US20250091130A1

US20250091130A1 - Shrouded wheel method of manufacture

Info

Publication number: US20250091130A1
Application number: US18/616,104
Authority: US
Inventors: Vijayasarathy Anbazhagan; Francis Rodriguez; Matthew Hake; Gururaj JK; Suryakant Gupta
Original assignee: Garrett Transportation I Inc
Current assignee: Garrett Transportation I Inc
Priority date: 2023-09-15
Filing date: 2024-03-25
Publication date: 2025-03-20

Abstract

A method for manufacturing a turbomachine shrouded wheel involves separately moulding a first green, moulded part forming a hub and blades, and a second green, moulded part forming a shroud, using a feedstock comprising a metal powder and a binder. The green, moulded parts are adjoined in a mated configuration, with additional feedstock placed between respective connection-surfaces on the moulded parts. The adjoined moulded parts are sintered to fuse them into a single unitary, monolithic structure. The moulded parts' connection-surfaces form conforming protrusions and depressions, which have surface discontinuities spaced at intervals along their respective lengths.

Description

The present invention relates to a method of manufacturing a shrouded wheel for a turbomachine, and more particularly, to a method of manufacturing a unitary, compressor shrouded wheel.

BACKGROUND

Turbomachinery are machines that transfer energy between a rotor and a fluid, typically either as a compressor adding to the total energy of a stream of centrifugally spiraling fluid, or a turbine extracting energy from a stream of centripetally spiraling fluid. The principal components of a turbomachine are: 1) a wheel having blades that operate on a stream of fluid, 2) a housing defining one or more walls that direct the stream of fluid to flow into an inducer of the blades, through and between the blades (to transfer the energy between the fluid and the wheel), and/or out from an exducer of the blades; 3) a shaft that connects to the wheel (and typically carries the wheel), and transfers the energy between the wheel and either an external energy source, or an external energy sink; and 4) bearings (typically supporting the shaft with respect to the housing) that support the wheel with respect to the housing.
The blades typically extend from a hub of the wheel to define fluid passageways between consecutive pairs of blades. These passageways can be further defined by portions of the housing walls that form an unmoving shroud wall directly surrounding the blades of the wheel. Alternatively, the wheel can incorporate a moving (rotating) shroud that rotates with the wheel (the hub and blades), thereby forming a “shrouded wheel” (as opposed to the “open wheel” that is surrounded by the unmoving shroud wall of the housing). While such a rotating shroud might increase the weight of the wheel, and thereby the loads carried by bearings, it can prevent a leakage of fluid that can occur between consecutive passageways (i.e., in gaps between the rotating blades of an open wheel and the unmoving shroud wall). Moreover, they can limit circumferential forces in the boundary layer next to the shroud wall of the fluid stream passing through the passageways.
For example, a turbomachine might be formed as a centrifugal compressor that transfers mechanical energy to a flowing stream of fluid to achieve an increased total energy level of the fluid. The compressor includes a centrifugal compressor wheel having a hub and a plurality of impellers. The impellers are formed as blades extending normal to a flow surface on a conically curved wall of the hub. While some designs can have impellers configured (i.e., shaped and positioned) to operate only on fluid flowing in a radial (outward) direction (as opposed to an axial direction), in a typical radial compressor design, the impellers and hub are configured to form fluid passageways that serially extend: axially from a primarily axial-facing inducer, to and through an axial-to-radial turn, and then radially to discharge through a primarily radial-facing exducer. Such centrifugal compressors are used in many applications, such as turbocharger systems and other automotive applications.
While some turbomachine operating conditions can effectively be served using fairly simple turbomachine configurations, others might require complex configurations that complicate the manufacture of the turbomachines (and more particularly, the manufacture of the wheels). For example, compressors for use in EV Cooling and Air Brakes can require high total-to-total pressure ratios over a wide range of flow conditions. This can lead to very small blade heights, small clearances, and harder materials than are typically used (e.g., harder than Aluminum).
Basic turbomachine open wheels can define passageways with simple shapes that are easily pullable from a mould using traditional methods, allowing the open wheels to be simple die cast parts. Even for these simple cases, the casting process can be limited by a requirement for very small features, such as small blade heights. Moreover, such basic open wheels are likely limited in their levels of efficiency, and their range of mass flow and pressure ratios over which the wheels can operate.
The use of metal injection moulding (“MIM”) can provide benefits in creating accurate features in the manufacture of open wheels. MIM is a metal forming process by which finely-powdered metal is mixed with a measured amount of binder material and processed through an injection mould forming process. Various types of binders have been developed (and are known in the industry) for use with various powdered metals, and for various binder removal methods.
The MIM process includes the steps of: 1) Compounding—mixing a metal powder with a binder to create a feedstock for moulding; 2) Moulding—heating the feedstock to melt the binder (but not the metal powder), and then injecting the feedstock into a mould; 3) Solidifying—passively or actively cooling the feedstock within the mould to form a solidified “green part” that is moulded in the shape (but not the size) of the final part; 4) Removing binder—using heat and/or chemicals to remove some of the binder to create a “brown part” that more closely resembles the finished part; and 5) Sintering—heating the brown part to temperatures close to (but below) the melting point of the powdered metal, thereby removing the binder and increasing the density of the metal (i.e., causing shrinkage) to become the final part in its desired size. In some cases, steps (4) and (5) of the MIM process can be combined into one process step, or step (4) can be omitted.
The MIM process provides for individual parts to be shaped in a single operation, and in high volume compared to some other methods. A limitation of the basic MIM process is that the final shape of the resulting part must be simple enough to be removable from a mould. To form MIM-manufactured parts into a complex structure, traditional metal manufacturing methods like riveting, welding, or adhesion can be used on the individual parts that have been MIM-manufactured.
For more complex turbomachine open wheels that provide for a turbomachine to efficiently operate over a wider range of operating conditions, more complex manufacturing methods and jigs have been developed to allow for the manufacture of the open wheels. Such methods can include a complete and separate process of fully machining open wheels from a metal body (e.g., by 5-axis machining, or by other known material-removal techniques), or combination process of casting in combination with various types of machining. Such machining of a cast part adds complexity and potentially high cost and cycle-time to the manufacturing process of casting, particularly for producing open wheels composed of hard metals. Moreover, not all fluid-dynamic surface finishes can be effectively machined.
Other methods of manufacturing complex wheels include additive manufacturing, e.g., building a structure up in a multitude of layers. Additive manufacturing provides another way to manufacture complex parts, but generally fails to offer the high surface finish desirable for fluid flow, and potentially produces burrs that require removal.
For wheels defining either simple or complex passageways, the incorporation of a rotating shroud onto a wheel significantly reduces access to the passageways for casting and/or machining purposes. This limits many of the above-described manufacturing methods to only the simplest of shrouded wheels.
One method to accommodate the manufacture of a shrouded wheel is to affix a complete and separate shroud portion of the shrouded wheel to a complete and separate open-wheel portion of the shrouded wheel (i.e., the remaining portion of the shrouded wheel) after the completed manufacture of both the shroud portion and the open-wheel portion. The open-wheel portion and shroud portion could each separately be manufactured using any of the methods described above. To affix the shroud portion to the open-wheel portion, joining techniques such as mechanical fixtures (e.g., rivets), adhesives, and/or welding techniques can be used. With some of these techniques, consecutive passageways can still have gaps through which fluid can leak from one passageway to the another.
Additionally, the resulting joins between the shroud portion and the open-wheel portion are likely not uniform, and are also subject to harm by the deleterious thermal and dynamic stresses of the operating conditions. This makes the connections potential weak links characterized by a higher risk of failure than an unstressed, unitary (e.g., cast) structure. Moreover, some of these joining techniques involve the application significant pressures and/or thermal gradients (e.g., such as from arc welding), which can lead to a high-stress join characterized by blade distortions that reduce rotational balance and desirable fluid flow characteristics (in addition to the aforementioned problems).
Another method to accommodate the manufacture of a shrouded wheel is investment casting, which involves the creation of parts through the use of disposable moulds (shells) crafted around an accurate pattern that is melted or dissolved away to form the mould. While this can increase accuracy over traditional die cast parts, the necessary creation of new patterns and shells for each shrouded wheel leads to high cost and lead-time for each manufactured shrouded wheel, limiting the high-volume manufacture of the wheels.
Yet another method to accommodate the manufacture of a shrouded wheel is to cast the body of the shrouded wheel using a core (shaped inserts) that are later melted, dissolved, etched, or otherwise destroyed after the formation of the shrouded wheel. The body is formed with powdered metal that is placed within a cavity and subjected to hot isostatic pressing. Each such manufactured shrouded wheel requires its own sacrificial core, leading to an expensive and complex manufacturing procedure with little subsequent access to the passageways for quality control inspection or surface treatment after the inserts are destructively removed.
Other known complex methods of manufacture include those disclosed in U.S. Pat. Nos. 9,028,744, and 10,697,465. The first of these pertains to a low melting temperature cast part (e.g., a cooling passage) being centered within a mould, into which metal power is injected and then sintered. The second of these pertains to the use of a sacrificial metal core that is later dissolved by acid. The resulting volume is then filled with metal powder, and the cavities are sealed and subjected to hot isostatic pressing followed by acid etching. For some cases, these processes might be characterized by high costs, difficulties in extraction, and potentially fragility.
There exists a need for a method of manufacturing high volumes of small, strong, durable, and complex structures, having fine tolerances, such as metal shrouded wheels, to be manufactured in a comparatively inexpensive process as compared to other methods. Preferred embodiments of the present invention may satisfy some combination of these and other needs, and provide further related advantages.

SUMMARY

In various embodiments, the present invention may solve some or all of the needs mentioned above. A method for manufacturing a turbomachine shrouded wheel under the invention features the steps of providing a first moulded part of the shrouded wheel, and providing a second moulded part of the shrouded wheel. The first moulded part and the second moulded part have one or more first-part connection-surfaces, and have one or more second-part connection-surfaces, respectively. The second-part connection-surfaces are shaped and sized to receive the first-part connection-surfaces fully and conformingly when the first moulded part and the second moulded part are positioned and adjoined to one another in a mated configuration.
The method further includes positioning and adjoining the first moulded part and the second moulded part in the mated configuration with respect to one another, such that the one or more second-part connection-surfaces fully and conformingly receive the first-part connection-surfaces. With the first moulded part and the second moulded part positioned and adjoined, the present invention further includes sinter-fusing the first-part connection-surfaces with the second-part connection-surfaces to form the turbomachine shrouded wheel.
Advantageously, the sinter-fusing of the first and second moulded parts provides for the moulded parts to be integrated into one another to form a unitary structure, i.e., a single monolithic whole, without overtly melting either/any of the parts. This unitary, sinter-fused part is differentiable from parts manufactured by casting, and also differentiable from parts manufactured by the various types of welding and other joining methods. Using such a method provides for high volumes of small, strong, durable, and complex parts, having fine tolerances, to be manufactured in a comparatively inexpensive process as compared to other methods of manufacture.
In an additional feature, under the method, each of the first and second moulded parts can be produced by solidifying a respective feedstock within a respective mould to form the respective moulded part, thereby cost-effectively taking advantage of existing metal injection moulding technologies that include similar processes.
Using these features, small-sized parts like turbomachine shrouded wheels, having a complex geometry and highly accurate small features, can be efficiently and cost-effectively manufactured in high volumes. The method can achieve very accurate sizing by using established shrinkage parameters for the materials of the feedstock(s). A homogeneous micro-structure is achievable in the manufacture of these complex parts, unlike parts made by other methods, e.g., such as adhesive bonding, brazing, welding, casting, riveting, and the like. Moreover, little to no post processing is needed to improve the finish of the part surfaces.
Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view depicting an axial compressor shrouded wheel made with a method of manufacture embodying the invention.

