Abstract:
An insert includes a rake angle set corresponding to the hardness of a material to be cut and that can suppress an increase in the material cost even when the strength of a cut edge section is increased. The insert has a polygonal shape and includes a cutting edge portion on at least one side of the polygonal shape. The cutting edge portion includes a rake face having a convex formed on one of opposite surfaces in the thickness direction, a flank face having a concave formed on a surface intersecting with the one surface in the thickness direction and a concave cutting edge that is formed between the rake face and the flank face.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an insert which has a polygonal shape and includes a cutting edge portion on at least one side of the polygonal shape. 
       BACKGROUND ART 
       [0002]    As one type of conventional inserts, there is an insert that is formed into a flat plate shape with its opposite surfaces in the thickness direction being flat and has a rake face formed on one of the flat surfaces (see Patent Document 1, for example) 
       CITATION LIST 
     Patent Document 
       [0003]    [Patent Document 1] JP 2000-71107A 
       SUMMARY OF INVENTION 
       [0004]    In the conventional insert, the rake face is formed on the same level as the flat surface of the insert or formed as a groove thereon. Therefore, if it is intended to obtain a rake angle corresponding to the hardness of a material to be cut, etc., the fixed posture itself of the insert with respect to a rotary cutting tool has to be set as appropriate. 
         [0005]    Also, with the rake face formed of the flat surface of the insert, in order to enhance the strength of a cutting edge portion, the entire thickness of the insert must be increased. This causes a drawback of increasing the material cost particularly when the insert is formed of sintered metal, etc. 
         [0006]    Moreover, in the conventional insert, one cutting edge portion is formed for one insert. This increases the frequency of insert replacement during working. 
         [0007]    The present invention was made in view of the situation described above, and it is an object thereof to provide an insert that can have a rake angle set corresponding to a material to be cut while keeping its fixed posture with respect to a rotary cutting tool constant and moreover can have enhanced use efficiency. 
         [0008]    The first feature configuration of the insert of the present invention is that the insert has a polygonal shape,
       the insert comprising: a cutting edge portion which is provided on at least one side of the polygonal shape,   and the cutting edge portion having,       
 
         [0011]    a rake face having a convex formed on one of opposite surfaces in the thickness direction; 
         [0012]    a flank face having a concave formed on a surface intersecting with the one surface in the thickness direction; 
         [0013]    and a concave cutting edge that is formed between the rake face and the flank face. 
         [0014]    By forming the rake face in a shape having a convex as in the above configuration, a predetermined rake angle can be obtained without the necessity of fixing the insert at an angle with respect to the rotary cutting tool. 
         [0015]    Also, since the convex for formation of the rake face is formed with the thickness of the convex added to the thickness of the insert, the strength of the cutting edge portion formed across the convex is enhanced. 
         [0016]    Moreover, since the cutting edge portion is formed on each side of the insert having a polygonal shape, one insert can be used repeatedly by the number of cutting edge portions. As a result, the work efficiency of the cutting work improves, permitting reduction in work cost. 
         [0017]    The second feature configuration of the present invention is that the rake face may be formed to have cutting edge portions of various sizes layered in a shape of contour lines. 
         [0018]    With the above configuration, any of concave cutting edges having different curvatures can be formed for one convex. For example, various types of cutting edges equal in rake angle can be obtained by grinding the convex using grinding tools different in curvature. Therefore, cutting edge portions having the same curvature, or cutting edge portions having different curvatures, can be formed on the sides of the polygon. Thus, with this configuration, an insert excellent in cost performance can be obtained. 
         [0019]    The third feature configuration of the present invention is that the flank face may be a concave face extending from the cutting edge portion toward the other surface in the thickness direction, and may be formed so that the cross-sectional shape of the concave face perpendicular to the thickness direction is equal at any position from the cutting edge portion toward the other surface, or so that the cross-sectional shape of the concave face perpendicular to the thickness direction is smaller in the curvature of the recess as the position is closer to the other surface from the cutting edge portion. 
         [0020]    With the above configuration, the flank face can be formed simultaneously with formation of the cutting edge by using a cylindrical rotary grinding tool, etc. having the curvature of the cutting edge to be formed, for example. This improves the manufacture efficiency of the insert. When the flank face is a concave face the curvature of which is smaller as the position is closer to the other surface from the cutting edge portion, a larger clearance can be secured between the object to be worked on and the flank face. This ensures prevention of interference between the insert and the object to be worked on and thus permits high-quality rounding. Thus, even when the curvature of the flank face changes, the cutting edge portion and the flank face can be formed simultaneously by using a conical grinding tool, etc., for example. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIGS. 1(   a ) and  1 ( b ) are plan views of an insert (throwaway chip), where  FIG. 1(   a ) shows the case where four cutting edge portions have concave cutting edges same in rounding size, and  FIG. 1(   b ) shows the case where four cutting edge portions have concave cutting edges different in rounding size from one another. 
