Rotary cutting tool

Abstract

To provide a rotary cutting tool that can appropriately curl a chip and smoothly discharge the chip, while reducing friction resistance of the chip in a chip discharge groove.SOLUTION: A rotary cutting tool comprises a shaft-shape tool main body that is rotated around a center shaft, which also comprises a chip discharge groove formed at an outer periphery of the tool main body and a cutting blade formed at a crossing ridge line part between the chip discharge groove and a surface of the tool main body. A wall surface of the chip discharge groove has a first region in a concave curve-shape including a deepest position in a radial direction of the chip discharge groove, and a second region in a convex curve-shape positioned at an end part on an outer periphery of a wall surface pointing to a front side in a tool rotating direction of the chip discharge groove, on a cross section orthogonal to the center shaft. Surface roughness of the first region is smaller than surface roughness of the second region.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to rotary cutting tools. [Background technology]

[0002] Conventionally, there has been known a drill in which the surface of a hard coating provided in a chip discharge groove is smoothed to improve chip discharge performance (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6828824 Summary of the Invention [Problem to be solved by the invention]

[0004] Smoothing the inner surface of the chip discharge groove can prevent chip clogging, but a smooth surface makes it difficult for the chips to curl, which is an issue.

[0005] An object of the present invention is to provide a rotary cutting tool that can reduce the frictional resistance of the chips in the chip discharge grooves, while favorably curling the chips and discharging the chips smoothly. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a rotary cutting tool including a shaft-shaped tool body rotated about a central axis, a chip discharge groove formed on the outer periphery of the tool body, and a cutting edge formed at an intersection ridge between the chip discharge groove and a surface of the tool body. In a cross section perpendicular to the central axis, a wall surface of the chip discharge groove has a first region having a concave curve shape including a deepest position in the radial direction of the chip discharge groove, and a second region having a convex curve shape located at an outer periphery end of the wall surface facing the front side in the tool rotation direction of the chip discharge groove. The surface roughness of the first region is smaller than that of the second region.

[0007] According to the above aspect, the surface roughness of the first region, which is a recess in the chip groove, is smaller than the surface roughness of the second region, which is a protrusion in the chip groove, so that the chips can be moved smoothly in the first region, and the protrusion in the second region, which has a larger surface roughness, can promote curling of the chips. This allows the chips to be smoothly moved in the chip groove while being well curled, promoting chip breakage. According to the above aspect of the present invention, a drill with excellent chip discharge performance is provided.

[0008] The wall surface of the chip discharge groove, in a cross section perpendicular to the central axis, may have a convex curved third region located at an outer peripheral end of the wall surface facing rearward in the tool rotation direction of the chip discharge groove, and the surface roughness of the first region may be smaller than the surface roughness of the third region.

[0009] A hard coating may be formed on a surface region of the tool body including the cutting edge.

[0010] The hard coating may be formed only on a portion of a wall surface of the chip discharge groove, and the area where the hard coating is not formed may include the deepest position of the wall surface.

[0011] The region where the hard film is not formed may be the first region of the wall surface of the chip discharge groove. Effect of the Invention

[0012] According to one aspect of the present invention, there is provided a rotary cutting tool that can reduce the frictional resistance of the chips in the chip discharge groove, while favorably curling the chips and discharging the chips smoothly. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a side view of a drill according to an embodiment. [Diagram 2] FIG. 2 is an enlarged partial side view showing a tip portion of the drill according to the embodiment. [Diagram 3] FIG. 3 is a front view of the drill according to the embodiment. [Figure 4] FIG. 4 is a cross-sectional view of the drill taken along line IV-IV in FIG. [Figure 5A] FIG. 5A is an explanatory diagram showing a process of chip generation in the drill of the embodiment. [Figure 5B] FIG. 5B is an explanatory diagram showing a process of chip generation in the drill of the embodiment. [Figure 5C] FIG. 5C is an explanatory diagram showing a process of chip generation in the drill of the embodiment. [Figure 5D] FIG. 5D is an explanatory diagram showing a process of chip generation in the drill of the embodiment. [Figure 6] FIG. 6 is a cross-sectional view perpendicular to the axis of a modified example of the drill. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Fig. 1 is a side view of the drill of this embodiment, Fig. 2 is a partial side view showing an enlarged tip portion of the drill of this embodiment, Fig. 3 is a front view of the drill of this embodiment, and Fig. 4 is a cross-sectional view of the drill taken along line IV-IV in Fig. 2.

