Patent Publication Number: US-6711817-B2

Title: Hypoid ring gear for differentials and method of producing the same

Description:
CROSS REFERENCE 
     This application is a continuation application of, and claims the priority benefit of, U.S. application Ser. No. 09/417,427 filed on Oct. 13, 1999 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a hypoid ring gear for FR (front engine rear drive) vehicle differentials and a method of producing the same. 
     This type of hypoid ring gear for differentials (hereinafter referred to as the hypoid ring gear) has heretofore been produced, as shown in FIG. 6, by heating a round rod blank A 1 , upset-forging it to form a first disk-like intermediate article A 2 , die-forging said first intermediate article A 2  to form a second intermediate article A 3  in the form of a bottom-closed annular body having substantially the same inner and outer diameters as the end product, punching out the bottom A 3 ′ of said second intermediate article A 3  to form a third intermediate article A 4  in the form of a bottom-opened annular body, normalizing and shot-blasting said third intermediate article A 4 , lathing said third intermediate article A 4  as by an NC lathe to form a fourth intermediate article A 5  in the form of a crude product, roughly gear-cutting said fourth intermediate article A 5  on a Gleason gear cutting machine for rough machining, and finish-gear-cutting it on a Gleason gear cutting machine for finish machining, thereby providing an end product A 6  having hypoid teeth g cut therein. 
     Since the conventional method of producing hypoid ring gears includes the step of directly die-forging the first disk-like intermediate article A 2  to form said second intermediate article A 3  in the form of a bottom-closed annular body having substantially the same inner and outer diameters as the end product A 6 , it needs a large-sized forge press. Besides this, it has to use two expensive Gleason gear cutting machines for cutting hypoid teeth g, thus presenting the drawback of the installation cost being very high. Further, since hypoid teeth g are formed by cutting, there are drawbacks in that the allowance for cutting (the amount to be lathed and the amount to be cut for tooth formation) increases, thus not only decreasing the yield of material but also prolonging the cutting time, thereby increasing the running cost. 
     Further, a hypoid ring gear produced by the conventional method has its hypoid teeth g formed by cutting, with the result that the flow of metal in the hypoid teeth g has been cut away by the cutter, thus decreasing the tooth surface strength. Therefore, a larger hypoid ring gear is required for transmission of a heavier load, thus presenting the drawback that the differential has to be increased in size. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed with the above drawback in the prior art in mind, and its object is to provide a hypoid ring for differentials and a method of producing the same, which are capable of reducing the installation cost and the running cost, minimizing the production cost and improving the tooth surface strength of the hypoid gear. 
     To achieve said object, the invention provides a method of producing hypoid ring gears for differentials, comprising the steps of upset-forging a round bar blank heated to a predetermined temperature to form a first disk-like intermediate article, die-forging said first intermediate article to form a second intermediate article in the form of a bottom-closed annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product, punching out the bottom of said second intermediate article to form a third intermediate article in the form of a bottom-opened annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product, shot-blasting said third intermediate article to remove the scale and then reheating it to a predetermined temperature and ring-rolling it to form a fourth intermediate article in the form of a crude product which is somewhat smaller in inner and outer diameters and somewhat larger in axial thickness than the end product, orbitally forging said fourth intermediate article to form a fifth intermediate article having hypoid teeth formed therein by orbital forging, normalizing and shot-blasting said fifth intermediate article to effect normalization and scale removal, punching out the internal burr formed on said fifth intermediate article during tooth forming operation based on orbital forging, and cold-coining it to form an end product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view explaining a process for producing hypoid ring gears for differentials according to the present invention; 
     FIG. 2 is a schematic explanatory view of a forge press used in the invention; 
     FIG. 3 is a schematic explanatory view of a rolling machine used in the invention; 
     FIG. 4 is a schematic explanatory view of an orbital forging machine used in the invention; 
     FIG. 5 is a schematic explanatory view of a punching machine used in the invention; and 
     FIG. 6 is a view explaining the conventional process for producing hypoid ring gears for differentials. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a process-explanatory view showing a method of producing hypoid ring gears according to the present invention. The method of producing hypoid ring gears according to the invention includes the steps of first heating a round bar blank W 1  cut to a fixed length to a predetermined temperature (e.g., 1,200° C.) by an induction heater, and upset-forging it by a forge press to form a first disk-like intermediate article W 2 . Then follows the step of die-forging said first intermediate article W 2  by a forge press to form a second intermediate article W 3  in the form of a bottom-closed annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product. Then follows the step of punching out the bottom W 3 ′ of said second intermediate article W 3  by a forge press to form a third intermediate article W 4  in the form of a bottom-opened annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product. Then follows the step of shot-blasting said third intermediate article W 4  to remove the scale and then reheating said third intermediate article W 4  to a predetermined temperature (e.g. 900-950° C.) by an induction heater and ring-rolling it by a ring-rolling machine to form a fourth intermediate article W 3  in the form of a crude product which is somewhat smaller in inner and outer diameters and somewhat larger in axial thickness than the end product. Then follows the step of orbitally forging said fourth intermediate article W 5  by an orbital forging machine to form a fifth intermediate article W 6  having hypoid teeth G formed therein by orbital forging. Then follows the step of normalizing and shot-blasting said fifth intermediate article W 6  to effect normalization and scale removal and then punching out by a punching machine the internal burr W 6 ′ formed on said fifth intermediate article W 6  during tooth forming operation based on orbital forging, and cold-coining it to form the end product W 7 . 
