An automated non-destructive testing system for seam bondings in automotive serial production

The joining process of seam bond is used in automobile construction because of the non-visible joints on mounted parts such as doors, hoods or luggage compartment doors. With these components, a structure-providing inner panel is joined with the outer panel, which is visible to the customer. Besides providing stability, particularly in the event of a crash, the joining level is also filled with adhesive to increase the stability and to prevent the ingress of moisture that causes corrosion. These mechanical connections must be tested to ensure that the requirements for proper bonding have been met. As the destructive test used today requires metallographic laboratory with special trained personnel, significant scrap cost and a time consuming process control loop, considerable efforts are being made to develop a capable non-destructive and as far as possible in-line test method. State of the art non-destructive inspection systems for seam bonds are insufficient regarding full part accessibility and reliability in terms of detectability and validation. This paper is focussed on new developed free configurable three-transducer ultrasonic phased array technology including algorithms for data validation and evaluation for an automated process control loop in the automotive car body shop. The paper end with an statistical classification based on an 5-month measurement campaign under industrial in-line conditions. In a first step, a list of possible defects was collected and the detectability in different seam areas was calculated by sound field simulation of the amplitude signals. Second, based on the results from simulation, a measurement setup as excitation sequence was defined. Based on the theoretical findings a inspection system was designed and realized. Within a measurement campaign the inspection system was evaluated in terms of detectability of minimal defect size under non-laboratory conditions. This includes a permanent proof of coupling conditions, monitoring of misalignments, e.g. tilting and surface defects of the car body. In the last step, the testing system is build up and tested within the assembly line. These measurement results show that the identification of common process defects is possible.