Drill

Abstract

Provided is a drill which makes it possible to reduce the likelihood of chipping at the outermost peripheral portion of an end cutting edge that is provided with a honed surface. A drill (1) comprises: a cylindrical tool body (2); an end cutting edge (3) that is formed at the tip end of the tool body; a helical groove (4) that is provided so as to be recessed from the outer peripheral surface of the tool body and that forms a rake surface (11) of the end cutting edge; a honed surface (20) that is formed by chamfering a ridgeline portion between the rake surface of the end cutting edge and a flank surface (12, 13) of the end cutting edge; a shoulder surface part (22) that is formed by chamfering an edge which is formed by the honed surface, the outer peripheral surface of the tool body, and the flank surface; and a remaining line part (24) that is formed by the ridgeline between the honed surface and the outer peripheral surface of the tool body.

Description

drill

[0001] This invention relates to a drill that can prevent chipping from occurring on the outermost part of the bottom cutting edge, which has a honed surface.

[0002] The drill comprises a bottom cutting edge provided at the tip of the tool body, and a helical groove recessed in the outer circumferential surface of the tool body to form the rake face of the bottom cutting edge. In this drill, a honing surface may be provided on the ridge between the rake face and the relief face of the bottom cutting edge to suppress chipping of the bottom cutting edge. In Patent Document 1, a honing surface is provided over the entire cutting edge length of the bottom cutting edge.

[0003] Japanese Patent Publication No. 2019-5882

[0004] However, even when the honing surface is provided up to the outermost part of the bottom cutting edge, as in the conventional technology described above, it may not be possible to sufficiently mitigate the sharpness of the edge at the outermost part. This is because a relatively sharp edge is newly formed at the outermost part of the bottom cutting edge by the honing surface, the outer surface of the tool body (such as the margin surface), and the relief surface of the bottom cutting edge. When cutting a workpiece with such a drill, stress concentrates at the outermost part, leading to the problem that chipping is likely to occur at that outermost part.

[0005] Furthermore, the honing increases cutting resistance, and the rotational speed is highest at the outermost part, making it particularly prone to overheating. This causes the chips generated at the outermost part to soften and stretch, making them less likely to break apart, and making them more likely to get stuck between the outermost part and the hole wall. As a result, chipping becomes even more likely at the outermost part.

[0006] The present invention was made to solve the above-mentioned problems, and aims to provide a drill that can prevent chipping from occurring on the outermost part of the bottom cutting edge with a honed surface.

[0007] To achieve this objective, the drill of the present invention comprises: a cylindrical tool body that rotates with its axis as the axis of rotation; a bottom cutting edge formed at the tip of the tool body so as to extend radially from the tool body; a twist groove formed in the outer circumferential surface of the tool body so as to twist toward the rear in the direction of rotation as it moves away from the tip in the axial direction, forming the rake face of the bottom cutting edge; a honing surface formed by chamfering the ridge portion between the rake face and the relief face of the bottom cutting edge; a shoulder surface formed by chamfering the edges of the honing surface, the outer circumferential surface and the relief face; and a residual portion formed by the ridge between the honing surface and the outer circumferential surface, by making the shoulder surface width, which is the dimension of the shoulder surface in a direction parallel to the honing width, smaller than the honing width, which is the dimension of the honing surface in a direction perpendicular to the cutting edge length direction of the bottom cutting edge when the honing surface is viewed from the front in the direction of rotation.

[0008] According to the drill described in claim 1, the edges formed by the honing surface, the outer circumferential surface of the tool body, and the relief surface of the bottom cutting edge are chamfered, and a shoulder surface is formed on the outermost part of the bottom cutting edge, thereby suppressing the concentration of stress on that outermost part. Furthermore, at that outermost part, the direction in which the effective cutting edges formed by the relief surface and the honing surface push out chips intersects with the direction in which the effective cutting edges formed by the shoulder surface and the honing surface push out chips. As a result, chips collide with each other at the outermost part, making them easier to break apart.

[0009] In this case, if the shoulder surface is formed over the entire ridge line between the honing surface and the outer surface of the tool body, the honing surface disappears at the outermost part of the bottom cutting edge, and the effect of suppressing chipping of the bottom cutting edge by the honing surface is lost. In contrast, in this drill, the shoulder surface width is made smaller than the honing width, so that a remaining ridge line is formed that preserves the ridge line between the honing surface and the outer surface of the tool body. Therefore, the effect of suppressing chipping of the bottom cutting edge by the honing surface can be obtained even at the outermost part. As a result, it is possible to make it difficult for chipping to occur at the outermost part of the bottom cutting edge where the honing surface is provided.

