Abstract:
A face gear manufacturing operation wherein a set of oversized teeth are formed on a face gear or tapered pinion gear by a gear cutting operation. The oversized teeth are of a predetermined profile. The gear bearing the oversize teeth is then subjected to metallurgical surface hardening operation. At the conclusion of the heat treatment surface hardening operation, the face gear or pinion gear is subjected to a continuous grinding operation wherein a grinding wheel having a worm profile of a predetermined shape is rotated to grind the previously cut teeth to produce a finished tooth profile. The operation is CNC controlled. The gear producing apparatus requires only a slight modification to produce a face gear or a tapered pinion gear by the simple interchange of work heads.

Description:
This application claims the benefits of provisional application Ser. No. 60/113,193 filed on Dec. 21, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The development of Face Gears for high power transmission is a relatively recent phenomenon. Historically, the transmission of power through a Face Gear set was limited to relatively low levels because of two factors: the tooth profile of the mating gears was generated by shaper cutting and, although as very acceptable tooth profile could be generated, the tooth produced by the shaping operation did not have a hardened surface. The tooth profile produced by the shaping operation required that the resulting Face Gear set be kept in almost perfect alignment. 
     Any operation performed on the Face Gear set to harden the surface of the shaped teeth tended to distort the shape of the Face Gear set during the hardening operation. 
     The current method of manufacture of Face Gears was developed by the Fellows Corporation using a gear shaper apparatus and the finished product is useful for the transmission of power for low power applications. 
     Recently however, development has been undertaken by McDonnell Douglas Helicopter Systems supported by NASA Lewis Research Center with regard to designing and developing Face Gears for use in high power applications (Ref. NASA Technical Memorandum 106101/AVSCOM Technical Report 92-C-009). 
     The applicant, herein, has successfully developed the manufacturing practices and the associated equipment required to produce Face Gear sets for high power transmission applications. 
     The Face Gear method of manufacture developed by the Fellows Corporation of shaping the gear teeth, is a metal cutting process, which can only be applied to materials with suitable hardness and metal cutting characteristics. If the material is too hard, the shaper tool will not cut effectively. This shaping process can only be used effectively for finish cutting Face Gear teeth from metals suitable for low power applications. This process does not give the accuracy and surface finish required for higher power applications. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Gear blanks are roughly machined as in the prior art, to produce toothed wheels wherein the gears produced have slightly enlarged teeth which makes allowance for a subsequent grinding operation. The Fellows shaper method is quite acceptable for the production of gears from blanks in this operation. 
     The gear (now having enlarged shaped teeth) is thence subjected to a heat treatment operation to increase the surface hardness of the gear teeth. During this operation, the rough cut gear will usually undergo some physical distortion which occurs during the heat treatment operation. The excessive material deliberately left on the gear teeth in the gear shaping operation, will be sufficient to allow a subsequently distorted gear to be restored to its required shape by a grinding operation. 
     The heat treated gear is now ground to the final shape and accuracy having the desired tooth profile. At this stage, the resulting gear has a hardened tooth on a gear platform which is quite stable because of the stress relieving operation. Grinding is the only known method that will produce the accuracy and surface finish required for high power transmissibility applications. 
     The surface grinding operation is a continuous operation with the grinding wheel and the face gear constantly rotating and moving such that the grinding wheel moves across the face of the rotating face gear in a controlled fashion. The grinding wheel has a surface which is commonly referred to as a “worm” and in grinding a face gear, the surface of the grinding wheel is being constantly eroded by its constant engagement with the hardened metal surface of the previously formed teeth on the face gear. After deposits of the grinding debris, both from the erosion of the grinding wheel and from the material removed from the gear teeth during the grinding operation tend to be redeposited on the surface of the grinding wheel during the grinding operation. A suitable dressing wheel mounted on the grinding machine periodically restores the worm profile to its proper configuration. 
     In the manufacture of spur gears, the movement of a diamond dressing disc used to restore the profile of the spur gear grinding wheel must be controlled in both X and Y axes. 
     This application requires that the movement of a suitable dresser disc be controlled in both the X and Y axes as previously for spur gears, but also the disc must be controlled for movement in a pivot axis (designated the “A” axis) to produce the desired grinding wheel worm profile to properly shape the teeth on the Face Gears being ground. 
     In addition to having the dresser tool move in the X, Y and A axes, the tool must be capable of manual adjustment in two additional axes. 
     Gear tooth grinding of spur gears is performed by the coordinated rotation of the grinding wheel and a gear blank so that the grinding wheel worm engages the gear blank in a constant meshing operation during the grinding operation. The area of engagements of the worm of the grinding wheel with the rotating spur gear is changed by moving the spur gear rectilinearly in its axial direction during a grinding operation to complete the tooth forming operation. 
     In face gear grinding operations, the axis rotation of the grinding wheel relative to the face gear is significantly different. The reason for this is that for face gear grinding operations, the grinding wheel must move the complete distance along the length of the teeth of the face gear and be parallel to the plane of the surface of the gear face in which the face gear teeth are being formed. 
     In grinding face gears, the angle of the teeth generated in the gear face may vary widely with respect to the rotational axis of the face gear, thus grinding of the teeth of a face gear presents a substantial challenge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a prior art spur gear cutting machine. 
     FIG. 2 is a partial view of a prior art blank grinding wheel (before the wheel is shaped). 
     FIG. 3 is a partial view of a spur gear grinding wheel of the prior art showing the dressing tool used to provide a cutting profile. 
     FIG. 4 is a perspective illustration of a face gear and a mating pinion gear. 
     FIG. 5 is a sectional view of a mating pinion and face gear. 
     FIG. 6 shows a sectional view of a face gear shaping apparatus of the prior art. 
     FIG. 7 shows an elevational view of the grinding apparatus of this invention for grinding teeth on a convex face gear. 
     FIG. 8 shows an elevational view of the grinding apparatus of FIG. 7 adapted for grinding teeth on a concave face gear. 
     FIG. 9 is a perspective view of a complete grinding machine for grinding teeth on a convex face gear. 
     FIG. 10 is a plan view of the grinding wheel of this invention showing associated dresser apparatus motion. 
     FIG. 11 is an elevational view of a grinding wheel showing a typical face gear grinding configuration used in this invention. 
     FIG. 12 is a plan view of the grinding machine of FIG. 9 with the face gear removed. 
     FIG. 13 is an end view of the machine of FIG.  9 . 
     FIG. 14 is a front elevation of a concave face gear grinding apparatus. 
     FIG. 15 shows a perspective view of a face gear grinding apparatus adapted for producing teeth on a pinion gear. 
     FIG. 16 is a plan view of an alternative embodiment of the machine shown in FIG.  9 . 
     FIG. 17 is an elevational view of the machine of FIG.  16 . 
     FIG. 18 is an end view of the machine of FIG.  16 . 
     FIG. 19 is a space representation of the three major components of the face gear machine, to more clearly illustrate the various component axes. 
     FIG. 20 is a space representation of the three major components of the machine illustrated in FIG. 15 to more clearly illustrate the various component axes. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a prior art spur gear grinding apparatus  10 . Here, a machine  12  (partially shown) is provided with a movable carrier  14  which is capable of executing rectilinear motion as shown by double arrow  16 . Carrier  14  is provided with a gear driving head  18  which is connected to lead shaft  20 . 
     Shaft  20  is centered at its remote end in tailstock  22  to stabilize the shaft  20 . A spur gear  24  is mounted on shaft  16  so as to be controllably rotated by driving head  18 . 
     A spur gear grinding wheel  26  is shown engaging the peripheral surface of spur gear  24 . Grinding wheel  26  takes the form of the grinding wheel as shown in FIG.  3  and must be capable of movement toward and away from gear  24  as indicated by double arrow  28 . The rotation of the grinding wheel is coordinated with the rotation of the spur gear. 
     To produce a ground spur gear, the grinding wheel  26  is advanced toward the gear  24  while the gear  24  is synchronously rotated to be in step with the “worm” profile at grinding wheel  26 , until the grinding wheel  26  has advanced to the desired depth into a selected area of the spur gear. The spur gear is now gradually moved in an axial direction to permit the grinding wheel to complete the grinding along the tooth length of the gear. This process is repeated for increased material removal until tooth size and profile are achieved. 
     FIG. 2 shows a grinding wheel  30  of the prior art before being dressed to have a grinding profile. 
     FIG. 3 shows a grinding wheel  36  which contains a peripheral worm profile  38  (used for grinding spur gear teeth as previously described), which profile is formed by dressing tool  40  which carries a special shaped dressing disc  42  to provide the worm profile. The dressing tool  40  is moved across the surface of the grinding wheel  36  as the grinding wheel  36  rotates. The disc  42  is advanced into the surface of the wheel  36  until the desired tooth form is achieved. Note that the shape of the profile on the surface of wheel  38  is formed by the shape of the profile of grinding disc  42  (i.e. the axis of rotation of disc  42  is usually parallel to the axis of rotation of wheel  36 ). 
