Drill bit

Abstract

The drill bit (1) has a flank face at the front end of the main body (3). An oil hole (12) is provided in the flank face. The oil hole (12) has a fan-shaped cross section. The fan-shaped cross section is formed surrounded by a front-side inner wall surface (121), a rear-side inner wall surface (122), an outer peripheral-side inner wall surface (123), and an inner peripheral-side inner wall surface (124). Compared with a round hole, the cutting oil ejection performance of the oil hole (12) is higher. The rear-side inner wall surface (122) is curved in an arc shape toward the front in the rotation direction (T). Thereby, the drill bit (1) can ensure a wide distance between the ridge line portion of the flank face and the rear-side inner wall surface (122). The drill bit (1) can suppress the stress applied to the portion between the ridge line portion of the flank face and the oil hole (12), and thus can increase the ejection amount of the cutting oil and can ensure the tool rigidity.

Description

Technical Field

[0001] The present invention relates to a drill bit. Background Art

[0002] The shape of the oil hole used in the drill bit includes a circular hole and a non-circular hole. In a machining environment where the ejection amount of cutting oil cannot be obtained or in a higher-efficiency machining environment, the circular hole mostly cannot fully exhibit the tool performance. The non-circular hole increases the flow rate and ejection amount compared to the circular hole, thereby seeking to improve lubricity and coolability.

[0003] The cutting oil supply hole of the drill bit disclosed in Patent Document 1 has a fan-shaped cross-section. The fan-shaped cross-section is formed by being surrounded by a front-side inner wall surface, a rear-side inner wall surface, an outer peripheral-side inner wall surface, and an inner peripheral-side inner wall surface. The front-side inner wall surface is located on the front side in the rotation direction of the drill bit along the radial direction. The rear-side inner wall surface is located on the rear side in the rotation direction of the drill bit along the radial direction and is circumferentially opposite to the front-side inner wall surface. The outer peripheral-side inner wall surface is formed by a partial cylindrical surface centered on the center line of the drill bit. The inner peripheral-side inner wall surface is formed by a partial cylindrical surface centered on the center line of the drill bit and having a curvature radius smaller than that of the outer peripheral-side inner wall surface, and is radially opposite to the outer peripheral-side inner wall surface. The above drill bit can achieve a large improvement in performance for viscous workpieces such as SUS and Ti alloys and workpieces with low thermal conductivity.

[0004] There is also known a drill bit having a recessed portion, and the recessed portion has a curved portion that is curved in an arc shape. The drill bit having the recessed portion can cut a relatively hard workpiece. The first ridge line between the curved portion and the flank surface extends from the radially inner end of the self-sharpening edge toward the radially outer side in a manner that bends toward the rotation direction.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 5926877 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] When applying the cutting oil supply hole described in Patent Document 1 to a drill bit having a recessed portion, since the cutting oil supply hole is close to the curved portion, stress concentration may occur in a portion where the distance between the curved portion and the cutting oil supply hole is short. Thus, in the case of a relatively thick drill bit with a large cutting resistance or high-feed machining, the tool performance may be unstable due to insufficient tool stiffness.

[0010] An object of the present invention is to provide a drill bit that increases the ejection amount of cutting oil and can ensure tool stiffness.

[0011] Solution for solving problems

[0012] A drill bit according to a technical solution of the present invention is characterized in that the drill bit includes: a rod-shaped tool body that rotates about an axis; a discharge groove that is spirally provided on the outer peripheral surface from the front end portion to the rear end portion of the tool body; a cutting edge that is formed at a ridge line portion between an inner surface of the discharge groove facing the front in the rotation direction of the tool body and a flank of the front end portion; and an oil hole that is provided in the flank and supplies cutting oil to the cutting edge side. The oil hole has a fan-shaped cross section surrounded by a front-side inner wall surface, a rear-side inner wall surface, an outer peripheral-side inner wall surface, and an inner peripheral-side inner wall surface. The front-side inner wall surface is located on the front side in the rotation direction of the tool body along the radial direction. The rear-side inner wall surface is located on the rear side in the rotation direction of the tool body along the radial direction and is circumferentially opposite to the front-side inner wall surface. The outer peripheral-side inner wall surface includes a partial cylindrical surface centered on the center line of the tool body. The inner peripheral-side inner wall surface includes a partial cylindrical surface centered on the center line of the tool body and having a curvature radius smaller than that of the outer peripheral-side inner wall surface, and is radially opposite to the outer peripheral-side inner wall surface. The rear-side inner wall surface is curved in an arc shape toward the front in the rotation direction.

[0013] Since the oil hole of this technical solution has a fan-shaped cross section, the amount of cutting oil ejected can be increased compared with a circular hole. Moreover, in this technical solution, the rear-side inner wall surface of the oil hole is curved in an arc shape toward the front in the rotation direction, so that a relatively wide distance between the ridge line portion of the flank and the rear-side inner wall surface can be ensured. In addition, the ridge line portion of the flank refers to the ridge line portion between the inner surface of the discharge groove facing the rear in the rotation direction of the tool body and the flank. Thus, this technical solution can suppress the stress applied to the portion between the ridge line portion and the oil hole, so that the tool stiffness can be ensured. Generally, when the cross-sectional area of the oil hole is enlarged, the tool stiffness decreases, but the drill bit of this technical solution can ensure the tool stiffness, so this technical solution can also be used for high-feed machining. High-feed machining refers to machining in which the tool is moved at high speed. This technical solution is also effective for relatively thick dimensions with relatively large cutting resistance.

[0014] Optionally, the drill bit of this technical solution has a recess, and the ridge line between the recess and the flank extends in an arc shape from the inner end of the cutting edge toward the outer side in the radial direction and is connected to the discharge groove. The rear-side inner wall surface is curved in an arc shape in the same direction as the recess at a position away from the recess. Although this technical solution has an arc-shaped recess, by curving the rear-side inner wall surface of the oil hole in an arc shape in the same side as the recess, a relatively wide distance between the rear-side inner wall surface and the ridge line portion of the flank can be ensured equally.

[0015] It is possible that the radius of curvature of the inner wall surface on the rear side of the drill bit in this technical solution is 0.35D or more and 0.45D or less in the cross section. Thereby, the drill bit can increase the ejection amount of the cutting oil and stabilize the cutting performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a side view of the drill bit 1.

[0017] Figure 2 is a perspective view of the front end portion of the drill bit 1.

[0018] Figure 3 is a front view of the drill bit 1.

[0019] Figure 4 is Figure 1 a sectional view taken along the line I-I shown in the direction of view.

[0020] Figure 5 is a table comparing the cross-sectional areas of the conventional product A, the conventional product B, and the product of the present invention respectively.

[0021] Figure 6 is a table comparing the cross-sectional areas of the conventional product A, the conventional product B, and the product of the present invention respectively when the drill bit diameter is changed.

[0022] Figure 7 is a table showing the results of the evaluation test.

[0023] Figure 8 is a graph showing the results of the durability test 1.

[0024] Figure 9 is a graph showing the results of the durability test 2.

[0025] Figure 10 is a graph showing the results of the durability test 3.

[0026] Figure 11 is a graph showing the results of the durability test 4.

[0027] Figure 12 is a graph showing the results of the durability test 5.

[0028] Figure 13 is a graph showing the results of the ejection amount test 1.

[0029] Figure 14 is a graph showing the results of the ejection amount test 2.

[0030] Figure 15 is a graph showing the results of the ejection amount test 3.

[0031] Figure 16This is the front view of a three-flute drill bit 100 (variant example). Detailed implementation mode

[0032] The implementation mode of the present invention will be described. The present invention is not limited to the following implementation mode, and design changes can be appropriately made. For the sake of clarity in the description, there are appropriately parts shown in the drawings with a dimensional ratio different from the actual dimensional ratio. The present invention is not construed as being limited to the shape of the following implementation mode.

[0033] Refer to Figures 1 to 3 The structure of the drill bit 1 will be described. The drill bit 1 is a double-flute long drill bit. The drill bit 1 is preferably formed of a hard material such as cemented carbide or high-speed tool steel (high-speed steel). The drill bit 1 includes a shank 2 and a body 3. The shank 2 and the body 3 are an example of the "tool body" of the present invention. The shank 2 is mounted on the spindle of a machine tool (not shown). The body 3 extends from the shank 2 along the axis AX. The drill bit 1 rotates around the axis AX to cut the material to be cut and form a processed hole. The rotation direction T of the drill bit 1 during processing is counterclockwise when viewed from the front end side of the body 3 (hereinafter referred to as "front view"). (Refer to Figure 3 )

[0034] Two discharge grooves 4 are provided on the outer peripheral surface 31 of the body 3. The two discharge grooves 4 open at the front end of the body 3. Each discharge groove 4 is formed in a spiral shape in the clockwise direction in the front view from the front end of the body 3 toward the rear end of the shank 2. The discharge groove 4 discharges the chips from the processed hole during processing. As Figure 2 , Figure 3 shown, the discharge groove 4 has an inner surface 41 and an inner surface 42. The inner surface 41 is the surface facing the rotation direction T side. The inner surface 42 is the surface facing the side opposite to the rotation direction T. The ridge line portion where the inner surface 41 intersects the outer peripheral surface 31 is the leading edge 33. The ridge line portion where the inner surface 42 intersects the outer peripheral surface 31 is the trailing edge 34.

[0035] Two flank faces 6 are provided at the front end of the body 3. The two flank faces 6 are provided at positions symmetric with each other about the axis AX. When the front end of the body 3 is viewed from the front, the two flank faces 6 and the two discharge grooves 4 are alternately arranged in the circumferential direction. A cutting edge 5 is provided at the ridge line portion where the inner surface 41 intersects the flank face 6. Since the front end of the body 3 has two inner surfaces 41 and two flank faces 6, there are two cutting edges 5. The cutting edge 5 is formed in a substantially letter S shape in the front view and cuts the material to be cut. The inner surface 41 near the cutting edge 5 is the rake face, and this rake face picks up the chips cut by the cutting edge 5.

[0036] A chisel edge 9 is formed at the center of the front end portion of the main body 3. A grinding edge 7 is provided near the chisel edge 9. The grinding edge 7 is curved in an arc shape from the inner end 51 of the cutting edge 5 toward the chisel edge 9 side in the rotation direction T. The grinding edge 7 is provided at the ridge line portion between the grinding surface 71 and the flank 6. The grinding edge 7 has a grinding surface 71. The grinding surface 71 extends from the grinding edge 7 toward the rear end portion side of the main body 3 and faces the rotation direction T. The grinding surface 71 is a rake face.

[0037] A recess 8 is provided on the inner surface 42 of the front end portion of the main body 3. The recess 8 curls the chips picked up by the rake face during machining and discharges them to the discharge groove 4. The recess 8 has a curved portion 81 and a straight portion 82. The ridge line between the curved portion 81 and the flank 6 is the first ridge line 811. The ridge line between the straight portion 82 and the flank 6 is the second ridge line 821.

