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Abstract
A novel hybrid laser-waterjet machining technology is developed in this thesis using a new material removal concept to achieve near damage-free micromachining. Using this concept, a laser is used to heat and soften the material while a waterjet is used to expel and remove the laser-softened material in a layer by layer manner, so that material is removed in its solid-state below its melting temperature. Water also takes a cooling action. An experimental rig has been built to realize this novel concept and an extensive experimental investigation has been carried out to understand the process and the effect of various parameters on the process using a single-crystalline silicon as the specimen material. It has been found that near free of heat-affected zone and high material removal rate can be achieved when using this hybrid laser-waterjet technology, as compared to the dry laser micromachining process. Specifically, a laser Raman spectroscopy study has found that a much thinner amorphous layer within 40 nm was formed than that found in the dry laser machining process.
In order to understand the coupled effect of laser and waterjet on the material removal process and to predict and control the process on a mathematical and quantitative basis, a temperature-field model has been developed whereby a model for the dry laser machining process is developed first before it is extended to the hybrid laser-waterjet process incorporating the waterjet cooling and expelling effects. The parabolic heat conduction associated with enthalpy method is numerically solved by using an explicit finite difference scheme for predicting the two-dimensional temperature field. The thermal model has been verified by comparing the predicted temperatures with the temperatures measured by an infrared camera. The simulated groove depths are also compared with the experimental data under the corresponding conditions and it is found that they are in good agreement. A simulation study of the hybrid laser-waterjet process is finally reported which provides an in-depth understanding of the material removal process and mechanisms and the interaction between laser, waterjet and material under the coupled effect of laser heating and waterjet cooling and expelling.