Abstract:
A cutting blade for face milling wherein the cutting blade is constructed to cut a predetermined final dimension of a tooth slot along a portion of the cutting end (i.e. the primary cutting edge portion) of the blade and to cut the remainder of the tooth slot at an amount less that the predetermined final dimension of the tooth slot along the remaining portion (i.e. the secondary cutting edge portion) of the cutting end. The construction of the inventive cutting blade provides sharing of the cutting load amongst the blade cutting edges and also provides sufficient clearance in the tooth slot whereby the cutting blade can be repositioned to allow truing of the cutter, particularly with respect to the primary portion.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to cutting blades for cutting gears and related toothed articles. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of bevel and hypoid gears it is well known to utilize face mill type cutters in both generating and non-generating gear cutting processes. In face mill cutters, cutting blades are arranged in the cutter head such that one tooth slot is formed with each cutting cycle (e.g. plunge, or feed-in and roll) of the cutter. The cutter must be withdrawn and the workpiece indexed to the next tooth slot position in order to form the next tooth slot. With face milling, all cutting blades of the face mill cutter pass through the tooth slot during the cycle until the desired slot geometry (and hence, tooth flank geometry) is formed. 
     Face milling tools include a plurality of blades projecting from a front face or periphery of a cutter head wherein the cutting blades are arranged in one or more concentric circles about an axis of rotation of the cutter head. Cutting blades may be of the type commonly referred to as stick-type or bar blades made of a length of bar stock (for example, U.S. Pat. No. 4,137,001 to Fountain; U.S. Pat. No. 4,575,285 to Blakesley; U.S. Pat. No. 6,120,217 to Stadtfeld et al.; or U.S. Pat. No. 3,760,476 to Kotthaus). Cutting blades may also be of the form-relieved type (for example, U.S. Pat. No. 3,192,604 to Whitmore or U.S. Pat. No. 3,268,980 to Blakesley et al.). Either type may be made of suitable material such as high speed steel (HSS) or carbide and the blades may have one or more surfaces coated with wear enhancing coatings such as TiN, TIAlN, AlTiN, etc. as is known by the artisan. 
     Typically in face mill cutters, a set of “inside” blades for cutting convex flanks of work gear teeth are arranged at a first radius from the cutter head axis, and a set of “outside” blades for cutting concave flanks within the same tooth space are arranged at a second larger radius. Examples of this type of cutter can be seen in U.S. Pat. No. 2,024,494 to Wildhaber or U.S. Pat. No. 4,137,001 to Fountain. In some cutters, separate bottom blades are included to cut the bottom of a tooth slot (e.g. U.S. Pat. No. 3,760,476 to Kotthaus) while in other cutters, the inside and outside cutting blades include cutting portions which also cut at the bottom of the tooth slot (for example, U.S. Pat. No. 4,278,370 to Spear). Alternatively, cutting blades that cut the convex side, concave side and the bottom of a tooth slot (i.e. the entire tooth slot) may also be utilized. Examples of this type of cutter are shown in U.S. Pat. No. 1,236,834 to Gleason; U.S. Pat. No. 1,667,299 to Wildhaber; or WO 2004/103624 to Ribbeck. 
     In producing gears with cutters having inside and outside cutting blades, uneven wear of the cutting blades is of significant concern as certain areas of the blades experience wear and break down earlier than other areas. With cutters having blades that cut the entire tooth slot, large chips tend to form which can result in chip flow problems and truing of such cutters cannot be accomplished since repositioning a cutting blade to true one cutting side of the cutting blade will also affect the position of other cutting side likely causing the other side to shift out of an optimal cutting position. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a cutting blade for face milling wherein the cutting blade is constructed to cut a predetermined final dimension of a tooth slot along a portion of the cutting end (i.e. the primary portion) of the blade and to cut the remainder of the tooth slot at an amount less that the predetermined final dimension of the tooth slot along the remaining portion of the cutting end (i.e. the secondary portion). The construction of the inventive cutting blade provides sharing of the cutting load amongst the blade cutting edges and also provides sufficient clearance in the tooth slot whereby the cutting blade can be repositioned to allow truing of the cutter, particularly with respect to the primary portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a face milling process to produce a gear. 
         FIG. 2  is a representative diagram of a gear tooth slot. 
         FIG. 3  illustrates the cutting positions of one type of prior art cutting blades for cutting a gear during face milling. 
         FIG. 4  illustrates a prior art cutting blade for cutting the entire tooth slot of a gear during face milling. 
         FIG. 5  shows an inventive cutting blade positioned to remove a portion of stock material from a tooth slot. 
         FIG. 6  shows an inventive cutting blade positioned to remove another portion of stock material from a tooth slot. 
