JP2014166660A - Drilling machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life drilling machine capable of reducing cutting resistance even to a material to be cut such as a heat-resistant alloy and of preventing early wear and loss.SOLUTION: A cutting blade 15 is formed on an intersecting ridge line of a tip flank 13 and a wall face facing in a drill rotational direction T of a chip discharge groove 14 which is formed on a tip outer periphery of a drill body 11 rotated around an axial line O. The cutting blade 15 is provided with a main cutting blade 15a extending from an outer peripheral edge to an inner periphery side, and a thinning blade 15b which is formed on the intersecting ridge line of the tip flank 13 and a thinning face facing in the drill rotational direction T of a thinning part 16 which is formed so as to cut out, to an axial line O side, the inner periphery part of the wall face facing the drill rotational direction T of the chip discharge groove 14, and which continues to the inner periphery of the main cutting blade 15a. The true rake angle of the cutting blade 15 is a positive angle over the whole length and gradually increases toward a positive angle side toward the outer periphery side from the inner periphery of the drill body 11.

Description

  The present invention relates to a drill used for drilling a work material made of a metal material.

  As such a drill, in Patent Document 1, a chip discharge groove extending with a twist in the axial direction is disposed at the tip of the drill body, and a main cutting edge is provided at the tip of the chip discharge groove. In a twist drill in which an X-shaped thinning is attached to the shaft center portion to form a thinning blade, in order to reduce the thrust load while maintaining the cutting edge strength, the thinning blade has a positive axial rake angle. A drill having a corner and a size of + 5 ° to + 15 °, specifically + 10 ° has been proposed.

  Similarly, in Patent Document 2, in a drill having a cutting edge having a main cutting edge and a thinning edge, in order to reduce the cutting resistance while improving the tool life, the thinning edge includes the thinning edge and the thinning edge. The rake angle that is the angle formed by the axis of the drill body, that is, the axial rake angle varies between the axial line side of the drill body inner periphery and the main cutting edge side of the outer periphery, and the axial rake angle of this thinning blade is A rake angle on the side of the main cutting edge is set to a positive angle larger than the rake angle on the axis side.

JP 2000-271811 A JP 2008-093805 A

  By the way, the cutting edge of such a drill is generally provided with a tip angle so as to go to the rear end side of the drill body as it goes to the outer peripheral side. For this reason, even if the axial rake angle of the thinning blade is a positive angle as in the drills described in Patent Documents 1 and 2, the plane perpendicular to the thinning blade passes through the one point on the axis. The angle between the intersecting lines obtained by intersecting the flat surface including the rake face of the thinning blade, that is, the true rake angle (vertical rake angle) is not necessarily a positive angle.

  In particular, when the axial rake angle of the thinning blade on the main cutting edge side is set to a positive angle larger than the axial rake angle of the thinning blade on the axial line side as in the drill described in Patent Document 2, A plane perpendicular to the thinning blade at one point on the thinning blade on the cutting edge side extends toward the rake face of the thinning blade on the axial side whose axial rake angle is relatively increased toward the negative angle side. For this reason, the true rake angle of the thinning blade on the main cutting edge side may be 0 ° or a negative angle.

  Here, FIG. 12 to FIG. 14 show the product drill of the invention filed in Japanese Patent Application No. 2001-209585 (Japanese Patent Laid-Open No. 2003-025125, Japanese Patent No. 4120185) by the applicant of the present invention. The drill body 1 of this product drill has a cutting blade 2 with a diameter of 13.0 mm, and FIG. 15 shows that the cutting blade 2 is perpendicular to the cutting blade 2 at a point P on the cutting blade 2 as shown in FIG. As shown in FIG. 14, the true rake angle that is an angle between the planes Q passing through the point P and the plane including the axis O of the drill body 1 and the rake face 3 of the cutting edge 2 is sandwiched between the planes Q. θ is measured for each point P on the cutting edge 2 having a diameter φ of about 1.0 mm (radius of 0.5 mm) from the axis O toward the radially outer peripheral side.

