Killer driller

German engineers have developed a laser-based spiral drilling machine that is capable of producing tiny precision circular drill holes far more accurately than alternative laser cutting techniques.

With conventional laser cutting, a large quantity of melt material is produced which has to be blown out under pressure from the laser. In contrast, the new technology, known as spiral drilling and developed at Germany’s Fraunhofer Institute for Laser Technology, can operate very precisely to achieve structural geometries of less than 10 micrometres with minimal thermal loading of the components. It is seen therefore as an ideal tool for use in the manufacture of precision microengineered products.

Unlike melt propulsion drilling, with the new technique, a form of vapourisation drilling, the cross-section of a drilled hole depends on the cross-section of the laser beam being used. To compensate for any deviation or inaccuracy from a perfect circle, the laser beam is made to rotate in itself and placed in a circular path over the workpiece.

Project leader Dr Arnold Gillner explained: ‘We move a beam very fast in a circular motion with a special prism-based optic and the laser is focused to spot sizes of 20-30 microns,’ he said.

The beam travels across the component several times, gradually removing the material. The helical drilling method also enables conical drill holes to be produced by tilting the laser beam relative to the workpiece.

The laser beam is rotated by directing it through a revolving image rotator, Gillner explained. This is integrated in a hollow shaft motor that allows the beam to be rotated at a maximum speed of 40,000rpm.

‘The speed may be somewhat slower than conventional laser drilling,’ Gillner said. ‘But, on the other hand, the precision of up to one micron in diameter is much higher.’

This technology has led to interest from a number of industries and is thought to be particularly well suited to the production of injecting nozzles used in diesel engines. There has also been interest from the medical sector using the system in the manufacture of micro-dosage systems.

In fact, potential applications can be found wherever drill holes of this geometry and precision can only be achieved at substantial expense if the more conventional methods are employed.

Gillner said his group has already sold one machine to an unspecified customer in the tooling industry. Customers in Germany and the US have also shown interest.