Variable back angle ball end mill and grinding method thereof

Abstract

The present invention provides a variable clearance angle ball nose end mill and a grinding method thereof, belonging to the field of metal cutting processing; the variable clearance angle ball nose end mill comprises a shank and a cutting portion, wherein the cutting portion has at least one set of chip grooves and back cutting surfaces symmetrically arranged on the circumference from the top of the ball nose to the junction with the shank; the first back cutting surface of the back cutting surface intersects with the chip groove, and a spiral edge and a ball nose edge are sequentially formed on the intersecting ridge line; the two opposite first back cutting surfaces intersect at the top of the ball nose to form a concave chisel edge; the back angle of the first back cutting surface changes linearly between the center of the chisel edge and the intersection of the ball nose edge and the spiral edge, that is, gradually decreases from the intersection of the ball nose edge and the spiral edge to the center of the chisel edge; and remains constant at any position on the spiral edge. The present invention provides a ball nose end mill structural solution that reduces the concave depth of the chisel edge, improves the contour of the ball nose center, thereby improving the surface finish of the workpiece being processed, and enhancing the strength and wear resistance of the chisel edge.

Description

Technical Field

[0001] The invention belongs to the field of metal cutting and processing, and particularly relates to a variable clearance angle ball end mill and a grinding method thereof. Background Art

[0002] Ball-nose end mills are primarily used for surface profiling and are widely used in machining, particularly in the mold and die industry. To enhance mold wear resistance, a high surface finish is typically required. This places demands on ball-nose end mills for both high wear resistance and low surface roughness. During profiling, the cutting edge at the center of the ball-nose end mill primarily performs the cutting action. Because the tool's cutting edge profile is "copied" to a certain extent onto the surface being machined, the profile of the center edge significantly influences the surface roughness of the profiling process.

[0003] However, when designing a ball-end mill, the cutting edge offset and chisel edge length are usually set to improve the cutting edge strength and profile at the center of the ball head. This causes the chisel edge center point to be lower than the ideal ball head edge profile during the complex ball head edge forming motion, forming an inward-concave chisel edge and reducing the profile of the ball head end mill. Therefore, by optimizing the design parameters of the center cutting edge of the ball head end mill, the height difference between the chisel edge center and the ideal cutting edge profile can be reduced, and the residual height of the machined surface material can be reduced to improve the surface finish of the machined surface.

[0004] The prior art discloses a chisel blade optimization structure at the center of a ball-end end mill. This structure uses a grinding wheel to grind a small plane at the center of the ball head, which can reduce or eliminate the concave depth of the chisel blade, thereby improving the surface processing quality. Although this invention can improve the surface processing quality and enhance the wear resistance of the chisel blade, the width of the small plane at the chisel blade is difficult to control, and the requirements for the grinding wheel and machine tool are relatively high. Moreover, the newly added small plane makes the back angle at the center of the ball head 0, which will increase the friction between the ball head chisel blade and the workpiece in actual processing, and may aggravate the wear of the tool center. In addition, the manufacture of the ball-end end mill with this structure requires an additional process for grinding the small plane at the chisel blade, which increases the production and grinding costs of the tool. Summary of the Invention

[0005] Technical issues to be solved:

[0006] In order to avoid the shortcomings of the prior art, the present invention provides a variable clearance angle ball nose end mill and its grinding, which combines a gradual first clearance angle of the flank face and a constant first clearance angle of the flank face, and limits the rate of change of the clearance angle of the gradual part so that the clearance angle becomes smaller as it is closer to the center of the transverse edge, thereby reducing the concave depth of the transverse edge and improving the center profile of the ball nose, thereby improving the smoothness of the machined surface of the workpiece and enhancing the strength and wear resistance of the transverse edge.

[0007] The technical solution of the present invention is: a variable clearance angle ball nose end mill, comprising a shank 2 and a cutting portion 1, wherein the cutting portion 1 is symmetrically provided with at least one set of chip grooves 4 and flank faces 5 on the circumference from the top of the ball nose to the junction with the shank 2; a first flank face 51 of the flank face 5 intersects with the chip groove 4, and a spiral edge 6 and a ball nose edge 7 are sequentially formed on the intersecting ridge line; two opposing first flank faces 51 intersect at the top of the ball nose to form a concave chisel edge 8;

[0008] The back angle of the first back cutting edge 51 changes linearly between the center of the chisel edge 8 and the intersection of the ball-end edge 7 and the spiral edge 6, that is, it gradually decreases from the intersection of the ball-end edge 7 and the spiral edge 6 to the center of the chisel edge 8; and remains constant at any position on the spiral edge 6.