           [0022]      FIG. 2(   a ) is an enlarged plan view of a cutting edge portion, and  FIG. 2(   b ) is a cross-sectional view taken along line IIb-IIb in  FIG. 2(   a ). 
           [0023]      FIG. 3  is a perspective view showing a blank before formation of the cutting edge portions. 
           [0024]      FIG. 4  is a plan view of the blank. 
           [0025]      FIG. 5  is a side view of the blank. 
           [0026]      FIG. 6  is a cross-sectional view taken along line VI-VI in  FIG. 4 . 
           [0027]      FIGS. 7(   a ) and  7 ( b ) show an insert fixed to a head of a rotary cutting tool, where  FIG. 7(   a ) is a plan view and  FIG. 7(   b ) is a side view. 
           [0028]      FIG. 8  is a plan view of an insert of the second embodiment. 
           [0029]      FIG. 9  is a cross-sectional view taken along line IX-IX in  FIG. 8 . 
           [0030]      FIG. 10  is a plan view showing a state of the insert of the second embodiment having cutting edge portions newly formed. 
           [0031]      FIG. 11  is a cross-sectional view taken along line XI-XI in  FIG. 10 . 
           [0032]      FIG. 12  is a plan view of a blank of the insert of the second embodiment before formation of the cutting edge portions. 
           [0033]      FIG. 13  is a side view of the blank of the insert of the second embodiment before formation of the cutting edge portions. 
           [0034]      FIG. 14  is a cross-sectional view taken along line XIV-XIV in  FIG. 12 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Embodiments of the present invention will be described hereinafter with reference to the drawings. 
       First Embodiment 
       [0036]      FIGS. 1 and 2  show examples of an insert of the present invention. An insert A is fixed to a rotary cutting tool C for chamfering a corner of a material D to be cut into a round shape (curved shape) as shown in  FIG. 7 . The insert A is formed using hard metal, etc., for example. 
         [0037]    The insert A has a base  1  formed into a generally square shape as viewed from top. One fixation hole  2  for fixing the base  1  to the rotary cutting tool C is provided in the center of the base  1 . Four cutting edge portions  3  are provided at the sides of the base  1 . 
         [0038]      FIG. 1(   a ) shows an example where concave cutting edges  4  same in rounding size (curvature of the curved face) are provided at the sides of the base  1 .  FIG. 1(   b ) shows an example where cutting edges  4  different in rounding size from one another are formed at the sides of the base  1 . 
         [0039]      FIGS. 3 to 6  show a blank B before formation of the cutting edge portions  3 . A convex  5  for formation of a rake face is formed in the thickness direction of the blank B at each of the four sides thereof. 
         [0040]    The base  1  includes flat top and back surfaces  6  and  7  parallel to each other on the top and back thereof in the thickness direction. Four planar side faces  8  are provided on the periphery of the top and back surfaces  6  and  7 . The side faces  8  are slightly inclined with respect to the thickness direction of the base  1 , forming, as a whole, a generally truncated cone shape that becomes narrower toward the back surface  7 . 
         [0041]    The convex  5  is formed at each of the sides of the top surface  6 , out of the pair of top and back surfaces  6  and  7 . The convex  5  will become a rake face  12  to be described later. The back surface  7  will come into contact with a fixing seat surface  9   a  of a fixing seat  9  of the rotary cutting tool C as shown in  FIG. 7 , functioning as a chip fixed surface. 
         [0042]    The convex  5  is formed into a generally conical shape as shown in  FIGS. 3 and 4 . The convex  5  is however not in a precise conical shape. As shown in  FIG. 4 , the cutting edge  4  having a predetermined curvature must be formed within the limited area of the convex  5 . In comparison among expected edges for the cutting edge  4  as shown in  FIG. 4 , the spacing between adjacent edges in the direction along a reference line X is smaller than the spacing between adjacent edges in the direction perpendicular to the reference line X. The reason for this is that, in grinding, etc. for formation of the cutting edges  4  of various sizes, it is necessary to reduce the work amount itself by reducing the grinding amount of the base  1  and also maintain the strength of the base  1  by minimizing the decrease in the volume thereof. The convex  5  therefore has a shape obtained by superposing such expected edges for formation of cutting edge portions in the above shapes. 
