Drill and machining method

Abstract

The present invention provides a drill that is less prone to chipping on the outermost part of the bottom cutting edge, which has a honed surface. The drill (1) comprises a cylindrical tool body (2), a bottom cutting edge (3) formed at the tip of the tool body, a helical groove (4) recessed in the outer surface of the tool body and forming the rake face (11) of the bottom cutting edge, a honed surface (20) formed by chamfering the ridge between the rake face and the relief faces (12, 13) of the bottom cutting edge, a shoulder surface (22) formed by chamfering the edges formed by the honed surface, the outer surface of the tool body and the relief face, and a remaining edge (24) formed by the ridge between the honed surface and the outer surface of the tool body.

Description

[Technical Field]

[0001] The present invention relates to a drill and a machining method that makes it difficult to cause chipping in the outermost part of the bottom cutting edge with a honed surface. [Background technology]

[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 flank 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. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-5882 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, even when the honing surface is provided up to the outermost edge 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 edge. This is because a relatively sharp edge is newly formed at the outermost edge 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 edge, leading to the problem that chipping is likely to occur at that outermost edge.

[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 and a machining method that can prevent chipping from occurring on the outermost part of the bottom cutting edge with a honed surface. [Means for solving the problem]

[0007] To achieve this objective, the drill of the present invention comprises a cylindrical tool body that rotates around its axis as the axis of rotation, two or three bottom blades formed at the tip of the tool body so as to extend radially from the tool body, a twist groove recessed 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 blade, a planar honing surface formed by chamfering the ridge portion between the rake face and the relief face of the bottom blade, and the honing surface, the outer circumferential surface and the The honing surface comprises a flat shoulder surface formed by chamfering the edge with a relief surface, and a straight residual portion formed by the ridge line between the honing surface and the outer peripheral 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 length direction of the bottom blade when the honing surface is viewed from the front in the direction of rotation, and wherein the cutting diameter of the bottom blade is 3 mm or less, and the shoulder surface width is 15% to 75% of the honing width. [Effects of the Invention]

[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 edge formed by the relief surface and the honing surface pushes out the chips intersects with the direction in which the effective cutting edge formed by the shoulder surface and the honing surface pushes out the 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. 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 become difficult to suppress stress concentration on the outermost part due to the shoulder, and the chip breaking performance may decrease due to differences in 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). 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 in the outermost part.

[0010] The drill according to claim 2 provides the following effects in addition to those of the drill according to claim 1: Let x be the number of bottom cutting edges. The axial feed rate of the drill during cutting is (4 / x)% or more of the cutting edge diameter of the bottom cutting edge, and when converted to per cutting edge, it is (4 / x)% of the cutting edge diameter of the bottom cutting edge. 2It is generally set to )% or more. Furthermore, it is common to make the honing width smaller than this 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 set to (4 / x) of the cutting edge diameter of the bottom cutting edge. 2 It is common to make it smaller than )%.

[0011] Unlike in such common cases, the honing width of this drill is (4 / x) the cutting diameter of the bottom cutting edge. 2 The value 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, the 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 diameter of the bottom cutting edge, 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 7% or less of the diameter of the bottom cutting edge, it is possible to easily discharge chips from the honing surface to the rake face. Brief Description of the Drawings

[0015] [Figure 1] It is a front view of a drill in one embodiment. [Figure 2] (a) is an enlarged front view of the drill showing the IIa portion of FIG. 1 in an enlarged manner, and (b) is an enlarged side view of the drill as viewed in the direction of arrow IIb in FIG. 2(a). [Figure 3] It is a bottom view of the drill as viewed in the direction of arrow III in FIG. 2(a). [Figure 4] It is a cross-sectional view of the drill taken along line IV-IV in FIG. 2(a). [Figure 5] It is a bottom view of a drill in a modified example. Modes for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments will be described with reference to the accompanying drawings. FIG. 1 is a front view of a drill 1 in one embodiment. The drill 1 is a drill that performs drilling on a workpiece W (see FIG. 4) by rotational force transmitted from a processing machine such as a machining center (not shown). The drill 1 is configured as a solid drill from a cemented carbide obtained by pressure sintering tungsten carbide (WC) or the like. The drill 1 may be made of high-speed tool steel.

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

[0018] The tool body 2 is formed in a cylindrical shape with a diameter D (D=3 mm in the present embodiment) centered on the axis C, and a shank 2a is provided on the rear end side (the upper side in Fig. 1) thereof. By holding this shank 2a in a holder (not shown), the drill 1 is attached to a processing machine via the holder. Then, the rotational force of the processing machine is transmitted to the tool body 2 via this holder, so that the drill 1 (tool body 2) rotates in the direction of arrow R about the axis C as the rotation axis. That is, the drill 1 rotates forward in the rotation direction R by the rotational force transmitted from the processing machine.

