Investment casting shell and method of making, investment casting method and part manufacturing method

Abstract

The present application provides a kind of investment casting mould shell, mould shell preparation method, investment casting method and part manufacturing method.The outer side of investment casting mould shell includes reticular projection.The mould shell preparation method includes: preparing face layer and the 1st layer to the Nth layer back layer;In the N+1 layer back layer, add the ceramic green body of reticular structure;Prepare the remaining back layer, and every time sand is removed from the mesh of reticular structure when starting from the N+2 layer. Investment casting method includes using the mould shell preparation method to prepare mould shell, by adding reticular structure in mould shell to improve the rigidity in the solidification process of casting, and form reticular hot spot to facilitate the liquid metal along the reticular channel to make up. The part manufacturing method includes using the investment casting method to prepare part blank and processing part blank, and processing part blank includes: detecting the actual size of part blank;Solve the offset between actual size and casting theoretical model;According to the offset, adjust the positioning reference of part blank.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of processing and casting, in particular to a lost foam mold shell, a mold shell preparation method, a lost foam casting method and a part manufacturing method. BACKGROUND

[0002] The economic benefit of an aero-engine is an important indicator of the aero-engine, and increasing the turbine inlet temperature of the aero-engine is a main means to improve the turbine efficiency of the aero-engine. With the increasing size of the aero-engine or in order to match the structure shrinkage in cold and hot states, the casing of the aero-engine is more and more segmented, and the blade parts with large-size rim plate structures play an increasingly important role in the turbine parts of the aero-engine. The structure of the blade part 1 is shown in Figure 1 The blade part 1 includes a large-size rim plate structure 11 and a blade body structure 12, and examples of the blade part include a straightening vane casting, a casing support plate casting and related high-temperature alloy structure castings, etc. The blade part is designed by three-dimensional aerodynamics, has a complex structure and a curved surface structure, and is usually manufactured by a method of machining the casting blank after precision casting.

[0003] The main difficulties in casting the blade part 1 with the large-size rim plate structure 11 lie in the metallurgical defects such as shrinkage porosity caused by the change in thickness of the structure, and the profile tolerance caused by the deformation of the large-size rim plate structure 11 due to casting stress, etc. The metallurgical defects can be solved by optimizing pouring and increasing feeding, while the change in size and structure caused by the casting stress, etc. has no certain deformation rule for the blade part 1 with the large-size rim plate structure 11, and is difficult to solve by adjusting the mold, and is usually solved by cold or hot straightening in the later stage, but the straightening will affect the dimensional consistency and service reliability of the casting.

[0004] The main difficulty in machining the blade part 1 with the large-size rim plate structure lies in the accurate positioning of the part. Due to the complex outer shape of the blade part 1, it is difficult to directly establish a three-dimensional reference by using the original part structure characteristics, and currently the six-point positioning principle is used for part positioning and machining. However, due to the design of the six points on the surface of the theoretical model of the casting, the actual positions of the six points of the part blank will deviate from the theoretical points due to the influence of factors such as casting stress and mold shell expansion in the process of lost foam casting. When the size span of the part is large, the position deviation of the six points will cause the part blank to be unable to contact with some of the six points, or even if the part blank contacts with all the six points, the position deviation far from the position of the six points is accumulated and enlarged, resulting in the size deviation of the part machining, and therefore it is necessary to adjust the positioning reference according to the offset between the actual size of the part blank and the theoretical model of the casting.

[0005] For example, the patent document with the authorization announcement No. CN105423970B discloses a positioning method for manufacturing a casing support plate. Three positioning bosses A1, A2 and A3 are arranged on one side of the blade body of the casing support plate in a three-point positioning mode. A positioning boss is arranged at a positioning point B1 on the upper part of the installation side of the blade body, and a positioning boss is arranged at a positioning point B2 on the lower part of the installation side of the blade body. A positioning boss is arranged at a positioning point C1 on the flange back of the casing support plate. The three positioning bosses A1, A2 and A3 are used as the main reference to realize blade positioning. The positioning bosses B1 and B2 are used as auxiliary positioning points to position the axial height dimension. The positioning boss C1 is used as an auxiliary reference to position the circumferential dimension. The positioning bosses are formed on the casing support plate by casting, and the height of the bosses is adjusted by polishing during the machining process to adjust the machining position of the casting. The method casts multiple positioning bosses on the part body, which increases the structural complexity of the casting. The machining position is adjusted by polishing the bosses, and the bosses need to be cut off after the part is machined, which is low in operation efficiency and affects the surface quality of the part. SUMMARY

[0006] An object of the present application is to provide a mold shell for investment casting, which can reduce casting defects such as deformation and shrinkage of the casting.

[0007] To achieve the object, the mold shell for investment casting includes an inner side and an outer side, and the outer side includes a net-shaped protrusion.

[0008] In one or more embodiments of the mold shell for investment casting, the net-shaped protrusion is formed by adding a net-shaped structure of ceramic green body at the middle position of the shell thickness during the shell making process.

[0009] In one or more embodiments of the mold shell for investment casting, the mold shell for investment casting is used for casting a blade type part, which includes a rim plate structure and a blade body structure, and the position and size of the net-shaped protrusion correspond to the non-flow channel side surface of the rim plate structure.

[0010] In one or more embodiments of the mold shell for investment casting, the grid density of the center of the net-shaped protrusion is higher than the grid density of the edge.

[0011] In one or more embodiments of the mold shell for investment casting, the thickness of the center of the net-shaped protrusion is higher than the thickness of the edge.

[0012] The shell mold for investment casting can improve the rigidity of the shell mold, thereby improving the rigidity of the casting during solidification, reducing the deformation of the casting, and avoiding the profile tolerance of the casting being out of tolerance. In addition, the shell mold at the mesh line position of the mesh structure is thicker than the shell mold at the mesh position, and thus the cooling speed of the shell mold at the mesh line position and the corresponding position on the casting is slower, a mesh thermal joint can be formed, so that the metal liquid can supplement the casting along the mesh channel, thereby reducing the casting defects such as shrinkage.

[0013] Another object of the present application is to provide a shell mold preparation method, and the shell mold prepared by the method can reduce the deformation and casting defects such as shrinkage of the casting.

[0014] The shell mold preparation method for preparing a shell mold for investment casting comprises the following steps: preparing a face layer and first to Nth back layers; adding a mesh structure ceramic green body to an (N+1)th back layer; and preparing the remaining back layers, wherein from the (N+2)th layer, each time sand is sprayed, part of the sand accumulated in the mesh of the mesh structure is removed.

[0015] In one or more embodiments of the shell mold preparation method, N=2 or 3 or 4.

[0016] In one or more embodiments of the shell mold preparation method, the shell mold is used for casting a vane type part, the vane type part comprises a rim plate structure and a vane body structure, and the position and size of the mesh structure correspond to the non-flow channel side surface of the rim plate structure.

[0017] In one or more embodiments of the shell mold preparation method, the mesh density of the center of the mesh structure is higher than the mesh density of the edge.

[0018] In one or more embodiments of the shell mold preparation method, the thickness of the center of the mesh structure is higher than the thickness of the edge.

[0019] The shell mold for investment casting prepared by the method can effectively obtain the aforementioned shell mold with the outer side surface comprising the mesh protrusion. By adding the mesh structure to the shell mold, the rigidity of the shell mold can be improved, thereby improving the rigidity of the casting during solidification, reducing the deformation of the casting, and avoiding the profile tolerance of the casting being out of tolerance. In addition, the shell mold at the mesh line position of the mesh structure is thicker than the shell mold at the mesh position, and thus the cooling speed of the shell mold at the mesh line position and the corresponding position on the casting is slower, a mesh thermal joint can be formed, so that the metal liquid can supplement the casting along the mesh channel, thereby reducing the casting defects such as shrinkage.

[0020] Another object of the present application is to provide a shell mold preparation method, and the shell mold prepared by the method can reduce the deformation and casting defects such as shrinkage of the casting.

[0021] The investment casting method comprises the following steps: preparing a mold shell by using the mold shell preparation method, adding a net structure in the mold shell to improve the rigidity of the casting during solidification, and forming a net thermal joint to facilitate the feeding of the metal liquid along the net channel to the casting.

