Away with the sway

Milling device aims to put a stop to unwanted movements and allow small metal components to be produced more quickly. Siobhan Wagner reports.

A milling device that compensates for the rocking and swaying generated by machine vibrations will make micro-component manufacture faster and more precise, according to its developers.

Called MiniMill, the system uses multiple sliding shock absorbers to control the jolting of equipment and prevent oscillation of the workpiece. It was designed and developed at Fraunhofer Institute for Production Technology IPT.

‘Traditional machines can work with precision, but the machining speed is very low,’ said Rainer Klar, the researcher in charge of development. ‘You could say to make a machine faster, just use a faster motor. But this means you have to limit the drives because their force will impact the machine base’s vibrations.’

The MiniMill aims to put a stop to unwanted movements and allow small metal parts to be produced more quickly. On each of the device’s three axes is a small slide, which absorbs the momentum of the jolt and moves backwards.

Klar explained that it works a little like the recoil of a cannon. To ensure that the cannon doesn’t sink into the ground when fired, it is mounted on a carriage that works like a guide rail. The recoil causes the slide to roll backwards on the rail, thus absorbing the shock.

With traditional milling machines, a momentum decoupling system such as this has only existed on one of the three axes on which the tool or workpiece can move. Klar said he and his colleagues realised one system is not enough because most of the geometries that have to be milled are more complex than that.

‘For instance, the case of a mobile phone is a free form shape, and you have to machine along all axes, and so all machine axes must be very fast and they have to accelerate and decelerate very often,’ he said, adding that the shapes are also very small. Their surfaces must be milled with an accuracy of one micro- metre in each direction with milling tools that are only 50 micrometres thick.

A decoupling system on all three axes, said Klar, will not only increase accuracy but will also reduce the production time required for miniature metal components by up to 20 per cent.

Klar said the additional slides do not hamper the overall design of the milling machine. ‘You would see a normal machine tool, only moving faster,’ he said. ‘The slides are integrated below the motors in the machine base.’

Additionally, he said, the MiniMill is more compact that other milling machines. It only takes up one square metre of space, while conventional machines require about three times as much floor area.

‘It was very hard to make all these components compact,’ he said. ‘When the ranges between the different slides and the spindle are decreased it can lead to the introduction of geometrical errors.’

The MiniMill’s innovative integrated design solves that problem and makes the overall production process more flexible. If there is a change in site, for example, the compact system can easily be moved with a forklift truck.

Klar said he and the other researchers have garnered interest in their machine from several mould and die manufacturers.

He said their next step will be to work with their colleagues at Siemens to develop an advanced computer numerical control system.