Abstract:
A method and apparatus disclosed for cost-effective net shape precision ausform finishing the engagement surfaces of ball and roller bearings, for enhancing the surface strength and durability of bearing inner and outer races. The method consists of induction heating to austenitize the contacting surface layers of rolling element bearing races, followed by martempering (or marquenching), and then net shape roll finishing of the induction heated contacting surface layers in the metastable austenitic condition to finished dimensional accuracy requirements, and finally cooling to martensite. The apparatus utilizes a fixed vertical through-feed axis for the workpiece bearing race with capability for rotation and linear up and down positioning motion, and two coordinated and controlled laterally-moving infeed axes for roll finishing tooling dies. For finishing of the outer contacting surfaces of the bearing inner races, two suitably contoured power-driven dies are arranged symmetrically on diametrically opposing sides of the workpiece. A dual but asymmetric tooling arrangement employs a suitably contoured power-driven finish tooling die is positioned for the internal roll finishing operation, while a plane cylindrically shaped idling support tooling die is located on the opposing side of the work region. The apparatus includes specialized contoured finishing tooling for bearing inner and outer race ausform finishing utilizing specially contoured cylindrical roll finishing tolling dies to facilitate infeed ausforming of bearing inner and outer races, the structure and mechanism for asymmetric mounting, powered drive and infeeding of the roll finishing die and the idling support die with respect to the bearing outer race.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for net shape precision ausform finishing of rolling element bearing races by controlled induction heating and deformation devices to produce contacting surfaces with enhanced strength and durability by the application of thermal-mechanical techniques. 
     2. Description of the Prior Art 
     Ball and roller element bearings are critical machine components used in high performance drive train transmissions, and are heavily loaded with contact stresses of up to 250 K psi while operating over a broad speed range. Such rolling element bearing races require high surface strength for resisting contact fatigue, wear and plastic deformation, as well as high strength and toughness in the core with adequate fracture and crushing resistance. Furthermore, bearing races must be precision finished to high dimensional accuracy and fine surface finish to ensure interchangibility of parts and to minimize vibration and fatigue loading. Such a combination of mechanical properties and dimensional accuracy is achieved utilizing a complex manufacturing process sequence consisting of initial rough machining to approximate size, heat treatment to achieve the desired gradient of mechanical properties, and finally hard grinding and related processing steps for precision finishing to final dimensions. Optimal material properties exist in the as-hardened condition in terms of its surface fatigue response. However, the beneficial as-hardened near surface layers are removed by hard grinding to achieve the desired dimensional accuracy, thereby redressing the prior manufacturing errors and heat treatment distortions. Hard grinding is expensive and can be detrimental if grinding cracks and burns are produced due to abusive practice, requiring etching type inspection techniques, thereby further adding to production cycle time and costs. A method and associated apparatus are disclosed for integral surface heat treatment and precision finishing of rolling element bearing races, thereby eliminating the need for traditional hard grinding and related finishing operations. 
     The process disclosed by this invention, utilizes contour induction heating to austenitize the surface layers of the bearing races, followed by rapid quenching in marquenching oil maintained at appropriate temperature of up to about 600° F. to achieve a metastable austenitic condition in the surface layers. The surface layers in this metastable austenitic condition are then precision ausform finished to final dimensions and then quenched for transformation to martensite. The bearing race ausform finishing thus integrates the surface induction heating process with a precision roll finishing operations to net shape finish the contacting surfaces of roller element bearing inner and outer races. 
     Most bearing races are made of high carbon through-hardening type steels such as AISI-52100, whereas bearings used in more heavily loaded and critical transmissions are made of low carbon low-alloyed steels such as AISI-8620 which are case-carburized to produce a hardened case combined with a tough core. The present invention is applicable to both through hardening and carburizing grade bearing steels. Through-hardening steels are traditionally hardened by first austenitizing or heating over the upper critical temperature (approximately 843° C. or 1550° F.), and then rapidly quenching to about the room temperature or below to achieve desired martensitic transformation, followed by a tempering cycle to toughen the core material. The microstructure of such quenched and tempered AISI-52100 comprises plate martensite, alloy carbides and retained austenite; the surface hardness and amount of retained austenite depends upon the tempering temperature used. The heat treatment of carburizing grade surface hardening type steels require additional processes to case-carburize the components prior to the hardening and tempering steps. For through hardening steels, the present invention has the additional advantage of eliminating all batch manufacturing operations such as furnace heat treatment for hardening, and instead in-line induction heating and integral quenching is used. 
     It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a method and apparatus for precision ausform finishing of bearing inner and outer races, utilizing a fixed vertical through-feed axis for the workpiece bearing race with capability for rotation and linear up and down positioning motion, and two coordinated and controlled laterally-moving infeed axes for roll finishing tooling dies. For finishing of the outer contacting surfaces of the bearing inner races, the method of the invention utilizes two suitably contoured power-driven dies arranged symmetrically on diametrically opposing sides of the workpiece. However, for finishing the inner contacting surfaces of the bearing outer races, a dual but asymmetric tooling arrangement will be described. In this case, a suitably contoured power-driven finish tooling die is positioned for the internal roll finishing operation, while a plane cylindrically shaped idling support tooling die is located on the opposing side of the work region. The apparatus disclosed in the present invention includes specialized contoured finishing tooling for bearing inner and outer race ausform finishing, and specifically required modifications to the present double die ausform finishing machine, previously described in commonly assigned U.S. Pat. No. 5,451,275 to Amateau et al. issued Sep. 19, 1995, in order to achieve precision ausform finishing of rolling element bearing inner and outer races. The apparatus includes the structure and mechanism for specially contoured cylindrical roll finishing rolling dies to facilitate infeed ausforming of bearing inner and outer races, the structure and mechanism for asymmetric mounting, powered drive and infeeding of the roll finishing die and the idling support die with respect to the bearing outer race. 