  In FIG. 15, the reference symbol A indicates the region of the main cutting edge 2 a of the cutting blade 2, and the reference symbol B indicates the region of the thinning blade 2 b of the cutting blade 2. As shown in FIG. 5, in the region B of the thinning blade 2b, there is a portion where the true rake angle θ of the cutting blade 2 is 0 ° and a negative angle. In such a drill, since the thinning blade 2b crushes the work material, the cutting resistance increases, and the cutting blade cuts the work material hardened by being crushed and compressed. Therefore, if a high load acts on the cutting blade and the cutting blade strength is insufficient, there is a possibility of causing a chipping. For example, in the region B of the thinning blade 2b, a portion where the true rake angle θ is 0 ° Even if it is formed to be a positive angle, a portion where the true rake angle θ is a negative angle remains at the boundary with the region A of the main cutting edge 2a.

  On the other hand, as the tip angle is given as described above, chips generated in the region A of the main cutting edge 2a of the cutting edge 2 are scraped from the outer peripheral side of the drill body 1 while rubbing the rake face 3. It flows out so that it may be caught in the circumference side. Therefore, as described above, if a portion where the true rake angle θ is a negative angle is left at the boundary between the region A of the main cutting edge 2a and the region B of the thinning blade 2b, the chips run on this portion. It will flow and the part will receive a heavy load. For this reason, even with such a drill, particularly when drilling is performed on a work material made of a heat-resistant alloy or the like that is likely to cause work hardening, scratch marks are formed in which the chips are strongly rubbed at the boundary portion. Therefore, if such drilling is continued, a portion subjected to a high load may be worn or chipped early, and the drill life may be consumed.

  The present invention has been made under such a background, and is intended to reduce cutting resistance and to reduce the cutting force even for a work material having high hardness, high toughness, and high heat resistance, such as a heat-resistant alloy. An object of the present invention is to provide a long-life drill capable of preventing wear and breakage.

  In order to solve the above problems and achieve such an object, according to the present invention, a chip discharge groove is formed on the outer periphery of the tip of the drill body rotated about the axis, and the drill rotation direction of the chip discharge groove is changed. A drill in which a cutting edge is formed at an intersecting ridge line portion between a facing wall surface and a tip flank of the drill body, the cutting edge including a main cutting edge extending from an outer peripheral end of the cutting edge to an inner peripheral side, The inner peripheral part of the wall surface facing the drill rotation direction of the chip discharge groove is formed at the intersecting ridge line part of the thinning surface facing the drill rotation direction of the thinning part formed so as to cut out on the axis side and the tip flank surface. A thinning blade connected to the inner periphery of the main cutting edge, and the true rake angle of the cutting edge formed by the thinning blade and the main cutting edge is a positive angle over the entire length of the cutting edge, and Positive as it goes from the inner circumference to the outer circumference of the drill body Characterized by comprising gradually increases on the side.

  In the drill configured as described above, the rake angle of the cutting blade formed by the thinning blade and the main cutting blade is a positive angle over the entire length of the cutting blade, and the true rake angle is 0 as described above. Since there is no part that becomes an angle or a negative angle, the cutting edge can be sharpened over the entire length to reduce cutting resistance. Moreover, the true rake angle of this cutting edge is continuously changed so as to gradually increase toward the positive angle side from the inner circumference to the outer circumference side of the drill body, and is partially true along the cutting edge. Even when the rake angle is within the positive angle range, there is no formation of a portion that increases toward the negative angle side after it increases toward the negative angle side. Or it can prevent that a defect | deletion arises.

  Furthermore, in the thinning blade among the cutting blades, the true rake angle is a positive angle, so the main cutting edge is reduced toward the inner peripheral side of the drill body while reducing the thrust load by improving the sharpness. In contrast to this, since a large true rake angle is formed toward the negative angle side, it is possible to ensure the cutting edge strength and reliably prevent wear and chipping. Therefore, according to the drill having the above-described configuration, work hardening can be suppressed even for a work material such as a heat-resistant alloy, so that the drill body can be prevented from being worn or chipped at an early stage. And stable drilling can be performed.

  Here, the bottom surface of the thinning portion where the thinning surface of the thinning portion that faces the drill rotation direction and the thinning wall that faces the thinning surface and faces the back side of the thinning portion in the drill rotation direction intersects the thinning surface and the thinning surface. The wall surface may be crossed at an angle with a V-shaped cross section. In such a case, the chips generated by the thinning blade and flowing on the thinning surface collide with the thinning wall surface and are pressed. In addition, since it is discharged to the chip discharge groove while being rubbed strongly along the thinning wall surface, there is a possibility that a welding mark is formed on the thinning wall surface or crater-like wear occurs to cause the drill body to be damaged.

