Wax mold assembly, mold shell and high-precision casting processing method

Abstract

This invention discloses a wax mold assembly, a mold shell, and a method for processing high-precision castings, belonging to the field of investment casting technology. The wax mold assembly includes a sprue bar with a sprue portion. The sprue portion has an annular flange around its perimeter, and the bottom of the annular flange has an annular groove. The annular groove is used to coat the upper end of the mold shell surface layer, or to coat the upper ends of both the surface layer and the back layer, thereby making the upper end of the mold shell surface layer higher than the upper end of the back layer. The mold shell is formed by sequentially coating the wax mold assembly with the surface layer and the back layer. At the sprue of the mold shell, the top of the surface layer forms an annular peak, and the upper end of the back layer is lower than the upper end of the surface layer. The wax mold assembly, mold shell, and high-precision casting processing method provided by this invention, through the structure of the annular groove making the upper end of the surface layer higher than the upper end of the back layer, physically increases the difficulty for the back layer material to enter the sprue, effectively preventing the back layer material, such as mullite, from mixing into the casting interior, and improving the uniformity of the internal structure of the casting.

Description

Technical Field

[0001] This invention belongs to the field of investment casting technology, specifically relating to a wax mold assembly, a mold shell, and a method for processing high-precision castings. Background Technology

[0002] In the production of medical prosthesis castings, investment casting has become a commonly used processing technology due to its ability to manufacture complex shapes and high-precision parts. Investment casting, also known as lost-wax casting, involves creating wax patterns and welding multiple wax patterns onto a wax gate rod. Afterward, a shell is formed by coating the wax and the shell has a gate.

[0003] Currently, in the shell-forming process, refractory materials, specifically sand-based materials, are used. For example, zircon sand can be used as the surface layer, and mullite as the back layer. However, this choice presents certain problems. Due to operational processes or material distribution, near the gating gate of the mold, where the back layer is close to the surface layer, some back layer material may remain. During the subsequent casting process, this material flows into the gating system with the molten metal and eventually mixes into the interior of the casting.

[0004] Mullite, as an impurity, has physical and chemical properties that differ from the main material of the casting, which can disrupt the uniformity of the casting's internal structure. This can not only reduce the casting's strength, toughness, and other mechanical properties, but also affect the surface finish and smoothness, thus negatively impacting the quality of medical prostheses. For medical prostheses, even minor quality defects can lead to serious consequences in actual use, endangering the health and safety of patients.

[0005] Therefore, preventing mullite from entering castings and improving the quality of medical prosthesis castings has become an urgent problem to be solved in the current investment casting process. Developing a new wax model, shell, and high-precision casting processing method to optimize the selection of shell materials or improve the shell-making process and prevent mullite from entering the castings is of vital importance for improving the quality and safety of medical prostheses. Summary of the Invention

[0006] The purpose of this invention is to provide a wax mold assembly, a shell, and a high-precision casting processing method to ensure that the backing material of the shell made in investment casting is not mixed into the prosthetic casting.

[0007] To achieve the above objectives, embodiments of the present invention provide a wax module, including a sprue bar, the sprue bar having a sprue portion, the sprue portion having an annular flange around its perimeter, the annular flange having an annular groove at its bottom, the annular groove being used to coat the upper end of the shell surface layer, or to coat the upper ends of the surface layer and the back layer, thereby making the upper end of the shell surface layer higher than the upper end of the back layer.

[0008] For example, at least one embodiment of this disclosure provides a wax module in which the wall of the annular groove has an outer annular inclined downward surface, the height of which gradually decreases from the inside to the outside.

[0009] For example, at least one embodiment of this disclosure provides a wax mold assembly in which the wall of the annular groove also has an inner annular inclined downward surface. The inner annular inclined downward surface gradually increases in height from the inside out. The inner annular inclined downward surface is located inside the ring of the outer annular inclined downward surface and is connected to the upper end of the outer annular inclined downward surface, thereby forming an annular peak. The annular peak is used to make the upper end of the shell surface layer higher than the upper end of the back layer. The inner annular inclined downward surface is used to guide the casting liquid to flow into the gate by the gate rod forming the gate of the shell.

[0010] For example, at least one embodiment of this disclosure provides a wax mold assembly in which the sprue bar has a hollow cavity in the middle, the hollow cavity is used to prevent wax expansion during shell dewaxing, and the bottom of the hollow cavity has a connecting nut part, the connecting nut part is used to connect the mold hook.

