For several decades the use of laser sources for cutting and engraving has been an industry standard thanks to their high processing eciency where, depending on the technology used, cut depths from centimeters to few micrometers are possible. In this application we will focus on high quality cutting and engraving for precise applications, looking for lowest possible thermal damage in the material. For some applications it is necessary to produce “clean” cuts or special structures with high density paths, where regular lasers (cw or nanosecond sources) produces high thermal accumulation generating melting eects or even bending the surfaces, making necessary the use of ultrashort pulse lasers from few ps to hundreds of femtoseconds. The use of these special sources will be more common in a near future, as their cost is reducing close by 50% per decade, at the same time that main manufacturers are targeting power levels close to 1 KW.
The machine used to carry out the test is the LS-fPRO with a simple confguration comprising a laser source with a pulse width of 400fs, energies per pulse of 50 microjoules at frequencies of hundreds of Kilohertz, 2D galvanometric scanner with Fth lens and optical beam conditioning to accommodate the beam to the scanner entrance in order to get a theoretical focused spot size diameter close to 50 micrometers. According to the precision needed, the spot size can be reduced using shorter effective focal length lenses, but cutting effciency is greatly reduced producing lower penetration into the material.
For this setup, a 255 mm focal length lens is used with a theoretical spot size of 50 micrometers. With this configuration, metals with few millimeters width are easily cut at low speed. There is a limitation from the ratio width/depth due to the interaction of the beam with the cut walls, that produces energy dispersion and reduces the effciency resulting in “V” cutting shapes. Special cutting heads with costs close to one hundred thousand Euros can be used to resolve this limitation thanks to the active beam tilting during process.
The Process has been carried out in 3 different materials: stainless steel, aluminum and molybdenum . Their composition is unknown and the test result should serve only as an application guide. In all of them the quality process result is very high allowing create micrometric structures as the picture shown. The laser used has a maximum power of 5W. It allows removal speeds of >0.1mm3/s, but today there are lasers with powers 25 times higher, which allows to increase the processing speeds noticeably.