FIG. 2 is a partial cross-sectional side view of the compressor shrouded wheel of FIG. 1 , taken along section A-A of FIG. 1 .

FIG. 3 is a front view of a green, moulded wheel used in the method of manufacture, to manufacture the axial compressor shrouded wheel of FIG. 1 .

FIG. 4 is a partial, cross-sectional side view of the moulded wheel of FIG. 3 .

FIG. 5 depicts detail B of the moulded wheel of FIG. 3 .

FIG. 6 is a cross-sectional bottom view of detail B, taken along section C-C of FIG. 5 .

FIG. 7 is a back view of a green, moulded shroud used in the method of manufacture, to manufacture the axial compressor shrouded wheel of FIG. 1 .

FIG. 8 is a partial, cross-sectional side view of the moulded shroud of FIG. 7 .

FIG. 9 is the method of manufacture embodying the invention that was used to make the axial compressor shrouded wheel of FIG. 1 .

FIG. 10 recites additional details of the method of manufacture embodying the invention of FIG. 9 .

FIG. 11 recites additional details of the method of manufacture embodying the invention of FIG. 9 .

FIG. 12 is a partial cross-sectional side view of a radial compressor shrouded wheel view made with a method of manufacture embodying the invention.

FIG. 13 is a partial cross-sectional side view of a green, moulded wheel and a green, moulded shroud used in the method of manufacture, to manufacture the radial compressor shrouded wheel of FIG. 12 .

FIG. 14 is a partial cross-sectional side view of the moulded wheel and the moulded shroud of FIG. 13 , being adjoined with a layer of binding material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention summarized above and defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read with the accompanying drawings. This detailed description of particular preferred embodiments of the invention, set out below to enable one to build and use particular implementations of the invention, is not intended to limit the enumerated claims, but rather, it is intended to provide particular examples of them.
Typical embodiments of the present invention reside in methods of manufacturing complex unitary structures. More particularly, the methods entail forming a plurality of unitary moulded parts through the solidification of feedstocks within a mould, and then using an additional feedstock to sinter the parts into a unified structure constituting a single unit, typically being an undifferentiated and relatively rigid whole that usually exhibits or is characterized by a uniformity in material structure, i.e., it is usually monolithic in form.

