Short-process preparation method for hollow casting wax mold based on 3D printing and combined assembly

Abstract

The invention belongs to the field of precision casting of metal materials, particularly relates to a short-process preparation method for a wax mould of a hollow casting based on 3D printing and combined assembly, and is particularly suitable for preparing the wax mould of a high-temperature alloy large hollow casting such as a gas turbine blade. The method comprises the following steps: (1) subdividing a three-dimensional model; (2) printing a wax mold part; (3) assembling a mold core and the wax mold part; (4) bonding and combining; according to the method, the wax mold part of the precision casting wax mold is prepared by utilizing the 3D printing technology, and the wax mold part and the mold core are combined together through the combination tool, so that the processes of manufacturing an appearance mold and injecting wax into the mold core are avoided, the production cycle is shortened, the cost is saved, and meanwhile, the qualification rate of the mold shell is increased.

Description

Technical Field

[0001] This invention belongs to the field of precision casting of metal materials, specifically a short-process preparation method for wax patterns of hollow castings based on 3D printing and assembly. It is particularly suitable for the preparation of wax patterns of large hollow castings of high-temperature alloys such as gas turbine blades, and can meet the needs of new product development, trial production and small and medium batch production. Background Technology

[0002] Large hollow castings made of high-temperature alloys (such as gas turbine blades) are commonly produced using investment casting, with the traditional method of wax pattern preparation involving injection molding using metal molds. However, this method has significant drawbacks: (1) High mold cost: The manufacturing cost of large and complex metal molds is extremely expensive, especially for single-piece, small-batch or R&D stage products, which are not economically viable.

[0003] (2) Long cycle: The design, processing, debugging and modification of molds take a long time, which seriously delays the progress of new product development.

[0004] (3) Poor flexibility: After the mold is finalized, it is difficult to flexibly adjust and optimize the size and shape of the wax model.

[0005] (4) Low yield: As the internal air-cooled structure gradually becomes more complex, the huge impact force of the wax during the high-pressure injection of wax can easily cause the fragile ceramic core inside to break or shift. Even with the addition of processes such as X-ray inspection before assembly, a large number of shells are still scrapped during the dewaxing and shell burning stage due to core breakage.

[0006] While there have been attempts to directly manufacture integral wax models using 3D printing or machining, direct manufacturing is still not possible for large parts with complex internal cavities.

[0007] Patent CN105364006A discloses a wax model and its manufacturing method for a large-size hollow crowned blade casting system. This method requires pressing multiple components, including the casting wax model, blade crown ingate, tenon ingate, spherical riser, runner, sprue, and pouring cup, separately according to the casting structure. These components are then assembled into a single wax model through bonding. However, relying on metal molds for pressing the casting wax model results in long mold design, processing, and debugging cycles, extremely high manufacturing costs, and unavoidable core breakage during wax pressing and shell making. Patent CN118650118A discloses a method for integrally forming a wax model of a stainless steel casing casting. This method designs the wax model as multiple parts, presses the wax model into separate parts using metal molds, positions them using splicing fixtures, and then assembles them into a whole using adhesive wax. During the assembly process, adhesive wax needs to be poured into the receiving groove formed by the joint of adjacent parts to cool and fix it. The cooling and shrinkage of the adhesive wax can easily lead to gaps or deformation at the joint, affecting the overall accuracy of the wax model and making it difficult to guarantee the accuracy of the internal cavity dimensions. Furthermore, the lack of a precise positioning mechanism during core installation, coupled with the complex internal core structure of large hollow castings, makes it difficult to achieve precise alignment between the core and the wax model using only assembly fixtures. This can easily lead to core displacement, ultimately affecting the casting quality. Patent CN115673245A proposes an integrated molding method for wax models of complex thin-walled parts with ceramic cores. This method achieves integrated molding of the wax model through two pressing processes (single-blade wax model pressing and integral wax model pressing). While avoiding traditional welding processes, it requires the specialized design and manufacture of single-blade wax model molds, integral wax model molds, and ceramic core molds. The investment cost of these three types of molds is high, and once the molds are finalized, it is difficult to flexibly adjust them according to changes in the casting design. The method also still carries the risk of wax impacting the core during the two pressing processes, and the core breakage problem remains unresolved.

