Green ceramic machining: A top-down approach for the rapid fabrication of complex-shaped ceramics

Green ceramic machining (GCM) has been investigated as an alternative method for the mould-free fabrication of complex-shaped ceramics, where ceramics in ‘unsintered’ green state are machined to complex-shaped via CAD/CAM technology. Recent advancement of CNC machining technology makes GCM a potential alternative for the rapid fabrication of ceramics, especially for some one-of-a-kind products. In this work, we investigated two processing routes to make ceramic green bodies which were suitable for green machining. The effects of processing methods on the green ceramic strength and toughness, machinability and surface finishing of the final ceramics were discussed. Examples of applications of the GCM in the fabrication of ceramic lattice scaffolds for bone tissue engineering and dental restorations have been demonstrated. The results show that gelformed ceramics have better mechanical properties and machinability than protein coagulation cast ceramics. But the debinding for gelformed thick wall components was found more difficult. It is therefore more suitable for the fabrication of ceramic microcomponent or thin sheet structures such as ceramic lattice scaffolds. Protein coagulation cast ceramics have good machinability and surface finishing for thick wall ceramic components. However, inhomogeneous and anisotropic shrinkage of complex-shaped ceramics were observed during sintering stage. Possible causes and solutions have been discussed.