JP6519971B2 - drill - Google Patents

Description

  The present invention is mainly used in machine tools and the like, and has a function of enhancing chip dischargeability in metal drilling, particularly promoting chip formation even in high feed drilling and suppressing chip clogging. It relates to the drill I had.

  In machining with a drilling drill held and used by machine tools such as mold processing and parts processing, damage to the drill due to chip clogging etc. shortens the life of the drill, so that the chip dischargeability can be improved It becomes one goal in making a drill. The shape of the chips generated by the cutting edge differs depending on when the drill bites and starts cutting, but after the biting, the cutting edge mainly generates chips, and along the cutting face of the cutting edge The relationship between the rake face of the cutting edge and the shape of the groove is a factor that determines the chip dischargeability, as it is grown and discharged to the groove facing the rake face.

  A thinning portion is formed to shorten the length of the chisel edge and reduce the thrust during cutting from the rotation direction front side on the radial center side of the cutting edge to the rotation direction rear side of the flank of the adjacent cutting edge. However, this thinning portion is composed of a cutting edge side thinning surface on the front side in the rotational direction of the cutting edge and a flank surface thinning surface on the rear side in the rotational direction of the flank surface. The cutting edge side thinning surface also serves as the rake surface of the minor cutting edge on the radial center side of the cutting edge, and the flank surface thinning surface is continuous with the groove for chip discharge, so both chips are discharged. It is appropriate that the intersections of the surfaces have continuity, and they are formed in a concave curve (see Patent Documents 1 to 5).

  The groove bottom which is the intersection of the cutting edge side thinning surface and the flank side thinning surface is formed in a concave surface shape, and the sub cutting edge is cut, and the generated chips are on the cutting edge side thinning surface (rake surface) It is considered that there is an advantage that the chip dischargeability is improved because it is sent to the flank side thinning surface side while being guided to be rotated and discharged as it is into the groove for chip discharge. 1).

  However, the cutting edge is divided in the radial direction into the main cutting edge on the outer circumference side and the minor cutting edge (sinning blade) facing the cutting edge side thinning surface on the inner circumference (center) side, and the minor cutting edge is cut The chips are sent to the flank side thinning surface side (Patent Document 1), and the chips are grown along the cutting edge side thinning surface which becomes the rake surface of the sub cutting edge, so the generated chips are It is difficult to say that the groove bottom of the thinning portion is concave-curved only in order to discharge it into the groove while growing it.

  Among the cutting edges, the main cutting edge cuts, and the chips generated are grown along the surface of the groove and discharged from the groove in a curled form as it is (Patent Document 5), but the minor cutting edge is the main cutting edge Since the chips cut by the minor cutting edge are sent from the cutting edge side thinning surface (rake surface) to the flank side thinning surface side and then discharged into the groove, the main cutting edge It is believed that the blade can not be processed as well as cut chips.

  In patent documents 1 to 4, the thinning surfaces which are paired at point symmetrical positions with respect to the rotation axis (center) of the drill are formed so as to overlap each other, thereby expanding the volume of the thinning portion and enhancing the chip dischargeability. However, since the thinning surface itself does not form a continuous curved surface as a whole, it is imagined that chips are difficult to be generated smoothly in the thinning portion.

  In Patent Document 5, the cutting edge side thinning surface (first thinning surface 6) is formed separately from the rake surface 8 of the cutting edge (thinning blade 5), and the intersection of the cutting edge rake surface 8 and the cutting edge side thinning surface 6 By forming the portion in a concave surface, continuity between the rake surface 8 and the cutting edge side thinning surface 6 is secured (claim 2, FIG. 4- (b)).

JP, 2003-266225, A (claim 1, paragraphs 0012, 0014, 0017, FIG. 2) JP, 2009-18360, A (paragraph 0012, 0017, 0024, FIG. 3) JP, 2008-296313, A (claim 1, paragraph 0023, FIG. 3, FIG. 6) JP 2008-213121 A (paragraph 0018, FIG. 3) Unexamined-Japanese-Patent No. 2001-79707 (Claim 2, paragraphs 0010-0018, FIG. 2, FIG. 4)

  However, since the chips cut by the minor cutting edge try to grow along the cutting edge side thinning surface which is the rake face of the minor cutting edge as described above, the cutting edge side thinning surface and the flank surface thinning surface If the whole of both thinning surfaces is not continuous as a curved surface, including the intersection of the two, it is assumed that the resistance acts on the chips from the discontinuous boundaries, which may inhibit the growth of the chips. There is sex.

  From the above background, the present invention proposes a drill in a form that promotes the generation and growth of chips in the thinning section and is less likely to cause division and clogging of chips.