[0009] A further technical solution of the present invention is: the clearance angle of the first flank 51 is α, Wherein, α1 is the clearance angle of the first clearance face 51 located at the center of the chisel edge 8, δ is the rate of change of the clearance angle of the first clearance face 51 on the ball-end edge 7 and the chisel edge 8, It is the centripetal angle between the ball end and the chisel edge.

[0010] A further technical solution of the present invention is as follows: at the center position of the chisel edge 8, the back angle of the first back cutting edge 51 is α1; at the intersection position of the ball-end edge 7 and the spiral edge 6, the back angle of the first back cutting edge 51 is α2; at any position on the spiral edge 6, the back angle of the first back cutting edge 51 is constant at α2; and α1 and α2 satisfy: 2°≤α1≤5°, 7°≤α2≤25°.

[0011] A further technical solution of the present invention is that the rate of change of the back angle on the ball-end cutting edge 7 and the chisel cutting edge 8 is δ, δ=(α2-α1) / 90°, and δ satisfies: 0.06≤δ≤0.22.

[0012] A further technical solution of the present invention is: When α=α1; when , α=α2.

[0013] A further technical solution of the present invention is that the ideal contour radius of the ball-end cutting edge 7 is r0, the offset distance of the ball-end cutting edge 7 at the top of the ball head is p, and p satisfies: 0.01*r0≤p≤0.06*r0.

[0014] A further technical solution of the present invention is that the radial cross section of the chisel edge at the top end of the ball head is "S" shaped, and the axial cross section thereof is concave.

[0015] A further technical solution of the present invention is: the horizontal length of the chisel edge in the axial section is l, and l satisfies p≤l≤4*p.

[0016] A further technical solution of the present invention is that: the chisel edge is in the axial section, and its concave center is aligned with the ideal wheel of the ball head.

[0017]

[0018] A method for grinding a variable clearance angle ball nose end mill comprises the following steps: first, grinding a first clearance face 51 of the ball nose with a grinding wheel, with the grinding point moving along a spiral edge 6 and a ball nose edge 7 from the tail of a chip groove 4 toward a cutting end 3 of the ball nose; simultaneously, adjusting the grinding wheel grinding posture according to the clearance angle variation pattern of the first clearance face 51 to obtain a gradually varying clearance angle; then, after passing the center of the ball nose, the grinding wheel continues to move a set distance in a direction tangential to the ball nose edge 7 and then exits, finally obtaining a chisel edge 8.

[0019] Beneficial effects

[0020] The beneficial effects of the present invention are as follows: the variable clearance angle ball end mill of the present invention has a concave chisel edge; the clearance angle of the first clearance surface changes linearly from the center of the chisel edge to the intersection of the ball end edge and the spiral edge on the cutting edge, and the closer to the center of the chisel edge, the smaller the clearance angle. This structure can reduce the concave depth at the center of the chisel edge, improve the contour accuracy of the cutting edge, and thereby improve the smoothness of the machined surface, and can also increase the strength of the chisel edge, making the chisel edge more wear-resistant and increasing the service life of the ball end mill.

[0021] Experimental results show that when r0 = 5mm, p = 0.1mm, α1 = 3°, and α2 = 9°, the maximum profile deviation h is only 0.003mm, and the maximum residual height of the machined surface material is reduced to 0.12μm. Since the maximum residual height of the material is closely related to surface finish, the variable clearance angle structure can significantly improve the surface finish while maintaining machining accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the present invention.

[0023] Figure 2 It is a side view of the cutting end of the ball head of the present invention.

[0024] Figure 3 It is an end view of the cutting end of the ball head of the present invention.

[0025] Figure 4 It is a simplified outline of the chisel edge of the present invention projected in a side view.

[0026] Figure 5 It is a schematic diagram of the residual height of the processed surface during processing according to the present invention.

[0027] Explanation of the accompanying symbols: 1. Cutting part; 2. Shank; 3. Ball-end cutting end; 4. Chip groove; 5. Flank surface; 51. First flank surface; 52. Second flank surface; 6. Spiral edge; 7. Ball-end edge; 8. Chisel edge; 9. Ball-end edge rake surface; 10. Ideal contour line of the ball end. DETAILED DESCRIPTION

[0028] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0029] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are 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 understood as limiting the present invention.

