A drill bit with variable core diameter

Abstract

The present invention discloses a drill bit with a variable core diameter, which comprises a shank portion and a cutting portion. The cutting portion includes at least two spiral grooves extending from the drill tip to the shank portion and evenly distributed circumferentially, cutting lips having the same number as the spiral grooves and located between adjacent spiral grooves, and cylindrical guiding lands disposed on the cutting lips and close to the spiral grooves. The core diameter of the core portion of the cutting portion gradually changes along the axial direction of the drill bit with a variable core diameter. The core portion includes a connected forward taper section and a reverse taper section. The axial length of the forward taper section is less than that of the reverse taper section. The forward taper section starts from the drill tip. Along the direction from the drill tip to the shank portion, the core diameter of the forward taper section gradually increases, and the closer to the drill tip, the smaller the value of the core diameter change rate. The reverse taper section starts from the end of the forward taper section and ends at the tool lift position of the spiral groove tail. The core diameter of the reverse taper section gradually decreases, and the core diameter change rate is constant. The present invention has the advantages of ensuring its own stiffness, reducing the cutting force, and improving the chip evacuation performance, etc.

Description

Technical Field

[0001] The present invention mainly relates to the field of metal cutting, and particularly relates to a drill bit with a variable core diameter. Background Art

[0002] Due to its high hardness and good red hardness, cemented carbide materials are widely used in metal cutting tools. During the cutting process of hole machining with a drill bit, the drill bit is in a semi-surrounded state, and chips are not easily discharged, and cutting heat is not easily dissipated, and the application working conditions are very harsh. To improve the service life of the drill bit, when designing and optimizing the drill bit structure, key considerations are to improve the rigidity of the drill body and the chip removal performance to ensure drilling stability, and to improve the sharpness of the cutting edge to reduce its cutting force and torque.

[0003] To improve the chip removal performance of the drill bit, the core structure of the drill bit is usually optimized. For example, Chinese patent document CN204277009U discloses a high-speed steel twist drill. The core of this twist drill is a sudden increase type structure, that is, the core contains a first cone part and a second cone part. The taper of the second cone part is significantly greater than that of the second cone part. The first taper angle is 22.62° - 24.12°, and the second taper angle is 1.15° - 2.65°. The core thickness at the drill tip is very small, only 0.137 - 0.548 mm. This structural design can, on the one hand, avoid grinding the chisel edge and improve the cutting speed and service life; on the other hand, it is beneficial to improve the chip removal performance; however, the core diameter of the first cone part of the core of this structural drill bit is very small, which will greatly reduce the strength of the center part of the drill tip. Therefore, this structure is only suitable for high-speed steel drill bits with good strength, and may even have a negative effect on brittle cemented carbide drill bits; at the same time, the second cone part is also an increasing type structure, which also means that when the chip discharges from the drill tip to the end of the spiral groove, the chip-containing space of the spiral groove becomes smaller and smaller, which is not conducive to chip discharge.

[0004] In terms of reducing the cutting force through drill bit structure design, in the prior art, usually the rake angle of the cutting edge is increased and the clearance angle is reduced to improve the sharpness of the cutting edge, or the chisel edge is ground to shorten the chisel edge length. However, due to the poorer toughness of cemented carbide materials than high-speed steel, to ensure the rigidity and strength of the cemented carbide drill bit, when designing the spiral groove of the drill bit, the core diameter value is larger than that of the high-speed steel drill bit. The ratio of the core diameter to the cutting edge diameter of the drill bit is usually about 0.3, resulting in a large offset of the cutting edge of the finally designed drill bit and a small radial rake angle of the main cutting edge. Even in most positions, the radial rake angle is negative, resulting in an increase in cutting force. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a drill bit with a variable core diameter that can not only ensure its own stiffness, but also reduce the cutting force and improve the chip removal performance.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A variable core diameter drill bit, comprising a shank and a cutting part, wherein the cutting part includes at least two spiral grooves extending from the drill tip to the shank and evenly distributed circumferentially, cutting lips having the same number as the spiral grooves and located between adjacent spiral grooves, and cylindrical guiding cutting edges disposed on the cutting lips close to the spiral grooves. The core diameter of the core part of the cutting part gradually changes along the axial direction of the variable core diameter drill bit. The core part includes a connected forward taper section and a reverse taper section. The axial length of the forward taper section is less than that of the reverse taper section. The forward taper section starts from the drill tip and along the direction from the drill tip to the shank, the core diameter of the forward taper section gradually increases, and the closer to the drill tip, the smaller the value of the core diameter change rate of the forward taper section. The reverse taper section starts from the end of the forward taper section and ends at the tool lift position at the end of the spiral groove. The core diameter of the reverse taper section gradually decreases, and the core diameter change rate is constant.

[0008] As a further improvement of the above technical solution:

[0009] On the axial section of the variable core diameter drill bit, the forward taper contour line of the forward taper section is in the shape of a concave curve. The length of the forward taper section is L, and the cutting edge diameter of the drill tip is D, and it should satisfy: L = D.

[0010] The core diameter at the starting end of the forward taper section is W0, and it should satisfy: 0.18D ≤ W0 ≤ 0.25D.

[0011] The core diameter at the end of the forward taper section is Wt, and it should satisfy: 0.28D ≤ Wt ≤ 0.35D.

[0012] The core diameter of the forward taper section at a distance L1 from the left end face of the drill tip is W1, and it should satisfy: W1 = W0 + (L1 / D) δ × (Wt - W0), where 1.2 ≤ δ ≤ 2.

[0013] On the axial section of the variable core diameter drill bit, the reverse taper contour line of the reverse taper section is a straight line. The change rate of the core diameter per unit length of the reverse taper section is t, and it should satisfy: 0 ≤ t ≤ 0.005.

[0014] The core diameter of the reverse taper section at a distance L2 from the left end face of the drill tip is W2, and it should satisfy: W2 = Wt - (L2 - L) × t.

[0015] The offset of the main cutting edge on the drill tip is e, and it should satisfy: 0.06D ≤ e ≤ 0.1D.

[0016] The material of the variable core diameter drill bit is cemented carbide.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] The core diameter of the core part of the cutting part of the variable core diameter drill bit of the present invention gradually changes along the axial direction of the variable core diameter drill bit. The core part includes a connected forward taper section and a reverse taper section. The axial length of the forward taper section is less than the axial length of the reverse taper section. The forward taper section starts from the drill tip and along the direction from the drill tip to the shank, the core diameter of the forward taper section gradually increases. And the closer to the drill tip, the smaller the value of the core diameter change rate of the forward taper section. The reverse taper section starts from the end of the forward taper section and ends at the tool lift position of the spiral groove tail. The core diameter of the reverse taper section gradually decreases, and the core diameter change rate is constant. The core diameter of the forward taper section takes a smaller value at the drill tip, which not only reduces the grinding amount of the web grinding, but also forms a small outer edge offset after grinding the web, and a smaller radial rake angle can be obtained, which is beneficial to reducing the cutting force during drilling and reducing machining vibration. The closer to the drill tip, the smaller the value of the core diameter change rate of the forward taper section, that is, the smoother the outer contour line of the forward taper section. In this way, it is ensured that the core diameter remains small within a relatively small axial distance of the drill tip. On the one hand, it is beneficial to design a smaller cutting edge offset, on the other hand, it can reduce the web grinding amount and is also beneficial to drill tip regrinding. The core diameter of the reverse taper section is larger, which ensures the overall rigidity of the drill bit. And the closer to the shank, the smaller the core diameter, that is, the larger the chip space provided by the drill bit during the chip discharge process, and the chips are easier to discharge, avoiding chip jamming leading to tool breakage. The core diameter change rate of the reverse taper section is constant, ensuring that the core diameter of the reverse taper section decreases linearly, and the core diameter at the end can be controlled not to be too small to cause insufficient rigidity, and the linearly changing core diameter reduces the processing difficulty of the reverse taper section. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the front view of Embodiment 1 of the variable core diameter drill bit of the present invention.

[0020] Figure 2 is Figure 1 the A-A cross-sectional view of

[0021] Figure 3 is Figure 1 the B-B cross-sectional view of

[0022] Figure 4 is Figure 1 the C-C cross-sectional view of

[0023] Figure 5 is the left view of Embodiment 1 of the variable core diameter drill bit of the present invention.

