| Laser forming (LF) is a non-traditional manufacturing technique that utilizes thermal strains induced by local temperature fields to alter the shape of a component without hard tooling or external forces. It can be potentially used for bending and forming of structures made of sheet or tubular metal, for compensation for distortion induced by, e.g., welding, and for adjustment of, e.g., micro-devices. This dissertation is part of the NIST-sponsored project "Laser Forming of Complex Structures," whose objective is to develop technologies for a controllable, repeatable laser forming process that shapes and re-shapes a range of three-dimensional objects. In order to achieve the objective, a number of issues concerning the effects of non-uniform material properties and geometry, on laser forming process analysis and process design need to be investigated.; To understand the effect of the cold-rolling induced anisotropy on laser forming, the textures of cold-rolled steel sheets are characterized, and the effects of the plastic anisotropy on bending deformation during the laser forming process are investigated experimentally and numerically. Geometric effects play an important role in laser forming processes; however, few investigations have explored the geometric effects other than those related to the sheet thickness. In this dissertation, the influence of component size, including sheet width and sheet length, on laser-induced deformation is investigated. Distinctive trends in bending angle are identified when sheet width, length or both vary. The results are interpreted in terms of heat sink effect and bending non-uniformity. An analytic model is developed to facilitate size effect prediction. The model is based on the solution to a moving strip heat source over a finite size sheet. It also accounts for the pre-bending effect among consecutive segments on the scanning path.; To utilize laser forming in shape tuning of compressor airfoils, process analysis and process synthesis (design process parameters such as scanning paths and heating conditions for a desired shape) of LF of non-uniform thickness plates are conducted in this dissertation. A strain-based strategy for LF process design for thin plates with varying thickness is proposed. The scanning paths are then determined by considering the relative importance of bending strain and in-plane strain. The heating conditions are determined by implementing the required ratio of the bending strain to the in-plane strain. The determination is aided by a database, which is established via the finite element method (FEM) over a wide range of process conditions. The approach is validated by numerical simulation and experiments involving several typical shapes.; In the present work, laser forming is investigated for the post correction of the butt-welding induced distortion. The LF correction paths are determined based on the magnitude and direction of bending angle and the longitudinal residual stresses. Through the experimental validation, it is found that the proposed laser forming strategies can reduce not only the welding-induced distortion, but also the tensile longitudinal residual stress on the welded surface. |
