JPH0718488Y2 - Ball end mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a ball end mill used for grooving a work material.

[Prior Art] Conventionally, in a multi-blade end mill having two or more cutting blades, the twist angles of all the cutting blades with respect to the tool axis line are equal to each other and are set to be constant from the tool tip to the rear end. It was customary.

However, in the end mill in which the twist angles of the respective cutting edges are completely equal to each other as described above, there is a drawback that chatter vibration is likely to occur because the cycle of vibration transmitted from each cutting edge becomes constant when the work material is cut. . Therefore, in order to eliminate such a defect, for example, as disclosed in Japanese Patent Laid-Open No. 63-89213, at least one helix angle of a plurality of cutting edges is set to an angle different from the helix angles of other cutting edges. There has been proposed an end mill in which vibrations are canceled by setting and irregularly changing the vibration cycle transmitted from each cutting edge.

[Problems to be solved by the invention] By the way, as a kind of end mill used for grooving of a work material, a so-called ball in which a tool tip is rounded into a hemispherical shape and a cutting edge is extended to the apex of the hemispherical part End mills are known, but simply changing the helix angle described above to such ball end mills may not yet yield a sufficient chatter vibration reduction effect. The tendency is great when doing.

That is, in the hemispherical portion of the ball end mill, the cutting edge gradually curves toward the tool radial direction center side toward the tip thereof, so that the cutting speed decreases toward the tip side of the cutting edge, and the cutting speed becomes 0 at the cutting edge tip. Becomes Therefore, in the conventional example in which the helix angle of some cutting edges is simply set to a different angle from other cutting edges, the cycle difference of vibration due to the difference in helix angle increases toward the apex of the hemisphere. Becomes relatively small,
As a result, the vibration canceling effect decreases as it goes to the tip of the cutting edge.

The present invention has been made under such a background, and provides a ball end mill capable of preventing chatter vibration in the hemispherical portion of the ball end mill and improving the machining accuracy and the machining efficiency. To aim.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a helix angle of a hemispherical portion of at least one cutting edge among a plurality of cutting edges formed on the outer circumference of a tool, as compared with another cutting edge. The angle is set to be different from the twist angle, and the difference in the twist angle is changed so as to gradually increase from the rear end of the hemisphere toward the tip side.

In this case, in order to more effectively exhibit the vibration reducing effect, it is preferable to set the circumferential pitch of the cutting edges at the rear end of the hemispherical portion to be unequal.

[Operation] According to the above configuration, since the difference in the twist angle between the cutting edges increases toward the tip side of the hemisphere, the difference in the vibration period transmitted from each cutting edge increases toward the apex of the hemisphere. However, even if the cutting speed in the hemisphere becomes smaller toward the tip of the cutting edge, the vibration canceling effect is not lost.

Further, particularly when the circumferential pitch of the cutting edge at the rear end of the hemisphere is set to be unequal, the difference in the vibration cycle transmitted from each cutting edge in the hemisphere becomes larger, and chatter vibration is more effective. Will be suppressed.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 1 to 3, reference numeral 1 is a tool body.
The tool main body 1 is made of high-speed steel, cemented carbide or the like as a raw material and is integrally formed into a shaft shape. A hemispherical portion 2 is formed on the tip side of the tool body 1, and the hemispherical portion 2
Of the cutting edge 3, which is twisted around the tool axis O, is formed on the outer circumference of the tool from the intersection of the apex P _{0 of the} hemisphere 2 and the tool axis O toward the rear end side of the tool body 1. .

These cutting edges 3 and 4 are all formed by sharply grinding the ridge line portion between the wall surfaces of the spiral grooves 5 and 6 formed on the outer peripheral portion of the tool and the outer peripheral surface 7 of the tool. The twisting direction is also set so as to be twisted rightward when viewed from the front of the tool, that is, to gradually twist in a direction opposite to the tool rotating direction (direction of arrow A in FIG. 1) toward the rear end side in the tool axial direction.

Here, as shown in FIG. 4, the helix angle φ ₁ of one of the cutting blades 3 and 4 is the cutting edge rear end from the tip P ₀ of the hemisphere 2 to the hemisphere rear end P _1. It is supposed to be constant up to P ₂ . On the other hand, the other cutting edge 4 is formed in a spiral shape twisting around the tool axis like the one cutting edge 3, but the twist angle is different from that of the one cutting edge 3. There is.

That is, as shown in FIG. 4, the helix angle of the other cutting edge 4 is first set to a constant helix angle φ ₂ from the rear end P ₁ of the hemispherical portion 2 to the rear end P ₂ of the cutting edge, Moreover, its size is larger than the helix angle φ _{1 of the one} cutting edge 3. The helix angle from the rear end P ₁ of the hemisphere to the apex P _{0 of the} hemisphere, that is, from the tip of the cutting edge 4 is gradually increased toward the tip of the cutting edge, and the helix angle φ at the tip P ₁ of the cutting edge is increased.
₃ is the largest. As a result, as shown in FIG. 5, the curve drawn by the cutting edge 4 in the front view from the tool axis direction has a larger curvature than the curve drawn by the one cutting edge 3. The difference between these screw angles φ _{1 to} φ ₃ is appropriately determined according to the tool diameter, the material of the work material and other cutting conditions, but the twist angle φ ₂ on the rear end side of the cutting edge 4 and the cutting edge 4 It is preferable that the difference from the twist angle φ _{3 of the} tip is set in the range of 30 ° to 60 °.

Further, as is apparent from FIGS. 1 and 5, the circumferential pitch of the cutting edges 3 and 4 is unequal at the rear end P ₁ of the hemisphere, that is, α ° ≠ β ° in FIG. (Α>
β). Pitch difference of these cutting edges 3,4 (α-β) is determined as appropriate according to the same manner as cutting conditions such as the twist angle phi ₁ to [phi] ₃ described above, the cutting edge 3,
Cutting blades 4 so that 4 have an equal pitch at the rear end P ₁ of the hemisphere.
A position (indicated by a two-dot chain line l ₁ in FIG. 5) displaced from the tool rotation direction by θ = 10 ° (indicated by a two-dot chain line l ₂ in FIG. 5), and the tool. It is preferable to set it within a range where the position (shown by the solid line in FIG. 5) deviated by θ = 10 ° in the direction opposite to the rotation direction is the limit. Circumferential pitch difference θ
Is more than 10 °, the difference in cutting resistance applied to the cutting edges 3 and 4 becomes too large, the balance of cutting resistance is lost, and there is a possibility that chatter vibration may grow. It is not always necessary to dispose the cutting edges 3 and 4 in such a manner that the cutting edges 3 and 4 are unequal at the rear end P ₁ of the hemisphere, and the vibration reduction effect due to the modification of the twist angles φ _{1 to} φ ₃ is sufficient. In this case, the pitch may be equal.

With the ball end mill configured as described above,
First, since the helix angle φ ₁ of the cutting edge 3 on the outer peripheral portion of the tool and the helix angle φ _{2 of the} rear portion from the hemispherical rear end P ₁ of the cutting edge 4 are different, these cutting edges 3, The cycle of the vibration transmitted from 4 changes irregularly in the tool axis direction, and as a result, the vibrations of the vibrations cancel each other out and the growth of the chatter vibration is hindered.

Moreover, in the hemispherical portion 2, the difference between the helix angle of the cutting edge 4 and the helix angle φ ₁ of the cutting edge 3 gradually increases from the rear end P _{1 of the} hemispherical portion toward the apex P _0. The difference in the vibration cycle transmitted from 3 and 4 increases as it goes to the tool tip side. Therefore, the cutting edge 3, as it approaches the apex P ₀ of the hemisphere,
Even if the cutting speed of No. 4 is reduced, a vibration canceling effect sufficient to compensate for this is obtained, and as a result, chatter vibration growth is reliably suppressed.

Further, since the circumferential pitches of the cutting blades 3 and 4 at the rear end P ₁ of the hemispherical portion 2 are set to be unequal, the cutting blades 3 and 4 are alternately cut into the work material in the hemispherical portion 2. The time intervals become unequal, and as a result, the growth of vibrations of the same frequency is further hindered, and the vibration reduction effect is more effectively exhibited.

In the present embodiment, the description has been made by taking a two-blade ball end mill as an example, but the present invention is not limited to this, and a ball end mill having three or more cutting blades may be formed. It is applicable in the same manner. Further, in this embodiment, the so-called solid end mill in which the cutting edges 3 and 4 are integrally formed with the tool main body 1 has been particularly described. However, a brazed ball end mill in which cutting edge tips are brazed and joined, or a throw-away tip is detachable. Of course, it can also be used for throwaway ball end mills that are freely mounted.

Further, in the present embodiment, in particular, the helix angles φ ₁ and φ ₂ of the cutting blades 3 and 4 other than the hemispherical portion 2 are also changed, but for example, in a ball end mill that performs grooving only with the hemispherical portion 2 If so, the twist angles of the parts other than the hemispherical part 2 may be set to be equal.

Further, regarding the magnitude of the helix angles φ ₁ and φ ₂ , in the above-mentioned embodiment, the helix angle φ ₂ of the equal helix angle portion of the cutting edge 4 is larger than the helix angle φ _{1 of the} cutting edge 3, but May be set so that φ ₂ is smaller than φ ₁ .

[Advantage of the Invention] As described above, according to the present invention, the helix angle of the hemispherical portion of at least one of the plurality of cutting edges formed on the outer circumference of the tool is different from the helix angle of the other cutting edge. Set, and the difference in the helix angle is changed so as to gradually increase from the rear end of the hemisphere toward the tip side, even in the hemisphere where the cutting speed decreases toward the tip side of the cutting edge. A sufficient effect of canceling chatter vibrations can be obtained, and as a result, an excellent effect that the machining accuracy and the machining efficiency of the work material can be significantly increased is achieved.

And, especially when the circumferential pitch of the cutting edges at the rear end of the hemisphere is set to be unequal, the vibrations in the hemisphere are more effectively canceled out, and chatter vibration growth is suppressed more reliably. The effect of being able to be obtained is obtained.

[Brief description of drawings]

1 to 5 each show an embodiment of the present invention. FIG. 1 is a front view showing the tool as seen from the tip end side in the axial direction, and FIG. 2 is the II direction in FIG. From FIG. 3, FIG. 3 is a view from the direction of the arrow III in FIG. 2, FIG. 4 is a development view of the outer circumference of the tool, and FIG. 5 is a simplified view of the shape of the tool in front view. 1 ... Tool body, 2 ... Hemisphere part, 3.4 ... Cutting edge, φ ₁
・ Φ ₂・ φ ₃ …… Twist angle, α, β …… Cutting edge circumferential pitch, θ …… Cutting edge circumferential pitch difference.

Claims (3)

[Scope of utility model registration request] 1. A ball end mill comprising a tool body having a hemispherical portion formed on the tip end side, and a plurality of cutting blades extending from the apex of the hemispherical portion toward the rear end side of the tool body. Setting the helix angle in the hemispherical portion of at least one of the cutting edges to a different angle from the helix angle of the other cutting edges,
Further, the ball end mill is characterized in that the difference in the helix angle is changed so as to gradually increase from the rear end of the hemispherical portion toward the front end side. 2. The ball end mill according to claim 1, wherein the circumferential pitch of the cutting edges at the rear end of the hemispherical portion is set to be unequal. 3. The circumferential pitch difference of the cutting blades at the rear end of the hemispherical portion deviates within ± 10 ° from the cutting blade position in the circumferential direction when the cutting blades are arranged at equal pitches in the circumferential direction. The ball end mill according to claim 2, wherein the ball end mill is set as follows.