     FIG. 4 shows an illustration of a face gear  50  and a meshing pinion  52 . The teeth  54  on face gear  50  extend in a radial direction; the teeth  56  on pinion  52  are parallel to the axis rotation of the pinion  52 . 
     FIG. 5 shows the face gear  50  and pinion in section. The teeth  54  and  56  are shown in a meshed condition. 
     FIG. 6 is an illustration of a prior art method of shaping the teeth on face gear  50  by shaper cutter  60 . The shaper cutter  60  is reciprocated in an axial direction (as shown by arrows  62 ) while it and the face gear  50  are simultaneously rotated so that the face gear  50  and the shaper cutter  60  are constantly moving in a simulated meshing engagement, until the desired tooth form has been generated. 
     FIG. 7 is an illustration of a face gear work head  68  and face gear grinding head  100  used for grinding the teeth of convex shaped face gear  70 . 
     In this illustration, convex face gear  70  is mounted on a controllable rotating table  72  so as to rotate about axis  74 . Rotating table  72  is pivotably mounted on base  76 . The pivoting action occurs about pivot  78 . Motor  80  serves to drive the rotating table  72  through a suitable drive. The degree of pivot of the rotating table  72  is closely controlled by pivot selector  82 . In the illustration shown, the gear face angle is maintained in a vertical orientation at the point of grinding. The whole rotating face gear head  68  must be capable of executing controlled motion in a vertical direction during a tooth grinding operation as shown by arrow  90 . 
     Grinding head  100  has a grinding wheel  102  rotatably mounted thereon. The grinding head  100  is precisely located with respect to face gear work head  68  and the grinding wheel  102 . CNC control permits controlled motion in the vertical and horizontal axis. 
     Grinding wheel  102  is provided with a special worm profile (see FIGS. 10 and 11) and the grinding operation is carried out by advancing grinding wheel  102  toward face gear  70  so that the grinding wheel profile and the face gear teeth mesh precisely i.e. the worm of the grinding wheel  102  has a profile which meshes with the teeth of the face gear  70 . The feed mechanism for generating the teeth on the face gear  70  slowly moves the face gear  70  in a vertical direction until the grinding wheel has traversed the entire width of the tooth face  71  of face gear  70 . The grinding wheel  102  is gradually advanced into the surface  71  of face gear  70  with each succeeding pass until the desired tooth profile is produced. 
     FIG. 8 shows the same machine adapted to grind teeth on a concave face gear  106 . In this instance, FIG. 8 shows face gear work head  68  having the face gear rotating table  72  pivoted through an angle of about 25° from the position shown in FIG.  7 . Again, the teeth of the concave face gear  106  are in a vertical plane at the point of engagement with grinding wheel  102 . The grinding of the teeth is accomplished in the same manner as the tooth generating operation carried out in FIG.  7 . 
     FIG. 9 shows the full gear grinding machine  200  in perspective. A base  202  is provided to permit the face gear work head  68  to be mounted thereon in a predetermined fashion. This apparatus drives a rotating table  72  on which face gear  70  is mounted in a controlled manner about its axis (designated axis B). The pivot  78  is used to set the face gear at a predetermined angle (face angle) in machine  200  manually and is locked in this position. This pivot mechanism  210  is mounted on a swivel  212  on work table  214  to permit the face gear to have a manually adjustable angular setting. The work table  214  is constrained to permit it to move in a vertical plane along rails  216  by drive motor  222 . This vertical axis is designated as the “W” axis. 
     Drive motor  80  drives face gear  70  through transmission  209  and this, in turn, is mounted via pivot mechanism  78  and pivot supports  220  to the work table swivel  212  which allows the pivot mechanism to also swivel about its mounting on the work table  214 . The swivel axis is designated as the WTS axis. 
     The grinding head  100  (on which grinding wheel  102  is mounted) is mounted on base  202  in such a manner that grinding wheel  102  may be moved toward and away from face gear work head  68  and grinding wheel  102  may move tangentially to face gear work head  68  as well. 
     Grinding head  100  is permitted to move along rails  259  to produce motion of the carriage  254  toward and away from the face gear work head  68 . The is a “feed” axis which is designated as the “V” axis. 
     Carriage  254  is also mounted on rails  252  to produce motion of the grinding wheel  102  in a tangential direction with respect to face gear  70 . This axis is designated as the “TF” axis. 
     Grinding table  258  is capable of pivoting carriage  254  about pivot  260 . This is the grinding wheel pivot axis and is designated as the “WT” axis. 
     Grinding wheel  102  rotates about an axis designated as axis “C” and is driven by motor  262  which is integrally mounted on carriage  254 . Grinding wheel  102  has a predetermined profile inscribed on its surface as shown in FIGS. 10 and 11. 
