JP4876539B2 - Ball end mill - Google Patents

Description

  The present invention is a ball end mill that is attached to a machine tool such as a machining center or a milling machine and cuts a workpiece, and in particular, a cubic boron nitride sintered body (hereinafter referred to as a cBN sintered body) It is related with the ball end mill provided with the cutting blade comprised.

In general, a ball end mill has a cylindrical end mill body that rotates around an axis, an outer peripheral blade formed on the outer peripheral portion of the end mill main body, and a ball blade formed so as to be connected to the front end side of the outer peripheral blade. And have.
As what cuts using said ball end mill, the metal mold | die used for injection molding etc. of a resin material is mentioned, for example. Such a mold is provided with a very hard hardened steel or the like for the purpose of improving the durability of the mold. In order to cut such a hardened steel, a cBN sintered body is used. The thing which comprised the whole front-end | tip part of the end mill main body containing a ball blade is proposed (refer patent documents 1 and 2). Here, the cBN sintered body has the second highest hardness after diamond and has excellent wear resistance and low reactivity with metals such as Fe, Co, Ni, etc., so it is most suitable for high-speed cutting such as hardened steel. It is a thing.

Moreover, in patent document 3, the outer peripheral part (part connected with the outer peripheral blade and the outer peripheral blade of a ball blade) of a ball end mill where cutting speed becomes high is comprised with a cBN sintered compact, and hard cutting materials, such as hardened steel, are used. A ball end mill has been proposed in which high-speed machining is achieved and the vicinity of the axis where the cutting speed is reduced, that is, the tip of the ball blade is made of cemented carbide.
JP 2002-144131 A JP 2002-144132 A JP-A-10-113810

However, the cBN sintered body has high hardness but is brittle and has low impact resistance. Therefore, the cBN sintered body is easily broken by an impact when being cut into a workpiece. Moreover, since a cBN sintered compact is produced | generated by sintering under high temperature and high pressure, it is very expensive.
Therefore, as in Patent Documents 1 and 2, when all of the tip portion of the end mill body including the ball blade is made of a cBN sintered body, these ball blades and the like are damaged, and the life of the ball end mill is remarkably shortened. There was a problem that the amount of use of the cBN sintered body was increased and the manufacturing cost was increased.

In addition, when machining a workpiece with a ball end mill, the outer peripheral portion of the ball end mill (the outer peripheral blade and the portion connected to the outer peripheral blade of the ball blade) has a large distance from the rotation axis and high cutting speed, and is intermittent. Since it is cut into the material to be cut, an impact load is applied, and when such an outer peripheral portion is made of a hard and brittle cBN sintered body, defects are likely to occur.
Further, when a workpiece is processed into a complicated shape using a ball end mill, the tip portion of the ball blade is mainly used for cutting. In the ball end mill described in Patent Document 3, this tip portion is used. Is composed of a cemented carbide alloy, there is a problem that wear progresses earlier than the cBN sintered body and the life of the ball end mill is shortened.

  Furthermore, when manufacturing a ball end mill in which the outer peripheral portion of the ball blade and the outer peripheral blade are formed of a cBN sintered body and the tip portion of the ball blade is formed of a cemented carbide, as described in Patent Document 3 Then, a material in which a cemented carbide is disposed in the central portion and a cBN sintered body is disposed in the outer peripheral portion is processed. The above material is formed by removing a part of the disc-shaped cBN sintered body and inserting a cemented carbide, or sintering the cBN sintered body with the cemented carbide placed in the center. Therefore, it takes a lot of labor and time to form this material. Further, since the amount of expensive cBN sintered body used is increased, there is a problem that the production cost of this ball end mill is increased.

  This invention is made | formed in view of said situation, Comprising: The cutting blade (peripheral blade and the outer peripheral blade of a ball blade) arrange | positioned on the outer periphery of the ball end mill cut | disconnected intermittently with respect to a to-be-cut material An object of the present invention is to provide a ball end mill that can prevent the loss of the connecting portion) and extend the life and can be manufactured at low cost.

In order to solve the above-mentioned problems, the present invention processes a material having a cubic boron nitride sintered body that is provided with a ball blade at the tip of an end mill body that is rotated around an axis and that is formed into a layer shape. The ball end mill is manufactured by the method, wherein the ball blade has a tip blade portion disposed on the tip side and an outer blade portion connected to the tip blade portion, and the tip blade portion and the outer blade The tip blade portion is made of a cubic boron nitride sintered body, the axial length L of the tip blade portion and the radius of the ball blade The ratio with R is in the range of L / R = 0.6 to 0.9.

