Ultrasonic machining

We introduced this technology as a result of winning a contract of technological transfer from ONERA – National Laboratory for Aerospace Research – who developed it for its own requirement. This technology contributes to the manufacturing of electrode plates in silica for space accelerometers – GOCE and Microscope project from ESA for instance.

The principle is based on an electrical current which at a given frequency - in the range of ultrasounds - is converted into a mechanical vibration activating a machining tool. The vibration frequency of the tool equals the frequency of the electrical signal – in this case 20 KHZ.

Our ultrasonic machining process differentiates itself from other processes because machining is carried out without contact between the tool and the part and no tool rotation. A resonating block made up of piezoelectric ceramics transfer the vibration to the tool through the sonotrode. The mechanical expansion of the tool – so-called tool elongation – can be adjusted and can vary from 0,005 mm to 0,07 mm. The device is fitted onto a NC machining unit and the tool moves along X,Y,Z axis without rotating.

The vibration accelerates an abrasive fluid purposely injected at a very high frequency between the tool and the part. The material is consequently machined out as a result of the abrasive wearing out the part. The efficiency and quality of the machining then depend upon the following parameters : quality and nature of the abrasive, tool grade, machining speed, vibration range.

The benefits of this technology compared with usual machining techniques are :

• capability to machine such fragile materials as silica because there is no contact between the tool and the part
• capability to machine such hard materials as boron carbide, silicon carbide, silicon nitride
• machining of such unusual shapes as square or hexagonal holes even in very small dimensions - less than 1 mm
• drilling of long holes - ratio diameter-to-length greater than 10 for small diameters.

This machining technique also makes it possible to carry out usual drilling operations of small diameter holes – down to approximately 0.4 mm.