WO2016024819A1

WO2016024819A1 - Cutting head, holder and rotating tool including the same

Info

Publication number: WO2016024819A1
Application number: PCT/KR2015/008459
Authority: WO
Inventors: Chang Hee Choi; Chang Gyu Park
Original assignee: Taegutec Ltd.
Priority date: 2014-08-14
Filing date: 2015-08-12
Publication date: 2016-02-18
Also published as: KR20160020886A

Abstract

A rotating tool capable of absorbing a stress caused by a cutting force during a cutting operation. The rotating tool has a holder having a plurality of groove portions in a front end surface, a cutting head having a plurality of protrusion portions in a rear end surface, and a screw clamping the cutting head to the holder. The groove portion has a pair of groove side surfaces and tapers in a radially outward direction. The protrusion portion has a pair of protrusion side surfaces and tapers in the radially outward direction. A bent portion is formed in one of the groove side surface and the protrusion side surface. When the cutting head is clamped to the holder, a relief angle is formed between the groove side surface and the protrusion side surface from the bent portion in the radially outward direction.

Description

CUTTING HEAD, HOLDER AND ROTATING TOOL INCLUDING THE SAME

The present invention relates to parts used for a cutting operation, particularly parts such as a cutting head and a holder for the cutting operation. Further, the present invention relates to a rotating tool including such parts used for the cutting operation.

A rotating tool such as a milling tool cuts a workpiece while being rotated. Some rotating tools include replaceable cutting inserts for cutting a workpiece. As to a rotating tool having a relatively large diameter, the cutting inserts are clamped to an outer periphery of a holder that is a body of the rotating tool. However, as to a rotating tool having a relatively small diameter, it is difficult to design such a rotating tool so that cutting inserts are clamped to an outer periphery of a holder due to the small periphery of the holder. As such, as an example of the rotating tool having a relatively small diameter, a cutting head integrated rotating tool, wherein a cutting head for cutting a workpiece is integrally formed with a front end of a holder, was proposed in the art.

However, since the holder and the cutting head of the cutting head integrated rotating tool must be manufactured into a single part by means of the same material, the cutting head integrated rotating tool has a low productivity and a high unit price of a product. Further, when the service life of the rotating tool ends due to wear of the cutting head, the entire rotating tool must be replaced. As such, the cutting head integrated rotating tool cannot be cost effective.

To address the aforementioned problem, a cutting head replaceable rotating tool, wherein a cutting head is replaceably clamped to a front end of a holder, was proposed in the art. U.S. Patent No. 7,150,590 discloses an example of the cutting head replaceable rotating tool.

In the cutting head replaceable rotating tool, a resistance force (i.e., stress) in response to a cutting force applied during cutting a workpiece is produced at respective contact portions of the holder and the cutting head. The stress may cause deformation or damage of the structurally weak contact portions of the holder and the cutting head. Thus, a contact configuration of the holder and the cutting head, which effectively absorbs and reduces the stress caused by the cutting force, may be considered as one of the design factors for the rotating tool.

According to the rotating tool disclosed by the aforementioned patent document, the holder has a plurality of radial grooves in a front end surface of the holder, and the cutting head has a plurality of radial ribs in a rear end surface of the cutting head opposite to the front end surface of the holder. However, in the rotating tool disclosed by the aforementioned patent document, when the cutting head is clamped to the holder, the outer end portion of the groove and the outer end portion of the rib come into contact with each other. That is, the contact portions of the holder and the cutting head, to which the stress caused by the cutting force is applied, are structurally weak. If the stress caused by the cutting force is concentrated to the contact portions of the holder and the cutting head, then the stress cannot be distributed to and absorbed at the peripheral portions of the contact portions. Thus, the contact portions of the holder and the cutting head can be unexpectedly deformed, damaged or broken and the stable performance of the rotating tool cannot be ensured.

The present invention is directed to solving the aforementioned problems of the prior art. The present invention provides a part for use in a cutting operation, specifically a cutting head and a holder, which is capable of effectively distributing and absorbing the stress caused by the cutting force during a cutting operation.

Further, the present invention provides a rotating tool including such cutting head and holder.

One aspect of the present invention provides a holder, to a front end of which a cutting head is replaceably clamped. In an exemplary embodiment, the holder includes a front end surface, a screw coupling hole formed in the front end surface, and a plurality of groove portions disposed in the front end surface radially about a center of the screw coupling hole. Each of the groove portions tapers in a radially outward direction. Each of the groove portions has a pair of groove side surfaces inclined with respect to the front end surface. Each of the groove side surfaces includes a bent portion between a middle and a radially inward end and is bent at the bent portion.

Another aspect of the present invention provides a cutting head replaceably clamped to a front end of a holder. In an exemplary embodiment, the cutting head includes a front end surface, a rear end surface opposite to the front end of the holder, a screw receiving hole extending through the front end surface and the rear end surface, and a plurality of protrusion portions disposed in the rear end surface radially about a center of the screw receiving hole. Each of the protrusion portions tapers in a radially outward direction. Each of the protrusion portions has a pair of protrusion side surfaces inclined with respect to the rear end surface. Each of the protrusion side surfaces includes a bent portion between a middle and a radially inward end and is bent at the bent portion.

A further aspect of the present invention provides a rotating tool. In an exemplary embodiment, the rotating tool includes a holder, a cutting head and a screw. The holder includes a front end surface, a screw coupling hole formed in the front end surface, and a plurality of groove portions disposed in the front end surface radially about a center of the screw coupling hole, each groove portion tapering in a radially outward direction. The cutting head includes a front end surface, a rear end surface opposite to the front end surface of the holder, a screw receiving hole extending through the front end surface and the rear end surface of the cutting head, and a plurality of protrusion portions disposed in the rear end surface radially about a center of the screw receiving hole and being received in the plurality of the groove portions respectively, each protrusion portion tapering in the radially outward direction. The screw is inserted to the screw receiving hole of the cutting head and is coupled to the screw coupling hole of the holder. Each of the groove portions has a pair of groove side surfaces inclined with respect to the front end surface of the holder. Each of the protrusion portions has a pair of protrusion side surfaces inclined with respect to the rear end surface of the cutting head. One of the groove side surface and the protrusion side surface includes a bent portion between a middle and a radially inward end. When the cutting head is clamped to the holder, a relief angle is formed between the groove side surface and the protrusion side surface from the bent portion in the radially outward direction.

In an embodiment, the relief angle is in the range of 0.2 degrees to 2.0 degrees or in the range of 0.5 degrees to 1.5 degrees.

In an embodiment, an angle of the groove side surface inclined with respect to a normal line of the front end surface of the holder is less than an angle of the protrusion side surface inclined with respect to a normal line of the rear end surface of the cutting head.

In an embodiment, the groove side surface includes the bent portion. The groove side surface includes an outer side surface extending from the bent portion in the radially outward direction and an inner side surface extending from the bent portion in a radially inward direction. An angle of the outer side surface inclined with respect to a radial reference line between the pair of the groove side surfaces is less than an angle of the protrusion side surface inclined with respect to a radial reference line between the pair of the protrusion side surfaces. In this embodiment, the angle of the outer side surface inclined with respect to the radial reference line between the pair of the groove side surfaces is less than an angle of the inner side surface inclined with respect to the radial reference line between the pair of the groove side surfaces.

In an embodiment, the protrusion side surface includes the bent portion. The protrusion side surface includes an outer side surface extending from the bent portion in the radially outward direction and an inner side surface extending from the bent portion in a radially inward direction. An angle of the outer side surface inclined with respect to a radial reference line between the pair of the protrusion side surfaces is greater than an angle of the groove side surface inclined with respect to a radial reference line between the pair of the groove side surfaces. In this embodiment, the angle of the outer side surface inclined with respect to the radial reference line between the pair of the protrusion side surfaces is greater than an angle of the inner side surface inclined with respect to the radial reference line between the pair of the protrusion side surfaces.

In an embodiment, the cutting head is made of cemented carbide.

In the rotating tool of the embodiment, when the cutting head is clamped to the holder, the holder and the cutting head do not come into contact with each other at structurally weak portions. In the initial stage of a clamping process, the cutting head is supported by the holder through point contact or line contact at the bent portion. Due to the clamping force in the subsequent stage of the clamping process or the cutting force during a cutting operation, the cutting head is contacted with the holder through surface contact at the bent portion and the peripheral portion of the bent portion. Thus, the contact portions between the cutting head and the holder do not become structurally weak and the stress produced by the clamping force or the cutting force can be effectively distributed to and absorbed at the contact portions between the cutting head and the holder. Further, in the rotating tool of the embodiment, the protrusion side surfaces of the cutting head and the groove side surfaces of the holder are inclined in the radial direction as well as in the axial direction. Therefore, the force applied to the cutting head can lead to a compressive force. Thus, the rotating tool prevents the cutting head and the holder from being unexpectedly deformed, damaged or broken during the cutting operation, thus ensuring a stable performance.

FIG. 1 is a perspective view showing a rotating tool according to an embodiment.

FIG. 2 is a front view of the rotating tool shown in FIG. 1.

FIG. 3 is a sectional view of the rotating tool taken along the line III-III of FIG. 1.

FIG. 4 is an enlarged view of the portion A of FIG. 3.

FIG. 5 is a perspective view showing a front end portion of a holder of the rotating tool according to an embodiment.

FIG. 6 is a front view of the holder shown in FIG. 5.

FIG. 7 is a side view of the holder shown in FIG. 5.

FIG. 8 is a perspective view showing a cutting head of the rotating tool according to an embodiment.

FIG. 9 is a rear view showing of the cutting head shown in FIG. 8 and shows only a mounting portion of the cutting head.

FIG. 10 is a sectional view of the cutting head taken along the line X-X of FIG. 9.

FIG. 11A is a diagram showing contact between a holder and a cutting head of a comparative example.

FIG. 11B is a diagram showing contact between a holder and a cutting head of another comparative example.

FIG. 11C is a diagram showing contact between a holder and a cutting head of a further comparative example.

FIG. 11D is a diagram showing contact between a holder and a cutting head of the rotating tool according to an embodiment.

FIG. 12 is a front view of the holder showing contact regions where surface contact is made.

FIG. 13A is a perspective view showing a stress distribution of the holder according to an embodiment.

FIG. 13B is a perspective view showing a stress distribution of the cutting head according to an embodiment.

FIG. 14A is a diagram showing contact between a holder and a cutting head of a comparative example.

FIG. 14B is a diagram showing contact between a holder and a cutting head of another comparative example.

FIG. 14C is a diagram showing contact between a holder and a cutting head of a further comparative example.

FIG. 14D is a diagram showing contact between a holder and a cutting head of the rotating tool according to another embodiment.

Detailed descriptions are made as to embodiments of a cutting head and holder according to the present invention and embodiments of a rotating tool including such cutting head and holder according to the present invention with reference to the accompanying drawings. Like or corresponding elements or components in the accompanying drawings are denoted by the same reference numeral.

The rotating tool 1000 according to an embodiment shown in the accompanying drawings may be referred to as a milling tool, particularly a cutting head replaceable milling tool in the art. By way of example, the rotating tool 1000 may be used for side machining, slitting, threading, undercut machining.

Referring to FIGS. 1 to 10, the rotating tool 1000 according to an embodiment extends in a direction of a rotating axis RA, which is a rotation center of the rotating tool 1000. Hereinafter, the direction of the rotating axis RA of the rotating tool 1000 is referred to as an axial direction. Further, the axial direction includes a forward axial direction, which is indicated by an arrow FAD in FIGS. 1 and 3 and is directed toward a front end of the rotating tool 1000, and a rearward axial direction that is indicated by an arrow RAD in FIGS. 1 and 3 and is directed toward a rear end of the rotating tool 1000. Further, to describe the rotating tool 1000, a radial direction perpendicular to the axial direction is used. The radial direction includes a radially outward direction, which is indicated by an arrow ROD in FIG. 2 and is directed from the rotation center of the rotating tool 1000 toward an outside of the rotating tool, and a radially inward direction that is indicated by an arrow RID in FIG. 2 and is directed toward the rotation center of the rotating tool 1000. The rotating tool 1000 may be mounted to a machine tool such as a milling machine in such a manner that the front end portion of the rotating tool faces downward and the rear end portion of the rotating tool is detachably attached to the machine tool. The rotating tool 1000 cuts a workpiece while being rotated by the machine tool.

The rotating tool 1000 according to an embodiment comprises a holder 100, a cutting head 200 and a screw 300. The holder 100 supports the cutting head 200 at its front end. The cutting head 200 is replaceably clamped to the front end of the holder 100. The cutting head 200 is detachably fixed to the holder 100 by the screw 300. Some embodiment may include an L-shaped lever to detachably fix the cutting head 200 to the holder 100.

The rotating tool 1000 is rotated about the rotating axis RA, which extends in a longitudinal direction of the rotating tool 1000. The rotating axis RA extends through a center C of sections of the holder 100 and the cutting head 200, which are taken perpendicularly to the rotating axis RA. The holder 100 has a shape of a shaft extending in the forward axial direction FAD and the rearward axial direction RAD. A cross-sectional shape of the holder 100 may be a circle or polygon. The holder 100 comprises a body portion 110 and a clamping portion 120. The clamping portion 120 is located at a front end of the body portion 110 and the cutting head 200 is clamped to the clamping portion 120 of the holder 100. The body portion 110 of the holder 100 is attached to the machine tool. As shown in FIG. 3, a rear end surface 102 of the holder 100, which is located at the body portion 110, may be formed with a hole 103 for attachment to the machine tool.

The body portion 110 includes a shaft section 111 and a neck section 112. The shaft section 111 and the neck section 112 have a circular cross-section. The circular cross-section of the shaft section 111 is constant in the axial direction. The neck section 112 tapers in the forward axial direction FAD. The neck section 112 interconnects the shaft section 111 and the clamping portion 120 without any step portion. As shown in FIG. 3, a front end surface 101 of the holder 100, which is located at the clamping portion 120, is formed with a screw coupling hole 130. The screw coupling hole 130 extends from a middle of the front end surface 101 toward an inside of the clamping portion 120 in the rearward axial direction RAD or approximately parallel with the rearward axial direction RAD. Further, to clamp the cutting head 200 to the holder 100, the front end surface 101 of the holder 100 is formed with a plurality of groove portions 140 which are concaved in the rearward axial direction RAD.

The cutting head 200 has a front end surface 201 and a rear end surface 202 opposite to the front end surface 201 in the axial direction. The cutting head 200 is formed with a screw receiving hole 230, which extends through the front end surface 201 and the rear end surface 202. The rear end surface 202 of the cutting head 200 is opposite to the front end surface 101 of the holder 100. The rear end surface 202 of the cutting head 200 is formed with a plurality of protrusion portions 240, which correspond to the plurality of the groove portions 140 respectively and protrude in the rearward axial direction RAD. The cutting head 200 has a plurality of cutting edges 221, which are located around the front end of the cutting head 200 and protrudes in the radially outward direction ROD. The plurality of the cutting edges 221 are disposed at equal angle about the rotating axis RA. When the rotating tool 1000 is rotated, the cutting edges 221 of the cutting head 200 make a circular rotation locus. A diameter D1 of the rotation locus of the cutting edges 221 is smaller than a diameter D2 of a maximum cross section of the holder 100. The cutting head 200 may have variously sized and shaped cutting edges depending upon various operations for a workpiece (e.g., T-grooving, threading, endmilling).

In an embodiment, the cutting head 200 is made of cemented carbide, which has high hardness and superior wear resistance. The cutting head 200 made of cemented carbide is capable of easily cutting a metallic workpiece. The cemented carbide has a characteristic that is weak against a tensile force, but is strong against a compressive force. Thus, it is advantageous that the cutting head 200 is clamped to the holder 100 such that a compressive force is applied to the cutting head 200 as much as possible, that is, a tensile force is applied to the cutting head 200 as little as possible.

As shown in FIGS. 3 and 4, the cutting head 200 has an inclined surface 231, with which a head portion 310 of the screw 300 is contacted, in the screw receiving hole 230. Further, the holder 100 has a threaded surface 131 in the screw coupling hole 130. The screw 300 is inserted to the screw coupling hole 130 through the screw receiving hole 230 and is coupled to the threaded surface 131 by thread engagement while being rotated by fastening the screw 300.

If the screw 300 is fastened and the cutting head 200 is fixed to the front end of the holder 100, then a clamping force F is produced at the inclined surface 231 of the cutting head 200 which is in contact with the screw 300. The clamping force F is applied to the cutting head 200 in a direction normal to the inclined surface 231. The clamping force F is applied to the cutting head 200 as a component force Fa parallel with the axial direction and a component force Fr in the radially outward direction ROD perpendicular to the axial direction. The component force Fa parallel with the axial direction acts as a force that presses the cutting head 200 toward the holder 100, while the component force Fr in the radially outward direction acts as a force that pulls the cutting head 200 in the radially outward direction ROD. When the cutting head 200 is clamped to the holder 100, a mounting surface MS formed in the rear end surface 202 of the cutting head 200 comes into contact with a clamping surface CS formed in the front end surface 101 of the holder 100. The mounting surface MS of the cutting head 200 and the clamping surface CS of the holder 100 are inclined in the axial direction as well as in the radially outward direction ROD. Thus, due to the mounting surface MS of the cutting head 200 and the clamping surface CS of the holder 100, the holder 100 supports the component force Fa parallel with the axial direction and suppresses the component force Fr in the radially outward direction, thus minimizing the tensile force which is applied to the cutting head 200 by the clamping force in a clamping process or a cutting force during a cutting operation. The clamping surface CS of the holder 100 is provided in the groove portion 140 formed in the front end surface 101 of the holder 100, and the mounting surface MS of the cutting head 200 is provided in the protrusion portion 240 formed in the rear end surface 202 of the cutting head 200.

Referring to FIGS. 5 to 7, the holder 100 has the screw coupling hole 130 in the middle of the front end surface 101. Further, the holder 100 has the plurality of the groove portions 140, which are disposed radially about the screw coupling hole 130. Each of the groove portions 140 extends from the screw coupling hole 130 in the radially outward direction ROD and is opened at a side surface 121 of the clamping portion 120.

The groove portion 140 is concaved in the axial direction (the rearward axial direction RAD) and becomes narrow toward the inside of the holder 100. Further, the groove portion 140 tapers in the radially outward direction ROD. As an example of the aforementioned clamping surface CS, the groove portion 140 has a pair of groove side surfaces 150 which are inclined with respect to the front end surface 101 of the holder 100. As shown in FIG. 6, the pair of the groove side surfaces 150 face toward each other symmetrically with respect to a reference line RL1. The reference line RL1 is an imaginary line that extends in the radially outward direction ROD from the center C of the front end surface 101 of the holder 100 intermediately between the groove side surfaces 150. Further, as shown in FIG. 7, each of the groove side surfaces 150 is inclined with respect to the axial direction. Specifically, each of the groove side surfaces 150 is inclined at an acute angle with respect to the forward axial direction FAD and at an obtuse angle with respect to the rearward axial direction RAD. A spacing L1 between the pair of the groove side surfaces 150 gradually decreases from the screw coupling hole 130 in the radially outward direction ROD. That is, the pair of the groove side surfaces 150 are inclined in the radially outward direction ROD.

The groove portion 140 has a plurality of

bottom surfaces

153, 154, 155 interconnecting the pair of the groove side surfaces 150. In this embodiment, the pair of the groove side surfaces 150 are interconnected by a curved bottom surface 153, a flat bottom surface 154 and a curved bottom surface 155. In some embodiment, the pair of the groove side surfaces 150 may be interconnected by a single curved bottom surface or a plurality of flat bottom surfaces.

Each of the groove side surfaces 150 has an inner end adjoining the screw coupling hole 130 (i.e., an end of the groove side surface in the radially inward direction RID) and an outer end located opposite the inner end in the longitudinal direction of the groove side surface (i.e., an end of the groove side surface in the radially outward direction ROD). The groove side surface 150 includes a bent portion 160 between the middle in the longitudinal direction of the groove side surface 150 and the inner end of the groove side surface 150. Thus, the groove side surface 150 is bent at the bent portion 160. Specifically, a portion of the groove side surface 150, which is located from the bent portion 160 in the radially inward direction RID (i.e., a portion of the groove side surface between the bent portion and the inner end), is bent further than the rest of the groove side surface 150, which is located from the bent portion 160 in the radially outward direction ROD (i.e., a portion of the groove side surface between the bent portion and the outer end), in the radially inward direction RID and the rearward axial direction RAD with respect to the radial reference line RL1. The bent portion 160 is formed in the groove side surface 150 so as to be inclined with respect to the radial reference line RL1. Further, in this embodiment, the bent portion 160 is also formed in the bottom surfaces 153 and 155.

The groove side surface 150 has an outer side surface 151 and an inner side surface 152 which are divided by the bent portion 160. The outer side surface 151 is located from the bent portion 160 in the radially outward direction ROD, and the inner side surface 152 is located from the bent portion 160 in the radially inward direction RID. Since the groove portion 140 is shaped so as to taper in the radially outward direction ROD, the spacing between a pair of the inner side surfaces 152 as well as the spacing between a pair of the outer side surfaces 151 gradually decrease in the radially outward direction. Further, as shown in FIG. 6, when viewing the front end surface 101 of the holder 100 from the front, the inner side surface 152 is inclined at an angle greater than the outer side surface 151 with respect to the radial reference line RL1. Thus, the radially inward space of the groove portion 140 from the bent portion 160 expands more than that of any groove portion without the bent portion 160. That is, the groove portion 140 expands from its radially outward end toward its radially inward end. A portion of the groove portion in the radially inward direction RID from the bent portion 160 expands more than a portion of the groove portion in the radially outward direction ROD from the bent portion 160.

Referring to FIG. 6, an angle α1 of the outer side surface 151 inclined with respect to the radial reference line RL1 is less than an angle α2 of the inner side surface 152 inclined with respect to the radial reference line RL1. In this embodiment, the angle α1 of the outer side surface 151 inclined with respect to the radial reference line RL1 is 6.5 degrees. However, the angle α1 of the outer side surface 151 and the angle α2 of the inner side surface 152 may vary depending on the diameter of the clamping portion 120, the size and number of the groove portions 140 formed in the clamping portion 120, etc.

Referring to FIG. 7, in this embodiment, an angle β of the outer side surface 151 inclined with respect to a normal line NL1 of the front end surface 101, which is parallel with the rotating axis RA of the holder 100, is 30 degrees. However, the angle β of the outer side surface 151 may vary depending on the diameter of the clamping portion 120 of the holder 100, the size and number of the groove portions 140 formed in the clamping portion 120, etc. The angle β of the outer side surface 151 inclined with respect to the normal line NL1 of the front end surface 101 of the holder 100 is different from an angle δ of a protrusion side surface 250 that is inclined with respect to a normal line NL2 of the rear end surface 202 of the cutting head 200 (see FIG. 10). Thus, when the cutting head 200 is clamped to the holder 100, the protrusion side surface 250 of the cutting head 200 does not come into surface contact with the groove side surface 150 of the holder 100, but can come into point contact or line contact with the bent portion 160 of the groove side surface 150. The outer side surface 151 of the groove side surface 150 serves as the aforementioned clamping surface CS for contact with the cutting head 200, while the inner side surface 152 of the groove side surface 150 functions to ensure a space for preventing the contact with the cutting head 200.

In the holder 100, edges of the front end surface 101 and edges between the front end surface 101 and the groove portions 140 are inclined to facilitate clamping of the cutting head 200. The body portion 110 and the clamping portion 120 of the holder 100 may be made of the same metallic material or different metallic material. Carbon steel, high speed steel obtained by alloying tungsten, chromium, etc., cemented carbide including tungsten carbide, etc. may be used as said metallic materials. Further, the body portion 110 and the clamping portion 120 of the holder 100 may be integrally formed.

Referring to FIGS. 8 to 10, the cutting head 200 according to an embodiment has a mounting portion 210 which is clamped to the holder 100, and a cutting portion 220 which extends frontward from the mounting portion 210 and includes the plurality of the cutting edges 221. The mounting portion 210 and the cutting portion 220 have a shape of a circular disk. The plurality of the cutting edges 221 protrude from an outer periphery of the cutting portion 220 in a radial direction about a center of the cutting portion 220. The cutting head 200 is clamped to the holder 100 such that the mounting portion 210 is opposite to the clamping portion 120 of the holder 100. The cutting head 200 is clamped to the holder 100 such that the rear end surface of the mounting portion 210 (rear end surface of the cutting head 200) is in contact with the front end surface of the clamping portion 120 (front end surface of the holder 100) or a predetermined gap exists between the rear end surface of the mounting portion 210 and the front end surface of the clamping portion 120. The cutting portion 220 and the cutting edges 221 may be integrally formed. Alternatively, the cutting portion 220 may have replaceable cutting edges. The mounting portion 210 and the cutting portion 220 may be integrally formed, or made individually and then coupled to each other.

The cutting head 200 has the screw receiving hole 230 extending therethrough in the axial direction. A plurality of the protrusion portions 240 are radially formed in the rear end surface 202 of the mounting portion 210 about the center of the screw receiving hole 230. In this embodiment, the cutting head 200 has three protrusion portions 240. The cutting head 200 of some embodiment may have two, four or more protrusion portions depending on the number of the groove portions 140 of the holder 100. When the cutting head 200 is clamped to the holder 100, the protrusion portions 240 of the cutting head 200 are fitted to the respective groove portions 140 of the holder 100.

The protrusion portion 240 includes a protrusion surface 242, which is spaced from the rear end surface 202 of the cutting head 200, and a pair of the protrusion side surfaces 250 that are located both sides of the protrusion surface 242 respectively in a circumferential direction of the cutting head 200 and interconnect the protrusion surface 242 and the rear end surface 202. Similar to the groove portion 140 of the holder 100, each of the protrusion portions 240 is shaped so as to taper from the screw receiving hole 230 in the radially outward direction ROD. The pair of the protrusion side surfaces 250 are symmetrically inclined with respect to the rear end surface 202. A distance L2 between the pair of the protrusion side surfaces 250 gradually decreases from the screw receiving hole 230 in the radially outward direction ROD. Further, each of the protrusion portions 240 has a shape narrowing from the rear end surface 202 toward the protrusion surface 242 (i.e., in the rearward axial direction RAD), thus corresponding to the concave shape of the groove portion 140. Since the groove side surface 150 of the groove portion 140 includes the bent portion 160, when the cutting head 200 is clamped to the holder 100, a relief angle θ is formed from the bent portion 160 in the radially outward direction ROD between the groove side surface 150 and the protrusion side surface 250 (see FIG. 11D).

A radial reference line RL2 shown in FIG. 9 is an imaginary line that extends from a center C of the rear end surface 202 of the cutting head 200 in the radially outward direction ROD intermediately between the pair of the protrusion side surfaces 250. An angle γ of the protrusion side surface 250 inclined with respect to the radial reference line RL2 is greater than the angle α1 of the outer side surface 151 inclined with respect to the radial reference line RL1. In this embodiment, the angle γ of the protrusion side surface 250 inclined with respect to the radial reference line RL2 is 7 degrees, but may vary as long as the aforementioned condition (i.e., γ > α1) is satisfied. Referring to FIG. 10, the angle δ of the protrusion side surface 250 inclined with respect to a normal line NL2 of the rear end surface 202, which is parallel with the rotating axis RA, is greater than the angle β of the outer side surface 151 of the groove portion 140 inclined with respect to the normal line NL1 of the front end surface 101 of the holder 100. In this embodiment, the angle δ of the protrusion side surface 250 inclined with respect to the normal line NL2 is 30.5 degrees, but may vary as long as the aforementioned condition (i.e., δ > β) is satisfied.

As shown in FIG. 10, a height H of the protrusion portion 240 at which the protrusion portion protrudes from the rear end surface 202 of the cutting head 200 has a size corresponding to the groove portion 140 of the holder 100. That is, the protrusion portion 240 protrudes at the height H at which the protrusion side surfaces 250 of the protrusion portion 240 are supported by the outer side surfaces 151 of the groove portion 140 in contact with the outer side surfaces 151. When the protrusion side surfaces 250 are supported by the outer side surfaces 151 in contact with the outer side surfaces 151, the protrusion surface 242 of the protrusion portion 240 is not in contact with the bottom surfaces 153, 154, 155 of the groove portion 140. As such, the protrusion portion 240 of the cutting head 200 is in contact with the groove portion 140 of the holder 100 only through the groove side surfaces 150, facilitating the tolerance maintenance in manufacturing the holder 100 and the cutting head 200. The pair of the protrusion side surfaces 250 of the protrusion portion 240 function as the aforementioned mounting surface MS for contact with the holder 100.

Both the groove portion 140 of the holder 100 and the protrusion portion 240 of the cutting head 200 have a shape tapering in the radially outward direction ROD, but their respective angles inclined with respect to the reference lines RL1 and RL2 are different. Thus, when the cutting head 200 is clamped to the holder 100, the protrusion side surface 250 of the protrusion portion 240 does not come into contact with the entire groove side surface 150 of the groove portion 140, but can come into contact with the bent portion 160 formed in the groove side surface 150. Further, since the angle between the groove side surface 150 and the protrusion side surface 250 (i.e., relief angle) is small, the groove side surface 150 and the protrusion side surface 250 come into point contact or line contact with each other in the initial stage of a clamping process wherein the cutting head 200 is fitted to the holder 100. However, the groove side surface 150 and the protrusion side surface 250 can come into surface contact with each other during the cutting operation or in the subsequent stage of the clamping process wherein the screw 300 is fastened. Reference is made to FIGS. 11A to 11D with regard to such contact between the groove side surface 150 and the protrusion side surface 250.

Referring to FIG. 11A showing a comparative example where a groove side surface 150a does not include the bent portion, an angle αa of the groove side surface 150a inclined with respect to the radial reference line RL1 and an angle γa of a protrusion side surface 250a inclined with respect to the radial reference line RL2 are the same. In this case (i.e. the case where the relief angle does not exist), in theory, the protrusion side surface 250a comes into contact with the groove side surface 150a in the longitudinal direction throughout the whole of the groove side surface 150a. This contact is an ideal contact, but it cannot be realized in practice due to the manufacture error and does not achieve a desired performance. In particular, it is disadvantageous that contact is mainly made at structurally weak portions in this case. Referring to FIG. 11B showing another comparative example where a groove side surface 150b includes a bent portion 160a, an angle αb1 of an outer side surface 151b inclined with respect to the radial reference line RL1 and an angle γb of a protrusion side surface 250b inclined with respect to the radial reference line RL2 are the same. In this case, the protrusion side surface 250b comes into surface contact with the outer side surface 151b of the groove side surface 150b. Referring to FIG. 11C showing a further comparative example where a groove side surface 150c includes a bent portion 160c, the angles αc1 and αc2 of the outer and inner side surfaces 151 and 152 of the groove side surface 150c inclined with respect to the radial reference line RL1 and an angle γc of a protrusion side surface 250c inclined with respect to the radial reference line RL2 are different. Further, the groove side surface 150c is bent at the bent portion 160c at a relatively large angle. In this case (i.e. the case where a relief angle θc is relatively large), the protrusion side surface 250c comes into point contact or line contact only with the bent portion 160c of the groove side surface 150c and cannot come into surface contact with the groove side surface 150c during the clamping process or during the cutting operation.

Referring to FIG. 11D showing the groove side surface 150 and the protrusion side surface 250 of the rotating tool 1000 according to an embodiment, the angles α1 and α2 of the outer and inner side surfaces 151 and 152 of the groove side surface 150 inclined with respect to the radial reference line RL1 and the angle γ of the protrusion side surface 250 inclined with respect to the radial reference line RL2 are different. Further, the groove side surface 150 is bent at the bent portion 160 at a very small angle. Thus, when the cutting head 200 is clamped to the holder 100, the protrusion side surface 250 comes into point contact or line contact with the bent portion 160 of the groove side surface 150 in the initial stage of the clamping process. Further, due to the clamping force in the subsequent stage of the clamping process or the cutting force during the cutting operation, the protrusion side surface 250 comes into surface contact with the groove side surface 150. In one embodiment, the relief angle θ is in the range of 0.2 degrees to 2.0 degrees, preferably 0.5 degrees to 1.5 degrees. Where the relief angle θ is less than 0.2 degrees, the whole of the outer side surface 151, which includes a structurally weak outer end portion, can come into surface contact with the protrusion side surface 250 before cutting a workpiece. This is similar to the comparative example shown in FIG. 11A. In this case, the start point of the contact between the cutting head 200 and the holder 100 does not become uniform and therefore the stable performance of the rotating tool 1000 cannot be guaranteed. Where the relief angle θ is more than 2.0 degrees, the outer side surface 151 fails to come into surface contact with the protrusion side surface 250 even though the clamping force in the clamping process or the cutting force during the cutting operation are applied to the outer side surface 151 and the protrusion side surface 250. This is similar to the comparative example shown in FIG. 11C. Thus, the cutting head 200 cannot be stably supported by the holder 100.

In the rotating tool 1000 according to an embodiment, the groove portion 140 of the holder 100 and the protrusion portion 240 of the cutting head 200 are shaped so as to taper in the radially outward direction ROD and come into contact with each other with the relief angle θ formed by the bent portion 160. Thus, the contact between the holder 100 and the cutting head 200 can begin at the radially inward portion of the groove portion 140, which is not structurally weak. Further, the relief angle θ is in the range of 0.2 degrees to 2.0 degrees. As such, due to the clamping force in the clamping process or the cutting force during the cutting operation, the surface contact is made between the groove portion 140 and the protrusion portion 240 throughout a predetermined length from the portion where the contact is first made.

In FIG. 12, surface contact regions CR, at which the groove portion 140 of the holder 100 and the protrusion portion 240 of the cutting head 200 can come into surface contact with each other in the clamping process of the cutting head 200 and during the cutting operation, are shown through hatched portions. The surface contact region CR is formed in the outer side surface 151 from the boundary between the outer side surface 151 and the inner side surface 152 (i.e., the bent portion 160) in the radially outward direction within a half of an overall length of the groove side surface 150.

As described above, the protrusion portion 240 of the cutting head 200 and the groove portion 140 of the holder 100 do not come into contact with each other at both the radially inward end portion and the radially outward end portion which are structurally weak. In the initial stage of the clamping process, the groove portion 140 of the holder 100 and the protrusion portion 240 of the cutting head 200 come into contact with each other through point contact or line contact at an approximately middle portion between the radially inward and outward ends of the groove portion 140 (e.g., the bent portion 160) and at a portion of the protrusion portion 240 between the radially inward and outward ends of the protrusion portion 240 corresponding to said approximately middle portion of the groove portion. In the clamping process and during the cutting operation, the groove portion 140 of the holder 100 and the protrusion portion 240 of the cutting head 200 come into contact with each other through surface contact made at the portion where point or line contact is made and portions located in the radially outward direction ROD from said portion where point or line contact is made. Thus, as shown in FIGS. 13A and 13B, the stress caused by the cutting force can be effectively distributed to and absorbed at a peripheral portion surrounding the portion where point or line contact is made (e.g., the bent portion 160 and the portion of the protrusion portion 240 corresponding to the bent portion 160). FIG. 13A illustrates the distribution of the stress produced at the contact portion of the holder 100 among the contact portions between the holder 100 and the cutting head 200 in the rotating tool 1000 according to an embodiment, and FIG. 13B illustrates the distribution of the stress produced at the contact portion of the cutting head 200 among the contact portions between the holder 100 and the cutting head 200 in the rotating tool 1000 according to an embodiment. According to the actual measurement, the stress distribution is obtained by a computer graphics software as a color image having various colors and color densities depending on the magnitude of the stress. FIGS. 13A and 13B show the shaded stress distribution instead of the color image. FIGS. 13A and 13B show the stress distribution wherein each area of the stress having a predetermined magnitude range is divided by a contour line and respective areas divided by the contour lines are shaded with different densities. FIGS. 13A and 13B show the stress distribution wherein a maximum stress is produced at an approximately central area of the contact portion (i.e., the area divided by the contour lines) and the stress gradually decreases toward the peripheral area of the central area. Since the contact portions between the holder 100 and the cutting head 200 are located at the approximately middle portion of the groove portion 140 and the approximately middle portion of the protrusion portion 240, the stress produced during the cutting operation is distributed to the peripheral portion of the middle portion and decreases. Thus, the rotating tool 1000 according to an embodiment can prevent the unexpected damage or breakage of the contact portions due to the local concentration of the stress and can ensure a stable performance.

In the foregoing embodiment, the bent portion 160 is provided in the groove side surface 150 of the holder 100. In a further embodiment, the above-described bent portion is provided in the protrusion side surface 250 of the cutting head 200. FIG. 14D shows the groove side surface 150 and the protrusion side surface 250 of the rotating tool according to such an embodiment. As shown in FIG. 14D, the protrusion side surface 250 has an outer side surface 251 and an inner side surface 252 which are divided by the bent portion 260. The outer side surface 251 is located in the protrusion side surface 250 in the radially outward direction ROD, and the inner side surface 252 is located in the protrusion side surface 250 in the radially inward direction RID. Reference is made to FIGS. 14A to 14D with regard to the contact made between the groove side surface 150 and the protrusion side surface 250.

Referring to FIG. 14A showing a comparative example where the protrusion side surface 250d does not include the bent portion, an angle αd of a groove side surface 150d inclined with respect to the radial reference line RL1 and an angle γd of a protrusion side surface 250d inclined with respect to the radial reference line RL2 are the same. In this case (i.e. the case where the relief angle does not exist), in theory, the protrusion side surface 250d comes in contact with the groove side surface 150d in the longitudinal direction throughout the whole of the groove side surface 150d. This contact is an ideal contact, but it cannot be realized in practice due to the manufacture error and does not achieve a desired performance of the rotating tool 1000. In particular, it is disadvantageous that contact is mainly made at structurally weak portions in this case. Referring to FIG. 14B showing another comparative example where a protrusion side surface 250e includes a bent portion 260e, an angle αe of a groove side surface 150e inclined with respect to the radial reference line RL1 and an angle γe of an outer side surface 251e inclined with respect to the radial reference line RL2 are the same. In this case, the outer side surface 251e of the protrusion side surface 250e comes into surface contact with a groove side surface 150e. Referring to FIG. 14C showing a further comparative example where a protrusion side surface 250f includes a bent portion 260f, an angle αf of a groove side surface 150f inclined with respect to the radial reference line RL1 and angles γf1 and γf2 of outer and inner side surfaces 251f and 252f of a protrusion side surface 250f inclined with respect to the radial reference line RL2 are different, and the protrusion side surface 250f is bent at the bent portion 260f at a relatively large angle. In this case (i.e. the case where the relief angle θf is relatively large), the groove side surface 150f comes into point contact or line contact with only the bent portion 260f of the protrusion side surface 250f and cannot come into surface contact with the protrusion side surface 250f in the clamping process or during the cutting operation.

Referring to FIG. 14D showing the groove side surface 150 and the protrusion side surface 250 of the rotating tool according to a further embodiment, the angle α of the groove side surface 150 inclined with respect to the radial reference line RL1 and the angles γ1 and γ2 of the outer and inner side surfaces 251 and 252 of the protrusion side surface 250 inclined with respect to the radial reference line RL2 are different, and the protrusion side surface 250 is bent at the bent portion 260 at a very small relief angle θ. Thus, in the initial stage of the clamping process, the protrusion side surface 250 and the groove side surface 150 begins to contact each other through the point contact or line contact between the bent portion 260 of the protrusion side surface 250 and the groove side surface 150. Further, due to the clamping force in the subsequent stage of the clamping process or the cutting force during the cutting operation, the protrusion side surface 250 and the groove side surface 150 come into surface contact with each other. In this embodiment, the relief angle θ is in the range of 0.2 degrees to 2.0 degrees, preferably 0.5 degrees to 1.5 degrees.

The above-described rotating tool 1000 has the holder 100 and the cutting head 200 which is replaceably clamped to the front end of the holder 100. The holder 100 includes, at its front end surface 101, the plurality of the groove portions 140 which are radially disposed. Each groove portion 140 tapers in the radially outward direction ROD from the center of the front end surface 101 of the holder 100. The cutting head 200 includes, at its rear end surface 202 opposite to the front end surface 101 of the holder 100, the plurality of the protrusion portions 240 which are radially disposed and are fitted to the respective groove portions 140. Each protrusion portion 240 tapers in the radially outward direction ROD from the center of the rear end surface 202 of the cutting head 200. Each groove portion 140 has a pair of the groove side surfaces 150, and each protrusion portion 240 has a pair of the protrusion side surfaces 250. If the cutting head 200 is clamped to the holder 100, the protrusion side surface 250 comes into contact with the groove side surface 150. The groove side surface 150 and the protrusion side surface 250 are inclined at an acute angle with respect to the radially outward direction ROD. Further, the groove side surface 150 and the protrusion side surface 250 are inclined at an acute angle with respect to the axial direction (the rearward axial direction RAD). Thus, the stress, which is applied to the mounting portion 210 of the cutting head 200 due to the clamping force F in the clamping process and the cutting force during the cutting operation, is absorbed as a compressive force, thus preventing the damage or breakage of the cemented carbide-made cutting head 200. Further, one of the groove side surface 150 and the protrusion side surface 250 includes the

bent portion

160, 260. For example, in case where the groove side surface 150 includes the bent portion 160, when the cutting head 200 is clamped to the holder 100, the protrusion side surface 250 of the protrusion portion 240 comes into point contact or line contact with the bent portion 160 of the groove portion 140 (the radially inward portion of the groove portion 140). Further, due to the clamping force in the clamp process or the cutting force during the cutting operation, the protrusion side surface 250 of the cutting head 200 and the groove side surface 150 of the holder 100 come into surface contact with each other from the bent portion 160. Thus, the stress produced by the clamping force or the cutting force can be distributed to the peripheral portion of the contact portion and thus be absorbed and reduced. Thus, deformation, damage or breakage caused by the stress concentrating to the contact portions of the cutting head 200 and the holder 100 can be prevented and a stable performance of the rotating tool can be ensured. Further, since one of the groove side surface 150 and the protrusion side surface 250 includes the

bent portion

160, 260, the tolerance maintenance can be easily carried out during the manufacture of the holder 100 and the cutting head 200.

While the present invention has been described hereinbefore with reference to the foregoing embodiments and the accompanying drawings, the present invention should not be limited thereto. It will be apparent to those of ordinary skill in the art that various substitutions, alternations or modifications may be made without departing from the scope of the present invention.

Claims

A holder, to a front end of which a cutting head is replaceably clamped, comprising:

a front end surface;

a screw coupling hole formed in the front end surface; and

a plurality of groove portions disposed in the front end surface radially about a center of the screw coupling hole, each of the groove portions tapering in a radially outward direction,

wherein each of the groove portions has a pair of groove side surfaces inclined with respect to the front end surface, and

wherein each of the groove side surfaces includes a bent portion between a middle and a radially inward end and is bent at the bent portion.
A cutting head replaceably clamped to a front end of a holder, comprising:

a front end surface;

a rear end surface opposite to the front end of the holder;

a screw receiving hole extending through the front end surface and the rear end surface; and

a plurality of protrusion portions disposed in the rear end surface radially about a center of the screw receiving hole, each of the protrusion portions tapering in a radially outward direction,

wherein each of the protrusion portions has a pair of protrusion side surfaces inclined with respect to the rear end surface, and

wherein each of the protrusion side surfaces includes a bent portion between a middle and a radially inward end and is bent at the bent portion.
A rotating tool comprising a holder, a cutting head and a screw,

wherein the holder comprises:

a front end surface;

a screw coupling hole formed in the front end surface; and

a plurality of groove portions disposed in the front end surface radially about a center of the screw coupling hole, each of the groove portions tapering in a radially outward direction,

wherein the cutting head comprises:

a front end surface;

a rear end surface opposite to the front end surface of the holder;

a screw receiving hole extending through the front end surface and the rear end surface of the cutting head; and

a plurality of protrusion portions disposed in the rear end surface radially about a center of the screw receiving hole and being received in the plurality of the groove portions respectively, each of the protrusion portions tapering in the radially outward direction,

wherein the screw is inserted to the screw receiving hole of the cutting head and is coupled to the screw coupling hole of the holder,

wherein each of the groove portions has a pair of groove side surfaces inclined with respect to the front end surface of the holder,

wherein each of the protrusion portions has a pair of protrusion side surfaces inclined with respect to the rear end surface of the cutting head,

wherein one of the groove side surface and the protrusion side surface includes a bent portion between a middle and a radially inward end, and

wherein when the cutting head is clamped to the holder, a relief angle is formed between the groove side surface and the protrusion side surface from the bent portion in the radially outward direction.
The rotating tool of Claim 3, wherein the relief angle is in a range of 0.2 degrees to 2.0 degrees.
The rotating tool of Claim 4, wherein the relief angle is in a range of 0.5 degrees to 1.5 degrees.
The rotating tool of Claim 3, wherein an angle of the groove side surface inclined with respect to a normal line of the front end surface of the holder is less than an angle of the protrusion side surface inclined with respect to a normal line of the rear end surface of the cutting head.
The rotating tool of Claim 3, wherein the groove side surface includes the bent portion,

wherein the groove side surface includes an outer side surface extending from the bent portion in the radially outward direction and an inner side surface extending from the bent portion in a radially inward direction, and

wherein an angle of the outer side surface inclined with respect to a radial reference line between the pair of the groove side surfaces is less than an angle of the protrusion side surface inclined with respect to a radial reference line between the pair of the protrusion side surfaces.
The rotating tool of Claim 7, wherein the angle of the outer side surface inclined with respect to the radial reference line between the pair of the groove side surfaces is less than an angle of the inner side surface inclined with respect to the radial reference line between the pair of the groove side surfaces.
The rotating tool of Claim 3, wherein the protrusion side surface includes the bent portion,

wherein the protrusion side surface includes an outer side surface extending from the bent portion in the radially outward direction and an inner side surface extending from the bent portion in a radially inward direction, and

wherein an angle of the outer side surface inclined with respect to a radial reference line between the pair of the protrusion side surfaces is greater than an angle of the groove side surface inclined with respect to a radial reference line between the pair of the groove side surfaces.
The rotating tool of Claim 9, wherein the angle of the outer side surface inclined with respect to the radial reference line between the pair of the protrusion side surfaces is greater than an angle of the inner side surface inclined with respect to the radial reference line between the pair of the protrusion side surfaces.
The rotating tool of Claim 3, wherein the cutting head is made of cemented carbide.