Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase application of International Patent Application No. PCT/JP2012/078198, filed on Oct. 31, 2012, which is hereby incorporated by reference in the present disclosure in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a T-cutter, a method of forming a rib which uses a T-cutter to cut out a rib which has an overhanging part, and an aircraft part which has a rib defining an overhanging part. 
     BACKGROUND OF THE INVENTION 
     For example, in order to form a “T-slot”, in the past, a “T-slot cutter” has been used. A T-cutter is also used for forming an undercut at a side surface of a workpiece. Such a method of forming an undercut on a side surface of a workpiece is, for example, also applied when forming a return flange at a rib of a skin panel of a wing of an aircraft. 
     A T-cutter has a shank and a head which is joined with a front end of the shank. Usually, the head has cemented carbide tips screwed or soldered to it. There are also T-cutters which have polycrystalline diamond (PCD) tips soldered to their heads. 
     For example, PLT 1 describes a T-cutter which is provided with a groove part, which extends from an edge part side to a side opposite to the edge parts so as to be inclined in a direction opposite to a rotation direction about an axial center, at an outer circumferential surface of the shank so as to improve the discharge of chips. This T-cutter has cemented carbide throwaway tips screwed to the edge parts. 
     PLT 2 describes a T-cutter comprised of front end part side tips and proximal end side tips screwed to a cutting head while alternately arranged in a rotational direction of a tool. 
     CITATIONS LIST 
     PLT 1: Japanese Patent Publication No. 2009-18354A 
     PLT 2: Japanese Patent No. 4830597B2 
     SUMMARY OF THE INVENTION 
     In a T-cutter with cemented carbide tips screwed to it as described in PLTs 1 and 2, due to variations in centrifugal force or the radii of rotation of the tips, the spindle rotational speed has been limited to about 1000 rpm and the feed speed to several hundred mm/min or so, so the processing efficiency, which is shown by rate of removal of material from the workpiece per unit time (MRR (cm 3 /min)), becomes low. Further, in the case of processing along a curved surface such as shown in  FIG. 13  or the case of processing on a slanted surface such as shown in  FIG. 14  by a T-cutter with tips soldered to it, a cutting force acts in the axial direction of the tool, and therefore there is the problem that the tips easily detach from the head of the T-cutter. To prevent this, it is necessary to further decrease the rotational speed or feed speed of the tool. Such processing of curved surfaces or slanted surfaces, for example, is necessary when producing skin panels or leading edges of the wings of aircraft, etc. 
     On the other hand, a T-cutter which has polycrystalline diamond (PCD) tips soldered to its head, compared with a T-cutter which has cemented carbide tips screwed or soldered to it, can increase the rotational speed of the tool and increase the processing efficiency. However, when performing processing along a curved surface such as shown in  FIG. 13  or when performing processing on a slanted surface such as shown in  FIG. 14  where a cutting force acts in the axial direction of the tool, in the same way as the case of tips made of cemented carbide, there is the problem of the tips easily detaching from the head and, again, it is not possible to increase the rotational speed or feed speed of the tool. 
     Therefore, the present invention has as its technical problem so solve such problems of the prior art and has as its object the provision of a T-cutter which can form a rib which has an overhanging part by high speed rotation and high speed feed, in particular can form a 3D undercut shape, a method of forming such a rib, and an aircraft part. 
     To achieve the already explained object, according to the present invention, a T-cutter comprising a shank and a head which is provided at one end of the shank and which alternately arranges in a peripheral direction of the T-cutter a plurality of bottom edge parts which have cutting edges at a distal end side of the T-cutter of an opposite side from the shank and a plurality of top edge parts which have cutting edges at a proximal end side of the T-cutter in proximity to the shank side, the cutting edges of the bottom edge parts and the top edge parts being formed integrally in structure with the shank and the head is provided. 
     Further, according to the present invention, a method of forming a rib which cuts out a rib which has an overhanging part at a workpiece is provided, the method of forming a rib comprising forming a rib part of the workpiece while leaving a thickness of at least a width dimension of the overhanging part, attaching a T-cutter, comprising a shank and a head which is provided at one end of the shank and which alternately arranges in a peripheral direction of the T-cutter a plurality of bottom edge parts which have cutting edges at a distal end side of the T-cutter of an opposite side from the shank and a plurality of top edge parts which have cutting edges at a proximal end side of the T-cutter in proximity to the shank side, the cutting edges of the bottom edge parts and the top edge parts being formed integrally in structure with the shank and the head, to a spindle of a machine tool, rotating it, and moving the workpiece and the T-cutter relative to each other so as to cut out the rib so that the overhanging part remains. 
     Further, according to the present invention, an aircraft part which has a rib which has an overhanging part which is formed by cutting a workpiece material by a machine tool is provided, in which an aircraft part is obtained by forming a rib part of the workpiece material while leaving a thickness of at least a width dimension of the overhanging part, attaching a T-cutter, comprising a shank and a head which is provided at one end of the shank and which alternately arranges in a peripheral direction of the T-cutter a plurality of bottom edge parts which have cutting edges at a distal end side of the T-cutter of an opposite side from the shank and a plurality of top edge parts which have cutting edges at a proximal end side of the T-cutter in proximity to the shank side, the cutting edges of the bottom edge parts and the top edge parts being formed integrally in structure with the shank and the head, to a spindle of a machine tool, rotating it, and moving the workpiece material and the T-cutter relative to each other so as to cut out the rib so that the overhanging part remains. 
     According to the present invention, the T-cutter is designed as a solid-type cutting tool where the head, including the edge parts, and the shank are formed integrally without soldering or other joining means, compared with a conventional T-cutter with cemented carbide tips screwed or soldered to it or a T-cutter of the prior art with PCD tips soldered to the head, not only when performing 2D processing, but also when performing processing along a curved surface or when processing a slanted surface to form a 3D undercut shape, the tips will not fall off, the rotational speed and feed speed can be made extremely high, and the processing efficiency can be extremely high. 
     In particular, by applying the T-cutter and method of forming a rib to processing of an aircraft part which has a rib with an overhanging part, for example, a skin panel of a wing, leading edge, wing rib, or other wing member, a high MRR can be obtained. They perform formidably in the production of aircraft parts where almost the entire large block material of an aluminum alloy is cut away to form ribs which has overhanging parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a T-cutter of a preferable embodiment of the present invention. 
         FIG. 2  is a semi-cross-sectional view in an axial direction of a T-cutter of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a head of a T-cutter along an arrow line III-III of  FIG. 2 . 
         FIG. 4  is an end view of a head of a T-cutter along an arrow line IV-IV of  FIG. 2 . 
         FIG. 5  is a partial enlarged side surface view which shows a head of a T-cutter of  FIG. 1 . 
         FIG. 6  is a partial enlarged side view similar to  FIG. 5  which is shown at a rotational position different from  FIG. 5 . 
         FIG. 7  is a schematic view which shows a method of production of a T-cutter according to the present invention. 
         FIG. 8  is a schematic view which shows a method of production of a T-cutter according to the prior art. 
         FIG. 9  is a perspective view which shows part of a skin panel of a wing of an aircraft which is formed by the T-cutter of the present invention. 
         FIG. 10  is an enlarged cross-sectional view which shows part of a skin panel of a wing of an aircraft which is formed by the T-cutter of the present invention. 
         FIG. 11  is a perspective view which shows a back surface of a skin panel of a wing of an aircraft. 
         FIG. 12  is a side view of a horizontal five-axis machining center which is shown as one example of a machine tool for forming a 3D return flange using the T-cutter of the present invention. 
         FIG. 13  is a schematic view shows a problem point when using a T-cutter according to the prior art to cut a curved surface. 
         FIG. 14  is a schematic view which shows a problem point when using a T-cutter according to the related art to cut a slanted surface. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Below, referring to the attached drawings, a preferred embodiment of the present invention will be explained. First, referring to  FIG. 1  to  FIG. 6 , a preferred embodiment of a T-cutter of the present invention will be explained. A T-cutter  10  is comprised of a shank  12  which is to be attached to a front end part of a spindle  116  and a head  14  which is formed at the distal end of the shank  12 . The head  14  is formed with a plurality of, in the present embodiment, six, edge parts. The edge parts are comprised of three bottom edge parts  16  which have cutting edges  16   a  at the distal end side of the T-cutter  10 , i.e., the opposite side to the shank  12 , and three top edge parts  18  which have cutting edges  18   a  at the proximal end side of the T-cutter  10 , i.e., the shank  12  side. The T-cutter  10  is a so-called “solid type” of cutting tool where the head  14 , including the edge parts  16 ,  18 , and the shank  12 , are formed integrally by a single base material of cemented carbide without soldering or other joining means. 
     The cutting edges  16   a  of the bottom edge parts  16  are formed by ridgelines P A -P B  where the bottom faces, side faces, and corners R between the two of the bottom edge parts  16  intersect the rake faces  16   b  (see  FIG. 5 ). Similarly, the cutting edges  18   a  of the top edge parts  18  are formed by ridgelines P C -P D  where the bottom faces, side faces, and corners R between the two of the top edge parts  18  intersect the rake faces  18   b  (see  FIG. 6 ). The sizes of the corners R are set to match the sizes of the fillets R which are formed at the workpiece. Further, the bottom edge parts  16  and the top edge parts  18  are arranged alternately at equal intervals in the peripheral direction of the head  14 . Further, if particularly referring to  FIGS. 5 and 6 , the rake faces  16   b  of the bottom edge parts  16  are slanted upward, i.e., so as to approach the shank  12 , while the rake faces  18   b  of the top edge parts  18  are slanted to the opposite side from the rake faces  16   b  of the bottom edge parts  16  so as to approach the distal end direction of the T-cutter  10 . 
     Furthermore, the T-cutter  10  is formed with coolant passages for feeding a coolant to the processing region. The coolant passages are comprised of an axial direction passage  12   a  which runs through the shank  12  along the center axial line O and radial direction passages  14   a  which run from the axial direction passage  12   a  in the radial direction through the head  14 , extend in the directions of the rake faces  16   b ,  18   b  of the bottom edges part  16  and top edge parts  18 , and open so as to eject coolant toward the cutting edges  16   a ,  18   a . The coolant passages communicate with a coolant feed pipe (not shown) which is provided at the inside of the spindle  116  so as to supply coolant toward the cutting edges  16   a ,  18   a , whereby generation of heat is reduced and the tool life and chip discharge become better. 
     Next, referring to  FIGS. 7 and 8 , in the past, when producing such a solid type of T-cutter, as shown in  FIG. 8 , a powder of cemented carbide was molded into a cylindrical shape and sintered to prepare a cemented carbide cylindrical member and this cylindrical member was ground down to prepare a T-cutter. As opposed to this, in the present invention, as shown in  FIG. 7 , cemented carbide powder can be molded into a shape forming a generally T-shape in the side view close to the final shape of the T-cutter  10  and sintered, then that can be ground down to form the shank  12  and head  14  of the T-cutter  10 . Due to this, the material which is removed by the grinding operation, which is shown by the hatching in  FIGS. 7 and 8 , is remarkably reduced and the cost of materials, manufacturing time, and manufacturing cost of the T-cutter  10  are reduced. Furthermore, the lifetime of the grinding stone which is used for the grinding operation also becomes remarkably longer. The coolant passages  12   a ,  14   a  can be formed by electrical discharge machining or other known methods for forming small holes. 
     Next, referring to  FIG. 9  to  FIG. 12 , using as an example the formation of ribs at the skin panel of the wing of an aircraft as 3D undercut shapes, the method of using a T-cutter  10  to cut out ribs which have overhanging parts, i.e., cut out return flange parts, will be explained. 
     A skin panel  50  of the wing of an aircraft which is shown as one example in  FIG. 11  is provided with an outer skin  52 , a pair of longitudinal ribs  54 ,  56  which extend in a longitudinal direction along an inner surface of the outer skin  52 , and a plurality of traverse ribs  58  which extend between the longitudinal ribs  54 ,  56 . At the traverse ribs  58 , return flanges (overhanging parts)  60  extend along the edge parts at the opposite sides from the outer skin  52 . The outer skin  52 , longitudinal ribs  54 ,  56 , traverse ribs  58 , and return flanges  60  are cut out from a single aluminum alloy block. Further, the outer skin  52  of the skin panel  50  which forms part of the wing of the aircraft is not a 2D flat surface, but extends in three dimensions so as to form part of the wing shape along with the shape of the wing surface. The longitudinal ribs  54 ,  56 , traverse ribs  58 , and return flanges  60  are also curved three-dimensionally so as to match with the three-dimensional shape of the outer skin  52 . 
     Next, referring to  FIG. 12 , a machine tool  100  which uses a T-cutter  10  to form a rib which has a 3D return flange such as with the skin panel  50  of the wing of an aircraft which is shown in  FIG. 11  will be shown. The machine tool  100  is configured as a horizontal machining center which is comprised of a bed  102  which forms a base part which is fastened to the floor of a factory, a column  104  which is attached to a top surface of a rear part of the bed  102  so as to be able to move through a Z-axis feed mechanism in a front-rear direction (Z-axial direction, in  FIG. 7 , left-right direction), a spindle table  106  which is attached to a front surface of the column  104  so as to be able to move through a Y-axis feed mechanism (not shown) in a top-down direction (Y-axial direction), and a table  108  which is attached to a top surface of a front part of the bed  102  so as to be able to move through an X-axis feed mechanism in a left-right direction (X-axial direction, in  FIG. 7 , direction vertical to paper surface). At the table  108 , a pallet P on which a workpiece W is fastened is attached. Further, a pallet P on which a workpiece W which has finished being processed on the table  108  is fastened is changed by a not shown pallet changer to a pallet P on which an unprocessed workpiece is fastened. In the present embodiment, the workpiece W can, for example, be made the skin panel  50  of the wing of an aircraft. Further, as the NC machine tool, a vertical machining center can also be employed. 
     At the spindle table  106 , a swivel base  110  is supported to be able to rotate about a C-axis direction centered about the Z-axis. The swivel base  110  has bracket parts  112  at the two side parts straddling the rotational axis of the swivel base  110 . At the bracket parts  112 , a spindle head  114  is attached to be able to rotate in an A-axial direction by a shaft  112   a  which is parallel to the X-axis. At the spindle head  114 , a spindle  116  is supported to be able to rotate about a rotational axis Os in the longitudinal direction. At the front end part of the spindle  116 , a T-cutter  10  is attached. 
     Note that, the X-axis feed mechanism may be provided with a pair of X-axis guide rails  102   a  which extend at the top surface of the bed  102  in the left-right direction horizontally, a guide block (not shown) which is attached to a bottom surface of the table  108  to be able to slide along the X-axis guide rails  102   a , an X-axis ball-screw (not shown) which extends in the bed  102  in the X-axial direction, a nut (not shown) which is attached to a bottom end part of the table  108  and engages with the X-axis ball-screw, and a servo motor (not shown) which is coupled with one end of the X-axis ball-screw and drives rotation of the X-axis ball-screw. 
     Similarly, the Y-axis feed mechanism may be provided with a pair of Y-axis guide rails (not shown) which extend vertically in the column  104 , a guide block (not shown) which is attached to the spindle table  106  to be able to slide along the Y-axis guide rails, a Y-axis ball-screw (not shown) which extends in the column  104  in the Y-axial direction, a nut (not shown) which is attached inside the spindle table  106  and engages with the Y-axis ball-screw, and a servo motor (not shown) which is coupled with one end of the Y-axis ball-screw and drives rotation of the Y-axis ball-screw. 
     Similarly, the Z-axis feed mechanism may be provided with a guide block (not shown) which is attached to the top surface of the bed  102  in the front-rear direction horizontally and which is attached to the bottom surface of the column  104  to be able to slide along the Z-axis guide rails  102   b , a Z-axis ball-screw (not shown) which extends in the bed  102  in the Z-axial direction, a nut (not shown) which is attached to the bottom surface of the column  104  and engages with the Z-axis ball-screw, and a servo motor (not shown) which is coupled with one end of the Z-axis ball-screw and drives rotation of the Z-axis ball-screw. In this way, the machine tool  100  forms a five-axis NC machine tool which has three linear feed axes of the X-axis, Y-axis, and Z-axis and two rotational feed axes of the A-axis and C-axis. 
     To use the T-cutter  10  to form return flanges on the skin panel of the wing of an aircraft, first, an aluminum alloy block which has dimensions larger than the skin panel  50  is attached as a workpiece W to the table  108  in the state fastened to a pallet P. Next, for example, a rotary cutting tool such as an end mill (not shown) is attached to the spindle  116  of the machine tool  100 . By controlling the feed operations of the five axes of the machine tool  100 , the workpiece W is processed whereby a skin panel which has an outer skin  52 , longitudinal ribs  54 ,  56 , and traverse ribs  58  (rib parts) not provided with return flanges  60  is formed. At this time, the traverse ribs (rib parts)  58  have thicknesses of at least the width dimension of the return flanges  60  which enable formation of the return flanges  60 . 
     Next, for example, an automatic tool changer (not shown) of the machine tool  100  is used to change the conventional end mill to the T-cutter  10 . Next, by feed control of the five axes of the three linear feed axes of the X-axis, Y-axis, and Z-axis and the two rotational axes of the A-axis and C-axis of the machine tool  100 , as shown in  FIGS. 9 and 10 , the T-cutter  10  is moved along the inside surface of the outer skin  52  and the side surfaces of the traverse ribs  58  while making predetermined depths of cuts to the side surfaces of the traverse ribs  58 . Due to this, 3D undercut shapes are cut at the side surfaces of the traverse ribs  58  and return flanges  60  are formed at the traverse ribs  58  along the edge parts (in  FIGS. 9 and 10 , top edge parts) at the opposite side from the outer skin  52 . The return flanges  60  may stick out from only single sides of the traverse ribs  58  or may stick out from both sides of the traverse ribs  58 . 
     According to the present embodiment, the T-cutter  10  is a solid-type cemented carbide cutting tool where the head  14 , including the cutting edges  16   a ,  18   a , and the shank  12  are formed integrally without soldering or other joining means, compared with a conventional T-cutter with cemented carbide tips screwed or soldered to it, not only when performing 2D processing, but also when processing along a curved surface such as shown in  FIG. 13  which is slanted with respect to a plane vertical to the axial line O of the T-cutter  10 , or when processing of a slanted surface such as shown in  FIG. 14 , the rotational speed and feed speed can be made extremely high, and the processing efficiency can be extremely high. 
     One example of the processing results will be shown. Aluminum alloy workpieces were processed to form 3D undercut shapes using φ45 outside diameter T-cutters. As the T-cutters, two types, a conventional cutter which has cemented carbide soldered edges and a cutter of the present invention which is a solid type of cemented carbide, were prepared. The heights of the edges from the bottom edge parts to the top edge parts were 16 mm in both cutters. The conventional cutter suffered from some vibration at a rotational speed of 1000 rpm, feed speed of 263 mm/min, and radial direction depth of cut of 11 mm and approached the limit of processing ability. The MRR at this time was 46 cm 3 /min. As opposed to this, the cutter of the present invention suffered from some vibration at a rotational speed of 33000 rpm, feed speed of 11000 mm/min, and radial direction depth of cut of 4 mm and approached the limit of processing ability. The MRR at this time was 704 cm 3 /min. The cutter of the present invention had an efficiency 15.3 times higher compared with the conventional cutter. Therefore, the T-cutter of the present invention exhibits a remarkable effect if used under processing conditions of an MRR of 100 cm 3 /min to 1000 cm 3 /min. 
     REFERENCE SIGNS LIST 
     
         
           10  T-cutter 
           12  shank 
           12   a  axial direction passage (coolant passage) 
           14  head 
           14   a  radial direction passage (coolant passage) 
           16  bottom edge part 
           18  top edge part 
           50  skin panel 
           60  return flange 
           100  machine tool 
           102  bed 
           104  column 
           108  table 
           114  spindle head 
           116  spindle

Technology Category: 7