[0011] For example, at least one embodiment of this disclosure provides a wax module in which the lower end of the outer annular inclined descending surface is also connected to a cylindrical surface.

[0012] For example, at least one embodiment of this disclosure provides a wax template in which the cylindrical surface has a plurality of recessed grooves arranged along the circumference, the recessed grooves being used to increase the bonding strength between the coated surface layer and the back layer.

[0013] For example, at least one embodiment of this disclosure provides a wax module in which a stop is provided on one side of the groove wall of the recessed groove. The recessed groove and the stop are used to form a hook-shaped groove on the outer wall of the coated surface layer in the recessed groove. The hook-shaped groove is used to form a hook-shaped part on the inner wall of the coated back layer on the surface layer. The hook-shaped part is stuck in the hook-shaped groove, thereby increasing the connection strength between the coated surface layer and the back layer.

[0014] For example, at least one embodiment of this disclosure provides a wax mold in which the baffle has a secondary groove on the side facing the recessed groove, the secondary groove being used to increase the connection strength between the coating surface layer and the back layer; The bottom of the recessed groove has an inclined baffle to prevent the coated back layer from extending upwards beyond the baffle.

[0015] This invention also provides a shell, which is formed by sequentially coating the wax mold with a surface layer and a back layer. At the gate of the shell, the top of the surface layer forms an annular peak, and the upper end of the back layer is lower than the upper end of the surface layer.

[0016] This invention also provides a high-precision casting machining method, utilizing the aforementioned wax mold, including the following steps: S1. Press wax to form a mold, and assemble it with a casting rod to obtain a wax film assembly; S2. Wax film coating for shell formation, wherein the coating is applied into the annular groove at the bottom of the annular flange of the gate, according to either method one or method two: Method 1: The annular groove is filled with the top layer material, and the back layer material does not enter the annular groove. The back layer material is only coated on the outer wall of the top layer material, and its upper end is lower than the lower end of the annular groove. The annular groove makes the upper end of the back layer lower than the upper end of the top layer. If the back layer material wants to enter the gate of the shell, it needs to bypass the upper end of the top layer. Method 2: The surface material is coated in an annular groove. The annular groove forms a surface groove, and the upper end of the back layer material is formed in the surface groove. This also makes the upper end of the back layer lower than the upper end of the surface layer. If the back layer material wants to enter the gate of the shell, it needs to bypass the surface groove and the upper end of the surface layer. S3. Dewaxing and casting to obtain the casting.

[0017] The significant technical effects of the embodiments of the present invention are as follows: The annular groove makes the upper end of the surface layer higher than the upper end of the back layer, which physically increases the difficulty for the back layer material to enter the gate, effectively preventing back layer material such as mullite from mixing into the casting and improving the uniformity of the internal structure of the casting. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a wax module in one embodiment of the present invention; Figure 2 for Figure 1 A schematic diagram of the wax module in the embodiment; Figure 3 This is a schematic diagram of the recessed groove in the wax module in another embodiment of the present invention; Figure 4 for Figure 3 A schematic diagram of the inclined baffle in the embodiment; In the figure: 100 sprue bar, 110 sprue section, 111 annular flange, 121 annular groove, 121 outer annular inclined downward surface, 122 inner annular inclined downward surface, 123 annular peak, 124 cylindrical surface, 1241 recessed groove, 1242 stop, 1243 secondary groove, 1244 inclined stop, 130 hollow cavity, 131 connecting nut section. Detailed Implementation

[0020] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0022] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship. In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0025] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to 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 embodiments of this application.

[0026] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation", "connection", "linking", and "fixing" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components.

[0027] Please see Figures 1-2 The illustration shows a wax mold assembly according to an embodiment of the present invention, including a sprue bar 100, the sprue bar 100 having a sprue portion 110, the sprue portion 110 having an annular flange 111 around its perimeter, the bottom of the annular flange 111 having an annular groove 120, the annular groove being used to coat the upper end of the shell surface layer, or to coat the upper end of the surface layer and the back layer, thereby making the upper end of the shell surface layer higher than the upper end of the back layer.

