Ultrasonic Welding

ULTRASONIC WELDING:

Ultrasonic welding is a process in which strong frictional heat is generated at the portions of moldings to be welded by simultaneously applying pressure and ultrasonic vibration, to melt and weld these portions.

Ultrasonic welding is an industrial technique wherein high-frequency (15 to 40 kHz) ultrasonic acoustic vibrations are used to weld plastics and especially for joining dissimilar materials. 

This type of welding is used to build assemblies that are too small, too complex, or too delicate for more common welding techniques. 

In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.

ULTRASONIC WELDING

Equipment consists of:-

Generator : - Converts electrical energy from main supply frequency of 50 HZ to an ultrasonic frequency of 20 KHz.

Mechanical Resonance Unit:-

Converts electrical output from generator into mechanical vibrations which consists of transducer, booster and sonotrode.

Transducer : uses a piezo electric material (lead zirconate titanate ) for conversion of electrical energy to mechanical vibrations.

Transformer(Booster) : Transmits mechanical vibratory energy to the sonotrode and transforms the vibrations amplitude delivered by the transducer to the valve required at the sonotrode.

Sonotrode:- is welding, stacking and insertion tool, performs the function of transmitting vibratory energy, and contact force and carrying on the forming operation.

1. Welding with rigid PVC is good and SPVC is poor Metal insertion is also possible.

2. When the insert is long, the sonotrode should be applied to the plastic part in the reverse side of the insert to avoid the risk of clamping the vibration.

3. Example of Ultrasonic Insertion of Metal insert showing the way in which plastic displac by the contact moves into the space around the undercut, thus sealing the insert in position.

4. When the insert is long, the sonotrode should be applied to the plastic part in the reverse side of the insert to avoid the risk of clamping the vibration.

Process

1. The parts to be assembled are held together under pressure between the oscillating horn (sonotrode) and an immobile anvil (nest) and are subjected to ultrasonic vibrations of frequency 20 to 40 KHz at right angles to the contact area. 

2. Common frequencies used in ultrasonic welding of thermoplastics are 15 kHz, 20 kHz, 30 kHz, 35 kHz, and 40 kHz).

3. The ultrasonic energy melts the point contact between two the parts to be welded creating a joint.

Advantage

1. This process is a good automated alternative to glue, screw or snap-fit designs. 

Disadvantage

1. The welding is limited to small components with weld lengths not exceeding few centimeters.

2. The tools for this process are quite expensive so that large volume production runs are preferred.

Application

1. It is typically used with small parts (e.g. cell phones, consumer electronics, disposable medical tools, toys, etc) 

2. Valves and filters used in medical equipment,

3. Automotive components and vacuum cleaner bodies welded on multi-head machines.