Optimization of loading path in incremental sheet metal forming

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For the small batch manufacture of non-symmetrical shallow shells, a flexible and incremental sheet metal bulging machine has been developed using a path-controlled spherical roller.The main results of this investigation are as follows.(1) The developed sheet metal bulging machine has the following performances.Stroke : x = 200 mm, y = 300 mm, z = 100 mmTraveling speed : 30 mm/secLocating accuracy : x, y direction <plus-minus>0.03 mm (under load 0.5 kN) z direction <plus-minus>0.03 mm (under load 2(2) The computer controlled bulging machine could perform a wide range of sheet metal shaping of complex shapes, for example pyramidal shells, shells of frustum of pyramid, shallow pans and embossed panels.(3) It was experimentally showed that the optimum loading path in the incremental sheet metal forming was the path which made the strain distribution in the shell uniform.(4) In order to predict the forming limit of the incremental shaping, a new incremental bulging test by a ball punch was performed with annealed aluminum sheet, and the experimental results showed that fracture occurred when the thickness strain reached a constant value.(5) An approximate calculation method of the maximum bulging height of the shell was proposed using this fracture limit and a geometrical deformation model. The predictions for the shells were reasonably in agreement with experimental values of the annealed aluminum sheet.(6) The relationships between the forming conditions of the incremental forming and the strain distribution, the forming limit and the spring-back were clarified by the numerical simulation using the finite element method.