Measurement of Weld Penetration Depth Using Non-Contact Ultrasound Methods
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Gas Metal Arc welding (GMAW) is one of the primary techniques used to join structural components together. The major obstacle precluding full closed-loop control of GMAW has been the lack of robust techniques using non-destructive and non-contact sensors capable of operating in high temperature and harsh environments typical of GMAW processes. This research uses laser generated ultrasound and electromagnetic acoustic transducer (EMAT) to receive ultrasound. Previous research has focused on ultrasonic shear wave time of flight (TOF) techniques to determine weld penetration depth, a key measure of weld quality. The objective of this research was to use a new technique, frequency modulation of a laser phased array (FMLPA), to determine weld penetration depth. Theoretical background of the FMLPA was developed. An analytical model of the FMLPA was derived and validated through experimentation. The FMLPA was experimentally validated. However, both the FMLPA and shear wave TOF techniques have proven to be impractical for real-time control. These techniques are impractical because the required ultrasonic waves are difficult to acquire due to attenuation and interference from other waves. A new type of wave called the RGLS wave was discovered during the course of this research. The RGLS wave was used to create a new RGLS TOF method for measuring weld penetration depth. The RGLS TOF method for measuring weld penetration depth has proven to be highly accurate, precise, and repeatable. The RGLS TOF method for measuring weld penetration depth has been demonstrated to work both off-line after welding and real-time during welding. Although the FMLPA and shear wave TOF technique was proven to be impractical, the RGLS TOF method has met the ultimate goal of this research area. Other new methods such as the RGSL, RGLL, and RGSS TOF methods related to the RGLS TOF method was also developed. The RGLS TOF method is suited for non-destructive and non-contact sensing. It will help future researchers achieve closed-loop control and automation of the GMAW process, which will help to improve quality and efficiency of welding, and also reduce waste and cost of welding parts together.