Axial Compressor Shrouded Wheel

With reference to FIGS. 1-8 , an embodiment of the invention is found in a method of manufacturing a turbomachine having a unitary, shrouded wheel (a turbomachine shrouded wheel), such as a compressor including an axial, unitary, compressor shrouded wheel 101, using injection-moulding-type devices. The compressor is of a typical configuration with the exception of the shrouded wheel 101.
The compressor shrouded wheel 101 manufactured under this method is purely axial in its pressure-inducing operation, as opposed to operating as a radial compressor (having an axially facing inducer and a radially facing exducer), or as a mixed flow compressor (e.g., one having an exducer facing both axially and radially). The shrouded wheel 101 has an annular (annulus-type) inlet section 103 leading axially from an opening 105 to a radially facing, annular-shaped inducer 107 formed by impellers 109. The impellers 109 can drive a fluid stream passing through the inducer 107 radially outward (and circumferentially) to pass through an annular exducer 111.
The compressor shrouded wheel 101 includes a hub portion 113 and a shroud portion 115. The impellers 109 extend between a hub-portion flow-surface 117 of the hub portion 113, and a shroud-portion flow-surface 119 of the shroud portion 115. The shrouded wheel 101 also forms an annular root portion 121 to mount the shrouded wheel 101 on a rotating shaft (not shown). The rotating shaft drives the compressor shrouded wheel 101 in rotation, providing the energy required to compress the fluid stream. As a whole, the hub portion 113, the shroud portion 115, the impellers 109, and the annular root portion 121 are a unitary, monolithic structure.
This purely axial compressor shrouded wheel 101 happens to be configured to operate at low mass-flow-rates while having high pressure ratios, such as might be used to in an electric vehicle for cooling certain components (among other uses). Such uses might require very small impeller blade-heights and/or other difficult-to-manufacture configurations. The manufacture of such wheels using conventional techniques could lead to significant manufacturing complications and costs, as well as potentially limiting the reliability and durability of the resulting wheels. Nevertheless, a wide range of shrouded wheels are contemplated within the scope of the claimed invention.
The compressor shrouded wheel 101 is a metal part formed from two moulded parts (a first moulded part and a second moulded part) that have been sinter-fused together. For the purposes of this application, a “green” part is defined to mean a part made of a moldable feedstock comprising a powdered material (e.g., a metal powder) and a binder (e.g., a material that can bind the powdered material into a defined shape that is structurally maintained by the binder), wherein the part has a defined shape structurally maintained by the binder (e.g., as formed within a mould), and wherein the binder is removable from the powdered material at a temperature lower than the meting point of the powdered material.
Additionally, for the purposes of this application, the terms “sinter-fusing” and “sinter-fused” are defined to mean that a plurality of separate, existing parts are being/have been integrated into one another to form unitary structure, i.e., a single monolithic whole, without overtly melting any of the parts. Thus, a sinter-fused part is differentiable from parts manufactured by casting, where there is no joining location. Likewise, a sinter-fused part is differentiable from parts manufactured by the various types of welding, both in process and result (e.g., in the uniformity of the fusion, and in the limiting of surface imperfections from the localized applications of various heating technologies like spot welding). Moreover, a sinter-fused part is differentiable from parts manufactured via other joining methods, such as adhesion or structural joining (e.g., riveting parts together), by the material and structural differences between the parts.
The first moulded part from which the compressor shrouded wheel 101 is made is a green, moulded wheel 131. The moulded wheel 131 forms a moulded hub 133, and moulded blades 135. The moulded hub 133 defines a moulded-wheel flow-surface 137, along which fluid flows during compressor operation. The moulded blades 135 extend from that moulded-wheel flow-surface 137. The moulded blades 135 spiral outward from the inducer 107 to the exducer 111. Extending along a distal tip of each blade 135 (i.e., distal with respect to the moulded-wheel flow-surface 137), spiraling along the length of the blade from the inducer 107 to the exducer 111, the moulded blades form moulded-wheel connection-surfaces 139 configured (i.e., shaped and sized) as longitudinally extending protrusions (i.e., extended tongues), extending outward from a remainder of the blade. The moulded wheel 131 also forms a moulded-wheel annular root 141.
The second moulded part from which the compressor shrouded wheel 101 is made is a green, moulded shroud 151. The moulded shroud 151 forms a moulded-shroud flow-surface 153, along which fluid flows during compressor operation. On the moulded-shroud flow-surface 153, the moulded shroud 151 forms moulded shroud connection-surfaces 155 configured (i.e., shaped and sized) as longitudinally extending depressions (i.e., extended grooves) that extend inward from the remainder of the moulded-shroud flow-surface 153. The moulded-shroud connection-surfaces 155 extend axially outward from the inducer 107 to the exducer 111 in a spiral that conformingly mirrors the spiral of the moulded blades 135. With the moulded-wheel connection-surfaces 139 mated to the moulded-shroud connection-surfaces 155, the moulded-wheel flow-surface 137 and moulded-shroud flow-surface 153 opposingly face one another to form spiral passages between the moulded blades 135.
The moulded-shroud connection-surfaces 155 are shaped and sized to receive the moulded-wheel connection-surfaces 139 fully and conformingly when the first moulded part (the moulded wheel 131) and the second moulded part (the moulded shroud 151) are positioned and adjoined to one another in a mated configuration. More particularly, the moulded-shroud connection-surfaces 155 are configured (i.e., shaped and sized) to mate, completely and conformingly, in a tongue-and-groove connection with the moulded-wheel connection-surfaces 139 along the length of the moulded blades 135 from the inducer 107 to the exducer 111. The connection surfaces are the specific surfaces that conformingly mate to form a connection (between the two moulded parts), but not the surrounding surfaces (around the conformingly mating surfaces) that do not mate to form a connection. Thus, the moulded-wheel and moulded-shroud connection-surfaces 155 are configured as mating surfaces, i.e., surfaces shaped and sized with features varying in shape from nearby adjacent surfaces to thereby mate with one another.
In the method, the moulded wheel 131 is sinter-fused to the moulded shroud 151 along their respective moulded-wheel connection-surfaces 139 and moulded-shroud connection-surfaces 155. The tongue-and-groove relationship of the moulded-wheel and moulded-shroud connection-surfaces, which is optional, can both aid in the process of sinter-fusing the moulded wheel 131 and moulded shroud 151 together (both in guiding the alignment and in guiding the application of connecting materials), and strengthen the resulting connection, particularly if any imperfections occur during the process.
Both (or alternatively at least one of) the moulded-wheel connection-surfaces 139 and the moulded-shroud connection-surfaces 155 are discontinuous, respectively having moulded-wheel surface discontinuities 161 and moulded-shroud surface discontinuities 163 at spaced at intervals along their respective spiraling lengths. It should be understood that the surface discontinuities are part of the conformingly mating surfaces and integral to the strength of their connection, as opposed to being a part of the surrounding surfaces around the conformingly mating surfaces, which are not configured to create a direct connection between the two parts.
The surface discontinuities are forms of surface roughness, such as scabrous outcroppings or clefts, like scales, points, serrations (as depicted), or other surface discontinuities that could measurably help anchor and bind one surface to another. The surface discontinuities, being spaced at intervals, can be formed as randomly shaped discontinuities, positioned randomly, and spaced apart randomly along the connection-surface lengths. Alternatively, the surface discontinuities, being spaced at intervals, can be formed as consistently shaped discontinuities, positioned consistently, and/or spaced at consistent intervals along the connection-surface lengths. Among other benefits, such discontinuities could strengthen the connection through any imperfections in the process of sinter-fusing the first and second moulded parts (i.e., the moulded wheel 131 and the moulded shroud 151) together.
At the completion of the manufacture of the compressor shrouded wheel 101, the moulded hub 133 becomes the hub portion 113, the moulded shroud 151 becomes the shroud portion 115, the moulded blades 135 become the impellers 109, and the moulded-wheel annular root 141 becomes the annular root portion 121. Likewise, the moulded-wheel flow-surface 137 and moulded-shroud flow-surface 153 respectively become the hub-portion flow-surface 117 and the shroud-portion flow-surface 119, and thus, the hub-portion flow-surface 117 and the shroud-portion flow-surface 119 opposingly face one another to form spiral passages between the impellers 109.

METHOD OF MANUFACTURE

Forming the First Moulded Part

With reference to FIGS. 9-11 , the method of manufacture includes a step of providing a first moulded part 201 (the moulded wheel 131) for use under the remaining steps of the method of manufacture. The step of providing the first moulded part 201 might include the step of obtaining the first moulded part 203, or alternatively, the step of forming the first moulded part 205.
Obtaining or creating a first mould 211 is a first sub-step in the step of forming the first moulded part 205. To create the first mould, a first feedstock is selected for the creation of the first moulded part, the first feedstock being a first metal powder and a first binder, combined at a first-feedstock composition ratio. Based on the selected first feedstock, two or more first-mould parts are designed and formed (manufactured) for use in forming the first moulded part. The two or more first-mould parts are configured (shaped and sized) to combine into a first mould defining a first cavity that can mould the first moulded part (the moulded wheel 131) using the first feedstock. The design and manufacture of the first-mould parts can be guided by technology used in injection moulding.
Because later stages of the method of manufacture can cause the shrinkage of moulded feedstock parts, the first cavity is designed larger than the desired final part dimensions for that portion of the compressor shrouded wheel 101 (to accommodate the anticipated shrinkage). The designed sizing is based on the anticipated shrinkage, which in turn is based on the types of first feedstock materials (the first metal powder and the first binder), and the first-feedstock composition ratio. This can be established experimentally if not previously known from metal injection moulding (“MIM”) technology. Furthermore, the two or more first-mould parts are typically configured so that the first moulded part is pullable, that is to say, that it can be removed from the two or more first-mould parts without the destruction of any of the two or more first-mould parts. Thus, the first-mould parts will only need be created once for many first moulded parts to be formed.
The two or more first-mould parts are then joined together to form the first mould that defines the first cavity. They may be positioned and held by jigs and other connectors, as is known for forming moulds. In variations on the method, a single first-mould part could be used to form the first mould, although this might limit the reusability of the first mould. Thus, in its broadest definition, the first mould might comprise one or more first-mould parts.
With the first mould obtained or created 211, the step of forming the first moulded part 205 further includes a series of sub-steps for the creation of moulded parts, these sub-steps being similar to the Compounding, Moulding and Solidifying steps known for use in MIM.
More particularly, the step of forming the first moulded part 205 further includes a sub-step of compounding the first feedstock 221, i.e., compounding the first metal powder and the first binder at the first-feedstock composition ratio to create the first feedstock. This can be accomplished by typical techniques for compounding a feedstock for MIM.
The step of forming the first moulded part 205 also includes a sub-step of moulding the first feedstock 223 in the first mould, such as by typical MIM techniques. For example, the moulding might entail heating the first feedstock adequately to melt the first binder within the first feedstock (but at a temperature below the melting point of the first metal powder), and then injecting the heated first feedstock into the first cavity. Alternatively, other MIM techniques for moulding may be used, such as the combined use of pressure and temperature, and/or the injection of feedstock into the mould prior to the final melting of the binder.
The step of forming the first moulded part 205 further includes a sub-step of solidifying the first feedstock 225 contained within the first cavity of the first mould to form the first moulded part. The first feedstock may be solidified by, for example, passively or actively cooling the first mould, and/or by reducing the pressure (if pressure is applied), to form the first moulded part. Alternatively, other MIM techniques for solidifying may be used. This solidification step 225 results in the solidification of the first binder within the first feedstock to hold the first moulded part in the shape of the first cavity. Under this method, the resulting solidified moulded wheel 131 is in the shape, but not the size, that it will be in its final form as part of the compressor shrouded wheel 101.

