JP5939208B2 - Ball end mill - Google Patents

Description

  The present invention relates to a ball end mill provided with an arcuate cutting edge at the tip of a tool body in order to perform three-dimensional finishing on a work material, and more particularly to a blade end replaceable ball end mill.

  Conventionally, a ball end mill is used as a milling tool for performing three-dimensional machining including a plane and a curved surface on a work material in a machining process for manufacturing a mold or the like. When three-dimensional machining is performed on a work material using a ball end mill, arc-shaped cutting edges (ball blades) that contribute to cutting work cover a wide range of areas including cutting edges located at the tip of the tool body. Since the rotational speed of the rotation axis of the tool body and the cutting edge in the vicinity thereof is extremely close to 0 or 0, a large cutting load is applied to the cutting edge in the vicinity of the rotation axis when performing planar machining. For this reason, chipping and chipping are likely to occur on the cutting edge in the vicinity of the rotation axis, and as a result, the surface roughness of the processed surface of the work material deteriorates. In addition, when three-dimensional machining is performed on a work material using a ball end mill, particularly when an inclined surface or a standing wall is machined, the cut is located near the outer peripheral side away from the vicinity of the rotation axis of the tool body. Processing using a blade is performed.

  When three-dimensional finishing is performed on the work material using a ball end mill, in order to improve the surface roughness of the finished surface, the occurrence of chatter vibration is suppressed and the chip discharge is improved. Therefore, it is necessary to prevent chipping and chipping from occurring on the cutting edge. For this purpose, it is important to set the rake angle for the entire area of the arcuate cutting edge to be the ball edge provided in the ball end mill, particularly how to set the rake angle for the arcuate cutting edge. It becomes a challenge.

  Conventionally, in order to improve the above-mentioned problems of the ball end mill, inventions relating to the configuration of the rake angle of the arcuate cutting edge have been proposed. For example, the inventions described in Patent Documents 1 to 5 below have been proposed.

  Patent Document 1 (Japanese Patent Laid-Open No. 10-80815) proposes an invention related to a ball end mill suitable for three-dimensional curved surface processing of a mold or the like. In the invention described in Patent Document 1, the rake angle in the radial cross section from the arc center point of the ball blade is a negative value (−2 ° to −20 °) in order to enhance the cutting edge strength in the vicinity of the outer peripheral cutting edge. In the vicinity of the nose (near the tool axis), the ball end mill is set to 0 or a positive value (0 ° to + 10 °) in order to improve chip discharging performance.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2008-110437) proposes an invention relating to a CBN ball end mill that suppresses chipping of the entire ball blade and has a long life. In the invention described in Patent Document 2, a ball blade and an outer peripheral blade are provided, and the normal rake angle of the ball blade is −5 degrees to −15 degrees at R10 degrees, and −5 degrees from R50 degrees to R70 degrees. +3 degrees, showing a peak, R90 degrees from −10 degrees to 0 degrees, and further, this rake angle gradually increases from R10 degrees to R50 degrees to R70 degrees in a positive direction, and gradually increases from a peak toward R90 degrees. Is a CBN ball end mill.

  Further, in paragraph 0006 of Patent Document 2, the normal direction rake angle is set to -5 degrees to -15 degrees at R10 degrees to increase the strength of the ball blade, and the cutting resistance in the rotation center axis direction is It can withstand chipping and chipping even when it is greatly affected. Furthermore, by setting the rake angle in the normal direction gradually in the negative direction from the peak position toward R90 degrees, the cutting speed is the highest and the strength of the outer peripheral ball blade that is most affected by the vibration of the end mill is increased and chipping is performed. It is described that can be suppressed.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2004-181563) proposes an invention related to a ball end mill with improved strength and chip dischargeability. The invention described in Patent Document 3 has a center blade formed by the rake faces of the ball blade continuously with the ball blade in the center portion of the end mill, and at the boundary between the flank surface of the ball blade and the flank surface of the center blade. A ball end mill having a step and having a clearance angle of the ball blade smaller than that of the central blade.

  Further, in claim 4 of Patent Document 3, it is described that the rake angle in the normal direction of the ball blade is gradually increased from the center of the end mill toward the outer circumferential direction. Furthermore, in paragraph 0006, “With regard to the ball blade, since the clearance angle of the ball blade is smaller than the clearance angle of the central blade, the cutting edge strength can be obtained. Can be gradually increased to the positive side in the outer circumferential direction, and the cutting performance and chip discharge performance of the ball blade can be improved. " Furthermore, paragraph 0007 describes as Example 1 that “the rake angle in the normal direction of the ball blade 2 is gradually increased from the center to the positive side in the outer peripheral direction from −45 ° to −10 °”. ing.

  In Patent Document 4 (Japanese Patent Laid-Open No. 2010-105092) and Patent Document 5 (Japanese Patent Laid-Open No. 2010-105093), a ball having improved cutting edge strength, smooth cutting, and smooth chip discharge effect. Inventions related to end mills have been proposed. In the inventions described in Patent Documents 4 and 5, the rake angle γ in the radial section from the arc center of the ball blade is set in the range of −10 degrees to 0 degrees, and the negative value of the rake angle γ is: The ball end mill is set to a maximum at a substantially intermediate point of ¼ circle by increasing from the tip of the ball blade and the radially outer end of the ball blade toward the radially intermediate point.

  Here, the negative value of the rake angle γ is set to the maximum, from the description of Paragraph 0029 and FIG. 4, −3 degrees at the tip of the ball blade, and − Since it is set to 3 degrees at the position of the ball blade radial outer end, it can be said that the absolute value of the negative value of the rake angle γ is set to the maximum. . This enhances the strength of the cutting edge by strengthening the vicinity of the radial center of the ball blade with high cutting speed, and reduces the sharpness by increasing the rake angle at the tip of the ball blade near the rotation center axis. It is described that the machinability is ensured by suppressing.

Japanese Patent Laid-Open No. 10-80815 JP 2008-110437 A JP 2004-181563 A JP 2010-105092 A JP 2010-105093 A

  The ball end mill described in Patent Document 1 to Patent Document 5 has an arcuate cutting edge that becomes a ball blade in order to improve chip discharge and improve the strength of the cutting edge to prevent chipping and chipping. The rake angle in the radial (normal) direction is the ball end mill with a negative angle (negative angle) at the cutting edge (or outermost circumference) of the arcuate cutting edge, or the cutting edge or intermediate point. Is a ball end mill with a positive angle and a negative angle at the outermost periphery. Patent Document 2, Patent Document 3, Patent Document 4 and Patent Document 5 also propose changing the rake angle in the radial (normal) direction in the cutting edge region of the arcuate cutting edge.

  An object of the present invention is to set a radial (normal) rake angle and an axial rake angle of the arc-shaped cutting edge to a negative angle for a ball end mill having an arc-shaped cutting edge. By gradually and appropriately changing over the cutting edge region of the cutting edge, even when three-dimensional finishing with a hard material is performed, the impact at the time of biting of the cutting edge is reduced, An object of the present invention is to provide a ball end mill capable of improving the surface roughness of the processed surface by ensuring the strength of the cutting edge, improving the chipping resistance, and at the same time enhancing the chip discharge.

  According to a first aspect of the present invention, the ball end mill includes a tip end portion of the end mill body rotated in the rotation direction R about the rotation axis, and a front end portion of the end mill body from the outermost peripheral portion in a plan view of the end mill body. The arc-shaped cutting edge has an S-shape when viewed from the front in the rotational axis direction, and the arc-shaped cutting edge is formed on the front side in the rotation direction R. In a ball end mill having a rake face of an arcuate cutting edge, the radial rake angle of the arcuate cutting edge is a radial straight line extending radially from the arc center point of the arcuate cutting edge toward the arcuate cutting edge. And an angle formed by the radial line and the rake face of the arcuate cutting edge at a position intersecting the arcuate cutting edge, and the rotation axis and the radiation straight line with respect to the rotation axis. Is defined as a radiation angle, the radial rake angle when the radiation angle is 5 degrees (°) is α, the radial rake angle when the radiation angle is 90 degrees (°) is β, and the S The radial rake angle α and the radial rake are defined as γ when the radial rake angle at the most projecting portion where the arcuate cutting edge forming a letter shape is the most projecting position forward of the rotation direction R is γ. The angle β and the radial rake angle γ are both negative angles, and the absolute values of the radial rake angle α value, β value, and γ value are | α |, | β |, and | γ |, respectively. At the time, | γ | ≦ | α | <| β |.

  The invention according to a second aspect of the present invention relates to the ball end mill according to the first aspect, wherein the absolute value of the radial rake angle is between the most protruding portion and the most protruding portion of the arcuate cutting edge. The minimum value is set at a position where the radiation angle is 15 to 30 degrees, and the absolute value of the radial rake angle is from the most protruding portion to the outermost peripheral portion. It is characterized by being set to increase continuously.

  The invention according to claim 3 of the present invention relates to the ball end mill according to claim 1 or 2, wherein the radial rake angle α, the radial rake angle β, and the radial rake angle γ are − It is characterized by being set to satisfy 6 ° ≦ α ≦ −0.5 °, −10 ° ≦ β ≦ −2 °, −6 ° ≦ γ ≦ −0.5 °.

  Invention of Claim 4 of this invention is related with the ball end mill in any one of Claims 1-3, In the position of the said arc-shaped cutting blade from which the said radiation angle turns into 30 degrees from 47 degrees, The most protruding portion is formed.

  The invention according to claim 5 of the present invention relates to the ball end mill according to any one of claims 1 to 4, wherein the outermost projecting portion and the outermost peripheral portion vicinity are based on the outermost projecting portion. When the radial rake angle is θ1 and the radial rake angle from the most projecting portion to the vicinity of the most distal portion is θ2, the absolute values of the radial rake angle θ1 value and θ2 value are | θ1 | , | Θ2 | is set so as to satisfy | θ1 |> | θ2 |.

  A sixth aspect of the present invention relates to the ball end mill according to any one of the first to fifth aspects, wherein a tangent line on the arcuate cutting edge is the rotational axis in a side view of the ball end mill. When the rake angle is an axial rake angle, the axial rake angle is set to a negative value until reaching the most projecting portion from the most distal portion of the arcuate cutting edge, and the most projecting portion It is characterized in that a positive value is set up to the outermost peripheral part beyond.

  The invention according to a seventh aspect of the present invention relates to the ball end mill according to the first aspect, wherein the ball end mill is provided with an insert having a detachable arc-shaped cutting edge at a tip portion of the end mill body. In the front view of the ball end mill, the insert has outlets of at least two coolant channels at positions corresponding to rotation axes, and the coolant channel extends from the flank portion of the arcuate cutting edge to the bottom surface. It penetrates the part (5f) and communicates with the end mill body.

  According to an eighth aspect of the present invention, there is provided the ball end mill according to the seventh aspect, wherein the coolant channel has an inclination angle with respect to the rotation axis.

The ball end mill of the present invention has the following three effects.
(1) Radial rake angles α, β, and γ formed on the arcuate cutting edge are all negative angles, and the absolute values of the radial rake angles α, β, and γ are respectively | When α |, | β |, and | γ | are set to satisfy | γ | ≦ | α | <| β |, the cutting edge strength is enhanced over the entire cutting edge region of the arcuate cutting edge. Is done. For this reason, the chipping resistance of the cutting edge is improved even in cutting using a high hardness material having a hardness of 45 HRC or more as a work material. In particular, the strength of the cutting edge is enhanced in the vicinity of the outer peripheral cutting edge. On the other hand, in the vicinity of the tool axis, consideration is given to reducing the cutting resistance and improving chip discharge performance, and the absolute value of the rake angle α value is set small. As a result, the occurrence of chatter vibration is also suppressed, so that it is possible to provide a ball end mill consisting of two blades that is suitable mainly for three-dimensional finishing of a work material.

(2) The rake angle in the axial direction of the ball end mill is a negative value from the most distal part to the most projecting part Q of the arcuate cutting edge, a positive value from the most projecting part Q to the most outer peripheral part S, The rake angle in the axial direction at the most protruding portion Q is set to “0”.
In the present invention, since the rake angle in the axial direction is set in this way, the first region where the arc-shaped cutting edge comes into contact with the work material becomes the most protruding portion Q, and then the workpiece is cut by rotation of the cutting edge. The contact area with the material extends to both the most distal portion and the outermost peripheral portion S of the cutting edge. And by setting the absolute value of the radial rake angle having a negative value to a small value from the most distal portion to the most protruding portion Q of the arcuate cutting edge, the axial rake angle is a negative value. Even if it exists, cutting resistance can be reduced.
Further, since the rake angle in the axial direction of the arc-shaped cutting edge is a positive value (about + 20 °) in the vicinity of the outermost peripheral portion S, the inclined surface of the work material is cut by the arc-shaped cutting edge in the vicinity of the outermost peripheral portion S. The chip is released in a direction perpendicular to the tangent to the rotation trajectory of the arc-shaped cutting edge, which improves chip discharge and suppresses chip clogging, so that the inclined surface of the work material can be finished. The surface roughness of processing can be improved.

  (3) Providing a coolant channel in the insert of the present invention to avoid an increase in the insert temperature during machining prevents a decrease in resistance to plastic deformation of the cemented carbide insert or a decrease in hardness. Since it can be avoided, it is particularly suitable for cutting using a hard material as a work material. Moreover, the temperature rise in the vicinity of the cutting edge in such a cutting process induces a phenomenon that chips generated from the work material are welded to the cutting edge. Since the wear resistance of the cutting edge is impaired by this, it is effective to avoid an increase in the insert temperature. Furthermore, the flow of coolant (for example, water-soluble cutting fluid, oil-based cutting fluid, liquid nitrogen, etc.) supplied to the chip interface through the coolant channel can effectively discharge chips, so that The surface finish properties are good, and the surface roughness of the finish processing can be made good.

1 is a perspective view of a blade end replaceable ball end mill showing an embodiment of the ball end mill of the present invention. It is a perspective view of the insert shown in FIG. It is the front view which looked at the end mill main body when the insert is not mounted | worn about the blade-tip-exchange-type ball end mill shown in FIG. 1 from the rotation axis direction. It is a side view in the front-end | tip part of the end mill main body shown in FIG. It is a top view in the front-end | tip part of the end mill main body shown in FIG. (A) is a top view of the insert shown in FIG. 2, (b) is a front view of the insert shown in FIG. 2, (c) is a side view of the insert shown in FIG. It is the front view which looked at the blade-tip-exchange-type ball end mill shown in FIG. 1 from the rotation axis direction. It is a side view in the front-end | tip part of the blade-tip-exchange-type ball end mill shown in FIG. It is a top view in the front-end | tip part of the blade-tip-exchange-type ball end mill shown in FIG. It is a figure for demonstrating the structure of the radial rake angle with which the example of this invention is provided about the circular arc-shaped cutting blade. It is a figure for demonstrating the structural example of the axial rake angle with which this invention is provided about the circular arc-shaped cutting edge. It is a graph which shows the condition which is changing this radiation direction rake angle according to a radiation angle about the structure of the radiation direction rake angle with which the example of this invention is provided. It is a graph which shows the condition which is changing the axial rake angle corresponding to a radiation angle about the structure of the axial rake angle with which the example of this invention is provided. It is a figure which shows the state of the rake face and flank face of a cutting edge, when the plane of a workpiece is cut using the ball end mill of this invention. It is a figure which shows the state of the flank of a cutting edge, when the inclined wall surface of a workpiece is cut using the ball end mill of this invention. It is a figure which shows the state of the rake face and flank of a cutting edge, when the inclined wall surface of a workpiece is cut using the ball end mill of this invention. It is a perspective view in another Example of the insert shown in FIG. (A) is a top view of the insert shown in FIG. 17, (b) is a front view of the insert shown in FIG. 17, and (c) is a side view of the insert shown in FIG. It is the front view which looked at the blade-tip-exchange-type ball end mill equipped with the insert shown in FIG. 17 from the rotation axis direction. It is a side view in the front-end | tip part of the blade-tip-exchange-type ball end mill equipped with the insert shown in FIG.

  Hereinafter, embodiments of a ball end mill according to the present invention will be described with reference to the drawings. The ball end mill of the present invention can be applied to a solid type ball end mill and a blade end replaceable ball end mill (hereinafter referred to as “blade replaceable ball end mill”). The embodiment of the present invention described below will be described by taking as an example a blade end replaceable ball end mill in which an insert provided with an arcuate cutting edge serving as a ball blade is detachably attached to an end mill body.

  FIG. 1 is a perspective view showing a configuration example of a blade tip replaceable ball end mill (1) showing an example of an embodiment of the present invention that rotates about a rotation axis L (hereinafter referred to as “axis L”). 2 is a perspective view of the insert mounted on the blade end replaceable ball end mill (1) shown in FIG. 1, and FIG. 3 is a view of the axis L when the insert is not mounted on the insert mounting seat of the end mill body shown in FIG. FIG. 4 is a side view of the tip portion of the end mill body, and FIG. 5 is a plan view of the tip portion of the end mill body. In the following description, the blade edge replaceable ball end mill (1) may be simply referred to as “ball end mill (1)”.

