The disclosure relates generally to processing of workpieces and more specifically to apparatus and methods for finishing internal surfaces of said workpieces.
Workpieces with internal cavities can require internal surface processing (roughening, smoothing, or introduction of compressive stresses) but current apparatus and methods do not form reliable and uniform application throughout the interior. Readily accessible surfaces (e.g., within the line of sight) may be addressed with machining, grinding, or a wide variety of abrasive media processes to improve the surface finish. Currently, these processes are most successful when applied to external surfaces and relatively short, straight internal passages with constant cross sections.
Non-line-of-sight internal passages with serpentine paths and irregularly shaped cavities are difficult or even impossible to effectively polish. Turbine engine components are one example of workpieces which contain such passages, and are subject to high cycle fatigue (HCF) and low cycle fatigue (LCF) service environments. The physics involved in additive manufacturing deposition processes for metal, polymer, and ceramic components results in a relatively rough, Ra 150 to Ra 1000 micro inches, as-built surface finish. An improved surface finish in the range of Ra 1 to Ra 125 micro inches can be required to avoid premature cracking and part failure.
An embodiment of an apparatus includes a centrifugal drive unit, an arm assembly operatively connected to the centrifugal drive unit and configured to revolve about a primary axis perpendicular to the arm, and a workpiece fixture. The workpiece fixture is mounted to the arm assembly, and is configured to rotate at least one workpiece about at least one axis outboard of the primary axis.
An embodiment of a method for processing a workpiece having at least one internal passage includes providing processing media within the internal passage of the workpiece. The workpiece is revolved around an external axis so as to accelerate the processing media against one or more targeted internal surfaces defining the internal passage. The workpiece is oriented to manipulate the processing media relative to the one or more targeted surfaces. The revolving step and the orienting step are controlled to uniformly process the one or more targeted surfaces.
This disclosure generally teaches that an enhanced acceleration field can increase the velocity, kinetic energy, and resultant abrasive action of media against external and internal workpiece surfaces. An apparatus and method utilize various particulates or other media disposed in an internal workpiece passage (or passages). The workpiece and particulates can be manipulated in a multiaxis format to provide enhanced gravity to the particles for both space-bound and earthbound processes. An accompanying fixture can be capable of reorienting the workpiece(s) on an intermittent, cyclical, or a continuous basis in a media flow field. Depending on the location, an enhanced gravity field can register from about 0.01 G up to about 10,000 G. A more typical range of acceleration values for earth bound industrial processes may be 1.01 G to 200 G. The enhanced acceleration field can be realized with rotary motion, linear motion, or a combination of both.
A centrifuge is the subject of an embodiment shown in
Workpiece holding fixture 12 can be configured to rotate at least one workpiece (better seen in subsequent figures) about one or more axes. In the example shown, gimbaled fixture 12 is secured to arm 14 via one or more attachments for rotation about one or more outboard axes (secondary axes 20, 22). Fixture 12 and secondary axes 20, 22 are thus configured to maintain the workpiece at an outboard location along arm 14.
Dynamic balancing ring 26 can be disposed at a junction of centrifugal drive unit 16 and arm 14, and is provided to compensate for the changing positions of fixture 12, as well as the workpiece and media (not shown in
A workpiece can be reoriented with a single or a multi-axis rotating fixture on either a continuous, semi-continuous, or periodic basis to present one or more targeted surfaces to moving media. Workpiece reorientation in the enhanced gravity field (provided by a centrifuge or substantially equivalent device) may be accomplished with constant velocity or intermittent rotary motion around a single axis, around multiple axes, or combinations thereof.
Here, fixture 12 is secured to arm 14 via clevis 28. One or both gimbaled attachments may be motorized (via fixture motors 30A, 30B) to drive selected orientations about one or both secondary axes 20, 22. Power for fixture motors 30A, 30B can be electrical, pneumatic, hydraulic, or a gear or belt driven mechanism. If electric, power can be supplied through a slip ring, an induction system, batteries, or other suitable means.