     The bearing race ausform finishing process disclosed herein is applicable to a variety of precision roller element bearing races including ball, roller and taper roller bearings. The precision finishing of bearing raceways results in enhanced strength induced in the contacting surfaces due to ausforming or plastic deformation of the metastable austenite, and thereby has the potential to significantly improve the surface fatigue strength of bearing elements inner and outer races. Ausforming of cylindrical rolling contact fatigue testing specimens made of AISI 9310 has demonstrated improved metallurgical characteristics such as finer grained microstructure and higher compressive residual stresses, combined with smoother surface finish of 6-8 μin Ra without hard grinding, and has been shown to improve the surface fatigue behavior as compared to conventional hard grinding techniques. 
     The invention also includes the ability for effecting dual frequency contoured induction preheating and austenitization of the bearing surface layers being ausform finished, using annular outer and inner coils each for inner and outer bearing races, respectively, and comprising automated power switching devices for furnishing the low audio frequency power for induction preheating and high radio frequency power for induction austenitization of the bearing race contacting surface layers. The invention includes the process for controlled preheating and final heating cycles to achieve the desired depth of austenitized surface layers and thermal gradients beneath the austenitized layers for surface layers ausforming cycle. Furthermore, the apparatus of the invention includes the use of a single annular contoured internal coil for a dual frequency, two cycle preheating and final heating (austenitization) of the inner contacting surface of the bearing outer race, and also a single annular contoured external coil for dual frequency preheating and final heating (ausenitization) of the outer contacting surfaces of the bearing inner races. Additionally, a suitable mechanism is provided to position the individual workpieces for the induction beating cycle and then to transfer and position the work pieces for the precision ausform roll finishing cycle. 
     The invention includes appropriate mechanisms for achieving controlled deformation and for precision alignment of the tooling axes with reference to the workpiece portioning axis, a processing tank and quenching medium maintained at the processing temperature, desirably under an inert atmosphere, to achieve the desired metastable austenitic condition in the bearing working surface layers after the dual frequency induction heating cycle, and mechanisms for performing timely transfer of the workpiece to achieve the optimum metallurgical condition at each stage of the ausform finishing process and structure and mechanism for final quenching of the bearing races to transform the deformed metastable austenite to martensite. 
     High strength metal components are often fabricated either from a medium-to-high carbon low alloy steel or from a low carbon alloy carburizing grade steel in which the surface and sub-surface regions have been enriched with carbon to a specified depth. The higher carbon content serves to increase the hardness and to strengthen the material along the contacting surfaces and beneath the surface. The elevation in hardness results from transformation during quenching of the steel from the face centered cubic crystal structure known as austenite to the body centered tetragonal crystal structure of very fine grain size known as martensite. Less hard but tougher properties can be obtained by isothermal transformation to bainite or a mixture of bainite and martensite upon quenching. 
     In a conventional processing method for producing rolling element bearing races, the austenitized workpiece is quenched rapidly through the austenitic region by immersion into quenching media below the MF temperature. The workpiece is subsequently tempered at a designated temperature to soften the structure and impart ductility. After the tempering treatment is complete, finishing is accomplished by grinding in a well known manner for high performance rolling element bearing races. 
     As mentioned above, the present invention eliminates the grinding operation to provide a microstructurally improved rolling element engagement surface as will now be described. An important part of this invention is to select a through hardening grade or a carburizing grade steel which has a transformation curve with a metastable austenitic condition just above the martensitic range for a period of time sufficiently long to allow shaping of the gear teeth surfaces. There is shown in FIG. 1 a generic time-temperature-transformation chart for carburized steel. A similar t-t-t chart exists also for the through hardening type steel used for bearing applications such as 52100 steel. 
     The time-temperature-transformation curve shows the times required for austenite to start and to complete transformation at each temperature. Temperature is indicated along the ordinate and time on a logarithmic scale is indicated along the abscissa. The thermal excursion of the present invention is also depicted in FIG.  1 . 
     After the workpiece is heated above its critical temperature to an initial temperature  20 , or approximately 1500° F., to render it austenitic, it is rapidly quenched (marquenched) from point  22  to point  24  at a rate exceeding a critical cooling rate in a liquid medium such as a standard marquenching oil which is maintained just above the temperature at which martensite starts to form and metastable austenite is obtained. A critical cooling rate is defined by the slope of line  22 - 24  that avoids the nose  26  of the transformation curve where austenite and cementite start to form. 
     To allow the maximum time for mechanically operating on the surfaces of a workpiece while in the metastable austenitic condition, the cooling step must terminate temporarily at a temperature just above the martensitic condition. In FIG. 1, the point  24  beginning a new temperature plateau ending at point  28  is shown positioned at about 450° F. 
     Shaping of bearing element races further in accordance with this invention employs a process which is performed between points  24  and  28  whereby swaging or rolling or other operations are used to shape the bearing element races by deforming the metastable austenitic layer prior to and before its conversion to martensite. This occurs during a pre-transformation time interval at a temperature below that for recrystallization of austenite and just above the Ms of the layer. This process, to be described, presents a structure and mechanism of developing ultra high strength in the current bearing element races processed by the conventional heat treatment. 
     Following the shaping operation, the bearing element race is transferred to a quench station, as indicated in FIG. 1 by line  28 - 30 . Final quench, preferably utilizing a pressurized gas stream, although a liquid is within the scope of the invention, is initiated at point  30  and is finalized at point  32  in the martensitic range. 