[0008] In summary, existing wax pattern preparation methods generally suffer from problems such as high mold costs, long production cycles, poor design flexibility, easy core breakage or displacement, and insufficient adaptability to large hollow castings. It is necessary to develop a wax pattern preparation method for large hollow castings that has short procedures, high precision, and can effectively avoid core damage. Summary of the Invention

[0009] In order to overcome the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a short-process preparation method for wax models of hollow castings based on 3D printing and assembly, which solves the defects such as high mold cost, long production cycle, poor design flexibility, easy breakage or displacement of core, and insufficient adaptability to large hollow castings, and achieves wax model preparation with low cost, short cycle and high flexibility.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A short-process preparation method for hollow casting wax models based on 3D printing and assembly includes the following steps: S1 3D Model Splitting: Splitting the 3D digital model of the target casting into at least two parts, the wax model, along the preset parting surface; S2 Printing wax model parts: Using 3D printing equipment, each part of the wax model sub-model obtained in step S1 is printed into a solid wax model part; S3 Core and Wax Model Assembly: The sintered ceramic core and the wax model parts printed in step S2 are placed in the assembly fixture. The assembly fixture is used to accurately align and fix the ceramic core and the wax model parts. S4 bonding assembly: Press and connect the various wax mold components to form an integral wax mold surrounding the ceramic core; S5 Post-processing: After bonding and assembly, the overall wax model is inspected for its external dimensions using blue light scanning or dimensional tooling. Once the inspection is passed, the overall wax model is transferred to the investment casting shell-making process.

[0011] The short-process preparation method for hollow casting wax models based on 3D printing and assembly is described in step S1. The parting surface is an arc surface along the hollow casting wax model or a curved surface or a combination of curved surfaces that facilitates core installation and positioning. The morphology of the inner cavity side ensures that the mold meets the requirements for accommodating and positioning the core after mold closing. Each part is subjected to reverse deformation according to the total deformation amount of subsequent steps. Each part of the wax model sub-model has a preset reverse deformation amount according to the deformation amount of subsequent processes. Each part of the wax model sub-model is provided with a positioning structure for cooperating with the assembly tooling.

[0012] In the aforementioned short-process preparation method for hollow casting wax molds based on 3D printing and assembly, in step S2, the 3D printing process is photopolymerization molding or material spraying molding, the printing material is wax-based photosensitive resin or wax-based powder material, and the ash content of the printing material after combustion meets the requirements of precision casting.

[0013] In the short-process preparation method for hollow casting wax models based on 3D printing and assembly, in step S3, the assembly fixture includes a base, a positioning pin set on the base for positioning the wax model components, a core holder for supporting and positioning the ceramic core, and a clamping mechanism for pressing the wax model components, ensuring that the six degrees of freedom of translation and rotation of the ceramic core and each wax model component in three-dimensional space are fully constrained.

[0014] The aforementioned short-process preparation method for hollow casting wax models based on 3D printing and assembly consists of a core holder composed of columns set on both sides of the wax model component. The lower end of each column is installed on the base, and the upper end of each column is connected to one end of the ceramic core. The two ends of the ceramic core overlap the upper ends of one column respectively. The ceramic core is located between the blade basin-side wax model component and the blade back-side wax model component, and is used to form the hollow structure of the casting.

[0015] In the short-process preparation method for hollow casting wax models based on 3D printing and assembly, in step S4, the wax model components are joined by bonding with special adhesives, tenon and mortise structures or hot melt wax liquid on the mating surfaces.

[0016] The aforementioned short-process preparation method for hollow casting wax models based on 3D printing and assembly uses a special adhesive that is a hot-melt wax-based adhesive, a hot-melt wax-based adhesive that is the same as or compatible with the wax model material, or molten wax liquid. Furthermore, the ash content of the special adhesive after combustion meets the requirements of precision casting.

[0017] The aforementioned short-process preparation method for hollow casting wax models based on 3D printing and assembly requires that pressure be applied when using a special adhesive to ensure bonding between the wax model components, and that the pressure and holding time should not cause plastic deformation of the wax model components; depending on the size and strength of the wax model, the holding time after bonding is 3 to 20 minutes, and the clamping force of the clamping mechanism is maintained at 50 to 100 N during the holding process.

[0018] The aforementioned short-process preparation method based on 3D printing and combined assembly of hollow casting wax models is applied to large-size hollow precision casting products with an internal cavity containing an air-cooling channel. The ceramic core is a SiO2-based, Al2O3-based, or ZrO2-based ceramic core, and its material is matched with the high-temperature alloy material and casting process of the casting.