         [0043]    Also, as shown in  FIG. 4 , the reference line X for each convex  5  is offset by a distance e from the fixation hole  2  provided at the center of the base  1 . 
         [0044]    With this offset setting, in formation of the cutting edge  4 , the spacing between the cutting edge  4  and the fixation hole  2  becomes large, and thus the size range permitted for the formation of the cutting edge  4  can be widened. Also, with the offset formation of the cutting edge  4 , when the insert A is mounted on the rotary cutting tool C as shown in  FIG. 7(   a ), the radius of gyration from the rotation center of the rotary cutting tool C to the cutting edge  4  becomes short. As a result, the work reaction force exerted on the cutting edge  4  from the material D to be cut at the time of working becomes small, and thus the drive torque to be provided by the rotary cutting tool C can be reduced. 
         [0045]    A concave face  10  expanding from the apex Q of the convex  5  toward the back surface  7  is formed on each side face  8  of the base  1 . 
         [0046]    The concave face  10  is formed from part of a predetermined conical face, for example. As shown in  FIG. 5 , the length T of the concave face  10  on the back surface  7  is equal to or larger than the length U of the convex  5  on the top surface  6 . While a flank face  11  corresponding to the size of the cutting edge  4  is to be formed on the back side of the convex  5 , the concave face  10  is formed prior to the formation of the flank face  11  by thinning each side face  8  of the base  1 . 
         [0047]    The length T is made equal to or larger than the length U because of the convenience of a grinding tool used at the formation of the cutting edge  4 , for example. To form the cutting edge  4 , the side face  8  is gradually ground using a cylindrical grind stone having the curvature of the cutting edge  4 , for example, with the grind stone tilted at a predetermined relief angle. The amount of grinding of the side face  8  is largest when the cutting edge  4  extending in advance to the entirety of the length U is formed. In this case, since the back surface side of the side face  8  is also ground naturally, such a portion is in advance formed into a concave shape to improve the working efficiency. 
         [0048]    As shown in  FIGS. 2(   a ) and  2 ( b ), when the cutting edge  4  is formed across the convex  5  of the insert A, the remaining portion of the convex  5  serves as the rake face  12 , and the back side thereof serves as the flank face  11 . The flank face  11  is formed by further grinding part of the concave face  10 . For example, the flank face  11  is formed by pressing a rotary grind stone, etc. against the concave face  10 . The portion of the convex  5  left non-ground serves as the rake face  12 , and the concave cutting edge  4  is formed as shown in  FIG. 2(   a ). 
         [0049]    As shown in  FIG. 3 , when the flank face  11  is viewed from the side of the side face  8 , a cylindrical flank face  11   a  is formed in the center of the flank face  11 , and flat flank faces  11   b  are formed on both sides thereof. The cylindrical flank face  11   a  is a portion formed by simply pressing the rotary grind stone, etc. As a result, as shown in  FIGS. 2(   a ) and  3 , the portion of the cutting edge  4  corresponding to the cylindrical flank face  11   a  becomes an arc-shaped cutting edge  4   a . Strictly speaking, the arc-shaped cutting edge  4   a  is not in a complete arc shape, but it is hereinafter referred to as the arc-shaped cutting edge for convenience sake. The flat flank faces  1  lb are formed to adjoin the cylindrical flank face  11   a  as shown in  FIGS. 2(   b ) and  3 . As a result, linear cutting edges  4   b  are formed on both sides of the arc-shaped cutting edge  4   a . Strictly speaking, the linear cutting edges  4   b  are not linear because they are formed on the curved surface of the convex  5 , but they are hereinafter referred to as the linear cutting edges  4   b  for convenience sake. 
         [0050]    The flat flank faces  11   b  and the linear cutting edges  4   b  are provided for the purpose of, in chamfering a corner of the material D to be cut, allowing a worked curved face to continue smoothly to a non-worked flat face. Such flat flank faces  11   b  and the linear cutting edges  4   b  are formed in the following manner, for example: the cylindrical rotary grind stone is once pressed against the side face  8  and, after the ark-shaped cutting edge  4   a  and the cylindrical flank face  11   a  are formed to a predetermined depth, the rotary grind stone is translated, from this position, in predetermined right and left directions. 
         [0051]    By setting the outer diameter of the tool for formation of the cylindrical flank face  11   a  in various ways, the cutting edges  4  having various rounding sizes can be formed using the blank B having a fixed size and shape. 
         [0052]      FIG. 7  shows a fixed structure of the insert A to a head  13  of the rotary cutting tool C. 
         [0053]    The head  13  rotates in the direction of arrow a in  FIG. 7  and includes the fixing seat  9  for fixing the insert A. The fixing seat  9  includes the fixing seat surface  9   a  with which the back surface  7  of the base  1  comes into close contact and turn stop seat surfaces  9   b  intersecting with each other with which two adjacent side faces  8  of the base  1  come into close contact to stop turning of the base  1 . In  FIG. 7(   a ), the turn stop seat surfaces  9   b  are provided in postures each intersecting at an angle of 45 degrees with respect to the rotation axis Z of the head  13 . The fixing seat surface  9   a  is provided to be in parallel with the rotation axis Z of the head  13 . 
         [0054]    The fixing seat surface  9   a  has a fixation internal screw hole  14  formed with its axis being orthogonal to the fixing seat surface  9   a . A fixing bolt  15  is inserted into the fixation hole  2  of the base  1  and engaged with the fixation internal screw hole  14  to fix the insert A. In the fixed state, two side faces  8  protrude from the head  13  outward in the radial direction of the head  13 . In this way, the material D to be cut can be chamfered by either the cutting edge  4  facing toward the bottom of the head  13  or the cutting edge  4  facing toward the top thereof. 
         [0055]    A head  15   a  of the fixing bolt  15  has a truncated cone shape. The fixation internal screw hole  14  and the fixation hole  2  are made eccentric to each other. When the fixing bolt  15  is screwed into the fixation internal screw hole  14 , the truncated cone portion of the head  15   a  abuts against the slope of the fixation hole  2 , pressing the insert A toward the turn stop seat surfaces  9   b.    
         [0056]    Note that, in chamfering a corner of the material D to be cut using the insert member of the present invention, the rake angles in all areas of the cutting edge  4  are not the same with respect to the material D to be cut. For example, from  FIG. 7(   a ), it is found that the distance between the cutting edge  4  and the rotation axis Z of the head  13  continuously changes as the position on the cutting edge  4  changes. Further, when the position of the rotation axis Z is viewed along the direction of the plane of the insert A as shown in  FIG. 7(   b ), it is found that the position of the cutting edge  4  and the position of the rotation axis Z is offset from each other. Therefore, in chamfering the material D to be cut by the cutting edge  4 , the rake angle is different depending on the position on the cutting edge  4 . Thus, in formation of the convex  5 , it may be better to devise the shape of the convex  5  in advance depending on where the cutting edge  4  is located with respect to the rotation axis Z. 
       Second Embodiment  
       [0057]      FIGS. 8 to 11  show an insert A of another embodiment. 
         [0058]    In this embodiment, a plurality of convex s  5  for formation of the rake face are provided for each side of the base  1 . For example, an outer convex  51  and an inner convex  52  are provided as the convex  5 , and a step  16  is provided therebetween.  FIGS. 8 and 9  show an example of forming the cutting edge  4  across the outer convex  51 , and  FIGS. 10 and 11  show an example of forming the cutting edge  4  across the inner convex  52 . Two or more convex s may be provided. 
         [0059]    Segmenting the convex in advance into different regions for formation of the cutting edge  4  as described above is convenient because such regions serve as a guide when the user works on the blank to form the cutting edge  4 . For example, this not only makes it easy to select the curvature of the cutting edge  4 , but also permits formation of the cutting edge  4  at a proper position with the contour lines serving as a guide when a grinding tool is pressed against the insert A. 
       Third Embodiment 
       [0060]      FIGS. 12 to 14  show an insert A before formation of the cutting edges  4 . 
         [0061]    In this embodiment, the step  16  between the outer convex  51  and the inner convex  52  is formed from the top surface  6  of the base  1  itself. Therefore, the difference in the height from the top surface  6  between the outer convex  51  and the inner convex  52  is small. 
         [0062]    The insert A of this embodiment is formed by casting and sintering, for example. The recess between the outer convex  51  and the inner convex  52  may be formed simultaneously with casting, etc., or only the recess may be formed by grinding, etc. after formation of the blank material for the insert A. 
       Other Embodiments  
       [0063]    In the above embodiments, cutting edges having a single round (part of a circle) shape were described, but the cutting edges are not limited to this shape. For example, concave cutting edges formed by combining a plurality of round shapes may be formed. 
       INDUSTRIAL APPLICABILITY 
       [0064]    The present invention is widely applicable to inserts provided with a cutting edge portion on at least one side of a polygonal shape.