Mechanisms of enhancing the machining performance in micro abrasive waterjet drilling of hard and brittle materials by vibration assistance

A study of the effect of vibration assistance on the machining performance in the micro slurry jet drilling of hard and brittle materials typified by single crystal 4H-SiC wafers is presented. It shows that this technology provides benefits to the machining process by improving both material removal rate and surface finish, and such improvements are more profound by increasing the vibration amplitude. Ductile-like mode deformation is noticed to be dominant on the surfaces processed with vibration assistance for this highly brittle material. It is found that major material removal is achieved through brittle fractures of the material by the direct impact of the jet. A smoothening process following the jet impact through a crossflow-driven motion of the particles over the brittle-fractured surface at an engaging depth below the critical value for the cleavage fracture of the material improves the processed surface quality. A finite element (FE) analysis of the particle impact reveals that the vibration applied to the target surface adds no energy to the impacting process, but makes the transfer and application of jet energy more effective by promoting a sweeping effect. This effect clears the surface from the accumulation of the after-impact particles, allowing the subsequent particles from the jet to impact directly onto the surface. The FE study also shows that the applied vibration does not change the engaging depth made by the after-impact particles, but raises the crossflow velocity through the sweeping effect. This enables the smoothening process to extend beyond the restriction imposed by a repeating action of dull particles, and results in the brittle-fractured surface to be flattened and smoothened.