drill

Abstract

To prevent occurrence of welding to prevent a shoulder part of a cutting blade from being damaged, while securing strength of the cutting blade in the shoulder part of the cutting blade at an outer periphery of the cutting blade and to suppress burr from occurring when the cutting blade gets out of a through-hole.SOLUTION: Chip discharge grooves 7 are formed at an outer periphery part of a tip of a drill main body 1 that is rotated in a drill rotation direction T around a shaft line O. Cutting blades 5 are formed at crossing ridge-line parts between wall surfaces pointing in the drill rotation direction T of the chip discharge grooves 7 and flank faces 6 of the tip. The cutting blade 5 is provided with a main cutting blade part 5B extending from an inner periphery side of the drill main body 1 toward an outer periphery side thereof and a cutting blade-shoulder part 5C extending from an outer peripheral end P of the main cutting blade part 5B to the outer periphery of the drill main body 1 and is subjected to honing. With respect to the outer peripheral end P of the main cutting blade part 5B, a true rake angle is made larger at a negative angle-side and a honing angle is made smaller in an outer peripheral end Q of the cutting blade-shoulder part 5C, in comparison with the outer peripheral end P of the main cutting blade part 5B.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a drill in which a chip discharge groove is formed on the outer periphery of the tip of a drill body that is rotated around an axis in the direction of drill rotation, the chip discharge groove opening onto the tip flank of the drill body and extending toward the rear end in the axial direction, and a cutting edge is formed at the ridgeline where the wall surface of this chip discharge groove facing the direction of drill rotation and the tip flank intersects. The wall surface serves as a rake surface. [Background technology]

[0002] For example, Patent Document 1 describes such a drill in which a chip discharge groove extending toward the rear end is formed on the outer periphery of the cutting edge, which is the tip end portion of the drill body that rotates around an axis, and a cutting edge is formed at the intersection ridge between the rake face in the tip end region of the inner wall surface of the chip discharge groove that faces forward in the direction of drill rotation and the tip relief surface of the cutting edge.

[0003] The drill described in Patent Document 1 has a margin portion that intersects the rake face and faces toward the outer periphery, a ridge portion where this margin portion intersects with the tip flank of the cutting edge, a shoulder portion that extends from the outer periphery of the cutting edge rearward in the direction of drill rotation, and a thinning portion that extends toward the tip side of the inner wall surface of the chip discharge groove.

[0004] The cutting edge has, in order from the center of rotation, a first cutting edge portion formed in the thinning portion, a second cutting edge portion formed further outward from the first cutting edge portion, a shoulder cutting edge portion formed in the shoulder portion, and a margin cutting edge portion formed in the margin portion, and the second cutting edge portion, margin cutting edge portion and shoulder cutting edge portion are honed.

[0005] In the drill described in Patent Document 1, the honing widths of these respective portions satisfy the relationship expressed by the following formula (1). Honing width of shoulder cutting edge > Honing width of margin cutting edge ≥ Honing width of second cutting edge (1) [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-209439 Summary of the Invention [Problem to be solved by the invention]

[0007] In the drill described in Patent Document 1, the honing width of the shoulder cutting edge portion is set to be the largest compared to the honing widths of the margin cutting edge portion and the second cutting edge portion. However, in a drill with the largest honing width of the shoulder cutting edge portion, damage is likely to progress in the honing area of ​​the shoulder cutting edge, making welding more likely to occur. When this welded material falls off, it can suddenly cause damage to the shoulder cutting edge, potentially shortening the life of the drill.

[0008] Furthermore, in a drill with such a large honing width at the cutting edge shoulder, the cutting resistance at the cutting edge shoulder increases, and when drilling a through hole, for example, there is a risk of large burrs being generated at the exit of the through hole.

[0009] The present invention has been made against this background, and aims to provide a drill that can ensure cutting edge strength at the cutting edge shoulder on the outer periphery of the cutting edge, prevent welding and damage to the cutting edge shoulder, and suppress burrs at the exit edge of the through hole. [Means for solving the problem]

[0010] In order to solve the above problems and achieve the above object, the present invention provides a drill body that is rotated around its axis in the drill rotation direction, and has a tip outer periphery at the tip end of the drill body, and a drill flank at the tip end of the drill body. axisa drill having a chip discharge flute formed therein extending toward the rear end in a linear direction, and a cutting edge formed at a ridge line between a wall surface of the chip discharge flute facing the drill rotation direction and the tip relief surface, the wall surface serving as a rake face; the cutting edge having a main cutting edge portion extending from the inner periphery side toward the outer periphery side of the drill body, and a cutting edge shoulder portion extending from the outer periphery end of the main cutting edge portion to the outer periphery of the drill body, and honed; and the cutting edge at the outer periphery end of the cutting edge shoulder is larger than the outer periphery end of the main cutting edge portion in a cross section perpendicular to the cutting edge. and axis The true rake angle, which is the inclination angle of the rake face with respect to the line connecting the line, is increased on the negative angle side, and the size of the honing is reduced.

[0011] In a drill configured in this manner, the true rake angle, which is the inclination angle of the rake face relative to a line connecting the cutting edge and the axis of the drill body in a cross section perpendicular to the cutting edge at the outer peripheral end of the cutting edge shoulder, is set to be larger than the true rake angle at the outer peripheral end of the main cutting edge portion, thereby increasing the cutting edge angle at the cutting edge shoulder and ensuring cutting edge strength. This prevents damage to the cutting edge shoulder and welding, and prevents the welding from falling off and causing sudden damage to the cutting edge shoulder, which could shorten the life of the drill.

