The present invention relates generally to inspection systems for use in assessing the performance of industrial manufacturing processes, and more specifically to a nondestructive inspection system for assessing the quality of brazed joints and fusion or solid-state sheet metal joints.
Sheet metal joining processes are widely used in many industries including the aerospace and automotive industries. Resistance spot welding, seam welding, weld bonding, adhesive joining, soldering, and brazing are used for various applications in different industries. Among these processes, the brazing procedure is used to join metal sheets where good electrical conductivity, as well as mechanical and thermal strength, is required from the joint. The quality control of such joining processes has been recognized as an important issue to manufacturers. The quality of brazed joints is affected by the joining process itself and by the design of the joint. Many factors are considered, including metallurgic reaction conditions; thermal behaviors; chemical composition; starting condition of the base metal; brazing and bonding conditions; and the particular brazing and bonding equipment used during the process. Furthermore, the intricate relationship between these factors makes it difficult to control the quality of the brazed joint and difficult to inspect the weld joint in a nondestructive manner. It is particularly difficult to inspect on-line small areas such as electrical contacts brazed to terminal or arm sheet metal conductors due to the strong geometry and edge effects presented by such items.
Certain acoustic methods enable nondestructive testing of welded parts that is useful for various inspection applications. Unlike other nondestructive testing methods, acoustic methods provide both surface and internal information about a particular weld joint. Moreover, acoustic methods allow for deeper penetration into test specimens and provide higher sensitivity regarding small discontinuities that may be present in a weld joint. Acoustic methods, however, do have limitations, including the requirement of having a skilled and knowledgeable operator for using a test device and then analyzing acoustic data derived from a test specimen. Accordingly, the field of ultrasonic nondestructive evaluation (NDE) is in need of a reliable process or technique for identifying poor quality brazed joints in a manner that eliminates the requirement of a skilled operator and the subjective interpretation of test data.