End mill and method for manufacturing end mill

Abstract

This end mill (1) has a rod-like base material (2) made of a cemented carbide. Two to four flutes (3) have torsion angles (3a) of 0° to 45° with respect to the axial direction of the base material (2), and extend from the surface of the base material (2). A positive blade groove (4) extends linearly between the flutes (3). A positive blade (11), which is a PCD tip (10), is installed in the positive blade groove (4) and protrudes from the positive blade groove (4). The lead angle (11a) of the cutting edge of the positive blade (11) is 15° to 55°. A reverse blade groove (5) is positioned farther from the tip of the base material (2) than the positive blade groove (4), and extends linearly between the flutes (3). A reverse blade (12), which is a PCD tip (10), is installed in the reverse blade groove (5) and protrudes from the reverse blade groove (5). The lead angle of the cutting edge of the reverse blade (12) is -55 to -15°.

Description

End mill and method for manufacturing the end mill

[0001] The present disclosure relates to an end mill and a manufacturing method thereof. End mills are used, for example, when processing wood such as wood boards, solid wood, laminated wood, and plywood, when processing non-ferrous metal workpieces such as aluminum and copper, and when processing resins, ceramic materials, and other workpieces.

[0002] Japanese Patent Publication No. 2021-053794, Japanese Patent Publication No. 2013-528504, Japanese Patent Publication No. 2019-508270, Japanese Patent Publication No. 2015-510845, Japanese Patent No. 5674815, Japanese Patent No. 5986254, and Japanese Patent No. 7244970 disclose tools known as end mills or milling cutters used when performing routing or other processing on workpieces. For example, when processing grooves, edge faces, cuts, etc. on workpieces such as wood boards with sheets attached to their surfaces, end mills equipped with PCD (polycrystalline diamond sintered compact) tips are generally used. The PCD tips that form the cutting edges are brazed to the base material of the end mill. Multiple PCD tips are arranged in the axial direction of the base material. The PCD tips are brazed near the tip of the base material as positive cutting edges with a positive lead angle. A PCD tip is brazed to the substrate as a reverse cutting edge with a negative lead angle, located farther from the tip of the substrate than the forward cutting edge. When cutting a wood board with an end mill, the forward and reverse cutting edges sandwich both surfaces of the wood board in the axial direction of the substrate. This prevents the sheet attached to the surface of the wood board from peeling off during cutting, and reduces surface chipping, corner chipping, burrs, and uncut edges.

[0003] The base material of an end mill is typically steel, such as alloy steel. Grooves are machined into the surface of the base material for brazing PCD tips. The grooves are formed by cutting the surface of the base material with an end mill that is smaller in diameter than the PCD end mill.

[0004] Conventionally, end mills have been offered that use heavy metal (sintered tungsten alloy powder) as the substrate material, which is more rigid than steel. By using a highly rigid material as the substrate, it is possible to withstand cutting vibrations, for example, during high-feed machining at increased feed rates or when a long, slender end mill with a large ratio of cutting length to cutting diameter is required. However, heavy metal substrates are expensive, and it takes a long time to form grooves on the surface. This increases the manufacturing cost of the end mill, and therefore the cost of the products machined with heavy metal end mills.

[0005] It is conceivable to provide an end mill using a cemented carbide substrate, which is less expensive and more rigid than heavy metal. A cemented carbide substrate must be ground with a relatively large-diameter, disk-shaped diamond grinding wheel. Therefore, when grooves are formed in the substrate using a diamond grinding wheel, the grinding wheel may interfere with, for example, the brazing surface surrounding the groove. If a small-diameter diamond grinding wheel is used to prevent interference, the processing time increases significantly. For this reason, end mills using a cemented carbide substrate and having PCD tips in each of multiple adjacent grooves have not previously been manufactured. Only limited groove shapes, such as simple straight grooves, have been formed in the cemented carbide substrate to which the PCD tips are bonded.

[0006] For example, the end mills described in JP 2021-053794 A, JP 2013-528504 A, JP 2019-508270 A, and JP 2015-510845 A have a cutting edge shape formed on the substrate. Therefore, they are not designed to bond multiple PCD chips or the like with cutting edges. The substrate is, for example, a cemented carbide alloy, and a diamond coating or the like is applied to the surface. Tips with cutting edges, such as PCD chips, are bonded to the end mills or milling cutters described in Japanese Patent Nos. 5674815 A, 5986254 A, and 7244970 A. In order to machine grooves to which chips are bonded, the material of the substrate must be limited to, for example, tool steel. Furthermore, in order to machine multiple grooves to which chips are bonded without interfering with each other, the spacing between the grooves must be widened. This reduces the number of chips that can be bonded. Therefore, there has not been provided an end mill having a highly rigid base material, an elongated shape, and a large number of PCD chips joined thereto.

[0007] Therefore, there is a need in the art for an end mill that has a high substrate rigidity, a large number of PCD tips, and is inexpensive to manufacture.

[0008] According to one aspect of the present disclosure, an end mill has a rod-shaped substrate made of cemented carbide. Two to four flutes extend on the surface of the substrate with a helix angle of 0° to 45° relative to the axial direction of the substrate. Lead grooves extend linearly between the flutes. Lead grooves, which are PCD tips, are installed in the lead grooves and protrude from the lead grooves. The cutting edges of the lead grooves are 15° to 55°. The reverse grooves are located farther from the tip of the substrate than the lead grooves and extend linearly between the flutes. The reverse grooves, which are PCD tips, are installed in the reverse grooves and protrude from the reverse grooves. The cutting edges of the reverse grooves are -55° to -15°.

[0009] Therefore, flutes, or grooves for leading edges and grooves for backing edges, or grooves for leading edges and grooves for backing edges, can be spaced apart from one another. Therefore, when the flutes, grooves for leading edges, and grooves for backing edges are machined with a grinding wheel, interference with other structures on the surface of the substrate, such as flutes, grooves for leading edges, and grooves for backing edges, can be prevented. This allows substrates made of highly rigid cemented carbide to be machined with a grinding wheel with a relatively large diameter. This reduces the manufacturing cost of the end mill.

[0010] According to another feature of the present disclosure, the maximum cutting diameter of the end mill's cutting edge, which is made up of a forward cutting edge and a reverse cutting edge, is 6 mm to 30 mm. Therefore, by using a highly rigid cemented carbide alloy as the base material, the durability of the base material against cutting vibrations when processing a workpiece can be increased. Therefore, the end mill can be used, for example, when performing high-feed processing by increasing the feed rate. Furthermore, the end mill can be provided with an elongated shape with a blade length longer than the maximum cutting diameter. This allows the end mill to be used to process, for example, router grooves in the workpiece that are deeper than the groove width. Furthermore, even with a small maximum cutting diameter, it is possible to perform hollowing out of thick plate materials.

[0011] Another feature of the present disclosure relates to a method for manufacturing an end mill. A rod-shaped substrate made of cemented carbide is prepared. A first disc-shaped grinding wheel is rotated on its axis and moved relative to the substrate to form two to four axially extending flutes on the surface of the substrate. A second disc-shaped grinding wheel is rotated on its axis and moved relative to the substrate to form straight cutting edge grooves that extend linearly between the flutes and have a positive lead angle. The second disc-shaped grinding wheel is rotated on its axis to form reverse cutting edge grooves that extend linearly between the flutes and have a negative lead angle at a location farther from the tip of the substrate than the straight cutting edge grooves. A plate-shaped PCD chip that serves as a straight cutting edge is brazed to the straight cutting edge groove, and a plate-shaped PCD chip that serves as a reverse cutting edge is brazed to the reverse cutting edge groove.

[0012] Therefore, two to four flutes can be formed on a rod-shaped substrate made of cemented carbide using a first grinding wheel with a relatively large diameter. When forming each flute, interference between other flutes can be prevented by the first grinding wheel. After forming the flutes, a second grinding wheel with a relatively large diameter can be used to form the standard cutting grooves and the reverse cutting grooves between the flutes. When forming each standard cutting groove and each reverse cutting groove, interference between the second grinding wheel and the flutes, other standard cutting grooves, and other reverse cutting grooves can be prevented. This allows a substrate made of a highly rigid cemented carbide alloy to be machined using the first and second grinding wheels with relatively large diameters. Furthermore, the standard cutting grooves are machined into a flat surface that allows for easy brazing of PCD chips as standard cutting edges with a positive lead angle. The reverse cutting grooves are machined into a flat surface that allows for easy brazing of PCD chips as reverse cutting edges with a negative lead angle. This shortens the end mill machining time and reduces the manufacturing costs of the end mill. The first grinding wheel and the second grinding wheel may be the same grinding wheel or different grinding wheels.

