High strain rate induced initial chip formation of certain metals during micromachining processes

As microtechnology and nanotechnology become increasingly important to the needs of society, the need to create devices in engineering materials becomes more apparent. High speed milling has been shown to provide a great deal of promise in creating microstructures and in nanotexturing surfaces in engineering materials. Cutting tool rotation is expected to reach 1 000 000 revolutions per minute (rev min⁻¹) compared with conventional cutting speeds of around 30 000 rev min⁻¹. Rotating the tool this quickly reduces cutting forces, which produces a higher quality of cut so that post- processing is not required. Clearly, strain rates imparted to the workpiece at these speeds are very high and this influences initial chip formation and chip removal mechanisms. High strain rates imparted cause distinct chip formations in engineering materials to occur which are similarly observed in other materials, most notably biological materials such as cancellous bone. Certain soft metals such as aluminium do not machine very well because the material adheres to the cutting tool. However, high strain rates tend to overcome these limitations. This paper examines high strain rate initial chip formation in metals, compares these results to other materials, and shows that an initial chip curl model can be applied to describe high strain rate machining phenomena at the microscale.