         FIG. 7  shows the cutting positions of the cutting blades of  FIG. 5  and  FIG. 6  for cutting a gear during face milling. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The details of the present invention will now be discussed with reference to preferred embodiments which represent the invention by way of example only. In the drawings, the same reference numbers will be utilized to refer to like elements. 
       FIG. 1  depicts a face milling process utilizing inside and outside cutting blades. A tooth slot  2  is being formed between opposing tooth surfaces  4 ,  6  of adjacent teeth  8 ,  10  of a workpiece  20  such as, for example, a spiral bevel gear. A face mill cutter  22 , having alternating inside cutting blades  24  and outside cutting blades  26  (only a portion shown) arranged about a circle with a center C, rotates in direction R such that all cutting blades on the cutter pass through slot  2  as the cutter is fed relative to the workpiece to a predetermined full depth position. Inside cutting blades  24  cut the lengthwise convex shaped tooth surface  6  of tooth  10  while outside cutting blades  26  cut the lengthwise concave shaped tooth surface  4  of tooth  8 . 
       FIG. 2  illustrates the general cross sectional form of tooth slot  2  in a gear, such as the gear  20  of  FIG. 1 . The tooth slot  2  comprises opposite sides  4 ,  6  of adjacent teeth  8 ,  10  and further includes a bottom portion  12  and radius portions  14  and  16 . 
       FIG. 3  shows, in an overlapping view, the respective positions of inside cutting blades  24  and outside cutting blades  26  of the prior art as they pass sequentially through the slot  2 . It can be seen that inside cutting blade  24  includes a pressure angle cutting edge  30 , for cutting the convex surface  6  of tooth  10 , and further includes a tip edge  32  for cutting a portion of the bottom  12  of the slot  2  as well as a pressure radius edge portion  34  for cutting corresponding tooth slot radius  16 . Inside cutting blade  24  also includes clearance side  36  which does not cut a tooth surface. It can also be seen that outside cutting blade  26  includes a pressure angle cutting edge  40 , for cutting the concave surface  4  of tooth  8 , and further includes a tip edge  42  for cutting a portion of the bottom  12  of the slot  2  as well as a pressure radius edge portion  44  for cutting corresponding tooth slot radius  14 . Outside cutting blade  26  also includes a clearance side  46 . 
       FIG. 4  shows another prior art arrangement for face milling wherein each cutting blade  50  passing through a tooth slot  2  cuts both sides  4 ,  6  of the tooth slot as well as the bottom  12  and radius portions  14 ,  16  of the tooth slot  2 . In other words, the cutting blade of  FIG. 4  is a full-slot blade in that each cutting blade  50  cuts with both side cutting edges  52 ,  54  as well as with a tip cutting edge  56  and radius cutting edge portions  58 ,  59 . 
     As previously mentioned, with cutters having inside and outside cutting blades as shown in  FIG. 3 , uneven wear of the cutting blades is of significant concern as areas of the blades, such as the pressure radius cutting edge portions  34 ,  44  in particular, experience wear and break down earlier than other areas due to high cutting loads. With cutters having blades that cut the entire tooth slot, as in  FIG. 4  for example, large chips tend to form which can result in chip flow problems. Also, truing of such cutters cannot be accomplished since repositioning a cutting blade to true one cutting side edge of the cutting blade will also affect the other cutting side edge likely causing the other side to shift out of an optimal cutting position. Furthermore, cutting blades having cutting edges on both sides usually include a zero front rake angle which is not optimal for cutting. 
     The inventors have discovered that by including a more encompassing cutting region on a cutting blade, one that dimensionally approaches a full-slot cutting blade, but provides some clearance on one side of the cutting blade, uneven blade wear is reduced, the cutting blade remains capable of being trued, and a front rake angle and/or hook angle can be included. 
     The inventive cutting blade is shown in  FIGS. 5-7 . In  FIG. 5 , an inside cutting blade  60  is illustrated comprising a pressure angle cutting edge  62 , a pressure radius cutting edge portion  64  and tip cutting edge portion  66  (collectively, the “primary” cutting edge portion) which together cut, respectively, side  6 , radius  16  and the entire bottom portion  12  of slot  2  to a predetermined form or geometry, for example, a desired rough form (stock allowance left for subsequent grinding) or a desired finished form, either of which may be understood as being exemplified by the form of tooth slot  2  in  FIG. 2 . It is to be understood that the present invention is not limited to the slot  2  form but is applicable to any tooth slot form or geometry produced by generated or non-generated face milling. 