The drill of the invention according to claim 1 comprises a plurality of cutting edges and a cutting edge having a groove between the cutting edges adjacent in the circumferential direction on the axial direction tip end side of the shank portion, the cutting edge being a cutting edge It consists of a main cutting edge on the outer peripheral side in the radial direction and a sub cutting edge located on the radial center side of the main cutting edge following the main cutting edge, and the groove on the rear side in the rotational direction of the flank of each cutting edge A drill with a thinning section facing the
The thinning portion is configured by a front side thinning surface formed on the rotational direction rear side of the flank surface, and a rear side thinning surface formed on the rotational direction front side of the sub cutting edge and also serving as a rake surface of the sub cutting edge. And
The back side thinning surface and the front side thinning surface respectively form a curved surface, and the back side thinning surface forms a continuous curved surface from the back side thinning surface to the front side thinning surface, and the front side thinning surface is the blade portion Continue to the outer peripheral surface of the
The rear side thinning surface and the front side thinning surface continue in a band shape to the radially outer peripheral side while having a width corresponding to a section of the sub cutting edge in the length direction of the sub cutting edge, the rear side It is characterized in that the thinning surface and the boundary line between the front side thinning surface and the flank surface draw a concave curve to the outer peripheral side in the radial direction .

  The cutting edge is located radially outward as shown in FIG. 1 and is a main cutting edge 51 facing the groove 5 and the main cutting edge 51, and a secondary cutting edge located on the radial center side of the main cutting edge 51. It is divided into blades 52. The “radial direction” refers to the direction of a straight line (diameter) passing through the rotation axis O of the drill 1 on a cross section orthogonal to the rotation axis (center) O of the drill 1. The thinning portion 30 comprises a front side thinning surface 31 and a rear side thinning surface 32. The front side thinning surface 31 is on the rear side in the rotational direction from the edge on the rear side in the rotational direction of the flank 100 (space side boundary line Q). It is formed. The “rotational direction” refers to the rotational direction of the drill 1 indicated by the arrow R in FIG. 1. The side on which the outer peripheral surface of the drill 1 advances is referred to as the front side, and the opposite side is referred to as the rear side.

  The rear side thinning surface 32 is formed on the front side in the rotational direction from the section of the sub cutting edge 52 so as to serve as the rake surface of the sub cutting edge 52 and continues to the front side thinning surface 31. The rear side thinning surface 32 and the front side thinning surface 31 form curved surfaces continuous from the rear side thinning surface 32 to the front side thinning surface 31 while forming the curved surfaces. There is no clear boundary between the rear side thinning surface 32 and the front side thinning surface 31.

  A continuous curved surface formed by the rear side thinning surface 32 and the front side thinning surface 31 is, for example, a straight line inclined from the blade portion 2 side of the drill 1 to the shank portion 3 side and inclined from the front side to the rear side in the rotational direction ) Is a curved surface drawn from the radial center side toward the radially outer peripheral side and moved in parallel along a certain curve, and is a curved surface whose curvature changes continuously (claim 2). However, the form of the curved surface does not matter as long as it is a continuous curved surface without steps. The curve on which the generatrix moves is, for example, a curve whose curvature changes continuously as in the case of a clothoid curve (claim 3), and the curvature (curvature radius) in that case is gradually increasing from the radial center side to the radial outer side It becomes smaller (larger) and the generatrix draws a "curved surface whose curvature changes continuously". Since the clothoid curve may include a straight line (it may be transitioned from a straight line to a curve), the rear side thinning surface 32 and the front side thinning surface 31 which are curved surfaces generated when the generatrix moves along the clothoid curve are flat (flat surface May be included.

  In FIG. 2, a curved line on which a generating line describing a curved surface moves is indicated by a broken line, and this curve is a rear side indicated by an area from the rear side thinning surface 32 to the front side thinning surface 31 by z-z line in FIG. A cutting line that appears when cutting from a thinning surface 32 to the front side thinning surface 31 and cutting with a plane inclined from the tip side toward the shank 3 is shown. 5 schematically shows a cross section when the region from the rear side thinning surface 32 to the front side thinning surface 31 is cut by a cutting plane passing through the yy line of FIG. 2 and FIG. 6 is orthogonal to the rotation axis O FIG. 4 shows a cut surface when cut by a cut surface indicated by the line x-x.

  Each of the rear side thinning surface 32 and the front side thinning surface 31 has a curved surface, and a continuous curved surface extending from the rear side thinning surface 32 to the front side thinning surface 31 forms a sub-cut of the rear side thinning surface 32. A region from the edge on the blade 52 side to the outer peripheral surface (the second chamfered surface 12) which is the edge of the front side thinning surface 31 is a continuous curved surface without a step. As a result, the chips formed by cutting by the minor cutting edge 52 grow while rotating along the rear side thinning surface 32 which is the rake face of the minor cutting edge 52, and along with the rotation of the drill, the anterior side thinning surface 31 Since it is sent to the side and is intended to be discharged to the groove 5 as it is, it becomes difficult to be divided in the thinning portion 30 until the chips reach the groove 5, and clogging in the thinning portion 30 becomes difficult to occur.

