A study of micro-machining thin workpieces.
Date of Issue2012
School of Mechanical and Aerospace Engineering
Thin sheet molds with micro-features are needed in the hot roller embossing process to mass produce cheaper and disposable polymer microfluidic devices. Fabrication of thin molds using mechanical micro-machining techniques has some advantages over lithography and MEMS based processes: capability to manufacture 2D, 2 ½D and 3D features, and ability to process a wide range of workpiece materials. However, several challenges remain in using the machining process where the micro-feature dimensions created in the surface of a thin mold can be comparable to mold thicknesses. This thesis examines micro-machining of thin (< 100 µm) workpiece materials, a topic rarely discussed in the literature. A significant difference in machining thin workpieces compared to thick ones is the ratio of depth of cut to the workpiece thickness; in the former this ratio is very small (~1) whereas in the latter it is very large (~1000). Hence, the machining induced mechanical and thermal loading can be significant on the machined workpiece material. This thesis studies four specific issues in machining such thin workpieces: • Effect of the reduced workpiece thickness on the cutting process. • Machining induced residual stress and warping due to the reduced workpiece thickness and substrate elastic properties. • Microstructural changes in the workpiece material. • Burrs reduction. The approach taken includes both experimental and simulation based investigations. Orthogonal cutting is used to study the effect of workpiece thickness reduction and machining induced warping. Oblique cutting, in the form of single point diamond turning process, is conducted to study the microstructural changes, while a micro-milling process is used to study burr reduction. Finite element simulations are utilized to understand the machining induced stress and the effect of the substrate properties.