Ultrasonic welding is a ‘solid-state’ welding process that can be used to join similar or dissimilar materials, by applying high frequency vibration and normal pressure to the weld interface. The major advantage of this method is the low heat input at the weld interface. Because of the cold welding technique, ultrasonic welding can be used to join thin foils to thick sheets and the properties related to the heat at the weld interface are less significant. So welds such as aluminium to copper, aluminium to steel, etc. can be made.