     A control subsystem for the invention, under the primary supervision of a microprocessor, may comprise both hardware and software supervising and controlling the thermomechanical operations. In this scenario, all of the functions necessary for the operation of the mechanical, environmental and thermal functions of the apparatus would be controlled from this computer. The machine operator has a choice of operating each function of the machine separately or initiating a sequence of operations that will actually perform the thermomechanical forming operation. The software is constructed in such a way that each separate function cannot proceed until a requisite condition exists in the apparatus. 
     A primary feature, then, of the present invention is the provision of a method and apparatus for net shape precision ausform finishing of hardened rolling element bearing races by controlled induction heating and deformation devices to produce contacting surfaces with enhanced strength and durability by thermal-mechanical techniques. 
     Another feature of the present invention is the provision of a method and apparatus for net shape precision ausform finishing of ball and roller bearings, thereby inducing ausform strengthening in localized contacting surface layers of bearing races. 
     Still another feature of the present invention is the provision of a method utilizing specially contoured roll finishing dies to achieve the precise finished geometry of the contacting surface of the bearing races, taking into account the elastic and plastic deformations and deformation gradients induced in the races. 
     A further feature of the present invention is the provision of apparatus for controlled deformation of the rolling element bearing inner and outer races utilizing symmetric double die design for the inner races and asymmetric double die design for the bearing outer races. 
     Yet a further feature of the present invention is the provision of a method and apparatus for dual frequency contoured induction austenitization of bearing inner and outer races including the low audio frequency preheating and high radio frequency final heating, utilizing individual annular internal or external induction coils for bearing outer and inner races, respectively, and associated automated switching means for furnishing the appropriate power to the coils. 
     Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a Time-Temperature-Transformation (T-T-T) Diagram of a typical low alloy steel, used for making hardened rolling element bearing races in accordance with the invention; 
     FIG. 2 is a diagrammatic front elevation view of apparatus for rolling element bearing race processing as embodied by the invention, the procedure being indicated for one component of the rolling element bearing race; 
     FIG. 3 is a diagrammatic front elevation view, similar to FIG. 2, the procedure being indicated for another component of the rolling element bearing race; 
     FIG. 4 is a diagrammatic side elevation view of the apparatus illustrated in FIGS. 1 and 2; 
     FIG. 5 is a diagrammatic cross section view in elevation of a high performance rolling element bearing of the type being operated on by the technique of the invention; 
     FIG. 6 is a schematic diagram of an induction heating system for use with the invention; 
     FIG. 7 is a schematic diagram of another embodiment of an induction heating system for use with the invention; 
     FIG. 8 is a diagrammatic side elevation view of a thermo-mechanical roll finishing operation, in accordance with the invention, being performed on the raceway of an inner race of a high performance rolling element bearing; 
     FIG. 8A is a cross section view taken generally along line  8 A— 8 A in FIG. 8; 
     FIG. 9 is a diagrammatic side elevation view of a thermo-mechanical roll finishing operation, in accordance with the invention, being performed on the raceway of an outer race of a high performance rolling element bearing; 
     FIG. 9A is a cross section view taken generally along line  9 A— 9 A in FIG. 9; 
     FIG. 10A is a detail cross section view illustrating one preferred contacting pattern between the raceway and the rolling elements of a high performance rolling element bearing produced according to the invention; 
     FIG. 10B is a detail cross section view illustrating another preferred contacting pattern between the raceway and the rolling elements of a high performance rolling element bearing produced according to the invention; and 
     FIG. 11 is a detail plan view of a portion of a ring gear having net shaped internal gear teeth formed according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The basic concept as presently disclosed is to thermo-mechanically roll finish surface layers and thereby induce ausform strengthening in the bearing raceways. This enhanced strength can result in substantially increased load capability and, therefore, improved performance and life of bearings. Attempts were made in the mid 1960s and 1970s to ausform bearing components. Entire inner and outer races and their associated balls were forged or bulk ausformed. Small 35 mm bore bearings were produced in this manner and tested and found to have up to seven fold increase in life. However, a very large forging capability was required to bulk forge the components, and several subsequent mechanical operations were necessary to achieve required dimensional accuracy and surface finish. The very large forging capability required was not cost-effective, and therefore the process was not industrially implemented. Furthermore, this technique was suitable only for high carbon through-hardening steels such as M-50 or 52100 steels. 
     The approach of the present invention eliminates all of the above problems. First, by the thermo-mechanical roll finishing concept, ausforming is applied only to the outer surface layers, thus substantially reducing the load requirements. As it is a net shape finishing operation with capability to achieve the final dimensional accuracy and surface finish sought, no further operations are required. Finally, since only the surface layers are induction heated and then ausform finished, the technique is also applicable to carburizing grade bearing steels, in addition to the through-hardening steels. 
     It may seem that once precision roll finishing a complex geometry such as a spur/helical gear has been successfully achieved, it would be a relatively straightforward task to roll finish a simpler cylindrical/conical geometry. In fact, the opposite is true considering the deformation and material flow patterns involved with these distinctly different component shapes, and to the best knowledge of the inventors, cylindrical/conical surfaces (either internal or external surfaces) have never been precision roll finished. Net shape finishing by rolling for gears as described in commonly assigned U.S. Pat. Nos. 5,451,275 and 5,221,513 to Amateau et al., the disclosures of which are hereby incorporated herein in their entirety by reference, utilizes a combined rolling and sliding action between meshing gears teeth. The sliding action occurs up and down the tooth surfaces, and that sliding action is exploited to induce material flow up and down the teeth. As the gear tooth surface is soft in the metastable austenitic state, rolling the gear under lateral load against a hard rigid die gear, produces material flow along the sliding direction. Therefore the controlled lateral infeed motion of the dies results in meshing tooth loads both tangential and normal to the tooth surfaces of the work gear which induces plastic deformation on the gear teeth. 
