Abstract:
A method and apparatus for processing a metallic workpiece with defined edges (e.g., a gear) comprises media blasting of the workpiece by directing a first media against exposed surfaces on the workpiece to increase the root strength of the gear, the blasting causing the defined edges to be radiused or mushroomed, ceasing the media blasting, loading the workpiece into a finishing apparatus, and subjecting the workpiece to a finishing process with a second media, the exposed surfaces on the workpiece being subjected to the finishing process to reduce the radiused edges on the workpiece created from the media blasting. The process of moving the workpiece to the spindle-finishing apparatus from the media blasting may be performed automatically by a machine. Once the workpiece has been subjected to the finishing process with the second media, it may be removed from the spindle-finishing machine, washed, and rinsed with rust inhibitor whereby wear properties of the workpiece are enhanced.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62/186,042, filed Jun. 29, 2015. The disclosure set forth in the referenced application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to a method for media blasting and finishing a gear or other workpiece or part. The powered part hold-down apparatus of U.S. Pat. No. 5,272,897 may be used for the peening step(s) of the present disclosure, and the disclosure of the U.S. Pat. No. 5,272,897 is hereby incorporated in its entirety by this reference. Elements of other known methods of media blasting and finishing, such as the peen finishing method and apparatus of U.S. Pat. No. 8,453,305, may be used for the present disclosure, and the disclosure of the U.S. Pat. No. 8,453,305 is hereby incorporated in its entirety by this reference. 
         [0003]    Media blasting or peening is used to increase the fatigue strength of a gear, workpiece or part. Gears, such as those utilized in automobile transmissions are media blasted to increase their surface durability and ensure that they are suitable for performing their intended functions. As an example, media blasting with steel peening may be used for strengthening the root radius of the teeth of a geared workpiece. The media blasting steps of the present invention includes the steps disclosed in U.S. Pat. No. 6,612,909 and the disclosure of the U.S. Pat. No. 6,612,909 is hereby incorporated in its entirety by reference. 
         [0004]    When media blasting a workpiece, such as a gear, the workpiece is placed in a closed chamber and the blasting system is actuated, whereby media are mixed with air. After mixing of the media and air, a stream of the air/media mixture is directed against the workpiece, often through increased or high-speed application. This process is referred to as peening. 
         [0005]    A variety of materials/media may be used for the workpiece, depending on the ultimate application or outcome desired by the workpiece. In automotive applications, it is often desires to increase the strength or hardness of the media in order to have more favorable KSI. In the present disclosure, toughness is discussed in terms of “KSI” (kilo-pound[-force] per square inch) or 1000 psi. KSI is often used in materials science, civil and mechanical engineering to specify stress and Young&#39;s modulus. A higher KSI is favorable for materials that will be under larger compressive stresses. 
         [0006]    When a workpiece, in particular a workpiece made of media that has a high KSI, is peened, the peening material is blasted against the surface of the workpiece, removing and modifying the microscopic landscape of the surface. When a workpiece includes sharp or distinct edges, such as the tip of a gear tooth, those edges or tips may be unintentionally radiused from the blasting of the peening material, such that a mushroom effect occurs on the edge or tip of the gear tooth. This mushroom effect may alter the operation or functionality of the workpiece. Even if the mushroom effect does not alter the operation or functionality of the workpiece, it may create unwanted noise when the workpiece engages with other components during operation. It is understood that the higher the KSI of a workpiece, the more the tips may be radiused during a peening process. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to remove or reduce the effect of radiused tips that may be created when a workpiece is subjected to a peening process by subjecting the workpiece to a spindle-finishing process after it has been peened. For a workpiece with gear teeth or other similar sharp edges, the peening process may be applied to strengthen the root radius and tooth face of gears by peening the gears and then optionally subjected to a vibratory finishing process. The peening step(s) toughen the gears and provide roughness to the gear surfaces. The spindle-finishing process after peening removes or reduces the mushrooming effect on the radiused tips that occurs during the peening process. 
         [0008]    An object of the present invention is to provide a method of processing a metallic workpiece with defined edges (e.g., a gear) comprising media blasting of the workpiece by directing a first media (e.g., cut wire) against exposed surfaces on the workpiece to increase the root strength of the gear, ceasing the media blasting, loading the workpiece into a spindle-finishing apparatus, and subjecting the workpiece to a finishing process with a second media (e.g., metal, plastic, synthetic, glass, ceramic or FINE STEEL®), the exposed surfaces on the workpiece being subjected to the finishing process to reduce radiused tips on the workpiece created from the media blasting. In illustrative embodiments, the process of moving the workpiece to the spindle-finishing apparatus from the media blasting may be performed automatically by a machine. Once the workpiece has been subjected to the finishing process (spindle machine or vibe machine) with the second media, it may be removed from the spindle-finishing machine, washed, and rinsed with rust inhibitor whereby wear properties of the workpiece are enhanced. Media blasting and subsequent finishing of gears according to the present invention accomplishes an important object which is to reduce or eliminate undesired radiused tips of the gears. 
         [0009]    Another object of the present invention is to provide a workpiece (e.g., a gear, shaft or other metal parts) with a higher KSI strength that has been media blasted/peened such that radiused tips exist on one or more tips or edges of the workpiece, and subsequently processing the workpiece with a fine finishing process (e.g., spindle-finishing or vibe-finishing process) to provide a reduction or elimination of the radiused tips of the workpiece as compared to before the fine finishing process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  is a front elevational view of an exemplary media blasting apparatus for treating a workpiece according to the first media blasting process of the invention; 
           [0012]      FIG. 2  is a right-side elevational view of the media blasting apparatus of  FIG. 1 ; 
           [0013]      FIG. 3  is a top plan view of the media blasting apparatus of  FIG. 1 ; 
           [0014]      FIG. 4  is an enlarged, partial fragmentary, side elevational view of a blast station of a first exemplary media blasting apparatus for treating a workpiece according to the invention; 
           [0015]      FIG. 5  is schematic of a first media blasting apparatus and a second spindle finishing apparatus, and an exemplary transportation process between a first media blasting apparatus and the second spindle-finishing apparatus; 
           [0016]      FIG. 6  is aside elevation view of an exemplary spindle-finishing apparatus; 
           [0017]      FIG. 7  is a top view of an exemplary part or workpiece that may be processed by an exemplary media blasting apparatus and an exemplary spindle-finishing apparatus; 
           [0018]      FIGS. 8A-8C  are detailed view of the gear teeth of the workpiece of  FIG. 7  before the workpiece is subjected to a first exemplary media blasting, after it is subjected to a first exemplary media blasting but before it is processed in the second spindle-finishing apparatus, and after it is processed in the second spindle-finishing apparatus, respectively; 
           [0019]      FIGS. 9A-9C  are microscopic views of a single gear tooth of the workpiece of  FIG. 7  before the workpiece is subjected to a first exemplary media blasting, after it is subjected to a first exemplary media blasting but before it is processed in the second spindle-finishing apparatus, and after it is processed in the second spindle-finishing apparatus, respectively; and 
           [0020]      FIGS. 10A-10C  are cross-sectional views of a single gear tooth of the workpiece of  FIG. 7  before the workpiece is subjected to a first exemplary media blasting, after it is subjected to a first exemplary media blasting but before it is processed in the second spindle-finishing apparatus, and after it is processed in the second spindle-finishing apparatus, respectively. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    Referring now to the drawings,  FIGS. 1-4  illustrate a first media blasting apparatus according to the invention, generally indicated by the number  10 .  FIGS. 5-6  illustrated a second finishing apparatus according to the invention, generally indicated by the number  200 .  FIGS. 8A, 9A and 10A  illustrate a teeth-portion of a workpiece prior to the workpiece being subjected to processing in the first media blasting apparatus  10 .  FIGS. 8B, 9B and 10B  illustrate the teeth-portion of the workpiece after processing in the first media blasting apparatus  10  but before it is subjected to processing in the second finishing apparatus  200 .  FIGS. 8C, 9C and 10C  illustrate the teeth-portion of a workpiece after processing in the second finishing apparatus  200 . 
         [0022]    The first media blasting apparatus  10  will now be described. As illustrated, the first media blasting apparatus  10  includes a blasting cabinet or chamber  15 , in which a stream of media is directed against a workpiece  20 . Such media may comprise, for example, cut wire, glass beads, ceramic beads or fine steel beads. The cabinet  15  is connected to a cabinet media hopper  25  for collecting the media that fall after collision with the workpiece  20 . The fallen media will include broken pieces of media which have been recycled, as well as virgin or unbroken pieces. A conduit  30  connects the cabinet media hopper  25  to a media reclaim system, generally indicated by the number  35 . As best illustrated in  FIG. 2 , the cabinet media hopper  25  is also connected to air supply means  40 . The air supply means  40  provides air flow to the cabinet media hopper  25 , for forcing the collected fallen media up through the conduit  30  to the media reclaim system  35 . 