[0028] The annular groove 120 has an outer annular inclined downward surface 121, the height of which gradually decreases from the inside to the outside. The annular groove 120 also has an inner annular inclined downward surface 122, the height of which gradually increases from the inside to the outside. The inner annular inclined downward surface 122 is located inside the annulus of the outer annular inclined downward surface 121 and is connected to the upper end of the outer annular inclined downward surface 121, thereby forming an annular peak 123. The annular peak 123 is used to make the upper end of the shell surface layer higher than the upper end of the back layer. The inner annular inclined downward surface 122 is used to guide the casting liquid to flow into the gate through which the sprue bar 100 forms the sprue of the shell.

[0029] For example, the sprue 100 has a sprue section 110 at one end. The sprue section 110 is usually cylindrical or conical, corresponding to the sprue of the subsequent shell. Its size and shape are designed according to the specific requirements of the medical prosthesis casting to ensure that the casting liquid can flow smoothly into the shell. The sprue 100 is generally made of a waxy material with good thermal stability and moderate strength so that it can withstand the coating and shell-making processes during investment casting without deformation.

[0030] The sprue 100 provides connecting support for multiple wax models, enabling them to form a unified wax model assembly. The sprue 110 guides the molten casting into the mold shell during the casting process and serves as the channel inlet for the molten casting to flow into the casting cavity. Its design rationality directly affects the quality and efficiency of casting.

[0031] An annular flange 111 surrounds the gate portion 110, extending outward from the side wall of the gate portion 110 to form an annular protrusion. The width and height of the annular flange 111 are designed according to actual process requirements to ensure effective guidance of the distribution of coating material.

[0032] The annular flange 111 serves to block and guide the coating material. During the coating and shell-making process, it can change the flow direction of the refractory material, making the material more evenly distributed around it. At the same time, it provides a basic structure for the formation of the annular groove 120, which helps to achieve a differential distribution of the surface and back layers in terms of height.

[0033] The annular groove 120 is located at the bottom of the annular flange 111 and surrounds the gate portion 110. The depth and width of the annular groove 120 vary depending on the coating method. The groove wall of the annular groove 120 has a special structure, including an outer annular inclined downward surface 121 and an inner annular inclined downward surface 122.

[0034] The annular groove 120 is the core structure that prevents the back layer material from entering the gate. During the shell coating process, two different coating methods are used to ensure that the upper end of the shell surface layer is higher than the upper end of the back layer. This means that if the back layer material wants to enter the gate, it must cross a higher surface layer, effectively preventing it from entering the gate and improving the quality of the casting.

[0035] The outer annular inclined descending surface 121 is the outer part of the groove wall of the annular groove 120. Its height gradually decreases from the inside to the outside, which helps to guide the backing material to flow outward during the coating process, making it difficult for it to enter the interior of the annular groove 120, thereby ensuring that the backing material is distributed below the lower end of the annular groove 120.

[0036] The outer annular inclined downward surface 121 can effectively change the flow direction of the back layer material, reduce the possibility of the back layer material entering the annular groove 120, further ensure that the back layer material is lower than the surface layer material, and enhance the effect of blocking the back layer material from entering the gate.

[0037] The inner annular inclined descending surface 122 is located on the inner side of the annular groove 120 wall, and its height gradually increases from the inside to the outside. It connects with the upper end of the outer annular inclined descending surface 121 to form the annular peak 123. The inclination angles of the inner annular inclined descending surface 122 and the outer annular inclined descending surface 121 are matched to form a structure that is conducive to guiding the distribution of materials and the flow of casting liquid.

[0038] The annular peak 123 increases the difficulty for the backing material to enter the mold gate, further preventing the backing material from mixing into the gate. The inner annular inclined descending surface 122 can guide the casting liquid smoothly into the mold gate during the casting process, making the casting liquid more concentrated and smoother into the mold cavity, which helps to improve the casting quality and the integrity of the casting.

[0039] In the production of medical prosthesis castings, a suitable wax material is used to fabricate a sprue bar 100 according to the design requirements of the medical prosthesis casting, ensuring the dimensional accuracy and surface quality of structures such as the sprue section 110, the annular flange 111, and the annular groove 120. Simultaneously, multiple medical prosthesis wax models are welded onto the sprue bar 100 according to the design layout to form a complete wax model assembly.

[0040] Prepare the refractory materials for coating and shelling, such as zircon sand as the surface layer material and mullite as the backing material. Ensure that the particle size, moisture content, and other parameters of the materials meet the process requirements, and thoroughly mix the materials to ensure their uniformity.

