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Study on Numerical Oscillations of Forming Load Occurring in Forward Open Cold Extrusion

A forward open cold extrusion process is evaluated to reveal the sensitivity of forming load to numerical factors including number of total degrees of freedom, time step size and mesh size. The allowable reduction of area was examined by varying number of finite elements and the total solution steps to determine the reliability, in which the results are affected significantly by the positions of the lowest and highest nodal points in contact with the die. An investigation of the oscillations of the forming load in forward open extrusion revealed a set of critical numerical conditions that minimize unwanted oscillatory behavior. The limits of the material initial radii were obtained, suggesting that rigid plasticity with rigid dies is inappropriate for simulations of forward open cold extrusion with extreme reduction of area. Due to artificial numerical deformation of the rigid zone and die elastic deformation thus each of which has a non-negligible influence on the maximum reduction of area.