Influence of variable loading path pattern on deformation and grain size in large-scale electric upsetting process of Nimonic superalloy

As for the electric upsetting process of large-scale valves, it is a significant issue to design and coordinate processing parameters aiming to achieve the control of deformation and grain size. Here, the multi-stage loading paths of variable parameters were proposed, and the principles of parameter loading path design in large-scale electric upsetting process were developed. Wherein the heating current and upsetting force were subdivided into multi stages with respect to upsetting cylinder displacement, and the astern speed of anvil is constant. Following which, the loading path patterns of variable parameters involving heating current, upsetting force, and anvil astern speed were designed, and their influence on deformation and grain size were thoroughly investigated based on the developed multi-field and multi-scale coupling FEM model in electric upsetting process of Nimonic80A superalloy. The results show that the coordination in deformation was achieved by adjusting the peaks of upsetting force and heating current as well as their locations. Under the specific loading patterns of upsetting force and anvil astern speed, the sunken defect in garlic head was eliminated by increasing heating current. Corresponding to various loading path patterns, the variations of maximal grain size and maximal temperature with time were analyzed. It indicates that higher heating current results in significant increase in temperature and grain coarsening, while higher upsetting force and slower anvil astern speed could decrease temperature thus exerting grain refinement. Physical experiment of large-scale electric upsetting process validated the optimized loading path pattern. It illustrates that the designed loading path pattern and developed FEM model can be utilized to guide the actual large-scale electric upsetting process.