     During the initial set up of the machine  200 , axes “TF” and “WT” are set with respect to the tooth configuration already existing on face gear  70  and locked. (Face gear  70  has already undergone tooth shaping and surface hardening operations before being mounted in machine  200 .) During the initial approach of the grinding wheel  102  to face gear  70 , motor  262  is rotating the grinding wheel  102  about axis “C” and the carriage  254  is fed along the “V” axis toward face gear  70  until the desired grinding position is reached. The face gear table  214  undergoes controlled movement along the feed axis “W” until the grinding wheel has moved sufficiently so that the entire tooth face  71  of face gear  70  has been traversed by grinding wheel  102 . The grinding wheel  102  is then moved slightly toward table  214  and the grinding operation is repeated until the desired depth of the tooth form and shape is generated. 
     A rotary diamond dressing tool assembly  264  is also mounted on grinding table  258  on rails  256 . The assembly  264  includes a rotary device  266  which rotates a diamond impregnated disc  280  (see FIG.  10 ). The disc  280  is used to generate (by abrasion) a prescribed form  268  in grinding wheel  102  (see FIG.  11 ). Device  266  is adjustable in height and angle on and about post  270  on which device  266  is mounted. The entire dresser assembly  264  is mounted on table  258  so as to be capable of controlled motion in three axes. A first axis of motion allows the dresser assembly mounted on feed table  274  to move backwards and forwards along rails  272  away from and towards grinding wheel  102 . This axis is designated as the “Y” axis. 
     Movement of the dresser tool along rails  256  in a translatory fashion (parallel to grinding wheel  102 ) is designated as the “X” axis. Movement of the dresser wheel  280  about post  270  in an angular fashion will define the angular axis “A”. 
     The grinding wheel profile  268  demands that the movement of the feed table assembly  274  for the dresser assembly  264  be synchronized with the rotation of grinding wheel  102  in order that disc  280  of the dresser assembly  264  properly meshes with the profile  268  of grinding wheel  102 . 
     The grinding operation of the partially completed and surface hardened face gear  70  is as follows: 
     The rotating table  72  is manually set to a predetermined tilt (WTT) and swivel (WTS) setting and these positions are locked. The partially finished gear is mounted on the face plate  72  so as to have a predetermined angular position on axis “B”. 
     The grinding wheel carriage  254  is set at the appropriate angle on the pivot axis WT and locked. Carriage  254  is moved along rails  252  until the grinding wheel  102  is set at a predetermined position on the “TF” axis with respect to face gear  70  and locked in this position. 
     The rotating grinding wheel  102  is now moved along the “V” “feed” axis to move toward the partially finished rotating face gear  70  until a desired face gear grinding position is achieved. 
     Work table  214  is now moved vertically along rails  216  to permit the grinding wheel  102  to traverse the entire face of the gear  70  as the grinding operation continues. This process is repeated in a series of grinding passes until the desired depth and tooth configuration is generated in face gear  70 . 
     Periodically during the grinding operation, the profile of the grinding wheel  102  must be restored. At this time, the grinding wheel  102  is retracted from the face gear  70  and the dresser assembly  264  is brought into position on rails  272  and  256  to engage grinding wheel  102  and to restore the profile  268  on wheel  102  to its original profile. 
     The grinding disc  280  is engaged with grinding wheel  102  in accordance with CNC control to move in a controlled manner to restore the profile  268  to wheel  102  to its required dimensional shape. 
     FIG. 15 shows the apparatus of FIG. 9 modified to permit the finish grinding of a pinion  300 . Pinion  300 , in this instance, is a tapered spur gear pinion. Grinding wheel  302  now carries a significantly different profile from the profile inscribed in the surface of grinding wheel  102  for face gear grinding. The profile inscribed on the surface of wheel  302  is similar to that shown in FIG.  3 . 
     The face gear work head  68  of FIG. 9 has been replaced with work table  304  which supports and rotates pinion  300  during grinding. 
     Tapered pinion  300  rotates about an axis designated as “B 1 ” in an angular motion synchronized with grinding wheel  302 . The work table assembly  304  is capable of vertical translatory motion along rails  216  designated the “W” axis as previously in FIG.  9 . The motion of the grinding wheel  302  along the “V” axis is CNC controlled; the movement of the pinion  300  along the “W” axis is CNC controlled. It will be obvious to those skilled in the art that the motion of the grinding wheel in the “V” axis must be carefully coordinated with the motion of table  304  along rails  216  in order to produce the tapered spur gear pinion  300 . 
     The dresser apparatus for grinding wheel  302  is required as previously, but is omitted from FIG. 15 for reasons of clarity. For the reader&#39;s convenience, an Axis Definition Table is set out below: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 AXIS 
                 DEFINITION 
                 CONTROL 
               
