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The ultrasonic welding technology for plastics is considered part of the melt welding processes. The process is based on a conversion of friction and vibration energy into heat. Using a welding tool called a sonotrode, the high-frequency vibrations generated by the ultrasonic system, in combination with pressure, are transferred to the parts to be joined, which leads to relative vibrations in the jointing zone. The micro melt resulting from the friction heat presents a vibration barrier, which causes vibration energy to be absorbed and converted into heat, which then causes the weld contour to melt in fractions of a second and thereby form a molecular connection. As a rule, the plastic parts to be welded have to have a weld contour that corresponds to the type of material and the requirements for the weld seam. When sealing with ultrasonic technology the required heat is exclusively generated within the thermoplastic sealing layer. Contours focus the energy input and result in very short sealing times. During ultrasonic sealing, the heat is generated inside the foil. This means that no heat input from the outside is required. The tools used in the welding process remain cold. The heat energy input into the product is very small. The temperature exchange between the carrier and sealing layer takes place very rapidly. This results in very good hot seam strength.
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