         [0023]    As illustrated in  FIGS. 1 and 2 , the media reclaim system  35  includes a conduit  45  for conveying collected media to separation means  50 . In illustrative embodiments, the separation means  50  may be a two-deck system comprising a top screen  55  and a bottom screen  60 . In a preferred embodiment of the present invention, the top screen is between 20 and 40 mesh gauge and the bottom screen is between 170-200 mesh gauge. The separation means  50  generally separates the fallen media into unbroken media and broken media of sufficiently large size to be recycled for use in the first blasting operation and fines or dust which cannot be reused in the first media blasting apparatus  10 . The separator screens  55  and  60  are constantly vibrated to increase the efficiency of separation. 
         [0024]    As illustrated in  FIG. 1 , the separation means  50  of the first media blasting apparatus  10  may be connected to a double pressure chamber  90  via a conduit  95 . A media path may be defined between the cabinet media hopper  25  and the pressure chamber  90 . In a preferred embodiment, the double pressure chamber is held between 70 and 80 psi. The conduit  95  delivers the reclaimed reusable media to the double pressure chamber  90  where the reclaimed and reusable media are mixed with virgin media. In a preferred embodiment, the reclaimed media are of a mesh size greater than 100 mesh and the virgin media are of a mesh size between 60-100 mesh and preferably between 60-80 mesh. As stated previously, in the present invention, the media of the first medial blasting apparatus  10  may comprise glass, ceramic, or fine steel beads. The virgin media are supplied to the double pressure chamber  90  through a plurality of media supply valves  97 . The double pressure chamber  90  is also coupled to a media sensor monitor  100  for automatically controlling the supply of the virgin media. The supply of the virgin media is controlled to ensure adequate peening of the workpiece. Specifically, the supply of the virgin media is controlled to ensure that adequate compression stress is provided to the workpiece  20  so that a sufficiently high fatigue strength is obtained upon blasting. The double pressure chamber  90  may further include a media metering on/off valve  105 . 
         [0025]    A further advantage of the pressurized system is that it helps ensure an adequate media velocity is obtained. As mentioned above, media velocity is an important control parameter in ensuring that sufficient compressive stress is provided to a workpiece  20 . The pressurized system helps ensure an adequate media velocity through control of the media flowrate and through the positioning of the air/media mix point. The media flowrate is controlled through the media metering valve  105 . The air/media mix point is located sufficiently far from the blast hose so that the media have time to develop a desired or adequate velocity before being blasted onto a workpiece. 
         [0026]    An exemplary blasting station  120  inside the blasting cabinet  15  of the first media blasting apparatus  10  will now be described. As illustrated in  FIG. 4 , the workpiece  20  to be processed, i.e., blasted with media, is mounted on a part holder  125 . Preferably, the part holder  125  has been hardened. In illustrative embodiments, the workpiece  20  is held in a predetermined position by a powered part hold-down apparatus  130 . In the present invention, the powered part-hold-down apparatus  130  is preferably that described in U.S. Pat. No. 5,272,897, to which reference is again invited. The subject matter of U.S. Pat. No. 5,272,897 is incorporated herein by reference. The patented powered part-hold-down apparatus  130  provides variable, compensating, cushioned clamping for maintaining the workpiece  20  in the predetermined position during media blasting. The device as taught in U.S. Pat. No. 5,272,897 is very important to facilitate processing high volume quantities of parts. This is especially important for parts such as gears which tend to rotate when peened since the hold-down device prevents free spinning of the parts. The hold-down device also controllably rotates the parts at a desired rate of rotation. Rotation of the powered part-hold-down apparatus  130  is provided via a rotatable shaft  135 . 
