A precise forming method for internal cores of light alloy precision castings

Abstract

The application provides an internal core precision forming method for light alloy precision castings, and relates to the technical field of precision casting, which comprises the following steps: the shape precision of a metal pipe itself is ensured by using a shape correcting die; then a plurality of wax mold radial positioning bands are prepared on the standard metal pipe, so that the metal pipe can obtain accurate position in the overall machine cartridge wax mold, and the problem that the metal pipe floats in the wax mold is solved; finally, the two ends of the metal pipe are used as fixed connection points with a mold shell, the final position of the metal pipe is locked in the mold shell by using the structural rigidity of the mold shell, and the problem that the metal pipe forming the machine cartridge oil way is difficult to accurately position in the molding process and the alloy pouring process is solved.

Description

Technical Field

[0001] This invention relates to the field of precision casting technology, specifically to a method for precise forming of internal cores in light alloy precision castings. Background Technology

[0002] Lightweight alloys such as aluminum and magnesium are widely used in the manufacture of structural castings with complex shapes and low load-bearing capacity, such as intermediate gearboxes, accessory gearboxes, and drive transmission system housings. These structural components typically have complex porous internal cavity structures. Due to the uneven thickness and large dimensional differences of their internal cavities, as well as the high precision requirements, they are difficult to manufacture using ordinary casting methods, resulting in a very low yield.

[0003] In actual production, stainless steel or copper pipes are typically used in a casting process to form complex oil passages. Chinese patent CN201410279607.8 discloses a method for manufacturing an aluminum engine casing. This method involves welding titanium alloy pipes into oil passage pipes and fixing them in a sand mold. These pipes are then cast into the aluminum alloy casing of an aero-engine to form complex oil passages. Finally, sulfuric acid anodizing is performed to obtain an aero-engine aluminum alloy casing that meets design requirements. For casings with particularly complex structures, precision casting can be used. However, accurately positioning the metal pipes forming the casing's oil passages during the molding and alloy pouring processes is difficult, often leading to poor dimensional accuracy of the pipe walls or the production of defective products. Therefore, ensuring the accurate positioning of the metal pipes is a challenge in the precision casting process of the casing. Summary of the Invention

[0004] The purpose of this invention is to provide a method for precise forming of the internal core of a light alloy precision casting, in order to solve the problem in the prior art that it is difficult to accurately position the metal pipe forming the oil passage of the casing during the molding process and the alloy pouring process.

[0005] To achieve the above objectives, this application provides a method for precise forming of the internal core of a light alloy precision casting, comprising the following steps:

[0006] Step 1: Shape the metal tube to be processed in the shaping mold fixture so that the shaped standard metal tube is consistent with the dimensions of the oil circuit structure.

[0007] Step 2: Place the standard metal tube in the composite wax mold, and use the multiple positioning protrusions in the composite wax mold to position the standard metal tube. Prepare a composite wax mold containing multiple radial positioning bands on the circumferential surface of the standard metal tube to form a composite wax mold metal tube, wherein the pipe joints at both ends of the standard metal tube are exposed in the composite wax mold.

[0008] Step 3: Apply sealing wax to both ends of the composite wax mold metal tube to seal the joints;

[0009] Step 4: Place the composite wax mold metal tube with sealing wax into the casing wax mold to form the overall casing wax mold;

[0010] Step 5: Use precision casting technology to prepare the mold shell for the integral casing wax model. The mold shell fixes and positions the two exposed ends of the metal tube. The mold shell is then dewaxed and sintered to finally obtain the finished mold shell.

[0011] Step 6: Cast the finished mold shell, and then cut off the pipe joints.

[0012] Furthermore, in step two, multiple wax mold radial positioning bands are distributed along the length of the standard metal tube at preset intervals.

[0013] Furthermore, in step two, the positioning protrusions are set at the two ends and the middle position of the standard metal tube along the radial direction of the standard metal tube, and the number of positioning protrusions is no less than 3 pairs.

[0014] Furthermore, the materials used for the metal tubes include stainless steel, copper alloy, or titanium alloy.

[0015] Furthermore, at least three radial positioning bands are provided along the length of the standard metal tube, and the maximum diameter of the wax layer at the radial positioning band is equal to the local casting wall thickness, in order to ensure the precise position of the composite wax model in the casing wax model.

[0016] Furthermore, in step two, the composite wax mold metal tube is formed using an injection molding process. The preheating temperature of the wax mold material is 55-69℃, the injection pressure is 3-8 atmospheres, the injection time is 10-60 seconds, and the holding time is 10-60 seconds.

