Lehrstuhl für Fertigungstechnologie, Universität Erlangen-Nürnberg

Laser beam drilling of flow rate determining through holes



Datum: 30.11.1993


Author


Reporter

  • Prof. Dr.-Ing. Dr. h.c. M. Geiger
  • Prof. Dr.-Ing. H.W. Bergmann

The aim of the work was the further development of the process of laser beam drilling of through holes in order to improve especially the geometric reproducibility of flow rate determining holes as well as multihole-pictures. The obtained quality of the hole finish by laser beam processing should not require any subsequent post processing. An important research result is the reduction of the flow tolerances of laser beam drilled holes to below 1 % of the average flow value. This equals a reduction of about one order of magnitude as opposed to conventional laser beam drilling. This is achieved by the new concept of the in-process-measurement of the flow of process gas through the hole in process. A prerequisite for the flow measurement is the gasproof connection between the tool position which is to be processed and the flow measurement device. For plane workpieces, usually in the form of sheet-metal, clamping devices are proposed which contain a so called process gas chamber. By means of a Computer based control system a hole can be corrected in its flow value by a specific laser beam refinishing and approximated to a predetermined flow rate. As a standard value the present flow value is used, as place values all adjusting Parameters of the laser system, i.e. the laser aggregate and the positioning unit, are used. The most effective control strategy is the one with an adaptive focus shift, which after the production of an initial hole with a first single laser beam pulse calculates the difference to the predetermined flow value and, proportional to it, makes the shift of the focus. The effectiveness of the proposed method of processing is proved with different processing examples at steel sheets of different thickness. At the same time different processing strategies with variable hole geometries and arrangements are examined.