         [0027]    In illustrative embodiments, hardened rods  140 , preferably steel, provide a support system for a gun-rack assembly  145  of the blasting station  120 . As illustrated in  FIG. 4 , the gun-rack assembly  145  holds a nozzle holder  150 . A blast nozzle  155 , to which the blasting hoses  115  are connected, is attached to the nozzle holder  150 . The blast nozzle  155  directs a stream of media, suspended in air, against the surface of the workpiece  20 . Preferably, the blast nozzle is positioned between approximately four to eight inches away from the workpiece  20 . Although only one blast nozzle  155  is illustrated in  FIG. 4 , it will be understood to those skilled in the art that a plurality of blast nozzles  155  could be used. In a preferred embodiment of the present invention, four such blast nozzles  155  are located in the blasting cabinet  15 , as shown in  FIG. 3 . The blasting cabinet  15 , containing the part-hold-down apparatus  130  and blasting apparatus  120  is also provided with a door  160  for installation of a new workpiece  20 . 
         [0028]    Operation of the first media blasting device  10  will now be described. After a workpiece  20  is placed in the part-hold-down apparatus  130 , door  160  is closed. A stream of media suspended in air is then directed against the workpiece  20  by the blast nozzle  155 . As the media are blasted, the workpiece is controllably rotated by the powered patented part-hold-down apparatus  130 . This controlled rotation ensures even peening of the surface of the workpiece  20  and obviates use of a high directivity stream of media, hence making the use of water-supported media unnecessary, allowing for the media to be streamed via an air-media mixture as discussed above. 
         [0029]    The powered part-hold-down apparatus  130  is preferably rotated at between 8-12 rpm. A rate of rotation of 10-12 rpm, however, has been found to be particularly effective for treatment of gears. The rate of rotation can be related to the degree of peening required and to the evenness of dimpling on the resulting surface. A slow controlled rotation permits even peening with uniform small dimpling and prevents the media stream from striking the surface unevenly, resulting in indentations that could act as crack precursors. Thus, for example, if the workpiece  20  is a gear, the controlled rotation ensures that media, e.g. cut wire, ceramic beads, fine steel beads, or glass beads, are directed towards the root and tooth face of the gear during the course of the rotation. By ensuring even peening, the operational characteristics of the workpiece  20  are improved. 
         [0030]    In a one embodiment a smaller mass flowrate of media is blasted at higher velocity and for a longer time than in the prior art methods. The preferred flowrate depends on the type and size of media used, as well as the particular application involved. For treatment of gears, we have found a media flowrate of approximately 1.5-3 lb/minute to be effective. Of course, other flowrates could be used, depending on the results desired. This flowrate was found to be effective with glass media, ceramic media, and fine steel media of mesh size falling in the range of 50-100 mesh. In a preferred embodiment of the present invention, however, 60-100 mesh glass media are used. When 60-100 mesh glass media were used to treat certain gears, including those made using 8620 steel or other material with a high KSI, a marked improvement in the operational characteristics of such gears was observed. The choice of media to be used depends upon the application and the relative economics. Ceramic and steel media last longer than glass; however, these media are more expensive. As with the rate or rotation, the flowrate and media used may be configured to ensure even peening of the workpiece. 
         [0031]    The process of even peening may provide unintentional material change in the part being processed. In particular and as relevant to the present disclosure, the rate of rotation, peening media, flowrate, etc, all affect the condition of the surface of the workpiece. When processing a gear or other workpiece with teeth or other types of features that have tips, edges, or corners (e.g. sharp edges), the intensity of the peening flow against the workpiece, and in particular against the tips or edges of the workpiece, has been known to cause an unintentional mushrooming effect on the tips or edges, as illustrated for example in  FIGS. 8B, 9B and 10B . This mushrooming effect causes the tips or edges to be radiused tips  350  that extend outward (e.g. from the side or top surfaces of the teeth). Such mushrooming may be considered problematic for the operation of a workpiece for a variety of reasons, including creating issues with the functionality, life-expectancy and/or noise output of the workpiece in operation. 
