Influence of die parameters on the deformation characteristics of cross wedge rolling steel balls: modelling, numerical simulation and experiments

Abstract How to choose appropriate tool parameters has always been a challenge in the cross wedge rolling (CWR) process, as different tool parameters affects the instantaneous metal deformation pattern and effective strain, thereby affecting the geometric dimensions and mechanical properties of the formed workpiece, especially for CWR steel balls with both radial and axial forming degrees of freedom. This paper proposed four novel forms of forming angle design for CWR dies and different sizes of spreading angles. The effect of different tool parameters on the deformation characteristics of CWR steel balls was analyzed using a combination of theoretical modelling and finite element (FE) simulation analysis. The analysis indicated that the axial deformation parameters increased linearly while the radial deformation parameters increasesd exponentially during the CWR process. The steel balls obtained from equal or small arc forming angles had better roundness and filling than those obtained from fixed forming angle and large arc forming angle. When the forming angle is fixed, the larger the spreading angle, the more metal volume participates in deformation per unit time, and the more severe the deformation. Finally, tool parameters with a fixed forming angle of 30° and an equal arc forming angle, as well as a spreading angle of 8°, were selected for comparative experiments on steel balls forming. The experimental results indicated that the size accuracy of steel balls obtained by equal arc forming angle was relatively high, and a larger spreading angle could improve forming efficiency significantly, which verified the reliability of FE simulation simultaneously.