[0010] The drill described in claim 2 provides the following effects in addition to those of the drill described in claim 1. Let D be the diameter of the bottom cutting edge and x be the number of bottom cutting edges (where x ≥ 2). The axial feed rate of the drill during cutting is D × (4 / x)% or more, and when converted to per cutting edge, D × (4 / x) ２ It is common to set the honing width to )% or more. Furthermore, it is common to make the honing width smaller than the feed rate per tooth so that the rake face of the bottom cutting edge bites into the workpiece during cutting. Therefore, the honing width is D × (4 / x ２ It is common to make it smaller than )%.

[0011] Unlike in such common cases, the honing width of this drill is D × (4 / x ２ The ratio is set to be greater than %). Therefore, with this drill, cutting within the honing surface is more likely to occur, where the workpiece is removed by the honing surface. In this cutting within the honing surface, chip fragmentation is promoted compared to when the workpiece is cut with a sharp blade. Furthermore, the chips generated in cutting within the honing surface move along the honing surface toward the rake face, and then move along the rake face which is facing a different direction. This difference in direction of movement further promotes chip fragmentation. As a result, damage to the outermost part of the bottom cutting edge caused by chip jamming can be further suppressed.

[0012] However, in honing-internal cutting, cutting resistance tends to increase, and if there is a relatively sharp edge on the outermost part of the bottom cutting edge, stress concentration on that edge tends to increase. However, in this drill, the shoulder and remaining edge are provided on the outermost part, so the relatively sharp edge is chamfered, which suppresses such an increase in stress concentration. Therefore, even in honing-internal cutting, where cutting resistance tends to increase, it is possible to make it less likely for damage to occur on the outermost part of the bottom cutting edge due to increased stress concentration.

[0013] The drill described in claim 3 provides the following effects in addition to those of the drill described in claim 2. Here, if the honing width is too large, chips may accumulate within the honing surface and become difficult to discharge to the rake face. In particular, the smaller the cutting diameter D, the smaller the axial feed amount per cutting edge becomes, making it difficult for chips to move axially, and even with a smaller honing width, chip discharge may become difficult. In contrast, by setting the honing width to D × 7% or less, it is possible to easily discharge chips from the honing surface to the rake face.

[0014] The drill described in claim 4 provides the following effects in addition to those achieved by the drill described in any of claims 1 to 3. The shoulder width is 15% to 75% of the honing width. If the shoulder width is less than 15% of the honing width, it may not be possible to suppress stress concentration on the outermost part due to the shoulder, or the chip breaking performance may decrease due to differences in the extrusion direction. On the other hand, if the shoulder width is greater than 75% of the honing width, it may not be possible to obtain the effect of suppressing chipping of the bottom cutting edge by the honing surface in the outermost part (small remaining wire portion). In contrast, by setting the shoulder width to 15% to 75% of the honing width, it is possible to effectively suppress stress concentration on the outermost part due to the shoulder, improve chip breaking performance, and suppress chipping of the bottom cutting edge by the honing surface of the outermost part.

[0015] This is a front view of a drill in one embodiment. (a) is an enlarged front view of the drill, showing the portion IIa in Figure 1, and (b) is an enlarged side view of the drill as seen in the direction of arrow IIb in Figure 2(a). This is a bottom view of the drill as seen in the direction of arrow III in Figure 2(a). This is a cross-sectional view of the drill along the line IV-IV in Figure 2(a). This is a bottom view of a modified example of the drill.

[0016] Preferred embodiments will be described below with reference to the attached drawings. Figure 1 is a front view of a drill 1 in one embodiment. The drill 1 is a drill that performs hole drilling in a workpiece W (see Figure 4) by rotational force transmitted from a machining machine (not shown), such as a machining center. The drill 1 is constructed as a solid drill from a cemented carbide alloy obtained by pressure sintering tungsten carbide (WC), etc. The drill 1 may also be made of high-speed tool steel.

[0017] The drill 1 mainly comprises a tool body 2 having an axis C, two bottom cutting edges 3 formed at the tip of the tool body 2 (the lower end in Figure 1), and two twisted grooves 4 recessed on the outer surface of the tool body 2 corresponding to the two bottom cutting edges 3.

[0018] The tool body 2 is cylindrical with a diameter D (D = 3 mm in this embodiment) centered on axis C, and a shank 2a is provided at its rear end (upper side in Figure 1). The shank 2a is held by a holder (not shown), thereby attaching the drill 1 to the machining tool via the holder. The rotational force of the machining tool is then transmitted to the tool body 2 via this holder, causing the drill 1 (tool body 2) to rotate in the direction of arrow R with axis C as the axis of rotation. In other words, the rotational force transmitted from the machining tool causes the drill 1 to rotate forward in the direction of rotation R.

[0019] The bottom cutting edge 3 is for cutting the workpiece W using rotational force transmitted from the machining center, and has a cutting edge diameter D that is the same as the diameter D of the tool body 2. The bottom cutting edge 3 is formed to extend radially (in a direction perpendicular to the axis C) from the axis C side. Further details of the bottom cutting edge 3 will be described later with reference to Figures 2(a) to 3.