         [0032]    An exemplary embodiment of a workpiece  201  with features that have tips, edges, or corners as envisioned within the scope of this disclosure will now be described, although other forms of such features with tips, edges or corners are also envisioned within the scope of this disclosure. As illustrated in  FIG. 7 , the workpiece  201 , such as a gear or other part, includes a plurality of teeth  220   a ,  220   b ,  220   c , etc with channels  240   a ,  240   b ,  240   c , etc. therebetween. The teeth  220  include at least a first side surface  230  and a second side surface  232 , as illustrated in  FIG. 7 , that extend upward from a base  250  of the workpiece  201  toward a top end  224  of the tooth  220 . The second side surface  232   a  of a first tooth  220   a  is spaced apart from the first side surface  230   b  of a second tooth  220   b  to form a channel  240   a  therebetween. After processing, the teeth  220  are illustratively designed and configured to engage with other gears or parts (not shown) in operation, as is known in the art, by positioning the teeth  220  of one gear into the channels  240  of a second gear. In illustrative embodiments, the teeth  220  may be tapered to be wider near the base  250  of the workpiece  201  than at the top end  224 . Further, in illustrative embodiments, the teeth  220  may be angled or curved in nature such that the teeth curve along the base  250 , as illustrated in  FIG. 7 . Other variations of teeth formation are well known in the art and envisioned as applicable to the present disclosure. 
         [0033]    Each tooth  220  includes one or more edges  222  along a top end  224  of the tooth  220 . In exemplary embodiments, the tooth  220  may include a single edge  222  along the top end  224 , the edge  222  defining the transition from the first side surface  230  and the second side surface  232  of the tooth  220 . In other exemplary embodiments, and as illustrated n  FIG. 8A , a tooth  220   a  may include at least a first edge  222   a  and a second edge  228   a  along the top end  224   a . In illustrative embodiments, the first edge  222   a  and second edge  228   a  may be spaced apart from each other, with the edge  222   a  positioned between the first side surface  230   a  and a top surface  236   a  of the tooth  220   a , and the edge  228   a  positioned between the top surface  236   a  and the second side surface  232   a  of the tooth  220   a . The corresponding channel  240  of the second gear with which the tooth  220   a  interacts should be sized accordingly to receive the tooth  220   a  (e.g. if the tooth  220   a  includes a first edge  222   a  and a second edge  228   a  spaced apart from the first edge  222   a , the corresponding channel  240  may have a larger width). As the workpiece  201  is typically cut from hardened media, such as steel, the edges  222  between the first side surface  230   a /second side surface  232   a  and the top surface  236   a  may be sharp or distinct after cutting, as illustrated for example in  FIGS. 8A, 9A, and 10A . 
         [0034]    After a geared workpiece  201  is processed in the first media blasting apparatus  10 , the edges  222  of the teeth  220  may have radiused tips  350 , as discussed previously and as illustrated in  FIGS. 8B, 9B and 10C . In order to reduce the undesired features of the radiused tips  350 , further processing by the second finishing apparatus  200  is disclosed. The second finishing apparatus  200  includes further processing media that eliminates or reduces the radiused tips  350  from the edges  222  of the teeth  220 , as illustrated in  FIGS. 8C, 9C and 10C . 
         [0035]    The operation of the second finishing apparatus  200  will now be described. The second finishing apparatus  200  may be, for example, a spindle apparatus or a vibe apparatus. In illustrative embodiments, the finishing apparatus  200  includes a bowl  208 , a spindle unit  260  that can transfer parts into the bowl  208 , and motor  282  that can rotate the bowl  208 , as illustrated in  FIGS. 5 and 6 . After peening occurs in the first media blasting apparatus  10 , the gear  201  is transferred to and secured on the spindle unit  260  of the second finishing apparatus  200 . The bowl  208  contains a fine finishing medium  212  which may be a wet or dry medium, such as plastic, synthetic, ceramic or steel media. As noted with the media of the first blasting apparatus  10 , the finishing media  212  may be of a variety of sizes and types and still fall within the scope of this invention. The fine finishing medium  212  is preferably a wet acidic medium or slurry, or it may be a dry medium. 