[0015] The drill (rotary cutting tool) 1 of this embodiment is a drill for deep hole drilling. The drill 1 is generally cylindrical and centered on a central axis (axis line) O. The drill 1 has an axis-shaped body (tool main body) 10 and a shank 11, each of which extends along the central axis O. The drill 1 drills a hole in the workpiece by rotating about the central axis O with the tip face of the body 10 facing the workpiece. The drill 1 of this embodiment is a solid drill having a substrate made of cemented carbide etc. The drill 1 has a hard coating made of metal nitride etc. that coats the surface of the substrate.

[0016] The direction along the central axis O of the drill 1 (the direction in which the central axis O extends) is called the axial direction. In the axial direction, the direction from the shank 11 to the body 10 is called the front end side, and the direction from the body 10 to the shank 11 is called the rear end side. The direction perpendicular to the central axis O is called the radial direction. Of the radial directions, the direction approaching the central axis O is called the radially inner direction, and the direction away from the central axis O is called the radially outer direction. The direction rotating around the central axis O is called the circumferential direction. In addition, within the circumferential direction, the direction in which the body 10 rotates during drilling is called the front side of the rotation direction, and the opposite side is called the rear side of the rotation direction.

[0017] The body 10 has a pair of cutting edges 15, 15 located at the tip of the body 10, and a pair of chip discharge grooves 14, 14 extending spirally around the outer periphery of the body 10 from the cutting edges 15, 15 toward the rear end side.

[0018] In the drill 1, two coolant holes 9 are formed symmetrically from the rear end surface of the shank 11 toward the tip side, twisted with the same lead as the chip discharge groove 14 with respect to the central axis O. These coolant holes 9 pass between the chip discharge grooves 14 in the body 10 and open to the tip flank 13. When drilling using the drill 1, coolant such as cutting oil or compressed air is ejected from the two coolant holes 9. In addition, the tip flank 13 is formed by a two-stage flank. Of the two-stage tip flank 13, the flank located on the opposite side to the tool rotation direction T has a larger flank angle. The coolant hole 9 opens to the flank located on the opposite side to the tool rotation direction T of the two-stage flank.

[0019] The chip discharge groove 14 is twisted at a constant twist angle toward the rear side in the tool rotation direction T from the cutting edge 15 toward the rear end side in the direction of the central axis O on the outer periphery of the body 10. The pair of chip discharge grooves 14, 14 are arranged symmetrically with respect to the central axis O. The drill 1 of this embodiment is for deep hole drilling, and the length of the chip discharge groove 14 along the direction of the central axis O is, for example, in the range of 8.0D to 30.0D with respect to the outer diameter D of the cutting edge 15 of the drill 1. The outer diameter of the cutting edge 15 is the outer diameter of a circle formed by the rotation locus around the central axis O at the outer periphery end of the cutting edge 15, that is, the drill diameter. The outer diameter D of the cutting edge 15 is the outer diameter of a circle formed by the rotation locus around the central axis O at the outer periphery end of the cutting edge 15, that is, the drill diameter.

[0020] The cutting edges 15, 15 are formed at the tip of the body 10 at the intersection ridge between the inner wall surfaces of the pair of chip discharge grooves 14, 14 facing forward in the tool rotation direction T and the tip flank 13. The pair of cutting edges 15, 15 are disposed symmetrically with respect to the central axis O. The cutting edge 15 extends toward the rear end as it approaches the outer periphery (radially outward) of the body 10, and is given a tip angle.

[0021] The body 10 has lands 16, 16 between the two chip discharge grooves 14, 14. A first margin 16A is provided at the end of the land 16 on the front side in the tool rotation direction T. A second margin 16B is provided at the end of the land 16 on the rear side in the tool rotation direction T. The first margin 16A and the second margin 16B extend spirally along the edge of the chip discharge groove 14. The body 10 has a chamfered surface 16C recessed radially inward between the first margin 16A and the second margin 16B.

[0022] As shown in FIG. 4, the wall surface of the chip discharge groove 14 has a first region 141 having a concave curved shape and a second region 142 having a convex curved shape connected to one end of the first region 141 in a cross section perpendicular to the central axis O. In this embodiment, the first region 141 and the second region 142 may be formed in a range excluding the leading end and rear end of the chip discharge groove 14. The leading end of the chip discharge groove 14 overlaps with the thinning, and the rear end of the chip discharge groove 14 has a groove depth that becomes shallower toward the rear end. The first region 141 and the second region 142 may not be formed in these leading end and rear end.

[0023] The wall surface of the chip discharge groove 14 has a curved shape concave toward the central axis O in a cross section perpendicular to the central axis O, and the second region 142 is a portion of the wall surface of the chip discharge groove 14 that partially protrudes into the internal space of the chip discharge groove 14. A boundary point 144 between the first region 141 and the second region 142 is a position where the curve of the wall surface of the chip discharge groove 14 changes from a concave curve to a convex curve.

[0024] An end of the first region 141 opposite the boundary point 144 is connected to an adjacent land 16 on the rear side of the chip discharge groove 14 in the tool rotation direction T. An end of the second region 142 opposite the boundary point 144 is connected to an adjacent land 16 on the front side of the chip discharge groove 14 in the tool rotation direction T. In FIG. 4, the first margin 16A, the second margin 16B, and the relief surface 16C are omitted.

[0025] The first region 141 is a region including the radially deepest position 14a of the chip discharge groove 14. In the present embodiment, the bottom of the chip discharge groove 14 has a concave curved shape, and the deepest position 14a is the position where the wall surface of the chip discharge groove 14 is closest to the central axis O. The second region 142 is located radially outward of the deepest position 14a of the chip discharge groove 14. In the case of this embodiment, the second region 142 is located at the outer circumferential end of the wall surface of the chip discharge groove 14 facing forward in the tool rotation direction T. The second region 142 is provided in the chip discharge groove 14 and is a convex portion that protrudes toward the forward side in the tool rotation direction T.

[0026] The first region 141 and the second region 142 have different surface roughnesses. The surface roughness of the first region 141 is smaller than the surface roughness of the second region 142. The difference in surface roughness between the first region 141 and the second region 142 can be achieved, for example, by partially performing a smoothing process by polishing on the wall surface of the chip discharge groove 14. That is, by performing a smoothing process only on the recess corresponding to the first region 141, the surface roughness of the first region 141 can be made smaller than the surface roughness of the second region 142. In this case, the area to which the smoothing process is performed is narrowed, which is advantageous in that the productivity of the drill 1 is improved.

[0027] In the drill 1 of this embodiment, a hard coating is formed on the surface region including the cutting edge 15, but the hard coating may be formed only on a portion of the wall surface of the chip discharge groove 14 to create a difference in surface roughness between the first region 141 and the second region 142. When a hard coating is formed on the surface of a cutting tool, the surface roughness of the tool surface on which the hard coating is formed is greater than the surface roughness of the tool surface on which the hard coating is not formed. Therefore, a hard coating may be formed on the second region 142, but not on the first region 141. With this configuration, the surface roughness of the first region 141 and the second region 142 can be differentiated depending on the presence or absence of a hard coating.

[0028] When a hard coating is formed partially, it is difficult to form the coating by accurately dividing the recesses and protrusions of the chip discharge groove 14. In this embodiment, the non-forming region where no hard coating is formed preferably includes at least the deepest position 14a in the cross section perpendicular to the axis of the chip discharge groove 14. The periphery of the deepest position 14a is the position in the first region 141 that comes into contact with the chips the most. By improving the smoothness of the periphery of the deepest position 14a, the chip discharge performance is improved.

[0029] The arithmetic mean roughness Sa of the surface in the first region 141 is preferably 0.8 times or less, or 0.5 times or less, of the arithmetic mean roughness Sa of the second region 142. The arithmetic mean roughness Ra of the lines in the first region 141 is preferably 0.8 times or less, or 0.5 times or less, of the arithmetic mean roughness Ra of the second region 142.

[0030] It is preferable that the arithmetic mean roughness Sa or Ra is 1.6 μm or less, or 0.4 μm or less, in the second region 142. If the surface roughness of the second region 142 is too large, the movement of chips is hindered, and the chips are likely to clog.

[0031] It is preferable that the first region 141 has a smaller value of the interface development area ratio Sdr defined in ISO25178 than the second region 142. The smaller the interface development area ratio Sdr value, the closer the measurement target region is to a flat surface. The interface development area ratio Sdr in the first region 141 is preferably 0.2 or less, and more preferably close to 0.

[0032] The surface roughness of the first region 141 is a value measured at the deepest position 14a of the chip discharge groove 14. The surface roughness of the second region 142 is a value measured on a curved surface extending from the apex position of the convex curved second region 142 toward the first region 141 in a cross section perpendicular to the axis. The arithmetic mean roughness Sa, Ra, and the developed area ratio Sdr of the interface are determined, for example, by using a laser microscope (VK-X3000) equipped with a white light interferometer manufactured by Keyence Corporation, observing with a cutoff value of 0.25 mm and a magnification of 100 times, measuring three areas of 50 μm × 50 μm, and averaging the obtained measurements.

[0033] 5A to 5D are explanatory diagrams showing the process of generating chips Wc in the drill 1 of this embodiment. Fig. 5A to Fig. 5D show cross sections perpendicular to the central axis O of the drill 1 when the drill 1 is used to drill a hole in a workpiece W. Fig. 5A to Fig. 5D show the process of generating chips Wc when the drill 1 is fixed and the workpiece W is rotated.

[0034] 5A, as the workpiece W and the drill 1 rotate relative to each other, chips Wc are generated at the cutting edge 15 and extend along the wall surface of the chip discharge groove 14 rearward in the tool rotation direction T and toward the rear end of the drill 1. The wall surface of the chip discharge groove 14 behind the cutting edge 15 is the first region 141 with a small surface roughness, so the generated chips Wc extend rearward without clogging. Then, the tip of the chip Wc extending rearward in the tool rotation direction T reaches the second region 142.

[0035] As shown in Fig. 5B, the chip Wc that comes into contact with the second region 142 is bent along the convex curved surface of the second region 142. At this time, since the surface roughness of the second region 142 is larger than the surface roughness of the first region 141, a resistance force acts on the chip Wc when the second region 142 and the chip Wc come into contact with each other. As a result, a larger bending force acts on the chip Wc. The chip Wc then comes into contact with the wall surface of the hole in the workpiece W.

[0036] As shown in FIG. 5C, when the chip Wc comes into contact with the wall surface of the hole in the workpiece W, a bending force is applied to the chip Wc at the contact position, accelerating curling of the chip Wc. As shown in FIG. 5D, the curled chip Wc comes into contact with other portions of the chip Wc within the chip discharge groove 14, which promotes the breaking of the chip Wc.

[0037] As described above, according to the drill 1 of this embodiment, the surface roughness of the first region 141, which is a recess in the chip groove 14, is smaller than the surface roughness of the second region 142, which is a protrusion in the chip groove 14, so that the chips Wc can be moved smoothly in the first region 141, and the protrusion of the second region 142, which has a larger surface roughness, can promote curling of the chips Wc. As a result, the chips Wc can be smoothly moved and curled well in the chip groove 14, promoting breaking of the chips Wc. According to this embodiment, a drill 1 with excellent chip discharge properties is provided.

[0038] (Modification) In this embodiment, a case has been described in which the second region 142 has a convex curved shape in a cross section perpendicular to the axis only at the outer peripheral end of the wall surface of the chip discharge groove 14 facing the forward side in the tool rotation direction T, but this configuration is not limited to this. Fig. 6 is a diagram showing a cross section perpendicular to the axis of a modified drill. In Fig. 6, the same components as those in Figs. 1 to 4 are denoted by the same reference numerals as those in Figs.

[0039] 6, the drill 1 of the modified example has a third region 143 on the wall surface of the chip discharge groove 14. The third region 143 is a convex curved portion located at the outer circumferential end of the wall surface of the chip discharge groove 14 facing the rear side in the tool rotation direction T in a cross section perpendicular to the central axis O. The third region 143 is a convex portion provided in the chip discharge groove 14 and protruding toward the rear side in the tool rotation direction T.

[0040] In the drill 1 of the modified example, the surface roughness of the first region 141 is smaller than the surface roughness of the third region 143. That is, the arithmetic mean roughness Sa or Ra of the first region 141 is smaller than the arithmetic mean roughness Sa or Ra of the third region 143. In addition, the developed area ratio Sdr of the interface in the first region 141 is smaller than the developed area ratio Sdr of the interface in the third region 143.

[0041] According to the drill 1 of the modified example, the third region 143 having a convex curved shape in a cross section perpendicular to the axis is provided on the outer periphery of the wall surface of the chip discharge groove 14 facing rearward in the tool rotation direction T, so that the chips Wc generated by the cutting edge 15 can be guided toward the inside of the chip discharge groove 14. Furthermore, the surface roughness of the third region 143 is greater than the surface roughness of the first region 141, so that the chips Wc that come into contact with the third region 143 can be more easily directed toward the inside of the chip discharge groove 14. The effect of promoting curling of the chips Wc by the second region 142 can be further enhanced.

[0042] In the present embodiment, a drill is used as an example of the rotary cutting tool, but an end mill may be used. If the rotary cutting tool has a chip discharge groove extending along the outer circumferential surface of the tool, the configuration of the chip discharge groove of the embodiment can be applied to the rotary cutting tool to obtain an effect of improving chip discharge performance. [Explanation of symbols]

[0043] 1...Drill (rotary cutting tool) 10. Body 11...Shank 13...Tip relief surface 14...Chip discharge groove 14a…Deepest position 15…Cutting edge 16…Rand 16A…First margin 16B…Second margin 16C...Second cut surface 50…Magnification 141...First area 141...area 142…Second area 143...Third area 144...Border point D…Outer diameter O…Central axis (axis line) T…Tool rotation direction W…Workpiece Wc…Chip

Claims

1. A rotary cutting tool comprising a shaft-shaped tool body that is rotated around a central axis, a chip discharge groove formed on an outer periphery of the tool body, and a cutting edge formed at an intersection ridge between the chip discharge groove and a surface of the tool body, a wall surface of the chip discharge groove, in a cross section perpendicular to the central axis, has a first region having a concave curved shape including a deepest position of the chip discharge groove in a radial direction, and a second region having a convex curved shape located at an outer circumferential end portion of the wall surface facing a front side of the chip discharge groove in a tool rotation direction, The surface roughness of the first region is smaller than the surface roughness of the second region. Rotary cutting tools.

2. a wall surface of the chip discharge groove has a third region having a convex curved shape located at an outer circumferential end portion of the wall surface facing the rear side of the chip discharge groove in the tool rotation direction in a cross section perpendicular to the central axis, The surface roughness of the first region is smaller than the surface roughness of the third region. The rotary cutting tool of claim 1 .

3. A hard coating is formed on a surface region of the tool body including the cutting edge.

3. A rotary cutting tool according to claim 1 or 2.

4. The hard coating is formed only on a part of a wall surface of the chip discharge groove, The region where the hard coating is not formed includes the deepest position of the wall surface. The rotary cutting tool of claim 3.

5. The hard coating non-formed region is the first region of the wall surface of the chip discharge groove.

5. The rotary cutting tool of claim 4.

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