Sound is the propagation of smallest pressure and density variations in an elastic medium (gas, liquid, solid-state body). For example, a noise is generated when the air in a specific spot is compressed more than in the surrounding area. Subsequently, the layer with changed pressure propagates remarkably fast in all directions at speed of sound of 343 m/s.
Acoustic frequencies between 16 kHz and 1 GHz are referred to as ultrasound; in industrial settings we call it “ultrasonics”. To clarify: people are able to hear frequencies between 16 Hz and 20 kHz; i.e. the lower frequencies of industrial ultrasonics are audible, especially if secondary frequencies are generated. And what is more, ultrasonics is palpable when touching the weld tool. For ultrasonic welding, the frequency range is between 20 kHz and 70 kHz. Additional fields of application: Imaging ultrasound in the field of medical diagnostics ranges between 1 and 40 MHz. It is not audible or palpable. In the field of industrial material testing, ultrasonics is used at frequencies from 0.25 to 10 MHz.
Classification of ultrasonic frequency ranges – the range audible to the human ear only makes up a fraction of the entire span
How does ultrasonics work?
Ultrasonic vibrations are mechanical longitudinal waves that
achieve deformation in plastic materials cause friction between moleculesThe resulting friction heat generates a melt that bonds the joining partners within the molecules.
Friction occurs due to impedances in the material, absorption and reflection of the mechanical vibration: internal friction in the molecule bond = dissipative work external friction between joining partners = surface friction
Thermographic illustration of temperature increase during welding
Due to:
high process speeds repeatable weld resultsthe technology is preferred for high-volume production in the automotive, electrical, medical, packaging, hygiene, and filter industry.
Good bonding quality in terms of strength, tightness and visual appearance are particularly achieved if the part material and design is suited for the ultrasonic process. This means that from the beginning they must be designed such that ultrasonic waves are focused in the weld zone.
The factors below control the weld process:
Component and ultrasonic weld factors
This is an example of a tongue -and- groove weld:
(“duck beak”) in different versions with vertical or horizontal fold, with or without breathing valve
(“duck beak”) in different versions with vertical or horizontal fold, with or without breathing valve
