A shear joint is a type of joint commonly used in ultrasonic welding that involves joining two materials in a parallel configuration. In this joint, the two materials are brought into contact and the ultrasonic horn is applied perpendicular to the joint line, causing a shearing force that creates frictional heat and melts the materials. The molten plastic flows across the joint line and fuses together, creating a strong, durable bond.

Shear joints are commonly used in the assembly of small plastic parts, such as electronic components, medical devices, and automotive parts. They are typically used in applications where the parts are small and require precise assembly, as well as in applications where a strong, leak-proof seal is required.

The design of shear joints is critical to achieving a successful weld, as factors such as the size and shape of the joint, the amplitude and frequency of the ultrasonic vibration, and the pressure applied by the horn all affect the quality and strength of the weld.