The Realities of Friction in Metal Plastic Flow With Corresponding Results During Metal Cutting

Metal cutting is a dynamic process with two types of friction: on the one hand, external friction between two different bodies, and on the other hand, an internal friction inside the same material, due to plastic flow. These two different types of friction lead to different chip formation processes. In the case of built-up-edge (BUE), low velocity creates low energy, resulting in a self-hardening effect with BUE. With increasing velocity, the energy will increase and will result in high temperatures with a built-up-layer (BUL). Furthermore, under special circumstances, friction will lead to a self-blockade (a self-blocking state). This situation describes the third stage in metal plastic flow — the creation of a segmental chip. In this case the internal friction takes over. One question arises: “How can we determine these two types of different friction?” For solving these phenomena new fundamental equations based on mathematics, physics and material behavior have to be developed. This paper presents newly developed equations, which deliver the theoretical distribution of yield shear stress as well as strain rate with corresponding grid deformation pattern in metal plastic flow. For an actual cut, the plastic deformation pattern remains when the process is stopped, and therefore the theoretical result can be compared with cross-sections of the relevant chip formation areas — contrary to outputs such as stress, strain rate and temperatures which are all functions of position and time. All this will be shown and discussed in the paper, and stands in good agreement with experimental results.