Orthogonal Machining of Copper Alloy With a Hardness Gradient

An experimental and analytical investigation of the effects of hardness upon the classical orthogonal machining geometries was conducted using copper alloy with 12 levels of hardness as measured on the Brinell hardness scale. A real time data collection method permitted the collection of a large body of data for analysis. 720 experimental runs were analyzed. The experimental results were compared to thirteen geometrical models that have been formulated including Merchant’s and Piispanen’s independently derived orthogonal machining equations of the 1940’s. One model [1] was verified by the results of the experiment in copper when a regression study of the data was conducted. Their application of the minimum energy principle in deriving an expression for the shear front angle ψ, the onset of shear plane angle ϕ, and the tool face rake angle α, provided an accurate shear strain model that is well supported by the physical evidence. The resulting relationship: ψ=45°-φ+α2 is predictive. It correlates directly and strongly with the measured material hardness.