[0019] The short-process preparation method based on 3D printing and assembly of hollow casting wax models requires the use of blue light scanning or measuring tools to assist in the inspection during the assembly of the core and wax model components, in order to ensure the overall dimensional accuracy.

[0020] The design concept of this invention is: This invention abandons the traditional core path of metal mold pressing and instead uses 3D printing technology to form wax model parts. By dissecting the large hollow casting wax model into 3D printable sub-parts through three-dimensional digital modeling, the wax model parts are directly printed using stereolithography (SLA) or material jetting (MJP) processes. There is no need to design or process any metal molds, which avoids the high cost and long cycle of molds and can quickly adapt to different castings by modifying the digital model.

[0021] This invention designs a precision assembly fixture including positioning pins, a core holder, and a clamping mechanism. First, the ceramic core is precisely fixed using the core holder. Then, the 3D-printed wax model components are fitted to the fixture using the positioning pins. The blade basin-side and blade back-side wax model components are physically fastened and low-pressure clamped to the ceramic core, fundamentally eliminating the risk of core breakage / displacement. The wax model components are pressed and connected in a single operation under the positioning of the precision fixture, reducing the number of bonding steps and ensuring bonding accuracy through fixture positioning.

[0022] The advantages and beneficial effects of this invention are as follows: 1. Moldless manufacturing, reducing costs and cycle time: This invention directly manufactures wax model parts through 3D printing, completely eliminating the high cost of metal molds and greatly shortening the product development cycle. It is particularly suitable for new product development, trial production and small and medium batch production, solving the problems of high mold costs and long cycles in existing technologies.

[0023] 2. Avoiding the risk of core breakage: This invention avoids the traditional high-pressure injection process of wax. By using precision assembly tooling to position and assemble the ceramic core and wax mold components before bonding, the risk of core breakage and subsequent shell scrap caused by wax impact is fundamentally eliminated, significantly improving the shell yield. At the same time, during the assembly process, the core and wax mold components are accurately positioned by blue light detection or measuring tooling, avoiding the impact of core displacement on casting quality and solving the problem of easy core damage in the prior art.

[0024] 3. Flexible design and easy optimization: The wax model is a digital model. When the casting design needs to be adjusted or optimized, only the digital model needs to be modified and the wax model parts need to be re-dissected and printed. There is no need to modify or manufacture new molds. Modification and iteration can be carried out quickly and at low cost, which facilitates continuous optimization of product design.

[0025] 4. High Precision: This invention, through high-precision 3D printing and precision assembly tooling, ensures high accuracy in the relative positions of the core and wax model, as well as among the various parts of the wax model, thereby guaranteeing the dimensional accuracy of the final casting. Furthermore, the precision assembly tooling achieves six-degree-of-freedom constrained positioning of the ceramic core and wax model components, ensuring the relative positional accuracy between the core and wax model, and among the various parts of the wax model, ultimately guaranteeing the dimensional accuracy of large hollow castings and solving the problems of large splicing errors and inaccurate core positioning in existing technologies. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the preparation of a hollow gas turbine blade wax model, which is divided into two parts along the mid-arc surface: a blade basin-side wax model component and a blade back-side wax model component.

[0027] Figure 2 This is a schematic diagram of the combined tooling in this invention.

[0028] Figure 3 This is a schematic diagram of the casting structure obtained in this invention.

[0029] In the figure, 1-blade basin side wax mold component, 2-blade back side wax mold component, 3-wax mold component, 4-base, 5-positioning pin, 6-core holder, 7-ceramic core, 8-gas turbine blade casting. Detailed Implementation

[0030] In practical implementation, this invention proposes a short-process preparation method for hollow casting wax models based on 3D printing and assembly, which includes the following steps: S1 3D Model Splitting: Splitting the 3D digital model of the target casting into at least two parts, the wax model, along the preset parting surface; In step S1, the parting surface (splitting surface) is preferably along the arc surface of the part or a curved surface that facilitates the installation and positioning of the core. The shape of the inner cavity side only needs to ensure that the core is placed after the mold is closed. Each part can be reverse-deformed according to the total deformation amount in subsequent steps. A positioning structure for cooperating with the assembly tooling is provided on some wax mold sub-models.