  Therefore, in order to mitigate such damage to the thinning wall surface, the bottom surface of the thinning part where the thinning surface intersects with the thinning wall surface is formed into a concave curved surface, and the chips collide against the thinning wall surface and are pressed against or strongly scratched. It is desirable to prevent the pair of cutting edges from being formed symmetrically with respect to the axis, and a chisel is formed at the intersecting ridge line portion between the tip flank faces connected to these cutting edges. In the case of a drill, if the bottom surface of the thinning part is formed in a concave curved surface in this way, the intersection ridge line part between the bottom surface and the tip flank surface becomes a concave curve, so the angle between the thinning surface and the thinning wall surface is as described above. The chisel will be longer than when crossing. The chisel is the intersection ridgeline between the flank surfaces of the tip, and only crushes the workpiece without cutting it.Thus, the longer the chisel, the larger the work hardening and the thrust load of the workpiece. As a result, the reduction in cutting resistance is impaired.

  Therefore, in such a case, in order to prevent the chisel from becoming long while reducing the damage of the thinning wall surface by making the bottom surface of the thinning portion concave, the bottom surface of the thinning portion is formed so as to intersect the tip flank. The concave curve is preferably positioned on the thinning wall side facing the rear side in the drill rotation direction of the thinning portion with respect to the intersection of the cutting edge and the chisel. As a result, the concave curve formed by the bottom surface of the thinning portion of the pair of cutting blades and the tip flank surface is arranged so as to enter the alternate cutting blade side across the chisel in the axial front end view. Thus, the cutting resistance can be surely reduced.

  By the way, when the concave curve formed by the bottom surface of the thinning portion having such a concave curved surface intersecting the tip flank surface is positioned closer to the thinning wall surface than the intersection of the cutting blade and the chisel, Even on the thinning wall side from the intersection of the cutting edge and chisel, if the angle that should be called the true rake angle of the thinning wall or bottom surface of the thinning part remains a regular angle, the wall thickness is the largest, especially at the center of the tip of the drill body. In a cross section including the axis, passing through a circular contact centered on the axis that is inscribed in the intersecting ridge line portion of the thinning surface or the bottom surface and the tip flank as viewed from the front end side in the axial direction. As the thinning surface or bottom surface of the thinning part of the pair of cutting blades approaches the rear end side of the drill body, they approach each other to form a wedge-shaped section in the cross section of the drill body. There is a possibility that the strength of decreases.

  On the other hand, the true rake angle of the thinning blade is positive toward the intersection with the chisel that is the inner peripheral edge of the cutting blade, but gradually increases toward the negative angle, so the intersection with this chisel Even in the part that goes to the thinning wall side beyond the angle, the angle that should be called the true rake angle of the thinning surface or the bottom surface is increased to the negative angle side, and the thinning surface or the bottom surface and the tip clearance are viewed from the axial front end side. In a cross-section including the axis line that passes through the circle inscribed in the intersecting ridge line with the surface, the tangent line at the contact point of the thinning surface or bottom surface is parallel to the axis line or after the drill body. In the tip of the drill body, the true rake angle of the thinning surface or bottom surface is set to 0 ° or a negative angle so as to be separated from the axis line toward the end side. To secure the thickness of the part and it is possible to prevent a decrease in strength as described above.

  As described above, according to the present invention, since the true rake angle is a positive angle over the entire length of the cutting edge, the cutting resistance can be improved and the cutting resistance can be reduced. It is possible to suppress work hardening, and there is no formation of a portion that partially increases to the negative angle side and then increases again to the positive angle side, so the load is concentrated on such a portion. Abrasion and chipping can be prevented. In addition, while maintaining the sharpness of the thinning blade, the true rake angle gradually increases to the negative angle side within the positive angle range toward the inner periphery, so that the cutting edge strength is improved. This makes it possible to perform stable drilling for a long work material over a long period of time.

