JP2016147328A - drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cutting resistance by improving sharpness of this cutting edge, needless to say to be capable of executing stable hole drilling, in a drill used, for example, for draft hole drilling and in which an outer peripheral part of the cutting edge has a tip angle of 180° or more.SOLUTION: A chip discharge groove 5 of extending to the rear end side by opening on a tip flank 4 of a drill body 1, is formed on the tip part outer periphery of the drill body 1 rotated around the axis O, and an outer peripheral part of a wall surface 5A of turning in the drill rotational direction T of this chip discharge groove 5, extends so as to turn to the opposite side on the drill rotational direction T toward the inner peripheral side of the drill body 1, and an outer peripheral cutting edge 7A is formed in a crossing ridge line part between the outer peripheral part 6A and the tip flank 4 of this wall surface 5A, and a positive radial directional rake angle α and a tip angle of 180° or more, are imparted to this outer peripheral cutting edge 7A.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a drill used for drilling a hole in a cast hole such as aluminum.

  Since such a punched hole is formed when casting a casting, it is difficult to accurately form in a predetermined position, and a general tip angle of less than 180 ° is given to the cutting edge. If you insert a single-edged drill into a hole and try to form a hole with a desired inner diameter at a predetermined position, one of the cutting edges will hit the hole first due to misalignment between the drill and the hole. There is a risk of hitting. For drills that come into contact with one piece, the force toward the inner periphery of the drill body acts as a component of the cutting force on the one of the cutting edges, causing deflection, which causes the drilled hole to bend or bend. As a result, machining accuracy is impaired.

  Therefore, for example, in Patent Document 1, in order to prevent drill runout in such a punched hole processing and improve processing accuracy, the cutting portion of the drill body includes a plurality of blade portions and a blade portion. A first rough cutting edge having a tip angle of 180 ° or more in order from the front side to the opposite side (rear side) in the drill rotation direction on the outer peripheral part of each blade part, and the first rough cutting edge. A finishing blade formed to be shifted toward the rear end side in the axial direction of the drill body with respect to the cutting blade, and a second blade having a tip angle of 180 ° or more formed identically with respect to the axial direction with respect to the first rough cutting blade. A drill having a rough cutting edge is proposed. Further, this Patent Document 1 also describes that a bottom cutting edge having a tip angle of 180 ° or less at the inner peripheral portion of the first rough cutting blade and projecting to the tip side from the first rough cutting blade is provided. Has been.

Japanese Patent No. 3847109

  However, in the drill described in Patent Document 1, the first and second rough cutting blades have a rake face formed on a plane including the axis of the drill body. The rake angle in the radial direction of the two rough cutting edges is 0 °. For this reason, the first and second rough cutting edges are located on a radial line with respect to the axial line when viewed from the front end side in the axial direction, and cut around the core hole at a position equal to the drill rotation direction. In rare cases, cutting will be performed, resulting in dullness and increased cutting resistance. And when cutting resistance increases in this way, cutting heat will also increase, especially in the case of the cast hole processing of a work material like an aluminum casting, there exists a possibility that chip | tip welding may generate | occur | produce and the lifetime of a drill may be impaired. .

  The present invention has been made under such a background. For example, in a drill having a tip angle of 180 ° or more on the outer peripheral portion of a cutting edge, which is used for, for example, punching holes, stable drilling can be performed. Of course, the object is to provide a drill capable of improving the sharpness of the cutting edge and reducing the cutting resistance.

  In order to solve the above-described problems and achieve such an object, the present invention provides an outer periphery of a tip end of a drill body that is rotated around an axis, an opening at a tip flank of the drill body, and a rear end side. An extended chip discharge groove is formed, and an outer peripheral portion of the wall of the chip discharge groove facing the drill rotating direction extends toward the opposite side of the drill rotating direction toward the inner peripheral side of the drill body. An outer peripheral cutting edge is formed at the intersection ridge line portion between the outer peripheral portion and the tip flank, and the outer peripheral cutting edge is given a positive radial rake angle and a tip angle of 180 ° or more. To do.

  In such a drill, first, like the first and second rough cutting edges of the drill described in Patent Document 1, a tip angle of 180 ° or more is given to the outer peripheral cutting edge. It is possible to suppress the occurrence of run-out without a force directed toward the inner peripheral side of the drill body acting as a radial component of the cutting force on the axis when cut around the punched hole. it can. In particular, when the tip angle is larger than 180 ° and the outer peripheral cutting edge extends toward the rear end side toward the inner peripheral side of the drill main body, the drill main body uses the component force of the cutting force by the outer peripheral cutting edge. Since a force toward the outer peripheral side acts on the outer peripheral cutting edge and the outer peripheral surface of the drill body tip adjacent to the outer peripheral cutting edge is pressed against the processing hole, stable drilling is performed. And processing accuracy is improved.

  And in the drill of the said structure, the outer peripheral part of the wall surface which faces the drill rotation direction of the chip discharge groove used as the rake face of this outer peripheral cutting edge goes to the opposite side of the drill rotation direction toward the inner peripheral side of the drill body. This gives the outer peripheral cutting edge a positive radial rake angle. For this reason, the outer peripheral cutting edge performs cutting while being gradually cut around the core hole from the outer peripheral end located on the drill rotation direction side toward the inner peripheral side, so the sharpness becomes sharper. Cutting resistance and cutting heat can be reduced. Accordingly, it is possible to prevent welding from occurring on the cutting edge even in the case of punching a hole in an aluminum casting, and to facilitate smooth machining over a long period of time.

  Also, since the clearance angle toward the rear end side of the drill body is given to the tip clearance surface of the drill body toward the opposite side of the drill rotation direction, this tip clearance surface and the inner periphery of the drill body as described above are provided. It is possible to easily give a tip angle of 180 ° or more to the outer peripheral cutting edge formed at the crossing ridge line portion with the outer peripheral portion of the wall surface of the chip discharge groove extending toward the opposite side of the drill rotation direction toward the side It becomes. For this reason, like the drill described in Patent Document 1, a plurality of (three) blade portions and a plurality of (two) groove portions between the blade portions are formed on the outer peripheral portion of the drill body. On the other hand, even if it is a small diameter drill, it becomes possible to form the above-mentioned peripheral cutting edge reliably and easily.

  Here, in order to give a positive radial rake angle to the outer peripheral cutting edge in this way, the outer peripheral portion of the wall surface facing the drill rotating direction of the chip discharge groove is arranged in the drill rotating direction with respect to the inner peripheral portion of the wall surface. A sub-groove recessed on the opposite side is formed, and the outer peripheral cutting edge may be formed at the intersecting ridge line portion of the sub-groove wall surface facing the drill rotation direction of the sub-groove and the tip flank. That is, this sub-groove wall surface becomes the outer peripheral part of the wall surface facing the drill rotation direction of the chip discharge groove as the rake face of the outer peripheral cutting edge, and goes toward the opposite side of the drill rotation direction toward the inner peripheral side of the drill body. For example, the wall surface facing the drill rotation direction of the chip discharge groove is formed as one flat surface or a concave curved surface toward the inner peripheral side of the drill body and toward the opposite side of the drill rotation direction. Compared to the above, there is no such a case that the chip width of the chip discharge groove becomes small and chip clogging is likely to occur.

  Further, similarly to the bottom cutting edge in the drill described in Patent Document 1, the tip angle of 180 ° or less at the intersecting ridge line portion between the inner peripheral portion of the wall surface facing the drill rotation direction of the chip discharge groove and the tip flank surface If the inner peripheral cutting edge provided with is formed, it can be used not only for punching holes, but also for ordinary solid holes for drilling holes in workpieces where pilot holes are not formed. In particular, in this case, by making the tip angle of the outer peripheral cutting edge larger than 180 ° and making the tip angle of the inner peripheral cutting edge smaller than 180 °, the above component force and inner peripheral force acting on these outer peripheral cutting blades can be obtained. Since the radial component force acting on the cutting edge cancels out, stable drilling can be performed while further suppressing the deflection of the drill body.

  When the inner peripheral cutting edge is formed in this way, the inner peripheral cutting edge and the distal end flank intersecting the outer peripheral cutting edge are continuous, that is, the distal flank and outer periphery intersecting the inner peripheral cutting edge. By forming the tip flank that intersects the cutting edge so as to be continuous without any step in the axial direction, even when the inner and outer peripheral cutting blades wear and the tip flank is re-polished, New inner and outer peripheral cutting edges can be easily sharpened simply by polishing along the clearance angle. In this respect, in the drill described in Patent Document 1, the bottom cutting edge protrudes from the first rough cutting edge to the tip side as described above, and a step is formed between the two cutting edges. In this case, it is necessary to polish the tip flank and the step of both cutting edges.

  Furthermore, in the drill having the above-described configuration, margin portions are formed on the outer peripheral surface of the drill body that is continuous with the drill rotation direction of the chip discharge groove and the opposite side of the drill rotation direction, so that these margin portions are formed in the machining holes. It can be slidably contacted with the inner periphery, and more stable drilling can be performed.

  As described above, according to the present invention, it is possible to prevent the drilling hole from being bent or bent due to the deflection of the drill body even when performing the punching hole processing, and to improve the cutting performance by the outer peripheral cutting edge. As a result, it is possible to reduce the cutting heat and to perform smooth drilling without causing welding even in an aluminum casting or the like.

It is a side view which shows one Embodiment of the drill of this invention. It is an enlarged front view of the drill shown in FIG. It is a side view of the arrow X direction view in FIG. It is a side view of the arrow Y direction view in FIG. It is ZZ sectional drawing in FIG. FIG. 6 is a side view showing a modification of the embodiment shown in FIGS. 1 to 5.

  1 to 5 show an embodiment of the present invention. In this embodiment, the drill body 1 is formed of a hard material such as cemented carbide and has a substantially cylindrical shape centered on the axis O, and the rear end portion (right side portion in FIG. 1) remains cylindrical. The tip portion (left side portion in FIG. 1) is the cutting blade portion 3 while being the shank portion 2. In such a drill, the shank portion 2 is attached to the main shaft of a machine tool such as a machining center or a drilling machine, and is rotated around the axis O in the drill rotation direction T and is sent to the front end side in the axis O direction. Hole processing is performed on the work material by the blade portion 3.

  The cutting edge portion 3 is formed to have an outer diameter slightly smaller than that of the shank portion 2, and a chip discharge groove that extends to the rear end side of the outer periphery of the cutting blade portion 3 that opens to the front end flank 4 that is the front end surface of the drill body 1. 5 is formed. The chip discharge groove 5 in the present embodiment is a straight groove extending in parallel to the axis O, and is cut out on the outer peripheral side in front of the shank portion 2. In the present embodiment, the two chip discharge grooves 5 are formed symmetrically with respect to the axis O.

  The chip discharge groove 5 is located between the wall surface 5A facing the drill rotation direction T, the wall surface 5B facing the opposite side of the drill rotation direction T, and the wall surfaces 5A and 5B. And a bottom surface 5C. However, a sub-groove 6 that is recessed on the opposite side of the drill rotation direction T with respect to the wall surface 5A is formed on the outer peripheral portion of the wall surface 5A facing the drill rotation direction T. Part or all of the outer peripheral side is occupied, and in this embodiment, in particular, the auxiliary groove 6 occupies the entire wall surface 5A. The wall surface 5B is formed in a planar shape extending parallel to the axis O, and the bottom surface 5C is formed in a concave curved surface shape such as a concave cylindrical surface in contact with the wall surface 5B.

  As shown in FIGS. 2 and 5, the sub-groove 6 has a V-shaped cross section perpendicular to the axis O, and is positioned on the outer peripheral side of the drill body 1 and toward the inner peripheral side in the drill rotation direction T. The first sub-groove wall surface 6A extending toward the opposite side of the first sub-groove wall surface and the second sub-groove wall surface 6B extending toward the drill rotation direction T toward the inner periphery side of the first sub-groove wall surface 6A And have. The first and second sub-groove wall surfaces 6A and 6B are formed in a planar shape extending in parallel with the axis O, and the second sub-groove wall surface 6B intersects the bottom surface 5C of the chip discharge groove 5 at an obtuse angle. The first and second sub-groove wall surfaces 6A and 6B may intersect with each other at an angle, and a concave curved surface such as a concave cylindrical surface having a smaller radius than the bottom surface 5C of the chip discharge groove 5 as shown in FIG. You may be in contact with each other.

