ACOUSTICAL FOCAL POSITIONING FOR MICROMACHINING USING A PICOSECOND PULSED UV-LASER

摘要

Picosecond pulsed UV-lasers enable micromachiningrndown to a few microns in nearly all kinds of solidrnmaterials like metals, ceramics and polymers.rnHowever, precise machining results with high surfacernquality require a defined sublimation process [1].rnProblems arise by accurate focal positioning on thernwork piece surface and by decreasing laser power forrnlong machining times caused by laser and temperaturerninfluence on optics and thus misalignment. Therefore,rncontrol units for monitoring and controlling ofrnsignificant process parameters like focal position andrnlaser power are necessary. While laser ablation emittedrnacoustic airborne-sound emissions are used for therncontrol unit. A precise adjustment of the focal depthrnwhich is +/-20 μm onto the work piece surface hasrnbeen investigated for cemented carbide and an Al_2O_3+rnZrO_2-ceramic by recording of acoustic emissions. Thernanalysis of the airborne-sound emissions by FastrnFourier Transformation gives information about thernfrequency spectrum and the correlation to the focalrnposition. A subsequent fitted algorithm search allowsrnan automated acoustical focal positioning.rnFurthermore, a power measuring instrument has beenrnintegrated into the working area for automaticallyrnmeasuring and adjusting of actual laser power at thernfocal spot due to the fact that the laser power has to bernkept constant for acoustical focal positioning.