[0017] Furthermore, the two ends of the composite wax mold metal tube are coated with a wax layer of 0.1-1 mm thickness, and the diameter of the wax layer needs to be 0.1-0.5 mm larger than the maximum outer diameter of the metal tube ends.

[0018] Furthermore, in step four, the overall casing wax model is formed using an injection molding process. The preheating temperature of the wax model material is 58-70℃, the injection pressure is 3-8 atmospheres, the injection time is 30-120 seconds, and the holding time is 60-120 seconds.

[0019] Furthermore, in step five, when preparing the mold shell, the surface layer of the mold shell is prepared by mixing alumina and silica sol, and the back layer slurry of the mold shell is prepared by mixing bauxite or mullite powder with silica sol; the sand spreading material is one of zircon sand, mullite or coal gangue, with a mesh size of 24-80 mesh.

[0020] Furthermore, in step five, the dewaxing temperature of the mold shell is 160-180℃, the dewaxing pressure is 0.6-0.8MPa, and the time is 10-30 seconds;

[0021] The sintering temperature of the mold shell is 850℃-1050℃; the holding time is 2-6 hours. After sintering, the mold shell is cleaned and dried.

[0022] By adopting the above technical solution, the method for precise forming of internal cores of light alloy precision castings provided in this application has the following technical advantages compared with the prior art:

[0023] In this solution, the shape accuracy of the metal tube is ensured by using a calibration mold; then, multiple radial positioning bands for the wax model are prepared on the standard metal tube, enabling it to obtain a precise position in the overall casing wax model, thus solving the problem of the metal tube floating in the wax model; finally, the two ends of the metal tube are cleverly used as fixed connection points to the mold shell, and the final position of the metal tube is locked in the mold shell by utilizing the structural rigidity of the mold shell itself; this overcomes the problem of the metal tube forming the casing oil passage being difficult to accurately position during the molding process and alloy casting process in the existing technology. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the process flow of the method for precise forming of the internal core of a light alloy precision casting provided in the embodiments of this application.

[0026] Icons: 1-Metal tube to be processed; 2-Shaping mold tooling; 3-Standard metal tube; 4-Composite wax mold; 5-Positioning protrusion; 6-Wax mold radial positioning band; 7-Composite wax mold; 8-Sealing wax; 9-Carrier wax mold. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0029] This application provides a method for precise forming of internal cores in light alloy precision castings. This method is particularly suitable for precisely embedding metal tubular cores to form complex oil passage structures in light alloy casing castings such as aluminum alloys and magnesium alloys. Figure 1 As shown, the steps of this method include:

[0030] Step 1:

[0031] The metal tube 1 to be processed is placed in the forming mold fixture 2 for precise forming. The purpose of the forming process is to eliminate any bending or twisting deformation that may have occurred in the metal tube 1 during the early manufacturing or transportation process, thereby obtaining a standard metal tube 3 that is completely consistent with the dimensions of the target oil passage structure. This fundamental step ensures that the metal tube itself, as the core, has extremely high dimensional consistency, providing a reliable geometric reference for all subsequent positioning and forming processes.

[0032] Step Two:

[0033] Preparation of the composite wax model: After obtaining the standard metal tube 3 through shaping, the operator places the standard metal tube 3 into a composite wax model mold 4. The inner cavity of the composite wax model mold 4 is provided with multiple positioning protrusions 5. These positioning protrusions 5 exert a constraint on the standard metal tube 3 in the radial direction, precisely fixing it in the preset installation position within the composite wax model mold 4.

[0034] A composite wax model 7 is prepared on the circumferential surface of a standard metal tube 3 using an injection molding process. It should be noted that this composite wax model 7 is not a uniformly thick, complete covering layer, but rather designed to include multiple radial positioning bands 6 spaced apart along the length of the tube. Simultaneously, the pipe joints at both ends of the standard metal tube 3 remain exposed during the molding process, without covering the wax model, to facilitate positioning and sealing in subsequent processes. In this way, a composite wax model metal tube is ultimately formed, consisting of an inner standard metal tube 3 and an outer composite wax model 7 with a specific structure. The beneficial effect of this composite wax model metal tube is that the outer composite radial positioning bands play a crucial positioning and supporting role in the subsequent overall wax model molding and mold shell preparation processes, effectively preventing the metal tube from shifting in subsequent processes.

