Sonotrode

Sonotrodes are tools which are added by the introduction of high-frequency mechanical vibrations ( ultrasonic ) to resonate. They establish the connection from the ultrasonic generator to the workpiece and adjust the ultrasonic vibration to the machining task at ( impedance matching ).

Horns are used in ultrasonic welding, due to different processes to produce a permanent connection of the components in the joining or contact zones.

They are also used in Ultraschallschwingläppen to transmit the vibration to the actual, imaging tool.

Horns are usually made ​​of aluminum, titanium or steel, its geometry depends on the provided by the generator frequency used and the processing task.

Properly functioning horns must satisfy a number of requirements. The most important are:

Geometric shape of the working surface

The horn is the only component of an ultrasonic welding machine direct contact with the welding part. Its working surface must therefore be designed so that the ultrasonic vibrations are optimally introduced into the joint zone and marks can be avoided on the components. In general, the mechanical vibrations are introduced perpendicularly into the joining zones of the weldment.

Different applications require different types of horns:

Katenoidale form with rivet geometry, 20 kHz, steel

Special form with solid joint, 20 kHz, titanium

Rotational sonotrode for ultrasonic seam welding, 35 kHz, aluminum

Cylinder stage with cutting edge, 35 kHz, steel

Special shape with cutting edge, 30 kHz, steel

Frequency

A sonotrode is typically constructed such that its resonant frequency coincides with the set provided by the generator frequency. Work depending on the application horns in a certain frequency range, usually this is between 20 and 90 kHz.

Waveform

The ultrasonic vibration is required to have a certain direction. A body can have many resonant frequencies with different vibration modes. In ultrasonic welding, the oscillation direction must be generally longitudinally, that act perpendicularly to the workpiece. Only the mechanical energy is actually in the active zone.

When ultrasonic wire bonding, the vibration direction is often directed transversely to the joint surface to tear through friction, the existing oxide layers of aluminum bonding wire used for this purpose.

Zero line

Due to the propagation behavior of the sound waves in objects sonotrode must have a minimal expansion zone. This zone is called the zero line. Hardly oscillations may be detectable in her.

Amplitude

The amplitude is the amplitude of a sonotrode in their work area, they will be given in microns ( micrometers). The magnitude of the amplitude is influenced by the output amplitude that provides the converter, and the respective amplified by the booster ( transition pieces) and the sonotrode itself

The amplitude required is determined inter alia by the melting behavior of the plastics used and can vary significantly. In the design of the horn, the amplitude needed to be considered in the light of the available booster.

The main usually adjustable parameters in ultrasonic welding, the welding time, the introducing energy and the contact pressure of the horn on the welding part. However, the sonotrode example, a too low amplitude available, the welding process is not or only insufficiently succeed.

Amplitude distribution

Is a sonotrode wrong constructed the amplitude at the working surface at different locations may be different sizes. This leads to a bad weld image or even faulty welding.

Idle power

To idle power, the power consumption, it is meant that is required to make a sonotrode in the resonant frequency to vibrate freely. If, for example, the share of undesired transverse vibrations too high, a high idle power is required.

High idle services are to be avoided; they are an indication of poor Sonotrodenqualität, the welding is not optimal and the lifetime of the sonotrode will be limited.

There are a number of requirements that must be met in the development of horns. Indications of a defective structure on false waveforms or to too high a content of undesirable transverse vibrations may be, inter alia:

• High idle power
• The sonotrode is hot
• High wear on the working surface
• Short life.

In operational practice is without proper measuring equipment, the quality of used horns practically impossible to determine. Moreover, there are, as opposed to most other tools, so far no binding quality standards for these characteristics, or even welding tools.