JP6780420B2 - Taper ball end mill - Google Patents

Description

The present invention relates to a tapered ball end mill.

For cutting of impellers and blisks, taper ball end mills suitable for machining deep parts are used (see, for example, Patent Document 1).

JP-A-2002-126929

The tapered ball end mill has a ball-shaped bottom blade provided at the tip and a tapered outer peripheral blade. In general, the taper ball end mill uses not only the bottom blade but also the outer peripheral blade more frequently than the general ball end mill. Therefore, there is a demand for a tapered ball end mill that secures the strength of the bottom blade and the outer peripheral blade in a well-balanced manner.

One object of the present invention is to provide a tapered ball end mill that simultaneously secures the strength of the bottom blade and the outer peripheral blade.

According to one aspect of the present invention, it is a tapered ball end mill having a spherical bottom blade and a tapered outer peripheral blade that rotates around an axis, and is a tool as it goes from the tip surface to the proximal end side of the tapered ball end mill. A chip discharge groove that spirally twists toward the side opposite to the rotation direction is provided, and the chip discharge groove is connected to a bottom surface of the chip discharge groove that faces radially outward with respect to the axis and a tool rotation. It is the distance between the bottom blade and the bottom surface in the spherical diameter direction of the bottom blade, including a tip rake face facing a direction and a boundary line formed between the tip rake surface and the bottom surface. The dimension of the tip rake face determined with reference to the boundary line is defined as the width of the tip rake face, and the percentage of the maximum width of the tip rake face along the ball diameter direction of the bottom blade with respect to the sphere radius of the bottom blade. A taper ball end mill satisfying the following two equations, where A is defined, the twist angle of the outer peripheral blade is θ °, and the taper angle of the outer peripheral blade is β °.

15 ≤ A ≤ 30
11 ≤ θ-β ≤ 21

Here, the percentage of the maximum width of the tip rake face along the ball diameter direction of the bottom blade with respect to the sphere radius of the bottom blade is referred to as the rake width ratio. According to the above configuration, it means that the rake width ratio is 15% or more and 30% or less. Further, according to the above configuration, it means that the difference between the twist angle of the outer peripheral blade and the taper angle of the outer peripheral blade is 11 ° or more and 21 ° or less. By making the difference between the rake width ratio and the twist angle and the taper angle the above-mentioned relationship, the strength balance between the bottom blade and the outer peripheral blade can be optimized, and a tapered ball end mill that is less likely to break can be provided.

Further, it is preferable that the taper ball end mill described above further satisfies the following formula.
A ≤ 25

According to the above configuration, it is possible to provide a tapered ball end mill that is less likely to break.

According to the present invention, it is possible to provide a tapered ball end mill that simultaneously secures the strength of the bottom blade and the outer peripheral blade.

The perspective view which shows the taper ball end mill of an embodiment. A side view of the tapered ball end mill of the embodiment. Front view of the tapered ball end mill of the embodiment. Enlarged view of region IV of FIG. The graph which shows the preferable relationship of the difference between a twist angle and a taper angle, and a rake width ratio.

Hereinafter, embodiments to which the present invention has been applied will be described in detail with reference to the drawings. In addition, in the drawing used in the following description, in order to make the feature portion easy to understand, the non-feature portion may be omitted for convenience.

FIG. 1 is a perspective view showing a tapered ball end mill 1 of the present embodiment. FIG. 2 is a side view of the tapered ball end mill 1. FIG. 3 is a front view of the taper ball end mill 1. Hereinafter, the taper ball end mill 1 is simply referred to as an end mill.

The end mill 1 is a substantially columnar member extending along the axis O. The end mill 1 is made of, for example, a hard material such as cemented carbide, cermet, or ceramics. The end mill 1 has a blade portion 3a located at one end in the axis O direction, and a shank portion 3b provided at a portion other than the blade portion 3a.

In the present specification, among the axial O directions of the end mill 1, the direction from the shank portion 3b to the blade portion 3a is referred to as the tip end side, and the direction from the blade portion 3a to the shank portion 3b is referred to as the base end side. Further, the direction orthogonal to the axis O is called the radial direction. Of the radial directions, the direction approaching the axis O is referred to as the inside in the radial direction, and the direction away from the axis O is referred to as the outside in the radial direction. Further, the direction of orbiting around the axis O is called the circumferential direction. Of the circumferential directions, the direction in which the end mill 1 rotates during cutting is called the tool rotation direction T.

The end mill 1 is gripped by the spindle of the machine tool or the like at the shank portion 3b, and is rotated in the tool rotation direction T around the axis O. The end mill 1 is used for cutting (rolling) a work material such as a metal material. Further, the end mill 1 is given a feed in a direction intersecting the axis O as it rotates around the axis O, and the blade portion 3a performs shoulder cutting, grooving, R cutting, copying, etc. on the work material. I do.

The blade portion 3a is formed in a tapered shape that tapers toward the tip end side of the end mill 1. Further, the tip of the blade portion 3a is formed in a spherical shape. In the blade portion 3a, the outer peripheral blade 6 is provided in the tapered region, and the bottom blade 9 is provided in the spherically formed tip. That is, the end mill 1 includes a ball-shaped bottom blade 9 and a tapered outer peripheral blade 6.

A plurality of (four in the present embodiment) chip discharge grooves 4 are formed on the outer periphery of the blade portion 3a. The plurality of chip discharge grooves 4 are formed at equal intervals in the circumferential direction. The chip discharge groove 4 is open to the tip surface of the end mill 1. The chip discharge groove 4 is spirally twisted at a constant twist angle θ ° from the tip surface of the end mill 1 toward the base end side toward the side opposite to the tool rotation direction T. The chip discharge groove 4 is cut up to the outer periphery of the end mill 1 at the end portion of the blade portion 3a on the proximal end side.

A cutting edge is formed at the edge of the chip discharge groove 4 on the tool rotation direction T side. The cutting edge includes an outer peripheral blade 6 located at the tapered portion of the blade portion 3a and a bottom blade 9 located at the tip of the blade portion 3a. The outer peripheral blade 6 and the bottom blade 9 smoothly continue along the chip discharge groove 4. The end mill 1 of the present embodiment has four outer peripheral blades 6 and two bottom blades 9. Therefore, two of the four outer peripheral blades 6 are smoothly continuous with the bottom blade 9, and the remaining two outer peripheral blades 6 are not continuous with the bottom blade 9 and are interrupted near the tip. A pair of chip discharge grooves 4 located on both sides in the circumferential direction of the outer peripheral blade 6 which is not continuous with the bottom blade 9 are connected near the tip of the end mill 1. The number of cutting edges of the end mill 1 (the number of outer peripheral blades 6 and bottom blades 9) is not particularly limited.

The wall surface of the chip discharge groove 4 includes a bottom surface 2 and rake surfaces 7 and 10.
The bottom surface 2 is a surface of the chip discharge groove 4 that faces outward in the radial direction with respect to the axis O.
Further, the rake faces 7 and 10 are wall surfaces facing the tool rotation direction T in the chip discharge groove 4. The rake surfaces 7 and 10 include an outer peripheral rake surface 10 formed in connection with the outer peripheral blade 6 and a tip rake surface 7 formed in connection with the bottom blade 9.

The outer peripheral blade 6 is formed on the outer peripheral surface of the blade portion 3a at the intersecting ridge line between the outer peripheral rake surface 10 and the outer peripheral relief surface 5. The outer peripheral relief surface 5 is a surface of the chip discharge groove 4 adjacent to the side opposite to the tool rotation direction T. The outer peripheral blade 6 extends in a spiral winding shape (spiral shape) along the outer peripheral edge of the chip discharge groove 4. The width of the outer peripheral flank 5 (the length in the direction orthogonal to the outer peripheral blade 6) gradually becomes wider toward the rear end side (shank portion 3b side) in the length direction of the outer peripheral blade 6.

The outer peripheral blade 6 is a tapered blade. Therefore, the diameter of the outer peripheral blade 6 (the distance from the axis O along the radial direction to the outer peripheral blade 6, that is, the radius) becomes smaller toward the tip side along the axis O direction. The rotation locus formed by rotating the outer peripheral blade 6 around the axis O is one conical surface centered on the axis O.

The bottom blade 9 is formed at the tip of the blade portion 3a at the intersecting ridge line between the tip rake face 7 and the tip flank surface 8. The tip flank surface 8 has a convex curved surface shape that is convex toward the outer peripheral side of the tip of the end mill 1. The base end portion of the tip flank surface 8 is connected to the tip end portion of the outer peripheral flank surface 5.

The bottom blade 9 has a convex arc shape that is convex toward the outer peripheral side of the tip of the end mill 1. Therefore, in the side view of the end mill 1 shown in FIG. 2, the rotation locus formed by the bottom blade 9 rotating around the axis O is one hemisphere centered on the center point C on the axis O.

(Scoop width ratio A)
FIG. 4 is an enlarged view of region IV of FIG. 2, which is a view seen from the direction facing the tip rake face 7 of the bottom blade 9.
The bottom blade 9 is a line segment on a spherical surface having a radius R centered on the center point C. As shown in FIG. 4, the width d is defined as the dimension of the tip rake face 7 along the spherical diameter direction of the bottom blade 9. The width d of the tip rake face is the distance between the bottom blade 9 and the bottom surface 2 in the ball diameter direction of the bottom blade 9. The width d of the tip rake face 7 gradually increases from the tip side toward the base end side to become the maximum width D, and further gradually decreases toward the base end side. The spherical radial direction of the bottom blade 9 means a direction in a linear direction passing through the center point C of the hemisphere, which is the rotation locus of the bottom blade 9.

Here, the percentage of the maximum width D of the tip rake face 7 along the ball diameter direction of the bottom blade 9 with respect to the ball radius R of the bottom blade 9 is referred to as a rake width ratio A. The rake width ratio A can be expressed as 100 × D / R.
The rake width ratio A preferably satisfies the following (Equation 1).
15 ≤ A ≤ 30 ... (Equation 1)

As shown in FIG. 4, a boundary line 2a is formed between the tip rake face 7 and the bottom surface 2. The boundary line 2a is located on the base end side in the protruding direction of the tip rake face 7. The bending moment caused by the reaction force received by the bottom blade 9 from the work material becomes maximum along the boundary line 2a. Further, the bending moment generated at the boundary line 2a is also maximized at the portion where the width d of the tip rake face 7 is maximized. Therefore, at the ball-shaped tip of the end mill 1 on which the bottom blade 9 is formed, the boundary line 2a is likely to be the starting point of breakage. In particular, breakage is likely to occur at a portion corresponding to the maximum width D at which the width d of the tip rake face 7 is maximum. By setting the rake width ratio A to 30% or less, the maximum width D of the tip rake face 7 can be suppressed, and the bottom blade 9 can be prevented from being broken during cutting.
Further, the width d of the tip rake face 7 correlates with the depth of the chip discharge groove 4 at the tip of the end mill 1. By setting the rake width ratio A to more than 15%, the chip discharge groove 4 can be made to have a sufficient depth, and the chip discharge property of the bottom blade 9 and the outer peripheral blade 6 at the time of cutting can be sufficiently ensured.

A curved surface portion (sumi R) that smoothly connects the tip rake face 7 and the bottom surface 2 may be formed on the boundary line 2a between the tip rake face 7 and the bottom surface 2. In such a case, the curved portion between the tip rake face 7 and the bottom surface 2 is virtually removed, and the boundary line 2a is virtually defined as if they intersect sharply, and the boundary line 2a is used as a reference. The width d of the tip rake face 7 shall be determined.

(Twist angle θ ° and taper angle β °)
Next, the relationship between the twist angle θ ° and the taper angle β ° of the outer peripheral blade 6 will be described.
As shown in FIG. 2, the twist angle θ ° of the outer peripheral blade 6 is an inclination angle of the outer peripheral blade 6 with respect to the axis O at the intersection of the axis O and the outer peripheral blade 6 when the end mill 1 is viewed from the side. The twist angle θ ° is constant along the axis O.

Peripheral cutting edge 6, thus stiffness in order to increase the twist angle theta ° is impaired. That is, when the twist angle θ ° is increased, the strength of the outer peripheral blade 6 is lowered and the outer peripheral blade 6 is easily broken.
On the other hand, the bottom blade 9 is less likely to break when the twist angle θ ° is increased. The bottom blade 9 is smoothly connected to the outer peripheral blade 6. As the twist angle θ ° of the outer peripheral blade is increased, the curvature of the bottom blade 9 in the front view (FIG. 3) also increases accordingly. As a result, the bottom blade 9 is formed to be long, and the cutting resistance by the bottom blade 9 can be reduced, and as a result, the bottom blade 9 is less likely to break.
On the contrary, when the twist angle θ ° of the outer peripheral blade 6 is reduced, the outer peripheral blade 6 is less likely to break and the bottom blade 9 is more likely to break.

As shown in FIG. 2, the taper angle β ° of the outer peripheral blade 6 is an angle formed by a pair of common tangents of a plurality of outer peripheral blades 6 arranged along the axis O when the end mill 1 is viewed from the side. When the taper angle β ° changes, the preferred twist angle θ ° of the outer peripheral blade 6 changes.

When the outer peripheral blades 6 have a tapered shape and the twist angle θ ° is constant along the axis O, the distance (pitch) between the outer peripheral blades 6 gradually shortens toward the tip. Here, the end mills having the same shape of the bottom blade 9 and the twist angle θ ° of the outer peripheral blade 6 but different taper angles β ° are compared. In this case, the end mill taper angle beta ° is large, than the taper angle beta ° is small, the shank portion 3b side of the peripheral cutting edge 6 ing and the large diameter. Therefore, in the end mill 1, the rigidity of the outer peripheral blade 6 is increased by increasing the taper angle β °, and as a result, the outer peripheral blade 6 is less likely to break. On the other hand, when the taper angle β becomes large, the rigidity of the outer peripheral blade 6 increases, so that the strength of the bottom blade 9 decreases relatively. Therefore, when the cutting load increases, the bottom blade 9 is likely to break. That is, the increase / decrease in the taper angle β ° acts in the opposite direction from the viewpoint of the ease of breaking of the outer peripheral blade 6 as compared with the increase / decrease in the twist angle θ °.
If the taper angle β ° is made too large, the end mill 1 tends to interfere with the non-cut portion of the work. Therefore, the taper angle β ° is limited.

The taper angle β ° is preferably 3 ° or more and 5 ° or less. By setting the taper angle β ° to 3 ° or more and 5 ° or less, it is possible to provide an end mill 1 having sufficient rigidity while facilitating machining of a deep shape.

In view of the above action, it is preferable that the twist angle θ ° and the taper angle β ° satisfy the relationship shown in the following (Equation 2).
11 ≤ θ-β ≤ 21 ... (Equation 2)

By setting the difference between the twist angle θ ° and the taper angle β ° to more than 11 ° and less than 21 °, the balance of strength between the outer peripheral blade 6 and the bottom blade 9 is optimized, and breakage of the outer peripheral blade 6 and the bottom blade 9 is suppressed. can do.

FIG. 5 is a graph showing a preferable relationship between the difference (θ−β) between the twist angle θ ° and the taper angle β ° and the rake width ratio A in the end mill 1. In FIG. 5, the region surrounded by the solid line L1 is the relationship between the preferable twist angle θ °, the taper angle β °, and the rake width ratio A.

It is more preferable that the twist angle θ °, the taper angle β °, and the rake width ratio A further satisfy the relationship shown in the following (Equation 3).
2 (θ-β) -17 ≤ A ≤ 2 (θ-β) -2 ... (Equation 3)

The twist angle θ °, the taper angle β °, and the rake width ratio A that satisfy the relationship of (Equation 3) are located in the region sandwiched between the chain lines L2 and L3 shown in FIG. By adopting a twist angle θ °, a taper angle β °, and a rake width ratio A that satisfy the relationship of (Equation 3), breakage of the outer peripheral blade 6 and the bottom blade 9 can be suppressed.

It is more preferable that the rake width ratio A further satisfies the relationship shown in the following (Equation 4).
A ≤ 25 ... (Equation 4)

The rake width ratio A satisfying the relationship of (Equation 4) is located in the region below the chain line L4 shown in FIG. By adopting a twist angle θ °, a taper angle β °, and a rake width ratio A that satisfy the relationship of (Equation 3), it is possible to provide an end mill 1 that is less likely to break.

Although the embodiments of the present invention have been described above, the configurations and combinations thereof in the embodiments are examples, and additions, omissions, substitutions, and other modifications of the configurations are made without departing from the spirit of the present invention. Is possible. Moreover, the present invention is not limited to the embodiments.

Sample No. for confirming the effect of the tapered ball end mill 1 of the embodiment. 1-No. 14 was created and its effect was confirmed.
Sample No. 1-No. A common configuration of the 14 end mills 1 will be described. The end mill 1 of each sample is made of a coated cemented carbide. Further, in the end mill 1 of each sample, the bottom blade 9 has two blades, the outer peripheral blade 6 has four blades, the ball radius R of the bottom blade 9 is 1 mm, and the taper angle β ° of the outer peripheral blade 6 is It is 4 °, the blade length of the outer peripheral blade 6 is 20 mm, and the clearance angles of the outer peripheral flank surface 5 and the tip flank surface 8 are 10 °.
In addition, sample No. 1-No. In the end mill 1 of 14, the twist angle θ ° and the rake width ratio A of the outer peripheral blade 6 are variously changed as shown in Table 1 in the subsequent stage.

Sample No. 1-No. Cutting test in which the feed rate of the end mill 1 is changed in the range of 1,020 mm / min to 4,080 mm / min at a rotation speed of 17,000 / min using 14 end mills 1 to perform grooving with a depth of 5 mm. Was done. A2618 was used as the work material.

When the rotation speed of the end mill 1 is kept constant and the feed rate is variously changed, the feed amount per rotation of the end mill 1 changes. When the feed amount per rotation is increased, the load applied to the end mill 1 is increased, and the outer peripheral blade 6 or the bottom blade 9 is likely to be broken. In the cutting test, breakage of the end mill 1 when the feed rate was changed was confirmed, and the feed amount at the time of breakage is summarized in Table 1. In addition, sample No. 1-No. The difference (θ−β) between the twist angle θ ° and the taper angle β ° and the rake width ratio A of 14 are illustrated in FIG.

As shown in Table 1, it was confirmed that when (Equation 1) and (Equation 2) are satisfied, the end mill 1 that does not cause breakage can be configured when the feed amount per rotation is less than 0.18 mm / rev. Further, when the condition (Equation 3) is satisfied, it has been confirmed that the end mill 1 can be configured without breakage when the feed amount per rotation is less than 0.21 mm / rev. Further, it was confirmed that when the condition (Equation 4) is satisfied, the end mill 1 can be configured without breakage when the feed amount per rotation is less than 0.24 mm / rev.

1 ... end mill (tapered ball end mill), 6 ... outer peripheral blade, 9 ... bottom blade, A ... rake width ratio, D ... maximum width, d ... width, O ... axis, R ... sphere radius, θ ... twist angle (°) , Β ... Taper angle (°)

Claims (2)

A tapered ball end mill that rotates around an axis with a spherical bottom blade and a tapered outer peripheral blade.
It is provided with a chip discharge groove that twists spirally from the tip surface of the tapered ball end mill toward the base end side toward the side opposite to the tool rotation direction.
The chip discharge groove is
The bottom surface of the chip discharge groove facing outward in the radial direction with respect to the axis,
The tip rake face that is connected to the bottom blade and faces the tool rotation direction ,
Includes a boundary line formed between the tip rake face and the bottom surface.
The distance between the bottom blade and the bottom surface in the spherical radial direction of the bottom blade, and the dimension of the tip rake face determined with reference to the boundary line is defined as the width of the tip rake face.
Let A be the percentage of the maximum width of the tip rake face along the ball diameter direction of the bottom blade with respect to the ball radius of the bottom blade.
The twist angle of the outer peripheral blade is set to θ °.
The taper angle of the outer peripheral blade is β °.
A taper ball end mill that satisfies the following two equations.
15 ≤ A ≤ 30
11 ≤ θ-β ≤ 21 Additionally, satisfying the following formula, tapered ball end mill according to claim 1.
A ≤ 25

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