The goal of this collaborative research project is to investigate a novel electromagnetic peening-assisted laser micromachining process. The research objectives of the project are to understand responses of a workpiece under the simultaneous action of laser beam radiation and compressive forces generated by electromagnetic induction during machining, and to test the hypothesis that, during the electromagnetic peening-assisted laser micromachining process, the application of electromagnetic forces can generate a beneficial peening effect, enhancing the mechanical properties of the workpiece. A physics-based model will be developed based on continuum mechanics and Maxwell's electromagnetic field theory, which can predict and help understand the process mechanism. The model will be tested by comparing with experiments that include both in-situ observations of the electromagnetic peening-assisted laser micromachining process and the characterization of the processed workpieces. The machining rate, microstructures and residual stresses will be characterized using an optical surface profilometer, scanning and transmission electron microscopes and X-ray diffraction respectively. The fatigue properties of machined samples will also be tested.
If successful, this research will provide an improved understanding of material response under laser radiation and electromechanical forces. The electromagnetic peening effect is expected to enhance the mechanical properties of laser-machined workpieces, with a potential to improve product quality. This technology is environmentally friendly as it does not involve harmful chemicals. Better product quality and longer lifetime decrease the need for re-manufacturing and hence imply less energy and material consumption and less waste generation.
Project Outcome Report This report mainly contains the major outcomes of this NSF award (Award : CMMI 0970079). Please read the outcome report of the collaborative NSF award (Award: CMMI 1000226) for additional information. During this project, the evolution of plasma produced by intense nanosecond laser ablation of metal in vacuum under an external magnetic field has been studied using a two-stage model. It has been found that under the investigated conditions, due to the presence of the magnetic field, the plasma velocity is reduced, while the plasma overall temperature is increased, and its parameter spatial distributions (e.g., temperature and density) become relatively more uniform. Using a three-dimensional electromagnetic (EM) and mechanical model, theoretical calculations under the simulated conditions have shown that passing a "coil" with an electric current pulse can induce EM forces in an aluminum alloy workpiece placed nearby, and can generate surface compressive residual stress at the bottom of a pre-existing hole in the workpiece, which, however, requires a very high coil current. An EM shot peening process that requires a lower coil current has been experimentally studied. It has been found that under the studied conditions, the EM shot peening process has enhanced the surface morphology quality around the boundary of a laser-machined microhole, and the surface morphology change also suggests that compressive surface plastic deformation has probably occurred around the hole boundary, which may be potentially beneficial to the material mechanical properties. Intellectual Merit: This project may improve our understanding of laser-material interactions during pulsed laser micromachining (ablation), particularly when magnetic field is present, and may also improve our understanding of the interaction of electromagnetic forces with materials. Broader Impact: The gained understanding from this study may potentially provide useful information to help improve laser machining processes or electromagnetic (EM) technologies that involve the interaction of EM forces with materials (such as EM peening or forming), and therefore may possibly benefit relevant products whose manufacturing needs laser machining or the EM technologies, and generate related benefits to the society.