[0012] Furthermore, the size of the honing applied to the cutting edge is smaller at the outer peripheral edge of the cutting edge shoulder than at the outer peripheral edge of the main cutting edge, which more reliably prevents welding at the cutting edge shoulder. Also, by making the honing smaller in this way, the sharpness of the cutting edge at the cutting edge shoulder can be improved, which makes it possible to suppress the generation of burrs at the exit edge when drilling a through hole.

[0013] In the case of a chamfer honing (angle honing) or composite honing in which the honing has a straight line in the cross section perpendicular to the cutting edge, the size of the honing refers to the width of the honing surface in the direction along the straight line connecting the cutting edge and the axis in the cross section perpendicular to the cutting edge. In the case of a round honing in which the honing has a convex curved shape such as a convex arc in the cross section perpendicular to the cutting edge, the size of the honing refers to the radius (radius of curvature) of the honing surface in the cross section perpendicular to the cutting edge.

[0014] To make the true rake angle at the outer peripheral end of the cutting edge shoulder larger in the negative direction than the true rake angle at the outer peripheral end of the main cutting edge, first, the outer peripheral end of the cutting edge is provided with the tip flank and a chamfer located on the wall surface, the chamfer being inclined in the opposite direction to the drill rotation direction as it approaches the ridgeline between the rake face and the outer peripheral surface of the drill body, which extends in the opposite direction to the drill rotation direction, and the cutting edge shoulder is formed at the ridgeline between the chamfer and the tip flank. In this case, for example, by forming a chamfer with a small area and a polygonal shape (such as a triangular or rectangular shape), the true rake angle of the cutting edge shoulder can be made larger in the negative direction than the main cutting edge.

[0015] Secondly, a band-shaped chamfer may be formed along the chip flute at the outer peripheral edge of the wall surface of the chip flute facing the rotation direction of the drill, the band-shaped chamfer intersecting the wall surface at an obtuse angle on the inner peripheral side of the outer peripheral edge, and the cutting edge shoulder may be formed at the ridge where the band-shaped chamfer intersects with the tip flank. In this case, even when a new cutting edge is sharpened after the cutting edge has become dull due to wear or the like, the true rake angle of the cutting edge shoulder can be made larger on the negative side than that of the main cutting edge simply by grinding the tip flank.

[0016] Thirdly, a flat chamfer may be formed on the outer periphery of the tip flank, the flat chamfer intersecting at an obtuse angle with the tip flank and the outer periphery of the drill body extending from the rake face in the opposite direction to the drill rotation direction, and the cutting edge shoulder may be formed at the ridge where the flat chamfer and the rake face intersect.Fourthly, a convex chamfer may be formed on the outer periphery of the tip flank, the flat chamfer contacting the tip flank and the outer periphery of the drill body extending from the rake face in the opposite direction to the drill rotation direction, and the cutting edge shoulder may be formed at the ridge where the convex chamfer and the rake face intersect.

[0017] In these cases, the true rake angle of the cutting edge shoulder can be made larger on the negative angle side than that of the main cutting edge without chamfering the rake face, thereby preventing situations in which chamfering the rake face would affect chip discharge performance.

[0018] In addition ,shaft Viewed from the tip of the line axis The width of the cutting edge shoulder in the direction of the line connecting the line and the outer peripheral end of the cutting edge shoulder is desirably 0.2 × D or less where D is the diameter of the cutting edge. If the width of the cutting edge shoulder exceeds 0.2 × D of the diameter D of the cutting edge, the portion where the true rake angle increases to the negative angle side becomes too long, which may result in an increase in cutting resistance.

[0019] Furthermore, it is desirable that the honing size of the cutting edge shoulder be 0.8×H or less relative to the honing size H of the main cutting edge portion. If the honing size of the cutting edge shoulder exceeds 0.8×H relative to the honing size H of the main cutting edge portion, the sharpness of the cutting edge shoulder may be impaired, making it impossible to suppress the generation of burrs at the exit edge of the through hole. Note that the honing size of the cutting edge shoulder may be 0.5×H or less, or 0.3×H or less relative to the honing size H of the main cutting edge portion.

[0020] Furthermore, the honing applied to the main cutting edge portion and the cutting edge shoulder portion of the cutting edge may be any of the above-mentioned chamfer honing, compound honing, or round honing, but it is desirable that the honing applied to the main cutting edge portion be chamfer honing and the honing applied to the cutting edge shoulder portion be round honing. This ensures sufficient cutting edge strength in the main cutting edge portion, which is mainly used for drilling, while at the cutting edge shoulder portion, an even sharper cutting edge can be obtained while maintaining cutting edge strength. [Effects of the Invention]

