Trennen mit Festkoerperlasern. Teilvorhaben: Trennen von Leichtmetallen, Superlegierungen und keramischen Werkstoffen Abschlussbericht

Conventional machining processes for cutting of ceramic materials due to the material are very time consuming and expensive, while some of them have limited geometrical flexibility. Laser beam cutting offers itself as an alternative, while the ND:YAG laser, contrary to CO_2 lasers, warrants expectations of reduced thermal impact and hence improved machining qualities. Similarly foreseeable are advantages for the cutting of light metals and super alloys using the Nd:YAG laser, which among others are due to their wavelengths and high pulse powers. Only little experience with regard to solid state laser cutting is available for the above materials. The objective of this project is to develop fundamental knowledge concerning the suitability of various Nd:YAG laser systems for the cutting of light metals, super alloys and ceramics, and concerning their influence on process efficiency and machining quality. For this purpose, extensive cutting tests were carried out using representative materials, and the results were assessed with regard to the objectives stated. Improved absorption of the Nd:YAG radiation for TiAl6V4 and various aluminum alloys of small sheet thicknesses observed during laser beam cutting using Nd:YAG lasers was due to the shorter wavelength as compared to the CO_2 laser. With an optimized ratio of the Rayleigh length to the sheet thickness and with an identical cutting gap width, the Nd:YAG laser produces high cutting speeds in the sheet thickness range up to 2 mm. The stated cutting method produces lower cutting surface roughnesses in the cw mode than it does in the pulsed mode. The cutting efficiency, i.e. the maximum achievable cutting speed as a function of mean laser power, can be optimized by adaptation of the laser/optical fiber system. The applicable variation ranges of process parameters were determined for the ceramics under investigation. Purposeful adaptation of these parameters permits a sufficient cutting quality for almost all engineering ceramics in pulsed mode of operation under the condition that fixed lens systems are used for beam guidance. The degraded beam quality associated with the use of optical fibers having a core diameter of 600 #mu#m limits the cuttability to tough ceramics such as Si_3N_4. Similarly, the high thermal load during cw operation limits the range of cuttable materials. Laser induced crack damage can be reduced by appropriate adjustment of the pulse parameters. The results with regard to industrial application show the capabilities and limitations of Nd:YAG laser cutting with different beam guidance systems for the materials under investigation. (orig.)SIGLEAvailable from TIB Hannover: F95B203+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman