Abstract:
A centerless microfinishing machine especially adapted for machining camshaft workpieces. The microfinishing machine causes the camshaft workpiece to rotate through the use of a centerless drive system including spaced rollers which frictionally engage the workpiece. A tooling head assembly strokes between engage and disengage positions and includes individual shoes which simultaneously engage the camshaft lobe and camshaft bearing journal surfaces. Through the use of separate compliant elements, these tools are caused to follow the contours of the surfaces being machined. The tooling head assembly allows these surfaces to be machined simultaneously; therefore, multiple machine functions can be accomplished in a single manufacturing step, which reduces the number of individual pieces of equipment which are required in accordance with typical machining approaches.

Description:
This application claims benefit of Ser. No. 60,144,555 filed Jul. 16, 1999. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention is related to a machine tool, and particularly, to a microfinishing machine for workpieces such as internal combustion camshafts operating on a centerless turning principle. 
     Numerous components for machines require microfinishing operations which produce high quality surface finishes of known characteristics. Microfinishing of surfaces is necessary to ensure proper friction and wear properties of the components in use. Microfinishing is especially significant where sliding contact between surfaces occurs during operation of a machine. Internal combustion engines of modem day motor vehicles include numerous components having microfinishing requirements. Crankshafts, which convert the reciprocating motion of the pistons into a rotary output, have numerous cylindrical journal surfaces which require microfinishing. The assignee of this invention, the Industrial Metal Products Corporation (IMPCO), has been an innovator of numerous machines and processes in the microfinishing area, particularly oriented toward crankshaft microfinishing. U.S. patents on these innovations include U.S. Pat. Nos. 4,682,444; 5,095,663; 5,148,636; and 5,531,631; which are hereby incorporated by reference. 
     In addition to internal combustion engine crankshafts, camshafts also require microfinishing. Camshafts typically have a number of cylindrical surfaces formed on them, rotating within simple journal bearings in the engine. Typically, a belt, chain, or gear, drives the camshaft to rotate in a synchronized manner with the rotation of the crankshaft. A number of cam lobes along the camshaft interact with cam followers to actuate the valves which control the intake and exhaust processes within the engine. In a typical four-stroke, internal combustion engine, two lobes are devoted to each cylinder, with one lobe controlling the intake valve and the other controlling the exhaust valve. More sophisticated internal combustion engines use multiple intake and exhaust valves per cylinder and require a corresponding increase in the number of lobes formed on the camshaft (or camshafts). Both the journal bearing surfaces and the cam lobe surfaces of the camshaft often require microfinishing operations. Camshaft blanks are normally formed from cast iron. The rough castings are machined in a number of steps including grinding operations to form the journal and cam surfaces. Microfinishing of camshafts is a known process which has been in use for many decades. In one process in use, the camshaft is turned between fixed centers in the manner of a lathe, with microfinishing tools acting on the bearing journal surfaces, and at a separate station, on the lobe surfaces. So-called “centerless” approaches are also known. In a centerless machine, a pair of rollers frictionally engage the cylindrical journal surfaces (or another cylindrical surface of the workpiece) and cause the camshaft to rotate. An abrasive tool, such as a stone or an abrasive-coated film may be used. An example of the centerless machine for the machining of ground shafts is found with reference to U.S. Pat. No. 5,231,798, which is hereby incorporated by reference and which is assigned to the assignee of this application. 
     In any machining process for workpieces, it is desirable to reduce the number of individual stations where metal finishing operations are completed. By reducing the number of stations, the part handling equipment is made simpler. Moreover, the probability for damage to workpieces, caused by mishandling, is reduced where individual stations can be eliminated. Plant floor space is also reduced in such conditions. The structure for the machine tools and drive system adds cost where multiple stations are required. In present microfinishing operations of camshafts, the machining of the cam lobes and journals occurs at different stations. This results in dedicated individual machining centers required for those surfaces. 
     In view of the foregoing, it is the object of this invention to provide a microfinishing machine which enables journal and camshaft lobe surfaces of a camshaft to be machined in a single operation by one machine. Workpiece handling is also facilitated through the use of a centerless system for the microfinishing machine. 
     Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a frontal view of the centerless microfinishing machine of this invention. 
     FIG. 2 is a side view of the tooling head assembly in accordance with this invention. 
     FIG. 3 is a side view of the upper portion of the tooling head assembly shown in FIG.  2 . 
     FIG. 4 is a front view of the upper portion of the tooling head assembly in accordance with this invention. 
     FIG. 5 is a front view of the lower portion of the tooling head assembly in accordance with this invention. 
     FIG. 6 is a side view particularly illustrating the camshaft lobe tooling of the tooling head assembly of this invention. 
     FIG. 7 is a side view particularly illustrating the bearing journal machining tool of the tooling head assembly of this invention and further showing the drive rollers of the machine. 
     FIG. 8 is a side elevational view of a centerless microfinishing machine in accordance with an alternate embodiment of this invention in which the drive rollers are oriented differently as compared with the prior embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Centerless microfinishing machine  10  includes, as principal components, frame  12 , tooling head assembly  14 , and drive rollers  16 . Tooling head assemblies  14  are mounted in the upper portion of frame  12  and include tooling elements which are described in more detail later in this description, which act on a workpiece. Drive rollers  16 , also shown in FIG. 7, are caused to rotate by a drive system within frame  12 . Drive rollers  16  engage a workpiece in the manner of a conventional centerless machining system. The centerless microfinishing machine  10  of this invention is especially adapted for machining camshaft workpieces  18 . As stated previously, camshafts are rotating shafts, featuring cam lobe surfaces which actuate valves in internal combustion engines. A portion of camshaft  18  is illustrated in FIG.  5 . Camshaft  18  (typically) features a plurality of cam lobes  20  and cylindrical journal bearing surfaces  22 . In accordance with a principal feature of this invention, one or more cam lobes  20  are machined simultaneously by the tooling head assembly  14 , along with one or more cylindrical bearing surfaces  22 . Cam lobes  20  and cylindrical bearing surfaces  22  are typically juxtaposed along the axial length of camshaft  18 . In the example of camshaft  18 , illustrated in FIG. 5, cylindrical bearing surface  22  is present between adjacent lobes  20 . 
     Tooling head assembly  14  is best illustrated with reference to FIGS. 2 through 7. As shown in FIG. 2, tooling head assembly  14  is mounted to frame  12  through the use of mounting bracket  24 . Cap screws  26  are threaded into mounting bracket  24  and cause mounting plates  28  to clamp against grooved surfaces of frame  12 . Mounting bracket  24  includes a top mounted actuating cylinder  30  which may be air or hydraulically operated and is capable of stroking between an upward disengaged position, causing the tooling to be disengaged from the workpiece, to a downward engaged machining position. Cylinder shaft  48  is affixed to coupler  50 , which is in turn, connected with slide plate  32  as best shown in FIG.  3 . Slide plate  32  includes yoke  34  having a pair of open slots  36  which engage with oscillating shafts  38 . Oscillating shafts  38  include a pair of protruding collars  40  which can be formed integrally by the oscillating shaft or through the use of installed ring elements which can be welded, braised, or mounted to the shafts  38  through the use of a set screw, roll pin, or other mechanical fastener. When actuating cylinder  30  is stroked to its downward position, yoke slots  36  engage oscillating shaft  38  as shown in FIG.  4 . Collars  40  abut yoke  34 . An oscillation drive mechanism (not shown) is affixed to frame  12  and causes oscillating shafts  38  to stroke in the direction of arrow  42 . This is provided to produce a desired machine effect on the workpieces, as will be described in more detail in the following description. 
