Abstract:
A gear rolling machine in which a work gear and a conjugate gear-like rolling die are rotated in tight mesh with relative radial pressure of metal deforming intensity applied between the rotating members. The radial feed which applies the pressure is applied by a power train which includes a worm-worm gear combination driving a screw shaft-nut combination. After maximum pressure has been applied, the center distance is reduced by limited predetermined axial movement of the worm, without rotation, in which the worm acts as a rack to provide a predetermined limited rotation of the worm gear, and hence of the screw-nut combination.

Description:
BRIEF SUMMARY OF THE INVENTION 
     In recent years a method of finishing gears by a metal deforming rolling operation has come into widespread use, as indicated by DiPonio U.S. Pat. No. 3,362,059, assigned to the Ford Motor Company, and Loos U.S. Pat. No. 3,709,015, assigned to Carl Hurth Company, a German manufacturer. 
     In this operation a hard steel die in the form of a gear is rotated in tight mesh and under metal deforming pressure conditions with a work gear, to which the die is conjugate. The metal deforming pressure is the result of a relative radial approach between the die and tool while they are rotated in mesh with their axes at least substantially parallel. Forces as great as 60,000 pounds may be applied to a movable die or work support. 
     It has been found that desirable results in surface finish, particularly in the elimination of very small metal particles displaced or partly separated from the surfaces of the gear teeth, are obtained when the rolling cycle comprises relative radial depth feed to provide a small reduction in size of the work gear, followed by a brief dwell in which the gear and die are maintained at a constant center distance, followed by a small incremental increase in center distance between the gear and die while rotation is continued. This increase in center distance will vary for different size gears, but in general may be on the order of 0.001&#34;. The increase in center distance is abrupt, and the gear and die are rotated for at least several revolutions while the increased center distance is maintained constant. 
     The present invention is directed to a novel feed apparatus for applying the requisite forces to a movable gear or tool slide to produce a cold flow of metal in the teeth of the gear, and in providing a very accurately controlled brief increase in the center distance between the gear and die during continued rotation as the final phase of the rolling operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation of the gear rolling machine. 
     FIG. 2 is a side elevation of the machine. 
     FIG. 3 is an enlarged partly sectioned elevation of the infeed mechanism. 
     FIG. 4 is a plan view of the mechanism shown in FIG. 3. 
    
    
     DETAILED DESCRIPTION 
     The gear rolling machine is seen in FIGS. 1 and 2. It comprises a frame of C-shape having a vertical column 10, a forwardly projecting base portion 12 at the bottom of the column, and a forwardly projecting head portion 14 at the top of the column overlying the base portion 12. 
     Vertically movable on guideways indicated at 16 is a knee or slide 18 which carries rugged stocks 20 for supporting a work gear G for rotation in mesh with a conjugate hardened steel die D. 
     Motor means are provided in the head portion 14 and are connected in driving relation to the die D through gearing contained partly in head 14 and partly in a transmission housing 19 which supports the die. 
     The portion of the base 12 which is beneath head portion 14 comprises a conical pedestal 21 having a flat support plate 22 welded thereto. A feed nut 24 is bolted to plate 22, which cooperates with a lift screw 26 rotatably supported in vertically movable knee 18. Fixed to the upper end of the shaft 28 which at its lower end is formed to provide the lift screw is a worm gear 30. Rotation of the worm gear 30 relative to the stationary nut 24 of course results in vertical movement of the shaft 28. A heavy duty thrust bearing 32 transmits lifting force from shoulder 34 on the shaft to the knee 18. 
     Vertical movement of the knee 18 is derived from a hydraulic motor 36 having an output shaft 38 to which is fixed a drive pinion 40. The hydraulic motor has the characteristic that when the flow of hydraulic fluid is terminated, rotation of the output shaft is positively blocked. 
     Accordingly, the motor 36 constitutes blocking means for blocking rotation of said motor when the supply of fluid under pressure to motor 36 is terminated. 
     Mounted for rotation in a longitudinally slidable sleeve 42 is a shaft 44 having an enlarged intermediate portion constituting a worm 46 which is in mesh with the worm gear 30. Shaft 44 has a bearing 48 retained between a shoulder 50 on the shaft and an externally grooved collar 52 fastened to an end of sleeve 42 as shown in FIG. 4. Sleeve 42 is slidable longitudinally in a bore guideway 54 provided in housing 56. 
     Gear 57 is fixed to shaft 44 and is in mesh with pinion 40. 