[0021] As explained above, according to the present invention, the cutting edge strength can be ensured by increasing the cutting edge angle at the shoulder of the cutting edge, and welding to the shoulder of the cutting edge can be prevented, thereby preventing damage due to the detachment of the welding material. Furthermore, according to the present invention, by improving the sharpness of the shoulder of the cutting edge, it is possible to suppress the generation of burrs at the exit when drilling a through hole. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a side view showing a first embodiment of the present invention. [Figure 2] 2 is an enlarged front view of a cutting edge portion of the embodiment shown in FIG. 1. [Figure 3] 3 is a side view as viewed in the direction of the arrow X in FIG. 2 (as viewed in a direction perpendicular to the straight line N1). [Figure 4] 3 is a side view as viewed in the direction of the arrow Y in FIG. 2 (as viewed in a direction perpendicular to the line N2). [Figure 5] 4 is an enlarged cross-sectional view taken along the line XX in FIG. 3. [Figure 6] FIG. 5 is an enlarged cross-sectional view of FIG. 4 taken along the line YY. [Figure 7] 4 is a cross-sectional view of FIG. 3 taken along the line Z-Z. [Figure 8] 1. FIG. 4 is an enlarged front view of a cutting edge portion showing a modified example of the embodiment shown in FIG. [Figure 9] 9 is a side view as viewed in the direction of the arrow X in FIG. 8 (as viewed in a direction perpendicular to the straight line N1). [Figure 10] FIG. 6 is an enlarged front view of a cutting edge portion showing a second embodiment of the present invention. [Figure 11] 11 is a side view as viewed in the direction of the arrow X in FIG. 10 (as viewed in a direction perpendicular to the straight line N1). [Figure 12] 12 is a cross-sectional view of FIG. 11 taken along the line Z-Z. [Figure 13] 11 is an enlarged front view of a cutting edge portion showing a modified example of the embodiment shown in FIG. [Figure 14] 14 is a side view as viewed in the direction of the arrow X in FIG. 13 (as viewed in a direction perpendicular to the straight line N1). [Figure 15] FIG. 10 is an enlarged front view of a cutting edge portion showing a third embodiment of the present invention. [Figure 16] 16 is a side view as viewed in the direction of the arrow X in FIG. 15 (as viewed in a direction perpendicular to the straight line N1). [Figure 17] FIG. 10 is an enlarged front view of a cutting edge portion showing a fourth embodiment of the present invention. [Figure 18] 18 is a side view as viewed in the direction of the arrow X in FIG. 17 (as viewed in a direction perpendicular to the straight line N1). [Figure 19] FIG. 10 is a side view showing a fifth embodiment of the present invention. [Figure 20] FIG. 20 is an enlarged front view of the cutting edge portion of the embodiment shown in FIG. [Figure 21] 21 is a side view as viewed in the direction of the arrow X in FIG. 20 (as viewed in a direction perpendicular to the straight line N1). [Figure 22] FIG. 10 is an enlarged front view of a cutting edge portion showing a sixth embodiment of the present invention. [Figure 23] 23 is a side view as viewed in the direction of the arrow X in FIG. 22 (as viewed in a direction perpendicular to the straight line N1). [Figure 24] FIG. 13 is an enlarged front view of a cutting edge portion showing a seventh embodiment of the present invention. [Figure 25] 25 is a side view showing the cutting edge portion of the drill of FIG. 24, and more specifically, a side view of the cutting edge portion of FIG. 24 as seen from a direction perpendicular to a straight line N1. [Figure 26] 25 is a cross-sectional view (transverse cross-sectional view) showing the cutting edge portion of the drill of FIG. 24. [Figure 27] FIG. 13 is an enlarged front view of a cutting edge portion showing a modified example of the seventh embodiment. [Figure 28] 28 is a cross-sectional view (transverse cross-sectional view) showing the cutting edge portion of the drill of FIG. 27. DETAILED DESCRIPTION OF THE INVENTION

[0023] 1 to 7 show a first embodiment of the present invention. In this embodiment, a drill body 1 is made of a hard material such as cemented carbide and is integrally formed into a multi-stage cylindrical shape centered on an axis O. The large-diameter rear end portion (the right-hand portion in FIG. 1) of the drill body 1 is a shank portion 2, and the smaller-diameter front end portion (the left-hand portion in FIG. 1) is a cutting edge portion 3. Between the shank portion 2 and the cutting edge portion 3 of the drill body 1 is a tapered neck portion 4 having a truncated cone shape centered on the axis O and gradually decreasing in diameter toward the front end.

[0024] Such a drill is held by the spindle of a machine tool at the shank portion 2 of the drill body 1, and is rotated around an axis O in a drill rotation direction T while being fed toward the tip side in the direction of the axis O. As a result, the drill uses the cutting edge 5 formed at the tip of the cutting edge portion 3 to drill a hole such as a through hole in the workpiece.

[0025] A chip discharge flute 7 is formed on the outer periphery of the cutting edge portion 3. The flute 7 opens onto a tip flank 6, which is the tip surface of the drill body 1, and extends rearward in the direction of the axis O. The cutting edge 5, whose tip serves as a rake face 8, is formed at the ridge where the wall surface of the chip discharge flute 7 facing the drill rotation direction T intersects with the tip flank 6. The cutting edge 5 extends rearward toward the outer periphery of the drill body 1, i.e., radially outward, and is given a point angle. A first margin 3A is formed on the outer periphery of the cutting edge portion 3 that connects to the chip discharge flute 7 on the side opposite the drill rotation direction T. A second margin 3B is formed on the outer periphery of the cutting edge portion 3 that connects to the chip discharge flute 7 on the side of the drill rotation direction T.