     The aforesaid forge press comprises a plurality of equispaced punches and dies operatively associated with each other to perform their forming operation, with a transfer feeder used to feed parts to be forged successively to one operating position of the punch and die. Thus, as shown in FIG. 2, a round bar blank W 1  heated to a predetermined temperature by an induction heater  1  is upset-forged using an upsetting set of punch  2  and die  3  to form a first disk-like intermediate article W 2 . This first intermediate article W 1  is die-formed by a punch  4  and a die  5  which are smaller in inner and outer diameters than the end product to form a second intermediate article W 3  in the form of a bottom-closed annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product. The bottom W 3 ′ of the second intermediate article W 3  is punched out by a punching-out set of punch  6  and die  7  to form a third intermediate article W 4  in the form of a bottom-opened body which is smaller in inner and outer diameters and larger in axial thickness than the end product. 
     The aforesaid rolling machine, as shown in FIG. 3, comprises a forming roll  8  supported for being driven for rotation and having on its inner peripheral surface a shape which is the same as the outer peripheral shape of the fourth intermediate article W 5 , a mandrel  9  supported for rotation and for radial slide movement and having on its outer peripheral surface a shape which is the same as the inner peripheral shape of the fourth intermediate article W 5 , and a pair of mandrel support rolls  10  for the radial sliding under pressure of the mandrel  9  through a pressure applying means (not shown), wherein with the third intermediate article W 4  held between the forming roll  8  and the mandrel  9 , the forming roll  8  is rotated to cause the contact rotation of the third intermediate article W 4  while the mandrel  9  is radially slid under pressure by the mandrel support rolls  10  to apply a radial holding pressure to the third intermediate article W 4 , whereby the latter is ring-rolled by the forming roll  8  and mandrel  9  to form the forth intermediate article W 5  which is somewhat smaller in inner and outer diameters and somewhat larger in axial thickness than the end product. 
     The aforesaid orbital forging machine, as shown in FIG. 4, comprises a pressure-forming die  11  having a pressure-forming surface  11   a  conforming in outer shape to the end product and installed so that it can be raised and lowered by pressure applying means (not shown), and a punch  12  having a conical pressing surface  12   a  and adapted to be rotated while orbiting along a circumference with its center axis included with respect to the center axis of the pressure-forming die  11 , the arrangement being such that with the fourth intermediate article W 5  fed into the pressure-forming die  11  and with the punch  12  rotating while orbiting along a circumference, the pressure-forming die  11  is raised to urge the fourth intermediate article W 5  against the pressing surface  12   a  of the punch  12 , whereupon the punch  12  locally urges the fourth intermediate article W 5  greater against the pressure-forming surface  11   a  of the pressure-forming die  11  to progressively circumferentially press it, thereby leaving the impression of the pressure-rolling surface  11   a  of the pressure-forming die  11  on the fourth intermediate article W 5 , thus forming the fifth intermediate article W 6  having hypoid teeth G formed therein by orbital forging. 
     The aforesaid punching machine, as shown in FIG. 5, comprises a die  13  having an inner shape conforming in outer shape to the end product and a punch  14  having a diameter which is the same as the inner diameter of the end product, the arrangement being such that the punch  14  is urged into the fifth intermediate article W 6  fed into the die  13 , whereby the fifth intermediate article W 6  has its inner burr W 6 ′, which is formed thereon during tooth forming operation based on orbital forging, punched out by the punch  14  and is cold-coined to provide the end product W 7 . 
     The hypoid ring gear producing method of the present invention includes the steps of forming the first disk-like intermediate article W 2  into the second intermediate article W 3  in the form of a bottom-closed body which is smaller in inner and outer diameters and larger in axial thickness than the end product, punching out the bottom W 3 ′ of the second intermediate article W 3  while securing the condition in which the inner and outer diameters are smaller than those of the end product and the axial thickness is larger than that of the end product, and ring-rolling it to form the fourth intermediate article W 5  in the form of a crude product which is somewhat smaller in inner and outer diameters and somewhat larger in axial thickness than the end product; therefore, the large-sized forge press is no longer necessary and the installation cost can be reduced. Further, the hypoid teeth G are generated by locally pressing the pressure-forming surface  11   a  of the pressure-forming die  11  against the fourth intermediate article W 5  so as to circumferentially and progressively press the press-rolling surface  11   a  of the pressure-forming die  11  against the fourth intermediate article W 5 , thereby leaving the impression of the pressure-rolling surface  11   a  of the pressure-forming die  11  on the fourth intermediate article W 5 ; therefore, as compared with the conventional tooth cutting using two Gleason gear cutting machines, the installation cost can be reduced while increasing the yield of material and reducing the processing time and the running cost. 
     Further, since the hypoid ring gear produced by the present production method has hypoid teeth G formed by orbital forging, the hypoid teeth G are formed with flow of grains extending along the tooth surface, so that the tooth surface strength is considerably increased as compared with that of hypoid teeth formed by cutting. Thus, a heavier load can be transmitted with a smaller hypoid gear, so that size-reduction of the differential is possible. Furthermore, as compared with the case of cutting teeth by a Gleason gear-cutting machine, the processing time can be reached and so can be the running cost. 
     As has been described so far, according to the present invention, it is possible to provide a method of producing hypoid ring gears which is capable of decreasing the installation cost and running cost and minimizing the production cost, and to provide a hypoid ring gear having the tooth surface strength of the hypoid teeth increased to the extent of enabling the differential to be reduced in size.