[0035] Considering that factors such as the shrinkage of the composite wax mold 7 and the bonding force between the standard metal tube 3 and the composite wax mold 7 may affect the positioning accuracy during the preparation of the composite wax mold metal tube, the distribution and quantity of the radial positioning band 6 of the wax mold are further optimized in step two of the embodiment of this application.

[0036] Specifically, multiple radial positioning bands 6 of the wax model are regularly distributed along the entire length of the standard metal tube 3 at preset intervals. This uniform or equidistant distribution provides balanced radial support for the slender standard metal tube 3, avoiding wax model deformation or metal tube bending caused by excessively dense or sparse local support.

[0037] Meanwhile, to better achieve stable clamping of the standard metal tube 3, the positioning protrusions 5 within the composite wax mold 4 are preferably designed to be positioned radially along the standard metal tube 3, corresponding to both ends and the middle position of the metal tube. These positioning protrusions 5 appear in pairs, clamping and positioning the metal tube from two opposing directions. The total number is set to be no less than three pairs, for example, three, four, or more pairs. This arrangement forms a stable three-point or more-point support system, effectively eliminating multiple degrees of freedom of the standard metal tube 3 within the mold, ensuring that it remains precisely positioned even under the high-pressure impact of the injected wax, thereby guaranteeing the uniformity of the thickness and the accuracy of the radial positioning band 6 of the wax mold.

[0038] In practical applications, the embedded metal tubes need to withstand the high temperatures and corrosion during the casting of lightweight alloys, making the selection of their material crucial. The metal tube materials used in the embodiments of this application may include stainless steel, copper alloy, or titanium alloy tubes. Stainless steel tubes possess good heat resistance and mechanical properties, with a relatively moderate cost; copper alloy tubes have excellent thermal conductivity, which helps to achieve a uniform temperature field after casting; titanium alloy tubes have the highest specific strength and excellent corrosion resistance, making them suitable for applications with extreme performance requirements. Designers can flexibly select one of the above materials based on the specific service conditions and cost budget of the lightweight alloy casting to achieve the best balance between performance and cost.

[0039] To further ensure that the composite wax model metal tube can be accurately positioned when it is subsequently placed into the larger housing wax model mold 8, this application embodiment proposes specific constraints on the external dimensions and quantity of the radial positioning band 6 of the wax model.

[0040] Specifically, at least three radial positioning bands 6 need to be set along the length of the standard metal tube 3. In practical applications, four, five, or more can also be set. Taking three as an example, the three radial positioning bands 6 are located near the two ends and the middle of the metal tube, respectively, forming a stable three-point positioning system. Furthermore, the maximum diameter of the wax layer at each radial positioning band 6 is designed to be equal to the casting wall thickness at that local location. That is to say, when the composite wax model metal tube is placed into the casing wax model mold 8, the outer edges of these radial positioning bands 6 will exactly contact the corresponding inner wall of the mold cavity, thus ensuring the precise radial and axial position of the composite wax model in the casing wax model through hard contact. This design directly links the size of the wax model with the inner cavity size of the final casting, avoiding the generation of cumulative errors.

[0041] In the specific implementation of step two, this application embodiment preferably uses injection molding to prepare the composite wax mold metal tube. The applicant has obtained an optimized range of process parameters through extensive experimental verification. For example, the preheating temperature of the wax mold material before injection is controlled between 55°C and 69°C. Too low a temperature will result in poor wax fluidity, failing to completely fill the small gaps in the mold; too high a temperature may cause the wax to over-expand or decompose, affecting dimensional accuracy.

[0042] The injection pressure is set to 3 to 8 standard atmospheres, and the injection time lasts for 10 to 60 seconds to ensure that the wax can quickly and evenly fill the cavity. Then, the pressure is held for 10 to 60 seconds to compensate for the volume reduction of the wax during the cooling and shrinkage process, and to prevent shrinkage cavities or depressions in key parts such as the radial positioning zone 6 of the wax mold. This combination of process parameters ensures that the composite wax mold has high dimensional stability and surface finish.

[0043] Once the composite wax mold metal tube is prepared, the process moves to step three, which is sealing.

[0044] In this embodiment, the operator applies a layer of sealing wax 8 to the exposed pipe joint surfaces at both ends of the composite wax model metal tube. The thickness of this sealing wax 8 is precisely controlled within the range of 0.1 to 1 mm, and the diameter after wax coating must be 0.1 to 0.5 mm larger than the maximum outer diameter of the metal tube end itself. The main purpose of this step is to prevent wax model material, mold shell slurry, or other impurities from entering the metal tube from the pipe opening during the subsequent overall casing wax model forming and mold shell preparation processes. If the inside of the tube is contaminated or blocked, a smooth oil passage cannot be formed subsequently, leading to the direct scrapping of the casting. By deliberately controlling the wax layer thickness to be slightly larger than the pipe diameter, a small protrusion can be formed after coating. This protrusion helps the mold shell material form a more reliable sealing and fixing structure around the pipe opening during the subsequent preparation of the mold shell.

