An experimental study for ductile mode control on cemented carbide micro-milling

Micro-milling of hard materials can be an efficient processing technique to attain high-precision parts in difficult-to-machine metal matrix composites, such as cemented carbide. Despite their brittle mechanical behavior, within specific operational conditions plastic-flow (ductile) cutting occurs, enabling significant technological advances on ultra-precision machines and components. This brittle-to-ductile threshold (which has been defined based on grinding operations) depends on material properties, such as the elastic modulus, material hardness and fracture toughness of the tool-workpiece materials pair. Despite the similar process size scale, grinding and micro-milling significantly differ on how well defined the cutting edges are, and the control of micro-milling operations towards stable ductile cutting is still rather unexplored. In the present work, micro-milling of WC-15wt.%Co sintered samples was performed with diamond coated end mills, confirming the influence of a ductile-to-brittle threshold on the cutting regime. Critical scale effects and structure-related behavior were also confirmed, as well as the impact of edge radius optimization with laser sharpened coating. A positive effect on machined surface quality was observed when ductile cutting regime mode was applied, likewise the effect of edge radius control with laser sharpness technology. Scanning electron microscopy and micro 3D topography were used to evaluate the machined surface microstructure features after different machining conditions, The experimental study confirmed the ability to control the cutting regime during micro milling of cemented carbide, the great impact of the edge radius on the ploughing effect and the ability to apply laser edge treatment as a solution to control this scale effect, however, the sharp edges promoted a reduction in the quality of the machined surfaces.