[0024] Figure 6 is the schematic diagram of the radial rake angle of the main cutting edge of Embodiment 1 of the variable core diameter drill bit of the present invention.

[0025] Figure 7 is the front view of Embodiment 2 of the variable core diameter drill bit of the present invention.

[0026] Figure 8 is the left view of Embodiment 2 of the variable core diameter drill bit of the present invention.

[0027] The reference numerals in the figure denote the following:

[0028] 1. Shank; 2. Cutting part; 21. Tapered section in the forward direction; 22. Tapered section in the reverse direction; 3. Drill tip; 31. Main cutting edge; 4. Helical flute; 5. Flute margin; 6. Cylindrical guiding land; 7. Core; 8. Forward tapered contour line; 9. Reverse tapered contour line; 10. Rake face of inner edge; 11. First flank; 12a. Main cutting edge; 12b. Inner edge; 12c. Chisel edge. Detailed implementation mode

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0030] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "horizontal", "inner", "outer", "top", "bottom", etc. indicating the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0031] Embodiment 1

[0032] As Figures 1 to 6As shown in the figure, the variable core diameter drill bit of this embodiment is made of cemented carbide and includes a shank 1 and a cutting part 2. The cutting part 2 includes two spiral grooves 4 extending from the drill tip 3 to the shank 1 and evenly distributed in the circumferential direction, two blade lips 5 respectively located between adjacent spiral grooves 4, and cylindrical guiding cutting edges 6 disposed on the blade lips 5 close to the spiral grooves 4. The core diameter of the core part 7 of the cutting part 2 gradually changes along the axial direction of the variable core diameter drill bit. The core part 7 includes a connected forward taper section 21 and a reverse taper section 22. The axial length of the forward taper section 21 is less than that of the reverse taper section 22. The forward taper section 21 starts from the drill tip 3. Along the direction from the drill tip 3 to the shank 1, the core diameter of the forward taper section 21 gradually increases, and the closer to the drill tip 3, the smaller the value of the core diameter change rate of the forward taper section 21. The reverse taper section 22 starts from the end of the forward taper section 21 and ends at the tool lift position at the end of the spiral groove 4. The core diameter of the reverse taper section 22 gradually increases, and the core diameter change rate is constant. The core diameter of the forward taper section 21 has a relatively small value at the drill tip 3, which not only reduces the grinding amount of the chisel edge grinding, but also has a small outer edge offset formed after grinding the chisel edge, and a smaller radial rake angle can be obtained, which is beneficial to reducing the cutting force during drilling and reducing machining vibration; the closer to the drill tip 3, the smaller the value of the core diameter change rate of the forward taper section 21, that is, the smoother the outer contour line of the forward taper section 21. In this way, it is ensured that the core diameter of the drill tip 3 remains relatively small within a relatively short axial distance. On the one hand, it is beneficial to design a smaller cutting edge offset, on the other hand, it can reduce the chisel edge grinding amount, and it is also beneficial to the regrinding of the drill tip 3; the core diameter of the reverse taper section 22 is relatively large, which ensures the overall rigidity of the drill bit, and the closer to the shank 1, the smaller the core diameter, that is, the larger the chip space provided by the drill bit during the chip discharge process, and the chips are more easily discharged, avoiding chip jamming resulting in tool breakage. The core diameter change rate of the reverse taper section 22 is constant, ensuring that the core diameter of the reverse taper section 22 decreases linearly, which can control the core diameter at the end from being too small and resulting in insufficient rigidity, and the linearly changing core diameter reduces the processing difficulty of the reverse taper section 22.

[0033] In this embodiment, on the axial section of the variable core diameter drill bit, the forward taper contour line 8 of the forward taper section 21 is in the shape of an inward concave curve. The length of the forward taper section 21 is L, and the cutting edge diameter of the drill tip 3 is D. The length of the forward taper section 21 cannot be set too long, otherwise the relatively small core diameter structure of the forward taper section 21 will reduce the overall rigidity and strength of the variable core diameter drill bit. Therefore, it should satisfy: L = D. In this embodiment, D = L = 6 mm.