               
                   
               
             
             
               
                 C 
                 Grinding Wheel 102 (302) Rotation 
                 CNC 
               
               
                 V 
                 Grinding Wheel 102 (302) in Feed 
                 CNC 
               
               
                 WT 
                 Grinding Wheel 102 (302) Tilt 
                 Manual 
               
               
                 TF 
                 Grinding Wheel 102 (302) Tangential Feed 
                 Manual 
               
               
                 B 
                 Rotating Table 72 Rotation (Face Gears) 
                 CNC 
               
               
                 B1 
                 Driving head 318 Rotation (Tapered 
                 CNC 
               
               
                   
                 Spur Gear Pinion) 
               
               
                 W 
                 Work Table 214 Axial Feed 
                 CNC 
               
               
                 WTS 
                 Work Head 212 (68, 304) Swivel 
                 Manual 
               
               
                 WTT 
                 Work Table 78 Tilt 
                 Manual 
               
               
                 A 
                 Dresser Tool 264 Rotary Feed 
                 CNC 
               
               
                 X 
                 Dresser Tool 264 Cross Feed 
                 CNC 
               
               
                 Y 
                 Dresser Tool 264 In Feed 
                 CNC 
               
               
                 DH 
                 Dresser Tool 264 Height 
                 Manual 
               
               
                 DT 
                 Dresser Tool 264 Tilt 
                 Manual 
               
               
                   
               
             
          
         
       
     
