Abstract:
A drill body of an indexable drill includes: a chip discharging groove which discharges chips produced by a cutting insert on a wall surface defining the chip discharging groove; and an insert attachment seat on which the cutting insert formed in a front end side, in a rotational axis direction, of a first wall surface of the chip discharging groove that faces a drill rotation direction is detachably mounted. A chip formation portion is formed which includes at least any of a plurality of protruding portions that protrudes outward from a second wall surface and a plurality of concave portions that is concave inward from the second wall surface, at least in a front end portion of the second wall surface of the chip discharging groove that faces a rear side of the drill rotation direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Continuation of International Patent Application No. PCT/JP2010/059134 filed May 28, 2010, which published as WO 2010/137701A1 on Dec. 2, 2010 and claims priority to Japanese Patent Application No. 2009-129767, filed May 29, 2009. The contents of the aforementioned applications are incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an indexable drill to which a cutting insert is detachably attached and to the drill body of the indexable drill. 
         [0004]    2. Description of the Related Art 
         [0005]    Japanese Patent Laid-Open No. H06-91416 (1994) discloses an indexable drill in which a plurality of rows of grooves extending in an axis direction of a drill body is formed on a wall surface of a chip discharging groove. Since only a plurality of surfaces formed by these rows of grooves makes contact with chips, a contact area between the wall surface and the chips is reduced, and a friction force produced between the both of them is reduced. Thus, it is possible to effectively facilitate the discharge of the chips, and it is therefore possible to smoothly discharge the chips when a hole having a relatively high ratio L/D between the depth L of the hole and the diameter D of the hole is processed or when a difficult-to-cut material such as a stainless steel or a mild steel is drilled. 
       SUMMARY OF THE INVENTION 
       [0006]    Incidentally, in the indexable drill disclosed in Japanese Patent Laid-Open No. H06-91416 (1994), although the plurality of rows of surfaces formed on the wall surface of the chip discharging groove allows the contact area between the wall surface of the chip discharging groove and the chips to be reduced, the friction produced between the plurality of rows of surfaces and the chips is increased, and the plurality of rows of surfaces is more likely to wear out. Hence, disadvantageously, the effect of smoothly discharging chips is unlikely to continue for a long period of time. 
         [0007]    The present invention is made to solve the foregoing problem; an object of the present invention is to provide an indexable drill that can smoothly discharge chips for a long period of time and a drill body. 
         [0008]    A drill body according to the present invention is a drill body of an indexable drill and includes: a chip discharging groove which is formed from a front end surface to a back end side in a rotational axis direction for discharging chips produced by a cutting insert; and an insert attachment seat on which the cutting insert formed on a front end side, in the rotational axis direction, of a first wall surface of the chip discharging groove that faces a drill rotation direction is detachably attached, wherein a chip formation portion is formed which includes at least any of a plurality of protruding portions that protrudes outward from a second wall surface and a plurality of concave portions that is concave inward from the second wall surface, among wall surfaces that define the chip discharging groove, at least in a front end portion of the second wall surface of the chip discharging groove that faces a rear side of the drill rotation direction. 
         [0009]    Preferably, the chip formation portion includes, in the vicinity of a surface thereof, a hardened layer that has a hardness greater than that of the other regions of the wall surface. 
         [0010]    More preferably, a surface roughness of the wall surface other than the chip formation portion is smaller than a surface roughness of the chip formation portion. Preferably, the surface roughness of the wall surface other than the chip formation portion is set such that the maximum height Rz is not more than 3 μm (JIS•B0601-2001). 
         [0011]    The insert attachment seat includes an inner attachment seat for mounting the cutting insert close to the rotational axis and an outer attachment seat for mounting the cutting insert away from the rotational axis, a part of the wall surface of the chip discharging groove is formed in a thinned wall portion that is thinned by the inner attachment seat and the outer attachment seat, and the hardened layer is formed in a vicinity of a surface of the thinned wall portion. 
         [0012]    Preferably, the protruding portions or the concave portions are formed by laser processing. The hardened layer is hardened by laser quenching. 
         [0013]    Preferably, on the wall surface, a marking that defines a formation range of the chip formation portion is formed. 
         [0014]    The indexable drill according to the present invention includes the drill body according to the present invention. 
         [0015]    According to the present invention, the chip formation portion is formed which includes a plurality of protruding portions that protrudes outward from the wall surface in the front end portion of the groove that faces the rear side of the drill rotation direction and a plurality of concave portions that is concave inward from the wall surface, and thus it is possible to significantly reduce a friction force produced between the chip formation portion and the chips. Hence, the deformation (curling) and the breaking of the chips and the discharge of the chips are facilitated, and the vibration and the chatter of the drill are also reduced. Furthermore, the hardness of the vicinity of the surface of the chip formation portion is increased, and thus it is possible to prevent the wear of the chip formation portion from developing at an early stage. In this way, the facilitation of the deformation (curling) and the breaking of the chips and the discharge of the chips and the reduction of the vibration and the chatter described above are continuously maintained for a long time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
           [0017]      FIG. 1  is a side view of an indexable drill according to an embodiment of the present invention; 
           [0018]      FIG. 2  is an enlarged view of a front end portion of the indexable drill of  FIG. 1 ; 
           [0019]      FIG. 3  is a front view of the front end portion of the indexable drill of  FIG. 1 , when viewed in a rotational axis direction; 
           [0020]      FIG. 4  is a perspective view of the indexable drill of  FIG. 1 ; 
           [0021]      FIG. 5  is an enlarged view of the front end portion of the indexable drill shown in  FIG. 4 ; 
           [0022]      FIG. 6  is another perspective view of the indexable drill shown in  FIG. 1 ; 
           [0023]      FIG. 7  is an enlarged view of the front end portion of  FIG. 6 ; and 
           [0024]      FIG. 8  is a diagram schematically showing a cross-sectional structure of a hardened layer. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    An embodiment of an indexable drill and a drill body according to the present invention will be described below with reference to  FIGS. 1 to 8 . 
         [0026]    The indexable drill shown in  FIGS. 1 to 7  includes a drill body  1  and two cutting inserts  7 A and  7 B that are attached to the drill body  1 . 
         [0027]    The drill body  1  is a member that has a rotational axis O of the indexable drill and that is substantially cylindrical, and includes a shank portion  3 , a flange portion  4 , a first chip discharging groove  5 A and a second chip discharging groove  5 B and an inner attachment seat  6 A and an outer attachment seat  6 B. 
         [0028]    The shank portion  3  is formed on the back end side (on the right side of  FIG. 1 ) of the rotational axis O of the drill body  1  so that the drill body  1  is detachably attached to machine tool such as a machining center. As shown in  FIG. 6 , the shank portion  3  has a surface  3   f  parallel to the rotational axis O. The flange portion  4  is provided next to the shank  3 ; the flange portion  4  has an end surface  4   a  that makes contact with, when mounted on a machine tool, the main shaft of the machine tool or an end surface of a retainer. 
         [0029]    The first and second chip discharging grooves  5 A and  5 B are formed in a helical shape from the front end surface if of the drill body  1  toward the back end side halfway through the flange portion  4 . The first and second chip discharging grooves  5 A and  5 B are grooves that discharge chips produced by the cutting inserts  7 A and  7 B from the front end surface if of the drill body  1  toward the back end side. The first and second chip discharging grooves  5 A and  5 B are symmetrical with respect to the rotational axis O of the drill body  1 . In the present embodiment, the first and second chip discharging grooves  5 A and  5 B are respectively defined by first wall surfaces  5 A- 1  and  5 B- 1  that are curved and face in a drill rotation direction R shown in  FIG. 3  and second wall surfaces  5 A- 2  and  5 B- 2  that are curved and connected to the first wall surfaces  5 A- 1  and  5 B- 1 , and face in a direction opposite to the tool rotation direction R. 
         [0030]    The inner attachment seat  6 A is formed concavely in the first wall surface  5 A- 1  of the front end portion of the first chip discharging groove  5 A so as to mount the cutting insert  7 A. The outer attachment seat  6 B is formed concavely in the first wall surface  5 B- 1  of the front end portion of the second chip discharging groove  5 B so as to mount the cutting insert  7 B. The inner attachment seat  6 A arranges the cutting insert  7 A close to the rotational axis O; the outer attachment seat  6 B arranges the cutting insert  7 B away from the rotational axis O. 
         [0031]    Since, in the front end portion of the drill body  1 , the inner attachment seat  6 A and the outer attachment seat  6 B are formed, as shown in  FIG. 3  and the like, a portion between the inner attachment seat  6 A and the second wall surface  5 B- 2  and a portion between the outer attachment seat  6 B and the second wall surface  5 A- 2  are formed into a thinned wall portion  1   w  that is thinner than a wall portion on the rear side. 
         [0032]    Two oil holes  9  are formed within the drill body  1 , and one end of each of the oil holes  9  is open to the front end surface if and the other end is open to the back end surface of the shank  3  of the drill body  1 . The oil holes  9  are formed to discharge cutting oil from the front end surface if to the point (the bottom edge of a cutting edge) where the cutting insert makes contact with an item to be cut. 
         [0033]    The cutting inserts  7 A and  7 B, which are respectively attached with clamp bolts BT to the inner attachment seat  6 A and the outer attachment seat  6 B, have the same structure, and are flat plate-shaped positive type cutting inserts, in the present embodiment, that are formed of hard material such as a cemented carbide, a cermet, a ceramic or the like and that are formed substantially in the outside shape of a parallelogram. As shown in  FIG. 2  and the like, when the cutting inserts  7 A and  7 B are attached to the inner attachment seat  6 A and the outer attachment seat  6 B, an upper surface opposite a seating surface forms a rake surface, and a side surface forms a flank surface. The flank angle given to the flank surface is 11 degrees in the present embodiment. On the rake surface, a chip breaker that is raised upward from the rake surface is formed. In the inner portions of the cutting inserts  7 A and  7 B, attachment holes are formed that penetrate from the rake surface to the seating surface. 
         [0034]    In the cutting inserts  7 A and  7 B, as shown in  FIG. 2 , of the intersection portion where the rake surface intersects the flank surface, each of the short side portions of an approximate parallelogram forms a first cutting edge  7   a , each of the long side portions forms a second cutting edge  7   b  and each of the corner portions that form an acute angle forms a corner cutting edge  7   c . In the state shown in  FIG. 2 , in drilling or the like, for the cutting insert  7 A (hereinafter also referred to as an inner insert  7 A), the cutting edges  7   b  and  7   c  contribute to the cutting, and, for the cutting insert  7 B (hereinafter also referred to as an outer insert  7 B), the cutting edges  7   a  and  7   b  contribute to the cutting. With respect to the inner insert  7 A and the outer insert  7 B, the width of the cutting made by the outer insert  7 B is shorter than the width of the cutting made by the inner insert  7 A. 
         [0035]    As shown in  FIG. 5  and the like, in the front end portion of the second wall surface  5 A- 2  of the first chip discharging groove  5 A, a chip formation portion  8  is formed. Although not illustrated, in the second wall surface  5 B- 2  of the second chip discharging groove  5 B, the chip formation portion  8  is also formed. 
         [0036]    The formation region of the chip formation portion  8  forms the thinned wall portion  1   w  described above. The surface of the chip formation portion  8  has projections and recesses; as described later, the projections and recesses reduce the actual contact area when chips produced by the cutting insert  7 A make direct contact with the surface and thereby decrease the friction. Furthermore, in the vicinity of the surface of the chip formation portion  8 , a hardened layer having a greater hardness than other parts of the second wall surface  5 A- 2  is formed, and thus the hardness of the surface is increased. 
         [0037]      FIG. 8  schematically shows an example of the cross-sectional structure of the chip formation portion  8 . The chip formation portion  8  has a plurality of protruding portions  8   a  and concave portions  8   b , and also has the hardened layer  8   c  of high hardness in the vicinity of the surface. The chip formation portion  8  is formed by, for example, laser processing. Specifically, when the surface of the front end portion of the second wall surface  5 A- 2  is irradiated with laser light, in the portion irradiated with the laser light, the protruding portions  8   a  and the concave portions  8   b  are formed by its expansion and evaporation caused by rapid heating. 
         [0038]    When the laser light is irradiated to a portion broader than a predetermined range to form the chip formation portion  8 , the production efficiency may be reduced, and the strength of the drill body  1  may be reduced. Hence, it is preferable that the formation range of the chip formation portion  8 , that is, the range to be irradiated with the laser light can be previously recognized. Therefore, as shown in  FIGS. 5 and 7 , a marking MK that defines the formation range is formed in advance in a boundary portion or the like of the chip formation portion  8 . For example, the marking MK is formed with a plurality of shallow grooves or holes processed with a small-diameter end mill or a small-diameter drill. 
         [0039]    Furthermore, in the laser processing described above, laser quenching is simultaneously performed on the chip formation portion  8 , and thus the hardened layer  8   c  is formed. In other words, the portion irradiated with the laser light is rapidly heated and then is air-cooled, and is thereby formed into the hardened layer  8   c  having a higher hardness than the hardness that the drill body originally has. 
         [0040]    As a laser processing device used in the laser processing, a known laser processing device can be used. Conditions such as the output (average output) of the laser light, the speed of the processing and an irradiation angle of the laser light can be appropriately selected according to the height of the protruding portion  8   a , the depth of the concave portion  8   b , the thickness of the hardened layer  8   c  and the like. In order to maintain a substantially constant state of contact with the chips, preferably, the protruding portions  8   a  and the concave portions  8   b  are regularly arranged and evenly distributed; however, the present invention is not limited to this configuration. 
         [0041]    In order to acquire hardness and toughness necessary and sufficient for the cutting, the drill body  1  is subjected to thermal processing such as quenching and tempering, and thus has a substantially constant basic hardness as a whole. In order for the hardened layer  8   c  of the chip formation portion  8  to have a higher hardness than the basic hardness, a carbon steel, an alloy steel, a tool steel or the like that has property of being hardened when it is quenched is used as the formation material of the drill body  1 . Specifically, an alloy tool steel such as SKD11 (JIS•G4404-2006) is used. 
         [0042]    The hardness of the hardened layer  8   c  of the chip formation portion  8  is higher than the basic hardness of the drill body  1  but the upper limit is preferably about Hv 800. In order to prevent the thinned wall portion  1   w  from undergoing brittle fracture, the thickness of the hardened layer  8   c  is preferably adjusted according to the thickness of the thinned wall portion  1   w ; in the present embodiment, the thickness falls within a range of 0.05 mm to 0.50 mm. 
         [0043]    Since the projections and the recesses are formed, the surface roughness of the chip formation portion  8  is set such that the maximum height Rz is more than 3 μm (JIS•B0601-2001). On the other hand, the wall surfaces  5 A- 1  and  5 A- 2  other than the chip formation portion  8  are preferably smoothed as much as possible in order to increase the flowability of the chips and the cutting oil; in the present embodiment, the maximum height Rz is set not more than 3 μm (per JIS•B0601-2001) by cutting. 
         [0044]    The chip formation portion  8  preferably covers the range in which chips cut from the item to be cut first make contact with the chip formation portion  8 . In the indexable drill of the present embodiment, the length of the chip formation portion  8  in the direction of the rotational axis O preferably falls within a range up to about the cutting edge diameter D of the drill, from the front end portion to the back end side of the second wall surface  5 A- 2 . The size of the drill body  1  of the chip formation portion  8  in the radial direction preferably extends over a substantially entire region in the width direction of the second wall surface  5 A- 2 . 
         [0045]    In the drilling processing performed with the indexable drill of the present embodiment, the chips are continuously formed by the cutting of the item to be cut by the inner insert  7 A and the outer insert  7 B. The formed chips are discharged to the back end side of the drill body  1  through the first chip discharging groove  5 A and the second chip discharging groove  5 B. During the drilling processing, the cutting oil is continuously supplied through the opening of the oil holes to a part to be cut. The cutting oil supplied to the part to be cut flows within the first chip discharging groove  5 A and the second chip discharging groove  5 B to the back end side together with the chips. In this way, the chips are forcibly washed to the back end side of the drill body  1 , and this facilitates the discharge. 
         [0046]    The chips that are cut from the item to be cut by the inner insert  7 A and the outer insert  7 B during the drilling processing described above first make contact with the chip formation portion  8  of the first and second chip discharging grooves  5 A and  5 B. The contact of the chips with the chip formation portion  8  causes the chips to be deformed (curled) and broken. In other words, since the projections and recesses described above are formed in the surface of the chip formation portion  8 , against which chips cut from the item to be cut first make contact, the actual contact area between the surface of the chip formation portion  8  and the chips is reduced as compared with a smooth surface. Thus, it is possible to reduce the friction force produced between the surface of the chip formation portion  8  and the chips. Consequently, the chips more smoothly pass through the chip formation portion  8 . In addition, since the friction force between the chip formation portion  8  and the chips is reduced, the vibration and the chatter of the drill are also reduced. 
         [0047]    Furthermore, since the hardened layer  8   c  of the chip formation portion  8  has a hardness beyond the basic hardness of the drill body  1 , the wear of the chip formation portion  8  caused by the chafing of the chips is reduced. Therefore, the effect of reducing the friction force between the chip formation portion  8  and the chips is maintained for a long period of time. 
         [0048]    The chips that are continuously cut from the item to be cut are deformed (curled) and broken by making contact with the chip formation portion  8 , and thereafter the chips are completely freed from the item to be cut. Hence, the wall surface on the downstream side of the chip formation portion  8  is smoothed, and thus the chips and the cutting oil are not prevented from flowing, with the result that the chips can be smoothly discharged within the first chip discharging groove  5 A and the second chip discharging groove  5 B to the back end side. 
         [0049]    Although, in the above embodiment, the first chip discharging groove  5 A and the second chip discharging groove  5 B are formed in a helical shape, the grooves can be changed into grooves that extend linearly in a direction parallel to the rotational axis O. Although a description is given of the case where the chip formation portion  8  is formed both in the first chip discharging groove  5 A and in the second chip discharging groove  5 B, the chip formation portion  8  can instead be formed in only one of them. 
         [0050]    Instead of the laser quenching, the quenching of the hardened layer  8   c  of the chip formation portion  8  may be performed by electron beam quenching or high-frequency wave quenching. If the desired projections and recesses cannot be formed in the chip formation portion  8  by the laser quenching, the projections and recesses can be formed in the chip formation portion  8  with an end mill by machining after the formation of the hardened layer by the laser quenching. 
         [0051]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.