Fabrication of Free-Standing Structures Using Abrasive/Slurry Jet Micro-Machining

Abstract

<p>Many advanced engineering materials are machined using abrasive water jets, a non-traditional machining method that has certain advantages compared to other approaches. This dissertation aims at developing methodologies to use abrasive water and slurry jets to micro-machine free-standing structures for heat sink and microfluidics applications.</p> <p>The first aim was to fabricate high aspect ratio free-standing structures with a minimum distance between each other that would lead to maximum heat transfer performance in heat sinks. The effect of machining process parameters on the quality of the resulting free-standing structures was studied. It was demonstrated that high-quality free-standing structures with aspect ratios of more than 40 to be used as fins in heat sinks could be fabricated.</p> <p>There is an increasing demand for metallic micro-molds that can be used for inexpensive mass production of polymeric microfluidic chips. Therefore, the feasibility of using abrasive water jet micro-machining (AWJM) and abrasive slurry jet micro-machining (ASJM) to fabricate such micro-molds was studied. Jet raster scans under various combinations of process parameters were used in order to machine micro-pockets containing free-standing structures, representing molds for casting microfluidic chips with channel networks. The optimum process parameters and material were determined in order to fabricate the molds with the best possible surface finish.</p> <p>Because unmasked machining could not be used to fabricate molds with sharp-edged intersecting features, a hybrid AWJM/ASJM masked machining technique was introduced. By careful selection of the process parameters, high quality molds with both single and intersecting free-standing structures at multiple heights could be fabricated, thus making three-dimensional microfluidic chip mold fabrication feasible.</p> <p>Finally, a new method of mold fabrication that utilized water jet cutting technology to cut free-standing structures out of mild steel sheets, to be used as a mold for PDMS casting, was developed. This enabled 3D features having very abrupt changes in depth with almost 90o angles for use in microfluidic devices. As a proof-of-concept, a polydimethylsiloxane (PDMS) chip was made and tested. It was shown that this alternative approach to create microfluidic molds is versatile and may find utility in reducing the cost and complexity involved in fabricating 3D features in microfluidic devices.</p>