JP2001198722A - Christmas tree formed milling cutter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Christmas three formed milling cutter with the blade tip diameter gradually decreased to become smaller toward the tool tip side while the blade tip diameter is increased and decreased in which flank butting at the smallest diameter part is restricted while preventing the relief angle of a large diameter part from becoming excessively small or the relief angle of a small diameter part from becoming excessively large. SOLUTION: The relief angle α of an outer circumferential cutting tip is set to roughly satisfy the following equation (1) predetermined under consideration of difference in abrasion amount due to difference of blade tip diameters D so that flank butting caused by abrasion near the blade tips occurs roughly simultaneously along the whole ranges of the outer circumferential cutting tips regardless of the difference in the blade tip diameters D. α=-(D/15)+12+(8/15)...(1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Christmas cutter for cutting a tree-shaped groove. In particular, the second cutting of the outer peripheral cutting edge is performed using a three-dimensional processing machine or the like, and the flank shape is arbitrarily set. It is about improvement of Christmas cutter which can be done.

[0002]

2. Description of the Related Art As a mounting structure for mounting a turbine wheel of a gas turbine on a rotating shaft, as shown in FIG. 6, a plurality of tree-shaped grooves 12 formed on the outer periphery of a rotating shaft 10 have blades of the turbine wheel. 14 are fitted one by one. FIG. 7 is a cross-sectional view showing the tree-shaped groove 12 in an enlarged manner. The groove width is symmetrical with respect to the groove center S and increases and decreases in the groove depth direction (downward in the figure) like an inverted Christmas tree. It is provided with three wide portions 16, 18, 20 which are gradually narrowed and are spaced apart in the groove depth direction and have a wide groove width, and the widths of the wide portions 16, 18, 20 are set at a deep position. (The bottom of the groove) is smaller.

[0003] As a tool for cutting such a tree-shaped groove, the diameter of the cutting edge of the outer peripheral cutting edge is gradually reduced while increasing and decreasing toward the tool tip side in response to a change in the groove width of the tree-shaped groove. The known Christmas cutter is known. The Christmas cutter described in Japanese Patent Application Laid-Open No. H11-245112 is an example, and the flank of the outer peripheral cutting edge is formed continuously from the cutting edge, and in a state where the flank is developed around the axis, the flank is extended in the axial direction. Irrespective of the change of the cutting edge diameter, the diameter is determined so that the diameter decreases linearly at a constant clearance angle α (°) with respect to a constant straight line, and forms an arc shape in a cross section perpendicular to the axis. It has become. FIG. 8 is a cross-sectional view showing a state in which such an outer peripheral cutting edge 22 is developed around an axis, and a flank 24 is shown.
Is a clearance angle α with respect to a straight line L representing the same diameter as the cutting edge 26.
It is formed using a three-dimensional processing machine or the like so that the diameter dimension is reduced linearly. According to such a flank shape, the clearance angle of the large-diameter portion is too small or the clearance angle of the small-diameter portion is too large compared to the cam dropping method in which the clearance is constant regardless of the dimensional change of the cutting edge diameter. Is prevented.

[0004]

However, even in the Christmas cutter in which the clearance angle α is fixed as described above, if the vicinity of the cutting edge is worn by use, the Christmas cutter is rotated around the axis and moved in a direction perpendicular to the axis. When the grooving is performed, the flank contact is made at the minimum diameter portion where the cutting edge diameter is the smallest (in the case of the tree-shaped groove 12 in FIG. 7, the portion for processing the small diameter portion between the wide portions 18 and 20). (2nd hit), there is a problem that the rotational resistance increases and the tool breaks. That is, as shown in FIG. 8, a predetermined angular position θ from the cutting edge 26 around the tool axis.
The clearance amount δ (θ) in (°) is expressed by the following equation (3) using the cutting edge diameter (outer diameter) D and the clearance angle α. If the clearance angle α is the same, it is proportional to the cutting edge diameter D. In the small diameter portion where the blade edge diameter D is small, the clearance amount δ (θ) is small, and the flank contact caused by the tool feed occurs from the minimum diameter portion.
Further, in the case of the Christmas cutter, since the cutting edge diameter D increases and decreases in the axial direction, stress concentration is likely to occur at the minimum diameter portion, and the cross-sectional area of the minimum diameter portion is minimized. There is a high possibility that the tool will break due to resistance. δ (θ) = tanα · π · D · θ / 360 (3)

The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent a clearance angle of a large diameter portion from becoming too small and a clearance angle of a small diameter portion from becoming too large. The object is to suppress the flank contact of the minimum diameter portion.

[0006]

In order to achieve the above object, the first invention is directed to a device which is driven to rotate in a direction perpendicular to the axis while being rotated about the axis. In order to cut a tree-shaped groove that is symmetric and gradually narrows while increasing and decreasing the groove width in the groove depth direction like an inverted Christmas tree, the cutting edge diameter of the outer peripheral cutting edge changes with the change in the groove width. In the Christmas cutter, the diameter of which gradually decreases while increasing and decreasing as it goes toward the tool tip side, (a) the flank of the outer peripheral cutting edge is formed substantially continuously from the cutting edge, and around the axis. In the expanded state, the diameter is determined so that the diameter decreases linearly at a predetermined clearance angle α (°) with respect to a constant straight line, and has an arc shape in a cross section perpendicular to the axis. On the other hand, (b) The angle of inclination α is ± 3 around the variable y expressed by the following equation (1) with respect to the edge diameter D over the entire range of change of the edge diameter (outer diameter) D (mm) of the outer peripheral cutting edge. And the cutting edge diameter D is set so as to decrease as the cutting edge diameter D increases. y = − (D / 15) +12+ (8/15) (1)

According to a second aspect of the present invention, in the Christmas cutter of the first aspect, the clearance angle α is such that the flank contact caused by wear near the cutting edge is substantially equal to the entire outer cutting edge regardless of the difference in the cutting edge diameter D. It is characterized in that the cutting edge diameter D is set in accordance with a predetermined relationship in consideration of the difference in the wear amount due to the difference in the cutting edge diameter D so as to occur simultaneously.

According to a third aspect of the present invention, in the Christmas cutter according to the second aspect, the clearance angle α is set so as to substantially satisfy the relationship of the following equation (2) predetermined using the blade diameter D as a parameter. It is characterized by the following. α = − (D / 15) +12+ (8/15) (2)

[0009]

In such a Christmas cutter, since the clearance angle α of the outer peripheral cutting edge is set so as to decrease as the cutting edge diameter D increases, the clearance angle α of the minimum diameter portion increases. In addition, flank contact due to wear near the cutting edge and tool breakage due to the flank contact are suppressed. The clearance angle α is determined so as to fall within a range of ± 3 ° with respect to the variable y represented by the equation (1) with respect to the variable diameter of the cutting edge D over the entire range of the change of the cutting edge diameter D. Therefore, it is possible to prevent the clearance angle of the large-diameter portion from being too small to impair the cutting performance (sharpness, etc.), and prevent the clearance angle from being small-diameter portion from becoming too large to easily cause chipping.

In the second invention and the third invention, the flank contact caused by abrasion near the cutting edge is generated almost simultaneously over the entire outer peripheral cutting edge regardless of the difference in the cutting edge diameter D.
The clearance angle α is set in accordance with a predetermined relationship using the cutting edge diameter D as a parameter in consideration of the difference in the amount of wear due to the difference in the diameter, so that the preferential flank contact of the minimum diameter portion is more reliably prevented. Tool life is improved.

That is, if the amount of wear in the vicinity of the cutting edge is the same, the escape amount may be the same regardless of the dimensional change of the cutting edge diameter D as in the conventional cam dropping method. If it is different, the cutting length per rotation (πD / 2) is different, and the wear amount changes accordingly. Therefore, it is not necessary to reduce the clearance angle α of the small diameter portion so that the clearance amount becomes the same. The optimum relationship is determined by simulation or the like.

Incidentally, the coefficient of the cutting edge diameter D in the expressions (1) and (2) minus (1/15) indicates that the flank contact occurs almost simultaneously in the entire outer peripheral cutting edge regardless of the difference in the cutting edge diameter D. Is a value that greatly contributes to the operation, and a constant of 12+ (8/15)
Is a value that greatly contributes to the cutting performance (such as sharpness) of the outer peripheral cutting edge and the prevention of chipping.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A Christmas cutter according to the present invention has a flank of an outer peripheral cutting edge formed substantially continuously from a cutting edge, and has a margin width of substantially zero. Or, even if a margin is provided, it means that the margin width is about 0.1 mm or less.

The outer peripheral cutting edge may be a straight blade parallel to the axis, but may be a torsion blade twisted around the axis. The change range of the cutting edge diameter D of the outer peripheral cutting edge is appropriately set according to the width dimension of the tree-shaped groove.
It can be changed within a range of about 60 mm.

The clearance angle α is desirably set so as to decrease continuously as the cutting edge diameter D increases. In the first and second inventions as well, for example, the cutting edge diameter D is set in advance as a parameter. The clearance angle α is set so as to linearly decrease according to the relational expression. However, the first
In the invention and the second invention, the clearance angle α may be set using a data map or the like in which the clearance angle α changes nonlinearly (curved) or stepwise with respect to the cutting edge diameter D.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The Christmas cutter 30 shown in FIG. 1 is for cutting the tree-shaped groove 12 and is provided with a shank 32 and a blade portion 34 integrally. FIG. 2 (a)
Is a cross-sectional view perpendicular to the axis of the blade portion 34. In this embodiment, three chip discharge grooves 36 are provided at equal angular intervals around the axis, and three pieces of outer periphery are provided along the chip discharge grooves 36. The cutting edge 38 and the bottom edge 3 continuous with the outer peripheral cutting edge 38
9 are provided. The outer peripheral cutting edge 38 and the bottom edge 39 perform cutting by rotating the Christmas cutter 30 clockwise as viewed from the shank 32 side, and the chip discharge groove 36 has a twist of about 5 °. It is twisted clockwise at the corner. In addition, the outer peripheral cutting edge 38 is gradually reduced in diameter while increasing or decreasing the cutting edge diameter toward the tool tip side corresponding to the uneven shape of the groove side surface of the tree-shaped groove 12. The cutting edge diameter (outer diameter) D of the outer peripheral cutting edge 38 is
It is appropriately set according to the width dimension of the tree-shaped groove 12, and in the present embodiment, is changed within a range of about 10 mm (minimum diameter dimension between the wide sections 18 and 20) to 46 mm (diameter dimension of the wide section 16). Have been. The blade portion 34 in FIG.
FIG. 2B is a vertical cross-sectional view taken along a chip discharge groove 36. FIG.

FIG. 3 is a cross-sectional view of the outer peripheral cutting edge 38 developed around the axis. The flank 40 has a cutting edge side portion 40a within a predetermined angle range θ ₁ (see FIG. 2) from the cutting edge 42 around the axis. The heel side portion 40b on the side of the heel 44 is formed in a cylindrical shape having a constant diameter (a constant relief amount). The angle range θ ₁ is
In the present embodiment, the angle is about 30 °, and the cutting edge side portion 40a has a margin so that the diameter is linearly reduced at a predetermined clearance angle α (°) with respect to a straight line L representing the same diameter as the cutting edge 42. The blade is formed continuously from the cutting edge 42 without the blade. Such a flank 40 of the cutting edge side portion 40a is formed by, for example, rotating a tool material around an axis at a constant speed and relatively bringing a grinding wheel relatively close at a constant speed with a three-dimensional processing machine or the like. it can. The cutting edge side portion 4 in which the diameter dimension is linearly reduced in a state of being developed around the axis as described above.
0a has an arc shape in the cross section perpendicular to the axis shown in FIG. The outer peripheral cutting edge 38 is provided with a rake angle γ of about 11 ° to 13 °.

The clearance angle α is set in accordance with the above-mentioned equation (2), which is set in advance using the blade diameter D as a parameter, over the entire area of the outer peripheral cutting edge 38 where the blade diameter D changes. Is changing. The solid line in FIG. 4 illustrates the equation (2), and the clearance angle α decreases linearly as the cutting edge diameter D increases. Also, this (2)
The formula considers the difference in the amount of wear due to the difference in the cutting edge diameter D so that the flank contact caused by the wear near the cutting edge 42 occurs almost simultaneously over the entire area of the outer peripheral cutting edge 38 regardless of the difference in the cutting edge diameter D. The clearance angle α is determined by experiments, simulations, etc., compared with the case where the amount of clearance is the same regardless of the dimensional change of the blade edge diameter D as in the conventional cam dropping method.
Change | Δα / ΔD | is small. Thus, the cutting edge side portion 40 in which the clearance angle α changes in response to the change in the cutting edge diameter D
The flank 40 of a is, for example, using a three-dimensional processing machine or the like, while changing at least one of the rotational speed of the tool material and the approaching speed of the grinding wheel in accordance with the change in the clearance angle α, such tool material and The grinding wheel is relatively moved in the axial direction of the tool material, and the flank surface 40 of each portion in the axial direction of the tool material is sequentially ground in the circumferential direction.

In such a Christmas cutter 30, the clearance angle α of the outer peripheral cutting edge 38 decreases linearly as the cutting edge diameter D increases, and a relational expression predetermined using the cutting edge diameter D as a parameter. (2), the clearance angle α at the minimum diameter portion is maximized, and the flank contact due to wear near the cutting edge 42 and the tool breakage due to the flank contact are suppressed. In particular, the relational expression (2) indicates that the flank contact due to wear near the cutting edge 42 occurs at the same time in the entire area of the outer peripheral cutting edge 38 regardless of the difference in the cutting edge diameter D. Since it is determined in consideration of the difference in the amount of wear, preferential flank contact of the smallest diameter portion is more reliably prevented, and tool life is improved.

In the above-mentioned relational expression (2), the change in the clearance angle α is not so large that the clearance amount becomes the same regardless of the dimensional change of the blade edge diameter D as in the conventional cam dropping method. This prevents the cutting angle (e.g., sharpness) from being impaired due to an excessively small clearance angle, and the clearance angle at the small diameter portion from becoming excessively large, which tends to cause chipping.

The dashed line in FIG. 4 is within a range of ± 3 ° of the clearance angle α in the equation (2). Within this dashed line, for example, the clearance angle α increases linearly as the edge diameter D increases. The clearance angle α may be set according to a predetermined relational expression, data map, or the like that is predetermined so as to be smaller in a characteristic or curvilinear (non-linear) manner. In addition, as shown by a solid line in FIG. 5, the clearance angle α may be set according to a data map or the like defined to change stepwise according to the equation (2).

Although the embodiments of the present invention have 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 a Christmas cutter according to an embodiment of the present invention.

FIG. 2 is a sectional view of a blade portion of the Christmas cutter of FIG. 1,
(a) is a transverse sectional view perpendicular to the axis, and (b) is a longitudinal sectional view cut along a chip discharge groove.

FIG. 3 is a cross-sectional view of an outer peripheral cutting edge of the Christmas cutter of FIG. 1 developed around an axis.

FIG. 4 is a diagram illustrating a relationship between a cutting edge diameter D of an outer peripheral cutting edge of the Christmas cutter of FIG. 1 and a clearance angle α.

FIG. 5 is a diagram illustrating another example of the relationship between the edge diameter D of the outer peripheral cutting edge and the clearance angle α.

FIG. 6 is a diagram showing a tree-shaped groove for mounting a blade of a turbine wheel.

FIG. 7 is an enlarged sectional view showing the tree-shaped groove of FIG. 6;

FIG. 8 is a cross-sectional view in which the outer peripheral cutting edge of a conventional Christmas cutter in which the clearance angle α is constant irrespective of a change in the edge diameter D is developed around an axis.

[Explanation of symbols]

12: Tree-shaped groove 30: Christmas cutter 3
8: Outer peripheral cutting edge 40: Flank 42: Cutting edge
D: Cutting edge diameter α: Relief angle

Claims (3)

[Claims] 1. A groove width is symmetrical with respect to the center of a groove and is set in a groove depth direction like an inverted Christmas tree by being moved in a direction perpendicular to the axis while being rotationally driven around the axis. In order to cut a tree-shaped groove that is gradually narrowing while increasing and decreasing, the cutting edge diameter of the outer peripheral cutting edge is gradually reduced to a smaller diameter while increasing and decreasing toward the tool tip side in accordance with the change in the groove width. In the Christmas cutter, the flank of the outer peripheral cutting edge is formed substantially continuously from the cutting edge, and has a predetermined flank angle α ( °), the radial dimension is determined to decrease linearly, and has an arc shape in a cross section perpendicular to the axis. On the other hand, the clearance angle α is the cutting edge diameter (outer diameter) D of the outer peripheral cutting edge. (M
m), within the range of ± 3 ° around the variable y expressed by the following equation (1) with respect to the cutting edge diameter D, and becomes smaller as the cutting edge diameter D increases. Christmas cutter characterized by y =-(D / 15) +12+ (8/15) (1). 2. The clearance angle α is determined so that the flank contact caused by wear near the cutting edge occurs almost simultaneously over the entire outer peripheral cutting edge regardless of the difference in the cutting edge diameter D. 2. The Christmas cutter according to claim 1, wherein the cutting edge diameter D is set as a parameter in accordance with a predetermined relationship in consideration of a difference in wear amount due to the difference. 3. The clearance angle α is set so as to substantially satisfy the relationship of the following equation (2) predetermined using the blade diameter D as a parameter: α = − (D / 15) +12+ (8) / 15) (2) The Christmas cutter according to claim 2, wherein: