Jun 15 2005
Spinnerets used in the textile industry are just one example of extremely fine holes in metal parts. Lasers are superior to mechanical methods of drilling such holes. At the LASER fair in Munich, scientists demonstrate how to drill holes of exotic shapes with a high degree of precision.
Drilling straightforward cylindrical holes presents no great problem in do-it-yourself or industrial applications. The task becomes more difficult when the hole has to be very small. Ease to imagine, that drill bits as thin as a human hair – with a diameter of about 70 micrometers – would be far from stable. This is why experts prefer to use the spark erosion method or lasers to make drawing dies for thin filaments, spinnerets or fiber guides.
For creating the very smallest of holes, a family of non-contact, frictionless methods operating with tightly focused light beams has also become established in microelectronic engineering and in the manufacturing of engine parts. Particular difficulties are encountered if the hole has to be conical, with its diameter increasing in the direction of drilling. Geometries of this type are needed in parts such as nozzle blocks whose reverse face is inaccessible. Scientists at the Fraunhofer Institute for Laser Technology ILT have developed a method of drilling holes of even this shape.
“Helical drilling optics enables us to apply circular holes with diameters down to 30 micrometers,” says Welf Wawers of the microstructuring department at the ILT. “If a hole is conical, its diameter may be twice as wide at the end as it is at the point of entry.” The researchers have processed tool-quality and high-grade steels up to two millimeters thick. The pulsed laser pierces a hole 50 micrometers in diameter through the metal sheets in less than a quarter of a minute. It is often important for the side walls of the drilled channel to be particularly even and smooth – a further advantage offered by helical drilling in contrast to conventional laser drilling methods.
But how can the machine drill a hole that gets wider as it progresses deeper? The laser beam is sent through a prism at a variable angle and exits at a different angle, thus also penetrating the workpiece at a variable angle. The dual-conical rotating beam works its way into the depths of the material like a spiral staircase that gets wider towards the bottom. The special geometry of the prism also causes the laser beam to rotate around its own axis at twice the speed of the electric motor, up to 660 times per second. This compensates for any fluctuations in the intensity of the beam as it hits the irradiated surface, resulting in a drilled hole of exceptionally high quality.
http://www.fraunhofer.de
Posted15th June 2005