  The first sub-groove wall surface 6A has an inclination angle α with respect to a straight line (radius line) L connecting the axis O and the outer peripheral end of the first sub-groove wall surface 6A in a cross section orthogonal to the axis O as shown in FIG. The second sub-groove wall surface 6B is formed so as to be smaller than the inclination angle β with respect to the straight line L. The width of the first sub-groove wall surface 6A along the straight line L direction and the actual width along the first sub-groove wall surface 6A are both wider than the second sub-groove wall surface 6B. ing.

  On the other hand, a thinning surface 5D is formed at the tip of the wall surface 5B and the bottom surface 5C of the chip discharge groove 5 so as to go to the inner peripheral side of the drill body 1 from the wall surface 5B and the bottom surface 5C toward the tip side. The thinning surface 5D intersects the tip flank 4 in an L shape as shown in FIG. 2 when viewed from the tip side in the axis O direction. Further, the second sub-groove wall surface 6B of the sub-groove 6 intersects the thinning surface 5D at the tip of the drill body 1.

  And the cutting edge 7 is formed in the intersection ridgeline part of the wall surface 5A which faces the drill rotation direction T of the chip discharge groove 5, and the front-end | tip flank 4, The 1st sub groove wall surface 6A of the sub groove 6 in this embodiment. The outer peripheral cutting edge 7A is formed at the intersecting ridge line portion between the tip flank 4 and the tip flank 4 and the portion of the intersecting ridge line portion that is L-shaped between the thinning surface 5D and the tip flank 4 faces the drill rotation direction T. The inner peripheral cutting edge 7B is formed, and the intermediate ridge line portion between the second auxiliary groove wall surface 6B and the tip flank 4 of the auxiliary groove 6 extends between the outer peripheral cutting edge 7A and the inner peripheral cutting edge 7B. A cutting edge 7C is formed. Accordingly, the outer peripheral cutting edge 7A extends toward the opposite side of the drill rotation direction T as it goes toward the inner peripheral side of the drill body 1, and the first auxiliary groove wall surface 6A is formed on the outer peripheral cutting edge 7A by the straight line. A positive radial rake angle α equal to the tilt angle α made with respect to L is given.

  Moreover, the clearance angle is given to the front-end flank 4 so that it may go to the rear-end side of the drill main body 1 as it goes to the opposite side of the drill rotation direction T from the cutting blade 7, and such a clearance angle is given. Accordingly, the outer peripheral cutting edge 7A extending toward the opposite side of the drill rotation direction T toward the inner peripheral side of the drill main body 1 extends along a virtual plane perpendicular to the axis O, or the drill main body 1 The outer peripheral cutting edge 7A is provided with a tip angle γ of 180 ° or more as it extends toward the rear end side toward the inner peripheral side. In the present embodiment, as shown in FIG. 3, the outer peripheral cutting edge 7 </ b> A extends toward the rear end side toward the inner peripheral side of the drill body 1, and is given a tip angle γ greater than 180 °. .

  In the present embodiment, the tip flank 4 has a narrow and constant first tip flank 4A that intersects the inner peripheral cutting edge 7B and continues to the opposite side of the drill rotation direction T, and the first tip flank. A second tip flank 4B is provided which is connected to the opposite side of the surface 4A in the drill rotation direction T and intersects the outer peripheral cutting edge 7A and the intermediate cutting edge 7C. The clearance angle of the second tip flank 4B is set to be larger than that of the first tip flank 4A, and the first and second tip flank 4A, 4B are connected via a straight line intersecting the axis O as shown in FIG. Moreover, as shown in FIG. 4, it is continuing so that it may be bent without having a level | step difference. Therefore, a negative radial rake angle is given to the inner peripheral cutting edge 7B, and the inner peripheral cutting edge is equal to the inclination angle β of the second auxiliary groove wall surface 6B with respect to the straight line L in the intermediate cutting edge 7C. A larger negative radial rake angle β is provided on the negative angle side than 7B.