[0022] Another object of the present application is to provide a part manufacturing method, which can improve the casting quality and machining quality of the part.

[0023] The part manufacturing method comprises the following steps: preparing a part blank by using the investment casting method, and machining the part blank, wherein the machining of the part blank comprises the following steps: detecting the actual size of the part blank, solving the offset between the actual size and the theoretical model of the casting, and adjusting the positioning reference of the part blank according to the offset.

[0024] In one or more embodiments of the part manufacturing method, the actual size is detected by using a three-coordinate measurement or optical three-dimensional scanning.

[0025] In one or more embodiments of the part manufacturing method, the offset is solved by using optimal fitting.

[0026] In one or more embodiments of the part manufacturing method, the positioning reference of the part blank is adjusted by using an adjustable positioning tool, the adjustable positioning tool is provided with six positioning members according to the six-point positioning principle, and the positions of some or all of the six positioning members are adjustable.

[0027] In one or more embodiments of the part manufacturing method, the part is a blade part, which comprises a rim structure and a blade body structure.

[0028] In one or more embodiments of the part manufacturing method, the positioning reference of the part blank is adjusted by using an adjustable positioning tool, the adjustable positioning tool is provided with six positioning members according to the six-point positioning principle, the positions of the six positioning members are all adjustable, three of the six positioning members are in point contact with one surface of the blade body structure, two of the six positioning members are in line contact with one side edge of the blade body structure, and the remaining one of the six positioning members is in point contact with a non-flow channel side surface of the rim structure.

[0029] The part manufacturing method can reduce the casting defects such as deformation and shrinkage of the part blank, improve the casting quality, and adjust the positioning reference of the part blank according to the offset between the actual size of the part blank and the theoretical model of the casting, so that the part blank can be accurately positioned in the deformed condition and the machining quality of the part can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and other features, aspects and advantages of the present application will become more apparent by reference to the following Description and appended claims in conjunction with the accompanying drawings in which:

[0031] Figure 1 is a schematic view of a vane-like part.

[0032] Figure 2 is a schematic view of adding a mesh structure in the process of making a mold shell.

[0033] Figure 3 is a schematic view of a six-point positioning scheme for a vane-like part.

[0034] Figure 4 is a schematic view of an adjustable positioning tool without auxiliary clamps. DETAILED DESCRIPTION

[0035] The following disclosure provides various different embodiments or examples of implementing the subject technology. For simplicity of disclosure, specific examples of elements and arrangements are described below to provide a thorough description of the present technology. It should be noted, however, that these are only examples and are not intended to be limiting of the overall scope of the present technology. It is also to be noted that the appended drawings are provided by way of example and are not to be construed as being strictly in accordance with scale. Furthermore, certain features, structures or characteristics of one or more embodiments of the application can be combined in any manner.

[0036] The investment casting mold shell according to embodiments of the present application comprises an inner side and an outer side, the inner side being the side facing the casting during casting, and the outer side comprising a mesh protrusion. The mesh protrusion can improve the rigidity of the mold shell, and thus the rigidity of the casting during solidification, and reduce the deformation of the casting, and avoid the profile tolerance of the casting being out of tolerance. In addition, the mold shell at the position of the mesh line of the mesh protrusion is thicker than the mold shell at the position of the mesh, and thus the cooling speed at the position of the mesh line of the mold shell and the corresponding position of the casting is slower, and a mesh thermal section can be formed, so that the metal liquid can supplement the casting along the mesh channel, and thus reduce casting defects such as shrinkage.

[0037] The mesh protrusion is formed by adding a mesh structure of a ceramic green body at the middle position of the thickness of the mold shell during the shell-making process, as described below.

[0038] The investment casting mold shell can be used to cast, for example, Figure 1The shown blade-like part 1 includes a large-size rim plate structure 11 and a blade body structure 12, and the position and size of the net-shaped protrusion correspond to the non-flow channel side surface 111 of the rim plate structure 11, that is, the position of the net-shaped protrusion can cover the center and most or all of the surface of the non-flow channel side surface 111, so as to improve the rigidity of the mold shell at the position of the corresponding rim plate structure 11 and form a net-shaped hot spot, so as to facilitate the feeding of the metal liquid along the net-shaped channel to the rim plate structure 11, thereby reducing the deformation and shrinkage porosity and other casting defects of the rim plate structure 11 and improving the casting quality. Optionally, the net-shaped protrusion can also be provided at other parts of the investment casting mold shell to further improve the casting quality of the blade-like part 1.

[0039] Optionally, the grid density of the center of the net-shaped protrusion is higher than the grid density of the edge. Since the center part of the casting solidifies later and is more affected by the casting stress and is more prone to deformation, the grid density of the center of the net-shaped protrusion is set to be higher, so as to further improve the rigidity of the mold shell, reduce the deformation of the center part of the casting, and play a role of sequential feeding to reduce shrinkage and other casting defects.

[0040] Optionally, the thickness of the center of the net-shaped protrusion is higher than the thickness of the edge, so as to further improve the rigidity of the mold shell, reduce the deformation of the center part of the casting, and play a role of sequential feeding to reduce shrinkage and other casting defects.

[0041] The mold shell preparation method according to the embodiment of the present application is used for preparing a mold shell for investment casting, and includes the following steps:

[0042] 1. Preparing a surface layer and 1st to Nth back layers;

[0043] 2. Referring to Figure 2 After the surface of the dried Nth back layer 3 is coated with slurry, the ceramic green body 4 with a net-shaped structure is added to form an N+1th back layer, and the N+1th back layer can not be sand blasted;

[0044] 3. Preparing the remaining back layers, wherein from the N+2th layer, the sand in the mesh of the net-shaped structure is removed each time the sand is blasted, for example, by compressed air blowing, so as to avoid excessive sand accumulation in the mesh, resulting in excessive thickness of the mold shell in the mesh part;

[0045] 4. Subsequent processes such as dewaxing and mold shell baking are performed.

[0046] The method can effectively obtain the aforementioned mold shell with the outer side including the net-shaped protrusions. By adding the net-shaped structure in the mold shell, the rigidity of the mold shell can be improved, thereby improving the rigidity of the casting during solidification, reducing the deformation of the casting, and avoiding the out-of-tolerance of the profile of the casting. In addition, the mold shell at the position of the net lines of the net-shaped structure is thicker than the mold shell at the position of the mesh, and thus the cooling speed of the mold shell at the position of the net lines and the corresponding position of the casting is slower, so that the net-shaped hot spots can be formed to facilitate the feeding of the metal liquid along the net-shaped channels to the casting, thereby reducing the shrinkage and other casting defects.

[0047] The total number of layers of the surface layer and the back layer of the mold shell is about 10 layers, for example, 7-15 layers. The ceramic green body 4 of the net-shaped structure is added at the middle position of the thickness of the mold shell, for example, N=2 or 3 or 4, so as to avoid affecting the surface layer and ensure the good combination of the net-shaped structure and other back layers.

[0048] The ceramic green body 4 of the net-shaped structure can be prepared by pressing or other methods commonly used in the art. The ceramic green body 4 can be a whole piece or can be spliced from multiple pieces. Multiple ceramic green bodies 4 of the net-shaped structure can be arranged at different positions of the mold shell as needed.

[0049] The material of the ceramic green body 4 can be an oxide, a nitride, a carbide, an aluminosilicate, or other materials commonly used in the art. The material can be one of the above materials or a mixture of multiple materials.

[0050] Alternatively, the ceramic green body 4 of the net-shaped structure can be prepared from the material used for sanding the mold shell, so as to simplify the mold shell preparation method and obtain the same thermal expansion coefficient and other properties as the other back layers. Alternatively, the ceramic green body 4 of the net-shaped structure can be prepared from a material different from the other back layers, so as to obtain different properties from the other back layers, for example, higher rigidity.