     For cylindrical and conical surfaces such as rolling element bearing races, however, there is no substantial sliding action and the lateral in feed loads produce compressive and axial shear material flow in the surface layers. Material flow patterns are therefore more complex, as the only path available for the plastic flow from the surface layers is in the axial direction. Material from regions near the edges can easily flow outwards, whereas material from the mid-regions must be induced to flow out over a substantially larger distance. Rolling die design is therefore more involved in order to allow for varying amount of axial flow material flow from the mid regions to the ends. Even for a straight cylindrical surface, the profiles of the rolling dies must be suitably contoured to achieve the desired precision and surface finish in the finished component. Rolling die design is further complicated for contoured cylindrical and conical surfaces. 
     Turn now to the drawings, and initially to FIGS. 2-4 which illustrate a preferred embodiment of a system  40  according to the invention devised for net shaping raceways  42 A,  42 B of high performance rolling element bearing races  44 A,  44 B (see FIG. 5) by controlled deformation using a fixed axis through-feed of a workpiece and in-feed of two rolling dies  46 ,  48  on moving axes. Throughout this description, viewing FIG. 5, bearing race  44 A and associated raceway  42 A refer to the inner race of a rolling element bearing  50  and bearing race  44 B and associated raceway  42 B refer to the outer race of the same rolling element bearing. Further, for ease of description, throughout this disclosure, the reference numerals for a particular component will remain consistent whether reference is being made to a “blank”, to a “workpiece”, or to a net shaped or finished item. The stage of the process for the particular item will be understood from the context. 
     Also, for purposes of the present disclosure, the workpiece  44 A,  44 B is referred to initially as a “near net shaped bearing race blank” and when all processes of the invention have been completed, it is referred to as a “net shaped bearing race”. As a near net shaped bearing race blank, it may have been formed using conventional techniques. As such, for purposes of the invention, the workpiece  44 A,  44 B is formed with its rolling element engagement surface approximately 0.001 to 0.002 inches oversized in thickness relative to the final or desired size so that the finished race can meet the dimensional tolerances required for high performance rolling element bearings without the necessity of grinding. The displacement of the metal during the deforming operations performed in accordance with the invention serves to remove the excess tooth thickness while assuring the proper profile. Grinding is eliminated, and for this reason alone, there can be as much as a 70% increase in surface durability at any given contact stress level. With continued reference to FIGS. 2-4, a brief overview of the operation of system  40  will be provided, after which a more detailed description of the components of the system  40  will be related. The system  40  provides for the timely and automatic transfer of each workpiece  44 A,  44 B to a plurality of processing stations. 
     In a ball bearing as diagrammatically illustrated in FIG. 5 which could also use rollers instead of balls, the inner race  44 A typically is mounted with a tight fit on a shaft  52 , and the outer race  44 B is pressed tightly into the bore of a housing  54 . Balls  56 , are the anti-friction elements and roll on the raceways  42 A,  42 B of the inner and the outer races. The raceways  42 A,  42 B are the load bearing surfaces and are the highly stressed contacting surfaces where the balls or rollers contact the races. These are the surfaces which must have the load carrying capacity, otherwise the bearing  50  will fail by spalling, cracking or plastic flow. The technique of the invention induces additional ausform strengthening to these surfaces. The ausforming effects are localized to the contacting surfaces only where the additional strength is beneficial to improve the performance of the bearings. 
     At the entrance to the system  40 , a workpiece in-chute  58  holds the workpieces  44 A,  44 B to be processed and, upon command from a suitable process controller (not shown), releases a workpiece to a workpiece loader  60  for subsequent transfer to an induction heating station  62  by means of a swivel robot  64 . The heating station  62  includes a support spindle  66  to accept the workpiece from the swivel robot and servo-drives  68  to impart linear and rotary motions to the workpiece. At appropriate times, the support spindle  66  positions the workpiece and drives it at appropriate linear and rotational speeds with respect to MF and RF induction coils  70 ,  72  respectively, in order for the surface austenitization to be performed then advances it into processing or quench media  74  in a processing tank  76 . Contour austenitization of the surfaces of each workpiece is achieved by energizing either or both of the MF and RF induction coils using their respective power supplies (not shown) and for appropriate periods of time. The complete surface austenitization cycle is controlled by a dedicated induction heating process controller (not shown), which in turn is supervised by a software driven process controller (not shown). After the induction austenitization of the surfaces of the workpiece and the rapid quenching thereof to the metastable austenitic condition, a transfer mechanism  78  transfers the workpiece to a through-feed holding spindle  80  for the roll finishing process, as supervised by the process controller. 
     A through-feed actuator  82  is mounted on a rigid main frame  84  of the system  40  and is connected to the through-feed spindle  80 , allowing the workpiece both the translatory and rotary motions required for the rolling action. The processing tank  76  is designed to contain the processing or quench media  74  maintained at a temperature of up to about 600° F. The tank is anchored to the rigid main frame  84  with suitable seals designed to contain the hot media. Housings for the rolling dies and the adjustment mechanisms to align the axes of the rolling dies in the in-plane, out-of-plane and axial direction are all contained in the processing or quench media  74  to maintain the rolling hardware at a thermally stable forming temperature. 
     The adjustments to the axes of the rolling dies are performed by remotely operated actuators. As seen in FIGS. 2-4, the rolling dies  46 ,  48  are power driven through constant velocity joints  86  which allow in-feed motion of the rolling dies  46 ,  48  towards and away from the workpiece  44 A,  44 B. This arrangement is particularly well seen in FIGS. 2 and 3. Both complete in-feed assemblies  88 ,  90 , including rolling die housings  92  and adjustment mechanisms  94  are guided on precision linear bearing elements  96  which, in turn, are suspended from bridge  98  of the rigid main frame  84 . The in-feed forces and motions are provided by the two in-feed actuators  100  mounted on spaced columns  102 ,  104  of the rigid main frame. The connections between the in-feed actuators  100  and the in-feed assemblies  88 ,  90  pass through the walls of the processing tank  76 , and are properly sealed to prevent drainage of the processing or quench media  74  while allowing the linear in-feed motions. 
     Throughout the thermo-mechanical processing cycle including surface austenitization, rapid quench to metastable austenitic condition, roll finishing, and the final quench to martensite, an enclosure  110  contains and maintains an inert environment of nitrogen or argon, for example, to protect the workpiece surfaces from oxidation, the recirculating inert gas being continuously monitored for oxygen level, and refurbished as required. 
     After the roll finishing cycle is completed, a transfer system  106 , similar to transfer mechanism  78 , then accepts the processed workpiece  44 A,  44 B and transfers it to an indexing quench station  108  (FIG. 4) for final transformation to martensite. The indexing quench station  108  includes a tank or vessel  112  which contains a thermally controlled liquid working medium  114  which may be similar to the quench media  74  utilized in the processing tank  76 . In this instance, the working medium  114  is maintained at a substantially uniform temperature in the range of approximately 50° F. to 250° F. which is broadly considered to be “room temperature”. The vessel  112  is so positioned in relation to the rest of the system  40  that the transfer mechanism  106  always remains in the inert atmosphere provided by the enclosure  110 . As seen in FIG. 4, a transfer arm  116  of the transfer mechanism is elevated until it overlies an upper rim  118  of the processing tank  76  positioning jaws  120  holding the workpiece  44 A,  44 B above and in line with a suitable spindle  122  of a workpiece receiving carousel  124 . The jaws  120  are then operated to release the workpiece which is, at this stage of the operation, a net shaped race, onto spindle  122 . In time, the completed workpiece descends through the working medium  114  until it comes to rest on the carousel  124  or onto a preceding net shaped race. Preferably, the carousel is caused to rotate about a hub  126 . This motion causes some measure of agitation of the working medium  114  and also presents the completed workpieces to an exit location  128  outside of the enclosure  110 . 
     The processed workpiece is finally unloaded from the indexing quench station for subsequent operations. 
     For programmed execution of the process sequence, the process controller, earlier mentioned, operates the various material transfer mechanisms which include modules such as the in-chute  58 , workpiece loader  60 , swivel robot  64 , the transfer mechanisms  78  and  106 , respectively, and the indexing quench station  108 . Each of these modules performs one or more of the following functions: gripping of the workpiece  44 A,  44 B, vertical (up/down) translation, rotation, extension and retraction of a gripping arm (to be described). The control of the bearing race finishing machine  130  involves the coordinated operation of the servo-controlled actuators for the through-feed of the workpiece and the in-feed of the two rolling dies, the drive from the prime movers to the rolling dies, and the operation of the workpiece holding chuck on the through-feed spindle  80 . The control of the workpiece surface austenitization process involves the operation of the servo-controlled drives  68  of the heating station  62 , and the energizing/deenergizing of the MF/RF power at induction coils  70 ,  72  supplied in a programmed sequence. The power supplies have built-in dedicated power levels and on-time controllers for precise monitoring and control of the induction heating process. 
     Returning to FIG. 4, it is seen that a plurality of workpieces  44 A,  44 B are advanced toward the system  40  by means of the in-chute mechanism  48  which includes an elongated magazine  132 . The workpieces  44 A,  44 B are advanced along the magazine  132  to a platform  134  of the workpiece loader  60 . With the workpiece  44 A,  44 B properly positioned on the platform  134 , an actuator  136  is effective to raise the platform  134  with the workpiece  44 A,  44   b  thereon from a lowered position to a raised position. 
     When the platform  134  reaches the raised position, as illustrated in FIG. 4, the workpiece  44 A,  44 B assumes the same elevation of that of a transfer arm  138  of the swivel robot  64  which is able to pivot through at least 180°. That is, it can move from a solid line position such that workpiece engaging finger members are generally aligned with the platform  134  of the workpiece loader  60  to a dashed line position generally aligned with associated components of the heating station  62 . The transfer arm  138  is then swung from the solid line, or pick-up, position to a delivery or dashed line position generally aligned with the induction coils  70 ,  72  at the heating station  62 . It will be appreciated that as the transfer arm  138  is swung from the workpiece loader  60  to the heating station  62 , it passes through an opening  140  in a wall of the enclosure  110 . The opening  140  is of a suitable construction to allow passage of the transfer arm  138  while retaining the inert environment provided by the enclosure. 
     When the transfer arm  138  is moved to the dashed line position illustrated in FIG. 4, the upper actuator mechanism  68  is operable to withdraw the support spindle  66  to an initial fully retracted position as indicated by solid lines. A terminal end of the support spindle  66  may have, for example, a pneumatically operated expandable chuck capable of retracting to gain entry into an inner cylindrical surface  150  of the workpiece  44 A or with the raceway  42 B of the workpiece  44 B, then be caused to expand into engagement therewith. Thus, when the transfer arm  138  has been moved to the dashed line position indicated in FIG. 4, the upper actuator mechanism  68  can be operated to advance the support spindle  66  until the expandable chuck is positioned so as to be generally coextensive with the inner cylindrical surface or raceway of the workpiece  44 A,  44 B. The chuck is then expanded so as to engage the workpiece and the finger members of the transfer arm  138  are caused to release their engagement with the outer peripheral surfaces of the workpiece. Again, the support spindle  66  is caused to be raised and, with it, the workpiece  44 A,  44 B. With the workpiece now out of alignment with the transfer arm  138 , the latter is returned to its solid line position (FIG. 4) and in position to receive a subsequent workpiece at the workpiece loader  60 . Induction coils  70  and  72  are suitably mounted on the frame  84  in a manner not illustrated. Viewing FIG. 4, the induction coil  70  defines a first heating zone  146  and the induction coil  72  defines a second heating zone  148 . A suitable source of electrical energy serves to energize the first induction heater at a medium frequency (MF) in the range of 2-20 Khz which is effective to impart adequate heat to the first heating zone  146  to thereby heat the workpiece  44 A,  44 B to a predetermined surface temperature and to a predetermined thermal gradient through the carburized case of the workpiece. Thus, the heat provided by the induction coil  70  is such as to heat the carburized case of the workpiece to a desired surface temperature and the sub case regions to a desired thermal gradient therethrough. The source for energizing the induction coil  72  and thereby heating the second heating zone  148  is operable at a radio frequency (RF) in the range of 100-450 Khz which is effective to impart adequate heat to the second heating zone  148  to thereby heat the carburized case of the workpiece  44 A,  44 B above its critical temperature to maintain the austenitic structure in the carburized case of the workpiece. In this instance, the frequency used is effective to austenitize the carburized case. 
     The upper actuator mechanism  68  is thus selectively operable to move the support spindle  66  from a fully withdrawn position within the rotary actuator mechanism  68  to a first position capable of receiving a workpiece  44 A,  44 B from the transfer arm  138  then to a second advanced position aligned within the first heating zone  146 , and then to a third advanced position aligned within the second heating zone  148 . 
     When the workpiece  44 A,  44 B supported on the support spindle  66  is positioned within the first heating zone  146 , the upper actuator mechanism  68  is operated to rotate the support spindle  66  on its longitudinal axis and, thereby the workpiece  44 A,  44 B. The induction coil  70  is simultaneously energized by an electrical source which is provided at a frequency effective, as mentioned above, to impart adequate heat to the heating zone  146  to thereby heat the workpiece to a predetermined surface temperature and to a predetermined thermal gradient through the carburized case of the workpiece. After a predetermined time, the rotary actuator mechanism operates to stop rotation of the support spindle  66  and the upper actuator mechanism  68  is operated to advance the workpiece  44 A,  44 B to a second heating zone  148  within the induction coil  72 . Again, the rotary actuator mechanism is effective to rotate the support spindle  66  on its longitudinal axis and, thereby, the workpiece  44 A,  44 B at a predetermined rotational speed. As in the instance of the induction coil  70 , the induction coil  72  is then energized at a frequency effective to impart adequate heat to the second heating zone  148  to thereby heat the carburized case of the workpiece  44 A,  44 B above its critical temperature to maintain the austenitic structure throughout its carburized case. 
     As heating proceeds within each of the induction coils  70 ,  72 , the temperature of the workpiece may be monitored by means of a suitable temperature sensor. 
     The heating operation may be more clearly understood with the aid of FIGS. 6 and 7, FIG. 6 being representative of the heating station illustrated in FIG.  4 . Such an arrangement is acceptable so long as the workpiece  44 A,  44 B is cylindrically shaped. However, for tapered rolling element bearings having the construction as illustrated in FIG. 5, the part geometry does not allow for efficient axial traverse of the workpiece from the MF coil  70  to the RF coil  72  as would be required. One possible solution would be to make the annular hole of the coils in FIG. 6 be much larger to allow passage of the workpiece. Another way would be to use a coil as shown, but then move the workpiece out, and then relocate the MF coil elsewhere and bring the RF coil into position. Both of these solutions would be inefficient, however, and may not be feasible from the metallurgical standpoint. 
     Accordingly, as schematically indicated in FIG. 7, it is proposed to use a switching box  152  where MF and RF power supplies  154 ,  156 , respectively, under the guidance of a controller  158  are connected in such a way as to power a single induction coil  160  from the MF power supply first through an MF output station  162 , then turn it off, switch the connections to the RF side, turning on the RF power supply so as to power the induction coil  160  through an RF output station  164 , and so on to complete the process. Such an arrangement would greatly simplify the structure of the system  40 . 
     Upon the conclusion of operations at the heating station  62  as just described, the upper actuator mechanism  68  then rapidly advances the support spindle  66  and the workpiece  44 A,  44 B it is holding beyond the coils  70 ,  72  and into the quench media  74  contained within the processing tank or vessel  76 . The quench media  74  may be a commercially available marquenching oil which is thermally controlled to maintain the workpiece at a uniform metastable austenitic temperature just above the martensitic transformation temperature. The workpiece  44 A,  44 B remains submerged in the quench media  74  for the duration of all net shaped forming operations, as will be described. 
     The workpiece transfer mechanism  78  includes a transfer arm  166  generally similar in construction and operation to transfer arm  138 . Transfer arm  166  is vertically movable between a raised, solid line, position indicated in FIG. 4 and a lowered, dashed line, position indicated in the same figure. In the raised position, the transfer arm  166  is positioned to receive a workpiece  44 A,  44 B from the support spindle  66  immediately after the workpiece has been deposited in the quench media  74  from the heating station  62 . 