Forming the Second Moulded Part

The method of manufacture also includes a step of providing a second moulded part 301 (the moulded shroud 151) for use under the remaining steps of the method of manufacture. The step of providing the second moulded part 301 might include the step of obtaining the second moulded part 303, or alternatively, the step of forming the second moulded part 305.
Obtaining or creating a second mould 311 is a first sub-step in the step of forming the second moulded part 305. To create the second mould, a second feedstock is selected for the creation of the second moulded part, the second feedstock being a second metal powder, and a second binder, combined at a second-feedstock composition ratio. Based on the selected second feedstock, two or more second-mould parts are designed and formed (manufactured) for use in forming the second moulded part. The two or more second-mould parts are configured (shaped and sized) to combine into a second mould defining a second cavity that can mould the second moulded part (the moulded shroud 151) using the second feedstock. The design and manufacture of the second-mould parts can be guided by technology used in injection moulding.
Similar to the first cavity, the second cavity is designed larger than the desired final part dimensions for that portion of the compressor shrouded wheel 101 (to accommodate the anticipated shrinkage). The designed sizing is based on the anticipated shrinkage, which in turn is based on the types of second feedstock materials (the second metal powder and the second binder), and the second-feedstock composition ratio. This can be established experimentally if not previously known from MIM technology. Furthermore, the two or more second-mould parts are typically configured so that the second moulded part is pullable. Thus, the second-mould parts will only need be created once for many second moulded parts to be formed.
The two or more second-mould parts are then joined together to form the second mould that defines the second cavity. They may be positioned and held by jigs and other connectors, as is known for forming moulds. In variations on the method, a single second-mould part could be used to form the second mould, although this might limit the reusability of the second mould. Thus, in its broadest definition, the second mould might comprise one or more second-mould parts.
Similar to the step of forming the first moulded part 205, with the second mould obtained or created 311, the step of forming the second moulded part 305 further includes a series of sub-steps for the creation of moulded parts, these sub-steps being similar to the Compounding, Moulding and Solidifying steps known for use in MIM.
More particularly, the step of forming the second moulded part 305 also includes a sub-step of compounding the second feedstock 321, i.e., compounding the second metal powder and the second binder at the second-feedstock composition ratio to create the second feedstock. This can be accomplished by typical techniques for compounding a feedstock for MIM.
In this embodiment of the method, the second feedstock is identical to (i.e., consists of the same substances, combined at the same ratios, as) the first feedstock. Thus, the second metal powder, second binder, and second-feedstock composition ratio, respectively, are identical to the first metal powder, first binder, and first-feedstock composition ratio. In other embodiments, the two feedstocks can have different compositions and composition ratios from one another. Thus, exceptions to their being identical are contemplated within the broadest scope of the invention.
The step of forming the second moulded part 305 also includes a sub-step of moulding the second feedstock 323 in the second mould, such as by typical MIM techniques. For example, the moulding might entail heating the second feedstock adequately to melt the second binder within the second feedstock (but at a temperature below the melting point of the second metal powder), and then injecting the heated second feedstock into the second cavity. Alternatively, other MIM techniques for moulding may be used, such as the combined use of pressure and temperature, and/or the injection of feedstock into the mould prior to the final melting of the binder.
Generally speaking, the step of moulding the second feedstock 323 will be procedurally similar to the step of moulding the first feedstock 223. Nevertheless, exceptions to this are contemplated within the broadest scope of the invention.
The step of forming the second moulded part 305 further includes a sub-step of solidifying the second feedstock 325 contained within the second cavity of the second mould to form the second moulded part. The second feedstock may be solidified by, for example, passively or actively cooling the second mould, and/or by reducing the pressure (if pressure is applied), to form the second moulded part. Alternatively, other MIM techniques for solidifying may be used. This solidification step 325 results in the solidification of the second binder within the second feedstock to hold the second moulded part in the shape of the second cavity. In this embodiment of the method, the resulting solidified moulded shroud 151 is in the shape, but not the size, that it will be in its final form as part of the compressor shrouded wheel 101.
Generally speaking, the step of solidifying the second feedstock 325 will be procedurally similar to the step of solidifying the first feedstock 225. Nevertheless, exceptions to this are contemplated within the broadest scope of the invention.

Forming the Turbomachine Axial Shrouded Wheel

After completing the steps of providing the first moulded part 201 and providing the second moulded part 301, the method of manufacture further comprises a step of forming the turbomachine shrouded wheel 401 from the first moulded part and the second moulded part. Included in this step are a sub-step of applying a binding material 411, a sub-step of positioning and adjoining the moulded parts 413, and a sub-step of sinter-fusing the moulded parts to one another 415.
The sub-step of applying a binding material 411 comprises applying a binding material including a third binder between the one or more first-part connection-surfaces and the one or more second-part connection-surfaces. The binding material may be applied to the first-part connection-surfaces 139, the second-part connection-surfaces 155, or both, and is typically applied to achieve coverage fully across the first-part and second-part connection-surfaces when they are adjoined.
The binding material used in this embodiment of a method is a feedstock that is identical in composition to (i.e., composed of a third binder that is identical to the first and second binders, and a third metal powder that is the same as the first and second metal powders, present (combined) in the same proportions as the first and second binders as) the first feedstock and the second feedstock. Alternatively, the binding material could be a combination of the first and second feedstocks (such as if they are not of the same composition), or some other type of feedstock (such as one having a significantly lower amount of metal powder, or such as one with a third binder and third metal powder different than the first and second binders, and first and second metal powders). It also might be possible to use purely the third binder (without a third metal powder) as the binding material. In broad constructions of the invention, it also might be possible to forgo the use of a binding material, particularly if the first-part connection-surfaces and the second-part connection-surfaces conformingly mate to a very fine degree.
In the sub-step of positioning and adjoining the moulded parts 413, the first moulded part and the second moulded part are positioned and held with respect to one another such that they are adjoined in the mated configuration. This is accomplished such that the one or more second-part connection-surfaces (of the second moulded part 151) fully and conformingly receive the first-part connection-surfaces (of the first moulded part 131). It is to be understood that they are fully and conformingly received when they form opposingly facing surfaces that are in direct contact, or are joined in contact via a thin layer of binding material that primarily fills the voids between tiny imperfections inherent in the mated nature of the configuration. The first and second moulded parts may be held in this mated configuration by jigs and other connectors as necessary. In this process, consideration is given to the limitations on handling and supporting green moulded parts, as is known for sintering green parts in MIM processes. Consideration is also given to the anticipated shrinkage that will later occur during the sinter-fusing of the parts.
In the sub-step of sinter-fusing the first and second moulded parts to one another 415, each of the first and second moulded parts is concurrently sintered to its final form, while the first-part connection-surfaces are concurrently sinter-fused to the positioned and adjoined second-part connection-surfaces, thereby integrally forming the turbomachine shrouded wheel. This sinter-fusing sub-step may be done through a combination of one or more processes, similar to those known for traditional MIM processes.
For example, the sub-step of sinter-fusing the first and second moulded parts to one another 415 might include the processes of first, removing a partial amount the first binder, and/or a partial amount the second binder, and/or a partial amount the binder within the binding material, using heat and/or chemicals, thereby creating a “brown part” of the turbomachine shrouded wheel; and second, heating the brown part to temperatures close to (but below) the melting point of the metal powder(s), thereby removing the rest of the binder and increasing the density of the metal (causing shrinkage) to become the final turbomachine shrouded wheel in the desired size.
Taken as a group, at least some connection-surfaces of the group of the first-part (moulded-wheel) connection-surfaces and the second-part (moulded-shroud) connection-surfaces can be configured to form surface discontinuities that are spaced at intervals along their respective lengths. As described above, the surface discontinuities can be forms of surface roughness, such as scabrous outcroppings or clefts, like scales, points, serrations (as depicted), or other surface discontinuities that could measurably help anchor and bind one surface to another.
The shrouded wheel formed in accordance with the method is unique in that the sinter-fused connection forms a single monolithic whole without individual spots being melted together. It is thus differentiable from cast parts, welded parts, and parts made from other joining methods. Moreover, it includes a means for sinter-fusedly holding the blades to the flow wall through their mating surfaces to form the shrouded wheel, in that it has an infusion of a third metal powder that fusedly joins the wheel to the shroud.
While this embodiment is directed to the manufacture of a complex turbomachine shrouded wheel, other aspects of the invention might be directed to a wide variety of parts, and particularly to small and/or complex parts or parts that would benefit from a monolithic structure. For example, a wide variety of mechanical joints, knobs and other physical structures that are typically made by multiple parts being joined by simpler methods such as riveting, bolting, using adhesives, or welding, could be manufactured under the invention when the advantages of a monolithic, sinter-fused connection outweigh any cost or complexity differential between the sinter-fusing and the simpler joining methods.

