Ball-nose end mill and method of manufacturing cut article

Abstract

The present invention reduces chatter vibrations in a ball-nose end mill. This ball-nose end mill has: bits in the form of projections; and discharge flutes. The bits have: a first cutting edge that, heading toward the rear end, parts away from the rotational shaft; and a second cutting edge that extends from the first cutting edge toward the rear end and that, heading toward the rear end, approaches the rotational shaft. The discharge flutes have a first rake face at least a portion of which is positioned along the first cutting edge, and a second rake face at least a portion of which is positioned along the second cutting edge. The rake angle of the first rake face and the rake angle of the second rake face grow larger heading toward the rear end, and the minimum degree of the rake angle of the second rake face is smaller than the maximum degree of the rake angle of the first rake face.

Description

Ball end mill and method for manufacturing machined product

[0001] The present disclosure relates to a ball end mill used for cutting a workpiece and a method for manufacturing a machined product.

[0002] Conventionally, a ball end mill described in Patent Document 1 is known as a type of cutting tool used in cutting workpieces such as metal members. In drilling, which is one type of cutting process, burrs may occur at the opening portions of a through hole on both the mouth side and the exit side.

[0003] The ball end mill described in Patent Document 1 can be used to remove burrs from both the base and exit sides. In the ball end mill described in Patent Document 1, the radial rake angle of the cutting edge gradually increases toward the positive angle side from the front end to the rear end of the ball end mill body.

[0004] Japanese Patent Application Laid-Open No. 2019-155545

[0005] In one non-limiting aspect of the present disclosure, the ball end mill has a rod shape extending from a front end to a rear end along a rotation axis, a convex cutting edge located on the front end side, and a discharge flute extending from the cutting edge toward the rear end. The cutting edge has a first cutting edge that moves away from the rotation axis toward the rear end, and a second cutting edge that extends from the first cutting edge toward the rear end and approaches the rotation axis toward the rear end. The discharge flute has a cutting surface that extends along the first and second blades. The cutting surface has a first cutting surface at least partially located along the first blade and a second cutting surface at least partially located along the second blade. The inclination angle of the rake face in a cross section perpendicular to the rotation axis is defined as the rake angle, and the rake angle at the first rake face increases toward the rear end, the rake angle at the second rake face increases toward the rear end, and the minimum value of the rake angle at the second rake face is smaller than the maximum value of the rake angle at the first rake face.

[0006] 1 is a perspective view of a ball end mill according to an embodiment and an enlarged view of region B1. It is a front view of the tip of the ball end mill shown in FIG. 1 as viewed from the front. It is a side view seen from the A1 direction and an enlarged view of region B2 in FIG. 2. It is a side view seen from the A2 direction and an enlarged view of region B3 in FIG. 2. It is an enlarged view of region B4 in FIG. 4. It is an enlarged view of region B5 in FIG. 3. It is a VII-VII sectional view and an enlarged view of region B6 in FIG. 6. It is a VIII-VIII sectional view in FIG. 6. It is an IX-IX sectional view in FIG. 6. It is an X-X sectional view and an enlarged view of region B7 in FIG. 6. It is an XI-XI sectional view and an enlarged view of region B8 in FIG. 6. It is an XII-XII sectional view and an enlarged view of region B9 in FIG. It is an XIII-XIII sectional view in FIG. 6. It is a diagram showing the relationship between the distance from the tip and the rake angle in the ball end mill shown in FIG. 1. It is a schematic diagram explaining a method for manufacturing a machined product according to an embodiment.

[0007] When performing cutting using the ball end mill described in Patent Document 1, there is a risk of large chatter vibrations occurring. This is thought to be because the ball end mill described in Patent Document 1 is configured so that the radial rake angle of the cutting edge simply increases gradually, resulting in an excessively large radial rake angle at the rear end of the cutting edge. If the radial rake angle becomes excessively large, the ball end mill becomes more likely to bend, which can result in chatter vibrations.

[0008] A ball end mill and a method for manufacturing a machined product, which are examples of embodiments of the present disclosure, will be described in detail below with reference to the drawings. However, for the sake of convenience, the figures referred to below show simplified views of only the components necessary for explaining the embodiments. Therefore, the ball end mill, as an example, may include optional components not shown in the figures. Furthermore, the dimensions of the components in the figures do not faithfully represent the actual dimensions of the components or the dimensional ratios of the components.