     Thus, when the support spindle  66  is in its fully extended condition holding the workpiece  44 A,  44 B submerged in the quench media  74  just beneath an upper surface  168  thereof (FIG.  4 ), the transfer arm  166  is raised to the level of the workpiece while holding opposed jaws thereon in an open position generally encircling the workpiece but not engaging it. Thereupon, a suitable jaw actuator is operable for firm engagement with the workpiece. Thereupon the chuck associated with the support spindle  66  holding it just beneath the upper surface  166  of the quench media  74  is deflated and the support spindle  66  withdraws, being elevated away from the region of the workpiece. Thereupon, the transfer mechanism  78  is operated to cause the transfer arm  166  to descend from the raised, solid line position to the lowered dashed line position. 
     When the transfer mechanism is in the lowered position, the transfer arm  166  lies generally in a plane for the reception of the workpiece by the through-feed spindle  80 . 
     The through-feed spindle  80  is of a construction similar to spindle  66  in that it has an expandable chuck which is engageable with the inner surface of a workpiece  44 A,  44 B. Thus, when the jaws of the transfer arm  166  have moved to a position such that the workpiece overlies the through-feed spindle  80 , operation of the through-feed actuator  82  causes elevation of the spindle  80  and its associated chuck until the chuck enters and engages the workpiece. Thereupon, the jaws are opened, the actuator  82  is operated to temporarily lower the workpiece out of the plane of the transfer arm  166 , and the latter is swung once again back to the solid line position of FIG.  4 . The through-feed actuator  82  then operates to elevate the workpiece  44 A,  44 B into a generally coextensive or coplanar relationship with the rolling dies  46 ,  48 . 
     As mentioned earlier, the system  40  includes a pair of opposed in-feed assemblies  78 ,  80  which are substantially similar in construction but positioned on diametrically opposite sides of the workpiece  44 A,  44 B when the latter is in the rolling positions as illustrated in FIGS. 8 and 9. Each in-feed assembly  78 ,  80  includes a rolling die housing  92  for rotatably supporting on a drive shaft  170  a rolling die,  46 ,  48 , respectively, each of which has an outer peripheral profiled surface for rolling the engagement surfaces of the workpiece  44 A,  44 B to a desired outer peripheral profiled shape. Of course, as previously noted, this is achieved while holding the temperature of the workpiece in a uniform metastable austenitic temperature range. It was also previously mentioned that the workpiece  44 A,  44 B has previously been formed as a near net shaped bearing race blank with oversized engagement surfaces. During the operations about to be described, the excess thickness of the engagement surfaces is removed and the proper, or desired, raceway profile achieved. 
     A rotary drive actuator  172  (see FIGS. 2 and 3) operates the drive shafts  170  for both of the rolling dies  46 ,  48  in a synchronous manner through a coupling transmission  174 , connecting shafts  176 , and constant velocity joints  86 . It will be appreciated that the longitudinal axes of the through-feed spindle  80  and the axes of rolling dies  46 ,  48  are nominally parallel. However, this relationship may be altered by reason of the adjustment mechanisms  94  in order to achieve a properly profiled gear from the workpiece  44 A,  44 B. 
     It was earlier mentioned that the degree of deformation of the engagement surfaces of the workpiece  44 A,  44 B must be controlled to very close tolerances by precise monitoring and control of the movements of each of the two rolling dies  46 ,  48  with respect to the workpiece. It was further mentioned that the workpiece axis as well as the axes of the two rolling dies must be precisely aligned to achieve the high lead and profile accuracy specified for ultra-high precision rolling element bearing races. The adjustment mechanisms  94  which have been broadly mentioned previously provide the adjustments for the rolling dies  46 ,  48  which are necessary to achieve the high dimensional accuracy being sought. 
     It was earlier mentioned that the spindle  80  carrying the workpiece  44 A,  44 B is elevated, that is, moved in a through-feed direction, into an operating position which is generally coextensive with the opposed rolling gear dies  46 ,  48 . Thereafter, the rolling dies  46  and  48  are each simultaneously advanced in an in-feed direction within a common plane which generally contains the axes of the spindle  80  and of both drive shafts  170 . The rolling dies  46 ,  48  advance, respectively, in opposite in-feed directions which are substantially perpendicular to the axis of the workpiece at diametrically opposed locations and at near net shaped center distances which establish initial center distances between the longitudinal axis of each drive shaft  170  and of the spindle  80 . The assemblies  88 ,  90  continue to advance their associated rolling dies  46 ,  48 , respectively, in the in-feed direction each by an additional increment of center distance thereby deforming the engagement surfaces of each workpiece and resulting in a finished net shaped bearing race. 
     The individual components for each of the in-feed assemblies  88 ,  90  are substantially similar. Therefore, the description will be substantially limited to in-feed assembly  88 , but it will be understood that such description also pertains to in-feed assembly  90 , unless otherwise noted. A trolley  178  (FIGS. 2 and 3) is laterally movable on the bearing elements  180  as generally indicated by a double arrowhead  182 . In turn, an in-feed assembly frame  184  is fixed to the trolley  178  and depends therefrom. A support block  186  is mounted on the in-feed assembly frame  184 . Finally, the bifurcated rolling die housing  92  is mounted on the support block  186  via the adjustment mechanisms  94 . The adjustment mechanisms  94  provide for a different types of movement of the rolling die  46  with respect to the workpiece  44 A,  44 B as indicated by double arrowheads  188 ,  190 . Such movement is effective to adjust the rolling gear die  46  out of a common plane nominally defined by the axes of the drive shafts  170  and of the through-feed spindle  80 , or within a common plane containing the longitudinal axes of the drive shaft  170  and of the through-feed spindle  80 , or movable along its own axis of rotation relative to the workpiece  44 A,  44 B. 