[0031] S2 Printing wax model parts: Using 3D printing equipment, each part of the wax model sub-model obtained in step S1 is printed into a solid wax model part; In step S2, the 3D printing is a process such as stereolithography (SLA) or material jetting (MJP). The printing material used is wax-based photosensitive resin or wax-based powder material, which are suitable for 3D printing and precision casting. The ash content after combustion meets the requirements of precision casting.

[0032] S3 Core and Wax Model Assembly: The sintered ceramic core and the wax model parts printed in step S2 are placed in the assembly fixture. The assembly fixture is used to accurately align and fix the ceramic core and the wax model parts. S4 bonding assembly: Press and connect the various wax mold components to form an integral wax mold surrounding the ceramic core; In step S4, the wax mold components can be joined by pressing together using a special adhesive on the mating surfaces, a tenon and mortise structure, or hot-melt wax liquid. The special adhesive is a hot-melt wax-based adhesive, a hot-melt wax-based adhesive that is the same as or compatible with the wax mold material, or molten wax liquid, and its ash content after combustion meets the requirements of precision casting.

[0033] S5 Post-processing: After bonding and assembly, the overall wax model is inspected for its external dimensions using blue light scanning or dimensional tooling. Once the inspection is passed, the overall wax model is transferred to the investment casting shell-making process.

[0034] In step S5, during the assembly process, the dimensional accuracy of the assembled wax model is ensured to meet the requirements by means of dimensional tooling or blue light detection.

[0035] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0036] Example: Taking a hollow blade of a certain type of heavy-duty gas turbine as an example In this embodiment, a short-process preparation method for hollow casting wax models based on 3D printing and assembly includes the following steps: Step S1: Using 3D CAD software (such as UG / NX), the 3D model of the hollow gas turbine blade is divided into a blade basin side wax model and a blade back side wax model along its central arc surface.

[0037] Step S2: Select an MJP multi-nozzle jet 3D printer (developed by 3D Systems, USA) and use a low-ash, medium-temperature wax material (ash content ≤0.05wt%, meeting precision casting requirements). Import the blade basin side wax model and the blade back side wax model into the printing software, optimize the placement and support structure, and then print the blade basin side wax model component 1 and the blade back side wax model component 2 respectively. Figure 1 After printing, high-precision solid wax model parts 3 are obtained through post-processing such as cleaning and curing.

[0038] Step S3: First, place the blade back side wax model component 2 on the positioning pin 5 of the assembly tooling according to the positioning structure (such as positioning holes). Then, carefully place the sintered ceramic core 7 on the core holder 6. The ceramic core 7 matches the hollow structure of the arc surface of the blade basin side wax model component 1 and the blade back side wax model component 2. Then, fasten the printed blade basin side wax model component 1 and the blade back side wax model component 2. The blade basin side wax model component 1 and the blade back side wax model component 2 are fixedly connected by the clamping mechanism to ensure that the three parts of the blade basin side wax model component 1, the ceramic core 7, and the blade back side wax model component 2 are accurately positioned.

[0039] Reference Figure 2 This invention provides a precision assembly tooling, which includes a base 4, a positioning pin 5 mounted on the base 4 for positioning the wax model component 3, a core holder 6 for supporting and positioning the ceramic core 7, and a clamping mechanism for clamping the wax model component 3, ensuring that the six degrees of freedom of translation and rotation of the ceramic core and each wax model component in three-dimensional space are fully constrained. The core holder 6 consists of columns mounted on both sides of the wax model component 3. The lower end of each column is mounted on the base 4, and the upper end of each column is connected to one end of the ceramic core 7. The two ends of each ceramic core 7 overlap the upper end of one column. The ceramic core 7 is located between the blade basin-side wax model component 1 and the blade back-side wax model component 2, and is used to form the hollow structure of the gas turbine hollow blade.

[0040] Step S4: Loosen the clamping mechanism and slightly separate the blade basin-side wax mold component 1 and the blade back-side wax mold component 2. Apply a layer of hot melt wax-based adhesive evenly to their mating surfaces. Then, clamp the blade basin-side wax mold component 1 and the blade back-side wax mold component 2 again using the clamping mechanism and hold the pressure at 80N for 10 minutes to allow the adhesive to cool and solidify, firmly combining the blade basin-side wax mold component 1 and the blade back-side wax mold component 2 into a complete integral wax mold component that covers the ceramic core 7.

