Abstract:
A cutter system that is designed to create a continuous cutting true helix while having cutting inserts that are indexable on at least two cutting edges by rotating the cutting insert. High positive radial and axial rakes enable free cutting machining with a fine finish and low horsepower consumption. The back face of the insert is substantially flat and is used for face contact on lockup with a mounting pocket on the cutter body when the insert screw is tightened. The mounting pocket is designed for ease of manufacture to limit tolerance buildup to ensure repeatable insert positioning and to maintain accuracy for a fine cutting finish. The insert screw hole is placed in the cross hole location for allowing an unobstructed cutting face and a larger diameter center core in the cutter body. The larger core creates maximum strength and allows longer cutting lengths. Prior to grinding, the insert blank can be used for multiple diameters of cutters. After grinding the insert blank, the inserts are made specific to the cutting diameter for which they were ground or a compromised grind may be employed for use with multiple cutting diameters.

Description:
CROSS-NOTING TO RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 10/161,489, entitled True Helical Cutter System, filed on May 31, 2002, the entire contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mill and milling cutters and cutting inserts used thereon, and in particular to a helical cutter system that includes a cutter body with indexable helical cutting inserts. 
     2. Description of the Related Art 
     Currently, the use of an indexable insert is not the first choice for small machine tools because the spindles on such small machines produce relatively lower horsepower and torque than larger machine tools. Because current cutting insert designs need more power to cut effectively, small machine tools are typically relegated to using solid end mill cutters and shell end mill cutters. However, solid end mill cutters and shell end mill cutters wear as they lose diameter, and if broken, can be entirely scraped. In addition, the limited size of the cutters that can be used with indexable insert designs may result in a loss of productivity. 
     The inventor of the present invention has recognized these and other problems associated with end mill cutters, such as solid end mill cutters and shell end mill cutters, which utilize a helical cutting edge geometry. 
     SUMMARY OF THE INVENTION 
     To solve these problems, the present invention provides an improved cutter body that utilizes an indexable cutting insert design that has at least two indexable cutting edges. High positive axial and radial rake angles of the improved indexable cutting insert design uses less power and torque than conventional inserts, thereby allowing smoother cutting action and increased feed rates that would have previously stalled a smaller machine tool. In addition, the cutting insert of the invention can be used in larger cutters with an increased number of cutting edges to increase productivity on both small and large machine tools. Further, the only scrap is the cutting insert and not the entire cutter body, thereby minimizing production costs as compared to conventional designs. 
     The present invention comprises an indexable cutting insert that includes a flat back that is held in a mounting pocket of a cutter body. The mounting pocket can be designed for ease of manufacture and repeatability. Stub length tooling may be used for rigid setups and lower cost. The cutting insert is located in the mounting pocket on two outboard walls. The cutting insert is secured to the cutter body by use of a screw in a cross hole fashion. The face of the cutting insert has a helical cutting edge on two sides and can be indexed by rotating the cutting insert approximately 180 degrees. With the use of the cutting insert of the invention, the cutter body has a maximum core diameter for strength and rigidity, thereby minimizing tool deflection and extending the life of the cutter body. The cutting insert of the invention can be used in a variety of milling cutter body designs, such as end mill cutters, shell end mill cutters, or the like. 
     Various aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side perspective view of a helical end mill cutter with improved cutting inserts according to an embodiment of the invention; 
     FIG. 2 is a side perspective view of the helical end mill cutter head with the cutting inserts removed; 
     FIG. 3 is a top perspective view of an improved cutting insert according to an embodiment of the invention; 
     FIG. 4 is a side perspective view of the cutting insert of FIG. 3; 
     FIG. 5 is another side perspective view of the cutting insert of FIG. 3; 
     FIG. 6 is another side perspective view of the cutting insert of FIG. 3; 
     FIG. 7 is a perspective view of the bottom of the cutting insert of FIG. 3; 
     FIG. 8 is a side perspective view of the bottom of the cutting insert of FIG. 3; 
     FIG. 9 is a another side perspective view of the cutting insert of FIG. 3; 
     FIG. 10 is a diagram showing the true helix of the cutting inserts of the invention; 
     FIG. 11 is a side perspective view of a helical shell end mill cutter body with the improved cutting inserts of the invention; and 
     FIG. 12 is a side perspective view of another end mill cutter body with the improved cutting inserts of invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, an improved cutter system, shown generally at  10 , includes a milling cutter body  12  with improved cutting inserts  14  that are indexable on at least two cutting edges. The milling cutter body  12  is embodied as a helical end mill which includes the plurality of general milling inserts  14  for ramping, circle interpolating, facing and end milling. Although the improved cutting inserts  14  are shown in a helical end mill embodiment, the improved cuttings inserts  14  are designed for use in any type of milling, such as shell end milling, face milling, fly cutting, or the like. In addition, several of the concepts described below on the helical mill including overlapping inserts by offsetting, staggering or other methods are also designed for use on other types of milling cutters. 
     The milling cutter body  12  is of an elongated and generally cylindrical shape. The milling cutter body  12  comprises a shank  16  and a head  18 . The shank  16  is configured so as to be capable of insertion and securing within the spindle of a milling machine (not shown) as is well known in the art. The shank  16  may be of any shape or design so as to be capable of this insertion and securing. Such designs include, but are not limited to, V-flange, taper, shell mill mount, and Weldon shank. 
     The head  18  is generally a cylindrical or substantially cylindrical body or shaft extending axially from the shank  16  to an end face  20 , thereby defining an exterior surface  22  therebetween. The exterior surface  22  of the head  18  preferably includes a plurality of helical chip grooves  24  and  26 . It will be appreciated that the invention is not limited by the number of helical chip grooves. For example, in the illustrated embodiment, four grooves out of a total of six grooves are shown in FIG. 1, although any number of helical grooves are contemplated by the invention. Each chip groove  24  and  26  is preferably cut into the exterior surface  22  in a helical or spiral manner that extends from the end face  20  to substantially the shank  16 . Each chip groove  24  and  26  is preferably located between a carved out flute area on which a helical grouping of cutting inserts  14  can be mounted thereon. For example, in the illustrated embodiment, the chip groove  24  is preferably located between the helical grouping  48  of a flute area  28  and the helical grouping  49  of a flute area  29 . Similarly, the chip groove  26  is preferably located between the helical grouping  49  of the flute area  29  and the helical grouping  49  of a flute area  30 . Each flute area  28 ,  29  and  30  spirals along the exterior surface  22  such that any cross sectional point thereon is substantially radial to a central axis (in the direction of the z-axis) of the substantially cylindrical shank  16 . 
     As best shown in FIG. 2, a plurality of pocket faces  32  are located along each flute area  28 ,  29  and  30 . Each pocket face  32  includes a mounting pocket  34  with a threaded hole  36  therein. It should be noted that configuration of the mounting pocket  34  substantially conforms to the configuration of the insert  14 . Thus, in the illustrated embodiment, opposed walls  34   a  and  34   b  of each mounting pocket  34  are generally parallel to each other. Each mounting pocket  34  also includes a back wall  34   c  to provide a three-point mounting system in which the cutting insert  14  positively engages the pocket face  32 , the side wall  34   a  and the back wall  34   c  when the cutting insert  14  is positively secured within the mounting pocket  34 . A relief  38  is located in one corner of each mounting pocket  34  formed by the side wall  34   a  and the back wall  34   c  to provide a locating surface and prevent the insert  14  from binding with the cutter head  18 . If desirable, another relief  38  can be located in the other corner of the mounting pocket  34  formed by the other side wall  34   b  and the back wall  34   c , as shown in the illustrated embodiment. The relief  38  also provides clearance for preventing the insert  14  from binding, as well as protecting the cutting edge of each insert  14  that is not being used from chipping or other damage. 
     Referring now to FIGS. 3-9, each pocket face  32  is adapted to receive a cutting insert, such as cutting insert  14 . Specifically, each cutting insert  14  includes a back face  40  that mates with the mounting pocket  34 . The mounting pocket  34  is designed for ease of manufacture to limit tolerance buildup, thereby ensuring repeatable insert positioning while maintaining accuracy and a fine cutting finish. After the insert  14  is seated or mated in the mounting pocket  34 , the insert  14  is tightly secured to the mounting pocket  34  by a locking fastener  44  (shown in FIG.  1 ), such as an Allen or Torx screw that passes through a clearance hole  46  located in the cross hole location of the cutting insert  14  and threads into the threaded hole  36 . The clearance hole  46  includes a tapered counterbore  46 A, which is engaged by a corresponding tapered surface on the head of the locking fastener  44 , thereby allowing the insert to be tightly secured to the pocket face  32  as the locating fastener  44  pushes downward against the tapered counterbore  46 A. The location of the clearance hole  46  in the cross hole location of the cutting insert  14  allows an unobstructed cutting face and a larger diameter center core in the cutter body  12 , thereby creating maximum strength and allowing longer cutting lengths. 
     As described above and in accordance with one of the features of the invention, the inserts in adjacent groupings are staggered, that is in any given cross sectional plane through the shank  16 , the inserts on a grouping  48  overlap and preferably start and end in the mid-section of one of the inserts in an adjacent grouping  49 , as is best shown by the inserts toward the end face  20  in FIG.  1 . As shown in the illustrated embodiment, there is a one-to-one correspondence between the number of groupings and the number of flute areas. Although the staggering may be any overlap, it is preferable that the midpoint of any given insert is substantially centered between the inserts in the adjacent helical grouping as this configuration provides a continuous cut for the best peak shaving on the milled surface. The measurement of effective flute areas or flutes can be determined by how many flutes need to pass in order to cut one complete profile on the workpiece. Because the groupings  48 ,  49 ,  50  overlap in the manner described above, two flutes (or groupings of inserts) are needed to cut one profile. Thus, in the illustrated embodiment, the six groupings or flute areas define a three effective flute cutter system. 
     As shown the illustrated embodiment of FIGS. 3-9, the cutting insert  14  is approximately diamond in general shape and includes a front face or top surface  52 , a pair of opposed side walls or surfaces  54  and  56 , another pair of opposed side walls or surfaces  58  and  60 , the base surface or back face  40 . The top surface  52  includes a substantially flat central portion  52   a , a first curved facet surface  52   b , and a second curved facet surface  52   c  located on the opposite side of the central portion  52   a . The side wall  58  includes a first substantially flat faceted surface  58   a , and a second substantially flat faceted surface  58   b  having a smaller surface area than the faceted surface  58   a . Similarly, the opposite side wall  60  includes a first substantially flat faceted surface  60   a , and a second substantially flat faceted surface  60   b  having a smaller surface area than the faceted surface  60   a . The other two side walls  54  and  56 , and the back surface  40  are substantially flat. 
     Formed at the intersection between the top surface  52  and the side walls  54 ,  56 ,  58  and  60  are principally four edges, namely a pair of opposed and spaced apart edges  62  and  64 , and another pair of opposed and spaced apart edges  66  and  68 . At least one of the edges  62 ,  64 ,  66  and  68  is a cutting edge, and preferably at least the two opposite edges  66  and  68  are cutting edges, thereby allowing the insert to be indexable by rotating the cutting insert by approximately 180 degrees. The edges  66  and  68  preferably form an angle, θ, of approximately 30° with the central, longitudinal axis of the cutter body  12  (along the z-axis) to cut a true 30° helix about the cutting diameter of the cutter  10 , as best shown in FIG.  3 . Although only the edge  66  is shown in FIG. 3 to have an angle of approximately 30°, it should be realized that cutting edge  68  is substantially parallel to cutting edge  66 , and thus will also have an angle of approximately 30°. It will be appreciated that the invention is not limited by the angle of the cutting edges, but the invention can be practiced with any desirable angle for the cutting edges. For example, other shapes of inserts are contemplated that include helical cuts in the side walls  66  and  68  with an angle, θ, for the helix that ranges between 0° and 60°. 
     In accordance with one of the features of the invention, a helical cut face  70  is formed in two opposite side surfaces  58  and  60  to form a side face helix that creates a smooth cutting action as a solid helical end mill, unlike conventional inserts. In addition, the helical cut face  70  on the opposite side surfaces  58  and  60  allows the cutting insert  14  to be indexable on two sides by rotating the cutting insert  14  approximately 180 degrees. High positive radial and axial rake angles enable free cutting machining with a fine finish and low horsepower consumption. 
     In accordance with another of feature of the invention, the top surface  52  of the insert  14 , and in particular the curved facet surfaces  52   b  and  52   c  form a rounded or radiused top surface having a radius of curvature, R, as best shown in FIG.  6 . Preferably, the radius of curvature, R, is approximately equal to a cutting diameter of the milling body as shown in FIG.  10 . Because of the radius of curvature, R, the top surface  52  follows the curvature of the outer surface of the head  18  to provide a true helical cutting insert that follows the curvature of the outer surface of the head  18 , unlike conventional inserts with front faces or surfaces that are substantially flat. 
     It will be appreciated that the indexable cutting insert  14  of the present invention is not limited to the type of cutter body  12 , and that the invention can be practiced with other types of cutter body designs. For example, the indexable cutting insert  14  of the present invention can be utilized in a cutter system  80  that includes a shell end mill type of cutter body, shown generally at  82  in FIG.  10 . In another example, the indexable cutting insert  14  of the present invention can be utilized in a cutter system  90  that includes another type of end mill cutter body, commonly known as a “router,” shown generally at  92  in FIG.  11 . 
     As described above, the cutter system  10  of the invention is designed to create a continuous true helical cut. In addition, the cutter system  10  of the invention provides an indexable helical insert that is indexable on at least two cutting edges by rotating the insert 180 degrees. Thus, the cutter system  10  of the invention provides for a more cost-effective cutter system because indexing the insert maintains cutting diameter and edges, unlike scrapping the entire cutter when the insert is worn or broken in a conventional solid endmill design. 
     While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.