阅读说明：本技术 精密铸造芯撑的方法 (Method for precisely casting chaplet ) 是由 斯图尔特·T·韦尔奇 于 2020-01-21 设计创作，主要内容包括：本发明提供了一种支承陶瓷注塑成型(CIM)工艺的铸模模具内的可溶插入件结构的方法,所述方法包括以下步骤：形成支承所述模具内的所述可溶插入件结构的至少一个芯撑,所述芯撑由具有与主要内部芯结构基本相似的物理化学性质的陶瓷材料形成；以及定位所述芯撑以使所述可溶插入件结构接触所述模具,所述可溶插入件与所述铸模模具的边缘间隔开。所述芯撑可包括耐火材料或耐火材料的组合。(The present invention provides a method of supporting a soluble insert structure within a mold die of a Ceramic Injection Molding (CIM) process, the method comprising the steps of: forming at least one chaplet supporting the soluble insert structure within the mold, the chaplet being formed of a ceramic material having substantially similar physicochemical properties as a primary internal core structure; and positioning the chaplet such that the soluble insert structure contacts the mold, the soluble insert being spaced apart from an edge of the casting mold. The chaplet may comprise a refractory material or a combination of refractory materials.)

1. A method of supporting a soluble insert structure within a mold die of a Ceramic Injection Molding (CIM) process, the method comprising the steps of: forming a soluble insert structure, forming at least one chaplet supporting the soluble insert structure within the mold, the chaplet being formed of a ceramic material having substantially similar physicochemical properties as the soluble insert structure; and positioning the chaplet such that the soluble insert structure contacts the mold, the soluble insert being spaced apart from an edge of the casting mold.

2. The method of claim 1, wherein the chaplet comprises a refractory material or a combination of refractory materials.

3. The method of claim 2, wherein the refractory material is selected from the group consisting of silica, zirconia, alumina, aluminosilicates, and combinations thereof.

4. The method of claim 1, wherein the chaplet is adhered to the surface of the soluble insert or the mold using glue.

5. The method of claim 1, wherein the chaplet is adhered to the surface of the soluble insert by contacting the chaplet with the surface of the soluble insert and melting a surface of the chaplet or the surface of the soluble insert.

6. The method of claim 1, wherein the chaplet is adhered to the mold by contacting the chaplet with the mold and melting the surface of the chaplet or the surface of the mold at a location where the chaplet will contact.

7. The method of claim 4, wherein the chaplet is mounted using a location feature on the mold.

8. The method of claim 5, wherein the chaplet is mounted using a location feature on the mold.

9. The method of claim 1, wherein the resulting soluble core and chaplet have a bulk density in the range of about 1.3g/cc to 2.5 g/cc.

10. The method of claim 1, wherein the resulting soluble core and the chaplet have a core with a porosity of about 20% to 40%.

11. The method of claim 1, wherein the resulting soluble core and chaplet are made of silica in the range of about 30-98 wt%.

12. The method of claim 1, wherein the CIM material used to form the soluble core and the chaplet comprises a binder in a range of about 10 to 25 wt%.

13. The method of claim 1 for producing a vane, blade, or seal for a gas turbine engine.

14. The method of claim 1, further comprising injection molding an object around the soluble insert structure and the at least one chaplet within the mold die.

Technical Field

The present invention relates to a method of supporting a core during dewaxing or precision casting.

Background

The use of dewaxing or precision casting in the production of blades or buckets for gas turbine engines is well known. Precision casting is an evolution of the dewaxing casting process in which the desired part is manufactured by injecting wax into a mold and then dipping the wax into a ceramic slurry to form a shell. The wax is then removed and the ceramic shell is fired to harden. The resulting shell has an open cavity for pouring metal into it to produce a product of the desired size and shape. Precision casting is an evolution of this process and is used to form hollow near net shape metal parts. The latter process is employed because it allows complex shapes to be reliably manufactured.

