Spot-welding machines
The mechanical part of an ultrasonic welding device accommodates the ultrasonic transducer system and is equipped with a pneumatic actuator for providing the required welding force. It enables the attachment of a anvil or fixture for holding and/or clamping the workpieces, if this should be required.

Horizontal arrangement vs. vertical arrangement

Whereas the transducer system is arranged in a vertical direction for welding plastics, ultrasonic metal welding requires a horizontal arrangement. The sonotrode does not hammer on the material in order to raise its temperature and to plastify it, but scrubs the parts to be welded onto one another under pressure.

Figure 9: Arrangement of the transducer system in the welding head

1. Sonotrode
2. High-tensile threaded pin
3. Height adjustment
4. Converter
5. Oscillating disk
6. Booster

Ultrasonic welding equipment is available for specific applications or in basic design to be tooled for a variety of applications.

In figure 9, a welding unit is depicted which can be used for virtually all types of spot-welding. The ultrasonic transducer system is accommodated between two oscillating disks which are arranged in the area of the maximum possible vibrations.

The disks are bolted to the front sides of a supporting tube which, in turn, is placed in a stable aluminum body and to be moved vertically using precision roller guides. The system is actuated (moves down) by means of pneumatic cylinders. In doing so, the required welding force is introduced onto the welding part via the sonotrode surface. In as far is there are several pneumatic cylinders, they can be switched on or off individually, so that different pressure forces will be produced.

Pressure forces between 700 and 3000 N

With a supply pressure of approximately six bar, the pressure force will be in the range of approximately 700N to 3000N. The pneumatic pressure can, in addition, be varied using a pressure gauge with manometer. The vertical movement of the stroke must be adjustable. This limits the unavoidable deformation of the parts to be welded to a pre-determined dimension or welds them using a defined pressure-reduction measure. The anvil support can be a threaded spindle to permit installation of various small fixtures via a dovetail guide.

Wire-splice-welding device
Quite another type of welding machine is depicted in figure 10. It shows a portable splice-welding device. Splice welding requires an enclosed compression chamber, otherwise the wires would protrude laterally because of the pressure. A quality welded splice would then be impossible. One side of this quadrilateral compression area (figure 11) is the work surface of the oscillating sonotrode, which borders on two non-oscillating working tool elements. The oscillating sonotrode and the non-oscillating working tool elements should not, under any circumstances, touch each other. Contact would not only lead to a very annoying and rather audible noise but would also very quickly damage the tools. The wires sometimes consist of very small strands (approximately 0.05 mm Ø).

Therefore the gap between sonotrode and work tool elements must be very narrow to ensure that single strands will not be pushed into this gap even under the influence of ultrasonics.

Figure 10: Mobile ultrasonics splice-welding machine

On the other hand, the gap should not be too narrow, otherwise the sonotrode may touch other tooling during vibration. In general the gap should be 0.02 mm. This condition should be maintained even in industrial high-volume production.

Figure 11: Tool arrangement for splice welding

1. Sonotrode
2. Anvil horizontal
3. Anvil vertical
4. Compression chamber open

The wires are inserted into the "compression chamber". The horizontal anvil moves sidewards until it touches the vertical anvil side.

Figure 12: Tool arrangement for splice welding

1. Sonotrode
2. Anvil horizontal
3. Anvil vertical
4. Compression chamber closed
5. Anvil shaft