[0034] In this embodiment, the core diameter at the starting end of the forward taper section 21 is W0. Cemented carbide drill bits usually need to grind the chisel edge 12c to reduce the cutting force by reducing the length of the chisel edge 12c. Grinding the chisel edge 12c forms the inner edge rake face 10, which intersects with the first flank 11 to form the inner edge 12b. The intersection point P of the inner edge 12b and the main cutting edge 12a is the inner edge corner. From Figure 5It can be seen that the offset e is greatly affected by the core diameter. The larger the core diameter, the greater the distance from point P to the center of the drill bit, and the larger the offset e will be. e should satisfy: 0.06D ≤ e ≤ 0.1D. Therefore, to design a drill bit with a small-offset cutting edge, the core diameter W0 at the drill tip 3 must be designed to be a smaller value, which should satisfy: 0.18D ≤ W0 ≤ 0.25D. In this embodiment, e = 0.08D = 0.48 mm, and W0 = 0.2D = 1.2 mm.

[0035] As Figure 6 shown, at any point M on the main cutting edge 12a, the tangent of the main cutting edge 12a is Q. According to the definition of the rake angle of the tool, the rake angle of the main cutting edge 12a at point M is the angle γ between the tangent Q and the line connecting point M to the center of the drill bit. Since the tangent Q is on the right side of the line, the rake angle at point M is a negative rake angle. Obviously, the smaller the value of the offset e, the smaller the absolute value of γ, that is, the larger the actual working rake angle of the main cutting edge 12a. Therefore, the cutting edge sharpness can be improved by reducing the offset e, thereby reducing the cutting force of the variable-core-diameter drill bit. In this embodiment, the rake angle γ at point M is -14°.

[0036] In this embodiment, the core diameter at the end of the taper section 21 is Wt. Since the taper section 21 with a small core diameter is short, while the back taper section 22 is very long and the core diameter change rate is constant, Wt directly determines the overall strength and rigidity of the variable-core-diameter drill bit. To balance the chip evacuation performance and rigidity of the variable-core-diameter drill bit, it should satisfy: 0.28D ≤ Wt ≤ 0.35D. In this embodiment, Wt = 0.35D = 2.1 mm.

[0037] In this embodiment, the core diameter of the taper section 21 at a distance L1 from the left end face of the drill tip 3 is W1, and it should satisfy: W1 = W0 + (L1 / D)δ×(Wt - W0), where 1.2 ≤ δ ≤ 2. When the variable-core-diameter drill bit is used to machine sticky materials that are difficult to break chips, a smaller core diameter design is beneficial for chip breaking and chip evacuation, and at this time, δ is taken as a larger value; when the drill bit is used to machine materials with a greater hardness, a larger core diameter is designed to ensure the strength of the drill tip, and at this time, δ is taken as a smaller value. In this embodiment, the drill bit is used to machine ordinary steel, δ = 1.7, L1 = 2 mm, and W1 = 1.339 mm.

[0038] In this embodiment, on the axial section of the variable core diameter drill bit, the reverse taper contour line 9 of the reverse taper section 22 is a straight line. Considering the semi-closed machining condition of the variable core diameter drill bit, to improve the chip evacuation performance, the core diameter of the reverse taper section 22 is set such that the closer it is to the drill tip 3, the larger the core diameter, and the closer it is to the tool lift position at the end of the spiral groove 4, the smaller the core diameter. This means that during the chip evacuation process, the chip accommodation space provided by the spiral groove 4 of the drill bit gradually increases, which is beneficial for chip evacuation. Of course, the core diameter change rate per unit length of the reverse taper section 22 cannot be too large. Otherwise, if the length of the spiral groove 4 is relatively long, the core diameter at the end of the spiral groove will be very small, and this is often the stress concentration area of the drill bit, increasing the risk of drill bit breakage. Therefore, the core diameter change rate per unit length of the reverse taper section 22 is set as t, and t satisfies: 0 ≤ t ≤ 0.005. In this embodiment, t = 0.004.

[0039] In this embodiment, the core diameter of the reverse taper section 22 at a distance L2 from the left end face of the drill tip 3 is W2, and it should satisfy: W2 = Wt - (L2 - L) × t. In this embodiment, L2 = 15 mm and W2 = 2.064 mm.

[0040] Embodiment 2

[0041] As Figure 7 and 8 shown, this embodiment is basically the same as Embodiment 1, with the only difference being that: this embodiment is a three-flute twist drill, and the number of spiral grooves 4, cutting lips 5, and cylindrical guiding lands 6 are all set to 3.

[0042] This embodiment is applicable to the working conditions with relatively high requirements for the diameter of the machined hole or high requirements for cutting efficiency. The three-flute twist drill has better guiding performance and more cutting edges. In this embodiment, the respective design parameters are D = 6 mm, Wt = 2.0 mm, δ = 1.5, t = 0, L = 6 mm, L1 = 2 mm, L2 = 15 mm, W0 = 1.2 mm, W1 = 1.392 mm, and W2 = 2.0 mm.

[0043] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the above-disclosed technical content without departing from the scope of the technical solution of the present invention, or modify it into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A variable core diameter drill bit, comprising a shank portion (1) and a cutting portion (2), wherein the cutting portion (2) includes at least two spiral grooves (4) extending from the drill tip (3) to the shank portion (1) and evenly distributed circumferentially, cutting lips (5) having the same number as the spiral grooves (4) and located between adjacent spiral grooves (4), and cylindrical guide cutting edges (6) disposed on the cutting lips (5) close to the spiral grooves (4), characterized in that: The core diameter of the core (7) of the cutting part (2) gradually changes along the axial direction of the variable-core drill bit. The core (7) includes a connected forward taper section (21) and a reverse taper section (22). The axial length of the forward taper section (21) is less than that of the reverse taper section (22). The forward taper section (21) starts from the drill tip (3) and along the direction from the drill tip (3) to the shank (1), the core diameter of the forward taper section (21) gradually increases, and the closer to the drill tip (3), the smaller the value of the core diameter change rate of the forward taper section (21). The reverse taper section (22) starts from the end of the forward taper section (21) and ends at the tool lift position at the end of the spiral groove (4). The core diameter of the reverse taper section (22) gradually decreases, and the core diameter change rate is constant.

2. The variable core diameter drill bit according to claim 1, wherein: On the axial section of the variable-core drill bit, the forward taper contour line (8) of the forward taper section (21) is in a concave curve shape. The length of the forward taper section (21) is L, and the cutting edge diameter of the drill tip (3) is D, and it should satisfy: L = D.

3. The variable core diameter drill bit according to claim 2, characterized in that: The core diameter at the starting end of the forward taper section (21) is W0, and it should satisfy: 0.18D ≤ W0 ≤ 0.25D.

4. The variable core diameter drill bit according to claim 3, wherein: The core diameter at the end of the forward taper section (21) is Wt, and it should satisfy: 0.28D ≤ Wt ≤ 0.35D.

5. The variable core diameter drill bit according to claim 4, characterized in that: The core diameter of the tapered section (21) at a distance L1 from the left end face of the drill tip (3) is W1, and it should satisfy: W1 = W0 + (L1 / D) δ × (Wt - W0), where 1.2 ≤ δ ≤ 2.

6. The variable core diameter drill bit according to claim 1, characterized in that: On the axial section of the variable-core drill bit, the reverse taper contour line (9) of the reverse taper section (22) is a straight line. The change rate of the core diameter per unit length of the reverse taper section (22) is t, and it should satisfy: 0 ≤ t ≤ 0.

005.

7. The variable core diameter drill bit according to claim 6, characterized in that: The core diameter of the reverse taper section (22) at a distance L2 from the left end face of the drill tip (3) is W2, and it should satisfy: W2 = Wt - (L2 - L) × t.

8. The variable core diameter drill bit according to any one of claims 2 to 7, characterized in that: The offset of the main cutting edge (12a) on the drill tip (3) is e, and it should satisfy: 0.06D ≤ e ≤ 0.1D.

9. The variable core diameter drill bit according to any one of claims 1 to 7, characterized in that: The material of the variable-core drill bit is cemented carbide.

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