Abstract:
A cutter blade for use with a face hob type cutter for producing the teeth of spiral bevel and hypoid gear members by a continuous index, face hobbing process comprises a cutter blade shank having a cutting member provided at one end thereof. The cutting member includes a tooth side cutting edge having a given axial pressure angle, and a tooth topland cutting edge. The tooth topland cutting edge of the cutting member simultaneously forms a topland surface of the tooth of the gear member as the tooth is cut by the tooth side cutting edge of the cutting member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to cutter blades for the production of gears and, more particularly, to cutter blades for the face hobbing of parallel depth spiral bevel and hypoid gears.  
           [0003]    2. Description of the Prior Art  
           [0004]    Spiral bevel and hypoid gear pairs are conventionally produced utilizing either an intermittent index face milling method or a continuous indexing face hobbing method. While most gear set manufacturers currently use the face milling method, the face hobbing process has been recently adopted by some manufacturers, especially those manufacturing such gear sets for vehicular applications. In a face hobbing machine, a circular face hob type rotary cutter carrying a plurality of cutter blades mounted in groups, is utilized, and a workpiece (gear blank) and the cutter continuously rotate in a timed relationship until the entire part is completed. During the cutting process, the workpiece indexes in a rotary manner so that each successive cutter blade groups engaging successive tooth slots as the gear or pinion member is being cut. Advantageously, the face hobbing method produces uniform depth teeth, and parts are produced from the solid in one operation. The face hobbing method also requires fewer production steps and less production time than the face milling method.  
           [0005]    Normally, in an operation separate from, and preceding to, the tooth cutting operation, a topland surface of the gear is machined while processing a ring gear or pinion gear blank before cutting the gear teeth. As well known to those skilled in the art, the additional production step is generally disadvantageous with regard to cost, labor, quality control, and manufacturing flexibility.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention relates to a gear cutter blade for use with a face hob type cutter for producing teeth of spiral bevel and hypoid gear members by a continuous index, face hobbing process. The gear cutter blade comprises a cutter blade shank adapted to be mounted on a rotatable cutter body, and a cutting member provided at one end of the blade shank. The cutting member includes a tooth side cutting edge having a given axial pressure angle, and a topland cutting edge adjacent the tooth side cutting edge. The topland cutting edge of the cutting member simultaneously forms a topland surface of the tooth of the gear member as a tooth side surface is cut by the tooth side cutting edge of the cutting member.  
           [0007]    Machining the topland surface simultaneously with the cutting the tooth side surface permits to reduce or completely eliminate the need to finish topland surfaces of the ring gears or pinions. Moreover, the elimination of a subsequent manufacturing operation improves the consistency and accuracy of the gear tooth whole depth, and part quality, as well as reduces manufacturing costs. In addition, the gear cutter blade of the present invention allows for greater manufacturing flexibility, as the cutting edge dimensions can be easily modified, and provides an ability to machine near-net forged parts without requiring precision control of the topland area of machining with an interrupted cut during a blanking operation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein:  
         [0009]    [0009]FIG. 1 is a plan view of a front face of a gear cutter blade in accordance with the preferred embodiment of the present invention and a portion of a gear member on which the cutter blade is operating;  
         [0010]    [0010]FIG. 2 is a partial perspective view of a ring gear;  
         [0011]    [0011]FIG. 3 is a view of the cutter blade of FIG. 1 illustrating geometry of a cutting edge thereof in accordance with the present invention;  
         [0012]    [0012]FIG. 4 illustrates the arrangement of a workpiece (a ring gear) and a cutter in a face hobbing process used in the present invention;  
         [0013]    [0013]FIG. 5 is a plan view of the front face of the gear cutter blade in accordance with the alternative embodiment of the present invention dimensioned to cut an entire topland surface of a gear tooth of the gear member. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    The preferred embodiment of the present invention will now be described with the reference to accompanying drawings.  
         [0015]    Referring to FIGS. 1 and 3, the reference numeral  10  represents a gear-cutting blade in accordance with the present invention and the reference numeral  12  depicts a portion of a ring gear member  12  having a plurality of gear teeth  14  on which the gear cutting blade  10  is operating during a face hobbing process. Each gear tooth  14  includes opposite side surfaces  16  and a topland surface  18 . The reference numeral A represents a whole depth of the gear teeth  14 . The gear member  12  is also illustrated separately in detail in FIG. 2.  
         [0016]    A plurality of the cutter blades  10  is mounted at a selected radius and depth on a rotatable, circular cutter head  2  of a gear cutter assembly  1  as part of a face hobbing cutter system, as illustrated in FIG. 4. Examples of such systems include Tri-Ac®, Pentac®, and Spiron®. During a face hobbing process, the gear member  12  (workpiece), mounted to a workpiece holder (not shown), and the cutter head  2  continuously rotate, with successive cutter blades  10  engaging successive tooth slots as the gear member  12  being cut. FIG. 4 also shows the face hobbing process and the relative interaction of the gear member  12  (workpiece), in this case the ring gear, as the gear teeth  14  are successfully cut by the cutter blades  10  mounted on the cutter head  2 . The gear member  12  and the cutter head  2  each rotate in the direction of the arrows indicated.  