  In particular, when the area from the end edge of the rear side thinning surface 32 on the side of the sub cutting edge 52 to the end edge of the front side thinning surface 31 forms a curved surface with continuously changing curvature (claims 2 and 3) Since there is no discontinuous boundary line which may become a projection which is generated when the curved surface is discontinuous, and it becomes difficult to receive a force to separate from the thinning surfaces 32 and 31 in the process of chip growth, chip growth and grooves Discharge to 5 is likely to occur smoothly. As shown by the broken line in FIG. 2, when the curvature of the curved surface gradually decreases from the radial center toward the outer peripheral side in the radial direction (claim 3), when the chips curl and grow, the thinning surface 32 , 31 become the guide surface corresponding to the chip dimensions which gradually increase, so that the chip growth is more promoted.

In the cutting edge 50, the chip produced by cutting the main cutting edge 51 and the chip produced by cutting the secondary cutting edge 52 are divided to form the honing surface 15 on the front side in the rotational direction of the cutting edge 50. At a boundary position between the main cutting edge 51 and the sub cutting edge 52 on the front side of the honing surface 15 in the rotational direction, it protrudes forward in the rotational direction from the main cutting edge 51 and the sub cutting edge 52 other than the boundary position. It becomes reliable by forming the protrusion 15a (claim 4). The tip V1 of the groove 5 side (the front side in the rotational direction) of the projecting portion 15a is the thinning surface side boundary line W1 between the honing surface 15 and the rear side thinning surface 32 as shown in FIG. 2 and FIG. This corresponds to a point where the groove side boundary line W2 between the groove 5 and the groove 5 and the outer peripheral side boundary line W3 between the rear side thinning surface 32 and the groove 5 intersect.

  A cutting edge is formed by forming a projecting portion 15a projecting to the front side in the rotational direction at the boundary position between the main cutting edge 51 and the sub cutting edge 52 on the front side in the rotational direction of the honing surface 15 formed on the cutting edge 50 Since the tip of the projecting portion 15a separates the chips into the main cutting edge 51 and the sub cutting edge 52 when the cutting material 50 cuts the material, the cutting edge 50 is a material to be cut. From the start of cutting, it is possible to divide the chips into chips generated by the main cutting edge 51 and chips generated by the secondary cutting edge 52.

  While the chips generated by the main cutting edge 51 and the chips generated by the sub cutting edge 52 are separated from each other, the chips generated by the main cutting edge 51 are discharged from the groove 5 while being grown in the groove 5 After the chips generated by the secondary cutting edge 52 are grown while being fed to the front side thinning surface 31, they can be discharged into the groove 5. In contrast to the case where the chips generated by the cutting edge 50 are not divided because the chips are divided from the beginning of the generation of the chips, the chips to be processed directly into the groove 5 are passed through the inside of the chips and the thinning portion 30. Then, since it is divided and discharged into the chips to be processed into the grooves 5, the possibility of the chips being clogged in the thinning portion 30 or in the grooves 5 is reduced, and the discharge performance of the chips is improved.

  Particularly, as shown in FIG. 2 and FIG. 3, an outer peripheral side boundary line W3 between the rear side thinning surface 32 and the groove 5 continues from the tip V1 on the front side in the rotational direction of the projection 15a toward the shank 3 side, In the case where the outer peripheral side boundary line W3 forms a convex ridge line (claim 5), the section from the tip V1 to the outer peripheral side boundary line W3 serves as a blade that divides chips into the radially outer peripheral side and the central side Therefore, the effect of dividing the chips generated by the cutting blade 50 into the main cutting edge 51 and the sub cutting edge 52 is enhanced, and the discharge effect by the division of the chips is improved.

  Each of the rear side thinning surface that doubles as the rake surface of the minor cutting edge and the front side thinning surface on the front side in the rotational direction form a curved surface, forming a continuous curved surface from the rear side thinning surface to the front side thinning surface, In order to make the area from the edge on the minor cutting edge side of the side thinning surface to the outer peripheral surface (No. 2 chamfered surface) which is the edge of the front side thinning surface to be a continuous curved surface without steps, the minor cutting edge is cut The formed chips can be grown along the rear side thinning surface and discharged directly into the groove. As a result, it is possible to make it difficult for the chips to be separated in the thinning portion and to prevent clogging in the thinning portion.

  In particular, when the area from the edge on the minor cutting edge side of the rear side thinning surface to the end edge of the front side thinning surface forms a curved surface in which the curvature changes continuously, the thinning surface in the process of chip growth Since it can be made hard to receive the force which divides from, it can be made easy to produce the growth of a chip, and discharge | emission to a groove | channel smoothly.

It is an end elevation showing the state of the cutting edge and the thinning portion when the blade portion is viewed in the axial direction of the drill. It is the end elevation which showed a mode that the blade part shown in FIG. 1 was seen at the angle inclined with respect to the axial direction of a drill. It is an enlarged view of the minor cutting edge part of FIG. It is an arrow line view of the aa line | wire of FIG. It is the schematic of the cross section of the yy line of FIG. It is sectional drawing of the xx line of FIG. It is a side view showing the whole of a drill.

