Enhancement of efficiency and accuracy of laser based bending and straightening processes

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Laser based bending process is an advanced process in sheet metal forming in which laser heat source is used to shape a metal sheet. The process has many advantages over conventional forming processes. It is a contact free forming process and is suitable to carry out bending and straightening at areas unachievable by conventional forming. The process is convenient to generate very small and accurate bend angles. The laser bending process can also bend brittle materials in some cases. It is also possible to generate complex shapes by employing a suitable scanning strategy. Basically it is a thermo-mechanical process. Literature contains effects of different laser process parameters, material and workpiece geometry on laser bending. The recent interest in laser bending research and development reflects the industrial potential of the process. Several research groups are currently investigating the fundamentals and applications of laser bending. Several analytical and numerical models have been developed. The forming mechanism of complex sheet geometries has been analyzed using software based on finite element method (FEM). Many studies involved moving laser sources with straight and curve laser beam paths. However, scant attention has been given to the reverse process i.e., laser based straightening. Limited research outputs are available in the literature about straightening. The focus of this thesis is on enhancement of accuracy and efficiency of the laser based bending as well as straightening. First, in this work the deformation of a sheet, subjected to irradiation, has been studied through a series of experiments where the metal surface was coated with black enamel paint for enhancing the absorptivity of laser and thereby acquiring a higher bend angle. Use of black enamel paint on laser bending resulted in a large increase of bend angle in a mild steel sheet. Later on, a strategy is proposed for choosing the parameters of multi-pass laser line heating for obtaining the accurate bend angle for a prescribed accuracy of prediction. The strategy was verified with experiments for three different materials.
Supervisor: Uday Shankar Dixit and Karuna Kalita