Controlled Depth Micro-Milling of Aluminum Oxide Using Abrasive Waterjet Machining to Create Micro-Molds with Free-Standing structures

Abstract

<p>Abrasive waterjet machining has gained popularity due to the many advantages it possesses over conventional machining systems. These include the high achievable tolerance as well as minimal tool wear since it is a non-contact machining method.</p> <p>Previous studies utilized stainless steel masks cut using abrasive waterjet micro-machining (AWJM) together with abrasive slurry jet micro-machining (ASJM) to mill micro-molds in Al6061-T6 for the casting of polymeric microfluidic chips with intersecting micro-channels. However, the deflection of the slurry jet from the mask edge was found to lead to two undesirable effects: a trench along the edges of the raised structures representing the channels, and an undercut of the mask. Both effects were linked to the propensity of ductile materials to erode more rapidly at oblique incidence rather than perpendicular incidence. This thesis investigates the hypothesis that these effects can be greatly reduced by using AWJM to machine the molds into more brittle materials which erode in the opposite fashion, i.e., more rapidly at perpendicular than oblique incidence.</p> <p>To demonstrate this, AWJM was used to machine masks from aluminum oxide and subsequently mill micro-molds with raised intersecting free-standing structures into aluminum oxide substrates. By controlling the process parameters, it was found that for molds of identical depth, the undercut was reduced by five times and the undesirable erosion was reduced by about four-fold when compared to molds machined in Al6061 using the AWJM/ASJM hybrid technique. It was also found that much deeper molds could be made in aluminum oxide, with intersecting raised free-standing structures of up to 435 μm in height while still maintaining an acceptable surface quality, undercut, and undesirable erosion. Finally, since the technique involved only AWJM, it was much more convenient than the previously utilized hybrid AWJM/ASJM.</p>