Development of an inline non-destructive monitoring method for ultrasonically welded seams during a continuous joining process

Abstract

The welding manufacturing process is increasingly being used as an alternative joining method to sewing for functional textiles including for medical and protective wear, high-performance reinforcement textiles for fiber-reinforced plastics, film materials, and smart textiles. Ultrasonic (US) welding technology is a universally applicable cost-effective joining method for thermoplastic membranes. A key issue with the quality of the welded seam is that many of the faults are not visible on the membrane surface. The traditional quality control of the seam cannot be performed because it is done by destructive testing methods. Therefore 100% assurance of compliance of product safety produced at a production scale is not possible. The objective of the study is to develop a nondestructive (NDT) inline testing method for the quality control of welded seams during the continuous ultrasonic welding process. Currently, the quality control of Ultrasonic (US) welded seams is performed based on sample destructive standard tests, where the quality control of complete welded seams is not ensured. The air-coupled US sensors are used to detect imperfections in the welded seam. A variety of membrane materials with base fabric made of polyester and coated with PVC coating were tested during this research. A superimposed type of seam was produced longitudinally by PVC-coated textiles with smooth surfaced anvil wheels and was welded using a welding width of 10 mm. These coated materials were provided by industrial partners and are used in diverse technical textile applications. A process-integrated NDT test method was developed. The imperfections in welded seams were identified during a continuous US welding procedure with the help of air-coupled ultrasonic sensors by developing an inline test method. A prototype to realize inline monitoring during continuous ultrasonic welding was developed and tested. Faults of different widths were artificially produced during welding. The inline monitoring of welded seams with faults was successfully performed and analyzed. The developed process can further pave the way for the development of inline monitoring of welding seams with US sensors for textile membranes joined with a continuous US welding technology.