Browsing by Author "Fetene, Besufekad Negash"

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    Study on the performance of laser based bending
    (2018) Fetene, Besufekad Negash
    Laser based bending is a process of bending of different workpieces by using a controlled moving or stationary laser heat source, which induces thermal stress to achieve the desired bending. Recently, laser bending has received attention for a wide variety of applications in industries due to its excellent bend quality with high productivity and flexibility. Researchers studied the effects of different process parameters related to the laser source, material and workpiece geometry on laser bending of sheets. In this thesis, experimental study and finite element method (FEM) simulations of various kinds of laser based bending are reported. The FEM was used to predict bend angle, edge effect, temperature variation, stress and strain. The focus of the work was to study the performance and robustness of the process for filling the research gap in the literature.First, the bending of small sized steel sheets was carried out with stationary and moving laser heat sources. Effect of laser power, workpiece geometry (length and width), laser spot diameter and laser scan speed on the achievable bend angle in a single pass is studied numerically as well experimentally. Afterward, the multi-pass laser bending of steel strips was studied. Effects of process parameters on bend angle, edge effect, temperature distribution, stress, plastic strain, flexure strength, microhardness and microstructure was studied. It was encouraging to note that FEM could predict the bend angle with the maximum error of 11%.Laser bending of friction stir welded aluminium alloy sheets was also studied. Considering the difficulty in obtaining the temperature dependent material properties, an inverse methodology was employed. The inverse methodology is based on the measurement of bend angle and temperature at two locations during laser bending. To reduce the computational time, the techniques of forced cooling and mesh optimization were used. The deviation between experimental and numerical simulation results was less than 10% in all except one case of 16% deviation.