     As part of the control system of the microfinishing machine  10 , a pair of proximity switches  44  and  46  are provided and mounted to frame  12 . Proximity switches  44  and  46  provide an electrical output indicating the position of slide plate  32  between the open and machining positions. 
     Now with reference to FIG. 5, details of the lower portion of tooling head assembly  14  are shown. Slide plates  32  are connected with tooling head block  52 . A pair of shoe supports  54  are provided for the camshaft finishing tool  56 . A shoe support  58  is also provided for the main bearing journal tool  60 . Each of the shoe supports  54  and  58  are able to stroke axially in the vertical direction relative to block  52  within a limited range of motion. Each of shoe supports  54  can stroke vertically against the compliant force provided by nitrogen filled cylinders  62 . The bodies of nitrogen filled cylinders  62  are mounted to block  52 , whereas their downwardly projecting plungers  64  engage shoe supports  54 . Shoe support  58  is loaded compliantly through the use of coil spring  66 . The range of vertical stroking motion of shoe support  58  is limited through pin  68  installed within elongated slot  70 . Block  52  is shown in FIG. 5 in the downward machining position of tooling head assembly  14 . 
     Microfinishing tools  56  for the cam lobe surfaces  20  are mounted to their shoe supports  54  through the use of a rocking pin  72 . Rocking pin  72  allows tool  56  to pivot during the machining process as will be described in more detail in the following description. 
     Now with reference to FIG. 6, details of the drive rollers  16  and the machining operation for the cam lobes  20  will be described. A pair of drive rollers  16  engage bearing surfaces  22  of the camshaft  18 . In order to provide clearance for rotation of lobes  20 , it may be necessary to provide a grooved or slotted surface around drive roller  16  to prevent interference with the cam lobes as the camshaft  18  is rotated. The separation distance and diameters of drive rollers  16  are chosen to provide a desired friction drive angle through their engagement with camshaft  18 . This angle is selected to cause a high turning torque to be applied to the workpiece during machining. This drive frictional force is in reaction to the vertically downward load applied to camshaft  18  through tooling head assembly  14 . This drive angle can be defined as the angle form between a first line between the centers of one drive roller  16  through the center of camshaft  18 , and a second line which extends between the centers of the drive rollers  16 . Excessively small drive angles result in extremely high contact forces being exerted by drive rollers  16  onto the workpiece  18 , which can lead to surface finish and form degradation at the points of contact with the workpiece. On the other hand, excessively large drive angles result in low drive torque as the rollers do not “bite” the workpiece. A drive angle of approximately 13° is believed to provide the desired balance of these factors. 
     FIG. 6 particularly shows the machining components which act upon camshaft lobes  20 . Tooling head assembly  14  is shown in FIG. 6 in the downward machining position. In this position, tool  56  is shown pressing abrasive coated film strip  74  against camshaft lobe  20 . As shown, tool  56  is able to pivot or rock as the lobe  20  is rotated. This allows the microfinishing film strip  74  to “follow” the contour of the camshaft lobe  20  as it rotates. Various profile configurations for tool  56  may be employed. Although a generally convex surface for tool  56  is illustrated in FIG. 6, other configurations, such as concave surfaces or “V” shaped grooves can be provided. During machining, finishing strip  74  is maintained in position through actuation of tape clamps  76 . As multiple parts are machined, finishing strip  74  becomes worn; therefore, there is a need to index finishing strip  74  between operations. This is accomplished through actuation of film indexing jaw  78 . Actuation of jaw  78  is coordinated with tape clamp  76  such that the tape clamps  76  are open as the film is indexed and clamped to fix the position of the film finishing strip during machining. Preferably, abrasive coated polymer films, such as those manufactured by the 3M Corporation, are used for this process. Alternatively, however, paper or cloth materials, which are coated with abrasive grains, can also be used. Moreover, it is possible to replace the machining film of this invention with tools  56  and  60 , which are formed of an abrasive material, such as honing stone or ceramic compounds and avoid the use of strip  74 . However, that approach is not preferred since it results in the need to frequently redress or replace the tools. 