[0019] The bottom edge 3 is for cutting the workpiece W by the rotational force transmitted from the processing machine, and has a cutting edge diameter D that is the same as the diameter D of the tool body 2. The bottom edge 3 is formed to extend in the radial direction (the direction orthogonal to the axis C) from the axis C side. Further detailed configuration of the bottom edge 3 will be described later with reference to Figs. 2(a) to 3.

[0020] The twisted flute 4 is for accommodating and discharging chips W1 (see Fig. 4) generated by the bottom edge 3 during cutting. The twisted flute 4 is recessed in the outer peripheral surface of the tool body 2 so as to twist rearward in the rotation direction R as it moves away from the tip end portion (the bottom edge 3 side) of the tool body 2 in the direction of the axis C. Two twisted flutes 4 are provided symmetrically with respect to the axis C so as to respectively form the rake faces 11 of the two bottom edges 3.

[0021] The twist angle α of the twisted flute 4 is preferably set within a range of 20 degrees or more and 40 degrees or less. When the twist angle α is set to be smaller than 20 degrees, there is a risk that the discharge performance of the chips W1 will deteriorate. In contrast, by setting the twist angle α to 20 degrees or more, the discharge performance of the chips W1 can be ensured.

[0022] On the other hand, when the twist angle α is set to be larger than 40 degrees, the path of the twisted flute 4 becomes long, and there is a risk that the chips W1 are likely to be clogged. By setting the twist angle α to 40 degrees or less, clogging of the chips W1 in the twisted flute 4 can be suppressed.

[0023] The tool body 2 is provided with a bottom cutting edge 3 and a helical groove 4, as well as a secondary chamfering surface 6. The secondary chamfering surface 6 is designed 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 furring 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 furring 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) has been 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 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 axis C. Furthermore, the bottom cutting edges 3 are linear when viewed in the direction of 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 flat surface 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 the outermost part of the bottom cutting edge 3 has a relatively sharp edge, 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, which is 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, which is 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] Furthermore, the shoulder width B is preferably 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 shoulder width B is too large and exceeds 75% of the honing width A, the result will be almost the same as when there is no remaining wire portion 24. In this case, the effect of suppressing chipping of the bottom blade 3 by the honing surface 20 may not be obtained at the outermost part of the bottom blade 3 (the small remaining wire portion 24).

[0040] In response to these issues, having a shoulder width B of 15% to 75% of the honing width A effectively suppresses stress concentration on the outermost part of the bottom cutting edge 3 by the shoulder 22, improves the chip breaking performance of W1, and suppresses chipping of the bottom cutting edge 3 by the honed surface 20 on the outermost part.

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

[0042] If the difference is less than 20 degrees, a relatively sharp edge is more likely to be formed by the honing surface 20, the shoulder surface 22, and the margin surface 7. Also, if the difference between angle γ and half of the tip angle β is greater than 40 degrees, a relatively sharp edge is more likely to be formed by the honing surface 20, the shoulder surface 22, and the secondary relief surface 12. By setting the difference between angle γ and half of the tip angle β to 20 to 40 degrees, it is possible to make it more difficult for the two aforementioned relatively sharp edges to be formed, thereby suppressing stress concentration on those edges and making it less likely for chipping to occur on the outermost part of the bottom blade 3.

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

[0044] If the number of bottom cutting edges 3 is x (where x≧2) (in this embodiment, x=2), and the cutting edge diameter D is used, the feed rate [mm / rev] of the drill 1 in the direction of the axis C during cutting is generally D × (4 / x)% or more. Converting this to per tooth, the feed rate ft [mm / tooth] per tooth is D × (4 / x 2 It is generally considered to be )% or higher.

[0045] Furthermore, it is common practice to make the honing width A smaller than the feed rate ft per tooth 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 general cases, the honing width A is D × (4 / x 2 This is set to be greater than the typical minimum feed rate per tooth (ft). 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 with a different orientation. 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-internal cutting, the ridge 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 this 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, which increases the contact area between the chip W1 and the honing surface 20 and 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. [Examples]

[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 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 drill 1 in embodiments where the honing width A and shoulder width B were varied, 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. -1 The feed rate in the axis C direction of drill 1 was set to 0.06 mm / rev (feed rate ft: 0.03 mm / tooth), the feed rate to 60 mm / min, the step size to 0.6 mm, and the machining depth to 21 mm.

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

[0058] In the evaluation of cutting stress, a "◎" rating 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 "○" rating 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 "×" rating was given.

[0059] In the durability evaluation, a score of "◎" was given if the maximum number of holes that could be machined before a chip occurred on the outermost part of the bottom cutting edge 3 was 120, "〇" if 10 or more holes were machined, and "×" if less than 10 holes were machined. 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. Drill No. 4, drill 1, broke during the first hole drilling process, so the durability item is marked as 0 holes.

[0061] [Table 1]

[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 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 No. 2, 6, and 7, which are provided with a honing surface 20, a shoulder surface portion 22, and a remaining edge 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] [Table 2]

[0070] [Table 3]

[0071] [Table 4]

[0072] According to Tables 2-4, it was found that when the shoulder width B is fixed and A / D increases from 1% or less (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 of bottom cutting edges 3 x = 2, as described above, when the honing width A is D × (4 / x 2 It was confirmed that when the value is greater than )%, it becomes more difficult to cause chipping on the outermost part of the bottom blade 3 where the honing surface 20 is provided.

[0073] According to Tables 2 to 4, it was found that with the flank face width B fixed, the durability evaluation changes from "×" to "○" when A / D is reduced from a value greater than 7% (the honing width A is greater than D×7%) to 7% or less. Therefore, it was confirmed that at least in the drill 1 of the present embodiment, when the honing width A is D×7% or less as described above, chipping can be made less likely to occur at the outermost peripheral portion of the bottom cutting edge 3 provided with the honing surface 20.

[0074] Here, in Table 1, when A / D is 6.7%, the chip evaluation is "○", when the value is smaller than that, the evaluation is "◎", and when the value is larger than that, the evaluation is "×". Therefore, it is inferred that when A / D is 7% or less, the chip breaking performance of the chip W1 is improved, and as a result, chipping is less likely to occur at the outermost peripheral portion of the bottom cutting edge 3.

[0075] Further, according to Tables 2 to 4, it was found that when B / A (the flank face width B is 15% to 75% of the honing width A) is 15% to 75%, the durability evaluation is "○" except for the lowermost part of Table 4. Therefore, it was confirmed that at least in the drill 1 of the present embodiment, when the flank face width B is 15% to 75% of the honing width A as described above, chipping can be made less likely to occur at the outermost peripheral portion of the bottom cutting edge 3 provided with the honing surface 20.

[0076] Note that the sample at the lowermost part of Table 4 has B / A of 15% to 75%, but A / D is larger than 7%, so it is inferred that the durability evaluation is "×". Therefore, from Tables 2 to 4, the honing width A is D×(4 / x 2 )% and greater, and D×7% or less, and the flank face width B is 15% to 75% of the honing width A, it was confirmed that chipping can be further made less likely to occur at the outermost peripheral portion of the bottom cutting edge 3 provided with the honing surface 20.

[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 forms, 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 axis C direction 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, even if the cutting edge diameter D is larger than 3 mm, it is presumed that 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 this is not necessarily the case. The honing surface 20 may be formed only on a portion 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, for example. [Explanation of symbols]

[0087] 1.30 Drills 2 Tool body 3,32 Bottom blade 4. Twisted groove 11 Scoop surface 12. Second escape route (part of the escape route) 13. Third escape face (part of the escape face) 20 Honed surface 22 Shoulder area 24 Remaining line part A Honing width B Shoulder width C axis D Cutting diameter R rotation direction

Claims

1. A cylindrical tool body that rotates around its axis, Two or three bottom blades are formed at the tip of the tool body so as to extend radially along the tool body, A helical groove is formed on the outer circumferential surface of the tool body such that it twists toward the rear in the rotational direction as it moves away from the tip in the axial direction, and which forms the rake face of the bottom cutting edge, A flat honing surface formed by chamfering the ridge portion between the rake face and the relief face of the bottom blade, A flat shoulder surface portion formed by chamfering the edges of the honing surface, the outer peripheral surface, and the relief surface, The honing surface is provided with a straight residual portion formed by the ridge line between the honing surface and the outer peripheral surface, by making the shoulder width, which is the dimension of the shoulder portion 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 blade when the honing surface is viewed from the front in the rotation direction, The cutting diameter of the bottom blade is 3 mm or less. The drill is characterized in that the shoulder width is 15% to 75% of the honing width.

2. Let x be the number of bottom cutting edges, and let x be the honing width be the cutting edge diameter of the bottom cutting edge. 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 7% or less of the cutting diameter of the bottom cutting edge.

4. (delete)

5. The drill according to any one of claims 1 to 3, characterized in that the drill is used such that the honing width is greater than the feed rate per cutting edge of the bottom cutting edge.

6. A machining method for drilling holes in a workpiece using a drill according to any one of claims 1 to 3, A machining method characterized in that the honing width is greater than the feed rate per cutting edge of the bottom cutting edge.

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