Laser machining of medical grade Zirconia ceramic for dental reconstruction applications

Abstract

The aim of this project is to provide a fundamental understanding of the processes involved in economically manufacturing complex component parts from medical grade Yttria Stabilised Zirconia. Such material is an attractive choice for many engineering applications, primarily due to its stiffness, hardness and wear resistance. Due to the hardness of the material however, conventional mechanical machining - especially at small micrometer scales - is difficult. As an alternative fabrication route this project investigated the precision limits of machining such ceramics using high power, pulsed lasers operating in millisecond, and nanosecond regimes and at wavelengths of 1075 nm, 1064 nm, 532 nm and 10.6 m. In order to establish the suitability of machined parts for biomedical implant, the use of a Raman Spectrometer was vital to establish the phases present in the final machined parts. The work focuses heavily on the use of Yttrium Oxide (Y2O3) Partially Stabilized Zirconia (PSZ) as it is the prime material used in dental reconstructions to date however a comparison with Alumina is carried out. In depth investigation of the processing parameters used in millisecond Nd:YAG and nanosecond Nd:YVO4 laser sources was conducted providing maximum material removal rates of 13 mm3/s and 2.1 mm3/min respectively. Successful CO2 laser processing was conducted on 8 mm thick samples however, when processing complex components, bulk failures were observed. An un-calibrated infrared camera was used in this process, highlighting potential thermal gradients responsible for bulk fracture. The particularly difficult process of blind hole drilling using a mechanical method has been investigated using a laser to pre-drill a suitable hole before mechanical machining takes place. This investigation has resulted in a 97% reduction in processing time using the developed laser process over the mechanical method used currently. Additionally, a dual laser process is examined in order to provide a two phase machining method utilising the speed and precision of two different lasers respectively. A novel high beam quality laser process is presented which offers a technique to section 14 mm thick samples of the material via a crack propagation method. Future research opportunities have been identified and discussed, focussing on ways to resolve these key issues and other possibilities in laser processing.