In laser milling a focused laser beam is scanned over the workpiece, removing material layer by layer. As with conventional milling, the scanning pattern can be different for each layer, and as a result this 2.5D machining method can produce 3D shaped surface structures. An example of such structure is presented here – a hexagonal pocket with elevated tetrahedrons machined in tungsten carbide.
The laser parameters and the scan pattern have a large influence on the process. The generation of optimized scan patterns, together with accurate control of the laser and scan system, are key to achieving high quality laser micro-milling. Lightmotif developed optimized control software for its machines that enables us to perform micro-milling with the highest achievable accuracy.
The accuracy that can be achieved (in lateral direction as well as the depth) is typically in the micrometer range. The end result of laser micro-milling – in terms of accuracy and surface quality – depends not only on the process settings, but also on the composition and finish of the material used. The best results are usually obtained with a fine grain or amorphous material structure and a polished surface to begin with.
Ultrashort pulse laser processes generate very little heat inside the processed material and apply no mechanical force. As a result, no heat related defects occur – e.g., no burrs, thermal stress, melt, chipping, or cracking – and very thin substrates can be processed without breaking or deformation. Lightmotif is able to micro-mill practically all materials. Metals and polymers can be machined, as well as materials that are more difficult using other techniques, such as glass, ceramics, and composite materials. Some examples of pockets and slots machined in alumina are shown below.
Typical applications are the shaping of micro molds, cutting tools, and stamps, and machining of lab-on-a-chip structures and other micro tools.
For lab-on-a-chip applications laser milling can be used to fabricate the microfluidic structures. This technology can achieve high aspect ratio channels, introduce a variable depth into the channels, and directly drill holes into the wafer for the microfluidic connections. Especially for rapid prototyping ultrashort pulse laser milling is very attractive.
The ability to accurately and reproducibly machine complex shapes in very hard materials can be used to machine cutting tools or stamps. This example below shows a structure machined in tungsten carbide that could be used for stamping or coining processes.
Laser micro-milling processes can be applied to an arbitrarily shaped object by using Lightmotif's 5-axis system and 3D micromachining software. This example shows a needle in which longitudinal grooves were machined. This needle serves as the inner part of a spinneret for the spinning of structured hollow polymer fibers.