  FIG. 1 shows a blade having a plurality of cutting edges 50 and a groove 5 for discharging chips between cutting edges 50 adjacent to each other in the circumferential direction on the tip end side in the axial direction of the shank portion 3 as shown in FIG. The end surface of the blade portion 2 of the drill 1 is provided with the portion 2, and the thinning portion 30 facing the groove 5 on the rear side in the rotational direction of the flank 100 of each cutting edge 50 is shown. The blade edge 4 which is the tip of the blade 2 is composed of a plurality of flanks 100 equally formed in the rotational direction of the drill 1, and a cutting edge 50 is formed on the forward side of each flank 100 in the rotational direction. A thinning portion 30 is formed on the rear side. The cutting edge 50 includes a main cutting edge 51 on the outer peripheral side in the radial direction, and a sub cutting edge 52 which is continuous with the main cutting edge 51 and located on the center side in the radial direction of the main cutting edge 51. The drawing shows an example in which the number of cutting edges 50 is two, but the number of cutting edges 50 may be three or more.

  The twist angle of the groove 5 is set to about 20 to 40 degrees. If the twist angle is smaller than 20 degrees, chips are difficult to ascend through the cutting holes, and if larger than 40 degrees, the amount of grinding (volume) of the groove 5 becomes large and the rigidity of the drill 1 decreases and it becomes easy to break. .

  The thinning portion 30 is formed on the front side thinning surface 31 formed on the rotational direction rear side of the flank 100 and the rear side thinning surface 32 formed on the rotational direction front side of the minor cutting edge 52 and also serving as a rake surface of the minor cutting edge 52. It consists of The rear side thinning surface 32 and the front side thinning surface 31 form curved surfaces extending from the rear side thinning surface 32 to the front side thinning surface 31 while forming the curved surfaces as shown in FIGS. 5 and 6 respectively. The “continuous curved surface” means that a curved surface having a discontinuous curvature is not sandwiched between the curved surface of the rear side thinning surface 32 and the curved surface of the front side thinning surface 31, and the rear side thinning surface 32 and the front side thinning It says that a clear border line does not appear between the faces 31.

  5 schematically shows the cross section of the drill 1 when the minor cutting edge 52 and the front side thinning surface 31 in FIG. 2 are cut along the direction of the line yy, and FIG. The cross section of the drill 1 when it cut | disconnects by the cut surface of the direction orthogonal to the rotating shaft O shown by these is shown. The yy line in FIG. 2 points in a direction that intersects with the rotational axis O, such as perpendicular to the rotational axis O. However, in reality, a cross section cut in a direction parallel to the rotational axis O is viewed in the direction of the yy line. Shows the cross section of the Therefore, FIG. 5 shows a vertical cross section (cross section parallel to the rotation axis O) when the drill 1 is erected, and FIG. 6 shows a horizontal cross section (cross section perpendicular to the rotation axis O). From FIG. 5 and FIG. 6, it can be seen that the rear side thinning surface 32 and the front side thinning surface 31 form a continuous curved surface while forming the curved surface in any cross section. In FIG. 4, the broken line between the rear side thinning surface 32 and the front side thinning surface 31 extends from the thinning surface side boundary line W1 to the outer peripheral side boundary line W3 to be described later between the rear side thinning surface 32 and the front side thinning surface 31. Although the boundary is shown as a boundary for convenience (virtual), since the section transitioning from the rear side thinning surface 32 to the front side thinning surface 31 forms a continuous curved surface, this boundary line is actually a boundary surface. can not see.

  Specifically, the continuous curved surfaces of both thinning surfaces 32 and 31 extend from the blade portion 2 side to the shank portion 3 side, and the generatrix (line) inclined from the front side in the rotational direction to the rear side from the radial center side It is a curved surface which moves in parallel along a curved line whose curvature changes continuously, for example, as shown by a broken line in FIG. Although this continuous curved surface is a tangent curved surface, a hyperbolic paraboloid, etc., a plane may be included in part.

  The flank 100 is continuous with the No. 2 face 10 continuous with the cutting edge 50 toward the rear side in the rotational direction of the cutting edge 50, and backward with the No. 2 face 10, and a relief angle larger than the relief angle of the No. 2 face 10 The front side thinning surface 31 is formed on the rear side in the rotational direction of the third surface 11 with the flank surface boundary line Q as a boundary. The rear side thinning surface 32 is formed on the front side in the rotational direction of the minor cutting edge 52 among the cutting edges 50 and is continuous with the front side thinning surface 31. The opening of the end of the oil hole 9 is located in the area of the third surface 11 having a large area when viewed from the end face of the cutting edge 4 among the flank 100.