  According to the ball end mill having this configuration, the outer peripheral portion (outer blade portion) of the ball blade, which is the portion with the highest cutting speed, is not formed by the cBN sintered body having inferior impact resistance. Although it is low in hardness compared to the sintered body, it has high toughness and is composed of a material with excellent fracture resistance and impact resistance, so that it is possible to prevent the ball blade from being broken and extend the life of this ball end mill. .

Moreover, since the tip portion (tip blade portion) of the ball blade mainly used for cutting is formed of a cBN sintered body, the wear resistance of the tip blade portion of the ball blade is improved and early wear is prevented, The life of the ball end mill can be further extended.
Moreover, since there are few parts comprised with an expensive cBN sintered compact, this ball end mill can be manufactured at low cost.

Here, by configuring the outer blade portion with a cemented carbide, it is possible to improve the impact resistance of the outer peripheral portion of the ball blade, which is the portion where the cutting speed is the highest, to prevent chipping, and to further improve the ball end mill. The life can be extended.
In addition, since the tip blade portion made of the cBN sintered body is arranged at the tip portion of the end mill body, this ball is formed by processing a material in which the cBN sintered body and the cemented carbide are integrally formed in a layered manner. End mill can be manufactured.

  Furthermore, by setting the ratio of the axial length L to the radius R of the ball blade within the range of L / R = 0.6 to 0.9, the outer peripheral portion of the ball blade In this case, the cBN sintered body is not disposed, and the ball end mill can be reliably prevented from being broken.

  As described above, according to the present invention, the cutting blade (the outer peripheral blade and the portion connected to the outer peripheral blade of the ball blade) disposed on the outer periphery of the ball end mill that is intermittently cut into the workpiece is lost. Thus, it is possible to provide a ball end mill that can reliably prevent this, extend the service life, and can be manufactured at low cost.

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a ball end mill according to an embodiment of the present invention.
The ball end mill 1 is composed of an end mill body 2 that is formed in a substantially cylindrical shape and rotated about an axis O, and a cutting edge portion 3 formed on the tip side (left side in FIG. 1) of the end mill body 2. Yes.

  On the outer periphery of the cutting edge portion 3, a plurality of strips (2 in the present embodiment) are twisted at a predetermined angle around the axis O toward the rear side in the end mill rotation direction T from the front end side toward the rear end side (right side in FIG. 1). ), The chip discharge grooves 4 are formed in a rotationally symmetrical manner with respect to the axis O by a predetermined angle (180 ° in this embodiment) at equal intervals in the circumferential direction. Further, an outer peripheral blade 5 is provided on a cross ridge line portion between a wall surface facing the end mill rotation direction T side of the chip discharge groove 4 and an outer peripheral surface continuous to the rear side in the end mill rotation direction T, that is, an outer peripheral side ridge portion of the wall surface. Is formed.

Therefore, the wall surface of the chip discharge groove 4 is a rake face, and the outer peripheral surface is a flank face of the outer peripheral blade 5. Further, the outer peripheral blade 5 is formed in a spiral shape that is twisted to the rear side in the end mill rotation direction T around the axis O as it goes to the rear end side in the same manner as the chip discharge groove 4, and in the positive rake axial direction. A rake angle is given. In addition, the rotation locus | trajectory which this outer periphery blade 5 makes around the axis line O is made into the cylindrical surface shape centering on the axis line O in this embodiment.
The outer peripheral blade 5 is made of a cemented carbide, and in this embodiment, for example, hard coating such as TiN, TiAlNi, TiCN or the like is applied to the outer peripheral blade 5 in order to improve wear resistance.

  On the other hand, the distal end portion of the cutting blade portion 3 is formed in a substantially hemispherical shape having a center on the axis O and convex toward the distal end side, and is formed on the distal end side of the chip discharge groove 4 opened to the distal end portion. The gash 6 is formed so that the opening of the chip discharge groove 4 is sharpened toward the inner peripheral side of the end mill body 2 as it goes toward the tip side.

  The edge of the edge of the cutting edge 3 is provided at the crossing ridge line portion of the wall surface facing the end mill rotation direction T side of the gash 6 and the curved surface connected to the rear side of the end mill rotation direction T, that is, the outer peripheral edge portion of the wall surface A ball blade 7 is formed in a generally convex arc shape centered on the axis O from the vicinity of the side axis O toward the rear end outer peripheral side of the end mill body 2 and continuing to the tip of the outer peripheral blade 5.

  Accordingly, the wall surface of the gash 6 is the rake face of the ball blade 7, and the curved surface is the flank face of the ball blade 7. Also, the rotation trajectory of the ball blade 7 around the axis O is a substantially hemispherical shape having a center on the axis O and convex toward the tip side, so that it smoothly connects to the rotation trajectory formed by the outer peripheral blade 5. Has been.

Here, in the ball blade 7, a portion connected to the outer peripheral blade 5 is an outer blade portion 8, and a portion positioned on the distal end side of the outer blade portion 8 is a distal blade portion 9.
The outer blade portion 8 connected to the outer peripheral blade 5 is made of the same cemented carbide as the cemented carbide forming the outer peripheral blade 5. In the present embodiment, in order to improve the wear resistance, for example, hard coating such as TiN, TiAlNi, TiCN or the like is applied to the outer blade portion 8.

And the tip blade part 9 located in the most advanced part of this ball end mill 1 is comprised by the cBN sintered compact which was harder than the cemented carbide and was excellent in abrasion resistance.
The length L of the tip blade portion 9 in the direction of the axis O is set so that L <R with respect to the radius R of the spherical surface formed by the ball blade 7, and preferably L / R = 0.6. In the present embodiment, L / R = 0.8 / 1.
The ball end mill 1 having this configuration is manufactured by processing a material obtained by integrally forming a cBN sintered body and a cemented carbide in layers.

  According to the ball end mill 1 configured as described above, the portion composed of the cBN sintered body is not disposed on the outermost peripheral side of the ball end mill 1, and the portion composed of the cemented carbide is disposed. Become. Accordingly, the outer blade portion 8 that has the highest cutting speed among the ball blades 7 and is subjected to an impact load by being intermittently cut into the workpiece, has low toughness compared to the cBN sintered body. Therefore, it is made of a cemented carbide excellent in chipping resistance and impact resistance, so that chipping of the cutting edge can be prevented and the life of the ball end mill 1 can be extended.

Further, since the tip edge portion 9 of the ball blade 7 mainly used for cutting of the ball end mill 1 is composed of a cBN sintered body having excellent wear resistance, early wear during cutting can be prevented. The life of the ball end mill 1 can be further extended.
Furthermore, in this ball end mill 1, since it can be manufactured by processing a material in which a cBN sintered body and a cemented carbide are integrally formed in a layered manner, the amount of expensive cBN sintered body used can be reduced. This ball end mill 1 can be manufactured at low cost.

  In the present embodiment, the outer blade portion 8 and the outer peripheral blade 5 have been described as being made of cemented carbide, but the present invention is not limited to this, and it may be made of other materials. Good, however, cemented carbide is preferable because it has a certain degree of hardness and is excellent in impact resistance. Further, it is preferable to apply a hard coating to the outer blade portion 8 and the outer peripheral blade 5 as in the present embodiment because the wear resistance is improved.

In the present embodiment, the radius R of the ball blade 7 and the length L in the direction of the axis O of the tip blade portion 9 are set to be L / R = 0.8 / 1. being limiting in rather than only to be in the range of L /R=0.6~0.9.
Moreover, although it demonstrated as a 2-blade ball end mill in which the chip | tip discharge groove | channel 4 was formed in 2 strips, a 3-flute and 4-flute ball end mill may be sufficient.

It is a side view of the ball end mill which is an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball end mill 2 End mill main body 3 Cutting blade part 4 Chip discharge groove 5 Outer peripheral blade 6 Gash 7 Ball blade 8 Outer blade portion 9 Tip blade portion

Claims (2)

A ball end mill provided with a ball blade at the tip of an end mill body rotated about an axis,
The ball blade has an outer blade portion connected to a tip blade portion arranged on the tip side , and the tip blade portion and the outer blade portion are joined via a planar joining surface ,
The tip blade portion is composed of a cubic boron nitride sintered body,
A ball end mill, wherein a ratio of a length L of the tip blade portion in the axial direction to a radius R of the ball blade is in a range of L / R = 0.6 to 0.9.   The ball end mill according to claim 1, wherein the outer blade portion is made of cemented carbide.

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