[0030] This embodiment provides a variable clearance angle ball nose end mill, which combines a gradually changing first clearance angle with a constant first clearance angle, and limits the rate of change of the clearance angle of the gradually changing portion so that the clearance angle decreases closer to the center of the chisel edge, thereby reducing the concave depth of the chisel edge and improving the center profile of the ball nose, thereby improving the surface finish of the workpiece being machined and enhancing the strength and wear resistance of the chisel edge. The ball nose end mill structure is specifically as follows:

[0031] This embodiment provides a variable clearance angle ball nose end mill, comprising a shank 2 and a cutting portion 1. The cutting portion 1 is symmetrically provided with at least one set of chip grooves 4 and flank faces 5 on its circumferential surface from the top of the ball nose to the junction with the shank 2. A first flank face 51 of the flank face 5 intersects with the chip groove 4, with a spiral edge 6 and a ball nose edge 7 being sequentially formed on the intersecting ridge line. The two opposing first flank faces 51 intersect at the top of the ball nose to form an inwardly concave chisel edge 8.

[0032] The back angle of the first back cutting edge 51 changes linearly between the center of the chisel edge 8 and the intersection of the ball-end edge 7 and the spiral edge 6, that is, it gradually decreases from the intersection of the ball-end edge 7 and the spiral edge 6 to the center of the chisel edge 8; and remains constant at any position on the spiral edge 6.

[0033] The clearance angle of the first flank surface 51 is α, Wherein, α1 is the clearance angle of the first clearance face 51 located at the center of the chisel edge 8, δ is the rate of change of the clearance angle of the first clearance face 51 on the ball-end edge 7 and the chisel edge 8, It is the centripetal angle on the ball end and the chisel edge.

[0034] The variable clearance angle ball end mill of this embodiment has a concave chisel edge 8; on the cutting edge 3, from the center of the chisel edge 8 to the intersection of the ball end edge and the spiral edge, the clearance angle of the first clearance surface changes linearly, and the closer to the center of the chisel edge, the smaller the clearance angle. This structure can reduce the concave depth at the center of the chisel edge, improve the contour accuracy of the cutting edge, and thus improve the smoothness of the machined surface. It can also increase the strength of the chisel edge, make the chisel edge more wear-resistant, and increase the service life of the ball end mill.

[0035] Example:

[0036] like Figure 1 As shown, the variable rake angle ball end mill of this embodiment includes a shank 2 and a cutting part 1, and at least one group of chip grooves 4 and flank faces 5 extending from the shank 2 to the ball cutting end 3 are symmetrically arranged on the cutting part 1, and the flank face 5 intersects with the chip groove 4; the flank face 5 includes a first flank face 51 and a second flank face 52, and a spiral edge 6 and a ball-end edge 7 are formed in sequence on the ridge line where the first flank face 51 intersects with the chip groove 4, and a transverse edge 8 is formed at the intersection of the two opposite first flank faces 51, and the transverse edge 8 is concave; the rake angle of the first flank face 51 on the cutting edge changes linearly from the center of the transverse edge 8 to the intersection of the ball-end edge 7 and the spiral edge 6, and the closer to the center of the transverse edge 8, the smaller the rake angle; the rake angle of the first flank face 51 at any position on the spiral edge 6 remains constant.

[0037] like Figure 2 As shown, in this embodiment, the back angle of the first back cutting surface 51 is α, Wherein, α1 is the clearance angle of the first clearance face 51 located at the center of the chisel edge 8, δ is the rate of change of the clearance angle of the first clearance face 51 on the ball-end edge 7 and the chisel edge 8, It is the centripetal angle between the ball end and the chisel edge.

[0038] The rate of change of the back angle of the first flank face 51 is set to δ, then δ=(α2-α1) / 90°. It is stipulated that δ satisfies 0.06≤δ≤0.22. If δ is too small, the expected effect of the present invention cannot be achieved. If it is too large, the first back angle 51 at the spiral edge 6 will be too large, reducing the cutting edge strength. Then the centripetal angle on the ball-end edge 7 and the chisel edge 8 is At any position, if the first flank angle 51 is α, then Obviously, when When α=α1; when In this embodiment, δ=0.1, α1=3°, and α2=9°.

[0039] In this embodiment, the clearance angle of the first flank 51 is α1 at the center of the chisel edge 8. At the intersection of the ball-end cutting edge 7 and the helical cutting edge 8, the clearance angle of the first flank 51 is α2, and 2°≤α1≤5°, 7°≤α2≤25°. At any position on the helical cutting edge 6, the clearance angle of the first flank 51 is constant at α2. In other words, the clearance angle of the first flank 51 gradually decreases from the intersection of the ball-end cutting edge 7 and the helical cutting edge 6 to the center of the chisel edge 8, and then remains constant.

