Modeling of heat transfer and material flow in friction extrusion process

Friction extrusion is a novel and efficient manufacturing process for producing high-value material (e.g., metal wires) from low-cost precursors (e.g., powders) or from recycled metal wastes (e.g., chips). In the friction extrusion process, the precursor material experiences high pressure and frictional heating and undergoes large deformation and material flow before it is extruded to create the final product in the form of a wire. A three-dimensional thermo-fluid computational fluid dynamicsmodel has been developed to study the heat transfer and material flow patterns in the friction extrusion process. The precursor material in this study is aluminum alloy 6061 and it is modeled as a viscous non-Newtonian fluid with a viscosity that is temperature and strain rate dependent. The heat source because of viscous dissipation and frictional heating is modeled with a user defined volume heat source in a thin layer volume near the tool–precursor interface. The total heat source is taken to equal to the mechanical power input in the friction extrusion experiment. It is found that temperature predictions match reasonably well with experimental measurements. In order to study material flow patterns in the friction extrusion process, a small wire of different material was inserted into the precursor material in the experiment as a marker material and the marker material can be observed on extruded wire cross sections. Correspondingly, in the modeling, massless solid particles were released in the fluid as marker particles and they can be tracked and observed on extruded wire cross sections. The massless marker particles do not affect the fluid field and they flow with nearby fluid so they can represent the motion of the fluid where they were initially released. Both predictions and experimental measurements about the markers observed on extruded wire cross-sections show some features in common, such as (a) markers form continuous spirals on the cross-sections, and (b) the number of spirals decreases as friction extrusion continues. Results of this study suggest that the proposed thermo-fluid model can capture the main features of the heat transfer and material flow phenomena in the friction extrusion process and can be used to provide reasonable predictions of the temperature and material flow fields in the friction extrusion process. KEY WORDS Friction extrusion; Particle tracking; Heat transfer; Thermo-fluid modeling; Material flow pattern ACKNOWLEDGEMENTS The financial support provided in part by NASA Consortium Agreement NNX10AN36A and by the National Science Foundation through NSF-CMMI-1266043 is gratefully acknowledged