Ultrasonic welding is a metal joining process in which high-intensity vibratory energy, usually at a frequency above audibility, or in excess of 15 kHz, is introduced into the area to be welded as the workpieces are held together under pressure. This process depends on the conversion of high-frequency alternating current to mechanical vibration. Ultrasonic welding involves complex relationships between the static clamping force, the oscillating shear forces, and a moderate temperature rise in the weld zone, creating conditions which result in atomic diffusion across the interface. The metal recrystallizes to a very fine grained structure having the properties of moderately cold-worked metal. The magnitude of the factors required to produce a weld are functions of the thickness, surface condition, and the mechanical properties of the workpieces. See ULTRASONIC WELDING.
Pieces to be joined are clamped at low pressure (4 to 160 kg [ l o to 350 Ib.]) between two welding members or sonotrodes, and the vibratory energy is introduced for a brief interval. The heart of the equipment is a magnetostrictive transducer, a rectangular stack built up of “A” nickel laminations wrapped with insulated wire. Nickel laminations are used for the transducer because of the transducer’s substantial change in length when magnetized. The equipment develops power at supersonic frequency to drive the transducer stack which, in turn, converts electrical current to mechanical vibrations, then transmits them to the upper sonotrode. The high frequency vibratory energy produced by the transducer passes from the welding head through the two pieces to be welded, where it disrupts the oxide film at the interface and eliminates the need for any further preparation.
All combinations of aluminum alloys form a weldable pair. They may be joined in any available form: cast, extruded, rolled, forged, or heat-treated. Soft aluminum cladding on the surface of these alloys facilitates welding. Aluminum can be welded to most other metals, including germanium and silicon, the primary semiconductor materials.
Applications include electronic components, electrical connections, foil and sheet splicing, encapsulation and packaging, and structural welding.