Comparison of different machine control modes during friction extrusion of AA2024

The friction extrusion process has recently been explored for manufacturing extrudates with unique microstructures and improved material properties. The process can be classified as a severe plastic deformation (SPD) process in which the compressive shear strains and friction induced heat play a key role in achieving an intensely refined microstructure. The micro structure can be orchestrated by distinctive heating and plastic deformation conditions from different process parameters, viz. extrusion force, extrusion speed, spindle rotation speed, etc. Notably, the process dynamics lead to different strains and temperatures across the traverse and longitudeinal sections of the extrudates, eventually resulting in distinctive microstructures. The present work focuses on comparing the responses of two different machine control modes viz., force and displacement control. The extru date produced using displacement-control mode exhibited superior process stability, whereas force-control mode resulted in a more unstable process characterized by fluctuating spindle torques, varying extrusion speeds, and elevated temperatures, ultimately leading to lower extrudate quality. These process variabilities were reflected in the micro structures of the extru dates, particularly in the grain structures and defect formations.