Effect of a protective coating on the surface integrity of a microchannel produced by microultrasonic machining

In micro-ultrasonic machining (μUSM), slight lateral vibration at the end of the tool inevitably occurs due to tool manufacturing installation errors and mechanical system vibrations. These vibrations cause overcutting and edge breakage, creating undesirable effects on heat transfer and flow deflection. Hence, this paper presented a new fabrication method that ensures high surface integrity by applying a protective coating on the substrate. To study the material removal modes during fabrication and the causes of overcutting and edge damage, a mathematical model of the microchannel surface integrity was established. The experimental parameters—feed rate, ultrasonic power, slurry viscosity, and protective coating—had a large impact on the surface integrity. The optimal parameters were a PE-Wax coating of 400 μm thickness, feed rate of 4 μm/s, 60 % ultrasonic power and 25 % slurry concentration. Under these conditions, the amount of overcutting decreased from 74.3 μm to 28 μm (62.3 % improvement) and the weighted edge damage decreased from 52.3 μm to 16 μm (69.4 % improvement), which led to a 65.85 % improvement in the surface integrity index. The experimental investigation revealed that the surface integrity of silicon microchannels and the quality of μUSM can be significantly improved by applying the protective coating.