By: Henrikki Pantsar1, Petri Laakso2, Mika Aikio2, Jouni Huopana2, Hans Herfurth1, Stefan Heinemann1
1 Fraunhofer USA, Inc. Center for Laser Technology, 46025 Port St, Plymouth, MI 48170
2VTT Technical Research Centre of Finland, Tuotantokatu 2, 53850 Lappeenranta, Finland
Helical laser drilling is a method for producing high quality holes with defined geometries in different materials among industries such as aerospace, medical device manufacturing and electronics. If the aspect ratio of the hole is small, drilling can be done using a fast scanner. However, a special drill head is needed for higher aspect ratio holes and improved precision. The drill head typically comprises wedges or a Dove prism to rotate the laser beam at high velocities. Using a pulsed laser, each pulse removes a portion of the material. Thermal effects and the thickness of the recast layer are significantly smaller than associated with single pulse or percussion drilling.
Combining a galvanometric mirrors together with rotating optics opens up possibilities for drilling and processing which cannot be accomplished with either of those devices separately. In addition to using the helical drill head for precision drilling and adjusting the hole diameter using the scanner mirror angles, it is possible to create non-circular geometric features by combining the movement of scanner mirrors and the rotational movement. Movement away from the origin along the x or y axis on the scanner’s Cartesian coordinate system is translated into the radial coordinate on the polar coordinate system and the angular coordinate is defined by the angle of the prism. In principle, the rotating prism creates a circular beam path which can be scanner at a rate up to 10,000 rpm. Using a sufficiently large prism, the helical drilling device can be stopped to engrave or mark the samples using the same optical setup. There is no need for removing the drill head.
VTT Technical Research Center of Finland has developed an add-on helical drill head which can be attached to typical galvanometric scanners. The head is based on a Dove prism which rotates at 5,000 rpm, creating 10,000 optical rotations per minute. Fraunhofer USA, Center for Laser Technology is currently using such a head to develop laser processes utilizing crystal and fiber based pulsed lasers for expanding the possibilities of helical drilling for industrial applications.
The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here