Ultrasonic welding (USW) is a solid-state welding process that produces a weld by local application of high-frequency vibratory energy while the work pieces are held together under pressure. 5. A sound metallurgical bond is produced without melting the base material.Ultrasonic welding is an industrial process 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 metals, and especially for joining dissimilar materials.