     A cylinder 58 is pivoted to an ear 60 on housing 56, and an operating piston rod 62 is pivotally connected to one end of lever 64, which in turn is pivoted to a lug fixed to housing 56. The other end of lever 64 has rounded ears 68 which are received without clearance in the annular groove of collar 52. Lever 64 is apertured to receive a threaded stud 70 carrying an adjustable stop nut 72 limiting pivotal movement of lever 64 in one direction. A threaded adjustable abutment pin 74 provided with a jamb nut 76 is engageable with housing 56 to limit pivotal movement of lever 64 in the other direction. 
     When the supply of hydraulic fluid to motor 36 is terminated, its rotor is blocked and pinion 40 and gear 57 prevent rotation of worm 46. However worm 46 and its support sleeve 42 are axially slidable by a small adjustable increment as determined by stop nut 72 and abutment pin 74 when operated by cylinder 58. 
     The relative great force required to raise the knee 18 and to apply metal deforming pressure to the gear teeth is provided by the transmission in which mechanical advantage is derived from the pinion-gear combination 40, 57; the worm-worm gear combination 46, 30; and the screw-nut combination 26, 24. A machine capable of generating a lifting force of 66,000 pounds is easily obtained with a 5 H.P. hydraulic motor designed to operate with hydraulic fluid supplied at 750 P.S.I. Hydraulic fluid under pressure is supplied to motor 36 and causes gradual movement of said knee to take place with corresponding deformation of the teeth of the work gear during several rotations of the work gear. When the supply of actuating fluid to motor 36 is terminated, motor 36 is blocked and no further approach between the work gear and die takes place during several additional rotations of the work gear. Thereafter, while the work gear and die continue to rotate, fluid is admitted to cylinder 58 and an abrupt accurately predetermined axial shifting of worm 46 occurs to provide slight downward movement of knee 18 to relax the pressure between the work gear and die. 
     In operation, the work gear G is mounted on the knee 18 in mesh with die D, which is positively driven in rotation, and which rotates freely rotatable gear G. Motor 36 is energized by providing a flow of high pressure hydraulic fluid through the motor and screw shaft 26 is rotated, moving gear G into tight mesh with die D. Since the gear is freely rotatable, the metal deforming pressure between the teeth of the die and gear is applied substantially equally in total to both sides of the gear teeth. 
     Since the hydraulic motor is inherently non-positive in operation, its output shaft, once tight mesh is achieved, is permitted only as deformation of the metal in the gear teeth is achieved. The work gear, which is ordinarily steel, at first undergoes elastic deformation, and when its elastic limit is reached, undergoes plastic deformation. It will be noted that the instantaneous contact between die teeth and work gear teeth, disregarding deformation, is line contact. Due to deformation, it is in the form of a narrow band extending from end to end of the teeth. Moreover this line or band of contact on the gear teeth travels from root to crest, or vice versa, as the parts rotate. In addition, rolling contact takes place only at the pitch diameter, and the heavy pressure contact above and below the pitch diameter is a variable sliding contact, increasing in magnitude with increased distance from the pitch diameter. 
     Accordingly, the action on the gear teeth may be visualized as an ironing action progressing across the teeth between root and crest. As a result of this action, while the metal is generally displaced in an elastic and ultimately plastic flow, it is found that some metal particles may be separated or partly separated from the tooth surface. 
     In accordance with the present invention, supply of hydraulic fluid under pressure to the hydraulic motor is terminated, and the hydraulic fluid trapped in the motor provides a positive blocking of the output shaft against rotation, thus terminating infeed. 
     At this time, while rotation of the gear and die is continued, hydraulic fluid is supplied to cylinder 58 in the appropriate direction, and as a result worm 46 is shifted axially to act as a rack in mesh with worm gear 30 to provide a very small but positively controlled rotation of screw shaft 26, to lower the knee 18 by a definite increment. The precise amount of separation thus provided between the gear and die required in particular instances will be variable, but a movement on the order of about 0.001&#34; is typical. 
     It will be understood that this action terminates plastic deformation of metal in the gear teeth, but the teeth of the gear and die remain in tight mesh at a pressure which continues to cause elastic deformation. At this time it is believed that any particles separated or partly separated from the surfaces of the gear teeth are ironed or pressure welded back into the finished gear teeth surfaces. In any event, the rolled teeth obtained by this apparatus have a superior finish, and the presence of partially separated or loose particles is avoided. 
     While lifting forces of 60,000 and 66,000 pounds have been mentioned, it may be said in general terms that the lifting force, or total pressure acting between the teeth of the gear and die, are in excess of 50,000 pounds.