A batch-mode micromachining process for spherical structures

This paper reports a self-aligned three-dimensional process (3D-SOULE) that incorporates batch-mode micro ultrasonic machining (μUSM), lapping and micro electro-discharge machining (μEDM) for fabrication of concave and mushroom-shaped spherical structures from hard and brittle materials. To demonstrate the process, 1 mm structures are fabricated from glass and ruby spheres. The μEDM technique is used to create the tool for μUSM from stainless steel spheres. Stainless steel 440, which provides a tool wear ratio <5%, is chosen as the tool material. A 2 × 2 array is used for batch processing. For an ultrasound generator frequency of 20 kHz and a vibration amplitude of 15 μm, machining rates of 24 and 12 μm min−1 are obtained for glass and ruby spheres, respectively. An approximate linear relationship is observed between the measured roughness (Ra) of the machined surface and the product of the fracture toughness (KIC) and the hardness (H) of the workpiece material (KICH).