JP2000334615A - End mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of visible striations as boundaries between machined surfaces stepped with end mills moved axially stepwise. SOLUTION: A cutting edge portion 14 has, in its back end, back-end cutting edges 20 forming an arc 20R having a constant center of curvature and a radius of curvature of 1 mm in a turning locus profile or section 14R of the cutting edge portion 14. The center of curvature of the arc 20R is set such that the arc 20R is tangent to that straight line or turning locus of peripheral cutting edges 16 which is parallel to the axis O.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an end mill,
In particular, the present invention relates to an end mill which is suitably used for step processing for cutting pocket holes, standing walls, and the like by performing cutting in a direction perpendicular to the axis while gradually moving in the axial direction.

[0002]

2. Description of the Related Art When cutting a relatively deep pocket hole or a standing wall having a high height, the use of a long blade end mill having a long blade length causes a decrease in rigidity or an increase in cutting resistance. In addition, there is a problem that processing accuracy is reduced or processing conditions are limited. For this reason, using an end mill with a short blade length, cutting is performed in the direction perpendicular to the axis while moving stepwise in the axial direction, and step processing is performed to cut the target height by joining several steps. Have been.

FIG. 2 shows an example of an end mill used for such a step machining. This end mill 100 has a shank 102 and a cutting edge portion 104 continuously and integrally in the axial direction, and a cutting edge portion 104. Is provided with a plurality of outer peripheral cutting edges 106 having a larger diameter dimension than the shank 102 and twisted around the axis O.
At the tip of the cutting edge portion 104, a bottom blade 108 is provided continuously to the outer peripheral cutting edge 106. 2 is a front view seen from a direction perpendicular to the axis O, and the left half is an outer peripheral cutting edge 106 of the cutting portion 104.
Is parallel to the axis O, and the outer peripheral shape of the left half thereof is the same as the rotation locus shape 104R of the cutting edge portion 104, that is, the cutting shape.

FIG. 3 is a view for explaining an example of the case where the standing wall 112 of the work 110 is step-processed by using the end mill 100 of FIG. 2. In the first step shown in FIG. The first step processing surface 114a is cut while being rotated in a direction perpendicular to the axis, specifically, in a direction parallel to and substantially horizontal to the standing wall 112 while being rotated around, and cut in the second step (b). The end mill 100 is shifted by a predetermined dimension toward the distal end side in the axial direction, and is similarly rotated around the axis while being moved in a direction perpendicular to the axis, specifically, in a direction parallel to the standing wall 112 and substantially in a horizontal direction. The two-step processing surface 114b is cut. By repeating such step processing, it is possible to cut a vertical surface having a desired height dimension. In addition, contrary to FIG. 3, it is of course possible to perform the step processing while moving the end mill 100 stepwise from below to above.

[0005]

However, at the time of cutting, the rear end 104 of the cutting edge 104 is formed by bending deformation of the tool.
Since the a side cuts into the work 110 side, the boundary 1 between the first step processing surface 114a and the second step processing surface 114b
A step occurs at 16. Although the step is reduced by the processing conditions and the like, a step of about several μm (for example, 1 to 2 μm) is unavoidable, and a streak is visually formed on the boundary 116 even if it is not understood only by hand. It will be. Japanese Patent Application Laid-Open No. 6-8029 describes an end mill in which a rear cutting blade is provided at a rear end 104a of a cutting edge portion 104 at a predetermined angle continuously to an outer peripheral cutting edge 106. If the corners (corners connected to the outer peripheral cutting edge) are sharp even at about 10 °, a streak is visually formed. In addition, this rear cutting blade is only provided with a rake face and a cutting edge by simply forming a groove up to the tapered surface, and since no flank is provided, the processing surface roughness is poor, and this point Visual streaks tend to occur due to differences in reflection characteristics from the processed surface portion.

The present invention has been made in view of the above circumstances, and an object of the present invention is to visually recognize a boundary of a processing surface when performing step processing while gradually moving an end mill in an axial direction. It is to prevent the occurrence of streaks.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a cylindrical shaft portion and a fixed outer diameter which is provided continuously at one end of the shaft portion and is larger than the shaft portion. A cutting edge portion having an outer peripheral cutting edge having a dimension, (a) a cross section including an axis of a rotation locus around an axis at an end of the outer peripheral cutting edge on the shaft portion side. In the shape, it is connected to the straight line parallel to its axis, which is the rotation trajectory of the outer peripheral cutting edge, smoothly connected so as to be connected tangentially, and continuously connected to the outer peripheral cutting edge so as to form an arc toward the axis side. And (b) the rear end cutting edge is provided with a flank escaping toward the front end side in the axial direction from the cutting edge in the circumferential direction.

According to a second aspect of the present invention, in the end mill of the first aspect, the outer peripheral cutting edge is a torsion blade twisted around an axis, the number of the outer peripheral cutting edges is N, and the outer diameters of the outer peripheral cutting edges are equal. The actual cutting length (length in the axial direction) 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.
Where n represented by the following equation (1) is a substantially natural number. n = B · N · tan β / (π · D) (1)

[0009]

In such an end mill, the rear end cutting edge of the rear end of the cutting edge portion is parallel to the axis which is the rotation locus of the outer peripheral cutting edge in a sectional shape including the axis of the rotation locus around the axis. Is formed so that it is smoothly connected so that it is connected to a straight line with a tangent line and forms an arc toward the axis, so that the step shape generated at the boundary of the processing surface when performing step processing Becomes a curved surface corresponding to the arc, and a sudden change in the direction of the surface is reduced. Further, since the rear end cutting edge is provided with the flank in the axial direction, the roughness of the processed surface is improved, and the difference in reflection characteristics from other processed surface portions processed by the outer peripheral cutting edge is reduced. As described above, a sudden change in the direction of the surface of the step portion is alleviated, and the surface roughness of the step portion is improved, so that the generation of visual streaks occurring in the step portion is suppressed.

Further, in the second invention, the specifications N, B, D, and β of each part of the outer peripheral cutting edge are determined so that n in the equation (1) becomes a substantially natural number. Since the number of outer peripheral cutting edges existing in the axial direction is substantially a natural number n at any position around the axis, the number of outer peripheral cutting edges involved in cutting regardless of rotation around the axis is substantially constant (= n). )become,
Variations in cutting resistance (load) are suppressed, and high machining accuracy can be obtained even when the shaft (the length from the rotary holder to the cutting edge) is long. In other words, when performing the above-described step machining, the length (shaft portion) from the holder of the machine tool to the cutting edge becomes long, so that the cutting edge fluctuates due to the fluctuation of the cutting resistance and chatter vibration is easily generated. Is suppressed, the run-out of the cutting edge portion is reduced.

The "substantially natural number" is a natural number 1
It means that it is a value close to the above integer, for example, actual cutting is performed including a part of the rear cutting edge, and in step processing, cutting is performed by overlapping in the axial direction It is not necessary to set strictly n to be a natural number.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, the end mill of the present invention
In the case of performing step machining while moving stepwise in the axial direction, a desired effect such that visual streaks are hardly generated at the boundary of the machining surface is obtained, but since the rear end cutting edge is provided, for example, Including the usual end mill usage, such as the ability to continuously move the end mill to the rear end side (shank side) in the axial direction and move it along a predetermined inner peripheral surface to perform helical machining of pocket holes It can be used in various ways.

[0013] The cylindrical shaft portion is intended mainly for a shank. However, when a neck portion is provided between the shank and the cutting edge portion, the outer peripheral cutting edge must have at least a larger diameter than the neck portion. good.

The circular arc having a sectional shape including the axis of the rotation locus of the trailing edge may be, for example, an arc having a constant radius of curvature centered on a constant center of curvature, but may be a continuous arc like an elliptical arc. It may be something that has changed. The radius of curvature of the arc is preferably 0.01 mm or more, and more preferably 0.02 mm or more, in order to prevent visual streaks. In addition, for 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 radius of curvature Δd / 2 centered on a constant center of curvature, the rear portion of the cutting edge portion can be formed. A quarter arc is formed at the end. An arc may be formed with a radius of curvature of Δd / 2 or more. In addition, it is needless to say that the corner of the outer peripheral cutting edge and the bottom edge can also be provided with a predetermined radius of curvature R as needed.

The flank of the cutting edge at the rear end preferably has a predetermined flank in the radial direction as well as the flank in the axial direction. In the above formula (1), it is desirable that both the number of blades N and the natural number n be 2 or more.

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A is a front view of an end mill 10 according to an embodiment of the present invention viewed from a direction perpendicular to an axis O. FIG. 1B is a front view in which a part of a shank 12 is cut away, and FIG. In the bottom view from the side, (c) is a diagram showing the rotation locus shape (the left outer peripheral shape is the same as the cross-sectional shape including the axis O) 14R in the left half of the axis O, and the right half. Is a diagram showing a cross-sectional shape in which the outer peripheral cutting edge 16 is illustrated in parallel with the axis O. The shank 12 has a cylindrical shape, and a cutting edge portion 14 is provided integrally and concentrically with the shank 12 at one end thereof. The cutting edge portion 14 is provided with a plurality (four in this embodiment) of outer peripheral cutting edges 16 twisted around the axis O with a constant outer diameter dimension larger than the shank 12. At the tip of the blade portion 14, a bottom blade 18 is provided continuously to the outer peripheral cutting edge 16 thereof. Also, at the rear end of the cutting edge portion 14, that is, at the end portion on the shank 12 side,
A rear end cutting edge 20 is provided continuously to the outer peripheral cutting edge 16. 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. Note that the shank 12 corresponds to a shaft portion.

Here, the number of the outer peripheral cutting edges 16 is N,
When the actual cutting length (axial direction length) of the outer peripheral cutting edge 16 having the same outer diameter dimension is B, the outer diameter of the outer peripheral cutting edge 16 is D, and the helix angle of the outer peripheral cutting edge 16 is β, Original is the above (1)
N represented by the equation is set to be a natural number.
In this embodiment, N = 4 and B ≒ 20 so that n = 2.
mm, D ≒ 14 mm, and β ≒ 48 °.

On the other hand, the rear end cutting edge 20 has a constant center of curvature and a radius of curvature of 1 m in the rotation locus shape (cross-sectional shape) 14R of the cutting edge portion 14 shown in the left half of FIG.
m is formed so as to form an arc 20R, and the center of curvature of the arc 20R is connected by a tangent line to the straight line parallel to the axis O which is the rotation locus of the outer peripheral cutting edge 16. So that they are connected smoothly and curved toward the axis O side. In this embodiment, the difference Δd in diameter between the shank 12 and the cutting edge 14 is 2 mm.
Since the step Δd / 2 in the cross-sectional shape is 1 mm, which is the same as the radius of curvature of the circular arc 20R in the cross-sectional shape of the rotation trajectory of the trailing edge 20, the rear end of the rotation trajectory 14R has a radius of 1 mm. An arc is formed.

The trailing edge 20 is also provided with a flank 28 which escapes from the cutting edge to the distal end in the axial direction as it goes circumferentially. The flank 28 has a predetermined flank in the radial direction as well as the flank in the axial direction.

The corner 26 between the outer peripheral cutting edge 16 and the bottom blade 18 has a constant center 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 an arc 26R having a curvature radius of 1 mm is formed. The center of curvature is set so that the arc 26R of the R-chamfer is connected by a 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.

In the end mill 10 of this embodiment, the rear cutting edge 20 at the rear end of the cutting edge portion 14 has a cross-sectional shape (14R) including the axis O of the rotation locus about the axis O.
Are provided so as to form a circular arc 20R toward the axis O side smoothly connected to a straight line which is the rotation locus of the outer peripheral cutting edge 16 at a tangent line, for example, as shown in FIG. When step processing is performed, the surface shape of the step generated at the boundary portion 116 between the processing surfaces 114a and 114b becomes a curved surface corresponding to the arc 20R, and a sudden change in the direction of the surface is reduced. Also, the trailing edge 20
Since the flank 28 is provided, the roughness of the machined surface is improved, and the difference in the reflection characteristics from other machined surfaces machined by the outer peripheral cutting edge 16 is reduced. As described above, a sudden change in the direction of the surface of the step portion (boundary portion) 116 is alleviated, and the surface roughness of the step portion 116 is improved. Suppression is achieved, and excellent machined surface quality can be obtained.

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 above equation (1), the actual cutting length B is within the range of the actual cutting length B. Since the number of outer peripheral cutting edges 16 existing in the axial direction is n, that is, “2” at any position around the axis O, the number of outer peripheral cutting edges 16 involved in cutting regardless of rotation about the axis O Becomes constant (n = 2), fluctuations in cutting resistance (load) are 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. That is, when the above-described step processing is performed, since the length from the holder of the machine tool to the cutting edge portion 14 is long, the cutting edge portion 14 fluctuates due to the fluctuation of the cutting resistance, and chatter vibration is easily generated. Is suppressed, the runout and chatter vibration of the cutting edge portion 14 are reduced.

The same effect can be obtained when stepping is performed while the end mill 10 is moved stepwise toward the shank 12 in the axial direction, contrary to FIG. FIG.
Is a case where the standing wall 112 is processed, but step processing can also be applied to the processing of the inner peripheral surface of the pocket hole.

Further, since the rear end cutting edge 20 is provided, for example, the end mill 10 is moved along a predetermined inner circumferential surface while continuously moving the end mill 10 toward the rear end side (the shank 12 side) in the axial direction. The pocket hole can be used in various modes including a normal end mill usage mode, such as helical processing.

Although the embodiment of the present invention has been described in detail with reference to the drawings, this is merely an embodiment,
The present invention can be implemented in various modified and improved aspects based on the knowledge of those skilled in the art.

[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 illustrating an example of a case where a standing wall is step-processed using a conventional end mill.

[Explanation of symbols]

10: End mill 12: Shank (shaft) 1
4: Cutting edge portion 16: Outer peripheral cutting edge 20: Rear end cutting edge 28: Flank

Claims (2)

[Claims] 1. A cylindrical shaft portion, and a cutting edge portion provided continuously with one end of the shaft portion and provided with an outer peripheral cutting edge having a constant outer diameter larger than the shaft portion. In the end mill, the end of the outer peripheral cutting edge on the shaft portion side has a straight line parallel to the axis which is the rotational locus of the outer peripheral cutting edge in a cross-sectional shape including the axis of the rotational locus around the axis. A rear end cutting edge is provided continuously with the outer peripheral cutting edge so as to be smoothly connected to be connected by a tangent line to form an arc toward the axis, and the rear end cutting edge includes: An end mill characterized in that a flank is provided for escaping toward a tip end in an axial direction from a cutting edge in a circumferential direction. 2. The outer peripheral cutting edge is a torsion blade twisted around an axis, wherein the number of the outer peripheral cutting edges is N, the outer diameter of the outer peripheral cutting edges is substantially equal to B, and the actual cutting length is B. When the outer diameter of the blade is D and the torsion angle of the outer peripheral cutting edge is β, n represented by the following equation is a substantially natural number: n = B · N · tan β / (π · D) The end mill according to claim 1, wherein