It is a front view of the cutting blade part of the drill body front-end | tip part which shows one Embodiment of this invention. It is a side view of the front-end | tip part of the cutting blade part of embodiment shown in FIG. It is an enlarged front view of the drill body front-end | tip center part of embodiment shown in FIG. FIG. 2 is an enlarged side view of the center portion of the tip end of the drill body according to the embodiment shown in FIG. 1. It is ZZ sectional drawing in FIG. It is a figure which shows the result of having measured the true rake angle of each point on the cutting blade in embodiment shown in FIG. It is an enlarged front view of the drill body front-end | tip center part which shows the 1st modification of embodiment shown in FIG. It is an enlarged front view of the drill body front-end | tip center part which shows the 2nd modification of embodiment shown in FIG. It is an enlarged front view of the drill main body front-end | tip center part which shows the 3rd modification of embodiment shown in FIG. FIG. 10 is an enlarged side view of the center portion of the tip end of the drill body of the third modification shown in FIG. 9. It is ZZ expanded sectional drawing in FIG. It is a front view of the cutting blade part of the drill main body tip part of the conventional drill. It is a side view of the cutting-blade front-end | tip part of the drill shown in FIG. It is ZZ expanded sectional drawing in FIG. It is a figure which shows the result of having measured the true rake angle of each point on the cutting blade in the drill shown in FIG.

  1 to 5 show an embodiment of the present invention. In the present embodiment, the drill main body 11 is formed in a substantially cylindrical shape centered on the axis O by a hard material such as cemented carbide, and a rear end portion (not shown) is a shank portion that remains in a cylindrical shape. The tip shown in FIGS. 1 and 2 is a cutting edge 12, and the shank is gripped by the main spindle of the machine tool and is sent to the tip in the axis O direction while being rotated around the axis O in the drill rotation direction T. Then, the work piece is drilled by the cutting edge portion 12.

  On the outer periphery of the cutting edge portion 12, a chip discharge groove 14 that opens to the front end flank 13 that is the front end surface of the cutting edge portion 12 and twists toward the rear side in the drill rotation direction T about the axis O as it goes to the rear end side. The cutting edge 15 is formed at the intersection ridge line portion of the wall surface of the chip discharge groove 14 facing the drill rotation direction T and the tip flank 13. Here, the drill of this embodiment is a two-blade twist in which each pair of tip flank 13, chip discharge groove 14, and cutting edge 15 is formed in a 180 ° rotationally symmetric shape with respect to the axis O on the cutting edge portion 12. It is a drill.

  The tip flank 13 is inclined so as to be directed toward the rear end side of the drill main body 11 from the cutting edge 15 toward the rear side in the drill rotation direction T, thereby giving a clearance angle to the cutting edge 15 and the drill main body 11. The tip is inclined toward the rear end side of the drill body 11 from the center of the tip toward the outer peripheral side, so that a tip angle is given to the cutting edge 15. Here, the tip flank 13 of the present embodiment has a first flank 13a having a small flank angle continuous with the cutting edge 15, and a large flank angle continuous to the rear side in the drill rotation direction T of the first tip flank 13a. The second tip flank 13b is formed. In the present embodiment, the intersecting ridge lines of the first and second tip flank surfaces 13a and 13b pass through the axis O when viewed from the tip of the axis O direction.

  On the other hand, a thinning portion 16 is formed in the inner peripheral portion of the tip of the wall surface of the chip discharge groove 14 facing the drill rotation direction T so as to cut out the inner peripheral portion further toward the axis O side of the inner periphery of the drill body 11. ing. In the present embodiment, the thinning portion 16 is connected to the inner peripheral side of the wall surface facing the drill rotation direction T of the chip discharge groove 14 and similarly faces the drill rotation direction T, and toward the inner axis side toward the axis O side. A thinning surface 16a that faces the drilling direction T of the chip discharge groove 14 and a thinning wall surface 16b that faces the rearward side of the drill rotation direction T in the same way, and a thinning surface 16a and a thinning wall surface 16b And a bottom surface 16c formed at a crossing portion.

  Further, in the cross ridge line portion between the outer peripheral side portion of the wall surface facing the drill rotation direction T of the chip discharge groove 14 and the thinning portion 16 and the first tip flank 13a of the tip flank 13 above, A main cutting edge 15a on the outer peripheral side of the cutting edge 15 is formed, and an intersection ridge line portion between the thinning surface 16a of the thinning portion 16 and the first tip flank 13a of the tip flank 13 Among them, a thinning blade 15b is formed which is connected to the inner peripheral side of the main cutting edge 15a and directed toward the axis O side. The main cutting edge 15a forms a straight line and extends toward the inner peripheral side when viewed from the front end in the direction of the axis O, and the thinning blade 15b forms a convex curve in contact with the main cutting edge 15a toward the inner peripheral side toward the axis O side. It extends like so.

