Ultrasonic Metal Welding, also named cold metal welding, is similar to friction welding but not always the same-ultrasonic welding takes a very short time and the temperature is lower than that of metal recrystallization. Ultrasonic Metal Welding is also different from pressure welding because the static pressure applied is much lower than that of pressure welding.
Three main stages of ultrasonic welding to joint workpieces together
- This vibrational energy at the contact between the two workpieces generates local friction and shear force and produces initial plastic deformation.
2. Ultrasonic vibrations disperse impurities/oxides and lead to further deformation. This increases the metal-to-metal contact and creates a weld zone. This process is also known as micro-welding. Repeated micro-soldering results in a larger contact area, making a stronger joint.
3. Continue to add ultrasonic vibration to expand the contact area, hence, expand the welding area.
At the same time, the weld area heats up and plastic deformation takes place on the interface. This results in the formation of a weld joint when the contact pressure makes the workpieces get more close to each other to a distance where atomic gravity can act. Too much welding time or excessive ultrasonic vibration may lead to a bad welding effect and even destroy the workpieces.
The combined use of the welding head and base can well clamp the workpieces with the lower workpiece completely fixed on the base.
The role of each component of the ultrasonic metal welder
The ultrasonic generator
The ultrasonic generator converts the 50/60Hz electricity to 15, 20, 30 or 40 KHz electrical energy.
Through the convertor, the high-frequency electric energy is converted to mechanical vibration of equal frequency. Then, the booster amplifies the vibrational energy which is supplied to the horn.
During the ultrasonic welding, no electricity or heat is supplied to the metal workpiece; During the welding process, with the help of the static pressure, the vibrational energy at the contact between the two workpieces generates local friction and shear force and produces plastic deformation thus generating heat and the two pieces are joint together at the interface metallurgically upon cooling.
The metallurgical joint at the interface is a solid-state weld that is created without melting the involved materials, hence, the ultrasonic welding effectively avoids the spatter and oxidation that occurs in resistance welding. The ultrasonic welding generates less heat because in the welding process only the friction works to generate heat. The heat can only reach 1/3 or 1/2 the melting point of the metal. The low temperature ensures the original properties of the metal traverse. Moreover, ultrasonic welding can weld a thin metal piece to a thick one without causing any damage to the thin piece. These advantages of ultrasonic welding are important to produce circuit groups.
The horn must have tooth on the working surface or else it cannot generate enough friction energy when working with the upper workpiece, hence, no relative motion occurs between the two workpieces.
The ultrasonic vibration transmitted to the contacts of two workpieces creates friction under pressure hence leads to the fusion of the metal molecular layers. The heat generated due to the friction melts the metal, effectively avoiding the spattering of sparks and oxidation of the metal in the weld area, which must takes place during the resistance welding process.