Experimental–numerical investigation of force-controlled friction extrusion process via feedback-controlled simulation

Friction extrusion is an emerging solid-state manufacturing technique for producing rods and tubes, but ensuring uniform microstructural properties along the extrudate length remains a major challenge. This work introduces, for the first time, a feedback-controlled friction extrusion framework in which high-fidelity smoothed particle hydrodynamics (SPH) simulations are coupled with a proportional–integral–derivative (PID) controller to regulate the force-controlled process numerically. Unlike existing numerical approaches that rely on experimentally prescribed die displacement or velocity profiles, the proposed PID–SPH framework allows die displacement to evolve naturally in response to material resistance while maintaining a prescribed extrusion force. The framework is implemented in a GPU-accelerated SPH solver, enabling fast and efficient simulation of the nonlinear thermomechanical behavior inherent to friction extrusion. The PID-SPH framework is validated against experiments on the extrusion of 14 mm rods from high-strength AA7075-T6 billets using a flat die, with comparisons in extrusion force, die plunging displacement, and temperature evolution. Thirteen thermocouples positioned at different radii and depths provided detailed thermal data at the die–billet interface and within the billet during the process. The results demonstrate that the PID–SPH framework accurately captures the force-controlled thermomechanical response of friction extrusion. Beyond predictive accuracy, the framework provides insight into the origin of microstructural nonuniformity along the extrudate length by resolving the coupled evolution of strain rate, material flow, and thermal fields under applied force. These insights support the identification of key factors governing grain size variation and the evaluation of mitigation strategies, such as controlled thermal management, to promote more uniform microstructural development.