excellent consistency. The prefabricated molds manufactured using this invention have a dimensional accuracy within ±0.05mm and a cavity surface roughness Ra≤0.8μm, ensuring the dimensional consistency and surface quality of the prefabricated manhole covers. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the overall process of 3D printing production of prefabricated molds for rainwater, sewage, and power manhole covers according to the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] Example 1 This embodiment provides a 3D printing production process for prefabricated molds of rainwater and sewage well covers, specifically used to produce circular prefabricated molds for rainwater well covers with a diameter of 700mm.

[0032] The 3D printing production process of the prefabricated mold for stormwater and sewage power manhole covers of this invention comprises eight main steps: Step 1: Requirements analysis and 3D modeling of the mold; Step 2: Topology optimization and lightweight design; Step 3: Layer slicing and printing path planning; Step 4: 3D printing molding; Step 5: Post-printing processing; Step 6: Preparation of functional coating; Step 7: Mold assembly and debugging; Step 8: Trial production of the prefabricated manhole cover. The order and interrelationship of the above steps are as follows: Figure 1 As shown.

[0033] In step one of this embodiment, the design parameters are first determined based on the usage scenario of the storm drain cover. This storm drain cover is used for storm drain inspection wells on urban roads, with a design load-bearing capacity of D400 (corresponding to EN 124 standard, applicable to roadways), a cover diameter of 700mm, a cover thickness of 60mm, and the surface of the cover must be provided with anti-slip texture and the word "storm water" markings.

[0034] Based on the above design parameters, a three-dimensional solid model of the prefabricated mold was created using SolidWorks 3D modeling software. This 3D solid model includes the three-dimensional geometric information of the upper mold assembly, lower mold assembly, cavity, conformal cooling channels, gating system, and ejection mechanism. The upper mold assembly forms the upper surface shape of the manhole cover, including the anti-slip texture and text marking structures; the lower mold assembly forms the lower surface and sidewall shapes of the manhole cover; the cavity is a closed space formed after the mold is closed, and its shape is consistent with the outline of the finished manhole cover.

[0035] In this embodiment, the mold cavity has a diameter of 700 mm and a depth of 60 mm, with a draft angle of 1.5°. The initial layout of the conformal cooling channels is arranged around the contour of the cavity, with three annular cooling channels spaced 30 mm apart. The gating system is located on one side of the mold and uses a top-gating method. The ejector mechanism is located at the bottom of the lower mold assembly, using four evenly distributed ejector pins.

[0036] In step two, the three-dimensional solid model established in step one is imported into the ANSYS finite element analysis software for finite element analysis and topology optimization.

[0037] First, the mold model was meshed using tetrahedral elements with a size of 5mm, generating approximately 1.2 million elements. Then, the material properties were set: the mold material is 18Ni300 maraging steel with an elastic modulus of 210GPa, a Poisson's ratio of 0.3, a yield strength of 1800MPa, and a density of 8.0g / cm³.

[0038] Boundary conditions are set as follows: The maximum pouring pressure that the mold withstands during the production of precast manhole covers is 15 MPa, and this pressure is applied uniformly to the surface of the cavity. The mold base is fixed and constrained, and the temperature field is set to 60°C for the surface temperature of the cavity at the moment of pouring and 20°C for the inner wall temperature of the cooling channel.

[0039] Topology optimization was performed using the variable density method, with the optimization objective being the minimization of the mold's flexibility. Constraints included a volume fraction not exceeding 70% of the original volume, a maximum stress not exceeding 80% of the material's allowable stress, and a maximum deformation not exceeding 0.1 mm. After 50 iterations, the optimized 3D mold model was obtained.

[0040] Before topology optimization, the mold structure had a relatively uniform material distribution and many low-stress areas. After topology optimization, the lightweight mold structure eliminated redundant material in the low-stress areas, forming a hollow, lightweight structure while ensuring structural strength and stiffness. Calculations show that the optimized mold reduced its mass by approximately 32%, while the maximum stress remained within the allowable stress range of the material, and the maximum deformation was 0.07 mm, meeting the design requirements.

[0041] In step three, the optimized 3D mold model obtained in step two is imported into the 3D printing preprocessing software in STL format, and layered and sliced ​​along the height direction according to the preset layer thickness.

[0042] The 3D mold model is cut into a series of thin layers with a thickness of 0.05mm along the Z-axis (i.e., the preset layer thickness is 0.05mm). Each layer contains the 2D contour information of the mold cross-section at that height. Through layer processing, the 3D model is converted into hundreds to thousands of layers of 2D contour data.

[0043] Based on the contour information of each layer and the process parameters of the selective laser melting equipment, the scanning path and printing strategy for 3D printing are planned. A strip-style scanning strategy is adopted for the scanning path, with the scanning direction rotating 67° per layer to reduce anisotropy. For critical areas such as the outer contour of the mold and the surface of the cavity, a contour scanning strategy is used for fine scanning. Finally, 3D printing control code containing information such as the scanning path, laser power, and scanning speed is generated.

