JP2003145334A - Curved-face machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a curved-face machining method allowing the efficient formation of a highly precise machined surface with a larger area forming a concave, convex or irregular surface. SOLUTION: With the movement in a predetermined tool feeding direction of a face milling cutter having a circular cutting edge rotating path 15 with its axis of rotation being inclined to the normal of a machined surface 21 at each machining point, machining work is applied to the surface of a workpiece 2 using a cutting edge passing through a region of the cutting edge rotating path 15 in the tool feeding direction, or a region in the range of a pick feed. A moving path 15a of the cutting edge for machining work is in an elliptical shape with a diameter 2r of the cutting edge rotating path 15 as a major axis L, permitting a cusp height H to be smaller without requiring the pick feed to be smaller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a curved surface cutting method for obtaining a curved processed surface by using a milling tool such as a face milling machine.

[0002]

2. Description of the Related Art Generally, as a curved surface cutting method, as shown in FIGS. 7 and 8, a method of using a ball end mill 101 having a spherical cutting edge 115 is well known. For example,
When the concave machining surface 21 as shown in FIG. 9 is obtained using the ball end mill 101, the machining is performed in advance according to the machining surface shape and machining mode (reciprocating mode, one-way mode, contour mode along contour line, etc.). Multiple cutting lines 2 on object 2
2 is set (see FIGS. 7 and 10). And the bow
As shown in FIG. 7, the run end mill 101 is moved in a predetermined direction (tool feed direction) A on one cutting line 22 to cut the work surface 20 along the cutting line 22. As a result, a band-shaped cutting surface 21a extending in the tool feed direction A with the cutting line 22 as the center line is formed on the surface 20 to be processed. Then, by repeating this cutting process for a plurality of cutting lines 22, ...
Is obtained.

Microscopically, each strip-shaped cutting surface 21a is an arcuate groove corresponding to the spherical shape of the cutting edge 115, and the tool feeding direction A is formed at the boundary between the adjacent strip-shaped cutting surfaces 21a, 21a.
A cusp 21b is formed in the shape of a ridge (see FIGS. 8 and 1).
0). As shown in FIGS. 8 and 10, the cusp 21b is an uncut portion with respect to the ideal machined surface 21 ', and the smaller the height H, the better the machining accuracy (surface waviness) of the machined surface 21. become.

By the way, the cusp height H is determined by the strip-shaped cutting surface 2
Radius of curvature R and pick feed P in the cross-sectional shape of 1a
Can be calculated by
When ′ is shown by a straight line as shown in FIG. 8, it becomes approximately P ² / 8R. That is, the cusp height H is as shown in FIG.
, H = R− (R ² − (P / 2) ² ) ^{1
/ 2} . Then, if this equation is transformed, H =
^{R - ((R- (P 2} / 8R)) 2 - (P 2/8
R) ² ) ^1/2 , but ball end mill 101
The radius of curvature R of the strip-shaped cutting surface 21a formed by the above corresponds to the radius of curvature r ₀ of the spherical cutting edge 115, and generally P <<
Since a r ₀ = R, term end in the above formula ^(P 2/8
R) ² can be neglected, and the above equation is approximately H = R
^{- ((R- (P 2 /} 8R)) 2) may be a ^{1/2, H = P 2 / 8R} = P 2 / 8r 0 is obtained.

Therefore, in order to improve the machining accuracy, that is, to reduce the cusp height H, the radius of curvature R of the strip-shaped cutting surface 21a, that is, the ball end mill 101.
It is necessary to increase the radius of curvature r ₀ of the spherical cutting edge 115 or reduce the pick feed P.

[0006]

However, in the ball end mill 101, the radius of curvature r ₀ of the cutting edge 115 is limited, and the radius of curvature R of the strip-shaped cutting surface 21a cannot be increased beyond a certain level. That is, the spherical cutting edge 11
The cutting speed (rotation speed) of No. 5 is not constant, and the rotation center portion 11 that is a portion on the rotation axis of the ball end mill 101
5a, the cutting speed difference increases as the radius of curvature r ₀ of the cutting edge 115 increases. In order to process the strip-shaped cutting surface 21a with high accuracy, the cutting speed by the cutting edge 115 should be as uniform as possible in each part of the strip-shaped cutting surface 21a, that is, the cutting speed difference between the cutting points should be small. It is necessary to be as small as possible. Of course, it cannot be increased due to the manufacturing of the ball end mill itself and the limitation of the mounting machine. Therefore, in the ball end mill 101, the curvature radius r ₀ of the cutting edge 115 cannot be increased beyond a certain level. On the other hand, if the pick feed P is reduced, the processed surface 2
The number of strip-shaped cutting surfaces required to form No. 1 increases, and the cutting process becomes longer than necessary. Therefore, cutting efficiency is reduced. Such a problem becomes more remarkable as the processed surface 21 becomes larger.

Further, the cutting speed at each part of the spherical cutting edge 115 is not uniform as described above, and the cutting performance greatly changes depending on the position where the cutting edge of the ball end mill 101 hits, so that the surface 20 of the workpiece 2 is made uniform. It cannot be processed into a perfect mirror surface. In particular, the rotation center 115a
The cutting speed at 0 becomes zero, and the cutting by the rotation center portion 115a is so-called plucking. Therefore, the cutting edge 11
No matter how the radius of curvature r _{0 of} 5 and the pick feed P are set, the accuracy of the machined surface 21 cannot be improved to a certain level or more, and further manual finishing is required after cutting by the ball end mill 101. .

As described above, according to the curved surface cutting method by the ball end mill 101, the highly accurate machined surface 21 cannot be efficiently machined, and in particular, it is impossible to obtain a large-area highly accurate machined surface. It was Further, since the chips produced by the ball end mill 101 have a bulky shape with a curvature, when the land width is wide, a scraping phenomenon occurs due to chip interference near the nose, which may hinder smooth discharge of chips and cause welding. There is also a problem that the tool life is short.

It is an object of the present invention to provide a curved surface cutting method capable of efficiently obtaining a large-area, high-precision machined surface without causing such a problem.

[0010]

According to the curved surface cutting method of the present invention, in order to achieve the above object, in particular, a milling tool having a circular cutting edge rotation locus is used, in which the axis of rotation is at each cutting point. The surface of the workpiece is cut by the cutting edge that passes through the area in the tool feed direction side of the cutting edge rotation trajectory by moving in the predetermined tool feed direction while inclining to the normal to the processing surface. In this case, the inclination angle of the rotation axis with respect to the normal line is the geometrical shape of the surface to be processed at each cutting point in the range where the cutting edge that passes through the area on the side opposite to the tool feeding direction in the cutting edge rotation trajectory does not interfere with the processing surface. By moving the milling tool in the tool feed direction while controlling so as to change it according to the geometrical conditions (curvature of the surface to be processed, amount of curvature change between adjacent cutting points, etc.),
It is proposed to obtain a processed surface having a concave shape, a convex shape or an uneven surface shape.

In such a curved surface cutting method, as a milling tool, a disk-shaped tool body rotated around a rotation axis and a plurality of cutting blades provided on the outer peripheral edge portion thereof at equal intervals in the circumferential direction. Using a face mill equipped with and cutting with a milling tool, the cutting is performed by using a cutting blade that passes through a region in the tool feed direction side of the cutting blade rotation trajectory that is within the range of the pick feed. It is preferable that the movement locus of the cutting blade is elliptical so that the cusp height is reduced without reducing the pick feed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIG.
~ It demonstrates based on FIG.

The embodiment shown in FIGS. 1 to 4 relates to an example in which the curved surface cutting method of the present invention is applied to obtain the concave processed surface 21 shown in FIGS. 9 and 10.

That is, according to the curved surface cutting method of the present invention, as shown in FIG.
Further, as shown in FIG. 2, the milling tool 1 is moved in a predetermined direction (tool feed direction) A on a preset cutting line 22 in a state where the rotation axis 11 thereof is inclined with respect to the workpiece 2. By repeating this process for each cutting line 22, the surface (working surface) 20 of the workpiece 2 is cut into a curved surface shape corresponding to the cutting line 22. The workpiece 2 has a plurality of cutting lines 22.
Are set (see FIG. 10), but these cutting lines 22 are set according to the desired curved surface shape of the processing surface 21 and the processing mode. As the processing mode that defines the cutting line 22 ... Which is the movement mode of the milling tool 1,
As shown in 0, the one-way mode is adopted.

The milling tool 1 includes a disk-shaped tool body 12 which is rotated around a rotation axis 11 and a plurality of cutting edges 13 (only a part of which are shown) provided on the outer peripheral edge of the tool body 12 at equal intervals in the circumferential direction. It is a well-known face mill equipped with. Each cutting edge 13 is on a surface 16 orthogonal to the rotation axis 11,
Circular locus around the axis of rotation 11 (cutting blade rotation locus) 1
5. Exercise constant velocity on the top. The cutting with the milling tool 1 is an area on the tool feed direction side of the cutting blade rotation trajectory 15 and an area within the range of the pick feed P (area shown by a solid line in FIG. 4) 1
It is done by the cutting edge 13 passing through 5 '. The radius r of the cutting blade rotation locus 15 is not limited by the tool radius r ₀ of the ball end mill 101 because the cutting blade 13 moves at a constant speed, and can be set appropriately as necessary. Needless to say, the radius r of the cutting edge rotation locus 15 in the face mill is significantly larger than the tool radius r ₀ of the ball end mill 101.

As shown in FIGS. 1 and 2, the milling tool 1 is set in a state in which the rotation axis 11 is inclined at a predetermined angle θ in the tool feed direction A with respect to the normal line 25 of the machining surface 21 at the cutting point 24. . That is, in the milling tool 1, as shown in FIG. 2, the surface 16 on which the cutting edge rotation locus 15 (see FIGS. 3 and 4) exists matches the angle θ with respect to the tangent line 26 of the cutting line 22 at the cutting point 24. It is held in a state of being inclined by an angle.

Therefore, the cutting edge 13 for substantially cutting
The movement radius 15a of the cutting edge rotation locus 15 has an elliptical shape with the diameter 2r of the cutting edge rotation radius 15 as the major axis L, and the radius of curvature R of the strip-shaped cutting surface 21a formed by the milling tool 1 passing through one cutting line 22 is It becomes significantly larger than the radius of curvature r of the cutting edge rotation trajectory 15 (see FIG. 3). That is,
The cross-sectional shape of the strip-shaped cutting surface 21a matches the shape of the minor axis side portion of the ellipse 15a obtained by projecting the cutting blade rotation trajectory 15 on a surface orthogonal to the tool feed direction A (a surface passing through the normal 25). Will be done. The ellipse 15a has a major axis L of 2r and a minor axis S of 2r · sin θ, and becomes flatter as the inclination angle θ of the milling tool 1 is smaller. That is, the radius of curvature R of the strip-shaped cutting surface 21a increases as the inclination angle θ of the milling tool 1 decreases.

As described above, the cutting edge 13 which substantially cuts
Since the movement locus 15a of No. 2 has an elliptical shape, the radius of curvature R of the strip-shaped cutting surface 21a can be made extremely larger than that when the ball end mill 101 is used.
Therefore, the cusp height H can be significantly reduced without reducing the pick feed P. Moreover, since each cutting edge 13 moves at a constant speed and a difference in cutting speed does not occur, uniform cutting performance can be ensured, and a highly accurate strip-shaped cutting surface 21a, that is, a processed surface 21 with no uneven cutting is obtained. be able to.

That is, the radius r of the cutting edge rotation locus 15 in the milling tool 1 is larger than the radius r ₀ of the spherical cutting edge 115 in the ball end mill 101, and the movement locus 15a of the cutting edge 13 for substantially cutting is the cutting edge. Rotation locus 15
Since it has an elliptical shape having the diameter (2r) of which is the major axis L, the radius of curvature R of the strip-shaped cutting surface 21a obtained by the inclined milling tool 1 is extremely larger than that obtained by the ball end mill 101. Become. Therefore, the cusp height H can be significantly reduced, and a highly accurate machined surface 21 that does not require manual finishing can be obtained. Moreover, the pick feed P can be significantly increased as compared with the case where the ball end mill 101 is used, and the cutting efficiency does not decrease even when the machined surface 21 having a large area is obtained. Further, the cutting is performed by the cutting edge 13 that moves at a constant speed on the elliptical locus 15a, and uniform cutting performance is ensured, so that the strip-shaped cutting surface 21a is cut uniformly. That is, it is possible to obtain the mirror-finished processed surface 21 having a uniform surface roughness.

The inclination angle θ of the milling tool 1 is controlled in accordance with the geometrical conditions of the surface to be machined 20 and the machined surface 21 to be obtained (curvature of the surfaces 20, 21 etc.). That is, the processed surface 20 and the processed surface 2 at each cutting point 24 ...
According to the geometrical condition 1, the cusp height H is controlled to be constant even when the surfaces 20 and 21 have extremely large curvatures. However, such control is performed on the precondition that a cutting edge (hereinafter, referred to as a "non-acting blade") 13 'passing through a region that does not substantially contribute to cutting does not contact the processing surface 21. That is, the inclination angle θ of the milling tool 1
As shown in FIG. 2, the non-operating blade 13 ′, which is the cutting blade 13 passing through the area on the side opposite to the tool feeding direction A in the cutting blade rotation trajectory 15, does not interfere with the processing surface 21 (strip-shaped cutting surface 21 a). That is, it is controlled so that an appropriate gap C is created between the non-acting blade 13 ′ and the processing surface 21. As described above, the radius of curvature R of the strip-shaped cutting surface 21a is equal to that of the milling tool 1
The smaller the tilt angle θ is, the larger the tilt angle θ is, but it is preferable to set the tilt angle θ of the milling tool 1 in a range in which the clearance C can be secured.

Thus, the non-acting blade 13 'and the working surface 21
If a suitable gap C is created between the cutting edge and the cutting edge, the non-working blade 13 'does not damage the processing surface 21 and the chips can be discharged smoothly. Therefore, the processing accuracy is further improved. It is possible to improve the tool life.

The present invention is not limited to the above-mentioned embodiments, and can be appropriately improved and changed without departing from the basic principle of the present invention. For example, the curved surface cutting method of the present invention is not limited to the case of obtaining the concave processed surface 21 described above, but also the convex processed surface 21 as shown in FIG. 5 and the uneven surface shape as shown in FIG. The same can be applied to the case of obtaining the processed surface 21 (including the case of having a shape) as described above.

[0023]

As can be understood from the above description, according to the curved surface cutting method of the present invention, various curved surfaces can be cut with high accuracy and efficiency as compared with the case where a ball end mill is used. It is also possible to improve the tool life. In addition, the cusp height can be significantly reduced without reducing the pick feed, which contributes to uniform cutting performance in combination with the fact that the cutting edge moves at a constant speed and there is no difference in cutting speed. It is possible to secure a high-precision machined surface without uneven cutting. Therefore, a curved surface having a large area, which cannot be obtained by a ball end mill, can be processed with high accuracy without requiring manual finishing.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view showing a cutting state of a concave surface by a curved surface cutting method of the present invention.

FIG. 2 is a vertical cross-sectional side view showing an enlarged main part of FIG.

FIG. 3 is a vertical cross-sectional front view taken along the line III-III of FIG.

FIG. 4 is an explanatory diagram showing a relationship between a cutting blade rotation trajectory and a pick feed in a milling tool.

FIG. 5 is a vertical sectional side view showing a cutting state of a convex surface by the curved surface cutting method of the present invention.

FIG. 6 is a vertical sectional side view showing a cutting state of an uneven surface by the curved surface cutting method of the present invention.

FIG. 7 is a vertical sectional side view showing a cutting state of a concave surface by a ball end mill.

8 is a vertical sectional front view taken along the line VIII-VIII in FIG. 7. FIG.

FIG. 9 is a perspective view showing an example of a processed surface.

10 is a perspective view showing a microscopic form of the processed surface shown in FIG.

[Explanation of symbols]

1 ... Milling tool, 2 ... Workpiece, 3 ... Table, 11
… Rotation axis, 12… Tool body, 13,13 ′… Cutting blade, 1
5 ... Cutting blade rotation locus, 15a ... Movement locus, 20 ... Work surface, 21 ... Machining surface, 21a ... Strip cutting surface, 21b ... Caps, 22 ... Cutting line, 24 ... Cutting point, 25 ... Normal line, 2
6 ... Tangent line, A ... Tool feed direction, C ... Gap, H ... Cusp height, P ... Pick feed, R ... Radius of curvature of strip-shaped cutting surface,
θ: inclination angle.

Claims (2)

[Claims] 1. A milling tool having a circular cutting edge rotation locus is moved in a predetermined tool feed direction with its rotation axis inclined with respect to the normal to the machining surface at each cutting point. A curved surface cutting method for cutting a surface of a workpiece by a cutting edge that passes through a region of the cutting edge rotation path on the tool feed direction side, wherein the inclination angle of the rotation axis with respect to the normal line is the cutting edge rotation path. In the range where the cutting edge passing through the area on the side opposite to the tool feed direction does not interfere with the machining surface, the milling tool is controlled while changing so as to change according to the geometric conditions of the machining surface at each cutting point. A curved surface cutting method characterized in that a processed surface having a concave shape, a convex shape, or an uneven surface shape is obtained by moving the tool in the tool feeding direction. 2. A face milling tool comprising a milling tool having a disk-shaped tool body that is rotated around a rotation axis and a plurality of cutting blades that are provided on an outer peripheral edge of the tool body at equal intervals in the circumferential direction. Yes, by performing cutting with a milling tool with a cutting edge that passes through the area in the tool feed direction side of the cutting edge rotation path and within the range of the pick feed, the movement path of the cutting edge to be cut is elliptical. 2. The curved surface cutting method according to claim 1, wherein the cusp height is reduced without reducing the pick feed.