Milling tool and workpiece machining method

Abstract

A milling tool is configured from a shank part and a head with a cutting edge that is provided on the leading end of the shank part. The head comprises an expanding diameter section, the diameter of which expands gradually from the base end that contacts the shank part in the direction of the leading end, and a decreasing diameter section, the diameter of which gradually decreases from the maximum diameter section in the direction of the leading end. At least one cutting edge is provided on each of the expanding diameter section and the decreasing diameter section.

1 . A milling tool composed of a shank part, and a head which is provided on a distal end of the shank part and which has a cutting edge, wherein
 the head has an expanding diameter section, the diameter of which gradually increases along a direction from a proximal end contiguous with the shank part toward a distal end, and a decreasing diameter section, the diameter of which gradually decreases along a direction from a maximum diameter section toward the distal end, and   cutting edges are provided on the expanding diameter section and the decreasing diameter section.   
     
     
         2 . The milling tool of  claim 1 , wherein at least one upper groove is formed in the expanding diameter section, at least one lower groove is formed in the decreasing diameter section, and a seat for attachment of an insert forming the cutting edge is formed in each of the at least one upper groove and the at least one lower groove. 
     
     
         3 . The milling tool of  claim 2 , wherein an upper seat is formed in the upper groove, a lower seat is formed in the lower groove, an upper insert is attached to the upper seat, and a lower insert is attached to the lower seat. 
     
     
         4 . The milling tool of  claim 3 , wherein the upper insert and the lower insert each have a main cutting edge which linearly extends from one end thereof and a convexly bent sub cutting edge which is connected to the main cutting edge and which is arranged on the other end of the upper inert or the lower insert, and the sub cutting edges of the upper insert and the lower insert are arranged so as to be adjacent to a joint of the expanding diameter section and the decreasing diameter section. 
     
     
         5 . The milling tool of  claim 4 , wherein a bottom cutting edge and an inner cutting edge are formed on an edge of the lower insert on the side opposite the sub cutting edge. 
     
     
         6 . The milling tool of  claim 2 , wherein a seat extending from the upper groove toward the lower groove is formed, and a V-shaped insert is attached to the seat. 
     
     
         7 . A workpiece machining method for undercutting interior portions of a rib of a workpiece attached to a table of a machine tool and a return flange formed contiguous with the rib, the method comprising the steps of:
 attaching the milling tool of  claim 1  to a spindle of the machine tool and rotating the milling tool, and   machining an interior of the return flange with a cutting edge of the expanding diameter section of the milling tool and machining a side surface of the rib with a cutting edge of the decreasing diameter section of the milling tool.   
     
     
         8 . The workpiece machining method of  claim 7 , wherein the machine tool is a five-axis machine tool having at least two rotary feed axes, and
 a posture and position of the milling tool are controlled relative to the workpiece to perform undercutting of a corner portion at which ribs having return flanges intersect.