US20090036031A1

US20090036031A1 - Coating assisted surface finishing process

Info

Publication number: US20090036031A1
Application number: US11/882,239
Authority: US
Inventors: Hua Dongyun; Thomas Anthony Beveridge
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2007-07-31
Filing date: 2007-07-31
Publication date: 2009-02-05

Abstract

A method of polishing a first component by a second component of a tribological pair is disclosed. The method includes mating the first component to the second component in a tribological configuration. The first component and the second component are moved such that a first surface of the first component and a second surface of the second component contact and slide against each other, so that the second component polishes the first component. The method further includes discontinuing moving of the first component and the second component when the first surface obtains a desired surface finish.

Description

TECHNICAL FIELD

The present disclosure relates generally to a surface finishing process, and more particularly, to a coating assisted surface finishing process.

BACKGROUND

On a microscopic scale, surfaces of most components are not perfectly smooth. Instead, these surfaces are characterized by numerous microscopic hills and valleys (termed “asperities”). When surfaces of two components contact and undergo relative motion with respect to each other, the asperities of one surface score and scratch the other surface. The surfaces of such interacting components are subject to surface failures, such as scuffing and wear, due to the interaction of these asperities. These contacting components that undergo relative motion often require premature component replacement due to wear related failures. In this disclosure, such components that contact and undergo relative motion with respect to each other are referred to as “tribological components.” Non-limiting examples of tribological components include mating gears, a shaft sliding on a bearing, piston sliding on a cylinder, ball bearing components, etc.
Typical manufacturing processes for tribological components include processes used to change the shape of the material (such as, for example, casting, forging, machining, pressing, etc.), and processes used to finish the component to a desired dimension (for example, grinding, shaping, milling, etc.). Some tribological components may also be subjected to a final polishing process, such as honing, lapping etc., to obtain a desired surface finish along the working surfaces of the components. In this disclosure “working surfaces” refer to surfaces of tribological components that contact each other while undergoing relative motion with respect to each other. For example, the contacting surfaces of the teeth of a pair of meshed gears, surfaces of a piston and a cylinder that contact each other during the sliding of the piston, etc. are all referred to as working surfaces. The term “polishing” is also used generally to refer to any process that improves the surface finish of a working surface.
One polishing process used to improve the surface finish of working surfaces of gears is described in U.S. Pre Patent Publication No: 2004/0088861 A1 (the '861 publication) issued to Vinayak et al. on May 13, 2004. In the polishing process of the '861 publication, the gear is immersed in a slurry containing ceramic elements and vibrated using a high frequency shaking apparatus. During the vibration process, the ceramic elements impact the exposed surfaces of the gear in a random manner resulting in an smooth gear surface. In the '861 publication, the gear geometry before polishing is designed to account for excess material removal from regions that are more exposed to the ceramic elements than regions that are protected by the geometry of the gear. For example, due to the geometry of the gear, the top surface of the gear may be more prone to impact by the ceramic elements than the root of the gear. Therefore, material removal from the top surface of the gear may be more than the root of the gear. To account for the uneven material removal during polishing, the top surface of the gear may be designed to include excess material that may be removed during polishing.
Although the process of the '861 publication may produce a tribological component with a smooth surface finish, the process may have drawbacks. For instance, the process of the '861 publication may also remove material from non-working surfaces of the component, and therefore, change other dimensions of the component. The process of the '861 publication may also be expensive. Also, having to account for uneven material removal by providing excess material at exposed regions of the gear may complicate the design process. Since the process of the '861 publication immerses and shakes the tribological component in a slurry, the size and motor rating of the shaking apparatus may have to be increase with the size of the component, thereby increasing the cost of the polishing operation.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above.

SUMMARY OF THE INVENTION

In one aspect, a method of polishing a component is disclosed. The method includes providing a first component with a first working surface and depositing a coating on a second working surface of a second component. The first component and the second component are tribological components. The method also includes mating the first component to the second component. The mating includes contacting the first working surface with the second working surface. The method further includes operating at least one of the first component and the second component, where the operating includes the first working surface and the second working surface undergoing relative displacement while contacting each other, and stopping the operation after polishing the first working surface.
In another aspect, a method of polishing a first component by a second component of a tribological pair is disclosed. The method includes mating the first component to the second component in a tribological configuration. The first component and the second component are moved such that a first surface of the first component and a second surface of the second component contact and slide against each other, so that the second component polishes the first component. The method further includes discontinuing moving of the first component and the second component when the first surface obtains a desired surface finish.
In yet another aspect, a component polishing system is disclosed. The system includes a first coupling mechanism configured to attach a first component. The first component includes a first working surface. The system also includes a second coupling mechanism configured to attach a second component and position the second component to contact the first working surface. The second component includes a second working surface with an abrasive coating thereon. The first component and the second component are tribological parts that are configured to slide on each other in an application. The system further includes a mechanical power source coupled to one of the first coupling mechanism or the second coupling mechanism. The mechanical power source is configured to induce relative displacement between the first component and the second component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an exemplary disclosed machine;

FIG. 2 is an illustration of a gear system of the machine of FIG. 1;

FIG. 3 is an illustration of a partial side view of a gear of the gear system of FIG. 2;

FIG. 4 is an illustration of a surface of the gear of FIG. 3;

FIG. 5 is an illustration of an embodiment of a surface polishing system used to polish the gear of FIG. 3;

FIG. 6 is an illustration of a coating on a surface of the surface polishing system of FIG. 5; and

FIG. 7 is a flow chart of a method of polishing the gear of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary machine 900 having multiple systems and components. Machine 900 may embody a fixed or mobile machine that performs any type of operation. For example, machine 900 may be a transportation machine such as a car, train, or an airplane, an earth moving machine such as an excavator, a dozer, a loader, a backhoe, a motor grader, a dump truck, or some other machine. Machine 900 may include a power source 200, a transmission system 300, a traction system 400, and many other systems which are not shown. Transmission system 300, traction system 400, and/or other systems of machine 900 may include a gear system.
FIG. 2 is an illustration of a gear system 100 of transmission system 300 of machine 900. Gear system 100 may include multiple gears meshed together. Gear system 100 may also include other gears, such as, for example a pinion 14, and a driver gear 14A. Some or all of the gears in gear system 100 may be coupled to parallel shafts. For instance, gear 12 may be coupled to a shaft 16 and pinion 14 may be coupled to a shaft 18. An external surface of gear 12 and pinion 14 may have a plurality of teeth 20. Teeth 20 of gear 12 and pinion 14 may be meshed so that a rotational motion of pinion 14 about the longitudinal axis of shaft 18 may also rotate gear 12 and shaft 16. Gear 12 and pinion 14 may thus transmit motion between shaft 16 and shaft 18. The embodiment of gear system 100 depicted in FIG. 2 is a spur gear system where teeth 20 are generally straight and run generally parallel to longitudinal axes of shafts 16, 18. However, gear system 100 may be any type of gear known in the art. Non limiting examples of gears in gear system 100 may include rack and pinion, internal ring gear, helical gear, helical rack gear, double helical gear, face gear, worm gear, double enveloping worm gear, hypoid gear, straight bevel gear, spiral bevel gear, and screw gear. gear system 100 may also include gears having other teeth forms, such as, for example, involute or cycloidal teeth forms. Gear 12 and pinion 14 may be fabricated from cast iron, steel, bronze and brass, or any materials used in the art.
FIG. 3 shows a partial side view of gear 12 depicting the parts of the gear. Teeth 20 of gear 12 may extend from a root 26 of gear 12 to a tip 24 forming a flank 28 between them. Flank 28 may be a region of gear 12 that forms the working surface of gear 12. That is, the region that contacts teeth 20 of pinion 14 when they mesh and transmit motion (depicted in FIG. 1). A region of teeth 20 between root 26 and flank 28 may form a root fillet 30. In some embodiments, root fillet 30 may not contact pinion 14 when they mesh and rotate. That is, root fillet 30 may not be part of the working surface. In these embodiments, root fillet 30 may be included for mechanical strength. However, in other embodiments, root fillet 30 may be part of the working surface.
Gear 12 may also include a pitch circle through a point on flank 28 where gear 12 contacts pinion 14 in the meshed configuration (depicted in FIG. 1). The pitch circle radius 34 may represent the size of gear 12. An outer circle of gear 12 may be a circle that passes through the tips 24 of the teeth 20, and a root circle may be a circle that passes through the roots 26 of the teeth 20. The outer circle radius 36 may be the radius of the outer circle, and the root circle radius 32 may be the radius of the root circle. An addendum 38 may be the radial distance between the pitch circle and the outer circle and a dedendum 40 may be radial distance between the pitch circle and the root circle.
As shown in FIG. 4, outer surface 42 of gear 12 may include multiple asperities 44 formed by the manufacturing process. These asperities 44 may create a rough surface finish on outer surface 42. Asperities 44 on outside surface 42 may include multiple peaks 44 a and multiple valleys 44 b. Each peak 44 a may be characterized by a peak height H_pand each valley 44 b may be characterized by a valley depth H_v. Peak height H_pof a peak 44 a may be the height of the peak from a mean surface line 48, and valley depth H_vmay be the depth of a valley from the mean surface line 48. Mean surface line 48 may represent a mean value of outer surface 42. The maximum peak to valley height H_zmay be a distance between the maximum peak height (maximum value of H_p) and the maximum valley depth (maximum value of H_v), and may represent the distance between the highest peak and the lowest valley on outer surface 42. Maximum roughness R_zmay be an roughness of the surface dependent on maximum peak to valley height H_z. Arithmetic mean roughness R_aof outer surface 42 may be the arithmetic mean of the roughness of outer surface 42. RMS roughness R_qmay be root mean square value of the roughness of outer surface 42. RMS roughness R_qmay be calculated as the square root of the mean of the squares of roughness of outer surface 42. Maximum roughness R_z, peak to valley height H_z, arithmetic mean roughness R_a, and RMS roughness R_qmay be components of surface roughness that define the surface finish of outer surface 42. Lower values of one or more of these components (maximum roughness R_z, peak to valley height H_z, arithmetic mean roughness R_a, and RMS roughness R_q) may indicate a smoother surface finish of outer surface 42. That is, polishing outer surface 42 may reduce the values of one or more of the roughness components—maximum roughness R_z, peak to valley height H_z, arithmetic mean roughness R_a, and RMS roughness R_q. Outer surface 42 may be polished by using a Coating Assisted Surface Finishing Process (CASFP).
FIG. 5 illustrates a part of a surface polishing system 500 that may be used to polish outer surface 42 by CASFP. In surface polishing system 500, gear 12 may be coupled to a shaft 16A, and teeth 20 of gear 12 may be meshed with teeth 20 of an abrasive pinion 50. Abrasive pinion 50 may be a gear configured to mesh with gear 12, and may be mounted on a shaft 18A. In the meshed configuration, abrasive pinion 50 and gear 12 may transmit motion. That is, rotation of shaft 18A may rotate abrasive pinion 50 resulting in the rotation of gear 12 and shaft 16A. Shaft 18A may be coupled to a power source 60. Power source 60 may include any mechanism configured to rotate shaft 18A about its longitudinal axis. For instance, power source 60 may be a motor configured to impart rotary motion to shaft 18A. It is also contemplated that power source 60 may include a manual mechanism to impart rotary motion to shaft 18A. Shaft 16A may be coupled to a mechanical load 70. Mechanical load 70 may be any mechanism that applies a resistance to the rotation of shaft 16A. Mechanical load 70 may include rotating or sliding mechanisms that resist the rotation of shaft 16A due to friction. Mechanical load 70 may also include mechanisms, such as a dynamometer, that may impart a variable resistance to shaft 16A. The variable resistance imparted by mechanical load 70 may be selectable by an operator of surface polishing system 500. It is also contemplated that power source 60 may be coupled to shaft 16A and mechanical load 70 may be coupled to shaft 18A. In this embodiment, power source 60 may impart rotary motion to shaft 16A and mechanical load 70 may apply a resistance to shaft 18A. It is also contemplated that in some embodiments, mechanical load 70 may be eliminated.
The outer surface 52 of abrasive pinion 50 may include a coating 54. In some embodiments, outer surface 52 may include the entire external surface of abrasive pinion 50, while in other embodiments, outer surface 52 may only include selected surfaces. These selected surfaces may include the working surfaces of abrasive pinion 50. During the transmission of motion between abrasive pinion 50 and gear 12, outer surface 52 of abrasive pinion 50 may rub against outer surface 42 of gear 12. When the outer surfaces 42 and 52 slide against each other, coating 54 on outer surface 52 may abrade outer surface 42 of gear 12. Rotation of gear 12 and abrasive pinion 50 may cause the entire working surface of gear 12 to be abraded by abrasive pinion 50. Repeated abrasion, resulting from continued rotation of gear 12 and abrasive pinion 50 may reduce the height of asperities 44 on outer surface 42 and polish outer surface 42. In some embodiments, such as, for example, in a pair of gears undergoing rolling contact, the two mating gears may be mated in a slightly off-pitch configuration to enhance the polishing action.
It is contemplated that, in some embodiments, a separate surface polishing system 500 may be eliminated, and the polishing of gear 12 may be carried out in machine 900. For instance, when polishing of gear 12 is desired, pinion 14 (see FIG. 2) of gear system 100 may be replaced with abrasive pinion 50 and machine 900 operated. During operation of machine 900, abrasive pinion 50 may transmit motion causing the working surface of gear 12 to be abraded by coating 54 of abrasive pinion 50. Repeated abrasion of the working surface of gear 12 during rotation of the gears polish outer surface 42. After a desired surface finish of gear 12 is achieved, abrasive pinion 50 may be replaced with pinion 14, and machine 900 operated normally.
FIG. 6 illustrates outer surface 52 of abrasive pinion 50 with coating 54. Coating 54 may include any material that may be deposited on outer surface 52. In some embodiments, coating 54 may be made of a hard material such as nitrides, carbides, and borides of transition metals (such as, titanium nitride, chromium nitride, silicon nitride, silicon carbide, etc.), carbon based coatings (such as, diamond, diamond like carbon (DLC), and DLC with inclusions such as tungsten), alumina, boron nitride, etc. Coating 54 may be a single layer coating or a multi-layers coating. Single layer coatings are coatings where the bulk of the coating may be made substantially of the same material. The interface of the coating with the component may, however, be of a different material. This different material may be an alloy of the coating material and the component material formed after deposition, or it may be an intentionally deposited material to improve some characteristic (such as, adhesion) of the coating. Multi-layer coatings may be periodic structures of different materials.
Coating 54 may be deposited on pinion 50 by a vapor deposition technique, such as chemical vapor deposition or physical vapor deposition. Any conventional CVD or PVD process known in the art may be used to apply coating 54. Coating 54 may form a conformal coating over outer surface 52. In this disclosure, “conformal coating” refers to a coating that substantially conforms to the shape of the underlying surface (that is, outer surface 52). A conformal coating may generally resemble the shape of the surface it is applied on. However, it is contemplated that a conformal coating may not be present on sharp discontinuities of the surface, including crevices, points, pores, cracks, sharp edges, and internal surfaces.
Coating 54 on outer surface 52 may have a thickness 56. Thickness 56 may have any value to suit an application. At very low values of thickness 56, coating 54 may wear off quickly and may need to be periodically refurbished. Very high values of thickness 56 may cause coating 54 to develop large internal stresses, and thereby, crack or peel. In general, the precise values of thickness 56 beyond which these issues may arise depends upon the application. For the gear polishing application illustrated herein, a preferred range of thickness 56 may be between about 1 micron and about 20 microns. However, it is contemplated that for other applications, thickness 56 may have different values. In some embodiments, thickness 56 of coating 54 may be substantially uniform. That is, thickness 56 of coating 54 at different regions of outer surface 52 may be substantially the same. However, it is contemplated that in some embodiments, thickness 56 of coating 54 may vary over the outer surface 52. In these embodiments, thickness 54 may vary between about 1 micron and about 20 microns. That is, a minimum coating thickness may be about 1 micron and a maximum coating thickness may be about 20 microns.
Although the description above illustrates polishing of gear tooth using CASFP, the working surface of any tribological component may be polished using CASFP. In general, to polish the working surface of a first component of a tribological component pair, a coating may be applied to the working surface of a second component. The coated second component is then allowed to contact and undergo relative motion with respect to the first component of the tribological component pair. While undergoing relative motion, the coating on the second component abrades and polishes the working surface of the first component.
For example, to polish a rough external surface (working surface) of a shaft that slides on a cavity of a bearing, the coating may be applied to the cavity surface (working surface of the bearing), and the shaft allowed to slide on the bearing with the coated working surface. Repeated sliding of the shaft on the bearing abrades and polishes the working surface of the shaft. The coated bearing may then be removed and replaced with a standard (uncoated) bearing. In embodiments, where the coated bearing is part of a machine dedicated to polishing shafts (polishing machine), the polished shaft may be removed from the polishing machine after polishing. A rough bearing surface may likewise be polished by applying the coating on the shaft.
FIG. 7 illustrates an exemplary method of polishing a rough working surface of a tribological component using CASFP. In the description below, a tribological component pair includes a first component and a second component that contacts and undergoes relative motion with respect to each other. The first surface is the working surface of the first component and second surface is the working surface of the second component. In the mated configuration, regions of the first surface rest on regions of the second surface. During operation, the first surface and the second surface slide against each other. As described earlier, the first component and second component may be tribological components of any tribological component pair. For instance, the first surface and second surface may be mating surfaces of gear system 100, or in the case of the shaft that slides on a cavity of the bearing, the first surface may be the shaft surface and the second surface may be the cavity surface.
The first component with the first surface is prepared (step 610) using any operation. Preparation of the first component may include manufacturing or remanufacturing the component. Manufacturing the component may include any component fabrication process, such as casting and machining. Remanufacturing refers to the process of cleaning and repairing a used component for reuse. The first working surface may be a rough surface. The rough surface may be manifested by a high value of one or more of maximum roughness R_z, peak to valley height H_z, arithmetic mean roughness R_a, and RMS roughness R_q.
A coating may then be deposited on the second working surface of the second component (step 620). The second component may be first cleaned to remove contaminants from its surfaces. This cleaning may include removing rust, debris, or other organic contaminants from the surfaces of the component. The cleaning may include mechanical cleaning, chemical cleaning, or a chemical assisted mechanical cleaning. Mechanical cleaning may include scrubbing the surfaces of the component. A chemical solvent may be used along with mechanical scrubbing. The component may also be rinsed in water and dried.
The deposition step (step 620) may also include depositing a coating on the surfaces of the second component. In some embodiments, the coating may be selectively applied to some surfaces, for instance, the second surface. In these embodiments, the surfaces of second component where the coating is not applied may be covered before depositing the coating. Covering these surfaces may include applying a mask on these surfaces. Any mask application process known in the art may be used to apply the mask.
Any conventional coating process, such as PVD or CVD techniques, may be used to apply the coating on second component. PVD techniques may include deposition processes such as, for instance, cathodic arc deposition, evaporative deposition, electron beam physical vapor deposition, pulsed laser deposition, and sputter deposition. CVD processes may include any conventional CVD techniques such as, for example, atmospheric pressure CVD, low pressure CVD, ultra low vacuum CVD, plasma enhanced CVD, etc. The coating on the second component may be applied to the desired thickness.
