A batch-mode micromachining process for spherical structures

Abstract

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 (R a) of the machined surface and the product of the fracture toughness (K IC) and the hardness (H) of the workpiece material (K IC 3/2 H 1/2).

Batch Mode Microultrasonic Machining (<inline-formula> <tex-math notation="LaTeX">$\boldsymbol \mu $ </tex-math></inline-formula>USM) Using Workpiece Vibration

“…The tool wear, i.e., the ratio of the tool height worn to the machined depth, was <4%. In comparison, µUSM performed by vibrating the tool has been reported to result in machining rates of >100 nm/sec and tool wear <6% for similar conditions [2], [3]. Further, simulations indicate that tools with 20-µm feature sizes provide fluid velocities that are similar to the 50-µm tools in each of the five regions (A-E).…”

High resolution micro ultrasonic machining for trimming 3D microstructures

“…These ceramic materials are mostly transparent, insulating, and brittle and are not well suited for machining by laser, electrodischarge machining, or micromilling/drilling. The μUSM process is appropriate for micromachining both planar and 3D structures of brittle materials without inducing stress or subsurface cracks [8][9][10][11]. The machined features can have an average surface roughness as low as 0.25 μm [12].…”

“…Conventional μUSM typically aims to rapidly remove material, with typical machining rates of >200 nm s −1 . The average surface roughness achievable using conventional μUSM is typically 200-400 nm [8][9][10][11].…”

High resolution micro ultrasonic machining (HR-&#x03BC;USM) for post-fabrication trimming of fused silica 3-D microstructures

“…Our previous work has demonstrated a µUSM process for die-scale pattern transfer in ceramics [4]. We have also presented a process that combines batch-mode µUSM, lapping, and micro electrodischarge machining (µEDM) for microfabrication of spherical structures [5]. In these µUSM processes, it is desired to rapidly remove material, with typical machining rates exceeding 200 nm/sec.…”

“…In these µUSM processes, it is desired to rapidly remove material, with typical machining rates exceeding 200 nm/sec. The surface roughness is typically 200-400 nm [4][5][6].…”