[0041] Step S5: Open the assembly fixture, remove the assembled and bonded integral wax model component, and use a blue light scanner (scanning accuracy 0.05mm) to comprehensively inspect the external dimensions of the integral wax model component. After passing the inspection (dimensional error ≤0.1mm), it can proceed to the next stage of coating, shell making, dewaxing, firing, and casting processes to obtain gas turbine blade casting 8 ( Figure 3 ).

[0042] The results show that this invention utilizes 3D printing technology to prepare wax model components for precision casting wax models, and combines these components with the core using assembly tooling. This avoids the need for manufacturing external molds and the wax injection process for the core, shortening the production cycle and saving costs, while also improving the shell yield. The shell yield rate is increased to over 98%, and the dimensional accuracy of the castings fully meets the precision manufacturing requirements for large hollow castings.

Claims

1. A short-process preparation method for hollow casting wax models based on 3D printing and assembly, characterized in that, Includes the following steps: S1 3D Model Splitting: Splitting the 3D digital model of the target casting into at least two parts, the wax model, along the preset parting surface; S2 Printing wax model parts: Using 3D printing equipment, each part of the wax model sub-model obtained in step S1 is printed into a solid wax model part; S3 Core and Wax Model Assembly: The sintered ceramic core and the wax model parts printed in step S2 are placed in the assembly fixture. The assembly fixture is used to accurately align and fix the ceramic core and the wax model parts. S4 bonding assembly: Press and connect the various wax mold components to form an integral wax mold surrounding the ceramic core; S5 Post-processing: After bonding and assembly, the overall wax model is inspected for its external dimensions using blue light scanning or dimensional tooling. Once the inspection is passed, the overall wax model is transferred to the investment casting shell-making process.

2. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 1, characterized in that, In step S1, the parting surface is an arc surface along the hollow casting wax model or a curved surface or a combination of curved surfaces that facilitates the installation and positioning of the core. The shape of the inner cavity side ensures that the core can be accommodated and positioned after the mold is closed. Each part is subjected to reverse deformation according to the total deformation amount of the subsequent steps. Each part of the wax model sub-model is preset with a reverse deformation amount according to the deformation amount of the subsequent process. Each part of the wax model sub-model is provided with a positioning structure for cooperating with the assembly tooling.

3. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 1, characterized in that, In step S2, the 3D printing process is photopolymerization molding or material jet molding, the printing material is wax-based photosensitive resin or wax-based powder material, and the ash content of the printed material after combustion meets the requirements of precision casting.

4. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 1, characterized in that, In step S3, the assembled fixture includes a base, a positioning pin disposed on the base for positioning the wax model components, a core holder for supporting and positioning the ceramic core, and a clamping mechanism for pressing the wax model components, ensuring that the six degrees of freedom of translation and rotation of the ceramic core and each of the wax model components in three-dimensional space are fully constrained.

5. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 4, characterized in that, The core holder consists of columns set on both sides of the wax model component. The lower end of each column is installed on the base, and the upper end of each column is connected to one end of the ceramic core. The two ends of the ceramic core overlap the upper end of a column. The ceramic core is located between the blade basin side wax model component and the blade back side wax model component, and is used to form the hollow structure of the casting.

6. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 1, characterized in that, In step S4, the wax mold components are joined by bonding with a special adhesive, mortise and tenon structure or hot melt wax on the mating surface.

7. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 6, characterized in that, The special adhesive is a hot melt wax-based adhesive, a hot melt wax-based adhesive that is the same as or compatible with the wax mold material, or molten wax liquid, and the ash content of the special adhesive after combustion meets the requirements of precision casting.

8. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 6, characterized in that, When using a special adhesive for bonding, pressure should be applied to ensure that each wax mold component is bonded together, and the pressure and holding time should not cause plastic deformation of each wax mold component; depending on the size and strength of the wax mold, the holding time after bonding is 3 to 20 minutes, and the clamping force of the clamping mechanism should be maintained at 50 to 100 N during the holding process.

9. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 1, characterized in that, The application target of this method is large-size hollow precision casting products with an internal cavity containing an air-cooling channel. The ceramic core is SiO2-based, Al2O3-based, or ZrO2-based, and its material is matched with the high-temperature alloy material and casting process of the casting.

10. The short-process preparation method for hollow casting wax models based on 3D printing and assembly as described in claim 1, characterized in that, During the assembly of the core and wax model components, blue light scanning or measuring instruments should be used to assist in inspection to ensure overall dimensional accuracy.

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