     Turn now to FIGS. 2,  8 , and  8 A for a description of net shaping an engagement surface or raceway  42 A of the inner race blank  44 A. The raceway is a peripheral profiled rolling element engagement surface with a hardened case in the metastable austenitic condition and slightly oversized from that of a desired formed engagement surface. In FIG. 8, the workpiece  44 A is illustrated by dashed lines being heated in the induction coil  160 , although it might just as properly be within the induction coils  70 ,  72  in the proper sequence, rotation of the workpiece being indicated by an arrowhead  192 . After completion of the proper heating cycle, the workpiece  44 A is immersed in the quench media  74  to a depth so as to be substantially coextensive with the first and second rolling dies  46 ,  48  in the through feed direction. At this stage, the rolling dies  46 ,  48  are sufficiently separated to freely allow entry of the workpiece. 
     When the workpiece is properly positioned, the rolling dies  46 ,  48  which are actually finishing dies are advanced until their outer peripheral surfaces respectively engage the workpiece at diametrically opposed locations (FIG. 8A) and at near net shaped center distances establishing initial center distances between the axes of rotation of the rolling dies and of the workpiece, respectively, when the workpiece and the rolling dies are initially engaged. Thereafter, the rolling dies continue to advance in the in-feed direction by an additional increment of center distance thereby deforming the peripheral profiled engagement surface of the bearing race blank  44 A, resulting in a final net shape of the rolling element engagement surface or raceway  42 A. 
     Turn now to FIGS. 3,  9 , and  9 A for a description of net shaping an engagement surface or raceway  42 B of the outer race blank  44 B. As with the inner race blank  44 A, the raceway  42 B of the outer race blank  44 B is a peripheral profiled rolling element engagement surface with a hardened case in the metastable austenitic condition. In this instance, however, the outer race blank includes a ring-shaped member  194  having an outer peripheral surface  196  and an inner raceway  42 B which is a contoured roller element engagement surface slightly oversized from that of a desired formed engagement surface. Also, similar to the inner race blank  44 A, the workpiece  44 B is illustrated by dashed lines being heated in the induction coil  160 , although it might just as properly be within the induction coils  70 ,  72  in the proper sequence, rotation of the workpiece being indicated by the arrowhead  192 . After completion of the proper heating cycle, the workpiece  44 B is immersed in the quench media  74  to a depth so as to be substantially coextensive with the first and second rolling dies  46 A,  48 A in the through feed direction. The rolling dies for the outer race blank  44 B are somewhat modified from those employed for the inner race blank  44 A, as will be noted below. One of the die housings, indicated by reference numeral  92 A is also somewhat modified and necessarily has an axis somewhat offset laterally from its mating die housing  92  used for operations on the inner race  44 A. In any event, at this stage, the rolling dies  46 A,  48 A are sufficiently separated to freely allow entry of the workpiece  44 B. 
     When the workpiece  44 B is properly positioned, the rolling dies  46 A,  48 A are advanced until their outer peripheral surfaces respectively engage the ring shaped member  194  at opposed locations (FIG. 9A) and at near net shaped center distances establishing initial center distances between the axes of rotation of the rolling dies and of the workpiece, respectively, when the workpiece and the rolling dies are initially engaged. In this instance, the rolling die  46 A moves only until such time that its outer peripheral surface tangentially engages the outer peripheral surface  196  of the workpiece  44 B, then stops, to provide a support for the operation to be performed by the rolling die  48 A. Indeed, the rolling die  48 A, which is a finishing die, continues to advance in the in-feed direction by an additional increment of center distance thereby deforming the peripheral profiled engagement surface  42 B of the bearing race blank  44 A, resulting in a final net shape of the rolling element engagement surface or raceway  42 B. 
     Further, according to the invention, FIGS. 10A and 10B are detail cross section views illustrating preferred contacting patterns between the raceway and the rolling elements of a high performance rolling element bearing produced according to the invention. More specifically, the bearing races and/or rolling elements are designed such that as the load increases, the contacting pattern between the rolling elements and the raceways spreads evenly from the middle towards the ends. In order to achieve this, either the raceways or the rollers are crowned, i.e. have a slightly raised and curved contour. In FIG. 10A, a raceway  198  of race  200  between spaced lateral surfaces  200 A and  200 B is indicated as being flat while an engaging surface  202  of a rolling element  204  is indicated as being crowned. Oppositely, in FIG. 10B, a raceway  206  of race  208  between spaced lateral surfaces  208 A and  208 B is indicated as being crowned while an engaging surface  210  of a rolling element  212  is indicated as being crowned. In this manner, as the load increases, the resulting deformations spread the contact area and the loads. The rolling dies must be designed to produce this specially contoured contacting surfaces of the bearing raceways. The design must allow for the above, as well as for material flow and elastic deformations. Once the dies have been developed to achieve the precise finished geometry, a very large number of repeatable and accurate raceways can be produced. On the other hand, grinding wheels wear away and therefore must be periodically dressed to correct the contoured form. 
     Although the present invention has been described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. Thus, while preferred embodiments of the invention have been disclosed in detail, it should be understood by those skilled in the art that various other modifications may be made to the illustrated embodiments without departing from the scope of the invention as described in the specification and defined in the appended claims.