Ultrasonic Welding (UW) can be defined as the use of acoustic vibrations (sound) to obtain a solid-state weld that will maintain two pieces together. Ultrasound welding has many industrial applications and you will be surprised at how many things we use everyday are welded using ultrasound welding. For example, plastic cups and blister packages are usually manufactured using ultrasonic welding. A typical butane lighter is also made using ultrasound welding techniques.
It is important to understand that UW usually is not caused entirely because of heating, at least in metals. Instead, what really happens is the dispersion of surface oxides and motion of the materials. Although there may be some heating involved, it is not sufficient to melt the materials.
Ultrasonic welding parts.
Although there is a great variety of UW equipments, all of them have the same basic parts: press, the ultrasonic system, and a movement controller.
Press: parts to be welded need to be kept together at high pressures to facilitate the welding process. This is achieved with a press where parts are fitted and pressure is applied.
Ultrasonic System: this is the core of the Ultrasonic welding system. Here is where acoustic vibrations are generated in frequencies that range from 20 to 80 MHz. The ultrasonic system is made of transducer, an optional booster and a sonotrode. You can red more about the sound generating system in part 2 of my sonochemistry series.
Transducer: This is the part where electrical inputs are converted into a mechanical (acoustic) vibration (ultrasound). Then the booster (which is optional) may amplify the sound if needed. Finally, the sonotrode is the actual piece that applies and transmits the acoustic signal to the parts to be welded.
Controller: this is the part of the system used to move in a controlled manner the press so the parts can be welded completely.
Applications
There are many areas and industries where UW can be utilized. Applications are extensive. Some of the industries were UW is used today are: automotive, electrical, computers, aerospace, and packaging.
Within the electronics and computer manufacturing industry Ultrasonic Welding is used to join wired connections and to create small and delicate circuits.
In the automobile industry, Ultrasonic Welding is used to weld large plastic parts such as door panels, instrument panels, air ducts, steering wheels, upholstery and certain engine parts.
The packaging industry is perhaps where more applications of ultrasonic welding can be seen. You will be surprised to know that many things that we use everyday are welded with UW. For example toothpaste tubes, diapers, plastic containers, butane lighters, blister packs. Milk and juice containers are some examples of everyday things that are usually sealed with UW. More packaging applications include: condiment dispensers, juice pouches, and plastic coated paper cups.
Sources:
1.- Welding Handbook: Welding Science and Technology. USA: American Welding Society.
2.- Ultrasonic Welding Technique.