Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld.

It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.

Ultrasonic welding of thermoplastics causes local melting of the plastic due to absorption of vibration energy. The vibrations are introduced across the joint to be welded. In metals, Ultrasonic welding occurs due to high- pressure dispersion of surface oxides and local motion of the materials. Although there is heating, it is not enough to melt the base materials. Vibrations are introduced along the joint being welded.

The ultrasonic effect upon the molten metal generates a smaller grain size, giving the metal more strength.

Ultrasonic welding combines pressure and high frequency vibration motions to form a solid state bond.

The range ultrasonic frequency used in this welding is from 20kHz to 60kHz. This cool, strong weld capable of joining such combination as aluminium to steel, aluminium to tungsten, aluminium to molybdenum and nickel to brass.

Ultrasonic welding has also made it possible to join metals with vastly different melting temperatures, making strong rigid joints. Thus many applications previously considered unweldable can now revaluated

Objectives:

Increasing the strength, reliability and durability of welded structures is an important problem in welding engineering. A significant influence is exerted by residual stresses. Uneven heating of the product during welding causes its uneven temperature deformation. The product material solidity prevents the free temperature deformation of its individual parts, resulting in the formation of stresses and plastic deformation of some parts of the joint metal during welding, and after cooling, welding stresses and deformations remain in the product So, Ultrasonic metal welding plays important role.