[0041] Method 1 Coating: First, apply the topcoat by immersing the wax model assembly in zircon mortar, filling the annular groove 120 with the topcoat material. Then, lift the wax model assembly, allowing excess mortar to drip off. Next, apply the backcoat by coating the mullite mortar onto the outer wall of the topcoat material. Because the annular groove 120 is filled with the topcoat material, the backcoat material will not enter the annular groove 120, and its upper end is lower than the lower end of the annular groove 120, thus making the upper end of the backcoat lower than the upper end of the topcoat.

[0042] Method Two Coating: First, a topcoat is applied by immersing the wax model in zircon mortar. This method is suitable for wider annular grooves (120mm), allowing the topcoat material to form a groove within the groove. Then, a backcoat is applied, with the backcoat material coated within the topcoat groove, ensuring the upper edge of the backcoat is lower than the upper edge of the topcoat.

[0043] The shell with the top and back layers coated is then fired to remove the wax mold and sinter the refractory material. During firing, it is crucial to ensure that the shell's temperature rises and falls uniformly to prevent defects such as cracks.

[0044] The molten casting liquid is poured into the mold shell through the gate portion 110 of the gate bar 100. Due to the obstruction effect of the annular peak portion 123 on the surface layer of the mold shell, the back layer material is difficult to enter the gate, while the inner annular inclined descending surface 122 guides the casting liquid to flow smoothly into the gate and into the mold cavity of the mold shell, thus completing the casting process.

[0045] The annular groove 120, through two coating methods, forms a structure where the upper end of the surface layer is higher than the upper end of the back layer. This physically increases the difficulty for the back layer material to enter the gate, effectively preventing back layer material such as mullite from mixing into the casting and improving the uniformity of the internal structure of the casting. The outer annular inclined downward surface 121 guides the structure of the surface layer and the back layer, ensuring that the back layer material does not approach the gate and reducing the risk of back layer material mixing into the casting.

[0046] The design of the inner annular inclined descending surface 122 and the annular peak 123 makes the casting liquid more concentrated and smooth when entering the gate, which helps to avoid problems such as turbulence and bubbles during the casting process, improves the casting quality, makes the internal structure of the casting more compact, and improves the surface finish and smoothness.

[0047] The structure of the annular flange 111 and the annular groove 120 helps to make the refractory material more evenly distributed during the coating and shell-making process, enhances the overall stability of the shell, reduces the possibility of cracking and deformation of the shell during firing and casting, and further ensures the quality of the casting.

[0048] By preventing backing material from contaminating the casting and improving casting quality, the quality of medical prosthesis castings has been effectively enhanced. Improved internal structural uniformity enhances the casting's strength, toughness, and other mechanical properties, reduces quality defects caused by impurities, lowers potential threats to patient health and safety during actual use, and improves the reliability and safety of medical prostheses.

[0049] In Method 1 coating, only the surface layer material is filled into the annular groove 120; the back layer material does not enter the annular groove 120 at all, and the upper end of the back layer material is lower than the lower end of the annular groove 120. This means that if the back layer material wants to enter the gate, it must bypass the significantly taller surface layer material. This structural combination of the annular flange 111 and the annular groove 120 creates a significant height difference, which is highly effective in preventing the back layer material from entering the gate. In this way, it is more effective in preventing the back layer material from mixing into the casting, maximizing the uniformity of the internal structure of the casting, and thus significantly improving the quality of the casting.

[0050] From a practical standpoint, the steps of this coating method are relatively straightforward and clear. First, the wax model is immersed in zircon mortar, filling the annular groove 120 with the surface layer material. Then, the wax model is lifted to allow excess mortar to drip off. Next, the backing layer material is applied to the outer wall of the surface layer. This method requires relatively low skill from the operator and is easy to master and implement, whether in manual coating scenarios or small-scale production, ensuring good consistency in coating quality.

[0051] In the second coating method, the annular groove 120 is widened, and the surface layer is coated within the annular groove 120 to form a surface layer groove, which is then filled with the back layer material. This structure allows the surface and back layers to bond more tightly in the annular groove 120 area, supporting each other. During the shell baking and casting process, the overall strength of the shell near the gate is enhanced, making it less prone to cracking and deformation. This is of great significance for ensuring the integrity of the casting and effectively improving the yield rate of production.

