Development of a laser-based surface finishing tool.

摘要

This dissertation describes an innovative laser-based technique for tangentially finishing axisymmetric parts without tool wear, tool breakage, or cutting forces. Specific points of discussion in this dissertation include: (1) A new laser-based finishing tool with tangential beam impingement setup. The two configurations of this finishing tool are fixed and scanned beam finishing. Design and assembly of the laser finishing system given a 1kW high-power CO{dollar}sb2{dollar} laser system (Coherent EFA-51) is performed. (2) Circular finishing experiments on PMMA and Si{dollar}rmsb3Nsb4{dollar}. The relationship between the achievable surface roughness and the relevant process parameters is qualitatively studied through process characterization. Surface roughness is measured through stylus-based profilometry. Finished workpiece microstructure is measured through Scanning Electron Microscopy (SEM). (3) Analyses for circular finishing process. A sensitivity analysis of the process parameters is performed through a Taguchi method-based three-level Design for Experiments. A comparative analysis of energy efficiency, material removal rate and achievable surface quality for laser finishing and mechanical grinding is conducted. (4) A steady-state model of the beam/workpiece interaction in circular finishing. This model is designed to estimate the groove profile and the material removal rate. An energy balance equation incorporating laser beam energy, material phase change energy and conduction loss is derived and solved in the static model with the employment of the conformal mapping technique and the discretized domain integration. (5) A dynamic model of the beam/workpiece interaction in circular finishing. This model is designed to estimate the resulting surface topography and the surface roughness. Dynamic factors in laser machining such as laser beam variations, workpiece positioning system variations and workpiece variations are considered in the dynamic model through the Taylor Series Expansion of a small perturbation of the nominal value. (6) A frequency-based approach for non-circular finishing. The frequency characteristics of a desired non-circular profile is extracted through a Fast Fourier Transform algorithm and implemented in the laser finishing system by oscillating the workpiece sinusoidally. Non-circular PMMA parts including continuous and discontinuous profiles are machined. The process capability of non-circular finishing is determined through dimensional accuracy analysis and measurement of the shaped profiles. (7) Simulation models of the beam/workpiece interaction in non-cirular finishing. Graphical simulation programs are structured in C language with X11 protocol. Laser beam kinematics models such as collimated and convergent/divergent beam model with graphical user interface (GUI) are developed to estimate the resulting non-circular profile for given input of process parameters. Static and dynamic models are developed to estimate the demensional accuracy parameters such as edge straightness, angularity, parallelism and feature size for the finished non-circular profiles. (8) A process control scheme to improve the dimensional accuracy in non-circular finishing. An analysis in performed on the regulation controller's performance such as stability and robustness. A simulation model of the plug-in repetitive controller is developed to determine the performance of tracking the desired trajectory. A feed-forward repetitive controller is implemented to achieve more precise tracking of the desired sinusoidal trajectory and compensation of the periodic disturbances. Non-circular shaping experiments with the repetitive controller are performed on PMMA. (Abstract shortened by UMI.)