Investigations on chip formation in micro-milling

In the current context of miniaturization, micro-machining processes are in full expansion. One of them is micro-milling able to produce parts with features ranging from several mm to several µm. Due to the down-sizing of the macro-milling process, micro-cutting is not a simple scaling-down of macro-cutting. A significant difference between micro- and macro-cutting is the ratio between the depth of cut and the tool edge radius. This ratio is often smaller than the unit in micro-cutting, implying changes in the chip formation process. The new forming chip way involves the so-called „minimum chip thickness? phenomenon, below which no chip is formed. Estimating the minimum chip thickness value is one of the main challenges in micro-milling. Unfortunately, this estimation is quite difficult because the minimum chip thickness depends on the machined material and the tool geometry. Moreover at this microscopic scale the microstructure of the machined material takes importance and its granular structure must be taken into account. A review of the current state of the art in chip formation and minimum chip thickness in micro-milling is reported in this paper from an experimental and numerical point of view. In order to model the chip formation process, numerical simulations are performed using the finite element method and a commercial software program, ABAQUS/Explicit v6.7. The model consists in a 2D plane strain orthogonal cutting model of the area close to the cutting edge of the tool, where the chip is formed. The Johnson-Cook plasticity model describes the workpiece material behaviour while the cutting tool is modelled with a finite edge radius. The Lagrangian formulation has been adopted and a chip separation criterion is used to make the chip formation possible. Results of the finite element simulations are presented and compared to results found in literature.