[0026] In this embodiment, two chip flutes 7 are formed on the cutting edge portion 3 symmetrically with respect to the axis O, twisting in the opposite direction to the drill rotation direction T as they move toward the rear end in the direction of the axis O, and reaching the tip of the tapered neck portion 4. A cutting edge 5 is formed on each of the chip flutes 7 at the ridge where the rake face 8 and the tip flank face 6 intersect. In other words, the drill of this embodiment is a two-flute twist drill.

[0027] The drill body 1 is formed with two coolant holes 9, symmetrically about the axis O, extending from the rear end face of the shank portion 2 toward the tip end, and twisted with the same lead as the chip discharge flutes 7. These coolant holes 9 pass between the chip discharge flutes 7 in the cutting edge portion 3 and open to the tip flank 6. During drilling, coolant such as cutting fluid or compressed air is ejected from these coolant holes 9. The tip flank 6 is formed by a two-stage flank whose relief angle increases in the direction opposite to the drill rotation direction T. The coolant hole 9 opens in the flank opposite to the drill rotation direction T of the two flanks.

[0028] Furthermore, a thinning portion 10 is formed on the inner peripheral portion of the tip of the chip flute 7 by cutting out the tip of the wall surface of the chip flute 7 that faces away from the inner peripheral portion of the rake face 8 and the direction of drill rotation T. The cutting edge 5 is provided with, in this order from the inner peripheral portion of the drill body 1, i.e., near the axis O, toward the outer peripheral portion, a thinning cutting edge portion 5A, a main cutting edge portion 5B that is continuous with the outer peripheral side of the thinning cutting edge portion 5A and is formed at the intersection ridge where the rake face 8 and the tip flank 6 meet, and a cutting edge shoulder 5C that extends from the outer peripheral end P of the main cutting edge portion 5B to the outer periphery of the drill body 1 and has an outer peripheral end Q. In this embodiment, the thinning cutting edge portion 5A is formed at the intersection ridge where the thinning portion 10 meets the tip flank 6 that is continuous with the thinning portion 10 on the side opposite to the direction of drill rotation T.

[0029] Honing is applied to the thinning cutting edge portion 5A, the main cutting edge portion 5B, and the cutting edge shoulder portion 5C to form honed surfaces 5a, 5b, and 5c, respectively. This honing may be chamfer honing (angle honing) which has a straight portion in a cross section perpendicular to the cutting edge 5, compound honing in which both ends of the straight portion are rounded into a convex curve, or round honing which forms a convex curve such as a convex arc in a cross section perpendicular to the cutting edge 5. In this embodiment, chamfer honing is applied to the thinning cutting edge portion 5A and the main cutting edge portion 5B, and round honing is applied to the cutting edge shoulder portion 5C.

[0030] As shown in FIG. 6, in a cross section perpendicular to the cutting edge 5 at the outer peripheral end P of the major cutting edge portion 5B, the true rake angle θB is the inclination angle of the rake face 8 with respect to a line L connecting the cutting edge 5 (the major cutting edge portion 5B) and the axis O. As shown in FIG. 5, in a cross section perpendicular to the cutting edge 5 at the outer peripheral end Q of the cutting edge shoulder 5C, the true rake angle θC is the inclination angle of the rake face with respect to a line M connecting the cutting edge 5 (the cutting edge shoulder 5C) and the axis O. The true rake angle θC is larger on the negative side than the true rake angle θB. In this embodiment, the true rake angle θB at the outer peripheral end P of the major cutting edge portion 5B is a positive angle as shown in FIG. 6, and the true rake angle θC at the outer peripheral end Q of the cutting edge shoulder 5C is a negative angle as shown in FIG.

[0031] Furthermore, as shown in FIG. 6, the size of the honing surface 5c at the outer peripheral end Q of the cutting edge shoulder portion 5C is smaller than the size of the honing surface 5b at the outer peripheral end P of the main cutting edge portion 5B.

[0032] In the first embodiment, as shown in FIGS. 3 and 4 , the cutting edge 5 has a tip flank 6 and a triangular chamfer (chamfer) 11 formed at its outer peripheral end. The triangular chamfer 11 is located at the tip outer periphery of the wall of the chip flute 7 facing the drill rotation direction T. The width (diameter perpendicular to the axis O) of the triangular chamfer 11 narrows with increasing distance from the ridge (cutting edge shoulder 5C) where the triangular chamfer 11 intersects with the tip flank 6 toward the rear end in the direction of the axis O. The triangular chamfer 11 slopes away from the drill rotation direction T as it moves from the rake face 8 toward the ridge (leading edge) where the triangular chamfer 11 intersects with the outer peripheral surface (first margin 3A) of the drill body 1, which extends in the opposite direction to the drill rotation direction T. That is, the triangular chamfer 11 slopes away from the drill rotation direction T as it moves radially outward. In this embodiment, the triangular chamfered portion 11 slopes away from the drill rotation direction T as it extends toward the tip end in the direction of the axis O. A cutting edge shoulder 5C is formed at the ridge line where the triangular chamfered portion 11 intersects with the tip flank 6, and the true rake angle θC of the cutting edge shoulder 5C is made larger on the negative side than the true rake angle θB of the main cutting edge portion 5B.

[0033] In this embodiment, the size of the honing surface 5b of the main cutting edge portion 5B, which is a chamfer honing, is the width H of the honing surface 5b in the direction of the straight line L in a cross section perpendicular to the cutting edge 5 at the outer peripheral end P of the main cutting edge portion 5B, as shown in Fig. 6. In contrast, in this embodiment, the size of the honing of the cutting edge shoulder portion 5C, which is a round honing, is the radius (radius of curvature) R of the honing surface 5c in a cross section perpendicular to the cutting edge 5 at the outer peripheral end Q of the cutting edge shoulder portion 5C, as shown in Fig. 5.

