Ultrasonic welding has applications in many fields including the thermoplastics industry. So how does it work?
Ultrasound is a mechanical vibration similar to that produced by musical instruments. These vibrations are called ultrasound because they are at a frequency above than the hearing capacity of the human ear (greater than 16 kHz).
In an acoustic assembly, these pressure waves are produced by a generator. This sends an alternating current of the same frequency as the converter (or transducer).
Then the converter, which is made of piezoelectric ceramics, transforms this energy into mechanical vibrations.
The mechanical vibrations then generate heat friction exciting the plastic molecules, which begin to move. The plastic softens and melts allowing the components to bond. The welding action is done by the sonotrode.
Plastic ultrasonic welding technology is very suitable for plastic hot riveting or heat stacking.
The generator converts the mains network (50/60 Hz) electrical frequency into a corresponding high frequency electrical energy, in this diagram, to 20,000 Hz.
Then, the piezoelectric converter (or transducer) transforms the electrical 20,000 Hz into mechanical vibrations of the same frequency. The energy is then mechanical.
The booster, or amplitude amplifier, is used to increase or reduce the amplitudeproduced by the converter.
Finally, the last element of the acoustic chain, the sonotrode transmits ultrasound energy to the welding workpiece.
Much more than a simple hardware manufacturer, SONIMAT provides a set of ultrasonic plastic assembly solutions: spot welding, continuous welding, hot riveting, riveting, flanging, insertion and more.
Ultrasound has always been a part of mother nature’s solutions. Bats use it in particular to orient themselves and to fly. By emitting brief ultrasound pulses of less than 1/1000 s duration at a frequency of 50,000 Hertz, they can locate obstacles, but also find the insects on which they feed. Dolphins and blue whales are also able to navigate using acoustic signals. They use a frequency of 170,000 Hertz audible only to their inner ear.
At the beginning of the sixties, the transformation of synthetic materials experienced a real boom. In fact, for the assembly of synthetic components, and with an understanding of the natural acoustic phenomenon, the ultrasound welder was developed and had a predominant role.
In the industrial field, SONIMAT began using very early on ultrasound for assembly, welding, cutting and slicing applications. Other professionals have also discovered the advantages of this technology:
Medicine: mainly for ultrasound and focused ultrasound thermotherapy.
Laboratory: sonication breaks down cell membranes. Ultrasound is also used to clean and disinfect equipment.
Remote sensing and telemetry: sonar and distance measurement.
Automotive: ultrasonic parking assistance system and obstacle avoidance.
Industry: non-destructive testing of materials.
Leisure and practical life: pest control devices, atomiser
Hairdressing: implants for hair extensions.
Assembly by energy applicator. Mainly reserved for amorphous thermoplastics. Ultrasound welding is done very quickly (less than 1 second), without adding material.
Ultrasound spot welding is particularly recommended for thermoformed parts without an assembly profile, or for parts whose geometry and actual conditions exclude the possibility of standard welding operations.
Applied to high speed processes, continuous ultrasound welding is a solution for the high flow rates in the fields of packaging and non-woven textiles.
The main advantage of this process is that it allows to assemble parts of different types of plastic.
This technique encloses a part within a completely different material, by deformation of the material.
The penetration of metal inserts by ultrasound makes it possible to avoid the stresses due to overmoulding, to increase the injection rates and to simplify the production of injection moulds.
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