Continuous Rotary Extrusion (CRE) is a continuous extrusion process capable of producing a range of profile shapes and sizes from rod or powdered non-ferrous metal feedstocks.
The CRE process has been in existence since the 1970s and was first invented as a way of recycling chopped copper cathode into new cables and producing special profiles for electrical conductors.
The real benefit of using CRE in industry comes from the large number of process steps that it can replace. When processing copper bus bar, the continuously cast rod feedstock is fed into the machine at room temperature. Through a combination of adiabatic heating and heat transfer from the extrusion tooling the flow path that the copper goes through can be very complicated. The resultant severe plastic deformation completely reworks the microstructure and it emerges from the extrusion die in a fully annealed condition with a cross section over 10 times larger than the feedstock that produced it. All of this is accomplished in a single process step.
Aluminium and copper rod make up the majority of the commercial feedstocks used with CRE and Conform due to their extremely ductile nature. Stronger materials have been harder to extrude and have limited uptake in industry. Powder or granular feedstock also have niche applications as the process conditions are not well understood.
Through a combination of EPSRC and InnovateUK funded projects the STAR group have successfully processed titanium powders into both wire and strip profiles on CRE and Conform machines. This demonstrates the highly flexible nature of the process with both feedstock materials and machines.
The Sheffield Titanium Alloy Research Group has used a multidisciplinary approach, implementing finite and discrete element modelling, lab based powder experiments and time with CRE machines in order to fully understand the powder and material flow through the CRE process. The knowledge developed allows for rapid changes to machine running parameters and tooling to optimise the process for different powder and rod feedstocks.