Ultrasonic machining

Ultrasound is a high-frequency vibration that cannot be heard by humans; the lower limit of the frequency band is around 20 kHz (the threshold of audibility for humans varies from 16 to 20 kHz depending on the individual); the upper limit is not well defined, and may be 100 kHz.

Ultrasound has several industrial applications:

• non-destructive testing of parts, but also of living organisms (ultrasound);

• surgery (artery unblocking, hip replacement, liposuction, etc.);

• mixing of difficult-to-mix fluids;

• parts cleaning ;

• flue gas dedusting ;

• plastic and metal welding ;

• machining.

Ultrasonic machining is an abrasion technique using free abrasive grains set in motion by an ultrasonic-frequency vibrating body (sonotrode). The grains are transported by a fluid (usually water) and projected onto the workpiece by the vibrations of the sonotrode tool: the material is removed by the mechanical action of the grains or by cavitation erosion due to the fluid. This technique is mainly used for machining hard and fragile materials: glass, ceramics, quartz, precious stones, semiconductors... It can also be used to finish surfaces by ultrasonic polishing.

The term "ultrasonics" can also be used to describe process assistance techniques, such as grinding, cutting (turning, drilling, milling), electro-erosion, injection molding, extrusion, etc. In this case, the physical principle of the process remains the same, with ultrasonic vibrations being used to improve performance, either by reducing frictional conditions, or by creating intense conditions.

In this article, we limit our presentation to machining techniques using power ultrasonics: machining, assistance with material removal processes.