         [0036]    The finishing apparatus  200  is depicted in  FIGS. 5 and 6 . In illustrative embodiments, the bowl  208  of the finishing apparatus  200  has an outlet  202 , an inlet  204 , sides  206 , an open top  209 , and a bottom  210 , as illustrated in  FIG. 6 . The inlet  204  may be configured to permit transfer of finishing medium  212  into the bowl  208 , while the outlet  202  may permit transfer of finishing medium  212  out of the bowl  208 . The bowl  208  may be configured to retain the finishing medium  212  during the second finishing process. In illustrative embodiments, the bowl  208  is vibrated at a high speed frequency. The vibration of the bowl  208  of the finishing apparatus  200  may be performed via one or more vibration belts or spindles  216  coupled to and driven by the motor  282 . In other illustrative embodiments, the bowl  208  is rotated to rotate the finishing medium  212 . The bowl  208  may be rotated such that the finishing medium  212  moves at a high number of revolutions. For example, the bowl  208  may rotate the finishing medium at speeds up to 1000 surface feet per minute. The bowl  208  may be configured to rotate clockwise or counterclockwise. In still other embodiments, the bowl  208  may include a supplemental mixing blade  252  positioned within the bowl  208  near the bottom  210 , the mixing blade  252  configured to rotate the medium  212  within the bowl  208  at a different speed that the rotation of the bowl  208 . The bowl  208  is typically made of steel and may have a polyurethane liner (not shown) which can transfer the vibrations or rotations of the bowl  208  to the medium  212 . 
         [0037]    In illustrative embodiments, the centrifugal force created within the bowl  208  during rotation may spin the selected finishing medium  212  into a form-fitting grinding wheel (not shown). In other embodiments, if the bowl  208  and/or medium  212  within the bowl  208  is rotated at a slower rotation speed, the slurry of finishing medium  212  may remain dispersed throughout the bowl  208 . As an example, it may be beneficial to rotate the bowl  208  at a slower speed in order to assure uniform deburring and finishing of all surfaces of a workpiece. 
         [0038]    In illustrative embodiments, the second finishing apparatus  200  includes two or more spindles  260   a ,  260   b , etc., as depicted in  FIG. 6 . In various embodiments, each spindle  260  may process a single part or a cluster of small parts depending on the design of the spindle  260 . The spindle  260  include a head  262  onto which the workpiece  201  may be securely coupled or connected. The spindle  260  may further include a connection arm  264  to which the head  262  is coupled, the connection arm  264  being permitted to pivot and rotation upon direction of a computer or other electronic system (not shown) accordingly to the requirements of operation or input from an operator of the finishing apparatus  200 . In illustrative embodiments, the head  262  may also be configured to rotate or pivot with respect to the connection arm  264 . Alternatively, the head  262  may be connected to an extension arm  266  that rotates with respect to the connection arm  264 , as indicated by the path of rotation  270  as illustrated in  FIGS. 5 and 6 . The extension arm  266  and/or head  262  may be configured to rotate clockwise or counterclockwise. The entire spindle  260  may work together to position the part  201  coupled to the head  262  within the slurry of finishing medium  212 , as illustrated in  FIG. 6 . 
         [0039]    In illustrative embodiments, prior to operation of the finishing apparatus  200 , finishing medium  212  may be pumped into the bowl  208  via a connection line  254  that is coupled to the inlet  204 . Similarly, a connection line  256  may extend from the outlet  202  of the bowl  208  to permit drainage of the finishing medium  212  when the finishing apparatus  200  is not in use or the finishing medium  212  is replaced. The finishing apparatus  200  may include an overflow tank  258  to receive and store finishing medium  212 , the overflow tank being connected to the connection lines  254  and  256 . In illustrative embodiments, a pump  268  may be positioned within the overflow tank  258  or along the connection line  254  to pump the finishing materials  212  into the bowl  208 . 
         [0040]    In illustrative embodiments, the finishing medium  212  may be a wet acidic fine finishing medium that is sufficient to wet the gears  201  and ceramic media  212 . In other embodiments, the finishing medium may be dry. The relative size of the gear  201  and media  212  may vary depending on the type of gear, media, and desired finished product. The relative size of the media  212  and gears  201  is such that the media  212  is small enough to fit into the space between the gear teeth  220  so that during fine finishing (vibration/rotation), the edges  222  and  228  of the teeth are subjected to the finishing process. One example of a fine finishing medium  212  comprises a mixture of ceramic media with a slightly acidic solution. Such finishing may be continued to reduce or remove the radiused tips  350  of the gear teeth  220 . 
         [0041]    In illustrative embodiments, the finisher apparatus  200  may be used to finish the side surfaces of the gear, including the surfaces of the gear teeth  230  and  232 , in addition to the edges  222  and  228 . In a preferred embodiment a gear is coupled to the spindle  260 , and the edges and surfaces of the gear that are desired to be fine-finished are submerged into the finishing media  212 . The head  262  or extension arm  266  of the spindle  260  rotates the gear or part  201 , while the spindle  260  holds the gear  201  in a stationary position relatively to the rest of the bowl  208 . In illustrative embodiments, the bowl  208  may also vibrate and rotate as discussed previously. The rotation and/vibration of the head  262 , extension arm  266 , and/or bowl  208  is continued for a time sufficient to reduce the radius of the tips or edges, as discussed herein. 
         [0042]    During rotation and/or vibration (fine finishing), additional water and/or fine finishing medium may be added via one or more inlets  204 . Excess fine finishing medium, water etc, may be removed via outlet  202 . In illustrative embodiments, fine finishing may be continued to smooth the gear (workpiece) surfaces in addition to reducing or removing the radiused tips  350  of the gear teeth  220 . Such finishing may also provide small indentations on the other surfaces of the gear, which may improve compressive stress and oil retention features of the gear. 
         [0043]    After sufficient processing in the second finishing apparatus  200 , the radiused tips  350  of the teeth  220  of the gear  201  may be substantially lower in profile, as shown at  370 , as illustrated in  FIGS. 8C, 9C and 10C , or be removed altogether. For example, in illustrative embodiments, the radiused tips  350  of the teeth  220  prior to the second finishing process may be a certain width W 1  across, as shown in  FIG. 9B . After the second finishing process, the radiused tips  370  may have a smaller width W 2  that the width W 1  of the radiused tips  350  prior to the second finishing process, as illustrated in  FIG. 9C . 
         [0044]    After fine finishing the gear is removed from the bowl, washed, and rinsed. The gear may be further treated with rust inhibitor in a final step whereby a gear with enhanced wear properties is provided. 
         [0045]    In illustrative embodiments, the gear may be transported from the first media blasting apparatus  10  to the second finishing apparatus  200  via any known conventional transportation means. In an exemplary embodiment, the transportation means may be fully automated without user input. For example, the transportation means may include a removal apparatus  380  that removes the part  201  from the part-hold-down apparatus  130  of the media blasting apparatus  10 , as illustrated in  FIG. 5 . The removal apparatus may include an electronically controlled hand  382  that can grasp and retain the part  201 , as well as a pivotable and/or rotatable arm  384  that can rotate the part to engage with the head  262  of the spindle  260  to connect the part  201  to the head  262 . In other embodiments, the rotatable arm  384  may rotate the hand  382  holding the part  201  to a movable track or conveyor system  386  which conveys the part  201  to a location where the spindle  260  may rotate or pivot to pick up the part  201 , as illustrated in  FIG. 5 . Other methods of automatic transportation are known in the art. 
         [0046]    In another embodiment the gears are fine finished in a bowl without the addition of liquid medium (i.e., with dry fine finishing medium). In this embodiment the gears are in effect fine finished while dry and in the presence of wear material that smoothes the gear surface, but wherein the wear material is not in liquid form. Coupling vibrations and/or rotations to the container to vibrate the fine finishing medium with the gear reduces the size of indentations on the surfaces of the gear during the second finishing process, leaving compressive stress and oil retention advantages remaining on the gear surface. The edges of the teeth resulting after finishing has smoothness and the radiused tips  350  are reduced, as discussed above, with the surface of the teeth, and in particular the edges of the teeth, having indentations resulting from peening and reduced by but remaining after finishing. 
         [0047]    For gears treated by the above-discussed preferred two-step process of media blasting followed by fine finishing, tests confirm that gears so treated exhibit superior performance relative to gears not treated with this process. It has been found that gears treated with this preferred process exhibit reduced noise-generation when the gears are used in operation. Other advantages may be found as well, including superior fatigue strength and less failure of gears to operate properly due to a misconnection between gear teeth from the mushrooming effect. 
         [0048]    While the method of media blasting and finishing for gears is disclosed herein with respect to a hold down apparatus, it is contemplated that other conventional part holders and blasting apparatus may also be used with the steps described herein. The above discussed process recognizes that most often gears need steel peening at the gear root to prevent fatigue bending in the root radius. 
         [0049]    The applicant has provided description and figures which are intended as an illustration of certain embodiments of the invention, and are not intended to be construed as containing or implying limitation of the invention to those embodiments. It will be appreciated that, although applicant has described various aspects of the invention with respect to specific embodiments, various alternatives and modifications will be apparent from the present disclosure which are within the spirit and scope of the present invention as set forth in the following claims.