[0045] After the sealing process is completed, the method proceeds to step four, which is the forming of the overall casing wax model.

[0046] The composite wax model metal tube, already coated with sealing wax 8, is placed as a single component into the final casing wax model mold 8. Then, through injection molding, another layer of casing wax model is applied to the outside of the composite wax model metal tube. This casing wax model not only shapes the external contour of the casing casting but also completely encloses the composite wax model metal tube (except for the pipe fittings at both ends).

[0047] To achieve high-quality casing wax model molding, this application also preferably adopts an injection molding process, and provides an optimized process: the preheating temperature of the wax model material is 58°C to 70°C, slightly higher than the preparation temperature of the composite wax model, to ensure good fusion between the old and new wax models; the injection pressure is also 3 to 8 atmospheres; since the casing wax model cavity is larger and the structure is more complex, the injection time is extended to 30 to 120 seconds, and the holding time is also extended to 60 to 120 seconds accordingly, to ensure that the wax material can completely and densely fill the entire large mold cavity and avoid defects such as under-injection or weld lines.

[0048] Subsequently, the method proceeds to step five, namely the preparation and processing of the mold shell.

[0049] This application utilizes a precision casting process to prepare the mold shell from the integral casing wax model obtained in step four. A key design element in the mold shell preparation process is that the mold shell material naturally wraps around and secures the two ends of the metal tube exposed from the wax model. Since the two end joints of the standard metal tube 3 are the only parts not covered by the composite wax model, they become the rigid connection points between the mold shell and the internal metal core. After multiple layers of slurry coating and sanding, the formed mold shell firmly grips the two end joints of the metal tube, thus achieving final fixed positioning of the metal tube within the entire mold shell. This positioning method utilizes the structural strength of the mold shell itself, avoiding the need for complex metal core supports or other positioning accessories.

[0050] After the mold shell is prepared, it needs to be dewaxed, which involves melting and removing all the wax mold inside through high temperature and high pressure. In the embodiments of this application, the dewaxing temperature is 160°C to 180°C, the dewaxing pressure is 0.6 to 0.8 MPa, and the processing time is only 10 to 30 seconds.

[0051] This high-temperature flash dewaxing method enables rapid dewaxing, minimizing the expansion stress on the mold shell caused by thermal expansion of the wax mold and preventing cracking. After dewaxing, a hollow mold shell with an internal cavity containing a fixed metal tube is obtained. The mold shell is then sintered at a temperature of 850℃ to 1050℃ for 2 to 6 hours. This process causes the particles in the mold shell to sinter at high temperatures, achieving sufficient mechanical strength and high-temperature resistance to deformation. After sintering, the mold shell needs to be cleaned and dried to remove residual ash and impurities, preparing it for casting.

[0052] To ensure that the mold shell has sufficient high-temperature strength and thermal shock resistance, the materials used to prepare the mold shell have been optimized in this application embodiment.

[0053] Specifically, the surface layer of the mold shell (the layer directly in contact with the wax model) is made of a mixture of alumina powder and silica sol. Alumina is chemically stable and does not react with the molten light alloy, ensuring a smooth casting surface free of chemically adhering sand. The back layer of the mold shell (the layer used for subsequent thickening) is prepared using a mixture of lower-cost, higher-strength bauxite or mullite powder and silica sol. The sand-sprinkling material is selected from zircon sand, mullite, or coal gangue, with a mesh size controlled between 24 and 80 mesh. The combination of sand particles of different sizes creates a dense mold shell structure with good permeability. This differentiated design of the surface and back layer materials ensures the quality of the interface with the casting while controlling costs and ensuring the overall strength of the mold shell.

[0054] In step six, the sintered and inspected finished mold shell is cast with molten light alloy. Under the influence of gravity or centrifugal force, the molten metal fills the cavity of the mold shell and tightly encases the pre-fixed metal tube inside. After the molten metal has completely solidified and cooled, a light alloy casting blank with an embedded metal tube is obtained.

[0055] Finally, the exposed pipe fitting portion on the outside of the casting, used for positioning, is removed using a cutting tool, and the cut is then trimmed and inspected as necessary. At this point, a light alloy precision casting with accurately positioned and dimensionally correct internal oil passages is complete.