[0040] like Figure 3 As shown, in the end view of the ball-end cutting end 3, the offset distance of the ball-end cutting edge 7 is p. Assuming the ideal profile radius of the ball-end cutting edge 7 is r0, then p satisfies the following: 0.01*r0≤p≤0.06*r0. A larger offset distance p results in a smaller radial rake angle of the ball-end cutting edge 7, resulting in poorer sharpness. Furthermore, a larger p value results in poorer profile accuracy of the ball-end cutting edge 7. In this embodiment, r0 = 5 mm and p = 0.1 mm.

[0041] The grinding method of the ball end mill is as follows: during the production process of the ball end mill, when the grinding wheel grinds the first back cutting edge 51 of the ball end, the grinding point moves along the spiral edge 6 and the ball end cutting edge 7 from the tail of the chip groove 4 to the cutting end 3 of the ball end. At the same time, according to the back angle change law of the first back cutting edge 51, the grinding posture of the grinding wheel is adjusted to obtain a gradual back angle; and after passing the center of the ball end, it continues to move a small distance in the direction tangent to the ball end cutting edge 7 and then exits to obtain a transverse edge 8. There are two ways to exit: exiting in the current direction of movement and exiting along the axial direction of the tool. Because the ball end mill is designed to improve the cutting edge strength and contour at the center, the following is designed. Figure 3 As shown in the figure, the cutting edge offset p is used, and the chisel edge length l is limited. The grinding wheel machining movement not only forms the current ball-end edge 7, but also interferes with the opposite ball-end edge to form a chisel edge 8 when the tool is retracted along the axial direction.

[0042] like Figure 3 As shown in FIG, due to the inherent arc of the grinding wheel tip, in the end view of the ball-end cutting end 3, the chisel edge 8 is in an "S" shape. Figure 2 In the side view of the ball-end cutting edge 7 near the center of the rake face 9, the chisel edge 8 has a concave profile and a horizontal length l. l is closely related to the cutting edge offset and satisfies the following: p≤l≤3*p. In this embodiment, l=0.3 mm.

[0043] Verification example:

[0044] like Figure 2 、 3 As shown, the ideal contour radius of the ball-end milling cutter 7 is set to r0. Since the ball-end milling cutter 7 has an offset p, the radius r1 of the projection curve of the actual contour of the ball-end milling cutter 7 in the side view of the ball-end cutting end 3 is:

[0045]

[0046] The distance h between the center B of the chisel edge 8 and the highest point C of the ideal ball end contour line 10 in the tool axis, that is, the maximum contour offset h of the ball end edge 7 can be expressed as:

[0047]

[0048] because Then there is

[0049]

[0050] The distance h reflects the contour accuracy of the ball-end cutting edge 7. The larger the h value is, the worse the contour accuracy of the ball-end cutting edge 7 is. It can be seen from formula (3) that the contour accuracy of the ball-end cutting edge 7 is related to the offset p of the ball-end cutting edge 7, the back angle α of the first back cutting edge 51 and the tool ball head radius r0. The larger the offset p and the back angle α, the worse the contour accuracy; the larger the ball head radius r0, the higher the contour accuracy. The following table shows the maximum offset of the ball-end cutting edge profile corresponding to different structural parameter groups. It can be seen that if a variable back angle structure is adopted, when the back angle α of the first back cutting edge 51 is reduced from 9° to 3°, the maximum contour offset h will be significantly reduced from 0.008mm to 0.003mm; when the offset p of the ball-end cutting edge 7 is increased from 0.1mm to 0.2mm, the maximum contour offset h will increase from 0.008mm to 0.017mm. In this embodiment, r0=5mm, p=

[0051] 0.1mm, α1=3°, α2=9°.

[0052]

[0053] Since the center part of the ball end mill is used with a high probability, the surface finish of the machined surface is greatly affected by the contour shape of the cutting edge in the center part. Generally, the larger the maximum contour offset h is, the worse the surface finish of the machined surface is. According to the contour characteristics of the chisel edge 8, the projection of the chisel edge 8 in the side view is simplified to Figure 4 The outline shown, Figure 4 The distance between the middle chisel edge turning point A and the highest point C of the ideal ball head contour line 10 in the tool axis is h1, then,

[0054]

[0055] According to formula (1) and (4), we can get:

[0056]

[0057] In this embodiment, r0=5 mm, p=0.1 mm, l=0.3 mm, and h1=0.0025 mm can be obtained by calculation.