Note that the fixture can be driven by a centrifuge or other relatively simple, economical machine consisting of a frame, a shaft, bearings, a drive motor, and an optional dynamic balancing wheel. The frame may be designed to accommodate an overhung rotor or a center hung rotor. The basic design of the centrifuge may be readily scaled to accommodate large or small workpiece families.
A programmable control module (PCM) 31 can be connected to provide drive commands to assembly 10, controlling manipulation of the workpiece and orientation and rotational velocity of the workpiece around each axis (e.g., axes 18, 20, 22 in
Generally, processing media can include, among other things, a transport agent and/or an abrasive agent. The transport agent can include a solid, a fluid, or a fluidized agent. Examples of suitable transport fluids include pressurized gas (air or inert gas), water, and mineral oil. The solid can be a metal, ceramic, or polymer.
In one example, internal workpiece surfaces may be polished by locating abrasive media within the cavities and passages of the workpiece. As the workpiece is reoriented within the enhanced acceleration field the sliding action of the media will polish the surfaces it contacts. However, the apparatus and method are not limited to polishing. In one non-limiting additional or alternative step, metal shot can take the place of polishing media for peening one or more interior surfaces, introducing residual compressive stresses.
Candidate abrasive media materials for this process include any of the common industrial abrasives. Typical media types can include alumina (aluminum oxide), silicon carbide, silica (sand, glass beads, or the like), diamond, garnet, metal (e.g., steel shot), organic material (e.g., walnut shell). The size and shape of individual media particles will be determined by the application. The media may be wet or dry.
Work piece holding fixtures may have features such as internal chambers and valves or external supply lines to control the movement, evacuation, and replacement of abrasive media during the surface finishing process. One example of such a system is shown in
It will be apparent that manipulation of workpieces with open ends and irregular shapes can have some sort of enclosure to prevent loss of media in use. Note that the path length and route the media travels may be tailored with polymer or metal orifice cap extensions which may dead end or loop around to another orifice to create a continuous circuit. Custom tooling of this nature provides additional options for managing media flow and abrasive action. The first example may work best with an oscillating motion of fixture 12 (shown in
In one example, a workpiece is formed at least in part by one or more additive manufacturing processes. In such a situation, the mounting tabs or other surfaces can be co-grown with the workpiece much like end caps and/or passage extensions in other examples.
Fixture 112 can include one or more attachments for mounting a workpiece (not visible in
Both external and internal work piece surfaces may be processed in this type of fixture. As fixture 112 rotates end over end (about secondary axis 120), loose media migrates under the influence of the enhanced acceleration field from one end of the fixture to the other, striking the workpiece located near the center (shown in
In the embodiment of arm assembly 114 shown in
Fixtures 212A, 212B are operatively connected outboard of centrifuge drive unit 216. Basic operation is similar to other example embodiments, in which centrifuge drive unit rotates arm assembly 214 about central or primary axis 218 to provide an enhanced gravity field. Outboard fixtures 212A, 212B are also rotatable about at least one secondary axis 220A, 220B outboard of primary axis 218. Fixtures 212A, 212B can be secured via devises 228A, 228B and driven via motors 230A, 230B or equivalent (See
Thus in addition to the above basic and optional elements, media change assembly 234 can also be incorporated into this or other embodiments. Here, various processing media can be stored in a plurality of hoppers (e.g., hoppers 236A, 236B, 236C), flow of each media controlled by a corresponding valve or plurality of valves (e.g., valves 238A, 238B, 238C). Media is fed to union 240 which can be disposed along or proximate to primary axis 218.
Media is transported from one or more of the hoppers to fixtures 212A, 212B (and the corresponding workpieces) by transport conduits 242A, 242B. Conduits 242A, 242B can generally be flexible metallic or nonmetallic tubing depending on a particular application. In certain limited embodiments, nonflexible tubing can be used where there would be minimal bending or twisting stresses such as where the yaw angle is fixed.
