Mar 25, 2010

Longitudinal and torsional ultrasonic welding - A comparison of the processes

Prof. Dr.-Ing.Michael Gehde
Dipl.-Ing. Sven Friedrich
Dipl.-Ing. René Fuhrich, TUChemnitz, Chemnitz


The present article deals with an initial comparison of both longitudinal and torsional ultrasonic welding processes. DVS test specimens made of PBT with and without energy directors are welded and the processes are optimised as far as the tensile strength is concerned. The results are to be compared with regard to the process windows and the maximum attainable tensile strength.

1 Introduction

Longitudinal US welding is an established process in the plastics sector. It is characterised, in particular, by very short cycle times and it is therefore hard to imagine large-scale series fabrication without it. However, there are also restrictions which do not allow this process to be utilised everywhere. One of the biggest problems is that the ultrasonic waves damage electronic components.

Torsional US welding does not seem to have a few of these disadvantages. For example, sensors which were destroyed during classical US welding could be joined with each other using this process without damaging the electronics. Furthermore, an adequate melt layer can be produced without making provision for any additional special design-related measures in order to shape the joining area (energy directors). Neverthe- less, it is possible to achieve a similarly short cycle time as in classical longitu- dinal US welding [1-2].

These advantages may be attributed to the direction in which the vibrations are introduced into the components to be joined. In classical longitudinal US weld- ing, this is vertical to the joining plane. The sonotrode strikes the joining parts like a hammer and this leads to high mechanical loads. In torsional US welding, the sonotrode rotates to and fro on the components. In addition to the inter- nal friction between the molecular chains, energy is also produced by macroscopic interfacial friction between the components to be joined. This permits welding without energy directors. Moreover, the lower joining member is not subjected to such high mechanical loads.

The present article supplies an initial comparison of both these processes with regard to the process windows and the attainable mechanical properties.

<< back

News Archive