[0013] FIG. 1 is a perspective view of an end mill according to an embodiment of the present disclosure; FIG. 2 is a side view of an end mill with a leading edge facing forward; FIG. 3 is a side view of an end mill with one of the reverse edges facing forward; FIG. 4 is a schematic perspective view of a machining center; FIG. 5 is a perspective view of a substrate when a flute is being machined; FIG. 6 is a perspective view of a substrate when a leading edge groove is being machined; FIG. 7 is a perspective view of a substrate when a reverse edge groove is being machined; FIG. 8 is a flowchart for machining an end mill; FIG. 9 is a perspective view showing conventional machining of a substrate made of steel; FIG. 10 is a perspective view showing generally when a substrate of a conventional shape is machined with a rotary grinding wheel;

[0014] One embodiment of the present disclosure will be described with reference to Figures 1 to 9. The same reference numerals throughout the description refer to the same elements having the same function, although the description will not be repeated. As shown in Figure 1, the end mill 1 includes a rod-shaped substrate 2 and multiple PCD tips 10 bonded to the substrate 2. The substrate 2 includes a tip 2c, a cutting portion (surface) 2b located within a predetermined distance from the tip 2c, and a cylindrical shank 2a located on the opposite side of the tip 2c. In the following description, the tip 2c side will be referred to as the tip side, and the shank 2a side will be referred to as the base side. The end mill 1 can perform grooves, edge cutting, cutting, and other processing on wood workpieces such as wood boards, solid wood, laminated wood, and plywood. Alternatively, the end mill 1 can process non-ferrous metal workpieces such as aluminum and copper. Alternatively, the end mill 1 can process workpieces such as resins and ceramic materials.

[0015] As shown in Figures 1 to 3, the substrate 2 is made of cemented carbide. A cemented carbide substrate 2 is less expensive and has approximately 1.6 times the rigidity of a substrate made of heavy metal. The PCD tip 10 is a substantially rectangular plate having a cutting edge 10a made of PCD (sintered polycrystalline diamond). The cutting edge 10a is the intersection of the rake face 10b and the flank face 10c. The cutting edge 10a extends in a curved shape so that the outer diameter of the end mill 1 is approximately constant. The cutting edge 10a cuts the workpiece. The PCD tip 10 is brazed to the cutting portion 2b of the substrate 2 using a brazing material such as silver solder.

[0016] 2 and 3, the cutting edge length (axial length) of the cutting portion 2b is, for example, 10 mm to 60 mm. The maximum cutting edge diameter D of the end mill 1 is twice the distance (radius) from the cutting edge 10a of the PCD tip 10 at one radial end of the end mill 1 to the axial center. The maximum cutting edge diameter D is, for example, 6 mm to 30 mm, for example, 10 mm to 20 mm, for example, 12 mm, 16 mm, etc.

[0017] As shown in FIGS. 1 to 3 , the cutting portion 2b is provided with flutes 3 extending in a spiral shape. In this embodiment, two flutes 3 are provided. The two flutes 3 equally divide the cutting portion 2b of the substrate 2 in the circumferential direction. The two flutes 3 are provided at 180° intervals in the circumferential direction of the substrate 2. One or more flutes 3 may be provided, for example, three or four flutes 3. In the case of three flutes 3, they are provided at 120° intervals in the circumferential direction of the substrate 2. In the case of four flutes 3, they are provided at 90° intervals in the circumferential direction. The flutes 3 extend clockwise from the tip end to the base end on the surface of the cutting portion 2b. The flutes 3 are provided with a twist angle 3a of 0° to 45° with respect to the axial direction of the substrate 2. The twist angle 3a of the flutes 3 is, for example, 5° or more, 10° or more, or 32° or more. The helix angle 3a is, for example, 32° or less, 35° or less, or 45° or less. The upper and lower limits of the helix angle 3a can be any combination of these. The width 3b of the flute 3 is, for example, 25% or more, or approximately 40% or more of the maximum cutting diameter D of the end mill 1. The width 3b is, for example, approximately 40% or less, or 45% or less of the maximum cutting diameter D. The lower and upper limits of the width 3b can be any combination of various values.

[0018] The multiple PCD chips 10 include positive edges 11 with a positive cutting edge lead angle 11a as shown in FIG. 2 and reverse edges 12 with a negative cutting edge lead angle 12a as shown in FIG. 3. The cutting edge lead angles 11a and 12a are the angles formed by the extension direction of the cutting edge 10a with respect to the axial direction of the substrate 2. The cutting edge lead angles 11a and 12a are positive when the tip side of the cutting edge 10a cuts into the workpiece before the base end side, and negative when the base end side of the cutting edge 10a cuts into the workpiece before the tip side. The positive edges 11 are provided in multiple rows toward the tip 2c of the substrate 2, or one toward the tip 2c. All PCD chips 10 on the base end side of the positive edges 11 are provided as reverse edges 12. The positive edges 11 cut the workpiece by pushing it toward the base end. The reverse edges 12 cut the workpiece by pushing it toward the tip end. Therefore, the forward blade 11 and the reverse blade 12 work together to cut the workpiece by sandwiching it in the axial direction of the base material 2. This prevents sheets or the like attached to the surface of the workpiece from peeling off during cutting, and prevents chipping of the surface, chipping of corners, burrs, uncut pieces, and the like.

[0019] As shown in Figures 1 to 3, the substrate 2 has two convex portions extending spirally between the two flutes 3. Multiple PCD chips 10 are joined between the two flutes 3 at approximately equal intervals along the extension direction of the flutes 3. In this embodiment, one straight edge 11 is provided at the tip 2c. Multiple PCD chips 10 joined at locations farther from the tip 2c than one straight edge 11 are all reverse edges 12. The lead angle 11a of the cutting edge of the straight edge 11 is, for example, 5° or more, 15° or more, 30° or more, or 45° or more. The lead angle 11a is, for example, 45° or less, 55° or less, or 65° or less. Various combinations of the lower and upper limits of the lead angle 11a are possible. The lead angle 12a of the cutting edge of the reverse edge 12 is, for example, -65° or more, -55° or more, or -45° or more. The lead angle 12a is, for example, equal to or less than −5°, equal to or less than −15°, or equal to or less than −45°. The upper and lower limits of the lead angle 12a can be variously combined.

[0020] As shown in Figures 1 to 3, the substrate 2 is provided with a straight edge groove 4 to which the straight edge 11 is bonded and a reverse edge groove 5 to which the reverse edge 12 is bonded. The straight edge groove 4 has a first brazing surface 4a and a second brazing surface 4b that intersect with each other. The first brazing surface 4a extends in a plane along the cutting edge 10a of the straight edge 11. The second brazing surface 4b extends in a plane perpendicular to the first brazing surface 4a. The straight edge groove 4 extends linearly in a direction inclined by the lead angle 11a of the cutting edge relative to the axial direction of the substrate 2. The reverse edge groove 5 has a first brazing surface 5a and a second brazing surface 5b that intersect with each other. The first brazing surface 5a extends in a plane along the cutting edge 10a of the reverse edge 12. The second brazing surface 5b extends in a plane perpendicular to the first brazing surface 5a. The back cutting edge groove 5 extends linearly in a direction inclined at a lead angle 12 a of the cutting edge relative to the axial direction of the substrate 2 .

[0021] As shown in Figures 1 to 3, the substrate 2 is provided with back grooves 6 that communicate with the straight edge grooves 4 and the reverse edge grooves 5. The back grooves 6 are recessed radially inward from the radial outer edges of the straight edge grooves 4 and the reverse edge grooves 5. The back grooves 6 of the straight edge grooves 4 are located on the base end side of the straight edge grooves 4. The back grooves 6 of the reverse edge grooves 5 are located on the tip end side of the reverse edge grooves 5. The back grooves 6 are narrower in width and shallower in depth than the straight edge grooves 4 and the reverse edge grooves 5. The back grooves 6 extend from the reverse edge grooves 5 toward the base end along the extension direction of the flutes 3. The back grooves 6 allow chips generated during cutting of the workpiece to be smoothly discharged from around the cutting edges 10a of the PCD insert 10 to the rear (base end) in the rotational direction. The substrate 2 is provided with a base metal relief 7 on the base end side of the flutes 3 and the reverse edge grooves 5. The base metal relief 7 extends from the base end region of the back cutting groove 5 toward the base end side and communicates with the flute 3. The provision of the base metal relief 7 makes it possible to prevent the rotating grindstone from interfering with the base material 2 when regrinding the cutting edge 10a of the PCD chip 10 joined to the base material 2.

[0022] 1 to 3, a gash 8 is provided on the base material 2 between the tip 2c of the base material 2 and the flute 3. The gash 8 is a groove that connects the tip 2c of the base material 2 and the flute 3. A bottom cutting edge relief 9 is provided on the tip 2c of the base material 2, and is slightly inclined with respect to a direction perpendicular to the axial direction of the base material 2. The bottom cutting edge relief 9 gives the tip of the base material 2 an approximately conical shape.

[0023] As shown in FIG. 4 , a machining center 20 for machining a substrate 2 includes a tool holder 22 for holding the substrate 2, a holder support 22a for supporting the tool holder 22, and a table 21 for supporting the holder support 22a from below. The table 21 is rotatable horizontally around a rotation axis 21a extending vertically. The holder support 22a is supported so as to be movable horizontally (left and right as viewed in FIG. 4 ) relative to the table 21. The tool holder 22 can move the substrate 2 it holds vertically or horizontally (forward and backward as viewed in FIG. 4 ) relative to the axial direction of the substrate 2. The tool holder 22 can also rotate the substrate 2 around its axis. The tool holder 22 can also tilt the substrate 2 axially. The machining center 20 includes a rotary grinding wheel 23, which is a disk-shaped diamond grinding wheel. The rotary grinding wheel 23 rotates around a rotation axis 23a located at the center of the disk. While the cutting portion 2b is in contact with the rotary grindstone 23 that rotates at a predetermined position, the substrate 2 held by the tool holder 22 is moved, rotated around its axis, or tilted. As a result, the cutting portion 2b is ground by the rotary grindstone 23 into the shape shown in FIG.

[0024] Next, the steps of the manufacturing method of the end mill 1 will be described. First, as shown in Fig. 4, the tool holder 22 holds the cylindrical substrate 2 made of cemented carbide (ST01 in Fig. 9). The substrate 2 is held by the tool holder 22 so that the cutting portion 2b is exposed.

[0025] As shown in FIG. 5 , a disk-shaped first grinding wheel 24 is prepared as the grinding wheel 23. The first grinding wheel 24 has a disk-shaped main body on the right side of FIG. 5 and a truncated cone-shaped complement on the left side of FIG. 5 . The outer diameter of the first grinding wheel 24 is, for example, 40 mm or more, 60 mm or more, or 80 mm or more. The outer diameter of the first grinding wheel 24 is, for example, 80 mm or less, 150 mm or less, or 200 mm or less. Various combinations of the lower and upper limits of the outer diameter of the first grinding wheel 24 are possible. The thickness of the disk main body of the first grinding wheel 24 is approximately the same length as the width 3b of the flutes 3 (see FIGS. 2 and 3 ), for example, 4 mm to 8 mm. The substrate 2 is moved relative to the first grinding wheel 24 while rotating around its axis. At this time, the extending direction of the substrate 2 is inclined at a helix angle 3a (see FIGS. 2 and 3 ) with respect to the extending direction of the first grinding wheel 24. The rotating first rotary grindstone 24 grinds while moving relative to the cutting portion 2b of the substrate 2. As a result, the first rotary grindstone 24 forms flutes 3 with a helix angle 3a in the cutting portion 2b of the substrate 2 (ST02 in FIG. 9). The substrate 2 is rotated 180° around its axis, and flutes 3 are formed in the same manner. As a result, two flutes 3 are formed at 180° intervals around the circumferential direction of the substrate 2.

[0026] As shown in FIG. 6 , a disk-shaped second grinding wheel 25 is prepared as the grinding wheel 23. The second grinding wheel 25 has a disk-shaped main body on the right side of FIG. 6 and a truncated cone-shaped complement on the left side of FIG. 6 . The outer diameter of the second grinding wheel 25 is, for example, 40 mm or more, 60 mm or more, or 80 mm or more. The outer diameter of the second grinding wheel 25 is, for example, 80 mm or less, 150 mm or less, or 200 mm or less. Various combinations of the lower and upper limits of the outer diameter of the second grinding wheel 25 are possible. The thickness of the disk main body of the second grinding wheel 25 is, for example, 4 mm to 8 mm. The substrate 2 is maintained in an orientation inclined at the lead angle 11a of the cutting edge (see FIG. 2 ) relative to the extension direction of the second grinding wheel 25. The second grinding wheel 25 is placed at a position where the straight edge groove 4 is to be formed. The second grinding wheel 25 is moved relative to the cutting portion 2b of the substrate 2. The side surface of the second rotary grindstone 25 forms the first brazing surface 4a of the straight edge groove 4. The radial end surface of the second rotary grindstone 25 forms the second brazing surface 4b of the straight edge groove 4. At this time, the second rotary grindstone 25 can grind the straight edge groove 4 without interfering with the flutes 3 or the reverse edge groove 5. In this way, the second rotary grindstone 25 forms the straight edge groove 4 in the cutting portion 2b of the substrate 2 (ST03 in FIG. 9). The straight edge groove 4 extends linearly and is inclined at the lead angle 11a of the cutting edge relative to the axial direction of the substrate 2.

[0027] As shown in Figures 7 and 8, the substrate 2 is maintained in an orientation inclined at the lead angle 12a of the cutting edge (see Figure 3) relative to the extension direction of the second rotary grindstone 25. The second rotary grindstone 25 is moved relative to the cutting portion 2b of the substrate 2 so that the second rotary grindstone 25 contacts the position where the reverse-edged groove 5 is to be formed. The side surface of the rotating second rotary grindstone 25 is formed by grinding the first brazing surface 5a of the reverse-edged groove 5. The radial end surface of the rotating second rotary grindstone 25 is formed by grinding the second brazing surface 5b of the reverse-edged groove 5. At this time, the second rotary grindstone 25 can grind the reverse-edged groove 5 without interfering with the flutes 3, the normal-edged grooves 4, or other reverse-edged grooves 5. In this way, the second rotary grindstone 25 forms the reverse-edged groove 5 in the cutting portion 2b of the substrate 2 (ST03 in Figure 9). The back cutting edge groove 5 extends linearly and is inclined at a lead angle 12 a of the cutting edge relative to the axial direction of the substrate 2 .

[0028] As shown in Figures 6 to 8, after the straight edge groove 4 and the reverse edge groove 5 are formed, the back groove 6, the buttock relief 7, the gash 8, and the bottom edge relief 9 are formed by grinding with a grinding wheel 23. Although the figures show all of the structures provided in the cutting section 2b, in reality, each structure is ground in the order of grinding. The grinding wheel 23 used to grind the back groove 6, the buttock relief 7, the gash 8, and the bottom edge relief 9 may be the same as the first grinding wheel 24 or the second grinding wheel 25, or may be a third grinding wheel. When grinding the back groove 6, the buttock relief 7, the gash 8, and the bottom edge relief 9, the grinding wheel 23 does not interfere with other structures provided in the cutting section 2b, such as the flutes 3, straight edge groove 4, and reverse edge groove 5.

[0029] As shown in FIG. 1 , the PCD chip 10 serving as the leading edge 11 is brazed to the first brazing surface 4a and the second brazing surface 4b of the leading edge groove 4 using a brazing material such as silver solder. The PCD chip 10 serving as the reverse edge 12 is brazed to the first brazing surface 5a and the second brazing surface 5b of the reverse edge groove 5 using a brazing material such as silver solder (ST04 in FIG. 9 ). The cutting edges 10a of the leading edge 11 and the cutting edges 10a of the reverse edge 12 are sharpened by grinding with a grindstone or the like (ST05 in FIG. 9 ). The end mill 1 is now completed. The end mill 1, whose substrate 2 is made of cemented carbide, can be manufactured using the above procedure at approximately the same manufacturing cost as a steel substrate of the same shape. The end mill 1, whose substrate 2 is made of cemented carbide, can be manufactured using the above procedure at approximately one-third the manufacturing cost of a heavy metal substrate of the same shape.

[0030] FIG. 10 shows a conventional example of machining a steel substrate 30 using a small-diameter end mill 31. The substrate 30 has a tip 30c, a cutting portion (surface) 30b located within a predetermined distance from the tip 30c, and a cylindrical shank 30a located on the base end opposite the tip 30c. The maximum cutting diameter of the end mill 31 is, for example, 4 mm. When machining a steel substrate 30 using the end mill 31, the machining time required is, for example, 50 minutes. If the substrate 30 is made of cemented carbide, the end mill 31 must be replaced with a small-diameter cylindrical grinding wheel. This increases the number of steps, resulting in a machining time of, for example, 4 hours or more, more than four times that required for steel. When machining a narrow groove in a steel substrate 30, an end mill 31 with a maximum outer diameter of, for example, 2 mm is also used. In this case, the number of steps increases, further lengthening the machining time for the substrate 30. Therefore, when machining a substrate 30 made of cemented carbide with a small diameter cylindrical grinding wheel, the manufacturing cost increases compared to machining a substrate 30 made of steel.

[0031] FIG. 11 shows a conventionally shaped substrate 35 made of cemented carbide being machined with a grinding wheel 23. The substrate 35 has a tip 35c, a cutting portion (surface) 35b located within a predetermined distance from the tip 35c, and a cylindrical shank 35a located on the base end opposite the tip 35c. For example, when machining a back-edge groove 5 in the substrate 35 with the grinding wheel 23, the front-edge groove 4 and other back-edge grooves 5 are positioned to interfere with the grinding wheel 23. This makes grinding impossible with a grinding wheel 23 with a relatively large diameter. Reducing the diameter of the grinding wheel 23 increases the machining time and increases manufacturing costs. One possible solution is to reduce the lead angle of the front and back-edge cutting edges brazed to the front and back-edge grooves 4 and 5 to prevent interference with the grinding wheel 23. However, reducing the lead angle of the front and back-edge cutting edges increases cutting resistance and reduces machining quality. It is also difficult to increase the number of edges. For example, by forming the substrate 2 in the shape of this embodiment as shown in Fig. 1, it is possible to provide an end mill 1 made of cemented carbide, which has high rigidity and cutting performance. Moreover, the use of a rotary grinding wheel 23 allows for reduced manufacturing costs.

[0032] As described above, the end mill 1 has a rod-shaped substrate 2 made of cemented carbide, as shown in FIGS. 2 and 3 . The end mill 1 has two to four flutes 3 extending from the surface of the substrate 2 with a helix angle 3a of 0° to 45° relative to the axial direction of the substrate 2. The end mill 1 has straight edge grooves 4 extending linearly between the flutes 3. The end mill 1 has straight edge grooves 11, which are PCD tips 10 installed in the straight edge grooves 4 and protruding from the straight edge grooves 4, with the cutting edge having a lead angle 11a of 15° to 55°. The end mill 1 has reverse edge grooves 5, which are located farther from the tip of the substrate 2 than the straight edge grooves 4 and extend linearly between the flutes 3. The end mill 1 has reverse edge grooves 12, which are PCD tips 10 installed in the reverse edge grooves 5 and protruding from the reverse edge grooves 5, with the cutting edge having a lead angle 12a of -55° to -15°.

[0033] Therefore, the flutes 3 can be spaced apart from one another, or the standard edge grooves 4 and the reverse edge grooves 5, or the standard edge grooves 4 and the reverse edge grooves 5, or the standard edge grooves 4 and the reverse edge grooves 5. Therefore, when the flutes 3, standard edge grooves 4, and reverse edge grooves 5 are machined with a grindstone 23 (see FIGS. 5 to 8 ), interference between the grindstone 23 and other structures in the cutting portion (surface) 2b of the substrate 2, such as the flutes 3, standard edge grooves 4, and reverse edge grooves 5, can be prevented. This allows a substrate 2 made of a highly rigid cemented carbide alloy to be machined with a grindstone 23 having a relatively large diameter. This shortens the machining time of the end mill 1, thereby reducing the manufacturing cost of the end mill 1.

[0034] As shown in Figures 2 and 3, the maximum cutting diameter D of the cutting edge of the end mill 1, which is made up of the forward cutting edge 11 and the reverse cutting edge 12, is 6 mm to 30 mm. Therefore, by providing the substrate 2 with a highly rigid cemented carbide alloy, the durability of the substrate 2 against cutting vibrations when processing a workpiece can be increased. Therefore, the end mill 1 can be used, for example, when performing high-feed processing by increasing the feed rate. Furthermore, the end mill 1 can be provided with an elongated shape in which the cutting portion 2b has a long cutting edge length relative to the maximum cutting diameter D. This allows the end mill 1 to be used to process, for example, router grooves in the workpiece that are deep relative to the groove width. Furthermore, even with a small maximum cutting diameter D, it is possible to perform hollowing out of thick plate materials.

[0035] As shown in Figures 2 to 8, a rod-shaped substrate 2 made of cemented carbide is prepared. A disk-shaped first rotary grindstone 24 is rotated around its axis and moved relative to the substrate 2 to form two to four axially extending flutes 3 on the surface of the substrate 2. A disk-shaped second rotary grindstone 25 is rotated around its axis and moved relative to the substrate 2 to form straight edge grooves 4 extending linearly between the flutes 3 and having a positive lead angle 11a of the cutting edge. The disk-shaped second rotary grindstone 25 is rotated around its axis to form reverse edge grooves 5 extending linearly between the flutes 3 and having a negative lead angle 12a of the cutting edge at a location farther from the tip of the substrate 2 than the straight edge grooves 4. A plate-shaped PCD chip 10 forming the straight edge 11 is brazed to the straight edge groove 4, and a plate-shaped PCD chip 10 forming the reverse edge 12 is brazed to the reverse edge groove 5.

[0036] Therefore, two to four flutes 3 can be formed on a rod-shaped substrate 2 made of cemented carbide using a first grinding wheel 24 with a relatively large diameter. When forming each flute 3, the first grinding wheel 24 can be prevented from interfering with other flutes 3. After forming the flutes 3, the second grinding wheel 25 with a relatively large diameter can be used to form the standard edge grooves 4 and the reverse edge grooves 5 between the flutes 3. When forming each standard edge groove 4 and each reverse edge groove 5, the second grinding wheel 25 can be prevented from interfering with the flutes 3, other standard edge grooves 4, and other reverse edge grooves 5. This allows the substrate 2 made of a highly rigid cemented carbide alloy to be machined using the first grinding wheel 24 and the second grinding wheel 25 with a relatively large diameter. Furthermore, the standard edge grooves 4 are machined into a flat shape that allows the PCD chip 10 to be easily brazed to the standard edge 11 with a positive lead angle 11a. The back cutting groove 5 is machined into a flat shape so that the cutting edge lead angle 12a of the back cutting edge 12 can be a negative back cutting edge 12 to which the PCD tip 10 can be brazed. This shortens the machining time of the end mill 1 and reduces the manufacturing cost of the end mill 1.

[0037] Various modifications can be made to the end mill 1 of the present embodiment described above. For example, the base material 2 is exemplified as having two flutes 3. Alternatively, the base material 2 may be provided with three or four flutes 3. The end mill 1 is exemplified as having one straight edge 11 and the remaining PCD tips 10 all being reverse edges 12. Alternatively, multiple straight edges 11 may be provided on the tip 2c side of the base material 2. The number of PCD tips 10 bonded to the base material 2 may be increased or decreased from the number exemplified.

[0038] The dimensions exemplified in this embodiment, such as the maximum cutting diameter D and cutting length (axial length of the cutting portion 2b) of the end mill 1, the width 3b of the flute 3, and the outer diameter and thickness of the grinding wheel 23, may be changed as appropriate. The angles exemplified in this embodiment, such as the twist angle 3a of the flute 3, the lead angle 11a of the cutting edge of the normal cutting edge 11, and the lead angle 12a of the cutting edge of the reverse cutting edge 12, may be changed as appropriate. The rotation direction of the end mill 1 may be reversed, and the twist direction of the flute 3 may be reversed. The locations and numbers of the back grooves 6, base metal reliefs 7, gashes 8, and bottom cutting reliefs 9 may be changed as appropriate.

[0039] The grinding wheels 23 for forming the straight edge groove 4 and the reverse edge groove 5 may be separate. The order in which the straight edge groove 4 and the reverse edge groove 5 are formed is not limited to the order shown in the example, and may be changed as appropriate. The order in which the back groove 6, base metal relief 7, gash 8, and bottom edge relief 9 are formed is not limited to the order shown in the example, and may be changed as appropriate.

[0040] The first grinding wheel and the second grinding wheel may be the same grinding wheel or different grinding wheels.

Claims

1. An end mill, a rod-shaped substrate made of cemented carbide; two to four flutes extending from the surface of the substrate with a helix angle of 0° to 45° relative to the axial direction of the substrate; a straight edge groove extending linearly between the flutes; A PCD tip with a lead angle of 30° to 55° of a cutting edge that is installed in the groove for the straight edge and protrudes from the groove for the straight edge; a reverse edge groove located farther from the tip of the substrate than the normal edge groove and extending linearly between the flutes; The cutting edge is a PCD chip that is installed in the reverse edge groove and protrudes from the reverse edge groove, and the lead angle of the cutting edge is −55° to −30°, The maximum cutting edge diameter of the cutting edge of the end mill made up of the normal blade and the reverse blade is 6 mm to 30 mm.

2. A method for manufacturing an end mill, comprising: A rod-shaped substrate made of cemented carbide is prepared; a first grinding wheel having a disk shape and an outer diameter equal to or larger than the maximum diameter of the substrate is rotated around its axis, and the first grinding wheel is moved relative to the substrate to form two to four flutes extending in an axial direction on the surface of the substrate; A disk-shaped second rotary grindstone having an outer diameter equal to or larger than the maximum diameter of the substrate is rotated around its axis, and the second rotary grindstone is moved relative to the substrate to form grooves for straight edges extending between the flutes and having a positive lead angle for the cutting edge, and grooves for reverse edges extending straight between the flutes and having a negative lead angle for the cutting edge at a location farther from the tip of the substrate than the grooves for straight edges, The manufacturing method includes brazing a plate-shaped PCD chip that will become the forward cutting edge to the forward cutting groove, and brazing a plate-shaped PCD chip that will become the reverse cutting edge to the reverse cutting groove.