[0020] The helical groove 4 is for collecting and discharging the chips W1 (see Figure 4) generated by the bottom cutting edge 3 during cutting. The helical groove 4 is recessed on the outer circumferential surface of the tool body 2 so as it moves away from the tip of the tool body 2 (the side with the bottom cutting edge 3) in the direction of axis C, it twists toward the rear in the rotational direction R. Two helical grooves 4 are provided symmetrically with respect to axis C so as to form the rake faces 11 of the two bottom cutting edges 3.

[0021] It is preferable to set the helix angle α of the helical groove 4 within the range of 20 degrees or more and 40 degrees or less. If the helix angle α is set to less than 20 degrees, the chip evacuation performance of W1 may decrease. On the other hand, by setting the helix angle α to 20 degrees or more, the chip evacuation performance of W1 can be ensured.

[0022] On the other hand, if the helix angle α is set to a value greater than 40 degrees, the path of the helical groove 4 becomes longer, which may cause the chips W1 to clog easily. By setting the helix angle α to 40 degrees or less, clogging of chips W1 within the helical groove 4 can be suppressed.

[0023] The tool body 2 is provided with a secondary chamfering surface 6 in addition to the bottom cutting edge 3 and the helical groove 4. The secondary chamfering surface 6 is intended to reduce the contact area between the outer surface of the tool body 2 and the workpiece W during cutting, thereby suppressing cutting resistance. The secondary chamfering surface 6 is formed by recessing it radially inward from the outer surface of the tool body 2, which has a diameter D. The rear edge of the secondary chamfering surface 6 in the rotational direction R is connected to the helical groove 4.

[0024] The front edge of the secondary cutting surface 6 in the direction of rotation R is separated from the helical groove 4 in the direction of rotation R. As a result, a margin surface 7 of a predetermined width (0.36 mm in this embodiment) is formed on the outer circumferential surface of the tool body 2 as the remaining portion between the helical groove 4 and the secondary cutting surface 6. If the width of the margin surface 7 is too small, rigidity near the margin surface 7 may not be secured, and if it is too large, the cutting resistance may increase too much. Therefore, it is preferable to set the width of the margin surface 7 to about 3 to 15% of the cutting diameter D.

[0025] The margin surface 7 is for maintaining the straightness of the drill 1 during machining and is in contact with the inner wall surface of the hole machined in the workpiece W by the drill 1. The leading edge 8 is formed by the intersection of this margin surface 7 and the helical groove 4. The helical angle α of the helical groove 4 described above is the angle made between this leading edge 8 and the axis C.

[0026] Next, the detailed configuration of the tip (bottom cutting edge 3) of the drill 1 will be described with reference to Figures 2(a) to 3. Figure 2(a) is an enlarged front view of the drill 1, showing an enlarged portion of part IIa in Figure 1. Figure 2(b) is an enlarged side view of the drill 1 as seen in the direction of arrow IIb in Figure 2(a). Figure 3 is a bottom view of the drill 1 as seen in the direction of arrow III in Figure 2(a). Note that in Figure 3, a portion of the drill 1 visible towards the back of the page (other than the vicinity of the tip) is omitted from the illustration.

[0027] The tip of the drill 1 is provided with two second relief faces 12, two third relief faces 13, and two thinning faces 14, arranged symmetrically with respect to the axis C. The bottom cutting edge 3 is formed by the ridge between the second relief face 12 and the rake face 11 formed by the helical groove 4. That is, the two bottom cutting edges 3 are also formed axially symmetrically with respect to the axis C. Furthermore, the bottom cutting edges 3 are straight when viewed in the direction of the axis C. The tip angle β of the bottom cutting edge 3 (140 degrees in this embodiment) is preferably set to 115 to 160 degrees in order to balance straightness and cutting performance.

[0028] The second relief surface 12 and the third relief surface 13 are designed to reduce cutting resistance by decreasing the contact area between the tip of the drill 1 and the workpiece W during cutting. The second relief surface 12 is formed extending backward from the bottom cutting edge 3 in the direction of rotation R and slopes upward as it moves backward in the direction of rotation R. The third relief surface 13 is formed extending backward from the second relief surface 12 in the direction of rotation R and slopes upward as it moves backward in the direction of rotation R at a larger angle than the second relief surface 12.

[0029] On the axis C side of the drill 1, a chisel edge is usually formed by the boundary line between two relief surfaces (for example, the second relief surface 12). The thinning 14 is a groove provided on the rear side in the rotational direction R of the relief surfaces (the second relief surface 12 and the third relief surface 13) to shorten this chisel edge, and it communicates with the helical groove 4.

[0030] A thinning edge 14a is formed on the ridge between the thinning 14 and the second relief surface 12 located on the rear side in the rotational direction R, and is connected to the axis C side of the bottom cutting edge 3. This thinning edge 14a allows the workpiece W to be cut even near the axis C of the drill 1. In a view in the direction of axis C, the thinning edge 14a is curved convexly toward the front in the rotational direction R, relative to the straight bottom cutting edge 3.

[0031] The thinning blade 14a is provided with a thinning-side honing surface 21 along its entire length. The thinning-side honing surface 21 is a flat surface formed by chamfering the ridge between the rake face formed by the thinning blade 14 and the secondary relief surface 12. The sharp cutting edge formed by the rake face formed by the thinning blade 14 and the secondary relief surface 12 is chamfered by this thinning-side honing surface 21, thereby suppressing chipping of the thinning blade 14a and improving the durability of the thinning blade 14a.

[0032] Similarly, the bottom blade 3 is provided with a honing surface 20 along its entire length. The honing surface 20 is a plane formed by chamfering the edges of the rake face 11 and the secondary relief face 12 of the bottom blade 3, and is connected to the thinning side honing surface 21. The sharp cutting edge formed by the rake face 11 and the secondary relief face 12 is chamfered by this honing surface 20, which suppresses chipping of the bottom blade 3 and improves the durability of the bottom blade 3.

[0033] When the honing surface 20 is viewed from the front in the rotational direction R (when the drill 1 is viewed from the direction where the tip angle β is shown, as in Figure 2(a)), the dimension of the honing surface 20 in the direction perpendicular to the cutting edge length direction of the bottom cutting edge 3 is defined as the honing width A. This honing width A is substantially the same throughout the entire cutting edge length.

[0034] In this case, if the honing surface 20 is provided up to the outermost part of the bottom cutting edge 3, a relatively sharp edge is usually formed by the honing surface 20, the margin surface 7 (the outer surface of the tool body 2), and the secondary relief surface 12 of the bottom cutting edge 3. When a workpiece W is cut with a drill having such an edge, stress concentrates on the edge of the outermost part of the bottom cutting edge 3, which may easily cause chipping at that outermost part.

[0035] In contrast, in the drill 1 of this embodiment, the edges formed by the honing surface 20, the margin surface 7, and the secondary relief surface 12 are chamfered, and a flat shoulder surface 22 is formed on the outermost part of the bottom cutting edge 3. As a result, compared to the case where there is a relatively sharp edge on the outermost part of the bottom cutting edge 3, the concentration of stress on the outermost part can be suppressed by the shoulder surface 22.

[0036] Furthermore, at the outermost part of the bottom blade 3, the effective cutting edge formed by the ridge between the second relief surface 12 and the honing surface 20 pushes the chip W1 in the direction of arrow E perpendicular to the cutting edge. Similarly, the effective cutting edge formed by the ridge between the shoulder surface 22 and the honing surface 20 pushes the chip W1 in the direction of arrow F perpendicular to the cutting edge. Since the directions of arrow E and arrow F, in which these cutting edges push the chip W1, intersect with each other, the chips W1 collide with each other at the outermost part of the bottom blade 3, making them more likely to be broken up.

[0037] In this case, if the shoulder surface 22 is formed over the entire ridge line formed by the honing surface 20 and the margin surface 7, the honing surface 20 disappears at the outermost part of the bottom cutting edge 3, and the effect of suppressing chipping of the bottom cutting edge 3 by the honing surface 20 is lost. In contrast, in the drill 1 of this embodiment, the shoulder surface width B, which is the dimension in the direction parallel to the honing width A of the shoulder surface 22, is made smaller than the honing width A, so that a straight remaining line portion 24 is formed so that the ridge line between the honing surface 20 and the margin surface 7 remains. Therefore, the effect of suppressing chipping of the bottom cutting edge 3 by the honing surface 20 can be obtained even at the outermost part of the bottom cutting edge 3. As a result, it is possible to make it difficult for chipping to occur at the outermost part of the bottom cutting edge 3 where the honing surface 20 is provided.

[0038] Preferably, the shoulder width B is 15% to 75% of the honing width A. If the shoulder width B is too small and less than 15% of the honing width A, it will be almost the same as if there were no shoulder 22. In this case, it may become impossible to suppress the concentration of stress on the outermost part due to the shoulder 22, and the chip breaking performance W1 may decrease due to differences in the extrusion direction.

[0039] On the other hand, if the width B of the shoulder face part is too large and greater than 75% of the honing width A, it becomes substantially the same as the case where there is no remaining line part 24. In this case, in the outermost peripheral part of the bottom blade 3 (the small remaining line part 24), there is a possibility that the effect of suppressing the loss of the bottom blade 3 by the honing surface 20 cannot be obtained.

[0040] In contrast, when the width B of the shoulder face part is 15% to 75% of the honing width A, it is possible to effectively exert both the suppression of stress concentration on the outermost peripheral part of the bottom blade 3 by the shoulder face part 22, the improvement of the chip breaking performance of the chip W1, and the suppression of the loss of the bottom blade 3 by the honing surface 20 of the outermost peripheral part.