Since fixtures 212A, 212B are also rotatable about one or more different axes (here, respective secondary axes 220A, 220B), a pair of unions 244A, 244B can be provided at the outboard locations adjacent to workpiece fixture housings 224A, 224B. Unions 240, 244A, and/or 244B can include centrifugal vanes (not shown) or other suitable means for directing media to the respective workpieces.
For each type of media, it can be evacuated from fixtures 212A, 212B through outlets 246A, 246B. These can include an opposing discharge or dump valve, or additional unions adjacent to secondary axes 220A, 220B. Selection of a particular type of outlet will depend on whether the media will be continuously refreshed during processing, or whether each step is performed on a batch basis. Once the media is evacuated from fixtures 212A, 212B, additional conduits (not shown) can direct used media away from apparatus 210 and the media can be reused, recycled, regenerated, or otherwise suitably disposed of.
Arm assembly 314 includes telescoping sleeve portions 320A, 320B disposed outboard of primary axis 318, and which are configured to extend and retract radially relative to central arm portion 322. As the unit is driven circumferentially by the centrifuge unit (not shown in
Processing media can include, among other things, a transport agent and/or an abrasive agent. The transport agent can include a solid, a fluid, or a fluidized agent. Examples of suitable transport fluids include pressurized gas (air or inert gas), water, and mineral oil. The solid can be a metal, ceramic, or polymer. Abrasive media can be selected from a group including but not limited to alumina, silicon carbide (SiC), silica, carbon, metal, organic material, and combinations thereof.
With the media in place, step 404 can include revolving the workpiece around a primary axis so as to accelerate the processing media against one or more targeted internal surfaces defining the internal passage. This provides an enhanced gravity field to the workpiece (and processing media) as noted above. This step can take place via centrifuge with a circular or noncircular path, as well as a planar or nonplanar path. Rotation can be continuous or intermittent, with constant or variable rotational velocity during iteration(s) of step 404.
As part of step 406, the workpiece can be oriented to manipulate the loose processing media relative to the one or more targeted internal surfaces. For example, the workpiece can be mounted to or secured within an enclosure or other suitable fixture/housing and rotated about one or more secondary axes. The fixture/housing can also be adapted to impart reciprocating, oscillating, or other non-rotational motion to the workpiece and/or loose finishing media. The fixture can be disposed at an outboard location and rotatable about one or more secondary axes to reposition and manipulate the processing media located therein. When step 406 is done in conjunction with one or more iterations of revolving step 404 (either simultaneously or alternately), internal targeted surfaces can be processed according to step 408.
As part of step 408, controlling the revolving step and the orienting step to process the one or more targeted surfaces, a processing control module or other device can provide commands to the various motors and valves to provide a targeted surface with a desired finish. In scenarios which have a high risk of fatigue, a suitable surface roughness can be provided down to about Ra 16 microinches or less in some instances.
Optionally, step 410 includes iteratively repeating one or more of the above steps. For example, it may be that progressively finer grit may be needed to achieve the desired result. Additionally or alternatively, different internal surfaces (in the same or different passage) could require different parameters. As such, the processing media can be periodically moved and/or exchanged manually or automatically.
This apparatus and method are anticipated to be useful in a variety of manufacturing scenarios. One expected area of use is in conjunction with additive-manufactured high temperature materials such as those in turbine engine applications. A relatively rough surface finish with an attendant fatigue life reduction is an inherent feature of current additive manufacturing processes. Enabling directed, aggressive abrasive media action on both external and internal work piece passage surfaces such as walls, struts, ribs, fillets, and cavities will significantly open the turbine engine design space for components fabricated with additive manufacturing. The low cost of the apparatus combined with the accelerated abrasion rate this process offers means that rapid, low cost part finishing may be realized.
Discussion of Possible Embodiments
The following are non-exclusive descriptions of possible embodiments of the present invention.
An embodiment of an apparatus includes a centrifugal drive unit, an arm assembly operatively connected to the centrifugal drive unit and configured to revolve about a primary axis perpendicular to the arm, and a workpiece fixture. The workpiece fixture is mounted to the arm assembly, and is configured to rotate at least one workpiece about at least one axis outboard of the primary axis.