(Configuration of blade end replaceable ball end mill)
As shown in FIG. 1, a blade end replaceable ball end mill (1) includes an end mill main body (2) and a shank portion formed integrally with the end mill main body (2) on the rear end side of the end mill main body (2). (3) and an insert mounting seat (4) (see FIG. 4) formed from the tip (2a) of the end mill body (2) to the rear of the end mill body (2), and is detachably mounted. And a clamp screw (6) for fixing the insert (5) to the insert mounting seat (4) by screw tightening. The end mill body (2) and the shank portion (3) are manufactured from alloy tool steel such as SKD61, for example.

  As shown in FIGS. 3 and 4, the insert mounting seat (4) opens at the distal end (2 a) of the end mill body (2), and further extends in the radial direction of the end mill body (2) to end the end mill body (2 ) And a slit-like fitting formed to a predetermined length including the axis L from the tip (2a) of the end mill body (2) toward the rear shank (3). It consists of a groove (8). Reference numeral “7” shown in FIG. 4 is an inclined reduced diameter portion provided at the end of the shank portion 2.

  As shown in FIG. 4, the fitting groove (8) (insert mounting seat (4)) includes two inner side surface portions (8a) and inner side surface portions (8b) parallel to each other, and a bottom surface portion (8c) serving as a bottom portion. And is formed by machining so that the axis L passes through the intermediate position of the groove portion between the inner side surface portion (8a) and the inner side surface portion (8b) toward the bottom surface portion (8c). In the following description, the inner side surface portion (8a) may be referred to as one inner side surface portion (8a), and the inner side surface portion (8b) may be referred to as the other inner side surface portion (8b).

By forming a slit-like fitting groove (8) so as to include the axis L from the end portion (2a) of the end mill body (2), the end portion (2a) of the end mill body (2) becomes the bottom surface portion (8c). The tip half body portion (9a) and the tip half body portion (9b) which are divided into two with respect to the reference position are formed. Then, an insert fixing screw hole that crosses the fitting groove (8) and reaches into the other tip half body 9b (or 9a) from one surface of the tip half (9a), (9b) ( 10) (see FIG. 3). The direction of the insert fixing screw hole (10) is formed in a direction orthogonal to the direction in which the insert fitting groove (8) of the end mill body (2) extends in the radial direction of the end mill body (2), as shown in FIG. Has been.
Further, the male end of the insert clamp screw (6) is formed on the inner peripheral surface of the insert fixing screw hole (10) that passes through one tip half (9a) and reaches the other tip half (9b). A female screw portion for screw fitting with the screw portion is engraved.

(Insert configuration)
A configuration example of the insert (5) provided with a cutting edge will be described with reference to FIGS. 6A, 6B, and 6C are a plan view, a front view, and a side view of the insert (5) shown in FIG. 2, respectively.

  The insert (5) is manufactured from, for example, a cemented carbide containing tungsten carbide (WC) and cobalt (Co) (hereinafter referred to as “WC-based cemented carbide”). The insert (5) has a thickness (T) as shown in FIG. 6 (c) and has a substantially flat plate shape. Moreover, as shown in FIG. 6, it has a planar outer surface part (5g) and a planar outer surface part (5h) disposed at a position facing this outer surface part (5g). As shown in FIG. The pair of outer surface portions (5g) and the outer surface portion (5h) are formed in parallel.

  The reference numeral “5a” shown in FIGS. 2 and 6 is the most distal portion of the insert (5). The most advanced portion (5a) is a portion that intersects the axis L when the insert (5) is mounted on the insert mounting seat 4 (fitting groove 8) of the end mill body (2). This is the lowest point (the most advanced part) in the direction of the axis L.

  As shown in FIG. 6 (b), the insert (5) is a side surface portion connecting the pair of outer surface portions (5g) and the outer surface portion (5h), as shown in FIG. 6 (b). Arc-shaped side surface portions (second side surface portions) (5b1) and (5b2) and arc-shaped side surface portions (third side surface portions) (5c1) and (5c2) formed in an arc shape are formed. Further, a bottom side surface portion (5f) is formed at the rear end portion of the insert (5) as shown in FIG. The bottom side surface portion (5f) is a side surface portion that comes into close contact with the bottom surface portion (8c) of the fitting groove (8) when the insert (5) is attached to the insert mounting seat (4).

  A straight line L1 shown in FIG. 6A is a straight line passing through the most distal portion (5a) of the insert (5) and the arc center point O, and the insert (5) is inserted into the insert mounting seat 4 of the end mill body (2). When mounted on the straight line L1, the straight line L1 is mounted so as to coincide with the axis L of the end mill body (2). The arc center point O described above indicates the center of the arc of the arcuate cutting edge provided in the insert (5) described later. A straight line M shown in FIG. 6A is a straight line that passes through the arc center point O and is orthogonal to the straight line L1.

  As shown in FIGS. 2 and 6 (a), the insert (5) includes a screw insertion hole (5p) penetrating from one outer surface portion (5g) to the other outer surface portion (5h). . The screw insertion hole (5p) is a hole through which the clamp screw 6 is inserted when the insert (5) is mounted and fixed to the insert mounting seat 4. The arc center point O described above is a midpoint of the center line of the screw insertion hole (5p) and is located at the center of the thickness T of the insert (5).

  Next, a description will be given of the cutting edge provided in the insert (5), which is a characteristic feature of the ball end mill according to the present invention, in order to cut the workpiece. The insert (5) to be mounted on the insert mounting seat (4) of the end mill body (2) includes an arcuate cutting edge serving as a pair of ball blades and a peripheral cutting edge having a pair of twisted shapes. Here, the outer peripheral cutting edge having a twisted shape means that when the insert (5) is mounted on the insert mounting seat 4 and the end mill body (2) rotates about the axis L, the rotation trajectory of the outer peripheral cutting edge is approximately. It is a cutting blade formed so as to form a cylindrical shape.

As shown in FIGS. 2 and 6 (b), the pair of arcuate cutting edges described above are formed from the most distal portion (5a) of the insert (5), and are side portions (5b1) serving as one flank. An arcuate cutting edge (5i1) formed along the ridge line with the rake face (5d), an inclined side face (5b2) serving as the other flank, and a rake face (shown in FIG. 6 (a)) Not formed) and an arcuate cutting edge (5i2) formed along the ridge line portion. The pair of arcuate cutting edges (5i1) and (5i2) are formed as an integral cutting edge via the most advanced part (5a), but the cutting edge replaceable ball end mill equipped with one insert (5). (1) is said to be a two-blade ball end mill with two arcuate cutting edges.
In the following description, these arc-shaped cutting edges (5i1) and (5i2) are simply referred to as an arc-shaped cutting edge (5i1) and an arc-shaped cutting edge (5i2).

  The pair of arcuate cutting edges (5i1, 5i2) are ridgeline portions of the inclined side surface portions (5b1, 5b2) as shown in FIG. 2 and FIG. In the front view seen from the front side of the straight line L1, the arcuate cutting edges (5i1, 5i2) have a substantially S-shape centered on the most distal portion (5a). It is formed as follows.

  As shown in FIG. 6 (a), the outer peripheral cutting edges (5k1, 5k2) having a twisted shape connected to the pair of arc-shaped cutting edges (5i1, 5i2) from the most distal portion (5a) of the insert (5). Is formed. Among these peripheral cutting edges having a twisted shape, the outer peripheral cutting edge (5k1) is integrally connected from the end S of the arcuate cutting edge (5i1) formed from the most advanced portion (5a). Is formed. Similarly, the outer peripheral cutting edge (5k2) is integrally formed from the end S of the arcuate cutting edge (5i2) formed from the most distal end portion (5a).

  The end S of the arcuate cutting edge (5i1) is a point where the straight line M shown in FIG. 6 (a) intersects the arcuate cutting edges (5i1, 5i2), respectively. (5i1) and the outer peripheral cutting edge (5k1) are connected to each other, and the other end S is connected to the end of the arcuate cutting edge (5i2) and the outer peripheral cutting edge (5k2). Furthermore, in the plan view of the insert (5), these end portions S and S correspond to the outermost peripheral portion of the arcuate cutting edges (5i1, 5i2). Further, when the insert (5) is mounted on the end mill body (2), these end portions S become the outermost peripheral portion of the end mill body (2). Therefore, in the following description, these end portions S may be referred to as “connecting portion S” or “outermost peripheral portion S”.

These outer peripheral cutting edges (5k1, 5k2) having a twisted shape are cutting edges provided to act in the vicinity of the standing wall of the work material when machining the corner of the work material. This is an effective cutting edge in order to maintain the surface properties of the finish processing on the standing wall of the cutting material.
In addition, in the top view of insert (5) shown to Fig.6 (a), the outer periphery cutting edge (5k1, 5k2) which has a twist shape becomes a linear form, and the outer periphery cutting edge (5k1, 5k2) which has a twist shape with the straight line L1 Is a parallel straight line relationship. As a result, when the insert (5) is mounted on the insert mounting seat (4) and the blade tip replaceable ball end mill (1) is rotated around the axis L in the R direction, a pair of arcuate cutting edges (5i1, 5i2) The rotation trajectory is substantially semicircular, and the rotation trajectory of the pair of outer peripheral cutting edges (5k1, 5k2) is substantially cylindrical.

  As shown in FIG. 6 (c), the ridge line of the arcuate cutting edge (5i1) viewed from the side surface side is connected to the outer peripheral cutting edge (5k1) having a twisted shape through the connecting portion S. Similarly, the ridge line of the cutting edge (5i2) viewed from the side surface side is also connected to the outer peripheral cutting edge (5k2) having a twisted shape through the connecting portion S. As shown in FIGS. 2 and 6 (a), a curved surface portion having a gentle convex shape that becomes a rake face (5d) is formed on the front side in the rotation direction R of the arcuate cutting edges (5i1, 5i2). Is formed.

  6 and 7 indicates a position where the arcuate cutting edges (5i1, 5i2) protrude most toward the front side in the rotation direction R. In the following description, the position Q at which the arcuate cutting edges (5i1, 5i2) protrude most forward in the rotation direction R is referred to as “the arcuate cutting edge protrudes most toward the front side in the rotation direction R”. May be described as “the most protruding portion Q” or simply “the most protruding portion Q”. In addition, K shown in FIG. 6A is a straight line connecting the arc center point O and the most protruding portion Q.

(State when the insert is fixed to the insert mounting seat)
An edge mill replaceable end mill (1) showing an embodiment of the present invention has an insert (5) using a clamp screw (6) on an insert mounting seat (4) formed at a tip (2a) of an end mill body (2). Is detachably fixed. 7, 8, and 9 correspond to FIGS. 3, 4, and 5, respectively, when one insert (5) is mounted and fixed to the insert mounting seat (4) of the end mill body (2). It is drawing which shows this state.

When one insert (5) is mounted and fixed to the insert mounting seat (4), the outer surface portion (5g) and (5h) of the insert (5) are respectively one inner surface portion 8a of the insert fitting groove (8). And the other inner side surface portion (8b) is firmly attached, the bottom side surface portion 5f of the insert (5) is closely attached to the bottom surface portion 8c of the insert fitting groove (8), and the fixing position of the insert (5) is predetermined. It is made to ensure accuracy.
And when the insert (5) is mounted and fixed to the insert mounting seat (4),
The most distal portion (5a) of the insert (5) is projected from the insert mounting seat (4) along the axis L, and further, a pair of arcuate cutting edges (5i1, 5i2), a pair of outer peripheral cutting edges (5k1) 5k2), the second lateral side surface portion (5b1, 5b2), and the third lateral side surface portion (5c1, 5c2) also slightly protrude outward from the insert mounting seat (4).

As described above, in the blade end replaceable ball end mill (1) according to the embodiment of the present invention, as shown in FIGS. 6 (a) and 9, the arc-shaped cutting blades (5i1, 5i2) have their respective shapes. It is also an important feature that an outer peripheral cutting edge (5k1) having a twisted shape connected to the end S and (5k2) are provided.
As shown in FIG. 11, the tangent line of the arc-shaped cutting edges (5i1, 5i2) and the outer peripheral cutting edges (5k1, 5k2) are set to be inclined with respect to the axis L. This inclined state is expressed as “having a twisted shape”.

  The reason for this is that, as described above, when engraving is performed using the blade tip replaceable ball end mill (1) according to the embodiment of the present invention, particularly in corner processing, a pair of outer peripheral cutting edges (5k1 having a twisted shape) 5k2) is provided, so that it is possible to process the finished surface of the corner standing wall surface with good surface roughness. On the other hand, in the plan view of the insert (5), when each of the pair of outer peripheral cutting edges has an arc shape, it is effective for reducing the cutting resistance, but the stepped portion due to the uncut portion on the processing surface. Is generated, resulting in a disadvantage that the surface roughness of the processed surface is lowered.

  Moreover, as shown to Fig.6 (a), insert (5) is provided with the linear outer periphery cutting edge (5k1, 5k2), and can re-grind to the cutting edge of insert (5). It becomes possible and can be repeatedly reproduced. On the other hand, when the outer peripheral cutting edge has an arc shape, the outer diameter of the cutting edge is changed by subjecting the cutting edge to re-grinding. It is difficult to process.

(Features of rake angle of arc-shaped cutting edge)
Next, the rake angle of the arcuate cutting edges (5i1, 5i2), which is a structural feature of the ball end mill of the present invention, will be described. In the present invention, the rake angle of the arcuate cutting edge indicates two types of rake angles, “radial rake angle” and “axial rake angle”.
Among these, the “radial rake angle” means the rake face (d) with respect to a straight line (radial straight line) extending radially from the arc center point O of the arcuate cutting edge (5i1, 5i2) toward the arcuate cutting edge. Indicates the angle. This “radial rake angle” may be referred to as a “normal rake angle”.

Here, the negative value of “radial rake angle” means that the rake face (5d) of the arcuate cutting edge (5i1) is hemispherical in the rotation trajectory of the arcuate cutting edge (5i1), as shown in FIG. When the same direction as the tool rotation direction R is set opposite to the straight line connecting the center (O) and the arcuate cutting edge (5i1), the “radial rake angle” is a negative value. To do. On the other hand, a “radial rake angle” having a positive value means that the tool rotation direction R is set in the opposite direction to the above.
In addition, the “axial rake angle” indicates an angle between a tangent line on the arcuate cutting edges (5i1, 5i2) and the axis L of the ball end mill in a side view of the arcuate cutting edges (5i1, 5i2).
Here, the “axial rake angle” is a positive value, as shown in FIG. 11, the inclination angle of the rake face of the arcuate cutting edge (5i1) is the tool rotation R direction with respect to the rotation axis L. When the opposite direction is set, the “axial rake angle” is a positive value. On the other hand, a negative value for the “axial rake angle” means that the value is set opposite to the above.

  A configuration example of the “radial rake angle” provided in the arcuate cutting edge (5i1) will be described with reference to FIG.

  FIG. 10 is a diagram illustrating a configuration example of “radial rake angle” for the cutting edge (5i1) of the pair of arcuate cutting edges (5i1, 5i2). In FIG. 10, from the arc center point O to a circle over the cutting edge region between the tip (5a1) of the arcuate cutting edge (5i1) and the connecting part (outermost peripheral part) S between the outer peripheral cutting edge (5k1). The radial line toward the arcuate cutting edge (5i1) is a straight line connecting the arc center point O and the most distal portion (5a1), that is, with reference to the axis L when the insert (5) is mounted on the end mill body (2). The angle formed by the radiation straight line is defined as a radiation angle, and the values of the “radial rake angle” are illustrated with respect to the radiation angle values of 5 °, 15 °, 30 °, 45 °, 60 °, 75 °, and 90 °. FIG.

  As shown in FIG. 10, the present invention is characterized in that the “radial rake angle” is changed over the entire region of the arcuate cutting edge (5i1). For example, as shown in FIG. 10, the radial rake angle α value at a radiation angle of 5 ° is −2.5 °, the radial rake angle α value at a radiation angle of 30 ° is −2.0 °, and the radial rake angle γ value at a radiation angle of 45 °. Is set to -2.5 [deg.], And the radial rake angle [beta] value is set to -6.5 [deg.] At a radiation angle of 90 [deg.]. Of the pair of arcuate cutting edges, the other arcuate cutting edge (5i2) is also “radiated” over the entire area of the arcuate cutting edge (5i2) so as to be the same as the arcuate cutting edge (5i1) shown in FIG. The value of the “direction rake angle” is changed. The state in which the “radial rake angle” is changed corresponding to the radiation angle will be described later.

  FIG. 11 is a diagram illustrating a configuration example of the “axial rake angle” for the cutting edge (5i1) of the arcuate cutting edges (5i1, 5i2). In FIG. 11, in the side view of the arcuate cutting edge (5i1), the angle between the tangent at the position on the arcuate cutting edge (5i1) corresponding to the radiation angle of the radial line and the axis L of the ball end mill is expressed as “axis As the “directional rake angle”, the values of “axial rake angle” are illustrated for every 5 °, 15 °, 30 °, 45 °, 60 °, and 75 ° of the radiation angle. For example, as shown in FIG. 11, the “axial rake angle” at a radiation angle of 5 ° is −48.409 °, and at a radiation angle of 45 °. At 0 ° and a radiation angle of 60 °, it is set to + 12.069 °.

  As described above, the “axial rake angle” is the tangent of the arc at an arbitrary position on the arcuate cutting edge (5i1) with the axis L of the ball endmill in the side view of the arcuate cutting edge of the ball end mill. Any position on the arcuate cutting edge (5i1) can be related to the radiation angle. Therefore, the radiation angle related to the “radial rake angle” shown in FIG. 10 and the radiation angle related to the “axial rake angle” shown in FIG. 11 show the same content (definition).

  FIG. 12 shows a state in which the “radial rake angle” shown in FIG. 10 is continuously changed, that is, the relationship between the radial angle (vertical axis) and the radial rake angle (horizontal axis) is a curved line F1. It is the figure which showed from the most front-end | tip part (5a) vicinity to the outermost peripheral part (joint part) S of a cutting blade (5i1). As shown in FIG. 12, the “radial rake angle” is set to a negative (negative angle) over the entire area of the arcuate cutting edge (5i1), and the absolute value of the “radial rake angle” is The maximum radiation angle is set.

  FIG. 13 shows a state where the “axial rake angle” shown in FIG. 11 is continuously changed, that is, the relationship between the radiation angle (vertical axis) and the axial rake angle (horizontal axis) as a curve F2. It is the figure which showed from the front-end | tip part (5a) vicinity of the circular arc-shaped cutting edge (5i1) to the outermost periphery part (joint part) S. FIG. As shown in FIG. 13, the “axial rake angle” includes the arcuate cutting edge (5i1) area set to negative (negative angle) and the arcuate cutting edge set to positive (positive angle). A region of the blade (5i1) and a region where the “axial rake angle” is zero are provided.

  The “radial rake angle” and the “axial rake angle” of the other arc-shaped cutting edges (5i2) of the pair of arc-shaped cutting edges (5i1, 5i2) are continuously corresponding to the radial angles. The changing state is also the same as the changing state of the curves F1 and F2 shown in FIGS. 12 and 13, respectively.

  FIG. 17 is a perspective view of another embodiment of the insert shown in FIG. The insert in this another embodiment has two coolant channel outlets at the position of the rotation axis, and the coolant channel is from the flank face (5e) of the arcuate cutting edges (5i1, 5i2). It penetrates through the bottom side surface (5f) and communicates with the end mill body (2). Further, the coolant channel can be set at an inclination angle with respect to the rotation axis. The inclination angle when emphasizing chip discharge is preferably set in the outer circumferential direction with respect to the rotation axis, and the inclination angle when emphasizing coolant supply is the insert temperature near the axis of the cutting edge. In order to avoid the rise, it is preferable to set the rotation axis direction. 18 is a plan view, a front view, and a side view of the insert shown in FIG. FIG. 19 is a front view of a blade end replaceable ball end mill equipped with the insert shown in FIG. 17 as seen from the direction of the rotation axis, and FIG. 20 is a side view.

  In the present invention, the above-mentioned two types of rake angles of the arc-shaped cutting edges (5i1, 5i2), that is, “radial rake angle” and “axial rake angle” are as follows (feature 1) to (feature 6). The “coolant flow path” has the features described in (Feature 7) and (Feature 8).

(Feature 1)
The “radial rake angle” at a radial angle of 5 ° near the leading edge (5a) of the arcuate cutting edge is α, and the “radial rake angle at a radial angle of 90 ° that becomes the outermost peripheral portion S of the arcuate cutting edge”. Is “radial rake angle” α, β and γ, where γ is “radial rake angle” at the most protruding portion Q where the arcuate cutting edge protrudes most forward in the rotational direction R. Is set to a negative angle, and the absolute values of the radial rake angle α value, β value, and γ value are | α |, | β |, | γ | | Α | <| β |.

(Feature 2)
The absolute value of the “radial rake angle” of the arcuate cutting edge is set to a minimum value between the vicinity of the most distal portion (5a) of the arcuate cutting edge and the most protruding portion Q. The absolute value of the “radial rake angle” is set so as to continuously increase from the most protruding portion Q to the outermost peripheral portion S.

(Feature 3)
The “radial rake angle” α at a radiation angle of 5 ° (5 °) near the leading edge (5a) of the arcuate cutting edge is −6 ° ≦ α ≦ −0.5 ° and the radiation angle is 90 °. The “radial rake angle” β at the outermost peripheral portion S of the arcuate cutting edge becomes -10 ° ≦ β ≦ −2 °, and the “radial rake angle” γ at the outermost projection Q is −6 ° ≦ It is set so as to satisfy γ ≦ −0.5 °. The value of “radial rake angle” γ is set to −6 ° or more.

(Feature 4)
The position of the most protruding portion Q where the arcuate cutting edge protrudes most forward in the rotational direction R is set to the position of the arcuate cutting edge corresponding to a radiation angle of 30 ° to 47 °.

(Feature 5)
Any radial rake angle between the most projecting portion Q and the outermost peripheral portion S, with reference to the most projecting portion Q, is θ1, and any radiating rake angle between the most projecting portion Q and the most distal portion (5a) When the radial rake angle is θ2, when the absolute values of the radial rake angle θ1 and θ2 are | θ1 | and | θ2 |, respectively, | θ1 |> | θ2 | It is set to do.

(Feature 6)
The axial rake angle of the ball end mill is a negative value (negative angle) until it reaches the most protruding portion Q from the most distal portion (5a) of the arcuate cutting edge, and exceeds the most protruding portion Q to the outermost peripheral portion S. Is a positive value (positive angle), and is 0 at the most protruding portion Q. Further, the negative rake angle in the negative axial direction is gradually increased in the positive direction from the most distal portion (5a) to the most projecting portion Q, and the outermost portion S beyond the most projecting portion Q is positive. The rake angle in the axial direction is gradually increased.
Further, as shown in FIG. 13, the axial rake angle in the vicinity of the most distal portion (5a) of the arcuate cutting edge is about -70 ° to -80 °, and the axial rake angle in the outermost peripheral portion S is about + 20 °. I am trying to set it.

The most distal portion (5a), the outermost peripheral portion S, and the outermost projecting portion Q of the arcuate cutting edges (5i1, 5i2) are the positions of the most distal portion (5a), the outermost peripheral portion S, and the most projecting portion Q, respectively. The position of the cutting edge in the vicinity including is shown.
Since it may be difficult to measure the radial rake angle and the axial rake angle of the arcuate cutting edge with high accuracy using a non-contact type three-dimensional digitizer or the like, the state-of-the-art portion (5a ) May be the position of an arcuate cutting edge that forms a radiation angle of 5 ° from the most distal portion (5a).

(Feature 7)
In the ball end mill of the present invention, an insert having a detachable arc-shaped cutting edge is attached to the tip of the end mill body. In the front view of the ball end mill, the insert is used for at least two coolants at the position of the rotation axis. The coolant channel has an outlet of the channel and penetrates from the flank portion of the arcuate cutting edge to the bottom side surface portion (5f) and communicates with the end mill body.

(Feature 8)
The ball end mill of the present invention is provided with a detachable insert, and the coolant channel has an inclination angle with respect to the rotation axis.

In (Feature 1) to (Feature 6), the reason for limiting the size of each rake angle and the range of the numerical value thereof, and the reason for providing the coolant channel in (Feature 7) and (Feature 8) will be described below. become that way.

  As described above (feature 1), that is, the “radial rake angles” α, β, and γ are all set as negative angles, and the absolute values of the radial rake angles α, β, and γ are respectively | The reasons for setting so that | γ | ≦ | α | <| β | when α |, | β |, and | γ | are as described in the following (1) to (3).

  (1) By setting the radial rake angles α, β, and γ to negative angle values, the cutting edge strength is enhanced over the entire cutting edge region of the arcuate cutting edge. For this reason, the chipping resistance of the cutting edge is improved even in cutting using a high hardness material having a hardness of 45 HRC or more as a work material. However, if the negative angle value is used, the cutting resistance reduction effect and chip discharge performance are inferior, but the use of the ball end mill of the present invention is mainly for finishing with a hard material as the work material. Is set to be smaller than rough machining and intermediate finishing, so that the increase in cutting resistance is small and there is no problem with chip discharge.

  (2) The absolute value | γ | of the radial rake angle γ at the most protruding portion where the arcuate cutting edge having an S shape protrudes most forward in the rotation direction R is expressed as | γ | ≦ | α | The relation of <| β | is that the position of the radial rake angle γ is the first region in contact with the hard work material in the arc-shaped cutting edge, so that the cutting edge strength is enhanced. This is to maintain good fracture resistance and improve the biting property to the work material.

  (3) With respect to α and β, which are radial rake angle values, when α and β are absolute values | α | and | β |, respectively, so that | α | <| β | The reason for setting is that the cutting resistance at the cutting edge (5a) of the arcuate cutting edge is made as small as possible to keep the biting property to the work material good, while the outermost peripheral part S of the arcuate cutting edge is set. Then, since chip thickness increases, it is for ensuring cutting edge strength more.

  As described above (Feature 2), that is, the absolute value of the “radial rake angle” of the arcuate cutting edge is the minimum value between the vicinity of the most distal part (5a) of the arcuate cutting edge and the most protruding part Q. Is set. The minimum value of the “radial rake angle” in the entire region of the arcuate cutting edge is set so that the radial angle is in the range of 15 ° to 30 °. The absolute value of the “radial rake angle” is set so as to increase continuously from the most protruding position Q to the outermost peripheral portion S for the following reasons.

  By providing the most protruding portion Q on the arcuate cutting edge, the first region where the arcuate cutting edge comes into contact with the work material becomes the most protruding portion Q, and then the contact area with the work material by the rotation of the cutting edge. Spreads to both the cutting edge (5a) and the outermost periphery S. For this reason, the absolute value of the radial rake angle is decreased from the vicinity of the most distal portion (5a) of the arcuate cutting edge, and is the minimum value between the vicinity of the most distal portion (5a) and the most protruding portion Q. Is set, cutting resistance can be reduced even if the axial rake angle is a negative value. It is desirable to set the minimum value of the “radial rake angle” in the entire region of the arcuate cutting edge so that the radial angle is in the range of 15 ° to 30 °. The reason for this is that, in the arc-shaped cutting edge, the position where the radial rake angle is minimum is in the vicinity of the most protruding portion Q in the arc-shaped cutting edge, so that the cutting edge strength is enhanced and the fracture resistance is maintained. This is because the biting property to the work material is also good. Moreover, it is because the intensity | strength ensuring of a cutting edge can be measured by setting so that it may increase continuously from the most protrusion position Q to the outermost periphery part S. FIG.

  As described above (feature 3), that is, the “radial rake angle” α at the tip of the arcuate cutting edge is −6 ° ≦ α ≦ −0.5 °, and the “radial rake angle” β at the outermost peripheral portion S. Is set to −10 ° ≦ β ≦ −2 °, and “radial rake angle” γ at the most projecting portion Q is set to −6 ° ≦ γ ≦ −0.5 °, the following (1) to (3 ).

  (1) By setting the radial rake angle α to −6 ° ≦ α ≦ −0.5 °, cutting edge strength can be maintained, and cutting at the most advanced portion (5a) and its vicinity is performed. The resistance is small, and it becomes possible to keep good the biting property to the work material. On the other hand, when α> −0.5 °, the cutting edge strength at the foremost portion (5a) is weak, so that inconvenience such as chipping of the cutting edge occurs. In the case of α <−6 °, the cutting resistance of the arcuate cutting edge at the foremost portion (5a) and its vicinity is increased, and the sharpness is deteriorated and the heat generation becomes remarkable. For this reason, inconveniences such as a decrease in strength of the cemented carbide, abrasion, generation of chip deposits, and deterioration of surface properties of the processed surface of the work material occur.

  (2) The cutting edge strength at the outermost peripheral portion S can be ensured by setting the radial rake angle β to −10 ° ≦ β ≦ −2 °. On the other hand, in the case of β> −2 °, it is difficult to maintain the strength of the arcuate cutting edge at the outermost peripheral portion S, and it tends to be lost. When β <−10 °, the cutting resistance at the outermost peripheral portion S increases, chatter vibrations occur in the end mill body (2), and heat generation becomes significant. For this reason, the surface property of the processed surface of the work material cannot be kept good.

  (3) By setting the radial rake angle γ to be −6 ° ≦ γ ≦ −0.5 °, the cutting near the most protruding portion Q, which is the first region where the cutting edge comes into contact with the work material. The blade strength can be maintained and the effect of stabilizing the tool posture by appropriately controlling the back component force in the direction of the tool axis is particularly effective for cutting a hard material. On the other hand, when γ> −0.5 °, it is difficult to maintain the cutting edge strength at the most protruding portion Q. When γ <−6 °, the cutting resistance at the most projecting portion Q is large, and the biting property to the work material cannot be satisfactorily achieved.

  The reason for setting the above-described (feature 4), that is, the position of the most protruding portion Q of the arcuate cutting edge to the position of the arcuate cutting edge corresponding to a radiation angle of 30 ° to 47 ° is as follows.

  By setting the position of the most protruding portion Q to the position of the arcuate cutting edge corresponding to a radiation angle of 30 ° to 47 °, the rake angle in the axial direction of the arcuate cutting edge forming an S shape in a side view is negative. This is because it is possible to reduce the area where the value becomes and increase the area where the value becomes positive. By reducing the area where the rake angle in the axial direction becomes negative, the strength of the arcuate cutting edge can be maintained while the cutting resistance is high, and the rake angle in the axial direction becomes a positive value. This is because if the area is widened, it is convenient to keep both in good balance, such as maintaining the strength of the arcuate cutting edge and maintaining good chip discharge.

  As described above (feature 5), that is, with reference to the most protruding portion Q of the arcuate cutting edge, any radial rake angle between the most protruding portion Q and the outermost peripheral portion S is θ1, and the most protruding portion When any radial rake angle between Q and the vicinity of the most advanced portion (5a) is θ2, the absolute values of the radial rake angle θ1 value and θ2 value are | θ1 | and | θ2 | The reason for setting to satisfy | θ1 |> | θ2 | is as follows. The vicinity of the most advanced part (5a) indicates the position of the arcuate cutting edge in the vicinity of the most advanced part (5a) excluding the radiation angle of less than 5 °. In other words, θ1 represents the radial rake angle value in the range where the axial rake angle is positive in FIG. 13, and θ2 represents the radial rake angle value in the range where the axial rake angle is negative. .

  As described above, the cutting resistance in the region where the rake angle in the axial direction takes a negative value is reduced. In order to maintain the cutting edge strength, an arcuate cutting edge region that satisfies | θ1 |> | θ2 | is secured to be long. Further, in the vicinity of the outermost circumferential side S of the arcuate cutting edge, the chip thickness is thick, so that the strength of the arcuate cutting edge is secured, as shown in FIG. From the vicinity of the intermediate position to the outermost periphery S, the radial rake angle θ1 is set to “| θ1 |> | θ2 |”.

  As described above (feature 6), that is, the rake angle in the axial direction of the ball end mill is set to a negative value until it reaches the most protruding portion Q from the most distal portion (5a) of the arcuate cutting edge, and exceeds the most protruding portion Q. A positive value is used up to the outermost periphery S. Further, by changing the negative axial rake angle so as to gradually increase in the positive (+) direction until reaching the most protruding portion Q from the most distal portion (5a), the axial rake angle at the most protruding portion Q is changed to “ 0 ”. Further, the positive axial rake angle is gradually increased from the most projecting portion Q to the outermost peripheral portion S.

(1) As described above, the arc-shaped cutting edge is provided with the most protruding portion Q, so that the first region where the arc-shaped cutting edge comes into contact with the work material becomes the most protruding portion Q, and then the cutting edge rotates. Thus, the contact area with the work material extends to both the most distal end portion (5a) and the outermost peripheral portion S of the cutting edge. For this reason, even if the axial rake angle is a negative value by continuously decreasing the absolute value of the radial rake angle from the most distal portion (5a) of the arcuate cutting edge to the most protruding portion Q, Cutting resistance can be reduced.
Further, by setting the position of the most protruding portion Q to the position of the arcuate cutting edge where the radiation angle is 30 ° to 47 ° as described above, the region where the axial rake angle becomes a positive value is widened. Therefore, it is possible to maintain good chip discharge while maintaining the strength of the arcuate cutting edge.

  (2) The reason why the axial rake angle in the vicinity of the most distal portion (5a) is set to about -70 ° to -80 ° and the axial rake angle in the vicinity of the outermost peripheral portion S is set to about + 20 ° is as follows. ), As described in (b).

(A) By setting the rake angle in the axial direction to a positive value (about + 20 °) in the vicinity of the outermost peripheral portion S, the chips are discharged in a direction perpendicular to the tangent to the tool rotation trajectory, and the chip discharge performance is improved. On the other hand, when the axial rake angle in the vicinity of the outermost peripheral portion S is a value smaller than + 20 °, the chip discharging effect is reduced. Further, when the value is larger than + 20 °, the thickness of the cutting edge becomes thin, so that the rigidity of the arcuate cutting edge cannot be maintained.
(B) By setting the rake angle in the axial direction to a negative value (about -70 ° to -80 °) in the vicinity of the most distal portion (5a), the stress during cutting of the work material is in the direction of the rotation axis L. Since it acts on the end mill body (2) side, the deflection of the rotation axis of the end mill body (2) can be reduced. However, when the value is too large on the negative side, chip discharge becomes difficult, but if it is about -70 ° to -80 °, the difficulty is not a problem. When the axial rake angle is larger than −80 ° on the negative side, chip discharge becomes difficult.

As described above (feature 7), that is, in the ball end mill of the present invention, an insert having a detachable arc-shaped cutting edge is attached to the tip of the end mill body (2). And at least two coolant channel outlets at the position of the rotation axis, and the coolant channel extends from the flank portion (5e) of the arcuate cutting edge (5i1, 5i2) to the bottom side surface portion (5f). It penetrates and communicates with the end mill body (2). The reason for this is as follows.
Since the ball end mill of the present invention is applied particularly to cutting using a high-hardness material as a work material, it is possible to take measures to avoid an increase in insert temperature during cutting by providing a coolant channel in the insert. . As a result, it is possible to prevent a decrease in resistance to plastic deformation of the cemented carbide insert or to avoid a decrease in hardness.

  As described above (feature 8), that is, in the ball end mill of the present invention, the coolant channel provided in the insert has an inclination angle with respect to the rotation axis. The reason for this is as follows. The inclination angle when emphasizing chip discharge is preferably set in the outer circumferential direction with respect to the rotation axis, and the inclination angle when emphasizing coolant supply is the insert temperature near the axis of the cutting edge. In order to avoid the rise, it is preferable to set the rotation axis direction. The coolant flow supplied to the chip interface through the coolant channel can effectively discharge the chips, so that the work surface properties of the work material will be good and the surface roughness of the finish will be good. Can do.

(Insert manufacturing method)
Then, the manufacturing method of the insert (5) with which the blade end replaceable ball end mill showing an embodiment of the ball end mill of the present invention is mounted will be described. The insert (5) made of the WC-based cemented carbide can be manufactured based on, for example, the following procedures (1) to (4).

(Procedure 1):
Mixing granulated powder made by adding tungsten carbide powder and cobalt powder, and additives as needed, using insert manufacturing techniques such as powder molding using a mold that has been widely used in the past. Mold the molded body. At the time of molding the mold, a hole that is a prototype of the screw insertion hole is formed. When the molded body of the insert (5) is sintered, it shrinks by 20% to 30%. Therefore, the molded body of the insert (5) taking this into consideration is manufactured by die molding.

(Procedure 2):
Subsequently, the molded body of the insert (5) molded by mold molding is placed in a heating furnace heated to a predetermined temperature (about 1300 ° C. to 1400 ° C.) to perform a sintering (firing) treatment.

(Procedure 3):
Subsequently, the sintered compact of the insert (5) is subjected to grinding on each necessary portion using a NC control three-dimensional grinding (polishing) processing machine or the like. As this grinding, the arc-shaped cutting edges (5i1, 5i2) of the sintered insert (5) and the outer peripheral cutting edges (5k1, 5k2) having a twisted shape are ground using a rotating grindstone having diamond abrasive grains. Processing. Moreover, finishing is also performed on the bottom side surface portion (5f) of the sintered insert (5).
The formation of the radial rake angle and the axial rake angle corresponding to the radial angle on the arcuate cutting edge is performed by NC control processing using a diamond rotating grindstone or the like having a thin plate shape.

(Procedure 4):
About the insert (5) in which the grinding process is completed, a coating for imparting wear resistance and heat resistance is coated on the surface excluding the screw insertion hole. The material of the coating is, for example, any one of a coating made of Ti—Al based nitride, Ti—Si based nitride, Ti—B based nitride, etc., and the coating is formed by, for example, the PVD method.

  Further, in the same manner as described above, coating the end mill body (2) with a film for imparting wear resistance is effective in extending the service life of the blade end replaceable end mill of the present invention. In particular, the surface of the end mill main body (2) is preferably coated with Ti-B nitride that has lubricity in addition to wear resistance, so that the frictional resistance with chips is reduced, which is preferable.

(Example)
Subsequently, a blade end replaceable ball end mill, which is an embodiment of the ball end mill of the present invention, is manufactured and attached to a machining center, and cutting is performed on a work material made of cold die steel (SKD11 material (60HRC)). The damage state of the arcuate cutting edge was evaluated.

The tool body of the manufactured ball end mill has a shank type shape with a cutting edge diameter of 30 mm, a shank diameter of 32 mm, a total length of 200 mm, and a neck length of 120 mm.
The end mill body used was a cemented carbide material at the base and a SKD61 equivalent material joined to the tip by brazing. Further, the shank portion for chucking and fixing to the NC processing machine was made of cemented carbide and finished by polishing. The insert seating surface of the end portion of the end mill body was formed by milling with a machining center after adjusting the appearance shape of a SKD61 equivalent material by lathe processing and adjusting the surface hardness from HRC38 to 40.

  The insert made of cemented carbide to be mounted on the insert seating surface of the tool body has an arcuate cutting edge radius dimension of 15 mm, a thickness T of 7.2 mm, and a twisted outer peripheral cutting edge length of 3.0 mm. Three types of inserts (insert numbers 1 to 3) were manufactured. Regarding the three types of inserts produced, the rake angle in the radial direction and the rake angle in the axial direction for each of the radiation angles were set as shown in Table 1 for the numbers 1 to 3. As shown in Table 1, in the insert 1, the α value was set to −2.5 °, the β value was set to −6.5 °, and the γ value at the most protruding portion of the arcuate cutting edge was set to −2.5 °. The β value of insert 2 was set to −3.0 °, and the β value of insert 3 was set to + 3.0 °. Here, the ball end mill equipped with the insert number 1 corresponds to the example of the present invention, and the ball end mill equipped with the insert numbers 2 and 3 becomes the ball end mill corresponding to the comparative example.

  In this cutting process, cutting using a cutting edge in the vicinity of the outermost peripheral part of the arcuate cutting edge is performed on the work material of the SKD11 material (60HRC) in order to process a flat surface and a wall surface with an inclination angle of 85 °. The operation of the machining center was controlled to perform machining. The radial rake angle and the axial rake angle corresponding to the radiation angle formed on the arc-shaped cutting edge of each insert shown in Table 1 are measured using a commercially available optical three-dimensional data acquisition device (non-contact type). Measurement was performed using a three-dimensional digitizer.

In the above-described ball end mill, the cutting conditions for the flat surface processing and the wall surface processing including the inclination angle of 85 ° were as follows.
(1) Cutting conditions in flat machining Machining method: Dry cutting (air blow)
Cutting speed (Vc): 400 [m / min]
Number of rotations (n): 4244 [min ⁻¹ ]
Feed rate (Vf): 2550 [mm / min]
Feed per tooth (fz): 0.3 [mm / tooth]
Axial cut depth (ap): 0.3 [mm]
Radial cutting depth (ae): 0.5 [mm]
Tool protrusion (OH): 120 [mm]
(2) Cutting conditions for wall surface machining with an inclination angle of 85 ° Machining method: Dry cutting (air blow)
Cutting speed (Vc): 400 [m / min]
Number of rotations (n): 4244 [min ⁻¹ ]
Feed rate (Vf): 2550 [mm / min]
Feed per tooth (fz): 0.3 [mm / tooth]
Radial depth of cut (ae): 0.1 [mm], 0.3 [mm]
Pick feed (pf): 0.3 [mm]
Tool protrusion (OH): 120 [mm]
About the said radial direction cutting amount (ae), 2 types of cutting which set to ae = 0.1 [mm] and ae = 0.3 [mm] was implemented.

  The results of the above-described embodiment are shown in FIGS. FIG. 14 shows a photograph of the state of the cutting edge observed from the rake face direction and the flank direction when the working distance in flat machining reaches 650 m, and the value of the maximum flank wear width of the cutting edge. FIG. 15 shows a photograph of the cutting edge state observed from the flank direction when the ae value is 0.1 [mm] with respect to the radial cutting depth (ae) in the wall processing with an inclination angle of 85 °, and the cutting edge This is the maximum flank wear width. FIG. 16 is a photographic view of the cutting edge state with an ae value of 0.3 [mm] observed from the rake face direction and the flank face direction in the radial direction cutting amount (ae) in the wall surface processing with an inclination angle of 85 °. The maximum flank wear width of the cutting edge. The machining distance in the wall surface machining with an inclination angle of 85 ° in FIGS. 15 and 16 was advanced to 90 m. However, with regard to insert number 3, since the occurrence of sparks was confirmed when the cutting distance reached 10 m, the machining was stopped.

  Among the molds for forming automobile steel plates, a high-hardness material is used for the entire or part of the mold for forming a high-tensile steel plate or a thick steel plate for the purpose of improving the die life. In general processing steps, a roughing process and a semi-finishing process are performed, followed by a quenching process to perform the finishing process. Therefore, the finishing process has a non-uniform cut due to dimensional changes due to quenching. Therefore, the evaluation is performed using cutting conditions in which the axial cut (ap) is 0.3 [mm] in plane machining and the radial cut (ae) is 0.3 [mm] in wall surface machining with an inclination angle of 85 °. went. The following matters were clarified from the cutting results shown in FIGS.

  (1) As a result of the planar processing shown in FIG. 14, the ball end mill cut with the insert of the present invention example of insert No. 1 in which the α value of the radial rake angle at a radial angle of 5 ° is set to −2.5 °. The state of the blade was good with little damage. On the other hand, in the insert number 2 in which the α value was set to + 1.0 ° and the insert number 3 in which the α value was set to + 7.0 °, damage to the cutting edge was extremely severe. In particular, the insert number 3 having an α value of + 7.0 ° was severely damaged in the rake face direction.

  (2) As shown in FIG. 15, in the result of the wall surface processing with an inclination angle of 85 °, the β value was set to + 3.0 ° under the cutting condition in which the radial cut (ae) was 0.1 [mm]. In all the inserts including the insert number 3, the cutting edge showed a steady wear state and was good.

  (3) As shown in FIG. 16, in the inclined wall surface processing, the β value is set to −6.5 ° and −3.0 ° under the cutting condition in which the radial cut (ae) is set to 0.3 [mm]. The ball end mill equipped with the set insert numbers 1 and 2 could be processed up to a cutting distance of 90 m. The state of the cutting edge at this time was good because it showed a steady wear form generated on the flank side. On the other hand, the insert of insert number 3 with the β value set to + 3.0 ° was stopped because the generation of sparks and chip wrapping were confirmed when the cutting distance reached 10 m. When the damage state of the cutting edge at this time was confirmed, the defect | deletion to the rake face direction had generate | occur | produced.

  From the above (1) to (3), in the processing of the SKD11 material (60HRC) that assumes the high hardness material portion of the automobile steel plate forming mold for forming a high-tensile steel plate or a thick steel plate, the α value is −2.5. It can be judged that the tool of the present invention example in which the angle, β value is set to −6.5 °, and γ value is set to −2.5 ° is the most excellent. Therefore, as in the configuration of the present invention, the α value, β value, and γ value are all negative angles, and the relationship between these absolute values is set to be | γ | ≦ | α | <| β |. As a result, the impact at the time of biting of the cutting edge can be alleviated, the strength of the cutting edge can be ensured, the chipping resistance can be improved, and at the same time the chip discharge can be enhanced. Furthermore, it is considered to be a highly reliable radial rake angle that can improve the surface roughness of the processed surface of the work material.

  Although the embodiment of the present invention described above has been described with respect to a ball end mill including a two-blade having a single insert having an arcuate cutting edge, the present invention includes a two-blade made of cemented carbide. The present invention can also be applied to a solid type ball end mill. When the present invention is applied to a solid-type ball end mill composed of two blades, the following matters should be particularly taken into consideration regarding the formation of the radial rake angle and the axial rake angle of the arcuate cutting edge.

(1) The core thickness of the solid type ball end mill excluding the vicinity of the tool tip is preferably set to 0.2D to 0.5D, where D (mm) is the tool diameter of the end mill. This is because the depth of the blade groove can be sufficiently secured while maintaining the strength of the solid-type ball end mill.
(2) The arc-shaped cutting edge in the vicinity of the rotation axis in the solid-type ball end mill has the effect that the strength of the tip and the chip discharge performance are improved by appropriately setting the centering amount to an appropriate value. .

1: Cutting edge replaceable ball end mill (ball end mill)
2: End mill body 2a: End portion of end mill body 3: Shank portion 4: Insert mounting seat 5: Insert 5a: Cutting edge
5b1, 5b2: second side surface part,
5c1, 5c2: third side surface part,
5d: rake face part,
5e: flank face,
5f: bottom side surface part,
5 g: outer surface part,
5h: outer surface part,
5i1, 5i2: Arc-shaped cutting edges,
5k1, 5k2: outer peripheral cutting edge having a twisted shape,
5p: Screw insertion hole,
6: Clamp screw,
7: Inclined reduced diameter part,
8: Insert fitting groove,
8a, 8b: inner side surface part,
8c: bottom part,
9a, 9b: tip half part,
10: Insert fixing screw hole,
F1: A curve showing a change state of the radial rake angle,
F2: a curve showing a change state of the axial rake angle,
K: A straight line connecting the arc center point O and the most protruding portion Q,
L: rotation axis (axis),
L1: a straight line passing through the tip (5a) of the insert and the arc center point O,
L2: a straight line parallel to the straight line L1,
M: a straight line passing through the arc center point of the arcuate cutting edge and orthogonal to the rotation axis,
O: arc center point of the arcuate cutting edge,
Q: The most protruding part of the arcuate cutting edge,
S: A point where the straight line M and the arcuate cutting edge intersect (joining part S or outermost peripheral part S),
T: Insert thickness.

Claims (8)

An arc-shaped cutting edge extending from the most distal end portion of the end mill body to the outermost peripheral portion in a plan view of the end mill body is provided at the tip of the end mill body rotated in the rotation direction R around the rotation axis. In the ball end mill provided with a rake face of the arcuate cutting edge formed on the front side of the rotation direction R, the arcuate cutting edge has an S shape in front view from the rotation axis direction. The radial rake angle of the arcuate cutting edge is such that the radiation straight line extending radially from the arc center point of the arcuate cutting edge toward the arcuate cutting edge intersects the arcuate cutting edge. When defined as an angle formed by a straight line and the rake face of the arcuate cutting edge, and when an angle formed by the rotation axis and the radiation straight line is defined as a radiation angle with respect to the rotation axis, The radial rake angle when the radiating angle is 5 degrees (°) is α, the radial rake angle when the radiating angle is 90 degrees (°) is β, and the arcuate cutting edge having the S shape is the rotational direction R. The radial rake angle α, the radial rake angle β, and the radial rake angle γ are all given by γ as the radial rake angle at the most projecting portion that is the most protruding position on the front side of When the absolute values of the radial rake angle α value, β value, and γ value are | α |, | β |, | γ |
| Γ | ≦ | α | <| β |
A ball end mill characterized by being set to be   The absolute value of the radial rake angle is set at a position where the minimum value is set between the most distal part and the most protruding part of the arcuate cutting edge, and the minimum value of the radial rake angle is 15 degrees to 30 degrees. 2. The ball according to claim 1, wherein the absolute value of the radial rake angle is set so as to continuously increase from the outermost protruding portion to the outermost peripheral portion. End mill. The radial rake angle α, the radial rake angle β and the radial rake angle γ are:
−6 ° ≦ α ≦ −0.5 °,
−10 ° ≦ β ≦ −2 °,
−6 ° ≦ γ ≦ −0.5 °,
The ball end mill according to claim 1, wherein the ball end mill is set to satisfy the following.   The ball end mill according to any one of claims 1 to 3, wherein the most protruding portion is formed at a position of the arcuate cutting edge where the radiation angle is 30 ° to 47 °. When the radial rake angle from the most protruding portion to the vicinity of the outermost peripheral portion is defined as θ1, and the radial rake angle from the most protruding portion to the vicinity of the most distal portion is defined as θ2, with the most protruding portion as a reference. When the absolute values of the radial rake angle θ1 value and θ2 value are | θ1 | and | θ2 |
| Θ1 |> | θ2 |,
The ball end mill according to any one of claims 1 to 4, wherein the ball end mill is set so as to satisfy the following. In the side view of the ball end mill, when the angle formed by the tangent line on the arcuate cutting edge and the rotation axis is the rake angle in the axial direction,
The axial rake angle is set to a negative value until reaching the most protruding portion from the most distal portion of the arcuate cutting edge, and is set to a positive value beyond the most protruding portion to the outermost peripheral portion. Set,
The ball end mill according to any one of claims 1 to 5, wherein the ball end mill is characterized.   2. The ball end mill according to claim 1, wherein the ball end mill is provided with an insert having a detachable arc-shaped cutting edge at a tip portion of the end mill body (2), and in the front view of the ball end mill, The insert has at least two coolant channel outlets at a position corresponding to the rotation axis, and the coolant channel extends from the flank portion (5e) of the arcuate cutting edge (5i1, 5i2) to the bottom side surface portion ( 5f) and penetrating to the end mill body (2).   The ball end mill according to claim 7, wherein the coolant channel has an inclination angle with respect to the rotation axis.