[0041] The angle γ (45 degrees in this embodiment) formed by the axis C and the shoulder face part 22 when the honing surface 20 is viewed from the front in the rotation direction R is smaller than half of the tip angle β. In particular, it is preferable that the difference between the angle γ and half of the tip angle β is 20 degrees to 40 degrees.

[0042] If the difference is less than 20 degrees, it becomes easier to newly form a relatively sharp edge by the honing surface 20, the shoulder face part 22, and the margin surface 7. Further, if the difference between the angle γ and half of the tip angle β is greater than 40 degrees, it becomes easier to newly form a relatively sharp edge by the honing surface 20, the shoulder face part 22, and the second relief face 12. By setting the difference between the angle γ and half of the tip angle β to 20 degrees to 40 degrees, it is possible to make it difficult to newly form the above two relatively sharp edges, so that stress concentration on the edge can be suppressed, and it is possible to make it more difficult for the outermost peripheral part of the bottom blade 3 to have a loss.

[0043] Next, referring to FIG. 4, the preferable range of the honing width A will be described. FIG. 4 is a cross-sectional view of the drill 1 taken along the line IV-IV in FIG. 2(a). FIG. 4 shows a state in which the drill 1 is cutting the workpiece W.

[0044] Assuming the number of the bottom blades 3 is x (where x ≧ 2) (x = 2 in this embodiment) and using the blade diameter D, the feed amount [mm / rev] in the direction of the axis C of the drill 1 during cutting is generally set to be D×(4 / x)% or more. When converted to per tooth, the feed amount ft [mm / tooth] per tooth is generally set to be D×(4 / x ２ )% or more.

[0045] Furthermore, it is common practice to make the honing width A smaller than the feed rate ft per cutting edge so that the rake face 11 of the bottom cutting edge 3 bites into the workpiece W during cutting. Therefore, the honing width A is D × (4 / x ２ It is common to make it smaller than )%.

[0046] As shown in Figure 4, in the drill 1 of this embodiment, unlike in such a general case, the honing width A is D × (4 / x ２ The feed rate is set to be greater than % (the minimum value of the typical feed rate ft per cutting edge). Therefore, in the drill 1 of this embodiment, the rake face 11 of the bottom cutting edge 3 does not easily bite into the workpiece W during cutting, and cutting within the honing surface 20 tends to occur, where the workpiece W is removed by the honing surface 20.

[0047] In this honing-internal cutting process, compared to cutting the workpiece W with a sharp cutting edge, various forces are applied to the chip W1, thus promoting the fragmentation of the chip W1. Furthermore, the chip W1 generated during honing-internal cutting moves along the honing surface 20 toward the rake face 11, and then moves along the rake face 11 in a different direction. This difference in direction of movement further promotes the fragmentation of the chip W1. As a result, damage to the outermost part of the bottom cutting edge 3 caused by chip jamming can be further suppressed.

[0048] However, in honing cuts that remove material from the workpiece W, cutting resistance tends to increase. Therefore, if there is a relatively sharp edge on the outermost part of the bottom cutting edge 3, stress concentration on that edge tends to increase. As a result, in honing cuts where there is a relatively sharp edge on the outermost part of the bottom cutting edge 3, there is a risk of chipping occurring on that outermost part.

[0049] However, in the drill 1 of this embodiment, the shoulder portion 22 and the remaining edge portion 24 are provided on the outermost part of the bottom cutting edge 3, so that the relatively sharp edge is chamfered, and thus the increase in such stress concentration can be suppressed. Therefore, even in cutting inside honing, where cutting resistance tends to increase, it is difficult to cause chipping of the outermost part of the bottom cutting edge 3 due to increased stress concentration.

[0050] Furthermore, the feed rate ft per tooth is generally set to less than D × 3%. In contrast, it is even more preferable that the honing width A be larger than D × 3%. In this case, even when the feed rate ft per tooth is set to the general maximum value (D × 3%) during cutting with the drill 1, cutting within the honing can be performed. As a result, it becomes less likely for chipping to occur on the outermost part of the bottom cutting edge 3 where the honing surface 20 is provided.

[0051] In the case of cutting within a honing, if the honing width A becomes too large, the chips W1 may accumulate within the honing surface 20 and become difficult to discharge to the rake face 11. In particular, the smaller the cutting edge diameter D, the smaller the feed rate ft per tooth becomes, making it difficult for the chips W1 to move in the direction of the axis C, and even with a smaller honing width A, it may become difficult to discharge the chips W1. In contrast, by setting the honing width A to D × 7% or less, it is possible to make it easier to discharge the chips W1 from the honing surface 20 to the rake face 11.

[0052] In honing-in cutting, the ridge line between the secondary relief face 12 and the honing surface 20 effectively cuts the workpiece W, and the honing surface 20 functions as part of the rake face. The rake angle θ of the rake face formed by the honing surface 20 is negative (negative shape), and its absolute value is preferably between 15 and 35 degrees.

