The objective of this research project is the conception of a new micromanufacturing process that emulates the material removal mechanisms that characterize micro electro-discharge machining. It will not require the use of electrodes and will not be limited to conductive materials only. The process will use ultra-short laser pulses focused in a dielectric slightly above the workpiece surface - instead of electric discharges between an electrode and a conductive workpiece - to create plasma whose explosive expansion facilitates material removal. The work will involve a substantial experimental component focused on the physical realization of the process. In addition, process characterization will be performed through the use of embedded micro-sensors to measure the temperature and stresses just below the source of the shock waves created by the plasma. The theoretical work will focus on the modeling and control of plasma properties and on the investigation of the physical principles that govern the laser-induced plasma-assisted process with emphasis on plasma-matter interaction and the material removal mechanisms.
The new processes will offer unique capabilities not achievable by other currently existing competing methods for the manufacture of micro-scale components and features with high relative accuracy and complex geometries in a wide range of engineering materials. It will also entirely circumvent problems and costs associated with tool manufacture, wear and compensation in micro electro-discharge machining and the complexities of conventional laser processing. Real time process monitoring of the newly developed process through the use of embedded micro-sensors will offer an unprecedented instantaneous insight into the thermal and mechanical responses of the material during processing. This monitoring technique, once successfully realized, will also be applicable to other micro- as well as macro-scale process monitoring tasks.
The overarching objective of the project was the conception, physical realization and assessment of a novel laser-based multi-material tool-less micro-machining process – Laser Induced Plasma Micro-Machining – that was motivated by the need o complement existing micro-manufacturing process capabilities and to overcome ome of their limitations. The salient characteristic of this process is that n it, unlike in conventional laser ablation in which the laser beam is irectly focused on the surface of the part to remove material, the beam is ocused slightly above the surface of the part that is submerged in a ielectric medium, e.g., distilled water. In this scenario, the plasma that is enerated in the dielectric upon its expansion is the principal factor that leads o material removal through both mechanical and thermal mechanisms. The work performed has focused on: (a) generating and controlling plasma characteristics, and understanding its dependence on laser and processing parameters, (b) process characterization based on experimental investigations of the effects of various process parameters on the geometric characteristics of the components and micro-features generated, material removal rates as a measure of productivity and the heat-affected zones around the of micro-features generated, and (c) theoretical investigation of the physical principles that govern the process with particular emphasis on the different aspects of plasma-matter interaction and on the material removal phenomena. It has been confirmed that this newly conceived process is feasible; it offers a number of advantages over existing processes and has the potential to be further enhanced in terms of accuracy and productivity in the future. Specifically, it has been shown that features in the micro-meter range can be successfully machined and that materials that are difficult to process by conventional means, e.g., non-conductive, transparent, highly-reflective and polymers can also be processed. A comprehensive comparative assessment of the machining capabilities has also revealed that the process is capable of machining micro-features generally with better geometric characteristics, i.e., near vertical wall geometry, minimal built-up edges, uniform transverse and longitudinal depth profiles, low heat affected zone, and low surface roughness, than conventional micro-electro-discharge or laser ablation processes.