[0038] The first ridge line 811 extends from the inner end 72 of the grinding edge 7 toward the radially outer side and is curved in an arc shape toward the rotation direction T. The curved portion 81 is formed as a curved surface that extends from the first ridge line 811 toward the rear end portion side of the main body 3 and is curved in the rotation direction T. The curved portion 81 strengthens the curling of the chips cut by the grinding edge 7.

[0039] The second ridge line 821 extends linearly from the outer end 812 of the first ridge line 811 toward the radially outer side. The outer end 822 of the second ridge line 821 is connected to the discharge groove 4 at a position radially inside the outer peripheral surface 31. The straight portion 82 extends from the second ridge line 821 toward the rear end portion side of the main body 3 in a manner away from the axis AX and is formed along the inner surface 42. The straight portion 82 guides the chips curled by the curved portion 81 to the discharge groove 4. The discharge groove 4 allows the guided chips to flow toward the rear end side of the main body 3.

[0040] An arc groove 10 is provided at the connecting portion between the inner end of the curved portion 81 and the inner end of the grinding surface 71. The arc groove 10 extends from the chisel edge 9 toward the discharge groove 4 and is curved in an arc shape toward the radially inner side. The arc groove 10 allows the chips picked up by the grinding surface 71 to smoothly flow into the recess 8.

[0041] At the front end portion of the main body 3, oil holes 12 are respectively provided in the two flanks 6. The oil holes 12 extend spirally from the rear end of the shank 2 toward the front end portion of the main body 3 substantially parallel to the discharge groove 4 and open in the corresponding flank 6. The oil holes 12 supply cutting oil to the machining portion of the workpiece. The surface of the front end portion of the main body 3 is covered with DLC (Diamond-Like Carbon).

[0042] Refer to Figure 4 Describe the shape of the oil holes 12. Figure 4This is a cross-sectional view of the drill bit 1 perpendicular to the axis AX, and the first ridgeline 811 of the concave portion 8 is virtually shown by a double-dashed line near an oil hole 12. The oil hole 12 is a non-circular hole and has a fan-shaped cross section. The fan-shaped cross section means that the cross section of the oil hole 12 perpendicular to the axis AX is roughly fan-shaped. The fan-shaped cross section of the oil hole 12 is formed surrounded by the front inner wall surface 121, the rear inner wall surface 122, the outer inner wall surface 123, and the inner inner wall surface 124, and has four corners R1 to R4.

[0043] The front inner wall surface 121 is a plane located radially on the front side of the rotation direction T. The rear inner wall surface 122 is located radially on the rear side of the rotation direction T and is circumferentially opposite to the front inner wall surface 121. The rear inner wall surface 122 is curved in an arc shape in a direction substantially the same as the curvature direction of the first ridge line 811. The outer inner wall surface 123 includes a partial cylindrical surface with a curvature radius D1 centered on the axis AX. The radius D1 is equivalent to the radius of the circumscribed circle C1 of the oil hole 12. The inner inner wall surface 124 includes a partial cylindrical surface with a curvature radius D2 centered on the axis AX and is radially opposite to the outer inner wall surface 123. The curvature radius D2 is smaller than the curvature radius D1. The radius D2 is equivalent to the radius of the inscribed circle C2 of the oil hole 12. The two oil holes 12 are arranged at equal intervals on a pitch circle C3 of radius D3 centered on the axis AX, and have point-symmetric shapes with respect to the axis AX.

[0044] Corner R1 is a portion where the front inner wall surface 121 and the inner circumference inner wall surface 124 are connected to each other in an arc shape. Corner R2 is a portion where the front inner wall surface 121 and the outer circumference inner wall surface 123 are connected to each other in an arc shape. Corner R3 is a portion where the rear inner wall surface 122 and the inner circumference inner wall surface 124 are connected to each other in an arc shape. Corner R4 is a portion where the rear inner wall surface 122 and the outer circumference inner wall surface 123 are connected to each other in an arc shape.

[0045] In the circumferential central portion of the back cutting edge 6, a reference line extending radially outward from the axis AX is set as B1. A reference line rotated by an angle A1 to the rotation direction T side with the axis AX as the center relative to the reference line B1 is set as B2. A reference line rotated by an angle A1 to the side opposite to the rotation direction T with the axis AX as the center relative to the reference line B1 is set as B3. A reference line rotated by an angle A2 to the side opposite to the rotation direction T with the intersection of the inscribed circle C2 and the reference line B1 as the center relative to the reference line B1 is set as B4. Angle A2 is greater than angle A1. Angle A2 is preferably determined in a manner that the reference line B4 is opposite to the first ridge line 811. An example of angle A1 is 20°, and an example of angle A2 is 44°.

[0046] In the drill bit 1, since the oil hole 12 has the above-described fan-shaped cross section, the core thickness near the chisel edge 9 can be ensured. Thereby, the drill bit 1 can maintain the tool stiffness. Since the oil hole 12 is a non-circular hole, the cross-sectional area can be increased compared with the conventional circular hole. Thereby, the drill bit 1 can increase the ejection amount of the cutting oil compared with the circular hole. For example, in the case of comparison with a conventional circular hole having the same cross-sectional area, the closer to the outer peripheral side of the oil hole 12, the greater the length in the circumferential direction and the higher the pressure based on the centrifugal force. Thereby, for the drill bit 1, even without increasing the supply pressure of the cutting oil, the speed of the cutting oil in the oil hole 12 can be increased, and the supply amount of the cutting oil can be increased by using the centrifugal force generated by the rotation of the drill bit 1.

[0047] The front-side inner wall surface 121 is arranged along the reference line B2. The rear-side inner wall surface 122 is arranged on the reference line B4 and is curved in an arc shape toward the side substantially the same as the bending direction of the first ridge line 811. As Figure 3 shown, at the front end portion of the main body 3, the rear-side inner wall surface 122 faces the first ridge line 811 with the interposed wall portion 16 therebetween. The interposed wall portion 16 is the wall portion between the oil hole 12 and the first ridge line 811.

[0048] For example, in the case of an oil hole having a conventional fan-shaped cross section with a rear-side inner wall surface being linear, the vertex of the first ridge line 811 approaches the rear-side inner wall surface, resulting in stress concentration during machining. In contrast, in the oil hole 12 of the present embodiment, the rear-side inner wall surface 122 and the first ridge line 811 are substantially parallel curves with the interposed wall portion 16 therebetween. Therefore, the drill bit 1 can effectively suppress stress concentration in the interposed wall portion 16 during machining. In addition, as described later, for the relatively thick drill bit 1 with a diameter of φ6 or more, the cross-sectional area of the oil hole 12 can be reduced compared with an oil hole having a conventional fan-shaped cross section. Thereby, compared with an oil hole having a conventional fan-shaped cross section, the drill bit 1 can improve the tool stiffness, and thus can prevent sudden breakage due to insufficient stiffness. Further, the radius of curvature of the rear-side inner wall surface 122 is preferably 0.35D or more and 0.45D or less.

[0049] Next, the shapes and cross-sectional areas of the oil holes of the product of the present invention and the conventional products are compared. As Figure 5 shown, the conventional product A is a conventional drill bit having a circular hole with a circular shape. The conventional product B is a conventional drill bit having an oil hole with a fan-shaped cross section with a rear-side inner wall surface being linear. The product of the present invention is the drill bit 1 having the oil hole 12 of the present embodiment. The drill bit diameter D is φ3.2 for all. The cross-sectional area of the oil hole of the conventional product A is 0.126 mm 2 , the cross-sectional area of the oil hole of the conventional product B is 0.297 mm 2 , and the cross-sectional area of the oil hole 12 of the product of the present invention is 0.321 mm 2When the cross-sectional area of the oil hole of the conventional product A is set to 100%, the cross-sectional area of the oil hole of the conventional product B is 236%, and the cross-sectional area of the oil hole of the product of the present invention is 255%. It can be seen therefrom that in the case of φ3.2, compared with the conventional product A and the conventional product B, the product of the present invention can increase the cross-sectional area of the oil hole.

[0050] Next, for the product of the present invention and the conventional product, the cross-sectional area of the oil hole that varies according to the drill bit diameter is compared. As Figure 6 shown, the drill bit diameters of the conventional product A, the conventional product B, and the product of the present invention are changed respectively, and the cross-sectional area of the oil hole is measured. The basic shapes of the conventional product A, the conventional product B, and the product of the present invention are the same as the above shapes. The drill bit diameters to be compared are nine kinds: φ3, φ4, φ5, φ6, φ8, φ10, φ12, φ16, and φ20.

[0051] In the conventional product A, the cross-sectional area of the oil hole of φ3 is 0.126 mm 2 , the cross-sectional area of the oil hole of φ4 is 0.126 mm 2 , the cross-sectional area of the oil hole of φ5 is 0.385 mm 2 , the cross-sectional area of the oil hole of φ6 is 0.385 mm 2 , the cross-sectional area of the oil hole of φ8 is 0.785 mm 2 , the cross-sectional area of the oil hole of φ10 is 1.539 mm 2 , the cross-sectional area of the oil hole of φ12 is 1.539 mm 2 , the cross-sectional area of the oil hole of φ16 is 2.405 mm 2 , the cross-sectional area of the oil hole of φ20 is 3.142 mm 2 .

[0052] In the conventional product B, the cross-sectional area of the oil hole of φ3 is 0.15 mm 2 , the cross-sectional area of the oil hole of φ4 is 0.297 mm 2 , the cross-sectional area of the oil hole of φ5 is 0.489 mm 2 , the cross-sectional area of the oil hole of φ6 is 0.89 mm 2 , the cross-sectional area of the oil hole of φ8 is 1.575 mm 2 , the cross-sectional area of the oil hole of φ10 is 2.462 mm 2 , the cross-sectional area of the oil hole of φ12 is 3.546 mm 2 , the cross-sectional area of the oil hole of φ16 is 6.313 mm 2 , the cross-sectional area of the oil hole of φ20 is 9.079 mm 2 .

[0053] When the cross-sectional area of the conventional product A is set to 100%, the cross-sectional area of the φ3 oil hole of the conventional product B is 119%, the cross-sectional area of the φ4 oil hole is 236%, the cross-sectional area of the φ5 oil hole is 127%, the cross-sectional area of the φ6 oil hole is 231%, the cross-sectional area of the φ8 oil hole is 201%, the cross-sectional area of the φ10 oil hole is 160%, the cross-sectional area of the φ12 oil hole is 230%, the cross-sectional area of the φ16 oil hole is 262%, and the cross-sectional area of the φ20 oil hole is 289%. From the above, it can be seen that compared with the oil holes of the conventional product A, regardless of the diameter φ of the drill bit, the oil holes of the conventional product B can increase the cross-sectional area.

