Friction stir processing has become a popular method for welding, surface treatment, and more recently for producing extrusions such as tubing and cylinders. Currently, the extrusions produced usually have diameters from 6 to 19 millimeters because they are being produced in tooling that must be placed in conventional CNC mills located within university research settings and thus have limited available power as well as limited ability for plunge forces.
The machine described here is purpose built for producing large diameter friction stirred cylinders and tubes that are up to 125mm long and 50mm in diameter. Unlike conventional CNC machines, this machine is designed to accommodate the temperatures generated by the probe rotating against the work piece as well as the higher plunge forces generated by the extrusion processes which can damage the bearings, motor shaft and motor in conventional CNC mills. The need to produce larger friction stir processed parts is important because friction stir processing results in material properties that may be advantageous in parts, may be part of an additive manufacturing process, or may be useful as a preprocessing stage for metal recycling operations which can reduce energy costs and product contamination.
The current paper describes Phase 1 of the project. A-1100 aluminum will be the initial material tested and smaller diameters of harder alloys will be used at some future time. The current phase of the project is nearing completion and consists of the development of the machine frame, open-loop AC motor spindle speed controller, tooling and a method for plunging the probe into the work piece. Phase 2 will consist of implementing feedback control along with process monitoring.
In this paper the design process will be summarized, including forces and temperatures expected during friction stir extrusion and back extrusion. The evolution of the design will be summarized with emphasis on the final design. The current status of the project is the machine has been designed and the major components have been purchased and have been assembled. The speed controller for the 10 HP AC (7.5 kW) motor, the rotating probe plunge system, tooling mounting system, and machine frame have also been incorporated into the machine. The basic functionality of the machine has been demonstrated but the variable frequency drive that controls the probe rotation failed in early tests and is being replaced.