  In addition, a chisel 17 is formed at the intersection ridge line portion between the tip flank surfaces 13 connected to the pair of cutting blades 15. As described above, in the present embodiment in which the intersecting ridge lines of the first and second tip flank surfaces 13a and 13b of the tip flank 13 pass through the axis O when viewed in the direction of the axis O, the pair of tip flank 13 The first tip flank 13a of the tip flank 13 connected to one of the cutting blades 15 intersects with the second tip flank 13b of the tip flank 13 connected to the other cutting blade 15 via the chisel 17. It is done. Therefore, the intersection 15c of the cutting blade 15 with the chisel 17 is the inner peripheral end of the cutting blade 15, that is, the inner peripheral end of the thinning blade 15b.

  Here, the bottom surface 16c of the thinning portion 16 is formed in a concave curved surface shape such as a concave cylindrical surface in the present embodiment, and is in smooth contact with the thinning surface 16a and the thinning wall surface 16b. Further, a concave curve formed by intersecting the concave curved bottom surface 16c with the tip flank 13 is an intersection 15c between the cutting edge 15 and the chisel 17 which is the inner peripheral end of the cutting edge 15, as shown in FIG. It is arranged to be closer to the thinning wall surface 16b.

  Further, the thinning blade 15b having a convex curve shape as described above in the front view in the direction of the axis O is configured to contact the concave curve where the bottom surface 16c and the tip clearance surface 13 intersect at the intersection 15c directly or via a short tangent. Has been. On the other hand, the intersecting ridge line between the thinning wall surface 16b and the second tip flank 13b of the tip flank 13 adjacent to the drill rotation direction T side is in contact with the concave curve between the bottom surface 16c and the tip flank 13 and is linearly It extends to the side and reaches the outer peripheral surface of the tip of the drill body 11. That is, the thinning portion 16 is formed such that the thinning wall surface 16b cuts out to the tip of the heel of the cutting blade portion 12.

  The true rake angle formed by the cutting edge 15 is a regular angle over the entire length of the cutting edge 15 from the main cutting edge 15a to the thinning edge 15b, and at the inner peripheral end of the cutting edge 15. As it goes from the intersection 15c to the main cutting edge 15a on the outer peripheral side through the thinning blade 15b, it gradually increases toward the regular angle side. That is, a plane perpendicular to the cutting edge 15 at one point on the cutting edge 15 passes through the one point and includes the axis O of the drill body 11 and the rake face of the cutting edge 15 (the drill of the chip discharge groove 14 in the main cutting edge 15a). Wall surface facing the rotation direction T. In the thinning blade 15b, the true rake angle that is an angle between the intersecting lines obtained by intersecting with the thinning surface 16a) is a positive angle over the entire length of the cutting blade 15. The drill body 11 gradually increases from the inner circumference toward the outer circumference side toward the regular angle side.

  Here, as shown in FIG. 6, in the drill of this embodiment in which the diameter of the cutting edge 15 is 13.0 mm as in the conventional drill shown in FIGS. 12 to 14, as shown in FIG. The true rake angle of the cutting edge 15 is measured at each point P on the cutting edge 15 at a diameter φ of approximately every 1.0 mm (radius every 0.5 mm) from the axis O toward the radially outer peripheral side. is there. Further, in FIG. 6, the reference symbol A indicates the region of the main cutting edge 15 a of the cutting blade 15, and the reference symbol B indicates the region of the thinning blade 15 b of the cutting blade 15. The position of 0.0 mm substantially coincides with the position of the intersection 15 c with the chisel 17 that is the inner peripheral end of the cutting edge 15.

  As shown in FIG. 6, in this embodiment, the true rake angle of the cutting edge 15 is a positive angle of + 5 ° or more at the position of the intersection 15 c with the chisel 17 that is the inner peripheral end of the cutting edge 15. In the region B of the thinning blade 15b, it becomes larger on the regular angle side toward the outer peripheral side with a relatively small increase rate, and is about + 10 ° in the vicinity of the boundary with the region A of the main cutting edge 15a. Further, in the area A of the main cutting edge 15a, the true rake angle of the cutting edge 15 increases toward the outer peripheral side at a substantially larger increase rate than the area B of the thinning blade 15b, and becomes larger on the positive angle side. It reaches the end, and the outer peripheral end has a size of about + 20 ° to + 25 °.

  On the other hand, the true rake angle of the cutting edge 15 is gradually increased toward the negative angle side within the positive angle range as it goes toward the inner peripheral side of the drill body 11. In this embodiment, the tendency is maintained as it is even if it goes to the inner peripheral side beyond the intersection 15c with the chisel 17 which is the inner peripheral end of the cutting edge 15. That is, a plane orthogonal to the intersecting ridgeline portion at one point on the intersecting ridgeline portion between the thinning surface 16a or the bottom surface 16c and the tip flank 13 on the inner peripheral side with respect to the intersection 15c passes through the one point and the axis O of the drill body 11 is set. The angle between the intersecting lines obtained by intersecting the flat surface and the thinning surface 16a or the bottom surface 16c, that is, the true scoop of the intersecting ridge line portion between the thinning surface 16a or the bottom surface 16c and the tip relief surface 13 on the inner peripheral side from the intersection 15c. The angle that should be called an angle gradually increases toward the negative angle side as it goes from the intersection 15c toward the inner peripheral side.

  Then, this angle is such that the one point is directed from the intersection 15c toward the inner peripheral side, and as shown in FIG. 3, when viewed from the front end side in the axis O direction, the intersection ridge line portion between the thinning surface 16a or the bottom surface 16c and the front clearance surface 13 The angle is set to 0 ° until reaching the contact point S of the circle C with the axis O inscribed in the center. Therefore, in the present embodiment, the cross section of the thinning portion 16 of the pair of cutting blades 15 that passes through the contacts S of the circle C and includes the axis O, the thinning surface 16a or the bottom surface 16c of the cross section as shown in FIG. A tangent L at the contact S extends parallel to the axis O or away from the axis O toward the rear end side of the drill body 11. In the present embodiment, the contact S is a contact point between the concave curve formed by the concave curved bottom surface 16 c and the tip flank 13 in the thinning portion 16 and the circle C.

  In the drill constructed in this way, the true rake angle of the cutting edge 15 composed of the main cutting edge 15a and the thinning edge 15b, that is, a plane perpendicular to the cutting edge 15 at one point on the cutting edge 15 passes through the one point. The angle between the plane including the axis O of the main body 11 and the wall surface facing the drill rotation direction T of the chip discharge groove 14 serving as the rake face of the cutting edge 15 and the thinning surface 16a is sandwiched between the cutting edges 15. It is a positive angle over the entire length, and the true rake angle does not become 0 ° or a negative angle. For this reason, the sharpness of the cutting edge 15 can be sharpened from the main cutting edge 15a to the entire length of the cutting edge 15 of the thinning edge 15b, thereby reducing cutting resistance and suppressing work hardening of the work material. be able to.

  Further, in particular, the true rake angle of the cutting edge 15 is such that the main cutting edge 15a on the outer peripheral side passes through the thinning blade 15b on the inner peripheral side of the drill body 11 from the intersection 15c with the chisel 17 serving as the inner peripheral end of the cutting edge 15. Gradually increased toward the positive angle side and gradually increased, and even when the true rake angle was a positive angle, it partially increased along the cutting edge 15 once to the negative angle side. There will never be a portion that becomes larger toward the regular angle later. For this reason, it can also prevent that the cutting load at the time of a drilling process concentrates on such a part, and a wear and a defect | deletion arise in the cutting blade 15. FIG.

  Further, in the thinning blade 15b connected to the inner peripheral side of the main cutting edge 15a among the cutting blades 15, the true rake angle is a positive angle but increases toward the negative angle side toward the inner peripheral side. The sharpness can be sharpened to reduce the thrust load, and the strength of the cutting edge can be ensured to prevent wear and chipping. For this reason, according to the drill having the above-described configuration, even when a work material having high hardness, high toughness, and high heat resistance, such as a heat-resistant alloy, is prone to work hardening, the drill life is quickly consumed due to wear or chipping. It is possible to perform stable drilling for a long period of time.

  By the way, in the said embodiment, although the bottom face 16c where the thinning surface 16a of the thinning part 16 and the thinning wall surface 16b cross | intersect is formed in concave curved surface shape, the true rake angle of the cutting blade 15 is a regular angle, and a drill is carried out. If it is made to become gradually large as it goes to the outer peripheral side of the main body 11, the bottom surface of the thinning part 16 will be the thinning surface 16a and the thinning wall surface 16b like the 1st modification of this embodiment shown, for example in FIG. May have a V-shaped cross section formed so as to intersect at an angle. Note that, in the first modified example as well, in the second and third modified examples, which will be described later, the same reference numerals are assigned to portions common to the above-described embodiment, and the description thereof is omitted.