[0054] In the product of the present invention, the cross-sectional area of the φ3 oil hole 12 is 0.183 mm 2 , and the cross-sectional area of the φ4 oil hole 12 is 0.32 mm 2 , and the cross-sectional area of the φ5 oil hole 12 is 0.504 mm 2 , and the cross-sectional area of the φ6 oil hole 12 is 0.731 mm 2 , and the cross-sectional area of the φ8 oil hole 12 is 1.293 mm 2 , and the cross-sectional area of the φ10 oil hole 12 is 2.021 mm 2 , and the cross-sectional area of the φ12 oil hole 12 is 2.912 mm 2 , and the cross-sectional area of the φ16 oil hole 12 is 5.184 mm 2 , and the cross-sectional area of the φ20 oil hole 12 is 7.316 mm 2 .

[0055] When the cross-sectional area of the conventional product A is set to 100%, the cross-sectional area of the φ3 oil hole 12 of the product of the present invention is 145%, the cross-sectional area of the φ4 oil hole 12 is 254%, the cross-sectional area of the φ5 oil hole 12 is 131%, the cross-sectional area of the φ6 oil hole 12 is 190%, the cross-sectional area of the φ8 oil hole 12 is 165%, the cross-sectional area of the φ10 oil hole 12 is 131%, the cross-sectional area of the φ12 oil hole 12 is 189%, the cross-sectional area of the φ16 oil hole 12 is 216%, and the cross-sectional area of the φ20 oil hole 12 is 233%.

[0056] From the above, it can be seen that compared with the oil holes of the conventional product A, regardless of the drill bit diameter, the product of the present invention can increase the cross-sectional area of the oil hole 12. In addition, it can be known that in relation to the conventional product B, in the relatively small-diameter drill bits of φ3 to φ5, the product of the present invention can increase the cross-sectional area relative to the conventional product B. Therefore, it can be known that in the product of the present invention with relatively small diameters of φ3 to φ5, the ejection amount of the cutting oil can be increased compared with the conventional product B.

[0057] On the other hand, compared with a drill bit having a small diameter, a drill bit having a relatively thick diameter of φ6 to φ20 has a larger inertial force during rotation, and thus tool stiffness is required. Among the drill bits of φ6 to φ20, the cross-sectional area of the oil hole of the product of the present invention is larger than that of the oil hole of the conventional product A, but smaller than that of the oil hole of the conventional product B. Therefore, it is known that in the product of the present invention having a relatively thick diameter of φ6 to φ20, the ejection amount of the cutting oil can be increased compared with the conventional product A, and the tool stiffness can be improved compared with the conventional product B.

[0058] Refer to Figure 7 An evaluation test of the radius of curvature of the rear inner wall surface 122 will be described. In this test, eight drill bits 1 in which the radius of curvature of the rear inner wall surface 122 of the oil hole 12 is changed are manufactured, and three items, namely, the cutting oil ejection amount, the distance from the notch portion 8, and the cutting performance stability, are evaluated. The distance from the notch portion 8 is the width of the sandwiching wall portion 16 (the length in the direction orthogonal to the length direction).

[0059] The machining conditions will be described. The drill bit diameter is set to φ3. The material to be cut is S50C, a carbon steel material. The cutting speed is set to 100 m / min. The feed rate is set to 0.18 mm / rev. The machining depth of the material to be cut is set to 15 mm. The cutting oil used is a water-soluble cutting oil. The coolant pressure is set to 1 MPa.

[0060] The evaluation method will be described. When the cutting oil ejection amount is less than that of the oil hole of the conventional product B, it is judged as × (poor); if it is about the same, it is judged as △ (average); if it is more, it is judged as 〇 (good). Regarding the distance from the notch portion 8, the alignment accuracy of the oil hole 12 when machining the discharge groove 4 and the deviation of the symmetry of the two oil holes 12 when manufacturing the drill bit 1 are also included, and comprehensive evaluation is performed, and judgment is made according to three grades of 〇 (good), △ (average), and × (poor). Regarding the cutting performance stability, the durability and stability of the drill bit when repeatedly cutting holes in the material to be cut under the above machining conditions are comprehensively evaluated, and judgment is made according to three grades of 〇 (good), △ (average), and × (poor).

[0061] Refer to Figure 7, the results are described. For a drill bit with a curvature radius of 0.20D, the cutting oil ejection volume is ×, the distance from the concave portion is 〇, and the cutting performance stability is ×. For a drill bit with a curvature radius of 0.25D, the cutting oil ejection volume is ×, the distance from the concave portion is 〇, and the cutting performance stability is △. For a drill bit with a curvature radius of 0.30D, the cutting oil ejection volume is △, the distance from the concave portion is 〇, and the cutting performance stability is 〇. For a drill bit with a curvature radius of 0.35D, the cutting oil ejection volume is 〇, the distance from the concave portion is 〇, and the cutting performance stability is 〇. For a drill bit with a curvature radius of 0.40D, the cutting oil ejection volume is 〇, the distance from the concave portion is 〇, and the cutting performance stability is 〇. For a drill bit with a curvature radius of 0.45D, the cutting oil ejection volume is 〇, the distance from the concave portion is 〇, and the cutting performance stability is 〇. For a drill bit with a curvature radius of 0.50D, the cutting oil ejection volume is 〇, the distance from the concave portion is △, and the cutting performance stability is △. For a drill bit with a curvature radius of 0.55D, the cutting oil ejection volume is 〇, the distance from the concave portion is ×, and the cutting performance stability is ×.

[0062] Based on the above results, the curvature radii for which the cutting oil ejection volume, the distance from the concave portion, and the cutting performance stability are all 〇 are 0.35D, 0.40D, and 0.45D. Thus, it is confirmed that the optimal range of the curvature radius of the rear inner wall surface 122 is 0.35D to 0.45D.

[0063] Refer to Figures 8 to 12 , the durability comparison test of the drill bit 1 is described. The durability comparison test consists of durability tests 1 to 5. In durability tests 1 to 5, for three types of products, namely the product of the present invention, conventional product A, and conventional product B, the processing conditions are changed, and the number of processed holes and the state of the tool are investigated when performing hole opening processing on the work material repeatedly. The basic shapes of conventional product A, conventional product B, and the product of the present invention are the same as above. The processing conditions for durability tests 1 to 5 are as follows.

[0064] (Durability Test 1)

[0065] · Drill bit diameter D = φ8.5

[0066] · Work material = S50C

[0067] · Cutting speed = 100 m / min

[0068] · Feed rate = 0.255 mm / rev

[0069] · Hole depth = 42.5 mm

[0070] (Durability Test 2)

[0071] · Drill bit diameter D = φ6.8

[0072] ·Work material = S50C

[0073] ·Cutting speed = 120 m / min

[0074] ·Feed rate = 0.27 mm / rev

[0075] ·Hole depth = 25 mm (through the work material)

[0076] (Endurance test 3)

[0077] ·Drill diameter D = φ6.8

[0078] ·Work material = SCM440 (30 HRC)

[0079] ·Cutting speed = 70 m / min

[0080] ·Feed rate = 0.27 mm / rev

[0081] ·Hole depth = 25 mm (through the work material)

[0082] (Endurance test 4)

[0083] ·Drill diameter D = φ6.8

[0084] ·Work material = SUS304

[0085] ·Cutting speed = 80 m / min

[0086] ·Feed rate = 0.27 mm / rev

[0087] ·Hole depth = 25 mm (through the work material)

[0088] (Endurance test 5)

[0089] ·Drill diameter D = φ3.4

[0090] ·Work material = 51CrV4

[0091] ·Cutting speed = 64 m / min

[0092] ·Feed rate = 0.09 mm / rev

[0093] ·Hole depth = 17 mm

[0094] Refer to Figure 8, the results of durability test 1 are described. When the number of machined holes of the conventional product A was 1,122 holes, the drill bit was damaged. When the number of machined holes of the conventional product B was 818 holes, the drill bit was damaged. For the product of the present invention, when the number of machined holes was 1,685 holes, the drill bit had local defects but was not damaged. The reason why the number of machined holes of the conventional product B is less than that of the conventional product A is presumably because the cross-sectional area of the oil hole is large and the tool stiffness is reduced. Compared with the conventional products A and B, the number of machined holes of the product of the present invention increases. From the above results, it can be seen that under the machining conditions of durability test 1, compared with the conventional products A and B, the durability performance of the product of the present invention is improved.

[0095] Refer to Figure 9 , the results of durability test 2 are described. When the number of machined holes of the conventional product A was 6,000 holes, the drill bit had local defects. When the number of machined holes of the conventional product B was 1,578 holes, the drill bit was damaged. For the product of the present invention, when the number of machined holes was 6,000 holes, the drill bit had local defects, but hole machining could still be continued thereafter. Compared with durability test 1, the reason why the number of machined holes of the conventional product B is even less than that of the conventional product A is presumably that the cutting speed and feed rate are greater than those in durability test 1, so the drill bit of the conventional product B cannot withstand the stress during cutting. From the above results, it can be seen that under the machining conditions of durability test 2, compared with the conventional products A and B, the durability performance of the product of the present invention is improved.

[0096] Refer to Figure 10 , the results of durability test 3 are described. When the number of machined holes of the conventional product A was 1,500 holes, the drill bit had local defects. When the number of machined holes of the conventional product B was 447 holes, the drill bit was damaged. For the product of the present invention, when the number of machined holes was 1,800 holes, the drill bit had local defects. In durability test 3, the material to be cut was replaced with SCM440 for machining, but similarly to comparative tests 1 and 2, the number of machined holes of the product of the present invention was more than that of the conventional products A and B. From the above results, it can be seen that under the machining conditions of durability test 3, compared with the conventional products A and B, the durability performance of the product of the present invention is also improved.

[0097] Refer to Figure 11 , the results of durability test 4 are described. When the number of machined holes of the conventional product A was 4,000 holes, the wear of the drill bit was large. When the number of machined holes of the conventional product B was 658 holes, the drill bit was damaged. For the product of the present invention, when the number of machined holes was 5,000 holes, the wear of the drill bit was large. In durability test 4, the material to be cut was replaced with SUS304 for machining, but similarly to comparative tests 1 to 3, the number of machined holes of the product of the present invention was also more than that of the conventional products A and B. From the above results, it can be seen that under the machining conditions of durability test 4, compared with the conventional products A and B, the durability performance of the product of the present invention is also improved.

[0098] Refer to Figure 12 , the results of durability test 5 will be described. When the number of machined holes of the conventional product A was 5000, the drill bit had significant wear. When the number of machined holes of the conventional product B was 3500, the drill bit had local defects. The number of machined holes of the product of the present invention is 6000 and hole machining can still continue thereafter. In durability test 5, the work material was replaced with 51CrV4 and machining was carried out. However, similar to Comparative Tests 1 to 3, the number of machined holes of the product of the present invention was also increased compared to the conventional products A and B. From the above results, it can be seen that under the machining conditions of durability test 5, the durability performance of the product of the present invention is also improved compared to the conventional products A and B.

[0099] Refer to Figures 13 to 15 The ejection amount comparison test of drill bit 1 will be described. The ejection amount comparison test consists of ejection amount tests 1 to 3. In ejection amount tests 1 to 3, for the three products of the product of the present invention, conventional product A, and conventional product B, the type of cutting oil, drill bit diameter, and coolant pressure were changed, and the ejection amount of cutting oil per unit time was investigated. The basic shapes of conventional product A, conventional product B, and the product of the present invention are the same as above. In ejection amount test 1, a non-water-soluble cutting oil was used, the drill bit diameter was set to φ3.4, the coolant pressure was set to 1.5 MPa, and the measurement time was set to 1 minute. In ejection amount test 2, a water-soluble cutting oil was used, the drill bit diameter was set to φ3.4, and the coolant pressures were set to two modes of 1 MPa and 3 MPa, and the measurement time was set to 1 minute. In ejection amount test 3, a water-soluble cutting oil was used, the drill bit diameter was set to φ6.8, the coolant pressure was set to 1.5 MPa, and the measurement time was set to 30 seconds. In addition, in ejection amount tests 1 and 2, the oil hole of conventional product A was set to φ0.4. In ejection amount test 3, the oil hole of conventional product A was set to φ1.

[0100] Refer to Figure 13 , the results of ejection amount test 1 will be described. The ejection amount of conventional product A was 110 ml / min, the ejection amount of conventional product B was 220 ml / min, and the ejection amount of the product of the present invention was 220 ml / min. From the above results, it can be seen that in the case of a small diameter of φ3.4 and using a non-water-soluble cutting oil, the product of the present invention can ensure an ejection amount more than that of conventional product A and equal to that of conventional product B.

[0101] Refer to Figure 14, the results of the ejection volume test 2 will be described. When the coolant pressure = 1 Pa, the ejection volume of the conventional product A is 295 ml / min, the ejection volume of the conventional product B is 540 ml / min, and the ejection volume of the product of the present invention is 562 ml / min. When the coolant pressure = 3 Pa, the ejection volume of the conventional product A is 547 ml / min, the ejection volume of the conventional product B is 930 ml / min, and the ejection volume of the product of the present invention is 972 ml / min. From the above results, it can be seen that in the case of a small diameter of φ3.4 and using a water-soluble cutting oil, compared with the conventional products A and B, the product of the present invention can increase the ejection volume.

[0102] Refer to Figure 15 , the results of the ejection volume test 3 will be described. The ejection volume of the conventional product A is 1600 ml / 30 s, the ejection volume of the conventional product B is 2800 ml / 30 s, and the ejection volume of the product of the present invention is 2200 ml / 30 s. From the above results, it can be seen that in the case of a relatively large diameter of φ6.8 and using a water-soluble cutting oil, the ejection volume of the product of the present invention is less than that of the conventional product B, but it can increase the ejection volume compared with the conventional product A.

[0103] From the results of the above ejection volume tests 1 to 3, it can be seen that regardless of whether it is a water-soluble cutting oil or a non-water-soluble cutting oil, and regardless of the drill bit diameter, the product of the present invention can increase the ejection volume of the cutting oil by at least more than that of the conventional product A. In addition, it can be seen that in the case of a relatively small diameter, compared with the conventional product B, the product of the present invention can increase the ejection volume.

[0104] As described above, the drill bit 1 of the present embodiment includes a main body 3, a shank 2, a discharge groove 4, a cutting edge 5, and an oil hole 12. The main body 3 and the shank 2 are rod-shaped and rotate about the axis AX. The discharge groove 4 is provided in a spiral shape on the outer peripheral surface 31 from the front end portion of the main body 3 toward the rear end portion of the shank 2. The cutting edge 5 is formed at the ridge line portion between the front inner surface 41 of the discharge groove 4 facing the rotation direction T of the main body 3 and the flank 6 of the front end portion. The oil hole 12 is provided in the flank 6 and supplies cutting oil to the cutting edge 5 side. The oil hole 12 has a fan-shaped cross section. The fan-shaped cross section is formed by being surrounded by a front side inner wall surface 121, a rear side inner wall surface 122, an outer peripheral side inner wall surface 123, and an inner peripheral side inner wall surface 124. The front side inner wall surface 121 is located on the front side of the rotation direction T along the radial direction. The rear side inner wall surface 122 is located on the rear side of the rotation direction T along the radial direction and is circumferentially opposite to the front side inner wall surface 121. The outer peripheral side inner wall surface 123 includes a partial cylindrical surface centered on the axis AX. The inner peripheral side inner wall surface 124 includes a partial cylindrical surface centered on the axis AX and having a curvature radius smaller than that of the outer peripheral side inner wall surface 123, and is radially opposite to the outer peripheral side inner wall surface 123. The rear side inner wall surface 122 of the oil hole 12 is curved in an arc shape toward the front of the rotation direction T.

[0105] The drill bit 1 includes the oil hole 12 having a fan-shaped cross section. Therefore, the jetting performance of the cutting oil is higher than that of a circular hole. Moreover, since the rear side inner wall surface 122 of the oil hole 12 of the drill bit 1 is curved in an arc shape toward the front of the rotation direction T, a wide distance can be ensured between the ridge line portion of the flank 6 and the rear side inner wall surface 122. In addition, the ridge line portion of the flank 6 refers to the ridge line portion between the inner surface 42 of the discharge groove 4 facing the rear of the rotation direction T of the main body 3 and the flank 6. Thus, the drill bit 1 can suppress the stress applied to the portion between the ridge line portion and the oil hole 12. Therefore, the jetting performance of the cutting oil can be improved, and the tool stiffness can be ensured. Since the tool stiffness is improved, the drill bit 1 can also be used for high-feed machining. High-feed machining refers to machining in which the tool is moved at high speed. The drill bit 1 is also effective for relatively thick sizes with large cutting resistance.

[0106] The drill bit 1 further includes a recessed portion 8. The ridge line between the recessed portion 8 and the flank 6 extends in an arc shape from the inner end of the cutting edge 5 toward the radial outside and is connected to the discharge groove 4. The rear side inner wall surface 122 is curved in an arc shape toward the same direction side as the recessed portion 8 at a position away from the recessed portion 8. Although the drill bit 1 includes the arc-shaped recessed portion 8, by curving the rear side inner wall surface 122 of the oil hole 12 toward the same direction side as the recessed portion 8, a wide distance can be ensured equally between the ridge line portion of the flank 6.

[0107] In addition, the present invention is not limited to the above-described embodiments and can be variously modified. The drill bit 1 has two cutting edges, but it can also have three cutting edges or more than three cutting edges. For example, Figure 16 the drill bit 100 shown has three cutting edges. The drill bit 100 basically has the shape of the drill bit 1 of the above-described embodiment, and includes three discharge grooves 40, three cutting edges 50, three grinding edges 70, three recessed portions 80, three flank faces 60, three oil holes 120, etc., but detailed description thereof will not be given here. The oil hole 120 has the same fan-shaped cross section as that of the above-described embodiment, and the inner wall surface on the rear side is curved in an arc shape toward the rotation direction T side that is the same as the first ridge line 811 of the recessed portion 8. Thus, the drill bit 100 can also obtain the same effects as the drill bit 1 with two cutting edges.

[0108] The oil hole 12 spirally extends from the rear end portion of the shank 2 toward the front end portion of the main body 3, but it can also not be spiral, for example, it can be linear. Three arc grooves 10 are provided at the front end portion of the main body 3, but the arc grooves 10 can also be omitted. The drill bit 1 is a long drill bit, but it can also be a general drill bit. The material of the drill bit 1 is not limited. DLC is covered on at least the surface of the front end portion of the main body 3, but DLC can also be covered on the outer peripheral surface 31. DLC can also not be covered on the main body 3. The grinding edge 7 can also not be formed. The recessed portion 8 is arc-shaped, but it can also be linear. The grinding edge 7 and the recessed portion 8 can also be omitted. In the fan-shaped cross section of the oil hole 12, the inner wall surface 121 on the front side is linear, but it can also not be linear.

Claims

1. A drill bit (1), characterized in that the drill bit (1) comprises: a rod-shaped tool body (2, 3) that rotates about an axis (AX); a discharge groove (4) that is spirally provided on the outer peripheral surface (31) from the front end portion to the rear end portion of the tool body; a cutting edge (5) formed at the ridge line portion between the inner surface (41) of the discharge groove facing the front in the rotation direction (T) of the tool body and the flank (6) of the front end portion; an oil hole (12) provided in the flank (6) to supply cutting oil to the cutting edge (5) side; and a recessed portion (8), the ridge line between it and the flank (6) extends radially outward from the inner end of the cutting edge (5) and is curved in an arc shape toward the front in the rotation direction (T), and is connected to the discharge groove (4), the oil hole (12) has a fan-shaped cross-section surrounded by a front-side inner wall surface (121), a rear-side inner wall surface (122), an outer peripheral-side inner wall surface (123), and an inner peripheral-side inner wall surface (124), the front-side inner wall surface (121) is located on the front side in the rotation direction (T) of the tool body (2, 3), the rear-side inner wall surface (122) is located on the rear side in the rotation direction (T) of the tool body (2, 3) and is circumferentially opposite to the front-side inner wall surface (121), the outer peripheral-side inner wall surface (123) includes a partial cylindrical surface centered on the center line of the tool body (2, 3) and having a curvature radius corresponding to the radius of the circumscribed circle of the oil hole (12), the inner peripheral-side inner wall surface (124) includes a partial cylindrical surface centered on the center line of the tool body (2, 3) and having a curvature radius corresponding to the radius of the inscribed circle of the oil hole (12) and a curvature radius smaller than that of the outer peripheral-side inner wall surface (123), and is radially opposite to the outer peripheral-side inner wall surface (123), In the flank (6), a reference line extending radially outward from the axis (AX) of the tool body (2, 3) is set as the first reference line, a reference line rotated forward by a first angle in the rotation direction (T) about the axis (AX) relative to the first reference line is set as the second reference line, a reference line rotated backward by the first angle in the rotation direction (T) about the axis (AX) relative to the first reference line is set as the third reference line, and a reference line rotated backward by a second angle larger than the first angle in the rotation direction (T) about the intersection of the inscribed circle and the first reference line relative to the first reference line and opposite to the recessed portion (8) is set as the fourth reference line. In this case, the oil hole (12) is provided between the second reference line and the third reference line, the front-side inner wall surface (121) is arranged to be along the second reference line, The rear inner wall surface (122) is disposed on the fourth reference line, and is curved in an arc shape in a direction toward the front in the rotation direction (T) at a position away from the recess (8) and in a direction substantially the same as the bending direction of the ridge line between the recess (8) and the flank (6).

2. The drill bit (1) according to claim 1, wherein the radius of curvature of the rear inner wall surface (122) in the cross section is 0.35D or more and 0.45D or less, where D is the diameter of the drill bit.

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