[0009] In this disclosure, the rotation axis refers to the rotation axis (rotation axis center) of the ball end mill 1, the circumferential direction refers to the direction around the rotation axis, and the radial direction refers to the direction perpendicular to the rotation axis and the circumferential direction.

[0010] <Ball end mill according to an embodiment of the present disclosure> The configuration of a ball end mill 1 as an example of an embodiment will be described with reference to Figures 1 to 14. The example ball end mill 1 shown in Figures 1 to 4 is used for cutting a workpiece W (see Figure 15) made of a metal material or the like.

[0011] The ball end mill 1 may be a solid type made of a hard material such as cemented carbide, cermet, or cBN. The ball end mill 1 may be rod-shaped and extend from the tip 1a to the rear end 1b along the rotation axis O1. In Figures 2 and 7 to 13, the rotation axis O1 is indicated by a dot.

[0012] The ball end mill 1 has a cutting portion 10 at its tip end 1a that comes into contact with a workpiece W (see FIG. 15) to perform cutting. The ball end mill 1 does not have to be a solid type as long as at least the cutting portion 10 is made of a hard material such as cemented carbide, cermet, or cBN. The ball end mill 1 may have a shank portion 3 at its rear end 1b that is attached to the spindle of a machine tool via an arbor. The ball end mill 1 may have a large diameter portion and a small diameter portion, and the shank portion 3 may be located in the large diameter portion.

[0013] 1 to 5, the cutting portion 10 may have a convex cutting edge E located on the side of the tip 1a. The convex cutting edge E is convex outward in the radial direction and may have a convex curved shape or an overall arc shape. The convex cutting edge E may also have an elliptical shape including straight portions between curves, or a convex curved shape with partially different curvatures.

[0014] 1 and 3, the cutting edge E may have a first blade E1 that moves away from the rotation axis O1 toward the rear end 1b, and a second blade E2 that extends from the first blade E1 toward the rear end 1b and moves closer to the rotation axis O1 toward the rear end 1b. The first blade E1 and the second blade E2 may each have a convex curved shape.

[0015] 1 to 4, the cutting portion 10 may have a discharge groove 11 extending from the cutting edge E toward the rear end 1b. The discharge groove 11 serves as a passage for chips generated by cutting work when they are discharged to the outside. The discharge groove 11 may have a cutting face 12 extending along the first blade E1 and the second blade E2.

[0016] 1 and 3, the rake face 12 may have a first rake face 121, at least a portion of which is located along the first blade E1, and a second rake face 122, at least a portion of which is located along the second blade E2. It is sufficient that at least a portion of the first rake face 121 is located along the first blade E1. It is sufficient that at least a portion of the second rake face 122 is located along the second blade E2.

[0017] 1, 2, and 5, the cutting portion 10 may have a flank 14 behind the cutting edge E in the rotation direction O2 of the rotation axis O1. The cutting edge E may be located on the ridge line between the rake face 12 and the flank 14. A second flank 15 having a larger clearance angle than the flank 14 may be located behind the flank 14 in the rotation direction O2 of the rotation axis O1. In this case, the flank 14 is the second flank, and the flank 15 is the third flank.

[0018] A plurality of cutting edges E and discharge grooves 11 may be located at intervals in the circumferential direction on the side of the tip 1a. In the example shown in Figures 1 to 4, two cutting edges E are provided, and two discharge grooves 11 are provided corresponding to the two cutting edges E. The cutting portion 10 may have a chisel edge on the side of the tip 1a. The chisel edge has the effect of crushing a part of the workpiece W.

[0019] As shown in the example of Figures 6 to 13, the inclination angle of the rake face 12 in a cross section perpendicular to the rotation axis O1 is defined as the rake angle θ. For the sake of convenience, the example shown in Figures 6 to 13 does not include the third rake face 123 shown in Figures 1 to 5. The third rake face 123 will be described later.