After coating, the first component and the second component are mated together (step 630). The term “mating” refers to locating the first and second component in the same structural orientation as they would be in actual application. In this orientation, the first surface of the first component may contact the second surface of the second component. Mating the components may also include coupling the first component to a power source. The power source may be configured to impart relative motion between the first component and the second component. In some embodiments, the second component may be coupled to a resistance source. In these embodiments, the resistance source may apply mechanical resistance to the motion of the second component. It is also contemplated that, in some embodiments, the second component may be coupled to the power source and the first component may be coupled to the resistance source.
For instance, in an embodiment where the first component is gear 12 with rough surface 42 and the second component is abrasive pinion 50 with coating 54, mating the two components refers to the process of attaching the two components to their respective shafts (16A and 18A, see FIG. 5), and orienting the two components such that their teeth mesh as they would in actual application. Shaft 18A may then be coupled to power source 60 and shaft 16A to mechanical load 70. In some applications, as in an embodiment where the second component is stationary (for example, the bearing in an application where the shaft with a rough surface slides on the bearing), coupling the second component to a mechanical resistance may be eliminated.
In some embodiments, a lubricant may be applied to the contacting surfaces. The lubricant may include any conventional lubricant used in the art. It is also contemplated that, in some embodiments, an abrasive slurry may also be applied to the contacting surfaces.
After the components are mated, they may then be operated (step 640). Operating the component may include activating the power source to impart relative motion between the two components. In embodiments which include a resistance source, operating the components may also include activating the resistance source. Relative motion between the components may induce the contacting first surface (rough surface) and the second surface with the coating to slide/rub against each other. Repeated rubbing/sliding of the first component and the second component against each other may abrade the rough surface, thereby polishing it.
In the embodiment depicted in FIG. 5, operating the component may include activating power source 60 and mechanical load 70. Power source 60 may impart rotary motion to shaft 18A. Shaft 18A may in turn rotate abrasive pinion 50. The teeth of abrasive pinion 50 that mesh with teeth of gear 12 may apply a force on the mating teeth of gear 12 forcing gear 12 to rotate. Rotation of gear 12 may also rotate shaft 16A about its longitudinal axis. Mechanical load 70 may apply a force on shaft 16A resisting the rotation of shaft 16A. This resistance force may increase the force at the contact area (reaction force) between the teeth of abrasive pinion 50 and gear 12. This force at the contact area may act on asperities 44 on rough surface 42 causing them to abrade. Rotation of abrasive pinion 50 may cause abrasion of more asperities 44 on rough surface 42. Abrasion of asperities 44 on rough surface 42 may polish rough surface 42.
The first surface may then be inspected to determine if a desired surface finish has been attained (step 650). This inspection may include visual inspection of the first surface or may include measurements to determine one or more of the maximum roughness R_z, peak to valley height H_z, arithmetic mean roughness R_a, and RMS roughness R_q. Any means capable of measuring surface roughness, such as surface profilometer, atomic force microscope (AFM), etc., may be used to perform the roughness measurements. The roughness measurements may be compared to acceptable values of surface roughness (step 660). Acceptable values of surface roughness may be roughness values that an operator determines is suitable for the first component. If the surface finish of the rough surface is not within acceptable limits, the sliding/rubbing of the components against each other may be continued. If the surface finish is within acceptable limits, the sliding/rubbing motion may be discontinued and the first component removed (step 670).
In some embodiments, the inspection and the comparison steps (step 650 and 660) may be a visual operation where an operator looks at the first surface to judge if the surface finish looks acceptable to him. In some embodiments, the inspection and comparison steps may be automated. In these embodiments, the operation of the components (step 640) may be periodically stopped and roughness measurements of first surface taken. The measured values may then be compared to preset acceptable roughness values. If the measured values of roughness are less than or equal to the acceptable values, the operation of the components may be discontinued. It is also contemplated that, in some embodiments, the inspection and the comparison steps (step 650 and 660) may be eliminated. In these embodiments, operation of the components (step 640) may be continued for a predetermined time. Predetermined time may be a operating time which the operator knows will polish the first surface. In some embodiments, predetermined time may be determined based on a measured roughness of first surface. For instance, predetermined time may be read off a table that list operating times for different values of surface roughness.

INDUSTRIAL APPLICABILITY

The disclosed embodiments relate to a surface finishing process. The process can be used to polish a rough surface of a component that contacts a mating component and undergoes relative displacement with respect to each other. A coating of a hard material is applied to contacting surfaces of the mating component before the components are contacted and allowed to undergo relative displacements with respect to each other. As the components rub against each other, the hard coating on the mating component abrades the rough surface to polish the surface. To illustrate the application of the disclosed surface finishing process, an exemplary embodiment of the CASFP, where the outer surface of a spur gear is polished with a coated pinion will now be described.
Surface profilometer measurements of a selected region of an outer surface 42 of spur gear 12 may indicate a mean roughness R_aof about 0.213 microns. A coating assisted surface finishing process may be used to polish outer surface 42. A PVD process may be used to deposit an approximately 3 micron thick layer of tungsten containing diamond like carbon coating 50 (W-DLC) on an outer surface 52 of another gear (abrasive pinion 50). Since PVD deposition of W-DLC coating is well known the art, a description of the deposition process is not included herein. The abrasive pinion 50 may then coupled to shaft 18A (FIG. 5) attached to a electric motor. The electric motor may be configured to rotate shaft 18A and pinion 14 about a longitudinal axis of shaft 18A. Gear 12 may be coupled to one end of a shaft 16A. Shaft 16A may be parallel to shaft 18A and may be positioned such that teeth 20 of gear 12 meshes with teeth 20 of abrasive pinion 50 when the gears are coupled to the respective shafts. The opposite end of shaft 16A may be coupled to a stationary housing through a bearing. The bearing may be configured to allow shaft 16A to rotate about its longitudinal axis, while applying a finite resistance to the rotation (that is, the bearing may act as mechanical load 70 of FIG. 5). The electric motor may be switched on to rotate shaft 18A at about 1800 RPM. Rotation of shaft 18A may rotate abrasive pinion 50, and the meshed gears may transmit the rotation to shaft 16A. While the gears transmit the rotation, meshed teeth 20 of the gears may rub against each other. As the teeth rub against each other, coating 54 on outer surface 52 of abrasive pinion 50 may abrade outer surface 42. As the meshed gears rotate, different regions of outer surface 42 may be contacted and abraded by abrasive pinion 50. Continued rotation of the gears may, thus, abrade and polish all the contacting regions of gear 12. After rotation for about 5 minutes, the rotation of the electric motor may be stopped. Gear 12 may then be uncoupled from shaft 16A and washed to remove debris. Surface profilometer measurements of the selected region of outer surface 42 may now indicate a mean roughness R_aof about 0.135 microns. The decrease in the measured mean roughness value may indicate polishing of gear 12.
In the CASFP, a component is polished using the surface of another component that it will be in contact with during operation. Therefore, material removal and polishing will be confined to locations where the components actually contact each other, thereby minimizing material removal. Since material is only removed from selected regions, the component may not be weakened due to the polishing process. Moreover, since the overall dimensions of the component may not change due to polishing, the design process may be simplified by not having to account for dimensional changes at other surfaces of the component. Also, since specialized machinery may not be required to polish these components, the associated cost may be minimized.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed surface finishing process. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed surface finishing process. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.

Claims

1. A method of polishing a component comprising:

providing a first component with a first working surface;

depositing a coating on a second working surface of a second component, the first component and the second component being tribological components;

mating the first component to the second component, wherein the mating includes contacting the first working surface with the second working surface;

operating at least one of the first component and the second component, wherein the operating includes the first working surface and the second working surface undergoing relative displacement while contacting each other; and

stopping the operation after polishing the first working surface.

2. The method of claim 1, wherein depositing a coating includes depositing a coating made of one or more of a nitride, carbide, or boride of a transition metal, diamond like carbon (DLC), or DLC with inclusions.

3. The method of claim 1, wherein the depositing includes depositing the coating using a vapor deposition process.

4. The method of claim 3, wherein the vapor deposition process includes one of chemical vapor deposition or physical vapor deposition.

5. The method of claim 1, wherein the first component and the second component are a mating pair of gears and the first working surface and the second working surface include flank surfaces of the gears.

6. The method of claim 1, wherein the first component includes one of a shaft or a bearing and the second component includes one of a shaft or a bearing that mates with the first component.

7. The method of claim 1, wherein stopping the operation includes inspecting a surface finish of the first working surface.

8. The method of claim 7, wherein stopping the operation further includes continuing the operation if the surface finish is not an acceptable surface finish.

9. The method of claim 1, wherein stopping the operation includes stopping the operation when inspection of the first working surface indicates an improved surface finish, the improved surface finish being manifested by a reduction in value of one or more of a maximum roughness, a peak to valley height, an arithmetic mean roughness, and a RMS roughness.

10. The method of claim 9, wherein stopping the operation further includes removing the first component.

11. The method of claim 9, wherein stopping the operation further includes replacing the second component having the coating with a second component without such a coating.

12. The method of claim 1, wherein mating the first component to the second component includes coupling one of the first component or the second component to a power source that induces relative displacement between the first component and the second component.

13. The method of claim 1, wherein the first component and the second component are rotating parts of a machine.

14. A component polishing system comprising:

a first coupling mechanism configured to attach a first component, the first component including a first working surface;

a second coupling mechanism configured to attach a second component and position the second component to contact the first working surface, the second component including a second working surface with an abrasive coating thereon, wherein the first component and the second component are tribological parts that are configured to slide on each other in an application; and

a mechanical power source coupled to one of the first coupling mechanism or the second coupling mechanism, the mechanical power source being configured to induce relative displacement between the first component and the second component.

15. The polishing system of claim 14, wherein the coating is made of one or more of a nitride, carbide, or boride of a transition metal, diamond like carbon (DLC), or DLC with inclusions.

16. A method of polishing a first component by a second component of a tribological pair comprising:

mating the first component to the second component in a tribological configuration;

moving the first component and the second component such that a first surface of the first component and a second surface of the second component contact and slide against each other so that the second component polishes the first component; and

discontinuing moving of the first component and the second component when the first surface obtains a desired surface finish.

17. The method of claim 16, further including depositing an abrasive coating on the second surface of the second component, the abrasive coating being configured to polish the first surface.

18. The method of claim 16, wherein the first component and the second component are a mating pair of gears and the first surface and the second surface include flank surfaces of the gears.

19. The method of claim 16, wherein the first component includes one of a shaft or a bearing, the second component includes one of a shaft or a bearing that mates with the first component, and the first surface and the second surface are mating surfaces of the shaft and the bearing.

20. The method of claim 16, wherein the second component includes an abrasive coating, the method further including replacing the second component with another second component without the coating and replacing the first component with another first component requiring polishing.