Microusinagem a verde de cerâmica avançada

Abstract

The green ceramic machining has been excellent in solving some of the challenges of the hard ceramic machining. The requirements for stiff machine tools, ultra-hard cutting tools for ductile mode of removal make machining difficult, being the fragile mode the dominant one resulting in the introduction of critical defects given the relative high hardness and low fracture toughness of the sintered ceramics. An alternative is to perform the green ceramic machining. Due to the lower mechanical resistance among particles of the part in the green state, it is possible to use less hard cutting tools and considerably increase the removal rate in the formation of the profile with a mechanism similar to that of the ductile regime, with low probability of introducing critical defects. The present work aims to investigate the green ceramic micromilling process of Alumina Calcined A1000-SG parts manufactured with different pressing conditions and amount of PVB binder. Microchannels were manufactured on the surface of the ceramic block with 5 mm in length, under different machining conditions. The results showed that when cutting speeds were higher, material removal occurred predominantly by interagglomerated fractures and the edge detachment was smaller; in addition the down milling exhibited larger edge detachments comparing with the up milling. The chips obtained by interagglomerated fractures presented shear bands and small lamellae. In the analysis of the roughness profiles, typical milling marks on botton of the channels were observed. The numerical reduction of Ra roughness after sintering was approximately 8.99 % for workpieces pressed uniaxially at 100 MPa and 17.72 % for isostatically compacted workpieces at 200 MPa. In relation to volumetric contraction, the microchannels with a depth of cut of 150 μm had smaller contractions than those of 75 μm, due to the greater removal of the density gradient. Regarding to the microtool, it was able to machine 240 mm under different conditions, with a maximum wear of 9.4 μm. In this context, the results obtained validate the green ceramic micromachining as a process of microfabrication of advanced ceramic products.