[0044] In step four, the 3D printing control code generated in step three is imported into the selective laser melting 3D printing equipment, and the additive manufacturing method is used to deposit the molding material layer by layer to print the blank of the pre-made mold.

[0045] The 3D printing process is carried out in an inert gas protective atmosphere, with the protective gas being high-purity argon (purity ≥99.999%). The substrate is made of the same 18Ni300 maraging steel as the mold material, and the substrate preheating temperature is controlled at 100℃.

[0046] In this embodiment, the forming material is 18Ni300 martensitic aging steel powder with a particle size distribution of 15μm to 53μm and a sphericity ≥0.95. The process parameters of the selective laser melting equipment are as follows: laser power of 350W, laser spot diameter of 80μm, scanning speed of 800mm / s, scanning interval of 0.10mm, and preset layer thickness of 0.05mm.

[0047] During the printing process, a squeegee evenly spreads a layer of powder onto the molding substrate. The laser beam selectively melts the powder material according to the slice outline information. After one layer is printed, the molding cylinder descends to the height of one layer thickness, and the squeegee spreads powder again. This cycle continues until all layers are printed. The entire printing process lasts approximately 72 hours, resulting in a pre-made mold blank. The blank size allows for a machining allowance of 0.3mm to 0.5mm compared to the final size.

[0048] In this embodiment, the anti-slip textured molding structure and the text marking molding structure provided on the inner wall of the prefabricated mold cavity are modeled integrally with the mold cavity in the three-dimensional modeling of the mold in step one, and integrally printed with the mold body in the 3D printing molding in step four, without the need for additional machining processes.

[0049] In step five, the pre-formed mold blank obtained in step four is removed from the 3D printing equipment and subjected to powder cleaning. A combination of high-pressure gas purging and ultrasonic vibration is used to remove residual unsintered powder from the surface of the blank and its internal cooling channels. The powder cleaning process uses a gas pressure of 0.6 MPa, an ultrasonic vibration frequency of 40 kHz, and a processing time of 30 minutes.

[0050] After the powder cleaning is completed, the blank is subjected to heat treatment. In this embodiment, the heat treatment is a step-by-step heat treatment, including three heat treatment stages: The first heat treatment stage (stress-relief annealing): The temperature is increased from room temperature to 480°C at a heating rate of 5°C / min, and held at 480°C for 2 hours for stress-relief annealing. Then, it is cooled in the furnace to 200°C at a cooling rate of 3°C / min, and then removed and air-cooled to room temperature. This stage is used to eliminate the thermal stress generated during the 3D printing process.

[0051] The second heat treatment stage (solution treatment): The temperature is increased from room temperature to 920°C at a rate of 8°C / min, and held at 920°C for 1 hour for solution treatment, followed by rapid water quenching to room temperature (transfer time not exceeding 15 seconds). This stage is used to ensure that the precipitated phase is fully dissolved into the matrix.

[0052] The third heat treatment stage (aging treatment): The temperature is increased from room temperature to 540℃ at a heating rate of 5℃ / min, and held at 540℃ for 4 hours for aging treatment, followed by air cooling to room temperature. This stage is used to ensure uniform precipitation of the reinforcing phase, thereby improving the hardness and strength of the mold.

[0053] After heat treatment, the blank is finished. A CNC five-axis milling machine is used to precision mill the parting surface and mounting reference surface of the mold, achieving a dimensional accuracy of ±0.03mm. Grinding is then used to finely grind the cavity surface, achieving a surface roughness of Ra≤0.4μm. Polishing is then used to polish the corners and fine structural areas of the cavity, eliminating grinding marks. Sandblasting is used to treat the non-working surfaces of the mold, improving appearance quality and the adhesion of subsequent coatings.

[0054] After the above post-processing, the dimensional accuracy of the mold reaches ±0.03mm, and the surface roughness of the cavity Ra≤0.4μm, which meets the design requirements.

[0055] In step six, a functional coating is prepared on the surface of the mold cavity and the inner wall of the cooling channel after the treatment in step five. The functional coating in this embodiment is a composite coating, which includes a transition layer, a functional layer and a surface layer from the inside out.

[0056] The transition layer is made of titanium and is prepared using magnetron sputtering physical vapor deposition, with a thickness of 0.5 μm. The function of the transition layer is to improve the adhesion between the functional layer and the mold substrate, preventing coating peeling.

[0057] The functional layer is made of titanium nitride and is prepared using cathodic arc physical vapor deposition, with a thickness of 3 μm. The titanium nitride functional layer has high hardness (approximately 2300 HV), good wear resistance, and excellent chemical stability, effectively protecting the mold cavity surface from wear and corrosion by the casting material.

[0058] The surface layer is made of diamond-like carbon (DLC) and prepared using plasma-enhanced chemical vapor deposition (PECVD), with a thickness of 0.5 μm. The DLC surface layer has an extremely low coefficient of friction (approximately 0.05 to 0.1), which significantly improves the mold's release performance, making the demolding of precast manhole covers smoother and reducing demolding damage.

[0059] After the coating was prepared, the coating adhesion was tested using the scratch test, with a critical load ≥60N; the coating hardness was tested using a microhardness tester, with a hardness ≥2000HV; and the coating friction coefficient was tested using a tribometer, with a friction coefficient ≤0.12. All test results met the design requirements.

[0060] In step seven, the upper mold assembly and lower mold assembly processed in step six are assembled.

[0061] The assembled precast mold consists of an upper mold assembly and a lower mold assembly, which are precisely positioned and guided by a guide post and guide sleeve structure. The upper mold assembly contains a gating system, including a pouring cup, a sprue, and a runner, used to introduce the refractory material into the cavity. The lower mold assembly contains an ejection mechanism, including four ejector rods and an ejector rod fixing plate, used to eject the finished product from the cavity after the manhole cover has cured and formed.

[0062] The conformal cooling channels are located inside the upper and lower mold assemblies, with cooling medium interfaces at both ends for connecting to an external cooling circulation system. Circulating water is used as the cooling medium, with the inlet temperature controlled between 15°C and 20°C.

[0063] After assembly, the precast mold is tested by repeatedly opening and closing it 20 times to check the mold closing accuracy and smoothness of movement. The gap between the parting surfaces after mold closing should not exceed 0.02mm. Demolding is then tested by simulating ejection 30 times to check the smoothness of the ejector pin movement and the synchronization of ejection. Finally, a cooling system sealing test is performed by introducing 0.8MPa compressed air into the cooling channels and holding the pressure for 5 minutes. The pressure drop should not exceed 0.02MPa to confirm that the cooling system is leak-free.

[0064] In step eight, the prefabricated mold assembled in step seven is used to produce the rainwater well cover.

[0065] This embodiment employs a vibration molding process. The precast mold is placed on a vibration platform, and after mold closing, steel fiber reinforced concrete castable is filled into the mold cavity through a gating system. The mix ratio of the castable is: cement: sand: stone: water: steel fiber = 1:1.8:2.6:0.4:0.12 (mass ratio), with steel fibers having a length of 25mm and a diameter of 0.5mm.

[0066] After pouring, the vibration platform is activated for compaction. The vibration frequency is 50Hz, the amplitude is 1.0mm, and the vibration time is 60 seconds. During the compaction process, the castable material flows fully under the vibration and expels air bubbles, filling every corner of the cavity, including the fine parts of the anti-slip textured structure and the text marking structure.

[0067] After vibration, the mold is moved to the curing room for curing. The curing temperature is 20℃±2℃, the relative humidity is ≥95%, and the curing time is 24 hours. After curing, the precast manhole cover is ejected from the mold cavity and demolded using the ejection mechanism.

[0068] After demolding, quality inspection is performed on the prefabricated manhole cover finished product. The inspection contents include: appearance quality inspection (no defects such as honeycombs, pockmarks, cracks, etc.), dimensional accuracy measurement (diameter deviation ≤ ±1mm, thickness deviation ≤ ±0.5mm), load-bearing capacity test (meeting the D400 grade requirements), and anti-slip performance test (anti-slip coefficient ≥ 0.6). All inspection results are qualified.

[0069] According to the pilot production inspection results, all parts of the mold move smoothly, the cooling effect is good (the single production cycle time is reduced by about 30% compared with the traditional mold), the product dimensional consistency is good, and all performance indicators meet the design requirements. So far, the verification of the 3D printing production process for the rain and sewage manhole cover prefabricated mold is completed.

[0070] Second Embodiment This embodiment provides a 3D printing production process for a sewage manhole cover prefabricated mold, which is specifically used to produce a circular sewage manhole cover prefabricated mold with a diameter of 800mm. The differences between this embodiment and the first embodiment mainly lie in the mold specification, molding material, printing process parameters, coating scheme and other aspects.

[0071] The sewage manhole cover of this embodiment is used for urban sewage inspection wells, with a designed load-bearing grade of E600 (corresponding to the EN 124 standard, suitable for high-load-bearing areas), a manhole cover diameter of 800mm, a manhole cover thickness of 70mm, and the surface of the manhole cover needs to be provided with the "sewage" character mark and annular anti-slip patterns.

[0072] UG NX 3D modeling software is used to establish a 3D solid model of the prefabricated mold. Compared with the first embodiment, the diameter of the mold cavity in this embodiment is 800mm, the depth is 70mm, and the demolding taper is set to 2°. Since the load-bearing grade of the sewage manhole cover is higher, the wall thickness of the mold is increased accordingly, and the structural rigidity requirements of the upper mold assembly and the lower mold assembly are higher.

[0073] The layout of the conformal cooling flow channel adopts a spiral surrounding manner, which is distributed in a spiral shape from the center to the outside along the contour of the cavity. A total of five spiral channels are provided, the channel spacing is 25mm, and the channel cross-section is D-shaped (the plane faces the direction of the cavity) to enhance the cooling effect.

[0074] Import the 3D model into ANSYS Workbench for topology optimization. The material properties are set as follows: the mold material is CX stainless steel powder (a corrosion-resistant stainless steel), the elastic modulus is 200GPa, the Poisson's ratio is 0.3, the yield strength is 950MPa, and the density is 7.8g / cm³.

[0075] Boundary conditions: the pouring pressure is 18MPa, the cavity surface temperature is 65℃, and the inner wall temperature of the cooling flow channel is 20℃.

[0076] A two-way progressive structural optimization method was used for topology optimization, with minimizing the mold mass as the objective function and constraints including the maximum mold stress not exceeding 85% of the material's allowable stress and the maximum deformation not exceeding 0.15 mm. After 80 iterations of optimization, the mold mass was reduced by approximately 28%, the maximum stress was reduced to 72% of the material's allowable stress, and the maximum deformation was reduced to 0.09 mm, meeting the design requirements.

[0077] The preset layer thickness is 0.08mm, and Materialise Magics software is used for layer slicing. A checkerboard scanning strategy is adopted for the scanning path, dividing each layer into a 5mm×5mm checkerboard grid. The scanning directions of adjacent checkerboards are perpendicular to each other to further reduce anisotropy and internal stress.

[0078] This embodiment employs an electron beam melting 3D printing system. The molding material is CX stainless steel powder with a particle size distribution ranging from 45μm to 106μm. The process parameters of the electron beam melting system are as follows: electron beam power of 3kW, scanning speed of 3000mm / s, scanning spacing of 0.15mm, preset layer thickness of 0.08mm, and vacuum degree ≤5×10⁻⁶. -4 mbar, substrate preheating temperature controlled at 650℃.

[0079] During electron beam melting, the electron beam selectively melts the powder layer under a high vacuum environment. Due to the high preheating temperature of the substrate, the thermal stress during printing is relatively small. The entire printing process lasts approximately 96 hours, resulting in a pre-formed mold blank.

[0080] The powder cleaning process uses a combination of vacuum suction and high-pressure gas purging, and the processing time is 45 minutes.

[0081] The heat treatment scheme differs from that in Example 1. This example uses a one-step solution aging treatment: the temperature is increased from room temperature to 1050°C at a heating rate of 10°C / min, and held for 2 hours for solution treatment, followed by oil quenching to room temperature; then the temperature is increased to 550°C at a heating rate of 6°C / min, and held for 5 hours for aging treatment, followed by air cooling to room temperature.

[0082] The surface finishing is carried out by a five-axis linkage CNC milling machine for precision machining, and the surface roughness of the cavity reaches Ra≤0.6μm, and the dimensional accuracy reaches ±0.04mm.

[0083] The functional coating in this embodiment is a wear-resistant and corrosion-resistant composite coating. The transition layer is made of chromium, with a thickness of 0.3 μm, and is prepared by magnetron sputtering. The functional layer is made of chromium nitride, with a thickness of 3.5 μm, and is prepared by cathodic arc physical vapor deposition. The surface layer is made of molybdenum disulfide, with a thickness of 0.8 μm, and is prepared by magnetron sputtering.

[0084] The molybdenum disulfide surface layer exhibits excellent lubrication properties (friction coefficient approximately 0.03 to 0.06), making it particularly suitable for the humid and corrosive environments that may be encountered during the prefabrication of sewage well covers. After coating preparation, all performance indicators met the design requirements.

[0085] The mold assembly and debugging process is basically the same as in Example 1. However, because the mold in this example is larger and heavier, a mold closing force test was added during the mold closing debugging process to ensure that the mold closing force is uniform and sufficient.

[0086] This embodiment uses a compression molding process for the prefabrication of sewage well covers. The prefabrication mold is placed on the worktable of the compression molding equipment. After the mold is closed, steel fiber reinforced concrete castable is filled into the cavity, and then pressure is applied through the compression molding head for molding. The compression pressure is 20 MPa, and the holding time is 30 seconds.

[0087] After pressing and molding, the mold is moved to a curing room for curing at a temperature of 25℃±2℃ and a relative humidity of ≥95% for 48 hours. After curing, the mold is demolded to obtain the precast manhole cover.

[0088] Quality inspection results show that all performance indicators of the sewage well covers produced in this embodiment meet the E600 load-bearing capacity requirements, and the product qualification rate reaches over 98%.

[0089] Example 3 This embodiment provides a 3D printing production process for prefabricated molds of power manhole covers, specifically for producing square prefabricated molds for power manhole covers. The main differences between this embodiment and Embodiments 1 and 2 lie in the mold shape (square), molding material, printing equipment, and cooling channel design.

[0090] The power manhole cover in this embodiment is used for power cable manholes. The design load-bearing capacity is B125 (corresponding to EN 124 standard, applicable to sidewalks and non-motorized vehicle lanes). The manhole cover is square, with dimensions of 600mm×600mm and a thickness of 50mm. The surface of the manhole cover must be marked with the word "Power" and warning color markings.

[0091] A 3D solid model of the prefabricated mold was created using CATIA 3D modeling software. Since the mold in this embodiment has a square structure, stress concentration is more likely to occur at the corners of a square mold compared to a circular mold. Therefore, the four corners were rounded during modeling (with a radius of 15mm).

[0092] The prefabricated mold in this embodiment is a modular mold, including a mold base, a mold cover plate, and replaceable cavity inserts. The mold base and mold cover plate are integrally formed by 3D printing, constituting the main frame of the mold. The cavity inserts are independent components, detachably installed between the mold base and the mold cover plate, and the inner surface of the cavity inserts forms the cavity of the mold.

[0093] The cavity insert can be designed in various sizes to correspond to different specifications and patterns of power manhole covers. When it is necessary to change the size or pattern of the manhole cover, only the cavity insert needs to be replaced, without remanufacturing the entire mold, which greatly reduces the cost and time of mold replacement. The cavity insert is quickly positioned and fixed to the mold base and mold cover plate through locating pins and bolts.

[0094] The conformal cooling channels are respectively set in the mold base, mold cover plate and cavity insert. The cooling channels in the cavity insert are micro conformal cooling channels with an equivalent diameter of 4mm, which are closely distributed along the contour of the cavity insert.

[0095] The 3D model was imported into Altair OptiStruct for topology optimization. The material properties were set as follows: mold material was AlSi10Mg aluminum alloy powder (suitable for lightweight molds), elastic modulus was 70 GPa, Poisson's ratio was 0.33, yield strength was 240 MPa, and density was 2.68 g / cm³.

[0096] Boundary conditions: The pouring pressure is 8MPa (the load-bearing capacity of the power manhole cover is relatively low, so the pouring pressure is reduced accordingly), the surface temperature of the cavity is 50℃, and the inner wall temperature of the cooling channel is 20℃.

[0097] Topology optimization was performed using a variable density method, with the goal of minimizing the mold's strain energy and a constraint that the volume fraction should not exceed 65% of the original volume. After 45 iterations, the mold's mass was reduced by approximately 40%, achieving a significant weight reduction effect.

[0098] The preset layer thickness is 0.03mm (this embodiment uses a smaller layer thickness to achieve higher surface quality), and 3DSystems 3D Sprint software is used for layer slicing. The scanning path adopts a strategy combining contour scanning and infill scanning: contour scanning is performed along the outer contour of the mold at a scanning speed of 500mm / s; infill scanning adopts a zigzag scanning strategy at a scanning speed of 1200mm / s.

[0099] This embodiment uses a selective laser melting 3D printing system. The forming material is AlSi10Mg aluminum alloy powder with a particle size distribution of 20μm to 63μm. The process parameters of the selective laser melting system are as follows: laser power of 280W, laser spot diameter of 70μm, scanning speed of 1000mm / s, scanning spacing of 0.08mm, and preset layer thickness of 0.03mm.

[0100] Because aluminum alloys have good thermal conductivity but are prone to oxidation, the oxygen content needs to be strictly controlled (≤0.1%) during the printing process. The entire printing process lasts approximately 48 hours, resulting in a pre-made mold blank.

[0101] In this embodiment, a gradient printing strategy is employed for 3D printing. The outer layer of the mold is printed with fine powder (particle size 20μm to 40μm) and a low layer thickness (0.03mm) for high precision to achieve excellent surface quality and dimensional accuracy. The inner core layer of the mold is printed with coarse powder (particle size 40μm to 63μm) and a slightly higher layer thickness (0.08mm) for rapid printing to improve printing efficiency. The outer layer has a thickness of 0.5mm, and the inner core layer fills the remaining portion. This gradient printing strategy improves overall printing efficiency by approximately 35% while maintaining surface quality.

[0102] The powder removal process combines ultrasonic cleaning and high-pressure gas purging, and takes 30 minutes.

[0103] The heat treatment scheme is as follows: Heat from room temperature to 300℃ at a heating rate of 10℃ / min, hold for 2 hours for stress-relief annealing, and then air-cool to room temperature. Since the strengthening mechanism of AlSi10Mg aluminum alloy differs from that of steel, T6 heat treatment (solution treatment + artificial aging) is adopted: heat to 535℃ at a heating rate of 15℃ / min, hold for 1 hour for solution treatment, and water-quench to room temperature; then heat to 160℃ at a heating rate of 10℃ / min, hold for 6 hours for aging treatment, and then air-cool to room temperature.

[0104] The surface finishing process combines high-speed milling and polishing, achieving a surface roughness of Ra≤0.3μm and a dimensional accuracy of ±0.03mm.

[0105] The functional coating in this embodiment is a thermally conductive and release composite coating. The transition layer is made of nickel, with a thickness of 0.4 μm, and is prepared by electroplating. The functional layer is made of tungsten carbide, with a thickness of 2 μm, and is prepared by thermal spraying. The surface layer is made of polytetrafluoroethylene, with a thickness of 1 μm, and is prepared by spray curing.

[0106] The PTFE surface layer has an extremely low coefficient of friction (approximately 0.04) and excellent release properties, while also exhibiting good chemical stability. The thermally conductive release composite coating ensures rapid heat conduction within the mold cavity (facilitating rapid curing of the manhole cover) while providing excellent release performance.

[0107] The assembly process of the modular mold in this embodiment differs from that in Embodiment 1. First, the cavity insert is installed onto the mold base using locating pins, and then secured with bolts. Next, the mold cover plate is closed with the mold base, achieving precise positioning through guide pillars and guide sleeves. Finally, the gating system, ejection mechanism, and cooling system interface are installed.

[0108] After assembly, debugging is performed: Mold closing debugging checks the fit accuracy between the cavity insert and the mold base and mold cover plate; the parting surface gap should not exceed 0.015mm. Demolding debugging checks whether the ejection mechanism can smoothly eject the finished product from the cavity insert. The cooling system sealing test method is the same as in Example 1.

[0109] This embodiment employs a vibration molding process for the prefabrication of power well covers. After the modular mold is closed, steel fiber reinforced concrete refractory is filled into the cavity through a pouring system, and then a vibration platform is activated to compact the refractory material. The vibration frequency is 40Hz, the amplitude is 0.8mm, and the vibration time is 45 seconds.

[0110] After vibration, the mold is moved to a curing room for curing at a temperature of 22℃±2℃ and a relative humidity of ≥95% for 24 hours. After curing, the mold is demolded to obtain the finished square power well cover.

[0111] Quality inspection results show that the square power manhole cover produced in this embodiment has accurate dimensions (side length deviation ≤ ±0.8mm, thickness deviation ≤ ±0.4mm), excellent surface quality (clear anti-slip texture, complete text markings), and its load-bearing capacity meets the B125 grade requirements.

[0112] When producing power well covers of different specifications, only the cavity insert needs to be replaced (along with replacing the corresponding 3D model data and reprinting the cavity insert); the mold base and mold cover plate can continue to be used. Testing showed that the cavity insert replacement time is no more than 30 minutes, significantly improving the mold's versatility and production efficiency.

[0113] Example 4 This embodiment provides a 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers with optimal process parameter combinations. This embodiment achieves the optimal parameter combination by systematically optimizing the parameters of each process step.

[0114] A 3D solid model of the prefabricated mold was created using PTC Creo 3D modeling software. The mold type is a circular rainwater well cover prefabricated mold with a diameter of 700mm and a cavity depth of 60mm. Compared with the previous embodiment, this embodiment adds thermal-fluid coupling simulation analysis of the cooling channels during the mold modeling stage, and optimizes the layout and cross-sectional dimensions of the cooling channels through computational fluid dynamics simulation.

[0115] After CFD optimization, the conformal cooling channel adopts a rectangular cross-section (8mm wide and 6mm high), distributed in a wavy pattern along the cavity contour, with denser arrangement at the corners of the cavity. This wavy conformal cooling channel design generates turbulence in the cooling medium during flow, enhancing the heat transfer effect. Simulation calculations show that the cooling efficiency of this cooling channel layout is 45% higher than that of traditional straight-line drilled cooling channels.

[0116] Topology optimization was performed using TOSCA structural optimization software. The optimization method was a two-way progressive structural optimization method, with the objective function being minimizing the mold mass, and constraints including the maximum mold stress not exceeding the material's allowable stress and the maximum deformation not exceeding 0.08 mm, and the volume fraction not exceeding 60% of the original volume. After 60 iterations of optimization, a lightweight structure was obtained.

[0117] The preset layer thickness is 0.04mm. RPData software is used for layer slicing, ensuring uniform thickness in each slice. A spiral scanning strategy is employed, with the laser beam continuously scanning along a spiral path to minimize interruptions and jumps, thus improving printing efficiency.

[0118] This embodiment uses a selective laser melting 3D printing device, and the molding material is 18Ni300 martensitic aging steel powder.

[0119] The optimal combination of process parameters is as follows: powder particle size distribution: 15μm to 45μm; laser power: 320W; laser spot diameter: 75μm; scanning speed: 900mm / s; scanning spacing: 0.09mm; preset layer thickness: 0.04mm; substrate preheating temperature: 80℃; protective gas: high-purity argon (oxygen content ≤0.05%).

[0120] Under the above optimal parameter combination, the printing process is stable, the forming quality is excellent, and the printing time is approximately 60 hours.

[0121] The optimal heat treatment scheme is as follows: stress-relief annealing: heat up to 500℃ at 4℃ / min, hold for 2.5 hours, cool down to 150℃ at 2℃ / min and then air cool; solution treatment: heat up to 930℃ at 7℃ / min, hold for 1.5 hours, and then water quench; aging treatment: heat up to 530℃ at 4℃ / min, hold for 5 hours, and then air cool.

[0122] The optimal surface finishing solution is as follows: use a diamond grinding head to perform precision grinding on the cavity (grinding depth 0.05mm, feed speed 200mm / min), and then perform chemical mechanical polishing with nano polishing fluid (polishing time 30 minutes) to make the surface roughness of the cavity reach Ra≤0.2μm and the dimensional accuracy reach ±0.02mm.

[0123] The optimal coating scheme is as follows: Transition layer: titanium, 0.4 μm thick, prepared by magnetron sputtering; Functional layer: titanium aluminum nitride, 2.5 μm thick, prepared by cathodic arc physical vapor deposition; Surface layer: graphene, 0.3 μm thick, prepared by electrophoretic deposition.

[0124] The aluminum titanium nitride functional layer has higher red hardness (maintaining high hardness at 800℃), making it suitable for molds used in long-term continuous production. The graphene surface layer has an extremely low coefficient of friction (approximately 0.02) and excellent thermal conductivity, which improves demolding performance and facilitates rapid curing of the manhole cover.

[0125] The mold assembly and debugging methods are the same as in Example 1. After debugging, the gap between the mold parting surface does not exceed 0.01mm, the ejection action is smooth, and the cooling system has good sealing performance (pressure is maintained at 0.8MPa for 5 minutes, and the pressure drops by 0.01MPa).

[0126] Prefabrication is carried out using vibration molding technology. The optimal molding process parameters are: vibration frequency 60Hz, amplitude 1.2mm, vibration time 50 seconds, castable material is high-performance steel fiber reinforced concrete (compressive strength ≥80MPa), curing temperature 22℃, curing humidity ≥95%, and curing time 20 hours.

[0127] Trial production verification showed that the precast molds produced using the optimal combination of process parameters in this embodiment have a service life that is about twice that of traditional steel molds, a single production cycle time that is about 35% shorter, and a finished product qualification rate of over 99.5% for precast manhole covers.

[0128] The 3D printing production process for prefabricated molds of stormwater, sewage, and power manhole covers provided by this invention can be widely applied to the mold manufacturing of prefabricated components such as stormwater manhole covers, sewage manhole covers, and power manhole covers in municipal engineering. This invention utilizes additive manufacturing technology to achieve rapid, precise, and efficient manufacturing of manhole cover prefabricated molds, overcoming the shortcomings of traditional mold manufacturing methods such as long manufacturing cycles, difficulty in manufacturing complex structures, and significant material waste. The prefabricated molds manufactured by this invention can be used for mass production of high-quality stormwater, sewage, and power manhole cover products, possessing significant industrial practical value and broad market application prospects.

[0129] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A 3D printing production process for prefabricated molds for rainwater, sewage, and power manhole covers, characterized in that, Includes the following steps: Step 1: Based on the usage scenario, load-bearing capacity, specifications, and appearance requirements of the stormwater, sewage, and power manhole covers, determine the design parameters of the prefabricated mold. These parameters include mold type, mold size, cavity structure, draft angle, parting line position, and cooling channel layout. Use 3D modeling software to create a 3D solid model of the prefabricated mold. This model includes the 3D geometric information of the upper mold assembly, lower mold assembly, cavity, cooling channels, gating system, and ejection mechanism. Step 2: Perform finite element analysis and topology optimization on the 3D solid model established in Step 1. Based on the stress distribution, temperature field distribution, and thermal stress distribution of the mold in actual use, remove low-stress redundant materials from the model to form a lightweight structure while ensuring the strength and stiffness of the mold structure, thus obtaining the optimized 3D mold model. The topology optimization takes minimizing the mold mass as the objective function and uses the constraint that the maximum stress of the mold does not exceed the allowable stress of the material and the maximum deformation does not exceed the preset deformation threshold. Step 3: The optimized 3D mold model obtained in Step 2 is sliced ​​along the height direction according to a preset layer thickness, converting the 3D model into a series of 2D contour information; based on the contour information of each layer and combined with the process parameters of the 3D printing equipment, the scanning path and printing strategy for 3D printing are planned, and 3D printing control code is generated; the preset layer thickness is 0.02mm to 0.2mm. Step 4: Import the 3D printing control code generated in Step 3 into the 3D printing equipment, and use additive manufacturing to deposit the molding material layer by layer to print the blank of the pre-made mold; the 3D printing equipment is one of selective laser melting equipment, selective laser sintering equipment, electron beam melting equipment, or binder jet molding equipment; the molding material is one or a combination of mold steel powder, stainless steel powder, nickel-based alloy powder, cobalt-chromium alloy powder, or ceramic powder; Step 5: Remove the pre-made mold blank obtained in Step 4 from the 3D printing equipment and perform powder cleaning to remove unsintered powder remaining on the surface and inside of the blank. Then, perform heat treatment on the blank, which includes stress-relieving annealing and / or solution aging treatment to eliminate thermal stress and microstructure defects generated during the printing process. After heat treatment, perform surface finishing, which includes one or more combinations of grinding, polishing, sandblasting or CNC milling, so that the surface roughness of the mold cavity reaches Ra≤0.8μm and the dimensional accuracy of the mold reaches within ±0.05mm. Step Six: Prepare a functional coating on the mold cavity surface and the inner wall of the cooling channel after the treatment in Step Five; the functional coating is one or more of the following: wear-resistant coating, anti-corrosion coating, release coating, or thermally conductive coating; the preparation method of the functional coating is one of physical vapor deposition, chemical vapor deposition, thermal spraying, electroplating, or electroless plating. Step 7: Assemble the upper and lower mold components processed in Step 6, install the ejection mechanism, gating system, and cooling system interfaces, and assemble them into a complete precast mold; perform mold closing and demolding debugging, and cooling system sealing test on the assembled precast mold to ensure that the mold components move smoothly and that the fitting accuracy meets the design requirements; Step 8: Using the precast mold assembled in Step 7, precast rainwater, sewage, and power manhole covers are produced. Concrete, steel fiber concrete, or composite material is poured into the mold cavity, compacted by vibration, cured, and then demolded to obtain the precast manhole cover. The precast manhole cover is then subjected to quality inspection, and the mold is fine-tuned and optimized based on the inspection results.

2. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, The prefabricated mold is a modular mold, including a mold base, a mold cover plate, and replaceable cavity inserts. The mold base and mold cover plate are integrally formed by 3D printing. The cavity inserts are independent components that can be detachably installed between the mold base and the mold cover plate. Different specifications of cavity inserts correspond to manhole cover products of different specifications and patterns.

3. The 3D printing production process for prefabricated molds of rainwater and sewage power manhole covers according to claim 1, characterized in that, The cooling channel is a conformal cooling channel, and the direction of the conformal cooling channel is adapted to the surface contour of the mold cavity, so that the wall thickness of the cooling channel at each point is basically consistent with the distance from the surface of the mold cavity; the cross-sectional shape of the conformal cooling channel is one of circular, elliptical, rectangular or D-shaped, and the equivalent diameter of the conformal cooling channel is 4mm to 12mm.

4. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, In the 3D printing process of step four, a gradient printing strategy is adopted, that is, the outer layer of the mold is printed with fine powder and low layer thickness for high precision, while the inner core layer of the mold is printed with coarse powder and high layer thickness for rapid printing; the printing layer thickness of the outer layer is 0.02mm to 0.05mm, and the printing layer thickness of the inner core layer is 0.08mm to 0.2mm.

5. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, The heat treatment in step five is a step-by-step heat treatment, including: a first heat treatment stage, stress-relief annealing at 400°C to 600°C for 1 to 3 hours; a second heat treatment stage, solution treatment at 800°C to 1050°C for 0.5 to 2 hours; and a third heat treatment stage, aging treatment at 500°C to 700°C for 2 to 6 hours.

6. The 3D printing production process for prefabricated molds of rainwater and sewage power manhole covers according to claim 1, characterized in that, The functional coating in step six is ​​a composite coating, which includes a transition layer, a functional layer and a surface layer from the inside out. The material of the transition layer is one of titanium, chromium or nickel. The material of the functional layer is one of titanium nitride, chromium nitride, aluminum titanium nitride, diamond-like carbon or tungsten carbide. The material of the surface layer is one of polytetrafluoroethylene, molybdenum disulfide or graphene.

7. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, The topology optimization in step two adopts a two-way progressive structural optimization method or a variable density method, with the optimization objective being to minimize the strain energy or flexibility of the mold, and the constraint being that the volume fraction does not exceed 60% to 80% of the original volume. Iterative optimization is used to obtain a lightweight structure.

8. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, In the trial production of the precast manhole cover in step eight, the castable material is filled into the mold cavity using either vibration molding or compression molding. The vibration molding process has a vibration frequency of 30Hz to 80Hz, an amplitude of 0.5mm to 2mm, and a vibration time of 30 seconds to 120 seconds. The compression molding process has a compression pressure of 5MPa to 30MPa and a pressure holding time of 10 seconds to 60 seconds.

9. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, The 3D printing equipment is a selective laser melting device, the forming material is mold steel powder, the particle size distribution of the mold steel powder is 15μm to 53μm, the laser power of the selective laser melting device is 200W to 1000W, the scanning speed is 200mm / s to 2000mm / s, and the scanning spacing is 0.05mm to 0.15mm.

10. The 3D printing production process for prefabricated molds of stormwater and sewage power manhole covers according to claim 1, characterized in that, The inner wall of the cavity of the prefabricated mold is provided with an anti-slip texture molding structure, a text logo molding structure, or a pattern decoration molding structure. The anti-slip texture molding structure, text logo molding structure, or pattern decoration molding structure is modeled integrally with the mold cavity in the three-dimensional modeling of the mold in step one, and is printed integrally with the mold body in the 3D printing molding in step four.

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