Ceramic sponge Abrasive Waterjet (AWJ) precision cutting through a temporary filling procedure

Ceramic sponge machining after firing is a great issue, requiring special tools and procedures because of the material peculiar macro-structure and its intrinsic brittleness. This study approaches the problem by exploiting the Abrasive Waterjet technology (AWJ) and showing its potential as a flexible tool. Nowadays, AWJ is coming up as an alternative to other ceramic manufacturing processes such as Grinding, Ultrasonic Machining and Laser Machining. The influence of a temporary pore filling agent, infiltrated in the already sintered sponge, is evaluated and its effect on the jet coherence is investigated through both modelling and experimental approaches. The most suitable process parameters are assessed in order to reduce the main AWJ defects in these conditions, setting the feed rate (vf) at 150 mm/min on a 35 mm thick 30 PPI (pores per inch) ceramic sponge on a conventional cutting equipment. The overall kerf divergence is therefore reduced down to less than 1° thanks to the filling procedure and then it is compensated by exploiting a 5-axis cutting centre. Defects are measured, using both conventional and ad hoc tools (e.g. CMM, grazing light surface inspection and digital image analysis). No thermal or chemical actions are applied by the AWJ cutting process and the negligible forces exerted on the struts preserve their integrity. A case study geometry is machined, fulfilling tight tolerances of 0.1 mm on a Ø 10 mm ceramic sponge cylinder over a 15 mm thickness. A complex-shaped component is cut on 35 mm thick sponge.