  Furthermore, in this embodiment, the inner peripheral cutting edge 7B is given a tip angle θ of 180 ° or less, and the intermediate cutting edge 7C is given a tip angle smaller than the tip angle θ of the inner peripheral cutting edge 7B. ing. The tip flank 4 in the present embodiment is inclined so as to be directed toward the rear end side from the axis O toward the outer peripheral side of the drill main body 1, whereby the tip smaller than 180 ° is formed on the inner peripheral cutting edge 7B. An angle θ is given. The tip angle γ (°) of the outer peripheral cutting edge 7A is set so that 360 ° −γ (°) is smaller than the tip angle θ (°) of the inner peripheral cutting edge 7B. Further, the outer peripheral end of the inner peripheral cutting edge 7B is disposed at a position equal to the outer peripheral end of the outer peripheral cutting edge 7A in the direction of the axis O or on the rear end side of the drill body 1.

  Furthermore, as shown in FIG. 2, the thinning surface 5D at the tip of the two chip discharge grooves 5 is an inner peripheral cutting edge formed at a crossing ridge line portion with the tip flank 4 when viewed from the tip side in the axis O direction. 7B are formed so as to pass each other slightly beyond the axis O from the outer peripheral side. Further, in the drill body 1, two coolant holes 8 pass between the two chip discharge grooves 5 of the cutting edge portion 3 in the circumferential direction, and the axis O extends from the rear end surface of the shank portion 2 (rear end surface of the drill body 1). And open to the second tip flank 4B of the two tip flank 4 respectively.

  On the other hand, on the outer peripheral surface of the cutting edge portion 3, a first margin portion 9 </ b> A is formed in a portion continuous with the drill rotation direction T of the chip discharge groove 5, and continues to the opposite side of the chip discharge groove 5 with respect to the drill rotation direction T. A second margin portion 9B is formed in the portion. The first and second margin portions 9A and 9B have an outer peripheral surface centered on an axis O having a diameter equal to the diameter of the cutting edge 7 (the diameter of a circle formed by the outer peripheral end of the outer peripheral cutting edge 7A around the axis O). A total of four first and second margin portions 9A and 9B are arranged at approximately equal intervals in the circumferential direction of the drill body 1.

  The second margin portion 9B is formed so that the circumferential width is slightly wider than the first margin portion 9A. Further, the diameter of the drill body 1 is smaller than the diameter of the cutting edge 7 on the outer peripheral surface of the drill body 1 from the first margin portion 9A of the chip discharge groove 5 on the drill rotation direction T side toward the opposite side of the drill rotation direction T. The first outer peripheral flank 10A located on the cylindrical surface centering on the axis O of this, and the planar second concave recessed toward the inner peripheral side of the drill body 1 with respect to the cylindrical surface on which the first outer peripheral flank 10A is located. An outer peripheral flank 10B is formed.

  Further, an outer periphery that is substantially located on a plane including the axis O and faces the drill rotation direction T between the second outer periphery flank 10B and the outer periphery of the second margin portion 9B opposite to the drill rotation direction T. A wall surface 10C is formed, and at the intersecting ridge line portion between the outer peripheral wall surface 10C and the second tip flank 4B of the tip flank 4 as shown in FIG. A secondary cutting edge 7D is formed so as to be located at the position. Therefore, the tip angle of the auxiliary cutting edge 7D is set to 180 ° or less, and in this embodiment, is smaller than 180 ° and smaller than the tip angle θ of the inner peripheral cutting edge 7B.

  In the drill configured as described above, a tip angle γ of 180 ° or more is given to the outer peripheral cutting edge 7A of the cutting edges 7, and for example, a processing hole having a predetermined inner diameter is formed in a cast hole portion of a casting. In this case, when the outer peripheral cutting edge 7A is cut around the punched hole, a force directed from the outer peripheral cutting edge 7A toward the inner peripheral side of the drill body 1 as a radial component force with respect to the axis O of the cutting force. Does not work. For this reason, it is possible to suppress the deflection of the drill body 1 during drilling to prevent the drilling and bending of the drilled hole, and to improve the machining accuracy.

  In particular, in the present embodiment, the tip angle γ is larger than 180 °, the outer peripheral cutting edge 7A extends toward the rear end side toward the inner peripheral side of the drill body 1, and the outer peripheral cutting edge 7A is cast. When cut around the hole, the component of the cutting force acts in the radial direction with respect to the axis O toward the outer peripheral surface of the drill body 1 adjacent to the outer peripheral cutting edge 7A, that is, the first margin portion 9A. . Accordingly, the outer peripheral surface of the first margin portion 9A is pressed against the inner periphery of the processing hole, so that more stable hole processing can be performed. In addition, since the outer peripheral cutting edge 7A is formed symmetrically with respect to the two axes O, no one-sided contact occurs.

  Further, in the drill having the above-described configuration, the first sub-groove of the sub-groove 6 formed on the outer peripheral portion of the wall surface 5A facing the drill rotation direction T of the chip discharge groove 5 and serving as a rake face of the outer peripheral cutting edge 7A. The wall surface 6 </ b> A extends toward the opposite side of the drill rotation direction T toward the inner peripheral side of the drill body 1. Accordingly, the outer peripheral cutting edge 7A also extends toward the opposite side of the drill rotation direction T toward the inner peripheral side of the drill body 1, and the outer peripheral cutting edge 7A has a positive radial rake angle α. Given.

  Therefore, when the outer peripheral cutting edge 7A is cut around the punched hole during drilling, the outer peripheral end of the outer peripheral cutting edge 7A located on the drill rotation direction T side with the rotation of the drill body 1 is changed to the inner peripheral side. The cutting force is gradually cut toward the point, and the cutting resistance can be sharpened to reduce the cutting resistance. For this reason, generation | occurrence | production of the heat at the time of cutting can be suppressed, and even when a work material is an aluminum casting, it can prevent that outer periphery cutting blade 7A produces welding, and also more stable and smooth hole processing. Can be done for a long time. Moreover, in this embodiment, cutting heat can also be suppressed by supplying a coolant from the front flank 4 to the cutting edge 7 or the cutting site of the work material through the coolant hole 8 at the time of drilling.

  Furthermore, since the clearance angle is given to the front end flank 4 of the drill body 1 so as to go to the rear end side toward the opposite side of the drill rotation direction T, the front end flank 4 and the inner peripheral side of the drill main body 1 are provided. A tip angle γ greater than 180 ° or greater than 180 ° is easily given to the outer peripheral cutting edge 7A formed at the intersecting ridge line portion with the outer peripheral portion of the wall surface 5A extending toward the opposite side of the drill rotation direction T toward Can be done. For this reason, even if it is a small diameter drill with the said diameter of the cutting blade 7 small, it becomes possible to form the above-mentioned outer peripheral cutting blade 7A reliably.

  Further, in order to give a positive radial rake angle α to the outer peripheral cutting edge 7A in this way, in the present embodiment, the auxiliary groove 6 is formed in the outer peripheral portion of the wall surface 5A facing the drill rotation direction T of the chip discharging groove 5 as described above. The first sub-groove wall surface 6A facing the drill rotation direction T on the outer peripheral side of the sub-groove 6 is formed so as to extend toward the opposite side of the drill rotation direction T toward the inner peripheral side of the drill body 1. Yes. However, without forming such a secondary groove 6, for example, the wall surface 5 </ b> A of the chip discharge groove 5 is formed as a flat surface or a concave curved surface in contact with the bottom surface 5 </ b> C, and the wall surface 5 </ b> A itself is drilled toward the inner peripheral side of the drill body 1. It is possible to give a positive radial rake angle α to the outer peripheral cutting edge 7A formed at the crossing ridge line part with the tip flank 4 by forming it so as to extend toward the opposite side of the rotation direction T. In such a case, the groove width of the chip discharge groove 5 may be reduced and chip clogging may occur, but such a situation does not occur in the present embodiment.

  Further, in the present embodiment, the sub-groove 6 is formed in a V-shaped cross section, and on the inner peripheral side of the first sub-groove wall surface 6A facing the drill rotation direction T, the first sub-groove wall surface 6A with respect to the straight line L A second sub-groove wall surface 6B inclined at an inclination angle β larger than the inclination angle α is formed, and continuous chips are generated by the outer peripheral cutting edge 7A, for example, in the case of a normal hole processing that is not a casting hole processing. However, it is possible to expect an effect that the chips can be divided by being brought into sliding contact with the second sub-groove wall surface 6B and imparting resistance to ensure good chip dischargeability. In addition, when drilling is performed using even the intermediate cutting edge 7C formed at the tip of the second sub-groove wall surface 6B, the chips are generated in a V-shaped cross section, so that they are easily divided. It is possible to improve the performance. However, the second sub-groove wall surface 6B may have a concave curved surface shape, and the entire groove wall surface of the sub-groove 6 including the first sub-groove wall surface 6A may have a concave curved surface shape.