The process may further be used to form a complex series of internal cooling passages that are desirable in modern turbine blade and bucket designs. To produce these parts, ceramic cores are typically manufactured separately using Ceramic Injection Molding (CIM) techniques. In this process, a ceramic material (typically silica) is suspended in an organic binder prior to injection into a mold cavity of the desired shape. Prior to injecting the wax, the ceramic core is positioned in the mold and remains in the ceramic shell during the addition of the molten metal. The inner ceramic core may then be removed at a later stage of the process to leave voids where it is located. The ceramic core may be manufactured using a soluble core manufacturing technique. The soluble insert is prefabricated and placed in a mold prior to injecting the ceramic core material. The dissolvable insert may then be dissolved and removed. British patent GB 2096523B and US4384607 disclose methods for this process. The use of a soluble core manufacturing technique is desirable because it allows the manufacture of complex reentrant features.

One problem with producing hollow parts using precision casting processes is the ability to hold the ceramic core in its correct position while undergoing various process stages. One way to overcome this problem is to use a chaplet, which may be formed of a plastic material, that may be installed between the core and the outer mold prior to the wax injection process. Chaplets are an effective method of supporting the ceramic core during injection into the wax pattern, however, this practice is not directly convertible to overcome the problem of soluble insert movement during ceramic core manufacture. This is because the plastic chaplet leaves a depression in the formed ceramic shape. While efforts may be made to repair or design these recessed features, these problems limit the range of use of the plastic chaplet.

As discussed, current methods have the problem of removing marks left by the plastic core support during the process, which can affect the overall part and require further processing of the final product. Moreover, they may not hold the soluble insert in the correct position to the required tolerances. When using soluble core manufacturing techniques, the current way to hold the soluble insert in place is through the use of core prints, which are features of the soluble insert that extend beyond the soluble insert and thus alter the profile of the soluble insert, which is detrimental to the core design. Finally, it is desirable to reduce the number of contact points between the mold and the soluble insert so that a larger unsupported surface can be achieved, thereby allowing for the creation of improved cooling designs related to turbine component technology. However, to achieve this, the soluble insert must be well supported elsewhere to prevent movement, as any slippage or deformation of the soluble insert during the molding process can result in an inconsistent ceramic core. It is an object of the present invention to overcome or at least minimise one or more of these limitations in precision casting processes.

Disclosure of Invention

In a first aspect of the present disclosure, there is provided a method of supporting a soluble insert structure within a mold die of a Ceramic Injection Molding (CIM) process, the method comprising the steps of: forming a soluble insert structure, forming at least one chaplet supporting the soluble insert structure within the mold, the chaplet being formed of a ceramic material having substantially similar physicochemical properties as the soluble insert structure; and positioning the chaplet such that the soluble insert structure contacts the mold, the soluble insert being spaced apart from an edge of the casting mold.

The benefit of the invention is that the chaplet becomes an integral part of the ceramic core. This allows the core and the chaplet to be removed simultaneously in a downstream ceramic core removal process after the precision casting process is performed; this simplifies the precision casting process. The method may also limit damage to the soluble insert and subsequent inconsistencies of the ceramic core, or limit the compromise design that must be added at the design stage to accommodate the positioning of the soluble insert. Thus, the method allows for the manufacture of more complex internal structures, which in turn may result in components having improved cooling flow therein.

The chaplet may comprise a refractory material or a combination of refractory materials.

The refractory material may be selected from silica, zirconia, alumina, aluminosilicates, and combinations thereof.

The chaplet may be adhered to the surface of the dissolvable insert using glue.

The chaplet may be adhered to the surface of the soluble insert by contacting the chaplet with the surface of the soluble insert and melting the surface of the chaplet or the surface of the soluble insert.

The chaplet may be adhered to the mold surface by contacting the chaplet with the mold surface and melting the surface of the chaplet or the mold surface.

The chaplet is installed using a location feature on the mold.

The soluble core and the chaplet obtained in the process can have a bulk density in the range of about 1.3g/cc to 2.5 g/cc.

The soluble core and the chaplet obtained in the process may have a core with a porosity of about 20% to 40%.

The soluble core and the chaplet obtained in the process may be made of silica in the range of about 30 to 98 weight percent.

The CIM material for the soluble core and chaplet in the method includes a binder in a range of about 10 wt% to 25 wt%.

The method may be used to produce buckets, blades or seal segments for gas turbine engines.

The chaplets may be removed from the final casting simultaneously with the core.

A variety of soluble cores may be used in the casting process.

The method may further include injection molding the object around the soluble insert structure and the at least one chaplet in a mold die.