[0051] The mold shell prepared by the mold shell preparation method can be used to cast the aforementioned blade part 1. The position and size of the net-shaped structure correspond to the non-flow channel side surface 111 of the edge plate structure 11, that is, the position of the net-shaped structure can cover the center and most or all of the surface of the non-flow channel side surface 111, so as to improve the rigidity of the mold shell at the position of the corresponding edge plate structure 11 and form net-shaped hot spots to facilitate the feeding of the metal liquid along the net-shaped channels to the edge plate structure 11, thereby reducing the deformation and shrinkage and other casting defects of the edge plate structure 11 and improving the casting quality. Alternatively, the net-shaped structure can also be arranged at other positions of the mold shell to further improve the casting quality of the blade part 1.

[0052] Optionally, the grid density of the center of the net structure is higher than the grid density of the edge. Since the center part of the casting solidifies later and is more affected by the casting stress, it is more prone to deformation. By setting the grid density of the center of the net structure to be higher, the rigidity of the mold shell can be further improved, the deformation of the center part of the casting can be reduced, and the effect of sequential feeding can be achieved to reduce casting defects such as shrinkage.

[0053] Optionally, the thickness of the center of the net structure is higher than the thickness of the edge, so as to further improve the rigidity of the mold shell, reduce the deformation of the center part of the casting, and achieve the effect of sequential feeding to reduce casting defects such as shrinkage.

[0054] The investment casting method according to the embodiments of the present application comprises the steps of: preparing a mold shell by the mold shell preparation method described above, and adding a net structure in the mold shell to improve the rigidity of the mold shell, so as to improve the rigidity of the casting during solidification, reduce the deformation of the casting, avoid the profile tolerance of the casting being out of tolerance, and form a net thermal joint to facilitate the feeding of the metal liquid along the net channel to the casting, thereby reducing casting defects such as shrinkage.

[0055] Referring to Figure 2 Optionally, by using wax film pouring rods with different diameters to assemble the wax mold, the diameter of the sprue 5 near the center of the non-runner side surface 111 of the flange structure 11 is greater than the diameter of the sprue 6 near the edge of the non-runner side surface 111, so as to achieve the effect of sequential feeding and reduce casting defects such as shrinkage.

[0056] The part manufacturing method according to the embodiments of the present application comprises the steps of: preparing a part blank by the investment casting method described above, and processing the part blank, wherein the step of processing the part blank comprises:

[0057] S1, detecting the actual size of the part blank;

[0058] S2, solving the offset between the actual size of the part blank and the theoretical model of the casting;

[0059] S3, adjusting the positioning reference of the part blank according to the offset;

[0060] S4, processing the part blank.

[0061] The part manufacturing method can reduce the deformation and casting defects such as shrinkage of the part blank, and improve the quality of casting. By adjusting the positioning reference of the part blank according to the offset between the actual size of the part blank and the theoretical model of the casting, the positioning of the part blank in the deformed condition can be realized, and the processing quality of the part can be improved.

[0062] The actual size of the part blank can be measured by a coordinate measuring machine or an optical three-dimensional scanner, such as a blue light scanner, a white light scanner, or a laser scanner, so that the actual size data of the part blank can be conveniently and reliably obtained.

[0063] The offset between the actual size and the theoretical model of the casting can be solved by best fitting, and the algorithm provided by existing commercial calculation software can be used, so that the required offset can be conveniently and reliably obtained.

[0064] Referring to Figure 3 and Figure 4 In one embodiment, the part manufacturing method is used to manufacture the aforementioned blade part 1, and an adjustable positioning tool 2 is used to adjust the positioning reference of the part blank. The adjustable positioning tool 2 includes a support 20, and six positioning members are arranged on the support 20 according to the six-point positioning principle: a first positioning member 21, a second positioning member 22, a third positioning member 23, a fourth positioning member 24, a fifth positioning member 25, and a sixth positioning member 26. In addition, the adjustable positioning tool 2 also includes auxiliary clamping devices (not shown), which are only used to prevent the part from deflecting during machining without affecting the positioning of the part.

[0065] The first positioning member 21, the second positioning member 22, and the third positioning member 23 correspond to points A1, A2, and A3, respectively, and are used to contact one of the surfaces 121 of the blade body structure 12. The fourth positioning member 24 and the fifth positioning member 25 correspond to points B1 and B2, respectively, and are used to contact one of the side edges 122 of the blade body structure 12. The sixth positioning member 26 corresponds to point C1 and is used to contact the non-flow channel side surface 111 of the rim plate structure 11.

[0066] Each positioning member of the adjustable positioning tool 2 includes an axially movable pin shaft 27 and a support head 28 at one end of the pin shaft 27. By solving the offset A1Z, A2Z, A3Z, B1Y, B2Y, C1X between the actual size of the part blank and the theoretical model of the casting (wherein A1Z represents the offset of the A1 point of the part blank relative to the A1 point of the theoretical model of the casting on the Z axis, and the rest are sequentially similar), the position of each pin shaft 27 on the adjustable positioning tool 2 can be adjusted to adjust the offset of the six points A1, A2, A3, B1, B2, and C1 on the corresponding axis. By changing the six points in space, the six-point correction of the part blank under deformation is realized, the accurate positioning of the part blank is ensured, and the machining quality of the part is improved.

[0067] The support head 28 of the first positioning member 21, the second positioning member 22, the third positioning member 23 and the sixth positioning member 26 is designed as a needle, and point contact is formed between the blade-like part 1; the support head 28 of the fourth positioning member 24 and the fifth positioning member 25 is designed as a blade, and line contact is formed between the blade-like part 1, so that the blade-like part 1 can be limited when adjusted in the Z-axis.

[0068] In other embodiments, the adjustable positioning tool 2 can also be used for positioning other types of parts, and all the six positioning members can be adjustable, or only some of the positioning members can be adjusted.

[0069] Although the present application is disclosed with reference to the preferred embodiments above, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present application. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application, fall within the protection scope defined by the claims of the present application.

Claims

1. An investment casting method, characterized in that, Includes the following steps: The preparation of the mold shell, which is used for casting blade-like parts, includes a rim structure and a blade body structure. The mold shell preparation includes the following steps: Prepare the surface layer and the first to Nth back layers; A ceramic green body with a mesh structure is added to the N+1th back layer. The position and size of the mesh structure correspond to the non-flow channel side surface of the flange structure. The mesh structure is used to form a mesh heat joint. Prepare the remaining back layer, wherein starting from the N+2th layer, each time sand is applied, some of the sand accumulated in the mesh of the mesh structure is removed; The diameter of the sprue near the center of the non-runner side surface of the mold shell is made larger than the diameter of the sprue near the edge of the non-runner side surface, so as to achieve the effect of sequential shrinkage compensation.

2. The investment casting method as described in claim 1, characterized in that, The mesh density at the center of the mesh structure is higher than the mesh density at the edges.

3. The investment casting method as described in claim 1, characterized in that, The thickness of the center of the mesh structure is higher than the thickness of the edges.

4. The investment casting method as described in claim 1, characterized in that, N = 2, 3, or 4.

5. A method for manufacturing a part, characterized in that, The method for manufacturing the part includes: The part blank is prepared by the investment casting method as described in any one of claims 1-4; The machining of the part blank includes: Detect the actual dimensions of the part blank; Solve for the offset between the actual dimensions and the theoretical model of the casting; The positioning reference of the part blank is adjusted according to the offset.

6. The part manufacturing method as described in claim 5, characterized in that, The actual dimensions are detected using coordinate measuring machine (CMM) or optical 3D scanning.

7. The part manufacturing method as described in claim 5, characterized in that, The offset is solved by best fitting.

8. The method for manufacturing a part as described in any one of claims 5 to 7, characterized in that, An adjustable positioning fixture is used to adjust the positioning reference of the part blank. The adjustable positioning fixture is set with six positioning components according to the six-point positioning principle, and some or all of the six positioning components can be adjusted in position.

9. The method for manufacturing a part as described in any one of claims 5 to 7, characterized in that, The part is a blade-type part, including a rim structure and a blade body structure.

10. The part manufacturing method as described in claim 9, characterized in that, An adjustable positioning fixture is used to adjust the positioning reference of the part blank. The adjustable positioning fixture is set with six positioning components according to the six-point positioning principle. The positions of the six positioning components are all adjustable. Three of the six positioning components are in point contact with one side of the blade structure, two of the six positioning components are in line contact with one side of the blade structure, and the remaining one of the six positioning components is in point contact with the non-flow channel side surface of the flange structure.

Images