[0020] As shown in the examples of Figures 7 to 9 and 14, the rake angle θ of the first rake face 121 may increase toward the rear end 1b. As shown in the examples of Figures 10 to 14, the rake angle θ of the second rake face 122 may also increase toward the rear end 1b. Furthermore, as shown in the examples of Figures 9, 10 and 14, the minimum value of the rake angle θ of the second rake face 122 may be smaller than the maximum value of the rake angle θ of the first rake face 121.

[0021] Specifically, as can be seen by comparing Figures 9 and 10, the provision of the second rake face 122 causes the rake angle θ to be smaller in the cross section of Figure 10 than in Figure 9. The rake angle θ in the cross section shown in Figure 10 is negative. Dots D1 to D7 shown in Figure 14 are plots of the rake angles θ of the examples shown in Figures 7 to 13. Dot D1 corresponds to Figure 7, dot D2 to Figure 8, dot D3 to Figure 9, dot D4 to Figure 10, dot D5 to Figure 11, dot D6 to Figure 12, and dot D7 to Figure 13.

[0022] If the rake angle θ becomes excessively large, the force pulling the ball end mill toward the workpiece W (see FIG. 15) becomes excessively strong, which may cause chatter vibration. With the above configuration, the rake angle θ, which had gradually increased with increasing distance from the tip 1a, temporarily decreases with the provision of the second rake face 122, and then gradually increases again. Therefore, the rake angle θ at the portion located on the rear end side of the cutting edge E does not become excessively large. This makes the ball end mill 1 less likely to bend, thereby reducing chatter vibration.

[0023] As shown in the examples of Figures 1, 7 and 8, the first rake face 121 and the second rake face 122 may each have a flat shape. With this configuration, the rake angle θ in the radial direction is constant on each of the first rake face 121 and the second rake face 122. This makes the first rake face 121 and the second rake face 122 shaped to make it difficult for chips to become clogged, thereby improving chip discharge performance.

[0024] 10 to 13, the first rake face 121 and the second rake face 122 may each have a planar shape, and the second rake face 122 may be inclined with respect to the first rake face 121. With this configuration, the rake angle θ in the radial direction is constant on each of the first rake face 121 and the second rake face 122, thereby achieving the effect of improving chip discharge performance and avoiding a monotonous increase in the rake angle θ.

[0025] Furthermore, in this case, at least a portion of the first cutting face 121 may be located along the second blade E2. In other words, the first cutting face 121 may have a portion located along the second blade E2 beyond the boundary between the first blade E1 and the second blade E2 of the cutting edge E.

[0026] With this configuration, the first rake face 121 is located at the point on the cutting edge E farthest from the rotation axis O1, so the rake angle θ at that point is larger and the sharpness of that point is superior compared to a configuration in which the second rake face 122 is located. As a result, the sharpness of the cutting edge E makes it less likely for the inner peripheral surface of the hole to be torn off when drilling using the ball end mill 1.

[0027] 6 , at least a portion of the second rake face 122 may be located along the first blade E1, which is the opposite of the above. That is, the second rake face 122 may have a portion located along the first blade E1 beyond the boundary between the first blade E1 and the second blade E2 of the cutting edge E.

[0028] With this configuration, the second rake face 122 is located at the point on the cutting edge E farthest from the rotation axis O1, and the rake angle θ at this point is smaller than in a configuration where the first rake face 121 is located. The point on the cutting edge E farthest from the rotation axis O1 is prone to deflection due to the impulse, but because the rake angle θ at this point is relatively small, the ball end mill is even less likely to deflect, and chatter vibration can be further reduced.

[0029] 1 and 3 to 5, the rake face 12 may further include a curved third rake face 123 connected to the first rake face 121 and the second rake face 122. The third rake face 123 is a surface that smooths the corners located at the boundary between the first rake face 121 and the second rake face 122 that is inclined with respect to the first rake face 121. The third rake face 123 may be formed by performing a process to remove the corners at the boundary portion after the first rake face 121 and the second rake face 122 are created.

[0030] With this configuration, the first rake face 121 and the second rake face 122 are smoothly connected, and it is possible to prevent the rake angle θ from changing suddenly in the region from the first rake face 121 to the second rake face 122. This makes it possible to effectively reduce chipping of the cutting edge E.

[0031] As shown in the example of Figures 3 and 6, the first cutting face 121 may have a portion 121A located on the front end 1a side and whose width increases toward the rear end 1b. The width of the first cutting face 121 may be the radial dimension of the first cutting face 121 having a planar shape. In Figures 3 and 6, the portion 121A is cross-hatched.

[0032] The direction of travel of chips flowing into the first cutting face 121 tends to become perpendicular to the rotation axis O1 as they approach the rear end 1b, making clogging more likely to occur. With the above configuration, the first cutting face 121 is wider in areas where clogging is more likely to occur, thereby improving the overall chip discharge performance.

[0033] The second cutting face 122 may have a first portion 122A whose width increases toward the rear end 1b, and a second portion 122B which is located closer to the rear end 1b than the first portion 122A and whose width decreases toward the rear end 1b.

[0034] The width of the second rake face 122 may be the dimension of the second rake face 122 having a planar shape in a direction perpendicular to the boundary line with the first rake face 121, or, if a third rake face 123 is provided, the dimension in a direction perpendicular to the boundary line with the third rake face 123. In Figures 3 and 6, the first portion 122A is hatched and the second portion 122B is cross-hatched.

[0035] When the second cutting face 122 has the first portion 122A and the second portion 122B described above, it becomes easier to ensure space for the flow of chips that are generated during processing to remove burrs from the opening portion on the exit side of the through hole.

[0036] <Method for manufacturing a machined product according to an embodiment of the present disclosure> A method for manufacturing a machined product according to an embodiment of the present disclosure will be described with reference to Fig. 15. Fig. 15 is a schematic view for explaining the method for manufacturing a machined product according to an embodiment.

[0037] As shown in Figure 15, the method for manufacturing a machined product according to this embodiment is a method for manufacturing a machined product M, which is a workpiece W that has been machined, and includes a first step, a second step, and a third step. The first step is a step of rotating the ball end mill 1 around the rotation axis O1. The second step is a step of bringing the rotating ball end mill 1 into contact with the workpiece W. The third step is a step of separating the ball end mill 1 from the workpiece W. The specific details of the method for manufacturing a machined product according to this embodiment are as follows.

[0038] As indicated by reference numeral 1501 in Fig. 15 , the ball end mill 1 is rotated in the rotational direction O2 about the rotation axis O1 while being moved in the direction of arrow Y1 to approach the workpiece W. Here, a cylindrical workpiece W having a through hole H is shown as an example. Next, as indicated by reference numeral 1502 in Fig. 15 , the rotating ball end mill 1 is moved three-dimensionally, up and down, left and right, while in contact with the workpiece W. This performs a cutting process (milling process) to remove burrs W1 formed at the openings on the mouth side and exit side of the through hole H in the workpiece W.

[0039] 15, the ball end mill 1 is moved in the direction of arrow Y2 to separate it from the workpiece W. This completes the cutting of the workpiece W, and a machined product M can be produced, which is the machined workpiece W. Because the ball end mill 1 has excellent cutting ability with reduced chatter vibration for the reasons described above, a machined product M with excellent machining precision can be produced.

[0040] To continue cutting, the ball end mill 1 is rotated and repeatedly brought into contact with different locations on the workpiece W. In this embodiment, the ball end mill 1 is brought close to the workpiece W, but since it is sufficient that the ball end mill 1 and the workpiece W are relatively close to each other, for example, the workpiece W may be brought close to the ball end mill 1. This also applies when the ball end mill 1 is moved away from the workpiece W.

[0041] <Summary> The ball end mill in aspect 1 of the present disclosure has a rod shape extending from a front end to a rear end along a rotation axis, and has a convex cutting edge located on the front end side and a discharge groove extending from the cutting edge toward the rear end, the cutting edge having a first blade that moves away from the rotation axis toward the rear end and a second blade that extends from the first blade toward the rear end and approaches the rotation axis toward the rear end, the discharge groove has a rake face that extends along the first blade and the second blade, and the rake face has at least The cutting tool has a first rake face, at least a portion of which is located along the first blade, and a second rake face, at least a portion of which is located along the second blade, and the inclination angle of the rake face in a cross section perpendicular to the rotation axis is defined as a rake angle, the rake angle on the first rake face increases toward the rear end, the rake angle on the second rake face increases toward the rear end, and the minimum value of the rake angle on the second rake face is smaller than the maximum value of the rake angle on the first rake face.

[0042] A ball end mill according to a second aspect of the present disclosure is the same as that according to the first aspect, wherein the first cutting face and the second cutting face each have a planar shape, and the second cutting face is inclined relative to the first cutting face.

[0043] A ball end mill according to a third aspect of the present disclosure is the ball end mill of the first or second aspect, wherein at least a portion of the first cutting face is located along the second cutting edge.

[0044] In a fourth aspect of the present disclosure, the ball end mill is the same as in the first or second aspect, wherein at least a portion of the second cutting face is located along the first cutting edge.

[0045] The ball end mill in aspect 5 of the present disclosure is any one of aspects 1 to 4, wherein the cutting surface further has a third cutting surface having a curved shape connected to the first cutting surface and the second cutting surface.

[0046] A ball end mill in aspect 6 of the present disclosure is any one of aspects 1 to 5, wherein the first blade and the second blade each have a convex curved shape.

[0047] The ball end mill in aspect 7 of the present disclosure is any one of aspects 1 to 6, wherein the first cutting face has a portion located on the front end side that increases in width toward the rear end.

[0048] The ball end mill in aspect 8 of the present disclosure is any one of aspects 1 to 7, wherein the second cutting face has a first portion whose width increases toward the rear end, and a second portion located closer to the rear end than the first portion and whose width decreases toward the rear end.

[0049] A manufacturing method for a machined product in aspect 9 of the present disclosure includes the steps of rotating a ball end mill described in any one of aspects 1 to 8 around the rotation axis, bringing the rotating ball end mill into contact with a workpiece, and moving the ball end mill away from the workpiece.

[0050] [Additional Notes] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art could easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure.

[0051] 1 Ball end mill 1a Tip 1b Rear end 11 Discharge groove 12 Rake face 121 First rake face 122 Second rake face 123 Third rake face 121A Part 122A First part 122B Second part E Cutting edge E1 First cutting edge E2 Second cutting edge O1 Rotation axis O2 Rotation direction W Workpiece M Cutting workpiece θ Rake angle

Claims

1. It is a rod-shaped structure that extends from the tip to the rear end along the axis of rotation, A convex-shaped cutting edge located on the tip side, It has a discharge groove extending from the cutting edge toward the rear end, The aforementioned cutting edge is The first cutting edge moves away from the axis of rotation as it approaches the rear end, It has a second blade that extends from the first blade toward the rear end and approaches the axis of rotation as it approaches the rear end, The discharge groove has a scoop surface that extends along the first blade and the second blade, The aforementioned scoop surface is, A first rake face, at least a portion of which is located along the first cutting edge, It has a second rake face, at least a portion of which is located along the second cutting edge, The angle of inclination of the rake face in a cross-section perpendicular to the rotation axis is taken as the rake angle, The rake angle on the first rake face increases towards the rear end. The rake angle on the second rake face increases towards the rear end. A ball end mill wherein the minimum value of the rake angle on the second rake face is smaller than the maximum value of the rake angle on the first rake face.

2. The first rake face and the second rake face are each planar in shape, The ball end mill according to claim 1, wherein the second rake face is inclined with respect to the first rake face.

3. The ball end mill according to claim 2, wherein at least a portion of the first rake face is positioned along the second cutting edge.

4. The ball end mill according to claim 2, wherein at least a portion of the second rake face is positioned along the first cutting edge.

5. The ball end mill according to claim 2, wherein the rake face further has a curved third rake face connected to the first rake face and the second rake face.

6. The ball end mill according to claim 2, wherein the first blade and the second blade each have a convex curve shape.

7. The ball end mill according to claim 2, wherein the first rake face has a portion located on the tip side that becomes wider towards the rear end.

8. The second scoop face is, The first portion, which becomes wider towards the rear end, The ball end mill according to claim 2, further comprising a second portion located closer to the rear end than the first portion, and whose width decreases towards the rear end.

9. A step of rotating the ball end mill according to any one of claims 1 to 8 around the rotation axis, A step of bringing the rotating ball end mill into contact with the workpiece, A method for manufacturing a cut workpiece, comprising the step of separating the ball end mill from the workpiece.