Radial Compressor Shrouded Wheel

With reference to FIGS. 12-14 , a second implementation of the embodiment of the method of manufacturing a turbomachine, having a unitary, shrouded wheel (a turbomachine shrouded wheel), such as a compressor including a radial, unitary, compressor shrouded wheel 501, using injection-moulding-type devices. The compressor is of a typical configuration with the exception of the shrouded wheel 501.
The compressor shrouded wheel 501 of this second implementation of the method embodying the invention is for manufacturing a radial compressor wheel, having an axially facing inducer and a radially facing exducer. In other variations, this shrouded wheel can be configured as a mixed flow compressor (e.g., one having an exducer facing both axially and radially). The shrouded wheel 501 has an axially facing, washer-shaped (i.e., circular with a hole) inducer 507 formed by impellers 509. The impellers 509 can drive a fluid stream passing through the inducer 507 radially outward (and circumferentially) to pass through an annular exducer 511.
Other than the differences described herein, the radial compressor shrouded wheel 501 and its method of manufacture are similar or the same as the compressor shrouded wheel in its method of manufacture. Thus, the compressor shrouded wheel 501 includes a hub portion 513 and a shroud portion 515. The impellers 509 extend between a hub-portion flow-surface 517 of the hub portion 513, and a shroud-portion flow-surface 519 of the shroud portion 515. A rotating shaft 520 drives the compressor shrouded wheel 501 in rotation, providing the energy required to compress the fluid stream. As a whole, the hub portion 513, the shroud portion 515, and the impellers 509 are a unitary, monolithic structure.
This radial compressor shrouded wheel 501 happens to be configured to operate at low mass-flow-rates while having high pressure ratios. Such a configuration might require very small impeller blade-heights and/or other difficult-to-manufacture configurations. The manufacture of such wheels using conventional techniques could lead to significant manufacturing complications and costs, as well as potentially limiting the reliability and durability of the resulting wheels. Nevertheless, a wide range of shrouded wheels are contemplated within the scope of the claimed invention.
As with the axial compressor shrouded wheel, the radial compressor shrouded wheel 501 is a metal part formed from two green, moulded parts (a first moulded part, being a green, moulded wheel 531, and a second moulded part, being a moulded shroud 551) that have been sinter-fused together along moulded-shroud connection-surfaces 555 that are shaped and sized to receive moulded-wheel connection-surfaces 539 fully and conformingly when the first moulded part (the moulded wheel 531) and the second moulded part (the moulded shroud 551) are positioned and adjoined to one another in a mated configuration. More particularly, the moulded-shroud connection-surfaces 555 are configured (i.e., shaped and sized) to mate, completely and conformingly, in a tongue-and-groove connection with the moulded-wheel connection-surfaces 539 along the length of moulded blades 535 extending from the inducer 507 to the exducer 511. A binding material 557 is applied between the moulded-shroud connection-surfaces 555 and the moulded-wheel connection-surfaces 539 prior to the first and second moulded parts being sinter-fused together.
It is to be understood that the invention comprises apparatus and methods for designing and producing a turbomachine shrouded wheel, as well as the produced apparatus (e.g., the turbomachine shrouded wheel) itself. In short, the above disclosed features can be combined in a wide variety of configurations within the anticipated scope of the invention.
While particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. For example, a step of removing binder from the first and/or second moulded parts (as described above to create brown parts) might be conducted prior to the steps of applying a binding material 411, positioning and adjoining the first and second moulded parts 413, and/or sinter-fusing the first and second moulded parts to one another 415.
As another example, while the depicted compressor wheels have connecting surfaces on the ends of blades that are received in grooves on a shroud, other configurations are within the scope of the invention. For example, the wheel and shroud could each have some blades that extend to meet the opposing part, mating with one another. Also, the wheel and/or shroud could be made from sub-parts that are to be concurrently sinter-fused together. Thus, although the invention has been described in detail with reference only to the preferred embodiments, those having ordinary skill in the art will appreciate that various modifications can be made without departing from the scope of the invention. Accordingly, the invention is not intended to be limited by the above discussion, and is defined with reference to the following claims.