  The diameter of the oil hole 9 is suitably 15 to 20% of the blade diameter D. If the hole diameter is less than 15% of the blade diameter D, the coolant flow rate is not sufficiently supplied, making stable cutting difficult, and if it exceeds 20%, the cross-sectional area of the drill 1 decreases and the rigidity of the drill 1 Due to

  In FIG. 1, the boundary between the second surface 10 and the third surface 11 is indicated by the boundary line P, and the boundary between the third surface 11 and the front side thinning surface 31 is indicated by the flank side boundary line Q, and the second surface 10 and the front The boundary with the side thinning surface 31 is shown by the center side boundary line S, respectively. The end on the radially outer side of the flank side boundary line Q is denoted by T2, the end on the radial center side by T1, the boundary point of the center side boundary line S with the minor cutting edge 52 is U1, the minor cutting edge 52 The boundary point between the and the main cutting edge 51 is indicated by U2. Also in FIG. 1, the rotation axis (center) of the drill 1 is indicated by O, but in the case of two cutting edges 50, the cutting edge 50 and the flank 100 are formed point-symmetrically with respect to the center O of the drill 1, The chisel edge 13 is formed between the minor cutting edges 52, 52 sandwiching the two.

  As described above, the cutting edge 50 is located on the outer peripheral side in the radial direction, and the main cutting edge 51 facing the groove 5 side, and located on the central side in the radial direction thereof, faces the flank 100 (space side boundary line Q) side It is divided into an auxiliary cutting edge 52. The radially outer peripheral side of the main cutting edge 51 is continuous with the land 8, and the land 8 is continuous with the margins 6 and 7 of the outer peripheral surface of the drill 1. In a section on the rear side in the rotational direction from the margins 6 and 7 of the outer peripheral surface of the drill 1, a second chamfered surface 12 for reducing friction at the time of cutting is formed.

  The land width is set to about 1 to 25%, preferably about 3 to 20%, of the blade diameter D. If the land width is less than 1% of the blade diameter D, the stability of the drill 1 in the hole decreases, and it becomes difficult to be guided in the hole during cutting, and if it exceeds 25%, the area contacting the inner circumferential surface of the hole is It is because it increases and the frictional resistance becomes too large.

  The heart thickness is set to about 10 to 40% of the blade diameter D. If the core thickness is less than 10% of the blade diameter D, the rigidity of the drill 1 decreases and the possibility of breakage increases, and if it exceeds 40%, the volume of the groove 5 decreases and the chip dischargeability decreases. By doing. The heart thickness may be constant over the entire length of the blade 2 or may gradually increase from the cutting edge 4 to the shank 3.

  The blade portion 2 is provided with a back taper (taper depth / groove length) of about 0.1 / 100 to 0.4 / 100. If the back taper is smaller than 0.1 / 100, the margins 6 and 7 easily come into contact with the inner wall of the hole over the entire length of the blade 2, and the possibility of breakage is high, and if it is larger than 0.4 / 100 the margin This is because the drill 1 is easily vibrated and broken easily because the effect of guiding in the holes 6 and 7 is reduced.

  The chips generated by the cutting edge 50 are divided into the chips generated by the main cutting edge 51 and the chips generated by the secondary cutting edge 52 when the main cutting edge 51 and the sub cutting edge 52 face in different directions. Therefore, the chips generated by the main cutting edge 51 try to grow while curling in the groove 5, and the chips generated by the secondary cutting edge 52 tend to grow while curling along the thinning surface 31.

  Here, the rear side thinning surface 32 and the front side thinning surface 31 form curved surfaces continuous from the rear side thinning surface 32 to the front side thinning surface 31 while forming the curved surfaces respectively. Since there is no discontinuous boundary from the side to the front side thinning surface 31, chips in the growth process are less likely to receive resistance from any of the thinning surfaces 32 and 31, and the chips may break. Is declining. As a result, the chips cut by the minor cutting edge 52 tend to grow without breaking up to the end edge on the outer peripheral side in the radial direction of the front side thinning surface 31, and try to be discharged into the groove 5 as it is.

  When the curvature of the curved surface continued from the rear side thinning surface 32 to the front side thinning surface 31 gradually decreases from the radial center side to the radial outer peripheral side, the cutting by the minor cutting edge 52 When the chips grow into a conical shape while curling, the curved surface conforms to the gradually increasing outer diameter of the chips, so that the growth of the chips is not inhibited.

  On the front side in the rotational direction of the cutting edge 50, the main cutting edge 51 and the sub cutting edge 52 as shown in FIG. 2 showing a state in which the rotation axis O in FIG. The honing surface 15 is formed to prevent the chipping of the cutting edge 50. The boundary line on the front side in the rotational direction of the honing surface 15 is divided into the thinning surface side boundary line W1 of the section of the minor cutting edge 52 and the groove side boundary line W2 of the section of the major cutting edge 51. FIG. 2 shows a state in which the shank 3 side of the rotation axis O shown in FIG. 1 is inclined toward the front (viewpoint) side. In FIG. 2, a cutting line that appears from the rear side thinning surface 32 to the front side thinning surface 31 when the cross section of the z-z line in FIG. 4 is taken is indicated by a broken line. The broken line indicates a locus along which the generatrix passes.

