JP3891727B2 - End mill - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an end mill, and more particularly, to an end mill that is suitably used for step processing in which pocket holes and standing walls are cut by cutting in a direction perpendicular to the axis while moving stepwise in the axial direction. is there.
[0002]
[Prior art]
When cutting a relatively deep pocket hole or standing wall with a high height, using a long blade end mill with a long blade length decreases the rigidity and increases the cutting resistance. There is a problem that processing conditions are limited. For this reason, using an end mill with a short blade length, a step process is proposed in which cutting is performed in a direction perpendicular to the axis while moving stepwise in the axial direction, and the desired height is cut by joining several steps. Has been.
[0003]
FIG. 2 shows an example of an end mill used for such step processing. The end mill 100 includes a shank 102 and a cutting edge portion 104 that are continuously integrated in the axial direction, and the cutting edge portion 104 includes: A plurality of outer peripheral cutting edges 106 that are larger in diameter than the shank 102 and twisted around the axis O are provided. Further, a bottom blade 108 is provided at the tip of the cutting edge portion 104 continuously to the outer peripheral cutting edge 106. The right half of the axis O in FIG. 2 is a front view seen from the direction perpendicular to the axis O, and the left half is a cross section of the outer peripheral cutting edge 106 of the cutting edge portion 104 parallel to the axis O. It is a figure and the outer periphery shape of the left half is the same as the rotation locus | trajectory shape 104R of the cutting-blade part 104, ie, the cutting shape.
[0004]
FIG. 3 is a diagram for explaining an example of the case where the standing wall 112 of the workpiece 110 is stepped using the end mill 100 of FIG. 2. In the first step (a), the substantially vertical end mill 100 is rotated around the axis. In the second step (b), the end mill 100 is cut by moving the first step processed surface 114a in a direction perpendicular to the axis, specifically, parallel to the standing wall 112 and in a substantially horizontal direction. The second step machining is performed by shifting the axis to the tip end side in the axial direction by a predetermined dimension and moving it around the axis in the direction perpendicular to the axis, specifically, parallel to the standing wall 112 and in a substantially horizontal direction. The surface 114b is cut. By repeating such step processing, a vertical surface having a target height can be cut. In addition, it is of course possible to perform step machining while moving the end mill 100 stepwise from the bottom to the top, contrary to FIG.
[0005]
[Problems to be solved by the invention]
However, since the rear end 104a side of the cutting edge portion 104 bites into the workpiece 110 due to bending deformation of the tool during cutting, a step is generated at the boundary 116 between the first step processing surface 114a and the second step processing surface 114b. Although the level difference becomes small depending on the processing conditions, it is inevitable that a level difference of about several μm (for example, 1 to 2 μm) will occur. It will end up. Japanese Patent Laid-Open No. 6-8029 describes an end mill in which a rear cutting blade that is inclined at a predetermined angle continuously to the outer peripheral cutting edge 106 is provided at the rear end 104a of the cutting edge portion 104. If the corner (corner portion connected to the outer peripheral cutting edge) is angular even at about 10 °, a streak is visually added. In addition, this rear cutting blade is merely provided with a rake face and a cutting edge by forming a groove up to a taper surface, and is not provided with a flank surface. Visual streaks are likely to occur due to the difference between the processed surface portion and the reflection characteristics.
[0006]
The present invention has been made against the background of the above circumstances. The purpose of the present invention is to generate visual streaks at the boundary of the machining surface when performing step machining while moving the end mill stepwise in the axial direction. It is to prevent that.
[0007]
[Means for Solving the Problems]
In order to achieve such an object, the first invention includes a cylindrical shaft portion and an outer peripheral cutting edge that is continuously provided at one end of the shaft portion and has a constant outer diameter larger than the shaft portion. In an end mill used for step processing that has a cutting edge portion that is concentrically integrated with each other and performs cutting in a direction perpendicular to the axis while moving stepwise in the axial direction , (a) At the end on the shaft side, in a cross-sectional shape including the axis of the rotation trajectory around the axis, an arc from the straight line parallel to the axis that is the rotation trajectory of the outer peripheral cutting edge toward the axis A rear edge cutting edge that is smoothly connected to the straight line so that the tangent of the arc at the connection point connected to the straight line coincides with the straight line is formed continuously with the outer peripheral cutting edge, (b) After that Wherein the flank escaping in the axial direction of the distal end side toward the cutting edge in the circumferential direction is provided.
[0008]
According to a second aspect of the present invention, in the end mill of the first aspect, the outer peripheral cutting edge is a torsional blade twisted around an axis, the number of the outer peripheral cutting edges is N, and the outer cutting edge is substantially equal in outer diameter. When the length (axial length) is B, the outer diameter of the outer peripheral cutting edge is D, and the torsion angle of the outer peripheral cutting edge is β, n represented by the following equation (1) is a natural number. Features.
n = B · N · tan β / (π · D) (1)
[0009]
【The invention's effect】
In such an end mill, rear cutting edge of the rear end of the cutting edge portion, the sectional shape including the axis of rotation locus around the axis, from its axial center line parallel a rotational locus of the peripheral cutting edge A circular arc heading toward the axial center is formed, and it is provided so that the tangent of the arc at the connection point connected to the straight line is smoothly connected to the straight line so that it matches the straight line. In this case, the surface shape of the step generated at the boundary portion of the processed surface becomes a curved surface corresponding to the arc, and a sudden change in the direction of the surface is alleviated. Further, since the rear end cutting edge is provided with an axial flank, the machining surface roughness is improved, and the difference in reflection characteristics from other machining surface portions machined by the outer circumferential cutting edge is reduced. In this way, a sudden change in the direction of the surface of the stepped portion is alleviated and the surface roughness of the stepped portion is improved, thereby suppressing the occurrence of visual streaks occurring in the stepped portion.
[0010]
Further, in the second invention in which the specifications N, B, D, and β of each part of the outer peripheral cutting edge are determined so that n in the expression (1) is a natural number , the axial cutting direction exists within the range of the substantial cutting length B. Since the number of outer peripheral cutting edges is a natural number n at any position around the axis, the number of outer peripheral cutting edges involved in cutting is constant (= n) regardless of the rotation around the axis, and the cutting resistance Even when the fluctuation of (load) is suppressed and the shaft portion (length from the rotary holder to the cutting edge portion) is long, high machining accuracy can be obtained. That is, when performing the above step processing, since the length (shaft portion) from the holder of the machine tool to the cutting edge becomes long, the cutting edge is likely to shake due to fluctuations in cutting resistance, but chatter vibration is likely to occur. This suppresses fluctuations in the cutting edge, thereby reducing the fluctuation of the cutting edge portion.
[0011]
Although the natural number is an integer of 1 or more , for example, actual cutting is performed including a part of the rear end cutting edge, and in step processing, cutting is performed by overlapping in the axial direction. n it is necessary is not the name that is set to be a natural number.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Here, when the end mill of the present invention performs step machining while moving it stepwise in the axial direction, the desired effect that visual streaks hardly occur at the boundary of the machining surface is obtained. Therefore, for example, the end mill can be moved along a predetermined inner peripheral surface while continuously moving the rear end side (shank side) in the axial direction, and the pocket hole can be helically processed. It can be used in various modes including the usage form of a normal end mill.
[0013]
The cylindrical shaft portion mainly assumes a shank. However, when a neck portion is provided between the shank and the cutting edge portion, the outer peripheral cutting edge may be at least larger in diameter than the neck portion.
[0014]
The circular arc of the cross-sectional shape including the axis of the rotation trajectory of the trailing edge cutting edge may be, for example, an arc having a constant radius of curvature centered on a constant curvature center, but continuously changes like an elliptical arc. It may be what you have. The radius of curvature of the arc is preferably 0.01 mm or more and preferably 0.02 mm or more in order to prevent the occurrence of visual streaks. Further, with respect to the difference Δd in the diameter dimension between the shaft portion and the outer peripheral cutting edge, for example, if an arc is formed with a constant curvature radius Δd / 2 around the constant curvature center, A quarter arc is formed at the end. An arc may be formed with a curvature radius of Δd / 2 or more. Of course, the corner of the outer peripheral cutting edge and the bottom cutting edge can be provided with a radius R of a predetermined curvature as required.
[0015]
It is desirable that the flank face of the rear end cutting edge not only escapes to the tip side in the axial direction but also provides a predetermined relief in the radial direction. In the above equation (1), the number of blades N and the natural number n are both preferably 2 or more.
[0016]
Next, embodiments of the present invention will be described in detail with reference to the drawings.
1A is a view of an end mill 10 according to an embodiment of the present invention as viewed from a direction perpendicular to the axis O, and is a front view in which a part of the shank 12 is cut away. FIG. (C) is a bottom view as seen from the side, and the left half of the axis O shows the rotational trajectory shape 14R of the cutting edge portion 14 (the left outer peripheral shape is the same as the cross-sectional shape including the axis O), and the right half FIG. 3 is a diagram showing a cross-sectional shape illustrating the outer peripheral cutting edge 16 in parallel with the axis O. The shank 12 has a cylindrical shape, and a cutting edge portion 14 is provided concentrically with the shank 12 continuously at one end thereof. The cutting edge portion 14 is provided with a plurality of (four in this embodiment) outer peripheral cutting edges 16 that are twisted around the axis O with a constant outer diameter larger than that of the shank 12. A bottom blade 18 is provided at the tip of the blade portion 14 continuously to the outer peripheral cutting blade 16. Further, a rear end cutting edge 20 is provided continuously to the outer peripheral cutting edge 16 at the rear end of the cutting edge portion 14, that is, the end portion on the shank 12 side. The outer peripheral cutting edge 16 and the rear end cutting edge 20 are provided along a common twist groove 22, and the bottom blade 18 is provided along a gash 24 provided at the tip of the twist groove 22. The shank 12 corresponds to a shaft portion.
[0017]
Here, the number of outer peripheral cutting edges 16 is N, the substantial cutting length (axial length) of the outer peripheral cutting edges 16 is equal to B, the outer diameter of the outer peripheral cutting edges 16 is D, and the outer peripheral cutting edges are the same. When the twist angle of 16 is β, these specifications are set so that n represented by the above equation (1) is a natural number. In this embodiment, N = 4, B≈20 mm, D≈14 mm, and β≈48 ° are set so that n = 2.
[0018]
On the other hand, the rear end cutting edge 20 has an arc 20R having a constant curvature center and a curvature radius of 1 mm in the rotation locus shape (cross-sectional shape) 14R of the cutting edge portion 14 shown in the left half of FIG. 1 (c). And the center of curvature of the arc 20R is relative to a straight line parallel to the axis O which is the rotation trajectory of the outer peripheral cutting edge 16, and the tangent of the arc 20R at the connection point with the straight line is It is set so as to be smoothly connected so as to coincide with the straight line and bend toward the axis O side. In this embodiment, the difference Δd in the diameter between the shank 12 and the cutting edge 14 is 2 mm, the step Δd / 2 in the cross-sectional shape is 1 mm, and the radius of curvature of the arc 20R in the cross-sectional shape of the rotation trajectory of the trailing edge cutting edge 20 Since they are the same, a quarter arc having a radius of 1 mm is formed at the rear end of the rotation locus shape 14R.
[0019]
The rear end cutting edge 20 is also provided with a flank 28 that escapes toward the tip end in the axial direction from the cutting edge toward the circumferential direction. The flank 28 not only escapes toward the tip end in the axial direction, but also has a predetermined flank in the radial direction.
[0020]
Further, the corner 26 of the outer peripheral cutting edge 16 and the bottom cutting edge 18 has a constant curvature center and a radius of curvature in the rotation locus shape (cross-sectional shape) 14R of the cutting edge portion 14 shown in the left half of FIG. R chamfering is performed so that a 1 mm arc 26R is formed. The center of curvature is set so that the R chamfered arc 26R is tangent to a straight line parallel to the axis O, which is the rotation locus of the outer peripheral cutting edge 16. The rotation locus shape 14R (including the arcs 20R and 26R) represents the cutting shape of the cutting edge portion 14.
[0021]
In such an end mill 10 of the present embodiment, the outer peripheral cutting edge 16 has a cross-sectional shape (14R) in which the rear end cutting edge 20 of the rear end of the cutting edge portion 14 includes the axis O of the rotation locus around the axis O. An arc 20R is formed from the straight line that is the rotation trajectory to the axis O side, and is smoothly connected to the straight line so that the tangent of the arc 20R at the connection point connected to the straight line coincides with the straight line. For example, when step machining as shown in FIG. 3 is performed, the surface shape of the step generated at the boundary portion 116 between the machining surfaces 114a and 114b becomes a curved surface corresponding to the arc 20R, Sudden changes in direction are mitigated. Further, since the rear end cutting edge 20 is provided with the flank 28, the machining surface roughness is improved, and the difference in reflection characteristics from other machining surface portions machined by the outer circumferential cutting edge 16 is reduced. In this way, a sudden change in the direction of the surface of the stepped portion (boundary portion) 116 is alleviated, and the surface roughness of the stepped portion 116 is improved, thereby generating visual streaks generated in the stepped portion 116. Suppressed and excellent surface quality can be obtained.
[0022]
In addition, since the specifications N, B, D, and β of each part of the outer peripheral cutting edge 16 are determined so that n = 2 in the equation (1), the axial direction within the range of the substantial cutting length B is achieved. Since the number of the outer peripheral cutting edges 16 existing is n, that is, “2” at any position around the axis O, the number of the outer peripheral cutting edges 16 involved in the cutting is constant regardless of the rotation around the axis O ( n = 2), variation in cutting resistance (load) is suppressed, and even when the shank 12 (strictly, the length from the holder to the cutting edge) is long, high machining accuracy (surface roughness, etc.) can be obtained. It becomes like this. That is, when performing the above step processing, since the length from the holder of the machine tool to the cutting edge portion 14 becomes long, the cutting edge portion 14 is likely to shake due to fluctuations in cutting resistance, but chatter vibration is likely to occur. As a result, vibration of the cutting edge portion 14 and chatter vibration are reduced.
[0023]
In contrast to FIG. 3, the same effect can be obtained when step machining is performed while the end mill 10 is moved stepwise toward the shank 12 in the axial direction. Further, FIG. 3 shows a case where the standing wall 112 is processed, but step processing can also be applied to processing of the inner peripheral surface of the pocket hole.
[0024]
Further, since the rear end cutting edge 20 is provided, for example, the end mill 10 is moved along a predetermined inner peripheral surface while continuously moving the end mill 10 toward the rear end side (shank 12 side) in the axial direction, thereby forming the pocket hole. It can be used in various forms including normal usage forms of end mills, such as helical machining.
[0025]
As mentioned above, although the Example of this invention was described in detail based on drawing, this is an embodiment to the last, and this invention implements in the aspect which added the various change and improvement based on the knowledge of those skilled in the art. Can do.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an end mill according to an embodiment of the present invention.
FIG. 2 is a partially cutaway view showing an example of a conventional end mill.
FIG. 3 is a diagram for explaining an example when a standing wall is stepped using a conventional end mill.
[Explanation of symbols]
10: End mill 12: Shank (shaft part) 14: Cutting edge part 16: Outer peripheral cutting edge 20: Rear edge cutting edge 28: Flank

Claims (2)

A cylindrical shaft portion and a cutting edge portion provided continuously with one end of the shaft portion and having an outer peripheral cutting edge having a constant outer diameter larger than the shaft portion are integrally provided concentrically. In an end mill used for step processing, in which cutting is performed in a direction perpendicular to the axis while moving stepwise in the axial direction ,
At the end of the outer peripheral cutting edge on the shaft side, in a cross-sectional shape including the axis of the rotation trajectory around the axis, the axis extends from a straight line parallel to the axis that is the rotation trajectory of the outer peripheral cutting edge. A rear end cutting edge that forms an arc toward the center side and is smoothly connected to the straight line so that a tangent of the arc at a connection point connected to the straight line coincides with the straight line is continuously connected to the outer peripheral cutting edge As well as
The end mill is characterized in that the rear end cutting edge is provided with a flank that escapes toward the tip end in the axial direction as it goes in the circumferential direction from the cutting edge. The outer peripheral cutting edge is a torsional blade twisted around an axis, wherein the number of outer peripheral cutting edges is N, the substantial cutting length is equal to the outer diameter of the outer peripheral cutting edge, and the outer diameter of the outer peripheral cutting edge is D, where the twist angle of the outer peripheral cutting edge is β, n represented by the following equation is a natural number n = B · N · tan β / (π · D)
The end mill according to claim 1.

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