[0053] If the absolute value of the rake angle θ is greater than 35 degrees, when the honing width A is fixed to a predetermined value, the honing surface 20 becomes longer in the rotational direction R, increasing the contact area between the chip W1 and the honing surface 20, which may result in excessive machining load. If the absolute value of the rake angle θ is less than 15 degrees, the honing surface 20 becomes almost identical to the rake surface 11, and the effect of suppressing chipping of the bottom cutting edge 3 by the honing surface 20 may not be fully obtained. In contrast, by setting the absolute value of the rake angle θ to 15 to 30 degrees, excessive machining load can be suppressed, and the effect of suppressing chipping of the bottom cutting edge 3 by the honing surface 20 can be obtained. As a result, it becomes more difficult for chipping to occur on the outermost part of the bottom cutting edge 3 where the honing surface 20 is provided.

[0054] The present invention will be described in more detail below with reference to examples. In the following examples, the drill 1 described in the above embodiment was used. However, the present invention is not limited to the following examples.

[0055] In the example of drill 1, as partially described above, the material of the tool body 2 was cemented carbide, the cutting edge diameter D was 3 mm, the helix angle α was 30 degrees, the width of the margin surface 7 was 0.36 mm, the tip angle β was 140 degrees, the angle γ between the axis C and the shoulder surface 22 was 45 degrees, and the absolute value of the rake angle θ was 25 degrees.

[0056] Using drills 1 of embodiments with varying honing width A and shoulder width B, a test was conducted to machine multiple holes (maximum 120 holes) in a workpiece W, and the durability (resistance to chipping) of drill 1 was evaluated. In this test, the workpiece W was made of SUS304, the cutting speed was 9.4 m / min, and the rotational speed was 1000 min. －１ The feed rate in the axis C direction of drill 1 was 0.06 mm / rev (feed rate ft: 0.03 mm / tooth), the feed rate was 60 mm / min, the step size was 0.6 mm, and the machining depth was 21 mm.

[0057] In addition, this test included evaluations of chip formation, cutting stress, and durability. In the chip formation evaluation, "◎" was given when the chips W1 were efficiently divided (average length of multiple chips W1 less than 5 mm), "○" was given when the chips W1 were divided to some extent (average 5 mm or more but less than 10 mm), and "×" was given when the chips W1 were hardly divided (average 10 mm or more).

[0058] In the evaluation of cutting stress, a "◎" was given if the thrust load during machining the first hole was 600 N or less, and the difference between the maximum and minimum values ​​of the multiple peak values ​​of the thrust load, which changes according to the cutting time, was 200 N or less. A "○" was given if the thrust load was 800 N or less. In all other cases, or if drill 1 broke during machining the first hole and evaluation became impossible, a "×" was given.

[0059] In the durability evaluation, the number of holes that could be machined before a chip occurred on the outermost part of the bottom cutting edge 3 was rated "◎" if it was the maximum of 120 holes, "〇" if it was 10 holes or more, and "×" if it was less than 10 holes. The presence or absence of this chip was checked every 2 holes up to 10 holes, and every 20 holes thereafter.

[0060] Table 1 below shows the test results when the honing width A and shoulder width B were varied. In addition to "◎", "〇", and "×", the number of holes that were drilled is also indicated for the durability evaluation item. Drill No. 4, drill 1, broke during the drilling of the first hole, so the durability item is indicated as 0 holes.

[0061]

[0062] According to Table 1, the test results for No. 1, which does not have the shoulder surface 22, showed good evaluation of chips and cutting stress, but it was found to have inferior durability. As mentioned above, it is presumed that without the shoulder surface 22, stress concentrates on the relatively sharp edge formed on the outermost part of the bottom cutting edge 3, making it more prone to chipping at that outermost part.

[0063] Furthermore, in No. 3, where the shoulder width B is the same as the honing width A, and in No. 4, where the shoulder width B is greater than the honing width A, the remaining wire portion 24 was not formed in either case. The test results for these Nos. 3 and 4 showed that their durability was inferior. As mentioned above, it is presumed that when the remaining wire portion 24 is not formed, the honing surface 20 disappears at the outermost part of the bottom blade 3, and the effect of suppressing damage to the bottom blade 3 by the honing surface 20 is not obtained.

[0064] In the test results for No. 5, which did not have the honed surface 20, all evaluations were "X," and it was found that the durability was particularly low. This is because the effect of suppressing chipping of the bottom cutting edge 3 by the honed surface 20 was not obtained.

[0065] In contrast to these, in Nos. 2, 6, and 7, which are provided with a honing surface 20, a shoulder surface portion 22, and a remaining line portion 24, all evaluations were "◎" or "○", confirming that it is possible to make it difficult for chipping to occur on the outermost part of the bottom blade 3 where the honing surface 20 is provided.

[0066] In particular, in No. 2, where both chip and cutting stress evaluations were rated "◎", no chipping occurred on the outermost part of the bottom cutting edge 3 throughout the machining of 120 holes. From this, it was confirmed that improving the chip breaking performance of W1 and reducing cutting stress can further reduce the likelihood of chipping occurring on the outermost part of the bottom cutting edge 3.

