Friction Stir Welding (FSW) is a modern, solid-state joining processes, involving frictional heating and mechanical forging. High quality joints can be created using a control system that compensates for external disturbances by regulating the state of the weld zone (WZ) surrounding the tool. However, in this situation direct monitoring is complex since the rotating tool is embedded in plasticized material.
This research discusses the development of a Bluetooth-based Wireless Rotating Process Monitoring (WRPM) system to overcome limitations in inductive/capacitive telemetry systems. Communication channel performance was assessed to determine the suitability of Bluetooth for use in the feedback control loop for in-process FSW WZ temperature control.
Peak round-trip communications latencies of 300–650 ms for 20–200 byte payloads were observed. Additionally, electrical noise from the machine tool reduced the receive signal strength measured on the Bluetooth module. The bit error rate (BER) also increased from 0 to 0.001 % as spindle speed increased from 0 to 1400 rpm. Due to the communication latency, the signal strength and BER effects were not observed to affect throughput. The results support the use of the WRPM system for feedback control of FSW. However, deterministic communication latency must be achieved to enable the design of a stable control system.
