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Technical Procedure Description

 

The ultrasonic welding technology for plastics is to be assigned to fusion welding. The procedure is based on a conversion of friction and vibration energy into heat. The high-frequency vibration produced by the ultrasonic system will be transferred through the welding tool, called sonotrode, under influence of pressure on the parts to be welded, which causes a relative vibration in the fusion zone. The resulting micro melting as a consequence of friction heat forms a vibration-barrier whereby the vibration energy will be absorbed and converted to heat, which finally leads to the melting of the welding contour in split seconds and with that to a molecular bonding. The plastic parts to be welded normally have to show the welding contour matching the material type and the demands on the joint.

Types of welding

As for plant and process engineering, it is to differentiate between the linear and the torsional principle. The vibrations for linear technology will be fed vertically into the fusion zone, while with torsional technology, the joints will vibrate tangentially to the welding level. Torsional technology, necessary for low-vibration metal-welding, will be used preferably e.g. in medical applications (low production of particle flight) or components with integrated vibration-susceptible electronics. Related to the application, one differentiates between the molecular welding like spot-welded points (plastic-plastic), rivet/crimping (plastic-foreign material) and imbedding of metal inserts (e.g. bushing) in plastic injection-molded components. Equally, thermoplastic fabrics, non-wovens or foils can be cut and welded with ultrasonics at the same time (separation sealing procedures).

Fields of application

The ultrasonic plastic welding method can be practically used for all thermoplastic synthetics. Special attention must be paid to the geometry of the joint of the component from part-crystalline synthetics, since the welding behaviour with this type of plastic differentiates substantially from the amorphous type. Different thermoplastic types can also be joined, but in restricted measures. Thermosets cannot be welded with ultrasonics. Today the ultrasonic joining technology finds use in all branches of technology, where synthetics are processed.

Customer benfits

The substantial advantages of the ultrasonic plastic welding technology are very short welding times, joints at an inaccessible spot, no solvents and glues are necessary, a trouble-free integrability into production lines as well as the possibility to quality control by collection of welding parameters and settings from tolerance windows. In contrast to other fusion welding technologies, the ultrasonic welding technology offers an interesting cost/benefit analysis.

References

 

Automobile industry: 

Spotwelding, rivet and crimping connections on e.g. inside linings, instrument panels, seats and bumpers

Electrical industry/ electronics: 

PCB's rivet connections in casings, inspection windows, crimping/fixation electric contacts, battery packs

Medicine/Chemistry/Pharmaceutics: 

Shrink-wrap filter, syringes, containers for bacterial cultures, insulin-pens, pump casings, flavour filter

 
Entertainment electronics: 

Casings, inspection windows, installations rivet, spot-welding of case parts

Toy industry: 

Joining all kind of three-dimensional plastic-formed parts

White goods:

Welding, spot-welding, rivet, crimping and embedding applications of bushes

Textile industry:  Separation and edge-welding of labels, cutting selvages, connect roll endings with thebeginning