  The intersection point of the thinning surface side boundary line W1 and the groove side boundary line W2 is the tip end V1 of the protrusion 15a protruding toward the thinning surface 31 side or the shank portion 3 as shown in FIGS. An outer peripheral side boundary line W3 which is a boundary line between the rear side thinning surface 32 and the groove 5 continues from the tip end V1 of the projecting portion 15a toward the shank portion 3 side. The outer peripheral side boundary line W3 is also a boundary line between the thinning portion 30 and the groove 5, and continues to the heel 14 as shown in FIG.

  As shown in FIG. 3, the thinning surface side boundary line W1, the groove side boundary line W2, and the outer peripheral side boundary line W3 form a convex ridge line, but in particular, the outer peripheral side boundary line W3 forms a convex ridge line, the tip V1. The section continuous from the outer peripheral side boundary line W3 functions as a blade that divides the chips generated by the cutting edge 50 radially outward and the center side, so the chips generated by the cutting edge 50 are main cutting edges 51 The effect of dividing the side chips and the chips on the side of the auxiliary cutting edge 52 is exhibited.

  Since the outer peripheral side boundary line W3 starting from the tip V1 functions as a blade for dividing the chips in the radial direction, the chips cut by the main cutting edge 51 and the chips cut by the minor cutting edge 52 are chips. It is divided from the time of generation, and the chips tend to grow along the surface of the groove 5 and the thinning surfaces 32, 31. By dividing the chips generated by the main cutting edge 51 into the chips generated by the main cutting edge 51 and the chips generated by the sub cutting edge 52 from the start of cutting of the work material by the drill 1, the growth is not performed as in the case where the chips are not divided. Depending on the situation, it is not discharged directly into the groove 5 but it gets into the thinning part 30 and chips do not concentrate and stagnate in the thinning part 30, so that clogging of the thinning part 30 of chips occurs. It becomes difficult.

Example 1
Tables 1 to 3 show the comparison between the drill 1 of the embodiment of the present invention and the drill of the conventional example not having the requirements of the present invention when used for drilling under the same conditions. The requirement of the present invention is that “the rear side thinning surface 32 and the front side thinning surface 31 form curved surfaces and the rear side thinning surface 32 forms a continuous curved surface from the rear side thinning surface 32”. is there. Example 1 In the following, in order to reduce manufacturing unevenness of the drill as a sample, the same five samples are prepared for one type of drill satisfying the requirements of the present invention and the drill of the conventional example. The samples were averaged for evaluation.

  Both the drill of the first embodiment and the drill of the prior art have a shank diameter and a drill diameter of 6.0 mm, a total length of 250 mm, a groove length of 199 mm, and a pitch of 3.2 mm and a hole diameter of 0.7 mm. It has an oil hole, a twist angle of 30 degrees, and a hard coating of TiSiN with a thickness of 3 μm.

  The rear side thinning surface 32, which is the rake surface of the minor cutting edge 52 of the drill of the present invention, is a curved surface continuous to the front side thinning surface 31, while the rear side thinning surface of the prior art drill is flat. Conventional drills and drills of the present invention are different. The drill of the present invention and the conventional drill have two blades of the same shape and the same size (same specifications) using the same cemented carbide as a base except that the shape of the rear side thinning surface 32 is different.

  No drilling is performed on the carbon steel (S50C) with hardness 220HB as the work material, by wet cutting with internal oil supply through oil holes, at a rotation speed of 3500 rpm and at a feed speed of 700 mm / min (non-step machining) The goal was to make a hole 180 mm in depth). Machining with a single drill ends when either the margin reaches a certain flank wear width or the drill breaks, and the number of holes finished is the drill life evaluated. The flank wear width of the margin was 0.4 mm, and the same drilling was performed on five identical samples. The results are shown in Table 1, and the average number of holes is evaluated as good (○), 200 to 150 (good), and 150 or less as poor (×).

  “Open angle θ” in Table 1 is the angle between the minor cutting edge 52 (straight line U1U2) and the straight line connecting both ends T1 and T2 of the flank side boundary line Q as shown in FIG. It corresponds to the angle between the rotation direction rear side edge of the surface 32 and the rotation direction front side edge of the front side thinning surface 31. As the angle θ is larger, the angle between the edge of the rear side thinning surface 32 and the edge of the front side thinning surface 31 is larger, and the volume of the region near the radial center sandwiched by both thinning surfaces 32 and 31 is This means that the large capacity (discharge capacity) of the chips generated by the secondary cutting edge 52 is high. However, if the opening angle θ is too large, the rigidity of the drill 1 is reduced by decreasing the diameter of the drill 1 main body, such as the heart thickness, and vibration is easily generated at the time of cutting. Limited both in terms of waste dischargeability and rigidity.

  From Table 1, it can be seen that while the number of machined holes (lifetime) of the invention example 1 exceeds 200, the prior art example 1 is about half stronger than the invention example. Since both differ only in the point at which the rear side thinning surface 32 is a curved surface that is continuous with the front side thinning surface 31 or a non-continuous surface, and the opening angle θ, Example 1 of the present invention As a result of having the back side thinning surface 32 of a curved surface continuous to the side thinning surface 31 and having an open angle θ of an obtuse angle, it is considered to have a drilling ability close to less than twice that of the prior art example 1.