     Basic Operation of the Face Gear Grinding Machine  200   
     This machine  200  utilizes a CNC system that enables the axes under its control to be moved in a predetermined manner via a set of instructions in a program. Numerous programs will be created to control the dressing cycle and gear grinding cycle of the machine  200  for different configurations of gears. The CNC control enables the axes of motion to be continually synchronized even when switching between the dressing and grinding cycles. 
     Manual Settings 
     The work table  212  swivel “WTS” is usually set in the vertical position and locked. 
     The work table  214  tilt “WTT” is set to the required Face Gear face angle and locked. 
     Grinding wheel  102  ( 302 ) tilt “WT” is set for lead angle compensation. 
     The grinding wheel tangential feed “TF” is adjusted to center the wheel with respect to the central axis of the gear. 
     Dresser rotary device  266  tilt is set for angular clearance “DT” and diamond disc  280 /grinding wheel  102  ( 302 ) center line height “DH”. 
     These settings will not be adjusted while grinding, only when the gear configuration changes. 
     Grinding Wheel Dressings CNC Controlled 
     CNC programs stored in the memory of the CNC control are selected to control this process. These programs command the motion of dresser axes X, Y, A, and grinding wheel  102  ( 302 ) axis C in a prescribed manner to generate the required form on the grinding wheel (FIG. 11 work profile  268 ). These programs control the speed and direction of rotation of the grinding wheel  102  ( 302 ) with respect to the speed and direction of motion of the dresser assembly  264 , axes X, Y and A. 
     Gear Grinding, CNC Controlled 
     Via the CNC and the selected program the speed of rotation of the grinding wheel  102  ( 302 ) (axis C) relative to the speed of rotation of the gear  70  (axis B) being ground is controlled. This relationship is controlled via an electronic gearbox, which is a feature of the CNC. It is an important feature as the grinding process simulates the meshing of a worm gear which is the Grinding Wheel  102  ( 302 ) with a face gear such as  70  which is the gear being finish ground. Also via the program and CNC, the following functions are also controlled: 
     Depth of Cut (axis V)—infeed of grinding wheel  102  ( 302 ) to workpiece (Face Gear  70 ), 
     Vertical Feed of workpiece across grinding wheel  102  ( 302 ) (axis W), 
     Diamond Disc  280  Speed, 
     Dimensional offsets and adjustments, 
     Activation of periodic re-dressing of the grinding wheel  102  ( 302 ), 
     Coolant on/off, and Machine lubrication. 
     An alternative embodiment of this invention will now be described using FIGS. 16-18. In this embodiment, the grinding apparatus is physically much the same as apparatus previously described. The apparatus of FIGS. 16-18 is simplified somewhat in that the apparatus associated with the work table tilt along the WTT axis is now omitted. In order to provide the required tooth profile for a convex ( 70 ) or a concave ( 106 ) face gear mounted on the work table, two axis of motion are required for moving the grinding wheel along the “V” axis as the face gear is vertically moved up and down on its “W” axis. Motion in both these axes must be carefully coordinated by CNC control as those skilled in the art will know. 
     FIG. 16 is a plan view of the modified apparatus  400  for producing the desired tooth configuration on face gear  70 . 
     Modified face gear apparatus comprises the same base  202  which is shown in FIG.  9 . Work table  414  (See FIG. 17) is driven by a drive motor  222  to move up and down along rails  216  (along the “W” axis) in a vertical plane. Face gear  70  is mounted on face gear rotating table  407  which is driven by a CNC drive motor (similar to drive motor  218  of FIG. 9) for rotation of face gear  70  about the “B” axis. 
     Grinding wheel carriage  254  is confined to move in a translationary fashion along rails  256  along the “TF” axis. The grinding wheel carriage is also permitted to moved back and forth along rails  259  (“V” axis) as driven by drive motor  261 . It is this motion which must be very closely controlled and coordinated with work table motion along rails  216  during a grinding operation because the face plane  71  of gear  70  is no longer in a vertical plane at the grinding contact area. 
     In this instance the profile of grinding wheel  102  is exactly the same as shown in FIG.  11  and the function and operation of dressing disc  200  is exactly the same as shown in FIGS. 9 and 10. 
     Thus the hardware of FIGS. 16-18 is somewhat simplified but an increasing amount of software is required to control the motion of grinding wheel  102 . 
     Examples of the composition of the basic material for gear  70  or pinion  300  which may be used successfully to accomplish this invention is: 
     (a) SAE 9310 STL having components: 
     Iron—94.765% 
     Nickel—3.25% 
     Chromium—1.20% 
     Manganese—0.55% 
     Molybdenum—0.11% 
     Carbon—0.10% 
     Silicon—0.025% max. or, 
     (b) PYROWEAR ALLOY 53 having the following components: 
     Iron—90.2% 
     Molybdenum—3.25% 
     Copper—2.00% 
     Nickel—2.00% 
     Chromium—1.00% 
     Silicon—1.00% 
     Carbon—0.1% 
     Vanadium—0.1% 
     FIGS. 19 and 20 have been added to more clearly illustrate the orientation of the three major components in a face gear and a pinion gear grinding operation. The various axes about which component motion takes place are clearly shown in these figures.