     The inventive cutting blade also includes another radius cutting portion  68  (i.e. the clearance radius cutting edge) that is of a dimension less than that required to form the predetermined radius  14 . Therefore, clearance radius cutting edge  68  “roughs out” the other tooth slot radius  14  to a form near to the predetermined form but leaves a distance  67  between the predetermined tooth slot radius position  14  and the clearance radius cutting edge  68  that comprises excess stock material. Cutting blade  60  also includes clearance side  69  which may also be a cutting edge, along all or part of its length, to rough cut the other flank surface  4  of tooth slot  2 . The clearance radius cutting edge  68  and any cutting edge on clearance side  69  define a “secondary” cutting edge portion. 
     Of course, the discussion above likewise applies to outside cutting blade  70  as shown in  FIG. 6  wherein the cutting blade comprises pressure angle cutting edge  72 , radius cutting edge  74  and tip cutting edge  76  (collectively, the “primary” cutting edge portion) which together cut, respectively, side  4 , radius  14  and the entire bottom portion  12  of slot  2  to a predetermined form or dimension, for example, a desired rough form (stock allowance left for subsequent grinding) or a desired finished form either of which also may be understood as being exemplified by the form of tooth slot  2  in  FIG. 2 . 
     The inventive cutting blade  70  also includes another radius cutting edge portion  78  (i.e. the clearance radius cutting edge) that is of a dimension less than that required to form the predetermined radius  16 . Therefore, clearance radius cutting edge  78  “roughs out” the other tooth slot radius  16  to a form near to the predetermined form but leaves a distance  77  between the predetermined tooth slot radius position  16  and the clearance radius cutting edge  78  that comprises excess stock material. Cutting blade  60  also includes clearance side  69  which may also be a cutting edge, along all or part of its length, to rough cut the other flank surface of tooth slot  2 . The clearance radius cutting edge  78  and any cutting edge on clearance side  79  define a “secondary” cutting edge portion. 
     The amount of stock material remaining (i.e. the distance) after cutting at the roughed-out tooth slot radius (e.g.  67  in  FIG. 5  or  77  in  FIG. 6 ) may be any amount based on parameters such as the gear and/or cutting blade design including adequate blade strength and/or cutting edge support, wear tendencies of the cutting blade, whether the gear will undergo a finishing operation, the amount of slot tolerance desired for truing, etc. However, a preferred amount of stock material remaining in the roughed-out tooth slot radius after cutting is about 0.002-0.0002 inch (0.051-0.0051 mm). 
     The clearance edges  69  and  79  are shown with different configurations but the present invention is not limited thereto. The clearance edge may be straight as shown in  FIG. 5 , curved, or may more closely follow the contour of the tooth profile surface, as shown in  FIG. 6 , along all or only a portion of the flank profile. If desired, the clearance cutting edge may be spaced from the tooth flank profile at a distance the same or about the same as that of distance  67  or  77 , as shown in phantom in  FIGS. 5 and 6  respectively, or it may vary in distance from the tooth flank profile surface. The clearance radius cutting edge ( 68 ,  78 ) as well as any clearance side cutting edge (e.g.  69 ,  79 ) do not produce the final desired gear geometry. 
     With the inventive configuration, the pressure angle cutting edge and pressure radius cutting edge cut a tooth slot in the same manner as is known in the art. However, the expanded tip edge as well as the clearance radius cutting edge, and optionally, the clearance cutting edge itself, provide for a balanced load on the cutting blades. For example, looking at prior art  FIG. 3 , as either inside or outside cutting blade passes through the tooth slot, nearly all cutting occurs at the pressure angle edge, radius edge portion and tip portion of a cutting blade. However, the region between a respective clearance edge and the opposite side of the tooth slot is not contacted by the cutting blade. The next cutting blade through the tooth slot encounters the same conditions but only on the other side of the slot. In either instance, cutting loads in the vicinity of the pressure side radius edge are high and blade-wear in this region is more prevalent. With the present invention, each cutting blade coming through the tooth slot removes about the same amount of stock material along a greater portion of the cutting blade. Hence, cutting loads are more even and reduced overall. 
     Also as stated above, with the secondary cutting edge portion not cutting to the final desired geometry of a tooth slot, sufficient blade clearance is provided (e.g. distance  67  or  77 ) such that the inventive cutting blade can be trued. The pressure angle cutting edge can be adjusted to a proper position without adversely affecting the function or purpose of the clearance cutting edge or clearance radius cutting edge (which is not possible with full-slot cutting blades) due to the diminished dimension of the cutting blade at the clearance radius cutting edges  68 ,  78 . The distance  67 ,  77  between the location of the actual cut and the predetermined or desired location of the tooth slot allow for movement of the cutting blade thus providing the opportunity for truing. 
     While the invention has been described with reference to preferred embodiments it is to be understood that the invention is not limited to the particulars thereof. The present invention is intended to include modifications which would be apparent to those skilled in the art to which the subject matter pertains without deviating from the spirit and scope of the appended claims.