Sonotrode
Sonotrodes are tools that are set into resonance vibrations by introducing high-frequency mechanical vibrations ( ultrasound ) . They establish the connection between the ultrasonic generator and the workpiece and adapt the ultrasonic vibration to the machining task ( impedance adaptation ). Sonotrodes are used in ultrasonic welding to create a permanent connection between the components in the joining or contact zones due to various processes. Furthermore, they are used in ultrasonic lapping to transfer the vibration to the actual imaging tool. Sonotrodes are usually made of aluminum, titanium or steel; their geometry depends on the frequency provided by the generator used and on the processing task.
Geometric shape of the work surface
The sonotrode is the only component of an ultrasonic welding machine that has direct contact with the welding part. Your work surface must therefore be designed in such a way that the ultrasonic vibrations are optimally introduced into the joining zone and impressions on the components are avoided. The mechanical vibrations can be introduced vertically or horizontally into the joining zones of the welded part.
Different applications require different sonotrode designs:
Square stage with two slots, 35 kHz, steel
Katenoidale shape with rivet geometry, 20 kHz, Steel
Special shape with solid body joint , 20 kHz, titanium
Rotation sonotrode for ultrasonic roll 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 usually designed so that its resonance frequency matches the frequency made available by the generator used. Depending on the application, sonotrodes work in a certain frequency range, i. d. Usually this is between 20 and 90 kHz.
Waveform
The ultrasonic oscillation must have a certain direction. A body can have many resonance frequencies with the most varied forms of vibration. When ultrasonic welding thermoplastics , the direction of vibration must usually be longitudinal, i.e. act perpendicular to the workpiece. This is the only way that the mechanical energy actually reaches the effective zone.
When welding metals, the direction of oscillation is directed transversely to the joining surface so that the parts to be joined rub against one another.
Zero line
Due to the propagation behavior of sound waves in bodies, sonotrodes must have a zone of minimal expansion. This zone is the so-called zero line. There should hardly be any detectable vibrations in it.
amplitude
The amplitude is the amplitude of a sonotrode on its working surface; it is given in µm (micrometers). The size of the amplitude is influenced by the output amplitude provided by the converter and the respective amplification by the booster (transformation piece) and the sonotrode itself.
The required amplitude is determined, among other things, by the melting behavior of the plastics used and can vary considerably. When designing the sonotrode, the required amplitude must be taken into account, taking into account the booster available.
The most important parameters that can usually be set in ultrasonic welding are the welding time, the energy to be introduced and the contact pressure of the sonotrode on the welding part. However, if the sonotrode provides an amplitude that is too low, for example, the welding process will not succeed or will only succeed inadequately.
Amplitude distribution
If a sonotrode is designed incorrectly, the amplitude on the work surface can be different in different places. This leads to a poor weld pattern or even to faulty welds.
Idle power
Idle power refers to the power consumption that is required to make a sonotrode vibrate freely at resonance frequency. For example, if the proportion of undesired transverse vibrations is too high, a high idle power is required.
Avoid high idle power; they are an indication of poor sonotrode quality, the weld will not be optimal and the service life of the sonotrode will be limited.
When developing sonotrodes, there are a number of requirements that must be met. Indications of a faulty design, incorrect waveforms or too high a proportion of undesired transverse vibrations can include:
- high idle power
- the sonotrode becomes warm
- great wear and tear on the work surface
- short lifespan.
In operational practice, the quality of the sonotrodes used cannot be determined in practice without appropriate measuring equipment. In addition, in contrast to most other tools, there are no binding quality features or even standards for these welding tools.
Web links
Individual evidence
- ↑ Sonotrodes. soniKKs Ultrasonics Technology GmbH, accessed on February 11, 2014 .