Ultrasonic Riveting Technology
Ultrasonic riveting and forming:
The ultrasonic riveting makes possible an interlocking bonding of two thermoplastics or of thermoplastics with dissimilar materials, e. g. thermoset materials or metals.
In this process the sonotrode serves as a re-forming tool. It determines the forming of the riveting pin.
During the holding time (cooling phase) the sonotrode serves also as fixation stamp, thus the melted material cools down under pressure.
Advantages of ultrasonic riveting:
solid and seamless fitting joint by overcoming the return elasticity of the plastic material
short process times
low-stress bondings
quick thermal drain via the cold sonotrode; the sonotrode simultaneously serves as fixation stamp
also deeper areas of a plastic component can be reached with the riveting sonotrodes
reproducible bolding technology; dissimilar materials can be riveted
use of basic sonotrodes with screw-in riveting sonotrodes; thus several riveting steps are possible with one head
no connection elements
Disadvantages of ultrasonic riveting:
Long process times and short cycle sequences lead to warming up of the riveting sonotrode. Here the sonotrode tip should be ventilated.
Electronic components are very sensitive against ultrasonic waves. It can lead to destruction of the elements.
If the parts to be riveted have thin walls, the visible side can show shiny spots and imprints
If the parts to be riveted have thin walls and also in case of hooks or clips the ultrasonic waves can lead to fissuring
An optimal riveting joint should be based on the following preconditions:
Principally provide radiuses or rounded punctures at the riveting root; this will reduce the indenting effect
Do not exceed the relation of pin diameter and pin length of 1:2 in full pins, otherwise use hollow pins (see attachment ‘design of riveting head’)
For easier parts assembly use inclined insertion surface
When riveting reinforced plastics and bondings with metal parts the riveting sonotrodes have to be wear-resistant
In the following there are listed some established sonotrode materials:
Hardened steel sonotrodes
Hardened Ferrotitanite sonotrodes
Titanium sonotrodes with coated riveting surface
Moreover, for an optimum riveting joint not only the sonotrode form and the material to be riveted are important, but also the process parameters like:
amplitude
melting time
contact force
contact speed
cooling time
