The Ledge Tool: A New Cutting Tool Insert

Abstract

The salient features of a simple, wear-tolerant cemented carbide tool are described. Results are presented for high-speed machining (3 to 5 times the conventional speeds) of titanium alloys in turning and face milling. This tool, termed the ledge cutting tool, has a thin (0.015 to 0.050 in.) ledge which overhangs a small distance (0.015 to 0.060 in.) equal to the depth of cut desired. Such a design permits only a limited amount of flank wear (determined by the thickness of the ledge) but continues to perform for a long period of time as a result of wear-back of the ledge. Under optimum conditions, the wear-back occurs predominantly by microchipping. Because of geometric restrictions, the ledge tool is applicable only to straight cuts in turning, facing, and boring, and to face milling and some peripheral milling. Also, the maximum depth of cut is somewhat limited by the ledge configuration. In turning, cutting time on titanium alloys can be as long as ≈ 30 min. or more, and metal removal of ≈ 60 in.3 can be achieved on a single edge. Wear-back rates in face milling are about 2 to 3 times higher than in straight turning. The higher rates are attributed here to the interrupted nature of cutting in milling. Use of a grade of cemented carbide (e.g., C1 Grade) which is too tough or has too thick a ledge for a given application leads to excessive forces which can cause gross chipping of the ledge (rapid wear) and/or excessive deflection of the cutting tool with reduced depth of cut. Selection of a proper grade of carbide (e.g., Grades C2, C3, C4) for a given application results in uniform, low wear-back caused by microchipping. Because of the end cutting edge angle (though small, ≈ 1 deg) used, the ledge tool can generate a slight taper on very long parts; hence an N.C. tool offset may be necessary to compensate for wear-back. The ledge tool is found to give excellent finish (1 to 3 μm) in both turning and face milling. In general, conventional tooling with slight modifications can be used for ledge machining. The ledge tool can also be used for machining cast iron at very high speeds.