[0067] Furthermore, in No. 8, which was provided with a honing surface 20, a shoulder surface portion 22, and a remaining edge portion 24, all evaluations were "×". Therefore, it was found that even with these parts 20, 22, and 24 provided, there are cases where it is not possible to prevent chipping from occurring on the outermost part of the bottom blade 3, depending on other conditions.

[0068] Therefore, in order to obtain more favorable conditions, the test results when the honing width A and shoulder width B were further varied are shown in Tables 2 to 4. In the tests in Table 2, the honing width A and shoulder width B were further varied from the case in Table 1, but the evaluation item was limited to durability only, while all other conditions remained unchanged. In the tests in Table 3, the blade diameter D was changed to 2 mm compared to the tests in Table 2, but all other conditions remained unchanged. In the tests in Table 4, the blade diameter D was changed to 1.5 mm compared to the tests in Table 2, but all other conditions remained unchanged. Also, in Tables 2 to 4, items that were marked with "◎" or "○" in Table 1 are now both marked with "○".

[0069]

[0070]

[0071]

[0072] According to Tables 2 to 4, with the shoulder surface width B fixed, it was found that when A / D increases from 1% or less (the honing width A is D×1% or less) to more than 1%, the durability evaluation changes from "×" to "○". Therefore, at least in the drill 1 of this embodiment where the number x of the bottom blades 3 is 2, as described above, when the honing width A is greater than D×(4 / x ２ ), it was confirmed that it is possible to make it more difficult for a defect to occur in the outermost peripheral portion of the bottom blade 3 provided with the honing surface 20.

[0073] According to Tables 2 to 4, with the shoulder surface width B fixed, it was found that when A / D decreases from a value greater than 7% (the honing width A is greater than D×7%) to 7% or less, the durability evaluation changes from "×" to "○". Therefore, at least in the drill 1 of this embodiment, as described above, when the honing width A is D×7% or less, it was confirmed that it is possible to make it more difficult for a defect to occur in the outermost peripheral portion of the bottom blade 3 provided with the honing surface 20.

[0074] Here, in Table 1, when A / D is 6.7%, the chip evaluation is "○", when it is smaller than that, it is "◎", and when it is larger than that, it is "×". Therefore, when A / D is 7% or less, it is presumed that as a result of the improved chip separation performance of the chip W1, it was possible to make it difficult for a defect to occur in the outermost peripheral portion of the bottom blade 3.

[0075] Also, according to Tables 2 to 4, it was found that when B / A is 15% to 75% (the shoulder surface width B is the honing width A), except for the bottom part of Table 4, the durability evaluation is "○". Therefore, at least in the drill 1 of this embodiment, as described above, when the shoulder surface width B is 15% to 75% of the honing width A, it was confirmed that it is possible to make it more difficult for a defect to occur in the outermost peripheral portion of the bottom blade 3 provided with the honing surface 20.

[0076] Note that the bottom part of Table 4 has B / A of 15% to 75%, but since A / D is greater than 7%, it is presumed that the durability evaluation became "×". Therefore, from Tables 2 to 4, when the honing width A is D×(4 / x ２It was confirmed that when the ratio is greater than )% and less than or equal to D × 7%, and the shoulder width B is 15% to 75% of the honing width A, it becomes even more difficult to cause chipping on the outermost part of the bottom blade 3 on which the honing surface 20 is provided.

[0077] Although the present invention has been described above based on embodiments and examples, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention. The numerical values ​​of the helix angle α, the width of the margin surface 7, the tip angle β, the angle γ, the rake angle θ, etc. may be changed as appropriate. The diameter of the shank 2a may be made different from the cutting diameter D (the diameter D of the tip side of the tool body 2).

[0078] Furthermore, although the above embodiments described the cases where the cutting diameter D is 3 mm, 2 mm, and 1.5 mm, the cutting diameter D may be changed as appropriate. Note that the thrust load during cutting by the drill 1 increases approximately in proportion to the cutting diameter D (the feed amount in the direction of the axis C of the drill 1 corresponding to the cutting diameter D). Therefore, as the cutting diameter D increases, the possibility that excessive thrust load may easily cause chipping at the outermost part of the bottom cutting edge 3 cannot be ruled out.

[0079] On the other hand, when the cutting edge diameter D is 3 mm, it has been confirmed that, under the conditions of the above embodiment, it is difficult to cause chipping on the outermost part of the bottom cutting edge 3 with a thrust load. Therefore, it is clear that when the thrust load is smaller than this, and the cutting edge diameter D is 3 mm or less, substantially the same results as the above embodiment can be obtained without further confirmation. Accordingly, it is preferable to set the cutting edge diameter D to 3 mm or less in the drill 1 of the present invention. However, it is presumed that even if the cutting edge diameter D is larger than 3 mm, it is possible to make it difficult to cause chipping on the outermost part of the bottom cutting edge 3 by narrowing the conditions to reduce the thrust load.

[0080] In the above embodiments and examples, the case where the number x of bottom blades 3 is 2 has been described, but it is not necessarily limited to this, and the number x of bottom blades 3 may be 3 or 4 or more. However, when the blade diameter D is 3 mm or less, it is preferable that the number x of bottom blades 3 be 2 or 3 due to the difficulty of manufacturing.

[0081] Figure 5 is a bottom view of the drill 30 in a modified example in which the number of bottom cutting edges 32 is set to 3. Note that parts of the drill 30 that are the same as those in the above embodiment are denoted by the same reference numerals and their descriptions are omitted below. In Figure 5, a portion of the drill 30 visible towards the back of the page (except for the vicinity of the tip) is omitted from the illustration. The drill 30 mainly comprises a tool body 2, three bottom cutting edges 32 formed at the tip of the tool body 2, and three helical grooves 4 recessed in the outer circumferential surface of the tool body 2 corresponding to the three bottom cutting edges 32.

[0082] In addition, the drill 30 also has three of each of the following: the second bevel face 6, the margin face 7, the leading edge 8, the second relief face 12, the third relief face 13, the thinning 14, the thinning blade 14a, the honing surface 20, the shoulder surface 22, and the remaining edge 24, corresponding to the three bottom cutting edges 32 and the three helical grooves 4. Note that the thinning blade 14a of the drill 30 has a thinning-side honing surface 34 only on a portion of the radially outer side.

[0083] In this drill 30 as well, although a detailed explanation will be omitted, substantially the same test results were obtained under substantially the same test conditions as in the above embodiment. That is, it was confirmed that in the drill 30 as well, by providing the honing surface 20, the shoulder surface portion 22, and the remaining edge portion 24, it is possible to make it difficult for chipping to occur in the outermost part of the bottom cutting edge 32.

[0084] Furthermore, even in the drill 30 where the number of bottom cutting edges 32 is x = 3, the honing width A is D × (4 / x ２ It was confirmed that when the honing width A is greater than )%, it is less likely to cause chipping on the outermost part of the bottom cutting edge 32. In the drill 30 as well, it was confirmed that when the honing width A is 7% or less of D, it is less likely to cause chipping on the outermost part of the bottom cutting edge 32. In the drill 30 as well, it was confirmed that when the shoulder width B is 15% to 75% of the honing width A, it is less likely to cause chipping on the outermost part of the bottom cutting edge 32.

[0085] In the embodiments described above, the case in which the honing surface 20 and the shoulder surface 22 are planar has been explained, but the invention is not necessarily limited to this. At least one of the honing surface 20 and the shoulder surface 22 may be curved. When the honing surface 20 is curved, the remaining line portion 24 is formed in a curved shape.

[0086] In the embodiments described above, the case in which the honing surface 20 is formed over the entire length of the bottom cutting edge 3, 32 has been explained, but it is not necessarily limited to this. The honing surface 20 may be formed only on a part of the bottom cutting edge 3, 32, including the outermost portion. Furthermore, the honing width A is not limited to being substantially constant over the entire length of the bottom cutting edge 3, 32, but may gradually increase or decrease as it moves radially outward.

[0087] 1.30 Drill 2 Tool body 3.32 Bottom cutting edge 4 Twist groove 11 Rake face 12 Second relief face (part of relief face) 13 Third relief face (part of relief face) 20 Honing surface 22 Shoulder surface 24 Remaining wire A Honing width B Shoulder surface width C Axis D Cutting diameter R Rotation direction

Claims

1. A drill comprising: a cylindrical tool body that rotates with respect to its axis; a bottom cutting edge formed at the tip of the tool body so as to extend radially from the tool body; a twist groove formed in the outer circumferential surface of the tool body so as to twist toward the rear in the direction of rotation as it moves away from the tip in the axial direction, forming the rake face of the bottom cutting edge; a honing surface formed by chamfering the ridge portion between the rake face of the bottom cutting edge and the relief surface of the bottom cutting edge; a shoulder surface formed by chamfering the edges of the honing surface, the outer circumferential surface and the relief surface; and a residual portion formed by the ridge between the honing surface and the outer circumferential surface, by making the shoulder surface width, which is the dimension of the shoulder surface in a direction parallel to the honing width, smaller than the honing width, which is the dimension of the honing surface in a direction perpendicular to the cutting edge length direction of the bottom cutting edge when the honing surface is viewed from the front in the direction of rotation.

2. Let D be the cutting diameter of the bottom blade, and x be the number of bottom blades. When x is 2 or more, the honing width is D × (4 / x ２ The drill according to claim 1, characterized in that it is greater than )%.

3. The drill according to claim 2, characterized in that the honing width is D × 7% or less.

4. The drill according to any one of claims 1 to 3, characterized in that the shoulder width is 15% to 75% of the honing width.

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