Experimental and numerical study of the closure of voids with different size and various locations in the three-dimensional cogging process

In this paper, a new forging system was developed and a new complex methodology was tested for the analysis of the closure of voids. The effective geometric shapes of anvils and optimal the forging parameters has been determined. A new cogging process provided a complete closure of voids, which was confirmed by experimental tests. The effect of the reduction ratio, original anvil shape, forging ratio and the location and size of introduced voids on the efficiency of void closure during the multi-transition cogging process was assessed. Moreover, the following were used for the evaluation of void closure: the hydrostatic stress around voids, stress triaxiality, effective strain around voids, and the critical reduction ratio. Numerical examinations were performed using the finite element method (FEM) for the three-dimensional forging process at elevated temperature. Computer simulations of the cogging process under investigation were carried out using a program DEFORM-3D, and selected simulation results were compared with experimental test results. Void reduction predictions obtained from the FEM analysis were in good agreement with the experimental findings. The test results are supplemented with the prediction of crack formation in the zone of existing voids and within the forging volume during the multi-transition cogging process.