Abstract:
A cutting tool for machining large workpieces having relatively a large cutting amount and a cutting insert configured to be used with the cutting tool. The cutting tool includes a cutting insert and a wedge for clamping the cutting insert. The cutting insert has a polygonal top surface, which comprises a recessed portion having a plurality of inclined abutment surfaces which are inclined toward the center of the top surface. The outline of said recessed portion is twisted at a predetermined angle with respect to the outline of the top surface. The wedge includes a projecting portion that contacts the inclined abutment surface and pushes the cutting insert so that two side surfaces of the cutting insert can be supported by a radial inner side surface and a lateral supporting surface of an insert seat.

Description:
RELATED APPLICATIONS 
     This is a 35 USC 371 U.S. National Phase of International Application No. PCT/KR2010/003415, filed 24 Jun. 2009 and published in English as WO 2010/143768 A1 on 16 Dec. 2010, which claims priority to KR 10-2009-0061617, filed 10 Jun. 2009. The contents of the aforementioned applications are incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a cutting tool for machining large workpieces having relatively a large cutting amount and a cutting insert configured to be used with said cutting tool. 
     BACKGROUND ART 
     Cutting portions of cutting tools for machining metallic materials are easily worn out due to the friction occurring during machining. Thus, when the cutting portions are worn out, replacing only the worn cutting portions is absolutely advantageous in cutting operations. As such, in a cutting operation, a method of detachably mounting a replaceable cutting insert in the body of the cutting tool is generally used. 
     A clamping method of using a screw and a clamping method of using a wedge are typical examples of methods to clamp the cutting insert in the cutter body. The clamping method of using a screw is to form concentric screw holes in both the cutting insert and the insert seat, as well as to clamp a screw into both holes to secure the cutting insert in the cutting tool. It is the simplest clamping method. However, the method of clamping the cutting insert by using a screw is not so efficient when machining large workpieces such as a part of a vessel. This is because when separating the worn cutting insert from the cutting tool, the worker has to separate the cutting tool body from the machining equipment due to the difficulty in accessing the tool for disassembling the screw. Since the cutting tool body for machining large workpieces is generally large, separating the cutting tool from the machining equipment or mounting it on the machining equipment is very troublesome. 
     Thus, to machine the large workpieces, the workers prefer to use the wedge clamping method since there is no need to separate the tool body from the equipment when replacing the worn cutting insert. The cutting insert clamping structure, which uses the wedge, is disclosed in Korean Patent Laid-Open Publication No. 1996-703697. Present  FIGS. 1 and 2  illustrate such cutting tool. A milling cutter  110  includes a plurality of slots  130 , which are arranged at same intervals around the outer circumference of the cylindrical cutter body  111 . An adapter seat  140  is recessed within one side surface  133  of the slot  130 . A wedge  150  is received in the slot  130 , while an adapter  160  is received in the adapter seat  140 . A cutting insert  120  is seated and fixed on the top surface of the adapter  160 . When the adapter  160 , on which the cutting insert is seated, is mounted on the adapter seat  140 , the top surface of the cutting insert contacts one side surface of the wedge  150 . A screw  170  is clamped into a screw hole  172  of the slot  130  through a screw hole  171  of the wedge  150 . As the screw  170  advances into the screw hole of the slot  130 , the wedge  150  is pushed toward the screw hole of the slot  130 . Since the wedge  150  tapers inwardly, the cutting insert  120  is clamped in the adapter  160  by the wedge  150  as the wedge  150  advances toward the screw hole of the slot  130 . Disclosure of Invention 
     SUMMARY 
     In the prior art as discussed above, the contact portion between the cutting insert and the wedge is flat as shown in  FIG. 2 . The clamping force of the wedge is delivered to the cutting insert only in the direction perpendicular to the top surface of the cutting insert, not in the radial direction toward the center of the cutting tool. Thus, when the cutting insert is clamped by the wedge, the radial inner side surface  121  of the cutting insert is not sufficiently supported by the side surface of the adapter  160 . As a result, the cutting insert may rotate on the adapter due to the reaction force caused by the cutting force. As such, it cannot be securely mounted in the cutting tool. 
     The objective of the present invention is to provide a cutting insert, which overcomes the above disadvantages, and a cutting tool designed to use such a cutting insert. 
     To achieve the above objective, the present invention provides a cutting tool comprising one or more cutting portions. Each of the one or more cutting portions include a cutting insert, a wedge for clamping the cutting insert, a slot formed in a body of the cutting tool and receiving the wedge, and an insert seat recessed within a side surface of the slot and receiving the cutting insert. The insert seat has a radial inner side surface, a bottom supporting surface on which the cutting insert is seated, and a lateral supporting surface outwardly extending from the radial inner side surface and the bottom supporting surface. The cutting insert has a polygonal top surface, a bottom surface supported by the bottom supporting surface of the insert seat, and a plurality of side surfaces connecting between the top surface and the bottom surface. The top surface of the cutting insert comprises a recessed portion having a plurality of surfaces inclined toward the center of the top surface of the cutting insert. The outline of said recessed portion is twisted at a twist angle α with respect to the outline of the top surface of the cutting insert. The wedge includes a projecting portion, which contacts the surface inclined toward the center of the top surface of the cutting insert and pushes the cutting insert. This is so that two side surfaces of the cutting insert can be supported by the radial inner side surface and the lateral supporting surface of the insert seat. 
     According to one embodiment of the present invention, the twist angle α is in the range of 10° to 30°. 
     According to one embodiment of the present invention, the surface inclined toward the center of the top surface of the cutting insert forms an angle in the range of 3° to 10° with respect to the bottom surface of the cutting insert. 
     According to one embodiment of the present invention, the one or more cutting portions further comprise a shim received between the cutting insert and the insert seat. 
     According to the present invention, the recessed portion of the top surface of the cutting insert is configured to mate with the projecting portion of the side surface of the wedge. The clamping force of the wedge can be delivered in the direction perpendicular to the top surface of the cutting insert as well as in the radial direction toward the center of the cutting tool (or in the direction perpendicular to the radial inner side surface of the insert seat). The wedge clamping force, which is delivered in the radial direction toward the center of the cutting tool, can have one side surface of the cutting insert supported by the radial inner side surface of the insert seat. This can prevent the rotation of the cutting insert on the insert seat due to the reaction force of the cutting force. As a result, the cutting insert can be more securely mounted in the cutting tool. 
     Further, according to the present invention, the outline of the recessed portion of the top surface of the cutting insert is twisted at a predetermined angle relative to the outline of the top surface. The wedge clamping force in the radial direction toward the center of the cutting tool can be divided into the force in the direction perpendicular to the radial inner side surface of the insert seat and the force in the direction perpendicular to the lateral supporting surface of the insert seat. The force in the direction perpendicular to the radial inner side surface of the insert seat can have one side surface of the cutting insert supported by the radial inner side surface of the insert seat. The force in the direction perpendicular to the lateral supporting surface of the insert seat can have the other side surface of the cutting insert supported by the lateral supporting surface of the insert seat. That is, since two side surfaces of the cutting insert contact two side surfaces of the insert seat, the cutting insert can be more securely clamped in the cutting tool. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a cutting tool according to the prior art. 
         FIG. 2  is a cross-section view of the cutting tool according to the prior art. 
         FIG. 3  is a perspective view of a cutting tool according to the present invention. 
         FIG. 4  illustrates the cutting tool when a cutting insert is clamped by a wedge according to the present invention. 
         FIG. 5  illustrates the cutting tool having a slot in which the wedge is mounted and an insert seat on which the cutting insert is seated according to the present invention. 
         FIG. 6  illustrates wedge clamping forces working on the cutting insert according to the present invention. 
         FIG. 7  is a cross-section view taken along the line A-A of  FIG. 4 . 
         FIG. 8  is a perspective view of the cutting insert according to the present invention. 
         FIG. 9  is a top view of the cutting insert according to the present invention. 
         FIG. 10  is a side view of the cutting insert according to the present invention. 
         FIG. 11  is a cross-section view taken along the line B-B of  FIG. 9 . 
         FIG. 12  is a perspective view of a shim according to the present invention. 
         FIG. 13  is a perspective view of the wedge according to the present invention. 
         FIG. 14  is a top view of the wedge according to the present invention. 
         FIG. 15  is a front view of the wedge according to the present invention. 
         FIG. 16  is a bottom view of the wedge according to the present invention. 
         FIG. 17  is a side view of the wedge according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In view of the accompanying drawings, the present invention will be described below in detail. 
       FIGS. 3-6  are perspective views of a cutting tool according to the present invention.  FIG. 7  is a cross-section view taken along the line A-A of  FIG. 4 . The cutting tool  10  comprises a plurality of slots  30 , which are arranged at the same intervals around the outer circumference of the cylindrical cutter body  11 . An insert seat  40  is recessed within a side surface  33  of the slot  30 . The insert seat  40  includes a radial inner side surface  42  extending from the side surface  33  of the slot  30 , a bottom supporting surface  41  on which the cutting insert or the shim is seated, and a lateral supporting surface  43  outwardly extending from the radial inner side surface  42  and the bottom supporting surface  41 . The insert seat  40  has an axially and radially open shape so that the cutting insert  20  mounted on the insert seat  40  can perform the axial and radial cutting operation. Hereinafter, the “axial direction” of the cutting tool means the axial direction illustrated as ‘X’ in  FIG. 3 . Further, the “radial direction” refers to the direction headed from the center of the cutter body toward its periphery. 
     As illustrated in  FIG. 4 , the wedge  50  is received in the slot  30  and the cutting insert is received in the insert seat  40 . A shim  60  may be received between the cutting insert and the insert seat, as shown in  FIG. 12 . When the shim  60 , on which the cutting insert is seated, is mounted on the insert seat  40 , a top surface  21  of the cutting insert contacts a portion of a side surface  51  of the wedge  50 . A screw  70  is clamped into a screw hole  72  of the slot  30  through a screw hole  71  of the wedge  50 . As the screw  70  advances into the screw hole of the slot  30 , the wedge  50  is pushed toward the screw hole of the slot  30 . Since the wedge  50  tapers inwardly, the cutting insert  20  is clamped on the shim  60  or the insert seat  40  by the wedge  50  as the wedge  50  advances toward the screw hole of the slot  30 . 
       FIG. 8  is a perspective view of the cutting insert according to the present invention.  FIGS. 9 and 10  are respectively a top view and a side view of the cutting insert according to the present invention.  FIG. 11  is a cross-section view taken along the line B-B of  FIG. 9 . The cutting insert  20  includes a top surface  21  contacting one side surface of the wedge, a bottom surface  22  supported and contacting a top surface  61  of the shim  60 , and a plurality of side surfaces  23  connecting between the top surface  21  and the bottom surface  22 . A portion of the plurality of side surfaces  23  of the cutting insert contacts the radial inner side surface  42  and the lateral supporting surface  43 . The top surface  21  of the cutting insert is generally polygonal. In the present embodiment, however, it is generally square. As illustrated in  FIG. 9 , a square recessed portion  25  is formed on the top surface  21  of the cutting insert. The recessed portion  25  consists of triangular surfaces  26  inclined toward the center of the top surface of the cutting insert. The triangular surfaces are of the same number as the lines of the top surface  21  of the cutting insert. In the present embodiment, the recessed portion  25  includes four surfaces  26   a ,  26   b ,  26   c , and  26   d  inclined toward the center of the top surface of the cutting insert. A through hole may be formed along the center line E. As shown in  FIG. 11 , the four surfaces  26   a ,  26   b ,  26   c , and  26   d  inclined toward the center of the top surface of the cutting insert are formed at an inclination angle β relative to the bottom surface  22 . The inclination angle β is preferably in the range of 3° to 10°. The surface  26  inclined toward the center of the top surface contacts the side surface of the wedge  50  when the cutting insert is mounted on the insert seat. 
     As illustrated in  FIG. 9 , the recessed portion  25  is formed to be twisted with respect to the top surface  21  of the cutting insert. That is, the line D bisecting the recessed portion symmetrically is rotated at a twist angle α relative to the line C bisecting the top surface  21  symmetrically. The twist angle α is preferable in the range of 10° to 30°. The top surface  21  of the cutting insert has a plurality of main cutting edges  24  and a plurality of auxiliary cutting edges  28 . A transition portion  29  is formed between a rake portion  27  and the recessed portion  25 . 
       FIG. 13  is a perspective view of the wedge according to the present invention.  FIGS. 14-17  are respectively a top view, a front view, a bottom view and a side view of the wedge according to the present invention. The wedge  50  includes a top surface  53  exposed in the radial direction of the cutting tool, a first side surface  51  having a projecting portion  55  that contacts the recessed portion  25  of the top surface  21  of the cutting insert, a second side surface  52  disposed opposite to the first side surface  21  and contacts the side surface  32  of the slot  30  when mounting it on the cutting tool. A hollow portion  57  is formed at the center of the wedge  50 . The hollow portion  57  communicates with the upper hole  77  formed at the top surface  53  of the wedge and a lateral hole  56  formed at the first side surface  51 . Further, a screw hole  71 , into which the screw  70  is clamped, is formed at the bottom surface  58 , as shown in  FIG. 7 . The projecting portion  55  of the first side surface  51  of the wedge is substantially configured to correspond to the inclined surface  26  of the recessed portion  25  of the top surface  21  of the cutting insert. 
     The clamping structure of the cutting tool and the cutting insert of the present invention will be described below in detail. 
     As illustrated in  FIG. 7 , the shim  60  is seated on the insert seat  40 . The shim  60  is fixed on the insert seat  40  by the thread engagement between the shim screw  73  and the shim screw hole  74 . The cutting insert  20  is seated on the top surface  61  of the shim  60 . Two side surfaces  23  of the cutting insert contact the radial inner side surface  42  and the lateral supporting surface  43  of the insert seat  40 . The wedge  50  is inserted into the slot  30 . The wedge screw  70  is threaded into the screw hole formed at the bottom surface  31  of the slot  30  through the screw hole  71  of the bottom surface of the wedge. The wedge screw  70  consists of a head portion, a neck portion and a threaded portion. The head portion of the wedge screw is placed in the hollow portion  57  of the wedge  50 . The neck portion is located in the screw hole  71 . As the wedge screw  70  advances toward the screw hole  72 , the projecting portion  55  of the first side surface  51  of the wedge contacts the inclined surface  26  of the recessed portion  25  of the top surface  21  of the cutting insert, thus pushing the cutting insert  20  circumferentially. As such, the cutting insert  20  is securely mounted in the cutting tool  10 . 
     As illustrated in  FIGS. 13-16 , since the projecting portion  55  of the wedge has a shape corresponding to the inclined surface  26  of the recessed portion  25  of the cutting insert, the engagement between the projecting portion of the wedge and the inclined surface of the cutting insert can precisely set the mounting position of the cutting insert at the cutting tool. That is, the engagement between the projecting portion of the wedge and the inclined surface of the cutting insert functions to guide the mounting position of the cutting insert. In the prior art, since the contact surfaces of the wedge and cutting insert are all flat, there are some difficulties in setting the engagement position of the wedge and the cutting insert. In some cases, the prior art cutting insert may be mounted in the cutting tool in a slightly twisted state, and thus, the worker may not cut the workpiece precisely. In the present invention, since the engagement between the projecting portion of the wedge and the recessed portion of the cutting insert guides the mounting position of the cutting insert, the cutting insert can be positioned at the cutting tool simply and precisely. 
     Further, the inclined surface  26  of the cutting insert is inclined at the inclination angle β with respect to the bottom surface  22 . When the wedge clamps the cutting insert, the projecting portion  55  of the wedge puts a circumferential force Fc on the cutting insert  20  circumferentially, as well as a radial force Fr in the radial direction. The radial force Fr of the wedge can have the side surface  23  of the cutting insert more securely supported by the radial inner side surface  42  of the insert seat. As such, the cutting insert  20  can be more securely mounted at the cutting tool. The inclination angle β is preferably in the range of 3° to 10°. If the inclination angle β is less than 3°, then the wedge cannot sufficiently push the cutting insert in the radial direction. If it is greater than 10°, then it is difficult to detach or mount the wedge. 
     The recessed portion  25  of the cutting insert consists of the inclined surfaces  26 , which are of the same number of the lines of the top surface  21  of the cutting tool. That is, where the top surface  21  of the cutting insert is a square as it is in the present embodiment, the recessed portion  25  has four inclined surfaces  26   a ,  26   b ,  26   c  and  26   d . When the inclined surface  26   a  is clamped by the projecting portion  55  of the wedge and then the main cutting edge  24  opposite to the inclined surface  26   a  are worn out, after detaching the cutting insert, the worker can mount the cutting insert again so that the other inclined surface can be clamped by the projecting portion  55  of the wedge. 
     Further, the recessed portion  25  may be twisted at a predetermined angle relative to the top surface  21  of the cutting insert. Since the projecting portion  55  of the wedge has the shape corresponding to the inclined surface  26  of the cutting insert, the wedge  50  is mounted in the slot  30  in the direction parallel with the bisecting line D of the recessed portion  25  of the cutting insert. As illustrated in  FIG. 6 , the radial force Fr of the wedge is divided into a force component Fr 1  in the direction of the bisecting line C of the top surface  21  and a force component Fr 2  in the direction perpendicular to the bisecting line C. The force component Fr 1  has the side surface  23  of the cutting insert supported by the radial inner side surface  42  of the insert seat. The force component Fr 2  has the side surface  23  of the cutting insert supported by the lateral supporting surface  43  of the insert seat. Since the cutting insert is supported by the radial inner side surface  42 , the lateral supporting surface  43 , the shim or the bottom surface  41  of the insert seat, and the projecting portion  55  of the wedge, it can be more securely mounted. The twist angle α is preferably in the range of 10° to 30°. If the twist angle α is less than 10°, then the cutting insert is not stably supported by two side surfaces of the insert seat. If it is greater than 30°, since many portions of the top surface of the cutting insert contact the wedge, it is hard to ensure sufficient chip discharging spaces. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Further, the present invention can be used in various machine work using a cutting insert such as hole processing and turning operations.