  However, also in the first modified example, the true rake angle of the cutting edge 15 is a positive angle and gradually increases toward the outer peripheral side, thereby sharpening the cutting edge 15 and sharpening the cutting edge 15 itself. Although wear and breakage can be prevented, on the other hand, chips generated by the thinning blade 15b flow out on the thinning surface 16a and collide with the thinning wall surface 16b as they are, and are strongly pressed against the thinning wall surface 16b and rubbed. However, it is discharged into the chip discharge groove 14. For this reason, there exists a possibility that welding and crater wear may arise in the thinning wall surface 16b, and the front-end | tip part of the drill main body 11 may be damaged.

  On the other hand, in the above embodiment, since the bottom surface 16c of the thinning portion 16 is formed in a concave curved surface shape that contacts the thinning surface 16a and the thinning wall surface 16b as described above, the chips flowing out on the thinning surface 16a The chip is discharged into the chip discharge groove 14 while being smoothly curled along the concave curved surface formed by the bottom surface 16c, and does not collide with the thinning wall surface 16b and is strongly pressed. Therefore, it is possible to prevent the tip of the drill body 11 from being damaged due to welding of the thinning wall surface 16b and crater wear, and it is possible to further extend the drill life.

  However, even when the bottom surface 16c of the thinning portion 16 is formed in a concave curved surface, the thinning surface 16a intersecting the V-shaped cross section of the first modification example, for example, as in the second modification example shown in FIG. If the thinning wall 16b is simply continued by the concave curved bottom surface 16c, a concave curve formed by the intersection of the bottom surface 16c and the tip flank 13 is formed away from the axis O. The chisel 17 formed at the intersection ridge line portion between the tip flank surfaces 13 connected to the pair of cutting edges 15 intersects the cutting edge 15 at the intersection 15c on this concave curve. Therefore, in such a second modification, the chisel 17 that is processed to crush the work material becomes longer and the thrust load increases, and the effect of setting the true rake angle to a positive angle is offset. There is a risk of being.

  In contrast to this, in the above-described embodiment, the concave curve formed by the bottom surface 16c of the thinning portion 16 intersecting the tip flank 13 is a drill of the thinning portion 16 than the intersection 15c of the cutting edge 15 and the chisel 17. The concave curve formed by the bottom surface 16c of the thinning portion 16 of the pair of cutting blades 15 and the tip flank 13 is positioned on the thinning wall surface 16b side facing the rear side in the rotational direction T. In view, the chisel 17 is disposed so as to enter the alternate cutting blades 15 with the chisel 17 interposed therebetween, so that it is possible to avoid the chisel 17 from becoming long.

  That is, in the above-described embodiment, as compared with the first and second modifications shown in FIGS. 7 and 8, the thinning wall surfaces 16b of the pair of thinning portions 16 when viewed from the front in the axis O direction as shown in FIG. They are arranged so as to be spaced apart from each other with the axis O and the chisel 17 between them. Therefore, the intersection 15c with the chisel 17 that is the inner peripheral end of the pair of cutting blades 15 (thinning blades 15b) is more twisted along the axis O. The concave curve formed by the bottom surface 16c of the thinning portion 16 and the tip flank 13 from this intersection 15c is rounded up to the outer peripheral side after approaching the axis O side, and the thinning wall 16b and the tip flank 13 so as to be in contact with the intersection ridge line portion. For this reason, compared with the case where the chisel 17 extends from the concave curve formed by the bottom surface 16c and the tip flank 13 as in the second modification, the chisel 17 can be kept short, and the thrust load can be suppressed and reliably achieved. In addition, cutting resistance can be reduced.

  By the way, in the drill having the above configuration, the true rake angle is a positive angle over the entire length of the cutting blade 15 including the thinning blade 15b as described above. The true rake angle is also a regular angle at the intersection 15 c with 17. However, the true rake angle of the cutting edge 15 is gradually increased toward the positive angle side toward the outer peripheral side of the drill body 11, and conversely, toward the inner peripheral side, it is directed toward the negative angle side within a positive angle range. This is the same for the portion extending toward the inner peripheral side beyond the intersection 15c with the chisel 17, but at the inner peripheral portion immediately beyond the intersection 15c, the thinning surface of the thinning portion 16 is increased. Each plane obtained by intersecting the plane including the axis O and the thinning surface 16a or the bottom surface 16c at one point on the intersection ridgeline portion between the 16a or the bottom surface 16c and the tip flank 13 passes through the one point. The angle between the intersecting lines, that is, the angle that should be the true rake angle at the intersecting ridge line portion between the thinning surface 16a or the bottom surface 16c and the tip flank 13 remains a positive angle.