[0034] Furthermore, the honing size of the cutting edge shoulder portion 5C (radius R of honing surface 5c) relative to the honing size of the main cutting edge portion 5B (width H of honing surface 5b) is set to 0.8×H or less.

[0035] Furthermore, as shown in Figure 2, when viewing the drill body 1 from the tip side in the direction of the axis O, the width W of the cutting edge shoulder 5C in the direction of extension of a straight line N1 connecting the axis O and the outer peripheral end Q of the cutting edge shoulder 5C is set to be 0.2 x D or less, where D is the diameter of the cutting edge 5 shown in Figure 3 (the diameter of the circle of the rotational path made by the outer peripheral end Q of the cutting edge shoulder 5C around the axis O).

[0036] In this embodiment, the thinning cutting edge portion 5A extends linearly from the vicinity of the axis O toward the outer periphery as viewed from the tip end in the direction of the axis O, and then bends in a convex curve to connect to the main cutting edge portion 5B, as shown in Fig. 2. The main cutting edge portion 5B also extends linearly as viewed from the tip end in the direction of the axis O, as shown in Fig. 2.

[0037] Furthermore, by forming the cutting edge shoulder portion 5C into the triangular chamfered portion 11 as described above, as shown in Figure 2, when viewed from the tip side in the direction of the axis O, the cutting edge shoulder portion 5C is formed so that it bends at the outer peripheral end P of the main cutting edge portion 5B in the opposite direction to the drill rotation direction T, extends in a straight line, and then reaches the outer peripheral end Q.

[0038] In a drill configured in this manner, the true rake angle θC at the outer peripheral end Q of the cutting edge shoulder portion 5C on the outer peripheral side of the cutting edge 5 is made larger on the negative angle side relative to the true rake angle θB at the outer peripheral end P of the main cutting edge portion 5B, so that the cutting edge angle of the cutting edge 5 at the cutting edge shoulder portion 5C can be made larger as shown in Figures 5 and 6.

[0039] This ensures the strength of the cutting edge shoulder 5C and prevents damage to the cutting edge shoulder 5C. Furthermore, by preventing welding caused by such damage, it is possible to prevent fractures in the cutting edge shoulder 5C when the welded material falls off, thereby extending the life of the drill.

[0040] Furthermore, the size of the honing applied to the cutting edge 5 at the outer peripheral end Q of the cutting edge shoulder portion 5C (radius R of the honing surface 5c) is smaller than the size at the outer peripheral end P of the main cutting edge portion 5B (width H of the honing surface 5b), which makes it possible to more reliably prevent welding of the cutting edge shoulder portion 5C.

[0041] Furthermore, by reducing the honing size in this manner, the sharpness of the cutting edge 5 can be improved at the cutting edge shoulder 5C. This also makes it possible to prevent burrs from forming at the exit of a through hole when drilling the through hole. The honing size may be continuously reduced from the inner periphery (radially inward) of the drill body 1 toward the outer periphery of the cutting edge 5 (the outer periphery Q of the cutting edge shoulder 5C), or may be constant at the main cutting edge 5B and continuously reduced from the outer periphery P to the outer periphery Q. Alternatively, the honing size may be continuously reduced from the outer periphery P to the outer periphery Q, and then remain constant until it reaches the outer periphery Q.

[0042] In addition, in this embodiment, as described above, in order to make the true rake angle θC at the outer peripheral end Q of the cutting edge shoulder portion 5C larger on the negative angle side than the true rake angle θB at the outer peripheral end P of the main cutting edge portion 5B, a tip flank 6 and a triangular chamfered portion 11 are formed at the outer peripheral end of the cutting edge 5, and the cutting edge shoulder 5C is formed at the intersection ridge between this triangular chamfered portion 11 and the tip flank 6.

[0043] Therefore, by forming a triangular chamfered portion 11 of a relatively small area on the drill body of a normal drill, the true rake angle θC of the cutting edge shoulder portion 5C can be made larger on the negative angle side than the true rake angle θB of the main cutting edge portion 5B, making the manufacture of the drill body 1 easier, more efficient, and more economical.

[0044] Furthermore, in this embodiment, the width W of the cutting edge shoulder 5C in the direction of the straight line N1 connecting the axis O and the outer peripheral end Q of the cutting edge shoulder 5C as viewed from the tip side in the direction of the axis O is set to 0.2 × D or less where D is the diameter of the cutting edge 5, thereby preventing cutting resistance from becoming unnecessarily large. In other words, if the width of the cutting edge shoulder 5C exceeds 0.2 × D of the diameter D of the cutting edge 5, the portion where the true rake angle θC increases to the negative angle side becomes too long, which could result in increased cutting resistance.

[0045] In this embodiment, the honing size R of the cutting shoulder 5C is set to 0.8×H or less relative to the honing size H of the major cutting edge 5B, which further ensures sharpness of the cutting shoulder 5C. In other words, if the honing size R of the cutting shoulder 5C exceeds 0.8×H relative to the honing size H of the major cutting edge 5B, the sharpness of the cutting shoulder 5C may be impaired, making it impossible to prevent burrs from being generated at the exit edge of the through hole. Note that the honing size R of the cutting shoulder 5C may be set to 0.5×H or less, or may be 0.3×H or less relative to the honing size H of the major cutting edge 5B.

[0046] Furthermore, in this embodiment, the main cutting edge portion 5B is honed using chamfer honing, and the cutting edge shoulder portion 5C is honed using round honing. This ensures sufficient cutting edge strength in the main cutting edge portion 5B, which is mainly used for drilling, while the cutting edge shoulder portion 5C can achieve even sharper cutting edge while maintaining cutting edge strength.

[0047] However, conversely, the honing applied to the cutting edge shoulder 5C may be chamfer honing or compound honing, which has a linear cross section, while the main cutting edge 5B may be round honing, which has a convex curved cross section. Also, both the main cutting edge 5B and the cutting edge shoulder 5C may be chamfer honing or compound honing, or both the main cutting edge 5B and the cutting edge shoulder 5C may be round honing.

[0048] In the first embodiment, the main cutting edge portion 5B is formed linearly when viewed from the tip side in the direction of the axis O, but as in the modified example shown in Figures 8 and 9, the main cutting edge portion 5B may be formed so that it extends in a concave curve that is recessed in the opposite direction from the drill rotation direction T as it moves from the portion where the thinning cutting edge portion 5A is formed in a convex curve toward the outer periphery of the drill body 1, and then extends in the drill rotation direction T to connect to the cutting edge shoulder portion 5C. In this modified example and the second to sixth embodiments and their modified examples described below, the same reference numerals are used to designate parts that are common to the first embodiment shown in Figures 1 to 7.

[0049] 10 to 12 show a second embodiment of the present invention. This second embodiment is characterized in that a band-shaped chamfer 12 is formed along the chip discharge groove 7 at the outer peripheral edge of the wall surface of the chip discharge groove 7 facing the drill rotation direction T, and intersects the wall surface on the inner peripheral side of this outer peripheral edge at an obtuse angle, and the cutting edge shoulder 5C is formed at the intersection ridge between this band-shaped chamfer 12 and the tip flank 6.

[0050] In the second embodiment, as in the case shown in Figures 5 and 6, the true rake angle θC at the outer peripheral end Q of the cutting edge shoulder portion 5C is made larger on the negative angle side relative to the true rake angle θB at the outer peripheral end P of the main cutting edge portion 5B of the cutting edge 5, and the size of the honing at the outer peripheral end Q of the cutting edge shoulder portion 5C (radius R of the honing surface 5c) is made smaller relative to the size of the honing at the outer peripheral end P of the main cutting edge portion 5B (width H of the honing surface 5b), so that the same effects as in the first embodiment can be obtained.

[0051] In addition, in this second embodiment, as described above, a strip-shaped chamfered portion 12 is formed along the chip discharge groove 7 at the outer peripheral edge of the wall surface of the chip discharge groove 7 facing the drill rotation direction T, and intersects with the wall surface on the inner peripheral side of this outer peripheral edge at an obtuse angle, and the cutting edge shoulder portion 5C is formed at the intersection ridge between this strip-shaped chamfered portion 12 and the tip flank 6.

[0052] Therefore, when sharpening a new cutting edge 5 after the cutting edge 5 has become dull due to wear or the like, the true rake angle θC of the cutting edge shoulder 5C can be made larger on the negative angle side than that of the main cutting edge portion 5B simply by grinding the tip flank 6. Therefore, it is not necessary to form the cutting edge shoulder 5C by re-forming the triangular chamfer 11 after grinding the tip flank 6, as in the first embodiment, for example.

[0053] In this second embodiment, as in the modified example shown in Figures 13 and 14, similar to the modified example of the first embodiment, the main cutting edge portion 5B may be formed so that it extends in a concave curve that is concave in the opposite direction to the drill rotation direction T as it moves from the part where the thinning cutting edge portion 5A is formed in a convex curve toward the outer periphery of the drill body 1, and then extends toward the drill rotation direction T to connect to the cutting edge shoulder portion 5C.

[0054] Furthermore, in these first and second embodiments and their modified examples, a triangular chamfer 11 or a band-shaped chamfer 12 is formed on the rake face 8 side of the cutting edge 5, thereby making the true rake angle θC at the outer peripheral end Q of the cutting edge shoulder 5C larger in the negative direction relative to the true rake angle θB at the outer peripheral end P of the main cutting edge portion 5B, and making the size of the honing at the outer peripheral end Q of the cutting edge shoulder 5C smaller relative to the size of the honing at the outer peripheral end P of the main cutting edge portion 5B. However, as in the third embodiment shown in Figures 15 and 16 and the fourth embodiment shown in Figures 17 and 18, a chamfer may be formed on the tip relief face 6 side of the cutting edge 5.

[0055] Of these, in the third embodiment shown in Figures 15 and 16, a planar chamfered portion 13 is formed on the outer periphery of the tip flank 6, which intersects at an obtuse angle with the tip flank 6 located more inward than this outer periphery and the first margin 3A, which is the outer periphery of the cutting edge portion 3 of the drill body 1 extending from the cutting face 8 in the opposite direction to the drill rotation direction T, and a linear cutting edge shoulder 5C is formed at the intersection ridge between this planar chamfered portion 13 and the cutting face 8.