  In the present embodiment, the intersecting ridge line between the thinning surface 5D and the tip flank 4 is formed on the inner peripheral side of the intermediate cutting edge 7C formed at the intersecting ridge line portion between the second sub-groove wall surface 6B and the tip flank 4. An inner peripheral cutting edge 7B is formed at a portion of the portion facing the drill rotation direction T. For this reason, in the case of processing a solid hole that drills a work material that does not have a pilot hole such as a punched hole, or from the side where a blind hole-shaped pilot hole is not opened, Alternatively, the drill of this embodiment can be used by cutting from the inner peripheral cutting edge 7B to the intermediate cutting edge 7C and the outer peripheral cutting edge 7A.

  Since the inner peripheral cutting edge 7B is provided with a tip angle θ of 180 ° or less, the tip angle γ of the outer peripheral cutting blade 7A is particularly larger than 180 ° as in the present embodiment. When the tip angle θ of the blade 7B is smaller than 180 °, the component forces in the radial direction of the cutting force acting on the outer peripheral cutting blade 7A and the inner peripheral cutting blade 7B can be canceled out, and the drill body It is possible to perform highly accurate drilling while suppressing the swing of 1.

  Further, when forming the inner peripheral cutting edge 7B in this way, in the present embodiment, in the distal end flank 4 of the drill body 1, the first distal flank 4A intersecting the inner peripheral cutting edge 7B and the outer peripheral cutting edge 7A. The second tip flank 4B intersecting with the second end flank 4B is continuous only by being bent without passing through a step that is uneven in the direction of the axis O. For this reason, even when the cutting edge 7 is worn and re-polished, the first and second tip flank surfaces 4A and 4B and the thinning surface 5D thus bent are simply polished so as to recede in the direction of the axis O. The new outer peripheral cutting edge 7A, inner peripheral cutting edge 7B, and intermediate cutting edge 7C can be easily sharpened.

  In the present embodiment, the tip flank 4 is formed by the first and second tip flank 4A and 4B as described above, but may be formed by one continuous tip flank. Three or more tip flank surfaces may be formed. Further, the cutting edge 7 may be subjected to chamfering such as honing or R chamfering to improve the cutting edge strength. On the other hand, the inner peripheral cutting edge 7B may not be formed as long as it is a dedicated drill for processing a prepared hole previously formed in a work material such as a cast hole into a predetermined inner diameter.

  Moreover, in the drill of this embodiment, the 1st, 2nd margin parts 9A and 9B are formed in the outer peripheral surface of the drill main body 1 connected to the drill rotation direction T of the chip discharge groove 5 and the opposite side, and the drill main body Supporting the cutting edge 3 of the drill body 1 by bringing the outer peripheral faces of the first and second margin parts 9A and 9B into sliding contact with the inner peripheral face of the machining hole formed by the cutting edge 7 at one end. And more stable drilling can be performed.

  In addition, the above-mentioned cut at the tip of the drill body 1 is formed on the crossed ridge line portion between the outer peripheral wall surface 10C of the outer peripheral surface continuous with the second margin portion 9B and facing the drill rotation direction T and the second tip flank 4B of the tip flank 4. The auxiliary cutting edge 7D is formed so as to be positioned on the rear end side of the blade 7, and the inner peripheral surface of the processing hole formed by the cutting edge 7 can be finished by the auxiliary cutting edge 7D. For this reason, according to the present embodiment, it is possible to improve the processing accuracy such as straightness of the processed hole and improve the quality of the processed hole.

  Next, FIG. 6 shows a modification of the embodiment shown in FIGS. 1 to 5, and the same reference numerals are assigned to parts common to the embodiment, and the description is omitted. In the drill of this modified example, the cutting edge portion 3 at the tip end portion of the drill body 1 has a stepped shape in which the outer diameter increases stepwise toward the rear end side. A blade 11 is formed.

  Here, in this modified example, the outer diameters of the first and second margin portions 9A and 9B are formed so as to increase in a plurality of steps (two steps) toward the rear end side of the drill body 1, and thus the outer diameter is increased. In the portion where the diameter is increased, after the outer peripheral surfaces of the first and second margin portions 9A and 9B and the first outer peripheral flank 10A are once slightly recessed toward the inner peripheral side toward the rear end side of the drill body 1, the rear It forms so that it may incline toward an outer peripheral side as it goes to an end side, and the outer peripheral part (the 1st subgroove of the subgroove 6) of this inclined part and the wall surface 5A which faces the drill rotation direction T of the chip discharge groove 5 Stepped blades 11 are respectively formed at the intersecting ridge lines with the wall surface 6A) and the outer peripheral wall surface 10C. Therefore, the tip angle of these stepped blades 11 is less than 180 °.

  According to the drill of such a modified example, the machining hole can be formed into a stepped hole whose inner diameter is gradually reduced toward the bottom of the hole by the stepped blade. And since the structure of the front-end | tip part of the cutting blade part 3 is the same as the said embodiment, in the hole bottom side of this step hole, the fall and bending of the processing hole by the fluctuation | variation of the drill main body 1 do not arise, and a hole bottom The drill body 1 can be guided by the side to form a stepped hole having high concentricity and straightness, and the occurrence of welding due to an increase in cutting resistance can be prevented as in the above embodiment.

DESCRIPTION OF SYMBOLS 1 Drill main body 2 Shank part 3 Cutting blade part 4 Tip flank 4A 1st tip flank 4B 2nd tip flank 5 Chip discharge groove 5A Wall surface 5B of chip discharge groove 5 facing the drill rotation direction T 5B Drill of chip discharge groove 5 Wall surface facing opposite side of rotation direction 5C Bottom surface of chip discharge groove 5 facing outer peripheral side of drill body 1 6 Sub groove 6A First sub groove wall surface 6B Second sub groove wall surface 7 Cutting edge 7A Outer peripheral cutting edge 7B Inner peripheral cutting edge 7C Intermediate cutting edge 7D Sub cutting edge 8 Coolant hole 9A First margin portion 9B Second margin portion 10A First outer peripheral flank surface 10B Second outer peripheral flank surface 10C Outer peripheral wall surface 11 Stepped blade O Drill shaft 1 axis T Drill rotation direction α Radial rake angle of outer peripheral cutting edge 7A γ Tip angle of outer peripheral cutting edge 7A θ Tip angle of inner peripheral cutting edge 7B

Claims (4)

  A chip discharge groove is formed on the outer periphery of the tip of the drill body that is rotated around the axis, and the chip discharge groove extends to the rear end side of the drill body and extends toward the rear end. The outer periphery of the wall surface of the chip discharge groove faces the drill rotation direction. The portion extends toward the opposite side of the drill rotation direction as it goes toward the inner peripheral side of the drill body, and an outer peripheral cutting edge is formed at the intersection ridge line portion between the outer peripheral portion of the wall surface and the tip flank surface. The outer peripheral cutting edge is provided with a positive radial rake angle and a tip angle of 180 ° or more.   The outer peripheral portion of the wall surface is formed with a sub-groove that is recessed on the opposite side of the drill rotation direction with respect to the inner peripheral portion of the wall surface, and the outer peripheral cutting edge is a sub-groove that faces the drill rotation direction of the sub-groove. The drill according to claim 1, wherein the drill is formed at a crossing ridge line portion between the wall surface and the tip flank.   An inner peripheral cutting edge having a tip angle of 180 ° or less is formed at an intersecting ridge line portion between the inner peripheral portion of the wall surface and the tip flank, and intersects the inner peripheral cutting blade and the outer peripheral cutting blade. The drill according to claim 1 or 2, wherein the tip flank is continuous.   The margin part is formed in the outer peripheral surface of the said drill main body connected with the drill rotation direction and the opposite side of a drill rotation direction of the said chip | tip discharge groove | channel, The any one of Claims 1-3 characterized by the above-mentioned. Drill according to item.

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