         [0017]    The cutter blades  10  are generally mounted on the cutter head  2  of the gear cutter assembly in groups. For instance, in the systems offered by The Gleason Works, the cutter blades are arranged on the cutter head in groups of two, each cutter blade pair operating on a different tooth space. In other systems, the cutter blades may be arranged on the cutter head in groups of three. In such systems, there is an inner, outer and rougher blade, which operate to cut the sides and bottom of each tooth space, respectively. The rougher cutter blade is generally provided with both inner and outer cutting edges. The cutter blade  10  illustrated in the drawings is one of the side cutting blades suitable for use with either a two blade or a three blade group.  
         [0018]    While the ring gear member  12  is illustrated in FIGS. 1 and 2, the gear cutter blade of the present invention is equally applicable to the face hobbing of the pinion member of a gear set.  
         [0019]    The face hobbing cutting systems generally utilize cutter blades, which are profile ground at the end user&#39;s facility from uniform blanks to afford a variety of specified configurations. As illustrated in FIGS. 1 and 3, the cutter blade  10  includes a shank  20  and a cutting member  22  formed at a distal end  21  thereof. A front face of the cutting member  22  of each cutter blade  10  is provided, generally only on one side thereof, with a cutting edge  24 . The cutting edge  24  comprises a first section  26  for cutting the side surface  16  of the gear teeth  14 , and a second section  28  for cutting the top surface  18  of the gear teeth  14 . Thus, the first section  26  defines a tooth side cutting edge and the second section  28  defines a tooth topland cutting edge.  
         [0020]    The first section  26  of the cutting edge  24  extends from a tip  30  of the cutting member  22  at a predetermined axial pressure angle B. The axial pressure angle B of the first section  26  of the cutting edge  24  obviously depends on the angle desired for the sides of the gear teeth. As used herein, “axial pressure angle” is defined as the angle between the first section  26  of the cutting edge  24  (or tooth profile) and a central axis  11  of the cutter blade  10 .  
         [0021]    The second section  28  of the cutting edge  24  is a substantially straight line perpendicular to the central axis  11  of the cutter blade  10 , and is characterized by a width W, as illustrated in FIG. 3.  
         [0022]    A distance C from the tip  30  of the cutting member  22  to an intersection of the first section  26  and the second section  28  of the cutting edge  24  is a height of the first section  26  of the cutting edge  24  of the cutting member  22 . The distance C is substantially equal to the whole depth A of the gear teeth  14 .  
         [0023]    By modifying the specified blade grinding parameters for forming the cutter blade  10  from a blank, configuration of the cutting edge  24  can be altered to incorporate the second section  28 .  
         [0024]    Thus, the gear cutter blade  10  of the present invention cuts the side surface  16  of the gear tooth  14  by means of the first section  26  of the cutting edge  24 , and simultaneously forms a substantial portion of the topland surface  18  of the gear tooth  14  by means of the second section  28  of the cutting edge  24 . Alternatively, the second section  28  of the cutting edge  24  is dimensioned to cut an entire topland surface  18  of the gear tooth  14 , as illustrated in FIG. 6.  
         [0025]    The cutter blades  10  of the present invention are secured to the circular cutter head  2  in the conventional manner, and the face hobbing system is operated in the same manner as if conventional cutter blades were employed. However, during a face hobbing process of the present invention, as cutter head  2  continuously rotates, the successive cutter blades  10  cut the side surfaces  16  of the gear teeth  14  by means of the first section  26  of the cutting edge  24 , and simultaneously machines at least a substantial portion of the topland surface  18  of the gear tooth  14  by means of the second section  28  of the cutting edge  24 .  
         [0026]    Therefore, with the gear cutter blade  10  of the present invention, the topland surface is machined on the teeth of a gear or pinion member simultaneously with the tooth side cutting operation. This permits to reduce or completely eliminate the need to finish topland surfaces of the ring gears or pinions. Moreover, the elimination of a subsequent manufacturing operation improves the consistency and accuracy of the gear tooth whole depth, and part quality, as well as reduces manufacturing costs. In addition, the gear cutter blade of the present invention allows for greater manufacturing flexibility, as the cutting edge dimensions can be easily modified, and provides an ability to machine near-net forged parts without requiring precision control of the topland area of machining with an interrupted cut during a blanking operation.  
         [0027]    As an example of a working embodiment of the gear cutter blade of the present invention, gear cutting tools having the following characteristics have been designed:  
         [0028]    Material: High Speed Steel or Carbide;  
         [0029]    Axial Pressure Angle B: 5° to 35°;  
         [0030]    Distance C: 0.150″ to over 1.000″;  
         [0031]    Width W: 0.030″ to 0.200″.  
         [0032]    The foregoing description of the preferred embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.