Flow Fields and Particle Trajectories in Abrasive Slurry-jet Micro-machining of Sintered Ceramics and Metallic-layered Structures

摘要

The extreme hardness of sintered ceramics makes it difficult to machine them economically. Abrasive slurry-jet micro-machining (ASJM), in which a target is eroded by the impingement of a micro-jet of water containing fine abrasive particles, is a low-cost alternative for micro-machining of sintered ceramic materials without tool wear and thermal damage, and without the use of patterned masks. The experimental phase of the present research utilized several model systems that have industrial relevance while incorporating sufficient generality to illustrate generic characteristics of ASJM of ceramics and metallic-layered structures. Experiments were complemented by extensive computational slurry-flow modeling to understand the effects of the ASJM process parameters on the particle trajectories and the resulting erosion.;In this study for the first time, computational fluid dynamic (CFD) modeling was used to derive a generalized relation between channel geometry and erosive flow, which was used in an existing numerical-empirical model to predict the cross-sectional profiles of ASJM micro-channels in sintered ceramics. The predictions agreed with experimental measurements to within about 8%.;It was found that cavitation played a significant role in the slurry erosion of curved features such as the edges of holes and channels. Features with sharper edges, flat bottoms, and relatively steep sidewalls could be machined by minimizing cavitation through the use of liquids with low vapor pressure and relatively high viscosity.;The use of ASJM to polish channels was investigated experimentally and with CFD. Post-blasting channels after their initial machining under typical process conditions reduced the Rrms roughness to about 23 nm in brittle and ductile targets.;Flat micro-pockets in sintered ceramic substrates containing copper-filled through-holes were machined using a hybrid AJM (abrasive jet machining)-ASJM methodology, in which AJM was used to selectively erode the brittle ceramic without etching the ductile copper, followed by levelling of the protruding copper pillars to the depth of the ceramic using ASJM.;It was demonstrated that electrodeposited copper and nickel-phosphorous layers could be selectively removed without eroding the underlying ceramic or metallic substrate using over-lapping ASJM channels. A CFD-aided process design methodology was developed to predict the ASJM parameters to remove a given coating thickness.