The ultrasonic metal welding equipment consists of

• an ultrasonic generator
• the ultrasonic welder with
• ultrasonic transducer system

Ultrasonic generator
Three main components

The ultrasonic generator (figure 8) operates with AC line voltage (220/110 volts). It generates a sinusoidal wave of 20 kHz from the supplied power.

Figure 8: Ultrasonic generator

Equipment with 35 and 40 kHz operating frequency are also standard.

Automatic tuning adjustment for constant welding parameters

Generators for ultrasonic metal welding equipment usually do not differ greatly from generators for ultrasonic plastics welding equipment. However, certain characteristics must be specifically designed for high-quality metal welding, requiring the use of process-adapted generators.

Advanced ultrasonic generators feature an automatic tuning adjustment to optimize the generator to the transducer system, even if there is a change in the mechanical and/or electrical properties during the welding process. This may, for example, happen if the sonotrode couples to the workpiece and the welding pressure builds up. The resonance frequency of the transducer system tends to vary as the sonotrode heat rises due to long welding or high cycle rates.

The automatic tuning adjustment compensates for changes and ensures optimal efficiency. Above all, it guarantees that welding parameters remain constant. This is extremely important for ultrasonic metal welding.

Whereas there is a required welding time and a holding time for plastics welding, ultrasonic metal welding does not require such a holding time. However, it is advisable to have a short burst of ultrasonics (approximately 0.02 seconds) after welding to release loose particles from the sonotrode and prevent the welding parts from sticking to it.

It is imperative that a constant amplitude is maintained during the welding process.

While the workpieces scrub onto each other during the first phase of the welding process, oxides and other impurities are disrupted. The mechanical load required on the tools and thus the necessary energy is relatively low.

Keeping the amplitude constant

The welding phase when molecules intermingle will require a much higher mechanical load. The rise in mechanical load must not, under any circumstances, influence or reduce the amplitude. The electronic controls in the generator must detect this condition and maintain a constant amplitude by providing appropriate energy. A constant amplitude during the welding process is decisive for a successful weld.

The required welding amplitude is based on the application characteristics and/or tests of the weld strength. The physical amplitude generally varies between 0.015 mm and 0.045 mm at half of the travel distance.

Generators with amplitude adjustment

Different geometrical shapes of transducer will provide different values of amplitude. The amplitude for specific welds, however, can be varied by electric or electronic variation means. This is why ultrasonic generators are preferably equipped with electronic regulation controls for amplitude adjustments. By using a selector switch with up to ten steps or a regulating potentiometer, the amplitude can be adjusted in fine increments.