Patent Application
20090075564
The disclosure relates to machining. More particularly, the disclosure relates to superabrasive machining of metal alloy articles
Superabrasive quills for point and flank superabrasive machining (SAM) of turbomachine components are respectively shown in commonly-owned U.S. Pat. Nos. 7,101,263 and 7,144,307. Commonly-owned US Patent Publication 2006-0035566 discloses a quill having a tip protuberance.
One aspect of the disclosure involves a tool for use in an abrasive machining process. A body extends along a central longitudinal axis from a first end to a tip end. The body has a tip end protuberance. An abrasive material is located on the protuberance. A body lateral surface has, over a radial span of at least 20% of a radius of the protuberance, a continuously concave longitudinal profile diverging tipward.
In various implementations, the radial span may be at least 30% of said radius. The abrasive material may be along at least half of the radial span. The body may include a threaded portion for engaging a machine, a flange having a pair of flats for receiving a wrench, and a shaft extending tipward from the flange. The abrasive material may comprise a coating. The abrasive material may be selected from the group consisting of plated cubic boron nitride, vitrified cubic boron nitride, diamond, silicon carbide, and aluminum oxide. The tool may be combined with a machine rotating the tool about the longitudinal axis at a speed in excess of 10,000 revolutions per minute.
Another aspect of the invention involves a process for point abrasive machining of a workpiece. A tool is provided having a tip protuberance grinding surface coated with an abrasive. The tool is oriented relative to a surface of the workpiece so that there is contact between the surface and the grinding surface. A part is formed by removing material at the contact by rotating the tool about the central longitudinal axis and translating the tool relative to the workpiece and off-parallel to the longitudinal axis. The tool is cooled by guiding a cooling liquid flow to the tip grinding surface along a surface of the shaft and radially diverging to the grinding surface.
In various implementations, the tool may be rotated at a speed in the range of 40,000 to 120,000 revolutions per minute. The longitudinal axis may be reoriented relative to the workpiece while machining the workpiece. The workpiece may comprise an integrally bladed disk. The workpiece may comprise or may consist essentially of a nickel- or cobalt-based superalloy or titanium alloy.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicate like elements.
Near the aft end 30, the exemplary quill includes an externally threaded portion 36 for mating by threaded engagement to a correspondingly internally threaded portion of a central aperture 38 of the spindle 22. Ahead of the threaded portion 36, an unthreaded cylindrical portion 40 fits with close tolerance to a corresponding unthreaded portion of the aperture 38 to maintain precise commonality of the quill/spindle/rotation axis 500. A wrenching flange 42 is forward (tipward) of the unthreaded portion 40 and has a radially-extending aft surface 44 abutting a fore surface 46 of the spindle. The exemplary flange 42 has at least a pair of parallel opposite wrench flats 48 for installing and removing the quill via the threaded engagement. Alternatively, features other than the threaded shaft and wrenching flange may be provided for use with tools having different quill interfaces such as are used with automatic tool changers.
A shaft 50 extends generally forward from the flange 42 to the tip 32. In the exemplary embodiment, the shaft 50 includes a proximal portion 52 and a horn-like tip protuberance portion 54.
In the exemplary embodiment, the proximal portion 52 is relatively longer than the protuberance 54. The tip protuberance 54 is sized to make the required cut features. If a relatively smaller diameter protuberance is required, the shaft may be stepped (e.g., as in US Patent Publication 2006-0035566, the disclosure of which is incorporated by reference in its entirety herein as if set forth at length). The length of the proximal portion 52 (combined with the length of the protuberance) provides the desired separation of the tip from the tool spindle. Such separation may be required to make the desired cut while avoiding interference between the spindle and any portion of the part that might otherwise interfere with the spindle.
In longitudinal section, the surface of the protuberance 54 (
Alternative implementations may, for example, include a central recess in the end so as to leave a longitudinal rim. The presence of the recess eliminates the low speed contact region otherwise present at the center of the tip. This permits a traversal direction 502 at an angle θ close to 90° off the longitudinal/rotational axis 500.
The exemplary transition 64 radially diverges from a junction 80 with the adjacent straight portion of the shaft (e.g., the proximal portion 52). At this exemplary junction, the shaft and transition have a radius RS. Along the transition 64, the radius progressively increases toward the end 32. The tip has a largest radius RT. The divergence of the transition 64 may provide a structural reinforcement. For example, with RT larger than RS, and no transition, the protuberance would be formed as a disk at the end of the shaft. The disk would have a tendency to flex/wobble during use. The transition braces against such flex/wobble.
The transition 64 may also help direct coolant and/or lubricant to the contact area between the quill and the workpiece (the grinding zone). For example,
An exemplary transition 64 is concave in longitudinal section. This may provide an advantageous combination of strength, light weight, and guidance of the coolant flow.
The exemplary protuberance has a length LT from the junction 80 to the end 32. Of this length, the convex or radial rim portion 66 has a length LR. The exemplary concave transition 64 has a length LC. A radius at the junction 67 is RC. Exemplary RC is at least 80% of RT, more narrowly, 90%, or 95%. An exemplary change in radius over the transition (RC minus RS) is at least 20% of RT, more narrowly, at least 30% (e.g., 30-60%). Exemplary LT and LC are larger than RS, more narrowly, at least 150% of RS (e.g., 200-500%).
Other situations involve machining undercuts. Various examples of undercuts are used for backlocked attachment of one component to another and/or for lightening purposes. In various such undercut situations, during one or more passes of the quill, the grinding zone may extend up along the concave transition 64. For example,
Another optional feature is elongate recesses (e.g., as in US Patent Publication 2006-0035566), which may serve to help evacuate grinding debris.
In an exemplary manufacturing process, the basic quill body is machined (e.g., via one or more lathe turning steps or grinding steps) from steel stock, including cutting the threads on the portion 36. There may be heat and/or mechanical surface treatment steps. The abrasive may then be applied as a coating (e.g., via electroplating). Exemplary superabrasive material may be selected from the group of cubic boron nitride (e.g., plated or vitrified), diamond (particularly useful for machining titanium alloys), silicon carbide, and aluminum oxide. The exemplary superabrasive material may have a grit size in the range of 40/45 to 325/400 depending on the depth of the cut and the required surface finish (e.g., 10 μin or finer). A mask may be applied prior to said coating and removed thereafter to protect areas where coating is not desired. For example, the mask may confine the coating to the tip protuberance portion 54. Particularly for a vitrified coating, the as-applied coating may be dressed to improve machining precision. To remanufacture the quill, additional coating may be applied (e.g., optionally after a removal of some or all remaining used/worn/contaminated coating).
An exemplary projecting length L of the quill forward of the spindle is 57 mm, more broadly, in a range of 40-80 mm. An exemplary protuberance radius RT is 10 mm, more broadly 8-20 mm. An exemplary longitudinal radius of curvature of the convex portion is 1-3 mm, more broadly 0.5-4 mm.
One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the following claims.
