Ultrasonic Weld Joint

Ultrasonic welding lives or dies on joint design, not on the welder. Two families cover almost everything: the energy director — a raised triangular bead that concentrates the energy so melting starts at a point and flows through the joint — and the shear joint, a controlled interference melted progressively as the parts telescope together. The director’s peak must be sharp; a rounded or flat peak spreads the energy and the weld never initiates.

Director height is proportioned to the wall as a starting point; the size and position that actually work depend on the resin, the joint area and the welder, and every source insists on trials. Semi-crystalline resins behave differently from amorphous ones — they melt over a narrow temperature range and resolidify fast, so they generally need more energy delivered closer to the joint, which is what drives the choice of included angle and the shift to a shear joint. Add a flash trap on any visible face: the squeeze-out has to go somewhere.