SUMMARY

There is a growing demand for micro and meso scale devices in the field of optics, semiconductors and bio-medical applications. In response to this demand, mechanical micro-cutting (e.g. micro-milling) is emerging as a viable alternative to lithography based micromachining techniques. Mechanical micromachining methods are capable of generating three-dimensional free-form surfaces to sub-micron level precision and micron level accuracies in a wide range of materials including common engineering alloys. However, certain factors limit the types of workpiece materials that can be processed using mechanical micromachining methods. For difficult-to-machine materials such as tool and die steels, limited machine-tool system stiffness and low flexural strength of the tool are major impediments to the use of mechanical micromachining methods. This thesis presents design, fabrication and analysis of a novel Laser-assisted Mechanical Micromachining (LAMM) process that has the potential to overcome these limitations. The basic concept involves creating localized thermal softening of the hard material by focusing a solid-state continuous wave laser beam of diameter ranging from 70-120 microns just in front of a miniature (300 microns -1 mm wide) cutting tool. By suitably controlling the laser power, spot size and speed, it is possible to cause a sufficiently large decrease in flow stress of the work material and, consequently, the cutting forces. This in turn will reduce machine/tool deflection and catastrophic tool failure. The reduced machine/tool deflection yields improved accuracy in the machined feature. In order to use this process effectively, adequate thermal softening needs to be achieved with minimum heat affected zone in the machined surface. This requires experimental characterization and process modeling which has been accomplished by completing the following tasks: * Design and fabrication of a laser assisted mechanical micromachining (LAMM) setup with a 35 W fiber laser. * Experimental characterization of the LAMM process for cutting forces, surface integrity (hardness, microstructure, surface finish), and dimensional accuracy as a function of cutting parameters and/or laser variables * Modeling the process mechanics (temperatures and forces) * Optimization of the process variables using engineering-statistical models A key contribution of this thesis is the creation of the underlying scientific and empirical basis needed for future development of production-grade laser-assisted mechanical micro machine tools for milling/turning etc. Potential applications of these machine tools include manufacture of micro and meso scale features in steel/ceramic molds and dies for plastic injection molding of meso-scale biomedical parts, creation of three dimensional micro geometric patterns on hard bearing surfaces, etc.