Those skilled in the art will appreciate that features described in relation to any one of the above aspects may be applied to any other aspect, with appropriate modification, unless mutually exclusive. Furthermore, any feature described herein may be applied to any aspect and/or in combination with any other feature described herein, unless mutually exclusive.

Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional side view of a gas turbine engine; and

fig. 2 is one example of a chaplet suitable for use in the methods of the present disclosure.

Detailed Description

Referring to FIG. 1, a gas turbine engine, generally indicated at 10, has a main axis of rotation 11. The engine 10 includes, in axial flow series, an air intake 12, a propeller fan 13, an intermediate pressure compressor 14, a high pressure compressor 15, a combustion apparatus 16, a high pressure turbine 17, an intermediate pressure turbine 18, a low pressure turbine 19, and an exhaust nozzle 20. Nacelle 21 generally surrounds engine 10 and defines air intake 12 and exhaust nozzle 20.

The gas turbine engine 10 operates in a conventional manner such that air entering the air intake 12 is accelerated by the fan 13 to produce two air streams: a first flow into the intermediate pressure compressor 14 and a second flow through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the airflow directed thereto before delivering the air to the high pressure compressor 15 where further compression occurs.

The compressed air discharged from the high-pressure compressor 15 is led into a combustion device 16, where the compressed air is mixed with fuel and the mixture is combusted. The resulting hot combustion products are then expanded through a high pressure turbine 17, an intermediate pressure turbine 18, and a low pressure turbine 19, driving the high pressure turbine, the intermediate pressure turbine, and the low pressure turbine to provide additional propulsive thrust, before being discharged through a nozzle 20. The high pressure turbine 17, the intermediate pressure turbine 18 and the low pressure turbine 19 each drive the high pressure compressor 15, the intermediate pressure compressor 14 and the fan 13, respectively, via suitable interconnecting shafts.

Other gas turbine engines to which the present disclosure is applicable may have alternative configurations. By way of example, such engines may have an alternative number of interconnected shafts (e.g., two) and/or an alternative number of compressors and/or turbines. Additionally, the engine may include a gearbox disposed in the drive train from the turbine to the compressor and/or fan.

The production of turbine components for such engines requires complex casting. For this purpose, a precision casting process is used. Prior to injecting the wax, a ceramic core member is positioned within the recess of the mold. A soluble core manufacturing technique is used because it enables the formation of complex internal passages that cannot be formed by conventional means due to the pulling flat in the mold. During the process of preventing movement of the core, plastic chaplets are used within the pockets of the mold to support the ceramic core member. The plastic chaplet is placed within the mold, typically attached to the ceramic core, to prevent any movement of the ceramic core during the wax injection process. Thus, the chaplet serves to retain the smallest wall portion within the casting. Any movement of the ceramic core during this process may result in a faulty blade that must be rejected. In cases where design requirements dictate that only a small number of contact points be used or a large unsupported surface is required, the ceramic core portion has a greater likelihood of movement and/or fracture due to lack of support. To avoid this, it is crucial to select and locate the chaplet; thus, by having different sizes and shapes of these chaplets, allows for the fabrication of these complex structures.

In the manufacture of the blade, vane or seal section, standard processes are known. When a high level design is required, the soluble core manufacturing technique can be selected and the appropriately shaped ceramic core formed by injection molding the ceramic material into a mold containing a soluble insert. At least one chaplet for supporting a soluble insert structure within a mold is formed of a ceramic material. In this case, the chaplet is formed of a material having similar physicochemical properties to the core. That is, they may have similar density or solubility, physical or thermal properties of one or more. The chaplets and cores may be formed of ceramics including silica, zirconia, alumina, aluminosilicates, or other refractory materials, and may be bonded using wax or polymer-based binders. Refractory materials are used because they are resistant to decomposition by heat, pressure or chemicals, which is desirable in casting processes. The soluble insert is placed in place within the mold, along with the necessary chaplets, to prevent the soluble insert from moving. The positioning of the chaplet relative to the soluble insert requires consideration of the location of the soluble core and the dimensional variations of the soluble core. The soluble core is formed using ceramic injection molding techniques. The dissolvable core is then removed from the mold. It is then debinded and sintered in a firing process. A final inspection step is performed on the soluble core before the core is used in the wax injection process. Before the wax injection step, a check should be made to ensure that the correct chaplets are used and they are positioned in the correct location. The ceramic material is injected into the mold and then wax may be injected into the mold around the core. After the wax has solidified, the wax body with the core structure inside is removed from the mold and immersed in a ceramic slurry to form a shell, then the wax is removed and the shell is fired to harden with the core and the chaplet in. The molten metal is then poured into a shell to form a blade or other suitable component of the desired size and shape. After the metal solidifies, the shell fractures, leaving a cast blade with a ceramic core made by the soluble core manufacturing process and a chaplet that has become an integral part of the soluble core. These can then be removed by leaching the core material by dissolving it in a suitable solvent. The solvent may be, for example, sodium hydroxide or potassium hydroxide, or any other suitable solvent that will be apparent to those skilled in the art. Alternatively, the chaplets may be designed and configured to fall out of the casting after completion.

The formation of the chaplet itself is intended to satisfy two main criteria: first, minimizing any surface defects formed on the ceramic core; and second, ensuring that the chaplet maintains its position between the soluble insert and the mold surface. The chaplet also leaves a witness mark on the ceramic core surface that needs to be minimized. This means that the desired shape of the chaplet is such that the chaplet is a point contact, rather than a conventional chaplet that has a wide base and a small point of contact and is removed prior to the casting process. However, this is not practical to use since one of these sides needs to adhere to the mold surface or the soluble insert. Thus, it may be desirable to use point contact chaplets on critical areas and more complex chaplet designs in non-critical areas. Fig. 2 shows an example of a non-point contact chaplet 20. The chaplet in this example is formed by injection molding a material having similar physicochemical properties to the ceramic core. The material is injection molded in a conventional manner into a mold or gate of suitable shape and size. In the example shown, a depression 22 is added to the chaplet to allow a higher level of glue to be used. The materials used may include silica, zirconia, alumina, aluminosilicates or other refractory materials. They may also be bonded using wax or polymer-based binders. The chaplet is not limited to this shape but may be any suitable shape from a point contact to a more complex shape.

The physicochemical properties may include hardness, density, composition, solubility in different solvents, or any other suitable physicochemical property. This may mean that the chaplet and the core are made of the same or similar materials, or have the same or slightly different solubilities in common solvents. Similarity may mean that the physical properties are within 20% of each other. Preferably, they may be within 10% or 5% of each other. For example, the core and chaplet may be made of silica in the range of about 30% to 98%. Zirconium may be present in the range of about 0% to 30%. Alumina may be present in the range of about 0% to 30%. The aluminosilicate may be present in the range of about 0% to 30%. About 10% to 25% of a binder may be added to the injection molding formulation. In addition, minor additives may be included in the range of about 0% to 5%. This may provide a core with a porosity of about 20% to 40%. The core may have a bulk density in the range of about 1.3g/cc to 2.5 g/cc. The above example is only one example of a material that may be used, as those skilled in the art will appreciate that other suitable materials may be used, such as alumina instead of silica in the mixture. There are three options to secure the chaplet in place, which may be: adhering a chaplet to the dissolvable surface, adhering the chaplet to the mold surface; or use of location features. There are several options if the chaplet is adhered to the surface of the soluble insert or mold. The chaplet may be glued; these may be solvent-based adhesives, temperature change-based adhesives or adhesives based on chemical reactions. In this case, a thin layer is preferred to minimize the impact on the component surface, since the glue will burn out during the heat treatment and leave a depression on the surface. The chaplet may melt and push into contact with the surface to which it is adhered and allowed to cool. Alternatively, another material may be melted between the two and used as an adhesive. As shown in fig. 2, the chaplet may be designed to enhance glue adhesion, for example, this may be accomplished by forming a depression in the chaplet to allow a higher level of glue to be used. Another option is by adding location features to make the chaplet self-locate on the soluble insert or within the mold. This can be done for using a single chaplet at a critical point or for multiple chaplets positioned around the core structure. Interconnected channels may be required so that the chaplet does not contact the surface of the soluble insert or the surface of the mold. By not using glue, the number of process steps used is reduced.

It is to be understood that the present invention is not limited to the above-described embodiments, and various modifications and improvements may be made without departing from the concept described herein. Any feature may be used alone or in combination with any other feature or features unless mutually exclusive, and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein.