Milling tool and workpiece machining method

A workpiece machining method for undercutting interior portions of a rib of a workpiece attached to a table of a five-axis machine tool, having at least two rotary feed axes, and a return flange formed contiguous with the rib, the method comprising the steps of:

• attaching a milling tool to a spindle of the five-axis machine tool and rotating the milling tool, wherein the milling tool is composed of a shank part and a double truncated conical shaped head which is provided on a distal end of the shank part, wherein the double truncated conical shaped 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, wherein each of the expanding diameter section and the decreasing diameter section has cutting inserts with a respective linear main cutting edge, and wherein each cutting insert is attached to a cutting insert seat;
• obliquely orienting a rotation axis of the spindle relative to each of the rib and the return flange, wherein the rib extends perpendicular to a bottom surface of the workpiece and the return flange extends substantially parallel to the bottom surface;
• machining an undercut on an interior of the return flange with the linear main cutting edges of the expanding diameter section of the double truncated conical shaped head of the milling tool and machining a side surface of the rib with the linear main cutting edges of the decreasing diameter section of the milling tool resulting with a triangular columnar portion remaining between the rib and the bottom surface of the workpiece;
• exchanging the milling tool attached to the spindle with a T-shaped cutter;
• orienting the rotation axis of spindle parallel to the rib and perpendicular to the bottom surface;
• and
• removing the triangular columnar portion with the T-shaped cutter,
• wherein a length of the milling tool protruding from the spindle, when the milling tool is attached to the spindle, is shorter than a length of the T-shaped cutter protruding from the spindle when the T-shaped cutter is attached to the spindle, wherein each length is measured in a direction parallel to the rotation axis of the spindle.