[0056] In summary, the core principle of the method provided in this application is to obtain a reference through shape correction, achieve pre-positioning through the radial positioning band 6 of the wax model, and achieve final positioning through the clamping of the mold shell end, thereby accurately assembling dissimilar metal tubes into the interior of a light alloy precision casting.

[0057] The method first uses a calibrating mold to ensure the shape accuracy of the metal tube itself; then, by preparing multiple wax model radial positioning bands 6 on the standard metal tube 3, it can obtain a precise position in the overall casing wax model, solving the problem of the metal tube floating in the wax model; finally, the two ends of the metal tube are cleverly used as fixed connection points with the mold shell, and the final position of the metal tube is locked in the mold shell by utilizing the structural rigidity of the mold shell itself.

[0058] This solution effectively overcomes the problem of metal tube misalignment caused by uneven heating, stress, and material shrinkage during molding and casting in existing technologies. It significantly improves the positional accuracy of the embedded metal tube, thereby enhancing the yield and quality consistency of lightweight alloy castings with complex internal cavity structures. It is particularly suitable for the aerospace and high-performance automotive parts fields where the requirements for oil circuit size and positional accuracy are stringent.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for precise forming of internal cores in light alloy precision castings, characterized in that, Includes the following steps: Step 1: Shape the metal tube to be processed in the shaping mold fixture so that the shaped standard metal tube is consistent with the dimensions of the oil circuit structure. Step 2: Place the standard metal tube in the composite wax mold, and use the multiple positioning protrusions in the composite wax mold to position the standard metal tube. Prepare a composite wax mold containing multiple radial positioning bands on the circumferential surface of the standard metal tube to form a composite wax mold metal tube, wherein the pipe joints at both ends of the standard metal tube are exposed in the composite wax mold. Step 3: Seal the ends of the composite wax mold metal tube by applying sealing wax to the pipe joints. Step 4: Place the composite wax mold metal tube with sealing wax into the casing wax mold to form the overall casing wax mold; Step 5: Use precision casting technology to prepare the mold shell for the integral casing wax model. The mold shell is fixed and positioned by the exposed ends of the metal tube; the mold shell is dewaxed and sintered to finally obtain the finished mold shell. Step 6: Cast the finished mold shell, and then cut off the pipe joints.

2. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, In step two, multiple wax mold radial positioning bands are distributed along the length of the standard metal tube at preset intervals.

3. The method for precise forming of internal cores of light alloy precision castings according to claim 2, characterized in that, In step two, positioning protrusions are set at both ends and the middle position of the standard metal tube along the radial direction of the standard metal tube, and the number of positioning protrusions is no less than 3 pairs.

4. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, The materials used for metal tubes include stainless steel, copper alloy, or titanium alloy.

5. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, At least three radial positioning bands are provided along the length of the standard metal tube, and the maximum diameter of the wax layer at the radial positioning band is equal to the local casting wall thickness, in order to ensure the precise position of the composite wax model in the casing wax model.

6. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, In step two, the composite wax mold metal tube is formed by injection molding. The preheating temperature of the wax mold material is 55-69℃, the injection pressure is 3-8 atmospheres, the injection time is 10-60 seconds, and the holding time is 10-60 seconds.

7. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, The two ends of the composite wax mold metal tube are coated with a wax layer of 0.1-1 mm thickness, and the diameter of the wax layer must be 0.1-0.5 mm larger than the maximum outer diameter of the metal tube ends.

8. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, In step four, the overall casing wax model is formed using an injection molding process. The preheating temperature of the wax model material is 58-70℃, the injection pressure is 3-8 atmospheres, the injection time is 30-120 seconds, and the holding time is 60-120 seconds.

9. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, In step five, when preparing the mold shell, the surface layer of the mold shell is prepared by mixing alumina and silica sol, and the back layer slurry of the mold shell is prepared by mixing bauxite or mullite powder with silica sol; the sand spreading material is one of zircon sand, mullite or coal gangue, with a mesh size of 24-80 mesh.

10. The method for precise forming of internal cores of light alloy precision castings according to claim 1, characterized in that, In step five, the dewaxing temperature of the mold shell is 160-180℃, the dewaxing pressure is 0.6-0.8MPa, and the time is 10-30 seconds; The sintering temperature of the mold shell is 850℃-1050℃; the holding time is 2-6 hours. After sintering, the mold shell is cleaned and dried.

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