The apparatus of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
An apparatus according to an exemplary embodiment of this disclosure, among other possible things includes a centrifugal drive unit; an arm assembly operatively connected to the centrifugal drive unit and configured to revolve about a primary axis perpendicular to the arm; and a workpiece fixture mounted to a distal end of the arm assembly, the workpiece fixture includes at least one receptacle for receiving and retaining a workpiece and processing media, and is configured to rotate at least one workpiece about at least one secondary axis outboard of the primary axis.
A further embodiment of the foregoing apparatus, wherein the arm assembly is configured to revolve the workpiece fixture along a circular path about the primary axis.
A further embodiment of any of the foregoing apparatus, wherein the arm assembly has an adjustable length such that the arm assembly is configured to revolve the workpiece fixture along a noncircular path about the primary axis.
A further embodiment of any of the foregoing apparatus, wherein the apparatus further comprises at least one actuator connected to the arm assembly and configured to enable out-of-plane rotation of the arm assembly and the workpiece fixture.
A further embodiment of any of the foregoing apparatus, wherein the apparatus further comprises a dynamic balancing ring disposed at a junction of the centrifugal drive unit and the arm assembly.
A further embodiment of any of the foregoing apparatus, wherein the workpiece fixture comprises an open gimbaled fixture.
A further embodiment of any of the foregoing apparatus, wherein the workpiece fixture comprises an elongated tumbling fixture.
A further embodiment of any of the foregoing apparatus, wherein the tumbling fixture includes a wedge valve.
A further embodiment of any of the foregoing apparatus, wherein the workpiece fixture comprises a gimbaled housing with at least one enclosure.
A further embodiment of any of the foregoing apparatus, wherein the apparatus further comprises a transport conduit disposed along the arm assembly, and connecting a media reservoir and the workpiece fixture.
A further embodiment of any of the foregoing apparatus, wherein the arm assembly includes at least one telescoping portion disposed between the workpiece fixture and the primary axis.
A further embodiment of any of the foregoing apparatus, wherein the arm assembly includes at least one cam follower in communication with a track disposed on or about the centrifugal drive unit.
An embodiment of a method for processing a workpiece having at least one internal passage includes providing processing media within the internal passage of the workpiece. The workpiece is revolved around an external axis so as to accelerate the processing media against one or more targeted internal surfaces defining the internal passage. The workpiece is oriented to manipulate the processing media relative to the one or more targeted surfaces. The revolving step and the orienting step are controlled to uniformly process the one or more targeted surfaces.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
A method according to an exemplary embodiment of this disclosure, among other possible things includes providing loose processing media within the internal passage of the workpiece; revolving the workpiece around an external axis so as to accelerate the processing media against one or more targeted internal surfaces defining the internal passage; orienting the workpiece to manipulate the loose processing media relative to the one or more targeted surfaces; and controlling the revolving step and the orienting step to uniformly process the one or more targeted surfaces.
A further embodiment of the foregoing method, wherein the media comprises at least one of a transport agent and an abrasive agent.
A further embodiment of any of the foregoing methods, wherein the orienting step comprises continuously rotating the workpiece about at least one internal axis.
A further embodiment of any of the foregoing methods, wherein the orienting step comprises intermittently rotating the workpiece about at least one internal axis.
A further embodiment of any of the foregoing methods, wherein the method further comprises: exchanging at least a portion of the processing media in the workpiece; and repeating the revolving, orienting, and controlling steps.
A further embodiment of any of the foregoing methods, wherein the revolving step comprises: securing the workpiece to a centrifuge defining the external axis; operating the centrifuge to move the workpiece around the external axis; and dynamically balancing the centrifuge and the workpiece.
A further embodiment of any of the foregoing methods, wherein the method further comprises oscillating the workpiece during the revolving step.
A further embodiment of any of the foregoing methods, wherein the method further comprises modifying a path of the workpiece around the primary axis during the revolving step, wherein the modifying step comprises changing a distance of the workpiece relative to the second axis.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.