Assessing Weld Quality in Continuous Ultrasonic Welding of Thermoplastic Composites via In-Situ Monitoring
J.M. van Stuyvesant Meijen (TU Delft - Intelligent Manufacturing systems)
B.C.P. Jongbloed (TU Delft - Intelligent Manufacturing systems)
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Abstract
Continuous ultrasonic welding (CUW) of thermoplastic composites is a novel joining technique able to produce long welded seams at high welding speeds. Our state-of-the-art welding setup entails an industrial robot on a track and an in-house developed end effector. Currently, no quality inspection methodology has been implemented; therefore, it is not known how the weld quality can be correlated to sensor and generator data. Such a method would enable the prediction of the weld quality after the process and be a stepping stone for closed-loop controlled welding minimizing defects. The goal of the current study is to use two off-the-shelf sensors for in-situ monitoring of the welding process and correlating the sensor data to the weld quality.
A laser line scanner is introduced behind the consolidator, measuring the step height between the top surfaces of the overlapping adherends. A forward-looking infrared (FLIR) camera is introduced, looking at the region of the top adherend behind the consolidator. This camera captures the residual heat present in the top adherend. The main findings from this study are that it is possible to use these two sensors to monitor the welding process and that the data acquired from them can be used to make predictions of the weld quality along its length. The thickness of the welded interface, which can be measured from the laser line scanner data, can give an indication of whether the interface is unwelded, welded, or overheated.
Regarding the FLIR camera, variations in the temperature at the top surface do correspond to variations in the quality of the weld interface, and furthermore, the rate at which the measured temperature changes is positively correlated to the magnitude of the power consumed by the ultrasonic generator. The FLIR camera can therefore be a powerful sensor to determine weld quality and its consistency throughout the length of the weld.
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