  Specifically, the angle between the edge of the rear side thinning surface 32 and the edge of the front side thinning surface 31 is an obtuse angle, and the formation and growth of chips are not inhibited by forming a curved surface in which both surfaces are continuous, It is surmised that the reason is to be smoothly discharged into the groove 5 after growth. Since both the rear side thinning surface 32 and the front side thinning surface 31 are curved surfaces, a region near the radial center sandwiched by both thinning surfaces 32 and 31 becomes a three-dimensional space formed by the curved surfaces, so that the conical shape is formed. It can be said that the chips generated in the housing are easily accommodated.

  On the other hand, in the first prior art, since the rear side thinning surface 32 is a flat surface, the region near the radial center sandwiched between both thinning surfaces 32 and 31 becomes a solid having a shape not suitable for containing chips. It can be said that the generation of chips is easily inhibited and the chips are easily clogged. In addition, the reason why the volume of the space formed by both the thinning surfaces 32 and 31 is also reduced because the angle between the rear side thinning surface 32 and the front side thinning surface 31 is an acute angle, which also inhibits the generation of chips. It is considered to be.

(Example 2)
Based on the result of Example 1, a section (U1 to U1 in which the rear side thinning surface 32 is shifted to the front side thinning surface 31 when the drill 1 is viewed in the axial direction while keeping the opening angle θ constant at 110 degrees A test was conducted to compare the life of the drill of the present invention example and the conventional example in which the ratio of the curvature of T1) and the curvature of the section (T1 to T2) of the front side thinning surface 31 was changed. did. As an example of the present invention, four types of samples 2 to 5 are prepared: curvature ratio between U1 to T1: curvature ratio between T1 to T2 of 3: 1, 4.5: 1, 5.5: 1, 6: 1 As a conventional example, two types of samples 2 and 3 of 2.5: 1 and 6.5: 1 were prepared. The specifications of the drill of the present invention example and the prior art example are the same as those of the first embodiment, and the drilling procedure is also the same.

  According to Table 2, the average life is less than 150 holes in the prior art examples 2 and 3 while it exceeds 180 holes in the invention examples 2 to 5, and in particular, exceeds 250 holes in the invention examples 2 and 3, 2 of the prior art example 2 It can be seen that the life of about twice as large is obtained, and the life of the invention example 4 is 1.6 times that of the prior art example 2 as well. Conventional Examples 2 and 3 are different from the invention examples 2 to 5 in that the rear side thinning surface 32 is a flat surface and the curved surface continuous to the front side thinning surface 31 is not formed. , It is thought that there is an impact on the life mentioned above.

  Then, focusing on the results of Invention Examples 2 to 5, the curvature ratio between U1 and T1: the curvature ratio between T1 and T2 (curvature between U1 and T1 / curvature between T1 and T2) is 3 to 5. The range of about 5: 1 (3 to 5.5) is most appropriate, and in particular, the range of about 3 to 4.5 is more preferable, and when this ratio is less than 3 and more than 6, the cutting ability is reduced Show a tendency to That is, even if the curvature between U1 and T1 is smaller than the curvature between T1 and T2, the chip capacity decreases even if it is too large, and the ratio of the curvature between U1 and T1 to the curvature between T1 and T2 There is an appropriate range that does not inhibit chip formation and growth, and it can be said that the range is about 3 to 5.5.

  If the ratio of curvature between U1 and T1 to the curvature between T1 and T2 is less than 3 (if the curvature between U1 and T1 is small), the rear side thinning surface 32, which is the rake surface of the minor cutting edge 52, is minor cutting It is considered that the cutting edge strength of the sub cutting edge 52 is reduced by being deeply in the lower part of the blade 52, and chipping tends to occur. On the other hand, if the ratio exceeds 6 (if the curvature between U1 and T1 is large), the volume of the region between the rear side thinning surface 32 and the front side thinning surface 31 decreases, which inhibits the growth of chips. It is considered that it is easy to cause clogging.

(Example 3)
Based on the results of Examples 1 and 2, the curvature ratio between U1 and T1: The curvature ratio between T1 and T2 (curvature between U1 and T1 / curvature between T1 and T2) is fixed to 3: 1 (3). In the same manner, the same test as in Example 1 was performed on the drill of the present invention example and the conventional example in which the opening angle θ was changed. In the example of the present invention, four types of samples 6 to 9 having an opening angle θ of 120 to 90 degrees are prepared, and as the conventional example, two types of samples 4 and 5 of 130 degrees and 80 degrees are prepared. The specifications of the drill of the present invention example and the prior art example are the same as those of the first embodiment, and the drilling procedure is also the same.

