Flexible sheet metal forming processes possess significant potential in today's industrial goods market with the advent of the next generation manufacturing paradigm, which put stresses on products customization and cost efficiency. However, due to the unique tooling configurations and forming mechanisms adopted in different flexible sheet metal forming processes, there exist many technical challenges to be tackled to fully facilitate the manufacturing potential of the flexible forming processes. For example, the typical material deformation paths in double-sided incremental forming (DSIF) – a highly flexible dieless sheet forming technology – are rather different from that of conventional sheet metal forming processes (e.g., sheet metal stamping), and such a difference makes it challenging to analyze and optimize the process variables for securing satisfactory product qualities when varies part designs are targeted.In this study, technical challenges in selected flexible sheet metal forming processes will be addressed and new process design and analyses approaches will be introduced to tackle the challenges. More detailed outline of the research contents included in the current thesis for two kinds of flexible sheet metal forming processes, which are DSIF and press brake angle bracket forming, is as follows:1) A new DSIF toolpath strategy for accurately manufacturing corrugated structures is introduced for the purpose of extending the range of product families that are manufacturable by the forming process. The new toolpath strategy named Regional Plastic Incremental Bending (RPIB) is designed to enhance the overall manufacturing accuracy of formed corrugated parts by reducing the effect of in-process global springback occurs in DSIF by the contacts between the tools and sheet, and its development process is explained. A set of experimental verifications prove that the manufacturing accuracy with a use of the RPIB strategy is significantly enhanced compared with a more basic DSIF toolpath strategy for manufacturing corrugated structure (which will be referred to as linear toolpath in the chapter) that resembles the regular toolpaths used for forming generic three-dimensional features (e.g., truncated cones and pyramids).2) Detailed numerical analyses of full-scale DSIF processes using the finite element (FE) method are conducted, mainly considering the effects of materials kinematic hardening behavior and structural compliance of the forming machine on the numerical prediction of the forming forces and formed geometries. A simple method of virtually measuring the material softening by kinematic hardening with non-monotonic loading paths in the DSIF process is introduced, so that the material softening effect can be correlated with the observed changes in the numerically predicted forming forces and formed geometries.3) A study of a press brake operation for flexibly manufacturing darted angle brackets is conducted. A combined analysis approach utilizing both FE analyses and experimental trials is established to understand the materials deformation mechanics in the darted bracket manufacturing process. Furthermore, a systematic method of determining the minimum applicable sheet size for successfully manufacturing darted brackets based on the given material properties and tooling condition is established. To make the study more comprehensive, a testing method for quantitively measuring the stiffness of formed angle brackets is also introduced, with actual experimental examples for evaluating the stiffness improvements with darts in angle bracket design and manufacturing are given.The overall study will be concluded by addressing the highlights of each research section in the end of the thesis, along with several suggestions of possible future research directions that can be extended or branched out based on the contents introduced throughout the thesis.
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