  However, the axis O between the pair of thinning portions 16 formed so as to cut out the inner peripheral portion of the wall surface facing the drill rotation direction T of the chip discharge groove 14 at the tip portion of the drill body 11 is the smallest. The thinning surface 16a also passes through the contact point S of the circle C centering on the axis O inscribed in the intersecting ridge line portion between the thinning surface 16a or the bottom surface 16c and the tip flank 13 in the direction tip view and includes the axis O. Or, if the true rake angle at the intersecting ridge line portion between the bottom surface 16c and the tip flank surface 13 remains a regular angle, as in the third modification shown in FIGS. As shown, in the cross section, the thinning surfaces 16a (or the bottom surface 16c) of the pair of thinning portions 16 approach each other toward the rear end side in the axis O direction, It becomes a wedge shape tapering to the rear end side, the intensity of the drill body 11 end center portion becomes liable to damage decreases.

  In contrast, in the above embodiment, as described above, the angle that should be the true rake angle at the intersecting ridge line portion between the thinning surface 16a or the bottom surface 16c and the tip flank 13 is also on the negative angle side as it goes toward the inner peripheral side. In view of the fact that it becomes larger toward the surface, the tangent line at the contact S of the thinning surface 16a or the bottom surface 16c in the same cross section in the cross section so that the angle that should go with the true rake angle is 0 ° or a negative angle. L is formed so as to be separated from the axis O as it is parallel to the axis O or toward the rear end side of the drill body 11. For this reason, it is possible to provide a drill that secures the strength of the portion where the thickness of the tip center portion of the drill body 11 is the thinnest and does not cause a defect or the like even by a thrust load.

DESCRIPTION OF SYMBOLS 11 Drill main body 12 Cutting edge part 13 Tip flank 14 Chip discharge groove 15 Cutting edge 15a Main cutting edge 15b Thinning blade 15c Intersection of the cutting edge 15 and chisel 17 16 Thinning part 16a Thinning surface 16b Thinning wall 16c Bottom face 17 Chisel O Drill Axis line of main body T Drill rotation direction C Axis of circle S inscribed in thinning surface 16a or bottom surface 16c with axis O as a center in contact with the thinning surface 16a or bottom surface 16c in the direction of the axis O direction

Claims (3)

  A chip discharge groove is formed on the outer periphery of the tip end of the drill body rotated about the axis, and a cutting edge is formed at a crossed ridge line portion between the wall surface of the chip discharge groove facing the drill rotation direction and the tip flank of the drill body. The cutting blade has a main cutting edge extending from the outer peripheral end of the cutting blade to the inner peripheral side, and an inner peripheral portion of the wall surface facing the drill rotation direction of the chip discharge groove cut out to the axial line side. A thinning blade formed on the intersecting ridge line portion of the thinning portion of the thinning portion facing the drill rotation direction and the tip flank surface and connected to the inner periphery of the main cutting blade. The true rake angle of the cutting edge formed by the blade is a positive angle over the entire length of the cutting edge, and gradually increases toward the positive angle side from the inner periphery to the outer periphery side of the drill body. And drill.   The drill body is formed with a pair of cutting edges symmetrically with respect to the axis, and a chisel is formed at the intersecting ridge line portion between the tip flank faces connected to the cutting edges. The bottom surface of the thinning portion intersecting with the thinning wall surface facing the rear side of the drilling direction of the thinning portion is formed in a concave curved surface, and the concave curve formed by intersecting the bottom surface of the thinning portion with the tip clearance surface The drill according to claim 1, wherein the drill is located closer to the thinning wall surface than the intersection of the cutting edge and the chisel.   The thinning surface in a cross section passing through a contact point of a circle centered on the axis and inscribed in the intersecting ridge line portion of the thinning surface or the bottom surface and the tip clearance surface when viewed from the axial front end side, and including the axis The drill according to claim 2, wherein a tangent line at the contact point on the bottom surface is parallel to the axis line or is separated from the axis line toward the rear end side of the drill body.

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