Research On Accuracy Control Technology In Incremental Sheet Metal Forming

Incremental sheet mental forming is a novel kind of sheet metal forming technology which suitsspaceman and small batches. During the process, the sheet metal part is formed layer by layeraccording to the CAD model. Because of localized deformation, parts formed by incremental formingare of low accuracy, which makes it very difficult to popularize the novel process in the actualengineering. To solve the problem, some forming defects which affect the forming accuracy and finalappearance were investigated and some optimized processes, whose feasibility and validity have beenproved in experiments, were also proposed. Main achievements are shown as followed:(1) Study on forming mechanism. The deformation process was studied with more details, andthe deformed area was divided into three different zones, namely primary deformation zone,transitional deformation zone and completed deformation zone. The disciplinarian of strain, stress andforming force was studied based on pure shear deformation hypothesis. A method of stress calculation,considering the uneven stress distribution, was proposed. In addition, a method of forming forcecalculation, considering the working hardening of the material and more similar to the hypothesis ofpure shear deformation and rigid end, was proposed(2) Study on forming defects and influencing factors. Effect of the deformation of forming toolswas investigated by experiments and numerical calculation. Some accuracy defects, namely bulge innegative and positive incremental forming, bulge of the flat wall, spring back and involvingdeformation, were experimentally studied to find out the relationship between forming defects andprocess parameters.(3) Study on optimized process. Some optimized processes which benefit forming accuracywere proposed. The optimized processes are listed as followed: employing flat end forming tools toreduce bulge height in negative incremental forming and spring back; setting displacement of theclamping frame and employing flat end forming tool to avoid bulge in positive incremental forming,groove and edge warp; employing localized heating to reduce bulge of the flat wall and involvingdeformation and proposing a helical tool path generation method without interference and formingefficiency decrease. The validity of the optimized processes was proved by experiments.(4) Study on compensation forming process. A simple-measurement based method ofestablishing compensation model was proposed. Effects of spring back and bulge of flat wall werereduced significantly by the compensation forming process. In the study of establishing the compensation model of bulge of flat wall, a second-degree surface based model was proposed to fitthe bulging shape and makes it much easier to realize compensation forming process.(5) Study on trimming deformation. Rudimental stress was caculated by numerical method, andeffect of process parameters on trmming deformation was studied experimentally. The method ofreducing triming deformation by anneal treatment was proposed. Some extra experiments werecarried out to confirm320℃as the best anneal temperature.(6) Finally, the optimized processes proposed in the thesis were tested by manufacturing twoactual spacemen. For the cover board part, bottom bulge and edge warp was avoided by employingthe flat end tool and anneal treatment respectively. Meanwhile, edge warp was deleted by negativeincremental forming. In addition, localized compensation forming process was employed to reducebulge height of flat wall of complex parts.