Investigation of heat generation in ultrasonic metal welding using micro sensor arrays

A lack of sensing techniques with desired spatial and temporal resolutions at critical locations has hindered the real-time monitoring of many manufacturing processes. Micro thin film sensors, when properly implemented, can offer tremendous benefits for real-time sensing in those processes. In this study, a batch production of micro thin film sensor arrays on nickel was realized by transferring thin film sensors from silicon wafers directly into nickel substrates through standard microfabrication and electroplating techniques. To demonstrate the potential applications, micro sensor arrays that consist of multiple thermocouples and thermopiles were designed, fabricated and transferred into the electroplated nickel to study temperature field and heat generation during meso-scale ultrasonic welding. Sensor arrays are arranged immediately adjacent to the meso-scale welding area for in situ temperature and surface heat flux measurements. With the high temporal and spatial temperature data, a numerical method was developed to estimate the time resolved heat generation at the welding interface.