[0052] The relatively wide annular groove 120 provides more convenient coating and filling conditions for the spray nozzles or robotic arms when operating with automated coating equipment. Automated equipment can more precisely control the coating amount and distribution of material within the annular groove 120, thereby improving coating efficiency and quality consistency. In large-scale production using automated coating processes, Method Two demonstrates better adaptability and significant advantages.

[0053] In some examples, the sprue bar 100 has a hollow cavity 130 in the middle, which is used to prevent wax expansion during shell dewaxing. The bottom of the hollow cavity 130 has a connecting nut part 131, which is used to connect the mold hook.

[0054] For example, a hollow cavity 130 is provided in the middle of the sprue bar 100. The hollow cavity 130 extends along the axial direction of the sprue bar 100 and its shape can be cylindrical. The diameter is determined according to the overall size of the sprue bar 100 and the actual process requirements, and generally accounts for one-third to one-half of the cross-sectional area of ​​the sprue bar 100.

[0055] During the dewaxing process of the mold shell, the wax expands when heated. The hollow cavity 130 provides space for the wax expansion, preventing the sprue bar 100 from deforming due to wax expansion, which would affect the dimensional accuracy of the mold shell and the overall quality of the wax mold assembly. By setting the hollow cavity 130, the stress generated by wax expansion is effectively relieved, ensuring the stability of the wax mold assembly during the dewaxing process, and helping to improve the quality of the mold shell and the accuracy of subsequent castings.

[0056] The connecting nut part 131 is located at the bottom of the hollow cavity 130. Its shape is an internal thread structure, similar to a common nut. The thread specification is designed according to the size of the mold hook.

[0057] The connecting nut 131 is used to connect the mold hook. During the investment casting process, the mold hook can easily lift the wax mold assembly by screwing it into the connecting nut 131. This connection method makes the wax mold assembly more stable during handling, coating, shell making, and dewaxing operations, facilitating various process operations and improving the convenience and efficiency of the production process. At the same time, the combination of the connecting nut 131 and the hollow cavity 130 not only meets the space requirements for wax expansion but also provides a reliable connection point for the handling of the wax mold assembly, optimizing the overall performance of the wax mold assembly.

[0058] The hollow cavity 130 effectively alleviates the expansion stress of the wax during the dewaxing process, preventing the sprue 100 from deforming due to wax expansion. This helps maintain the dimensional stability of the sprue 100, thereby ensuring the dimensional accuracy of the shell and laying the foundation for obtaining high-precision castings in the future.

[0059] The reliable connection between the connecting nut 131 and the mold hook ensures greater stability of the wax mold assembly during handling, reducing the possibility of misalignment or damage due to improper handling. This further guarantees the precision of the mold shell, as the accurate positioning of the wax mold is crucial to the molding quality of the shell.

[0060] Please see Figures 3-4 In some examples, a cylindrical surface 124 is also connected to the lower end of the outer annular inclined descending surface 121. For example, the cylindrical surface 124 is connected to the lower end of the outer annular inclined descending surface 121, and its diameter matches the diameter of the lower end of the outer annular inclined descending surface 121 to achieve a smooth transition. The height of the cylindrical surface 124 is designed according to actual production needs and is generally not too high to avoid affecting the normal flow and accumulation of the backing material, while also ensuring that it can play a certain functional role. The cylindrical surface 124 is integrally formed with the main body of the gate bar 100 and the outer annular inclined descending surface 121 to ensure structural stability. The cylindrical surface 124 can effectively optimize the structural stability of the surface layer material forming, reduce the product quality risk caused by improper process adjustment, and further enhance the stability of the process.

[0061] In some examples, the cylindrical surface 124 has a plurality of recessed grooves 1241 arranged circumferentially. The recessed grooves 1241 are used to increase the bonding strength between the coated top layer and the back layer. One side of the groove wall of the recessed groove 1241 also has a stop 1242. The recessed groove 1241 and the stop 1242 are used to form a hook-shaped groove on the outer wall of the coated top layer in the recessed groove 1241. The hook-shaped groove is used to form a hook-shaped portion on the inner wall of the coated back layer on the top layer. The hook-shaped portion is locked in the hook-shaped groove, thereby increasing the bonding strength between the coated top layer and the back layer.

[0062] For example, recesses 1241 are provided on the cylindrical surface 124, and several recesses 1241 are evenly arranged along the circumference. The shape of the recesses 1241 can be triangular, trapezoidal, or semi-circular, etc., and the specific dimensions are adjusted according to actual process requirements and material properties. The design of these recesses 1241 aims to increase the contact area and mechanical interlocking force between the surface layer and the back layer. The design of the recesses 1241 and the baffles 1242 is suitable for coating in mode two. During the coating process, due to the presence of the recesses 1241, the coated surface layer material will fill them, forming an uneven surface structure. When the back layer material is coated on the surface layer, the back layer material will embed into these recesses 1241, thereby increasing the connection strength between the surface layer and the back layer, making the two layers of material bond more tightly, effectively preventing the back layer from falling off the surface layer, and improving the overall quality of the shell.

[0063] The baffle 1242 is located on one side of the groove wall of the recessed groove 1241. The baffle 1242 can be a straight plate structure perpendicular to the groove wall of the recessed groove 1241, or it can be a sloped structure with a certain angle of inclination, so as to better guide the flow and forming of the surface material.

[0064] When the topcoat material is applied, its small particle size allows it to flow and form along the surfaces of the baffle 1242 and the recessed groove 1241, creating hook-shaped grooves on the outer wall of the topcoat within the recessed groove 1241. When the backcoat material is applied, its larger particle size essentially fills the hook-shaped grooves on the outer wall of the topcoat, resulting in corresponding hook-shaped portions on the inner wall of the backcoat. This interlocking structure of the hook-shaped portions and grooves significantly increases the connection strength between the topcoat and backcoat, further enhancing the stability and reliability of the shell.

[0065] During the production of medical prosthesis castings, the wax model assembly is immersed in the surface slurry according to method two, ensuring that the slurry fully fills the annular groove 120 and forms a uniform coating within the recessed groove 1241 of the cylindrical surface 124 and on the surface of the baffle 1242. Due to the small particle size of the surface material, it can flow along the shape of the baffle 1242 and the recessed groove 1241, forming a hook-shaped groove on the outer wall of the surface material within the recessed groove 1241.

[0066] Lift the wax mold and allow excess topcoat paste to drip off naturally, ensuring a uniform coating thickness that meets process requirements.

[0067] The wax model assembly with the top layer applied is immersed in the back layer slurry. Due to the larger particle size of the back layer material, it will directly and almost completely fill the hook-shaped grooves formed on the outer wall of the top layer, forming hook-shaped sections on the inner wall of the back layer. At this point, the back layer material and the top layer material are tightly connected through the interlocking structure of the hook-shaped sections and the hook-shaped grooves.

[0068] After the surface and back coatings are applied, the mold shell is subjected to subsequent operations such as drying, firing, dewaxing, and casting according to conventional processes. During these processes, due to the strong connection structure formed between the surface and back coatings through the recessed grooves 1241 and the baffles 1242, the mold shell can withstand stress changes under various process conditions, ensuring the quality of the casting.

[0069] The recessed grooves 1241 are arranged circumferentially, increasing the contact area between the surface layer and the back layer. The back layer material is embedded in the recessed grooves 1241, which greatly improves the friction and adhesion between the two layers, effectively enhancing the connection strength and reducing the risk of the back layer falling off the surface layer.

[0070] The stop 1242 and the recessed groove 1241 work together to form an engaging structure between the hook-shaped groove and the hook-shaped part. This connection method with stronger mechanical interlocking force further improves the connection stability between the surface layer and the back layer. Even when the shell undergoes high-temperature and high-pressure processes such as baking and casting, it can maintain a good bonding state, thereby improving the quality of the shell and the yield of castings.

[0071] During the mold shell fabrication and subsequent processes, the mold shell is subjected to various stresses, including temperature changes, gravity, and casting pressure. Due to the enhanced bonding strength between the surface layer and the back layer, the mold shell can better resist these stress changes, reducing problems such as mold shell cracking and deformation caused by the separation of the surface layer and the back layer, and improving the stability of the mold shell throughout the entire investment casting process.

[0072] A stable connection between the surface and back layers helps maintain the dimensional accuracy of the shell. During firing and casting, the shell is less prone to dimensional changes due to internal structural instability, thus ensuring the production of high-precision castings.

[0073] The design of the recessed groove 1241 and the baffle 1242 makes the coating process more reliable. This structural design reduces the reliance on coating operation skills to a certain extent. Even if there are differences in the skill level of the operators, it can ensure a good connection between the top layer and the back layer, thus improving the stability and consistency of the process.

[0074] Please see Figures 3-4 In some examples, the side of the baffle 1242 facing the recessed groove 1241 has a secondary groove 1243, which is used to increase the connection strength between the coating surface layer and the back layer; the bottom of the recessed groove 1241 has an inclined baffle 1244, which is used to block the coated back layer from going up beyond the inclined baffle 1244.

[0075] For example, the secondary groove 1243 is located on the side of the stop 1242 facing the recessed groove 1241. Its shape can be rectangular, V-shaped or U-shaped, etc., and its depth is relatively shallow. The secondary groove 1243 can increase the micro-connection structure between the surface layer and the back layer.

[0076] During the coating process, the smaller particle size of the surface layer material fills the secondary groove 1243. When the back layer material is coated, it interlocks with the surface layer material filling the secondary groove 1243. This microscopic structure increases the contact area and mechanical interlocking force between the surface layer and the back layer, further increasing the connection strength between the coated surface layer and the back layer, making the shell structure more stable and improving its reliability in subsequent processes.

[0077] The inclined baffle 1244 is located at the bottom of the recessed groove 1241 and is inclined. Its height gradually changes from one side of the recessed groove 1241 to the other side. The inclined baffle 1244 can limit the filling height of the backing material.

[0078] During the back coating process, the back layer material is difficult to exceed the obstruction of the inclined baffle 1244. This helps to precisely control the filling height of the back layer material in the recessed groove 1241, ensuring that the back layer material forms a stable connection structure with the surface layer material at a predetermined position. This avoids problems such as loose connection or unstable shell structure caused by overfilling of the back layer material, thereby improving the quality and stability of the shell.

[0079] This embodiment also proposes a shell, which is formed by sequentially coating a surface layer and a back layer with a wax mold. At the gate of the shell, the top of the surface layer forms an annular peak, and the upper end of the back layer is lower than the upper end of the surface layer.

[0080] For example, it is made from a wax mold assembly. The sprue 100 of the wax mold assembly has a sprue portion 110, an annular groove 120 at the bottom of the annular flange 111 around the sprue portion 110, an outer annular inclined downward surface 121, an inner annular inclined downward surface 122 and an annular peak portion 123 on the wall of the annular groove 120, and a recessed groove 1241, a stop portion 1242, a secondary groove 1243 and an inclined stop portion 1244 on the cylindrical surface 124, etc., which provide a basis for the production of the mold shell.

[0081] According to the coating process, the top layer material is first coated on the wax model. For the annular groove 120, if coating method one is used, the annular groove 120 is filled with the top layer material; if coating method two is used, a top layer groove is formed in the annular groove 120.

[0082] At the gate of the shell, due to the annular peak 123 formed by the inner annular inclined downward surface 122 and the outer annular inclined downward surface 121 of the annular groove 120 of the wax mold assembly gate portion 110, the surface material accumulates at this location to form an annular peak. The height and shape of this annular peak correspond to the annular peak 123 of the wax mold assembly.

[0083] Similarly, at the gate, due to the design of the annular groove 120, regardless of whether it is coating method one or method two, the upper end of the back layer is lower than the upper end of the surface layer, forming a significant height difference. This effectively blocks the back layer material from entering the gate, preventing back layer material such as mullite from mixing into the casting and ensuring the uniformity of the internal structure of the casting.

[0084] This embodiment also proposes a high-precision casting machining method using a wax model, including the following steps: S1. Press wax to form a mold, and assemble it with a casting rod to obtain a wax film assembly; S2. Wax film coating for shell formation, wherein when coating is applied inside the annular groove 120 at the bottom of the annular flange 111 of the gate 110, it shall be done according to either method one or method two as follows: Method 1: The annular groove 120 is filled with the surface layer material, and the back layer material does not enter the annular groove 120. The back layer material is only coated on the outer wall of the surface layer material, and its upper end is lower than the lower end of the annular groove 120. The annular groove 120 makes the upper end of the back layer lower than the upper end of the surface layer. If the back layer material wants to enter the gate of the shell, it needs to bypass the upper end of the surface layer.

[0085] Method 2: The annular groove 120 is coated with the surface layer material. The annular groove 120 makes the surface layer material form a surface layer groove. The upper end of the back layer material is formed in the surface layer groove, which also makes the upper end of the back layer lower than the upper end of the surface layer. If the back layer material wants to enter the gate of the shell, it needs to bypass the surface layer groove and the upper end of the surface layer. S3. Dewaxing and casting to obtain the casting.