[0056] In the fourth embodiment shown in Figures 17 and 18, a convexly curved chamfered portion 14 is formed on the outer periphery of the tip flank 6, which is inward of the tip flank 6 and in contact with a first margin 3A, which is the outer periphery of the cutting edge portion 3 of the drill body 1 extending from the cutting face 8 in the opposite direction to the drill rotation direction T, and a cutting edge shoulder 5C that is convexly curved when viewed from the direction facing the rake face 8, is formed at the intersection ridge between this convexly curved chamfered portion 14 and the cutting face 8.

[0057] In the third and fourth embodiments, the true rake angle θC of the cutting edge shoulder 5C can be made larger on the negative angle side than that of the main cutting edge 5B without chamfering the rake face 8 with a triangular chamfer 11 or a band-shaped chamfer 12. This makes it possible to prevent a situation in which chamfering the rake face 8 would have an adverse effect on chip discharge performance.

[0058] 19 to 21 show a fifth embodiment of the present invention, and FIGS. 22 and 23 show a sixth embodiment of the present invention. These fifth and sixth embodiments are cases in which the present invention is applied to a drill for countersinking. That is, in the first to fourth embodiments and their modifications, the cutting edge 5 extends toward the rear end as it approaches the outer periphery of the drill body 1, and a point angle is given to the cutting edge 5. In contrast, in the fifth and sixth embodiments, the cutting edge 5 extends approximately along a plane perpendicular to the axis O, and the point angle is 180°.

[0059] In the fifth embodiment, the outer peripheral end of the cutting edge 5 is formed with a tip flank 6 and a triangular chamfered portion 11 arranged on the wall surface of the chip discharge groove 7 facing the drill rotation direction T, and the triangular chamfered portion 11 slopes in the opposite direction to the drill rotation direction T as it approaches the intersecting ridge portion (leading edge) with the outer peripheral surface (first margin 3A) of the drill body 1 extending from the rake face 8 in the opposite direction to the drill rotation direction T, and a cutting edge shoulder portion 5C is formed at the intersecting ridge portion between this triangular chamfered portion 11 and the tip flank 6.

[0060] In the sixth embodiment, a band-shaped chamfer 12 is formed along the chip discharge groove 7 at the outer peripheral edge of the wall surface of the chip discharge groove 7 facing the drill rotation direction T, intersecting the wall surface at an obtuse angle on the inner peripheral side of this outer peripheral edge, and a cutting edge shoulder 5C is formed at the ridge line where this band-shaped chamfer 12 intersects with the tip flank 6. Note that in these fifth and sixth embodiments, the second margin 3B and the coolant hole 9 are not formed.

[0061] In such drills for countersinking, the cutting edge 5 has a point angle of 180°, so that the cutting edge 5 bites into the workpiece all at once, making it easy for an impact load to act on the cutting edge 5. However, in the fifth and sixth embodiments, the true rake angle θC at the outer peripheral end Q of the cutting edge shoulder 5C is increased toward the negative angle side relative to the outer peripheral end P of the main cutting edge portion 5B, and the size of the honing is reduced. As described above, the cutting edge strength can be ensured by increasing the tool angle of the cutting edge shoulder 5C, thereby preventing damage to the cutting edge shoulder 5C due to an impact load.

[0062] 24 to 26 show a seventh embodiment of the present invention. In this seventh embodiment, a band-shaped chamfer 12 is formed along the outer peripheral edge of the wall surface of the chip flute 7 facing the drill rotation direction T, intersecting the wall surface on the inner peripheral side of the outer peripheral edge at an obtuse angle. Furthermore, a chamfer 11 is formed on the outer peripheral tip portion of the wall surface of the chip flute 7. That is, the drill of this embodiment has a configuration in which the band-shaped chamfer 12 and the chamfer 11 are combined. Furthermore, a cutting edge shoulder 5C is formed at the ridgeline where the chamfer 11 intersects with the tip flank 6, so that the true rake angle θC of the cutting edge shoulder 5C is larger on the negative side than the true rake angle θB of the main cutting edge portion 5B.

[0063] 25, in this embodiment, the chamfered portion 11 is formed on the wall surface so as to cut out the tip of the band-shaped chamfered portion 12, thereby forming a quadrangular shape when viewed from the drill rotation direction T. Specifically, the chamfered portion 11 is trapezoidal in shape, with the length of the lower base being longer than the length of the upper base. As described above, the chamfered portion 11 is not limited to the triangular chamfered portion 11 described in the first embodiment, but may be a quadrangular chamfered portion 11. The chamfered portion 11 may also be a polygonal shape other than a triangular or quadrangular shape.

[0064] In addition, in the seventh embodiment, as in the first embodiment described above, when the drill is viewed from the tip side in the direction of the axis O as shown in Figure 24, the main cutting edge portion 5B extends in a straight line, but this is not limited to this. 27 and 28 show a modification of the seventh embodiment. As shown in Fig. 27, when the drill is viewed from the tip side in the direction of the axis O, the main cutting edge portion 5B may have a concave curved shape that is concave toward the opposite side to the rotation direction T of the drill.

[0065] The present invention may be combined with the various configurations described in the above-described embodiments and modifications, and may also include additions, omissions, substitutions, and other modifications within the scope of the present invention, without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the above-described embodiments, but is limited only by the claims. [Industrial Applicability]

[0066] According to the drill of the present invention, the cutting edge strength can be ensured by increasing the cutting edge angle at the cutting edge shoulder, and welding can be prevented from occurring at the cutting edge shoulder, thereby preventing breakage due to the detachment of the welding material. Furthermore, by improving the sharpness of the cutting edge shoulder, it is possible to suppress the generation of burrs at the exit edge when drilling a through hole. Therefore, the drill has industrial applicability. [Explanation of symbols]

[0067] 1 Drill body 2 Shank 3 Cutting edge 3A First Margin 3B Second Margin 4 Tapered neck 5 cutting edge 5A Thinning cutting edge 5B Main cutting edge 5C Cutting edge shoulder 5a~5c Honing surface 6 Tip flank 7 Chip discharge groove 8. Rake face 9 Coolant holes 10 Thinning section 11 Chamfered portion (triangular chamfered portion, square chamfered portion) 12 Belt-shaped chamfer 13 Flat chamfered portion 14 Convex curved chamfered portion O Axis of drill body 1 T Drill rotation direction P Outer periphery of main cutting edge 5B Q Outer periphery of cutting edge shoulder 5C θB: True rake angle of the main cutting edge portion 5B at the outer peripheral end P θC: True rake angle of cutting edge shoulder 5C at outer peripheral end Q D Diameter of cutting edge 5 L is a straight line connecting the cutting edge 5 and the axis O in a cross section perpendicular to the cutting edge 5 at the outer peripheral end P. M is a straight line connecting the cutting edge 5 and the axis O in a cross section perpendicular to the cutting edge 5 at the outer peripheral end Q. N1: A straight line connecting the axis O and the outer peripheral end Q of the cutting edge shoulder portion 5C when viewed from the tip side in the direction of the axis O N2: A straight line connecting the axis O and the outer peripheral end P of the main cutting edge portion 5B when viewed from the tip side in the direction of the axis O H: Honing size of main cutting edge portion 5B (width of honing surface 5b in the direction of straight line L) R: The size of the honing of the cutting edge shoulder 5C (the radius of the honing surface 5c in the cross section perpendicular to the cutting edge 5) W: Width of the cutting edge shoulder 5C in the direction of the straight line N1

Claims

1. A drill in which a chip discharge groove is formed on the outer periphery of the tip of a drill body that is rotated around an axis in a drill rotation direction, the chip discharge groove opening on a tip flank of the drill body and extending toward the rear end in the axial direction, and a cutting edge is formed at an intersection ridge between a wall surface of the chip discharge groove facing the drill rotation direction and the tip flank, the wall surface serving as a rake surface, the cutting edge is provided with a main cutting edge portion extending from the inner peripheral side toward the outer peripheral side of the drill body and a cutting edge shoulder portion extending from the outer peripheral end of the main cutting edge portion to the outer periphery of the drill body, and is honed; a true rake angle, which is the inclination angle of the rake face with respect to a line connecting the cutting edge and an axis in a cross section perpendicular to the cutting edge, at the outer peripheral end of the cutting edge shoulder portion relative to the outer peripheral end of the main cutting edge portion, is increased toward the negative angle side, and the size of the honing is reduced.

2. The cutting edge has an outer peripheral end formed with the tip relief surface and a chamfered portion disposed on the wall surface, the chamfered portion is inclined in the opposite direction to the rotation direction of the drill toward a ridge line portion extending from the rake face toward an intersecting ridge line portion with the outer peripheral surface of the drill body in the opposite direction to the rotation direction of the drill, 2. The drill according to claim 1, wherein the cutting edge shoulder is formed at a ridge line where the chamfered portion and the tip flank intersect.

3. 2. The drill according to claim 1, wherein a band-shaped chamfer is formed along the chip discharge groove at an outer peripheral edge of the wall surface of the chip discharge groove facing the rotation direction of the drill, the band-shaped chamfer intersecting the wall surface at an obtuse angle on the inner peripheral side of the outer peripheral edge, and the cutting edge shoulder is formed at an intersection ridge line between the band-shaped chamfer and the tip flank.

4. 2. The drill according to claim 1, wherein a planar chamfer is formed on an outer periphery of the tip flank, the planar chamfer intersecting at an obtuse angle with the tip flank and an outer periphery of the drill body extending from the rake face in a direction opposite to the drill rotation direction, and the cutting edge shoulder is formed at an intersecting ridge line between the planar chamfer and the rake face.

5. 2. The drill according to claim 1, wherein a convexly curved chamfered portion is formed on an outer periphery of the tip flank, the chamfered portion being in contact with the tip flank on the inner peripheral side of the outer periphery and with an outer periphery of the drill body extending from the rake face in a direction opposite to the rotation direction of the drill, and the cutting edge shoulder is formed at an intersecting ridge line between the convexly curved chamfered portion and the rake face.

6. A drill described in any one of claims 1 to 5, characterized in that the width of the cutting edge shoulder in the direction in which a straight line connecting the axis and the outer peripheral end of the cutting edge shoulder extends when viewed from the axial tip side is 0.2 x D or less relative to the diameter D of the cutting edge.

7. 7. The drill according to claim 1, wherein the honing size of the cutting edge shoulder is set to 0.8×H or less relative to the honing size H of the main cutting edge portion.

8. 8. The drill according to claim 1, wherein the honing applied to the main cutting edge portion is chamfer honing, and the honing applied to the cutting edge shoulder portion is round honing.

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