The secret of ultrasonic welding is focusing the ultrasound with an energy director. In this way, it is possible to generate heat and subsequently melt, restricted to a locally defined area, while using only little energy. Large-area contact surfaces are counterproductive; they require high power and only achieve undefined joining areas with poor strength.
Energy focusing is achieved by:
- the energy director (ED)
- sonotrode design
- contouring of the anvil profile
Focusing by weld geometry of the plastic part. Thus, injection molded, thermoformed, or blow-molded parts often have specially shaped zones within the joining area. This is referred to as joint design, e.g. in the form of a tip or an edge. These special geometric features are the energy directors (ED). With the help of these defined, small contact surfaces, it is possible to apply the ultrasonic energy into the joining area in a targeted and locally defined manner.
Focusing by the sonotrode shape (weld tool); e.g. during the ultrasonic staking process, the sonotrode assumes the task of energy concentration.
The centering tip serves as melting initiation aid.
Focusing by means of contouring of the anvil structure for web materials such as film, cardboard, and nonwovens. Local deformation is achieved by anvil or sonotrode contours.