Claims

What is claimed is:

1. A method for manufacturing a turbomachine shrouded wheel, comprising:

providing a first moulded part of the shrouded wheel, the first moulded part having one or more first-part connection-surfaces;

providing a second moulded part of the shrouded wheel, the second moulded part having one or more second-part connection-surfaces, wherein the one or more second-part connection-surfaces are shaped and sized to receive the first-part connection-surfaces fully and conformingly when the first moulded part and the second moulded part are positioned and adjoined to one another in a mated configuration;

positioning and adjoining the first moulded part and the second moulded part with respect to one another in the mated configuration such that the one or more second-part connection-surfaces fully and conformingly receive the first-part connection-surfaces; and

sinter-fusing the first-part connection-surfaces to the second-part connection-surfaces to form the turbomachine shrouded wheel.

2. The method of claim 1, wherein:

the first moulded part is a moulded wheel including a plurality of blades that form the one or more first-part connection-surfaces, the first-part connection-surfaces forming protrusions;

the second moulded part is a moulded shroud shaped to conformingly receive the moulded wheel; and

the moulded shroud forms the one or more second-part connection-surfaces, the second-part connection-surfaces forming depressions shaped to conformingly receive and mate with the protrusions.

3. The method of claim 1, wherein:

the step of providing a first moulded part comprises solidifying a first feedstock within a first mould to form the first moulded part;

the step of providing a second moulded part comprises solidifying a second feedstock within a second mould to form a second moulded part;

the step of sinter-fusing comprises applying a binding material between the one or more first-part connection-surfaces and the one or more second-part connection-surfaces fully across the received first-part connection-surfaces; and

the step of sinter-fusing further comprises sintering the positioned and adjoined first moulded part and second moulded part to form the turbomachine shrouded wheel.

4. The method of claim 3, wherein:

the step of providing a first moulded part includes compounding a first metal powder with a first binder to create the first feedstock; and

the step of providing a second moulded part includes compounding a second metal powder with a second binder to create the second feedstock.

5. The method of claim 4, wherein the composition of the first feedstock, and the second feedstock, each includes the same metal powder.

6. The method of claim 4, wherein the composition of the first feedstock, and the second feedstock, each includes the same binder.

7. The method of claim 3, wherein the first feedstock and the second feedstock consist of the same substances.

8. The method of claim 7, wherein the substances composing the first feedstock, and the second feedstock, are present in the same proportions.

9. The method of claim 8, wherein the binding material is composed of the same substances in the same proportions as the first feedstock.

10. The method of claim 3, wherein the composition of the binding material includes a binder.

11. The method of claim 10, wherein the binding material consists of the binder.

12. The method of claim 3, wherein:

a) the step of providing a first moulded part includes

forming two or more first-mould parts,

joining the two or more first-mould parts together to form a first mould defining a first cavity,

heating the first feedstock adequately to melt a first binder within the first feedstock, and

injecting the first feedstock into the first cavity; and

b) the step of providing a second moulded part includes

forming two or more second-mould parts,

joining the two or more second-mould parts together to form a second mould defining a second cavity,

heating the second feedstock adequately to melt a second binder within the second feedstock, and

injecting the second feedstock into the second cavity.

13. The method of claim 3, and further comprising removing a partial amount of a first binder of the first feedstock from the first moulded part after the step of solidifying the first feedstock, and prior to the step of sintering.

14. The method of claim 13, wherein the step of removing is conducted prior to the step of applying the binding material.

15. A shrouded wheel formed in accordance with the method for manufacturing a turbomachine shrouded wheel of claim 3.

16. The method of claim 1, wherein:

the one or more first-part connection-surfaces form protrusions along respective lengths of the first-part connection-surfaces; and

the one or more second-part connection-surfaces form depressions along respective lengths of the second-part connection-surfaces, the depressions being shaped and sized to receive the protrusions fully and conformingly when the first moulded part and the second moulded part are respectively positioned and adjoined to one another in the mated configuration.

17. The method of claim 16, wherein:

the step of positioning and adjoining includes applying a feedstock between the first-part connection-surfaces and the second-part connection-surfaces; and

the step of sinter-fusing includes sintering the positioned and adjoined first moulded part and second moulded part.

18. The method of claim 16, wherein at least some connection-surfaces of the group of the first-part connection-surfaces and the second-part connection-surfaces form surface discontinuities spaced at intervals along their respective lengths.

19. A shrouded wheel formed in accordance with the method of claim 16.

20. A shrouded wheel, comprising:

a wheel including a plurality of blades, the plurality of blades having one or more mating surfaces;

a shroud having the one or more receiving surfaces on a flow wall, wherein the one or more receiving surfaces are shaped and sized to receive the mating surfaces fully and conformingly when the wheel and the shroud respectively are positioned and adjoined to one another in a mated configuration, and wherein the wheel and the shroud are positioned and adjoined with respect to one another in the mated configuration;

a means for sinter-fusedly holding the blades to the flow wall through the mating surfaces and the receiving surfaces to form the shrouded wheel.