[0086] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of protection of the claims of the present invention.

Claims

1. A wax pattern assembly, comprising: Includes a sprue bar (100), the sprue bar (100) having a sprue portion (110), the sprue portion (110) having an annular flange (111) around its perimeter, the annular flange (111) having an annular groove (120) at its bottom, the annular groove being used to coat the upper end of the shell surface layer, or to coat the upper end of the surface layer and the back layer, thereby making the upper end of the shell surface layer higher than the upper end of the back layer.

2. A wax pattern assembly according to claim 1, wherein, The annular groove (120) has an outer annular inclined downward surface (121) on its wall, and the height of the outer annular inclined downward surface (121) gradually decreases from the inside to the outside.

3. A wax pattern assembly according to claim 2, wherein, The wall of the annular groove (120) also has an inner annular inclined downward surface (122). The inner annular inclined downward surface (122) gradually increases in height from the inside to the outside. The inner annular inclined downward surface (122) is located inside the ring of the outer annular inclined downward surface (121) and is connected to the upper end of the outer annular inclined downward surface (121), thereby forming an annular peak (123). The annular peak (123) is used to make the upper end of the shell surface layer higher than the upper end of the back layer. The inner annular inclined downward surface (122) is used to make the gate bar (100) form the gate of the shell and guide the casting liquid to flow into the gate.

4. A wax pattern assembly according to claim 1, wherein, The sprue bar (100) has a hollow cavity (130) in the middle, which is used to prevent wax expansion when the shell is dewaxed. The bottom of the hollow cavity (130) has a connecting nut part (131), which is used to connect the mold hook.

5. A wax module according to claim 2, characterized in that, The lower end of the outer annular inclined descending surface (121) is also connected to a cylindrical surface (124).

6. A wax module according to claim 5, characterized in that, The cylindrical surface (124) has a plurality of recessed grooves (1241), which are arranged along the circumference. The recessed grooves (1241) are used to increase the connection strength between the coated surface layer and the back layer.

7. A wax module according to claim 6, characterized in that, The recessed groove (1241) also has a stop (1242) on one side of the groove wall. The recessed groove (1241) and the stop (1242) are used to form a hook-shaped groove on the outer wall of the surface layer coated in the recessed groove (1241). The hook-shaped groove is used to form a hook-shaped part on the inner wall of the back layer coated on the surface layer. The hook-shaped part is stuck in the hook-shaped groove, thereby increasing the connection strength between the coated surface layer and the back layer.

8. A wax module according to claim 7, characterized in that, The baffle (1242) has a secondary groove (1243) on the side facing the recessed groove (1241), and the secondary groove (1243) is used to increase the connection strength between the coating surface layer and the back layer. The bottom of the recessed groove (1241) has an inclined baffle (1244) to prevent the coated back layer from extending upward beyond the baffle (1244).

9. A shell, characterized in that, The mold is formed by sequentially coating a top layer and a back layer with the wax mold assembly described in any one of claims 1-8. At the gate of the mold shell, the top of the top layer forms an annular peak, and the upper end of the back layer is lower than the upper end of the top layer.

10. A method for machining high-precision castings, characterized in that, Using the wax mold according to any one of claims 1-8, the method includes the following steps: S1. Press wax to form a mold, and assemble it with a casting rod to obtain a wax film assembly; S2. Wax film coating for shell formation, wherein when coating is applied to the annular groove (120) at the bottom of the annular flange (111) of the gate (110), it is done according to either method one or method two: Method 1: The annular groove (120) is filled with the surface material, and the back material does not enter the annular groove (120). The back material is only coated on the outer wall of the surface material, and its upper end is lower than the lower end of the annular groove (120). The annular groove (120) makes the upper end of the back layer lower than the upper end of the surface layer. If the back material wants to enter the gate of the shell, it needs to bypass the upper end of the surface layer. Method 2: The annular groove (120) is coated with the surface material. The annular groove (120) makes the surface material form a surface groove. The upper end of the back material is formed in the surface groove, which also makes the upper end of the back layer lower than the upper end of the surface layer. If the back material wants to enter the gate of the shell, it needs to bypass the surface groove and the upper end of the surface layer. S3. Dewaxing and casting to obtain the casting.

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