Real-Time Thermal Stir Weld Temperature Monitor

Thermal stir welding (TSW) is a solid state welding process which has shown promise in joining high strength, high temperature metals needed for space launch systems. Although TSW offers an approach which allows more precise control of the temperature, better measurement of temperature in the weld zone is needed. The Industrial Measurement System Inc. (IMS Inc.) and University of Alabama in Huntsville (UAH) team propose to demonstrate the feasibility of ultrasonic thermometry technique to measure temperature, in real-time, in the fusion zone, during the TSW process. Using sensors attached to the containment plates, precise time-of-flight (ToF) measurements of ultrasound propagating through the fusion zone will be used to estimate temperature. This temperature measurement is non-intrusive and does not influence the thermal transport in the weld zone. Temperature data can be obtained at data rates as high as 1 kHz with the precision of a few degrees Centigrade. Thus, these measurements can be used as feedback controls in in-situ process control strategy for the TSW process. Precise temperature control will enable superior mechanical properties in the weld joint and thus maximize the capability of the TSW weld process.

NASA is using several manufacturing processes supporting the Space Launch System to create structures with superior mechanical properties and increased reliability. Solid state welding including ultrasonic, thermal, and friction stir welding is among the joining methods particularly well suited for high-strength, temperature-resistant materials such as titanium alloys, Inconel/Nickel-Based alloys. Real-time, in-process measurement of weld temperature can be used to control the joining process to produce high-strength, defect-free components and joints, improve weld quality, significantly reduce costs, and increase production rates. Potential NASA applications for the TSW technology include solid and liquid rocket motor casing, liquid rocket nozzle extensions, and other high temperature components.

The Navy is interested in effective titanium alloy welding technologies for ship building. Similarly the Army has a need to joining titanium for use in land vehicles and armor. Several commercial companies are pursuing TSW and FSW including Boeing, Airbus, Hayes Wheels, Williams International, and Lockheed-Martin. Many of the metals used in the oil and gas industry are difficult to fusion weld including titanium and its alloys. Thus, solid state joining processes which require precise temperature control are being pursued as alternatives to produce robust structures more amenable to high pressure applications.

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