  According to Table 3, while the average life is less than 150 holes in the conventional examples 4 and 5, in the invention examples 6 to 9, it exceeds 160 holes, and particularly in the invention examples 7 and 8, it exceeds 210 holes. It can be seen that it has a higher lifetime. The life of Inventive Example 7 is more than twice that of Conventional Example 4. Conventional Examples 2 and 3 also differ from Invention Examples 6 to 9 in that the rear side thinning surface 32 does not form a curved surface continuous with the front side thinning surface 31, and therefore, the influence on the life due to this point Is considered to be appearing.

  Therefore, focusing on the results of the invention examples 6 to 9, in the case of a two-edged blade, it is appropriate that the opening angle θ be in the range of about 100 to 110 degrees, and the cutting ability is reduced outside this range. It can be said that it shows a tendency. That is, even if the opening angle θ is less than 90 degrees or exceeds 110 degrees, the chip capacity decreases, and it can be said that the range of these numerical values is good, and around 110 degrees is the best numerical value.

  If the opening angle θ is less than 90 degrees, the volume of the region between the rear side thinning surface 32 and the front side thinning surface 31 decreases, so chip growth tends to be inhibited and clogging tends to occur, and 110 degrees If it exceeds, the rigidity of the drill itself tends to decrease due to an increase in the volume of the thinning portion 30, which is considered to have affected the life of the drill. Conventional Example 4 has a large opening angle θ, leading to a decrease in drill rigidity, and Conventional Example 5 has a small opening angle θ, so the volume of the region between the rear side thinning surface 32 and the front side thinning surface 31 is It is considered that the decrease and the chip being clogged easily affect the life.

1 ...... drill,
2 刃 blade portion 3 シ ャ ン ク shank portion 4 刃 先 blade edge portion
5 ...... groove,
6, 7 ...... margin, 8 ラ ン ド land, 9 ホ ー ル oil hole,
100: flank, 10: second side, 11: third side, 12: second side,
13: Chisel edge, 14: Heel,
15 ...... honing surface, 15a ...... projecting portion,
30: Thinning part, 31: Front side thinning surface, 32: Rear side thinning surface (rake surface of minor cutting edge),
50: cutting edge, 51: main cutting edge, 52: secondary cutting edge ,
O ...... Rotation axis,
P: A boundary line between the second and third surfaces, Q: A flank side boundary line (a boundary line between the third surface and the front side thinning surface),
R: Direction of rotation, S: Center side boundary line (boundary line between the second surface and the front side thinning surface),
T1 ··· Intersection of boundary line Q and boundary line S, T2 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · drill outer end point of the boundary line Q,
U1: Intersection point of boundary line S and minor cutting edge, U2: Intersection point of minor cutting edge and major cutting edge,
V1 ... intersection point of groove and rear side thinning surface and honing surface,
W1: Thinning surface side boundary line, W2: Groove side boundary line, W3: Outer peripheral side boundary line,
θ: The angle between the minor cutting edge and the straight line connecting both ends T1 and T2 of the boundary line Q.

Claims (5)

A plurality of cutting edges and a cutting edge having a groove between the cutting edges adjacent to each other in the circumferential direction on the tip end side in the axial direction of the shank portion, the cutting edge being a main cutting edge on the radially outer peripheral side and this main cutting edge It is continuous with a cutting edge, consists of a sub-cutting edge located on the radial center side of the main cutting edge, and a drill having a thinning portion facing the groove on the rear side in the rotational direction of the flank of each cutting edge Yes,
The thinning portion includes a front side thinning surface formed on the rear side in the rotational direction of the flank surface, and a rear side thinning surface formed on the front side in the rotational direction of the sub cutting edge and serving as a rake surface of the sub cutting edge. And
The back side thinning surface and the front side thinning surface respectively form a curved surface, and the back side thinning surface forms a continuous curved surface from the back side thinning surface to the front side thinning surface, and the front side thinning surface is the blade portion Continue to the outer peripheral surface of the
The rear side thinning surface and the front side thinning surface continue in a band shape to the radially outer peripheral side while having a width corresponding to a section of the sub cutting edge in the length direction of the sub cutting edge, the rear side A drilling characterized in that the thinning surface and the boundary line between the front side thinning surface and the flank face draw a concave curve to the outer peripheral side in the radial direction .   The continuous curved surface runs from the blade side to the shank side, and a generatrix inclined from the rotational direction front side to the rear side moves from the radial center side to the radial outer peripheral side, and moves parallel along a curve The drill according to claim 1, wherein the drill is a curved surface drawn with a continuously changing curvature.   The drill according to claim 2, wherein the curvature gradually decreases from the radial center side toward the radial outer peripheral side. A honing surface is formed on the front side in the rotational direction of the cutting edge, and on the front side in the rotational direction of the honing surface, at the boundary position between the main cutting edge and the sub cutting edge, the main cutting edge and the other than the boundary position The drill according to any one of claims 1 to 3, characterized in that a projecting portion is formed to project forward in the rotational direction from the auxiliary cutting edge .   An outer peripheral side boundary line between the rear side thinning surface and the groove continues from the tip on the front side in the rotational direction of the protrusion toward the shank portion, and the outer peripheral side boundary line forms a convex ridge line The drill according to claim 4, characterized in that: