Deformation Characteristics of Nickel Alloys During Machining

Machining experiments have been carried out on iron base and nickel base alloys in order to investigate the substantial differences in machinability between these materials. Calculations of the dynamic material strength show that the nickel base alloys have a much higher strength in both the primary and secondary shear zones. In addition, the nickel alloys are shown to “clean” the initial part of the chip-tool contact length more readily than do the iron base materials. The combination of the high primary shear zone strength and the high secondary shear stress close to the cutting edge means that, when machining the nickel alloys, the edge temperature is very high. By contrast, when machining ferrous materials the temperatures further back along the rake face are considerably greater than the cutting edge temperatures. The high strength of the nickel materials also causes high stresses to act normal to the cutting edge. The stress-temperature states at the cutting edge for the two kinds of workmaterials have been summarized in a deformation map for machining. The deformation map summarizes the tool material properties versus temperature, and the normal stress acting on the cutting edge versus temperature. Such maps lead to a prediction of cutting edge collapse and a ranking of materials in terms of their machinability.