[0058] During the ball end milling process, the feed per tooth is f z Usually not greater than 0.4 mm / z, if Figure 5 As shown, the maximum residual height y of the machined surface material can be expressed as:

[0059]

[0060] In the above formula, n=[l / f z ]([] indicates rounding a number). By sorting out formulas (3), (5), and (6), we can get:

[0061]

[0062] The theoretical value of the maximum residual height of the workpiece surface material after processing with 4 sets of ball end mills with different structural parameters is calculated. The calculation results are shown in the table below. z When the chisel edge length is less than l, if the variable clearance angle structure is adopted, when the clearance angle at the center of the chisel edge 8 is reduced from 9° to 3°, the maximum residual height of the machined surface material is reduced from 1.89μm to 0.12μm; when the feed per tooth f z When the chisel edge length l is greater than the chisel edge length, if a variable clearance angle structure is used, and the clearance angle at the center of the chisel edge 8 is reduced from 9° to 3°, the maximum residual height of the machined surface material is reduced from 6.92μm to 1.62μm. Since the maximum residual height of the material is closely related to the surface finish, it can be seen that the variable clearance angle structure can greatly improve the surface finish of the machined surface.

[0063]

[0064] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A variable relief angle ball end mill, characterized by: The cutting portion (1) comprises a shank (2) and a cutting portion (1), wherein the cutting portion (1) is symmetrically provided with at least one set of chip grooves (4) and flank faces (5) on the peripheral surface from the top of the ball head to the junction with the shank (2); a first flank face (51) of the flank face (5) intersects with the chip groove (4), and a spiral edge (6) and a ball head edge (7) are sequentially formed on the intersection ridge; the two opposite first flank faces (51) intersect at the top of the ball head to form an inwardly concave chisel edge (8); The back angle of the first back cutting edge (51) varies linearly between the center of the chisel edge (8) and the intersection of the ball-end edge (7) and the spiral edge (6), that is, it gradually decreases from the intersection of the ball-end edge (7) and the spiral edge (6) to the center of the chisel edge (8); and remains constant at any position on the spiral edge (6); The back angle of the first back cutting surface (51) is α , ,in, α 1 is the back angle of the first back cutting surface (51) located at the center of the chisel edge (8), δ is the rate of change of the back angle of the first back cutting edge (51) on the ball-end cutting edge (7) and the chisel cutting edge (8), φ It is the centripetal angle on the ball end and the chisel edge.

2. The variable relief angle ball end mill according to claim 1, characterized in that: At the center of the chisel edge (8), the back angle of the first back cutting edge (51) is α 1; At the intersection of the ball-end edge (7) and the spiral edge (6), the back angle of the first back cutting edge (51) is α 2. At any position on the spiral blade (6), the back angle of the first back cutting surface (51) is constant. α 2; and α 1 and α 2 Satisfaction: , .

3. The variable relief angle ball end mill according to claim 2, characterized in that: The rate of change of the back angle on the ball-end edge (7) and the chisel edge (8) is δ , , and δ satisfies: .

4. The variable relief angle ball nose end mill according to claim 3, characterized in that: when φ = 0, α = α 1; when φ = 90°, α = α 2.

5. The variable relief angle ball end mill according to claim 4, characterized in that: The ideal profile radius of the ball-end cutting edge (7) is r 0, the offset distance of the ball head blade (7) at the top of the ball head is p , p satisfy: 。 6. The variable relief angle ball end mill according to any one of claim 5, characterized in that: The radial cross section of the chisel edge (8) at the top of the ball head is in an "S" shape, and the axial cross section is in an inward concave shape.

7. The variable relief angle ball end mill according to claim 6, characterized in that: The horizontal length of the chisel edge (8) in the axial section is l , l satisfy, .

8. The variable relief angle ball end mill according to claim 7, characterized in that: The axial distance between the concave center of the chisel edge (8) and the ideal contour line (10) of the ball head in the axial section is h , .

9. A method for grinding the variable clearance angle ball end mill according to any one of claims 1 to 8, characterized in that: First, the first flank face (51) of the ball head is ground with a grinding wheel, and the grinding point moves along the spiral edge (6) and the ball head edge (7) from the tail of the chip groove (4) to the cutting end (3) of the ball head; at the same time, according to the change law of the back angle of the first flank face (51), the grinding posture of the grinding wheel is adjusted to obtain a gradual back angle; then, after passing the center of the ball head, the grinding wheel continues to move a set distance in a direction tangent to the ball head edge (7) and then exits, finally obtaining a chisel edge (8).

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