     Now with reference to FIG. 7, tool  60  is shown in more detail. Tool  60  includes a concave machining surface  80  which presses abrasive film strip  82  against the journal surface being machined. This figure also depicts coil spring  66  and pin  68  acting within slot  70 . Tape clamps  84  operate in an identical manner to tape clamps  76  as described previously. Since the surface of the cylindrical bearing journals  22  is concentric with the axis of rotation of the camshaft  18 , it is not necessary to provide significant rocking or pivoting motion for tool  60 . 
     Now, again, turning to FIG. 5, operation of centerless microfinishing machine  10  will be described. FIG. 5 illustrates tooling head assembly  14  in the downward machining position. As cylinder  30  is actuated to the downward position, yokes  34  become seated in contact with oscillating shafts  38 . The mechanisms are dimensioned such that, in the downward position, compression of spring  66  occurs through engagement of tool  60  with bearing surfaces  22 . Similarly, compression of nitrogen filled cylinders  62  occurs in the actuated position through engagement between tools  56  and cam lobes  20 . Upon rotation of camshaft  18 , engagement of lobes  20  with their tools  56  will cause nitrogen filled cylinder plungers  64  to stroke. This system enables the simultaneous machining through the use of tooling head assembly  14  of both camshaft lobe  20  and bearing surface  22 . Although stroking of nitrogen filled cylinder plungers  64  results in a variable net downward pressure being exerted onto camshaft  18  (which is the sum of the downward forces exerted through contact by tools  56  and  60  on the camshaft  18 ), this variable pressure does not adversely affect the drive conditions provided by drive rollers  16 . During the machining process, oscillating shafts  38  are stroked axially to cause tools  56  and  60  to also oscillate on their corresponding camshaft surfaces. This provides a desired cross hatch pattern in the surface finish generated on the surfaces. This is desirable to provide the desired friction, wear, and hydrodynamic bearing characteristics for the surfaces. 
     An alternate embodiment of centerless microfinishing machine  10  is illustrated in FIG.  8  and designated by reference number  110 . Elements of centerless microfinishing machine  110 , which are identical in function to those elements previously described, are identified by like numbers with one hundred added. Microfinishing machine  110  differs from machine  10  in that drive rollers  116  are located in a different orientation than described previously. Centerless microfinishing machine  10  includes drive rollers  16 , which are oriented such that a line drawn between their centers is horizontal. In other words, camshaft workpieces  18  are dropped directly vertically downward into engagement with rollers  16  during parts loading and unloading. Microfinishing machine  110  features drive rollers  116 , which are located at an angle of approximately 45° relative to a horizontal plane (the angle formed by a plane defined by the longitudinal axis of the drive rollers, and a horizontal plane). This enables more convenient access to the machining location for camshafts  18  during workpiece loading and unloading. Specifically, a gantry loading system can be used to deposit camshaft  18  from a vertical position indicated by reference number  186  to a load position shown by reference number  188 . Once in position  188 , the part can fall by gravity to its position of frictional engagement between drive rollers  116 . This orientation for drive rollers  116  also enables the use of a convenient “bale” type workpiece unloading system. Bale  190  is rotated about the center of rotation of the lowermost of drive rollers  116 . Bale  190  includes an elongated rail  192  which engages the workpiece. By rotating bale  190  about the drive roller center of rotation, the part can be engaged and “kicked out” of its engaged position between the drive rollers. This enables the workpiece to be easily ejected onto a unloading gantry mechanism (not shown). For microfinishing machine  110 , tooling head assemblies (not shown) can be actuated to move in a purely vertical or a direction or at some angle to engage the camshaft  18  without interference with drive rollers  116 . The tooling head assemblies for microfinishing machine  110  are identical to head assembly  14  described in connection with the first embodiment. 
     It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.