PART I: EUROPEAN SITE REPORTS

Site: Bayerisches Laserzentrum (BLZ)
(Bavarian Laser Center)Schallershoferstr. 108a
91056 Erlangen, Germany

Date Visited: 27 October 1995 (Note: This visit was only ~1.5 hours, due to travel constraints)

JTEC/WTEC Attendees: L. Weiss (report author), A. Lightman, F. Prinz

Hosts:

Dr.-Ing. Dipl.-Phys. Hutfless (representing Prof. Dr.-Ing. Dr. h.c. M. Geiger)
Ing. Arjan Coremans
Dipl.-Phys. Michael Kauf

BACKGROUND

The Bayerisches Laserzentrum (BLZ) was established in January 1994 and is managed by Dr. Geiger of the University of Erlangen-Nuremberg and by Dr. Hoffmann. BLZ is supported by the Circle of Friends for the Extension of Laser Technology at the Friedrich-Alexander University in Erlangen-Nuremberg, the Chamber of Commerce of Nuremberg, and the Chamber of Commerce of Bavaria. The 1995 gross revenue for BLZ was DM 6 million, of which DM 3 million was contributed by the state and federal governments. (Government financing is given solely on a project-by-project basis, and all research institutions, whether industrial, governmental, or university, may apply for government funds.) BLZ's manDate: is the transfer of university research to industry, especially to small- to medium-sized companies, in the area of laser-based manufacturing. BLZ develops prototypes of new laser technologies, manufacturing systems, and diagnostic tools, and it carries out feasibility studies. The BLZ has a staff of 70 people (30 scientists and 5 foreign guests). It has 20 laser systems (including CO2, Nd:YAG, excimer, and copper vapor lasers) with powers from 20 W to 18 kW.

RAPID PROTOTYPING AT THE BLZ

While BLZ conducts research across a broad range of laser manufacturing technologies, there are three areas of particular interest to this study: laser ablation, laser sintering, and lamination of laser-cut materials. There is also related work in other methodologies such as laser bending that facilitate rapid product development.

Laser Sintering

BLZ is working with EOS to make process improvements for the EOS laser sintering machine; in particular, for direct metal sintering using the Electrolux bronze-nickel alloy. One of the BLZ contributions is the development and refinement of a dual-beam, which has a central beam for sintering and a surrounding field for preheating, to reduce residual stress. BLZ researchers will apply a 750 W CO2 laser with the core (sinter) beam having between 0 and 20% of the energy. The primary application areas are making injection mold tooling and for EDM electrodes. BLZ representatives showed the JTEC/WTEC team several tooling artifacts, such as a mold for a Phillip's electric shaver, including complex-shaped internal cooling channels. These tools have not yet been fully tested or used in any production. The lifetime of these tools is expected to be ~500 shots; however, researchers had achieved at the time 47 shots and noted that the mold showed some failure. BLZ's performance claims for EOS with this material are tolerances of (0.15 mm (in overall dimensions of about 150 mm) and hardness of 150 HV when the material is infiltrated with a solder alloy, of 30 HV when uninfiltrated. The raw sintered material has mechanical attributes about equivalent to magnesium, and the infiltrated material has attributes about equivalent to aluminum.

Laser Ablation

In contrast to material deposition methodologies, laser ablation is a material removal process. It can be used to sink cavities into metal or ceramic stock in a downward, layer-by-layer fashion. The Lasercav® was originally developed by Maho.1 A high-power laser and oxygen source are simultaneously pointed to the surface to be cut and guided along a cutting path. The heated metal oxidizes, and oxidized chips break away due to thermal stresses in the oxide fragments. The Lasercav® at BLZ is manufactured by LCTec, which split off from Deckel Maho Company and holds the Lasercav® patents. BLZ is cooperating with LCTec for further development.

The current system combines a 5-axis CNC horizontal milling machine base and a 750 W CO2 laser. Parts are mounted on the machining table and are moved relative to the fixed laser beam. The system costs about $500,000. The achievable accuracy is 0.05 mm with corresponding material removal rate for finishing of 5 mm3/min., surface roughness of about 10 (m, and minimum tooling radius of 0.1 mm. The overall machining time can be reduced by first roughing out material using the laser in a melting mode, where a removal rate of about 1,000 mm3/min. is possible

The primary applications at BLZ are cutting cavities in tools and texturing tooling surfaces. The JTEC/WTEC team saw examples of machined steel dies and leather-textured patterns; their quality was excellent. The surfaces can be glass-beaded to remove oxide; otherwise, no additional processing is required. BLZ is currently working on an improvement of the machining accuracy and processing speed.

An optical method for measuring cutting depth, based on locating the IR emission of the workpiece surface, is used to control the laser in a closed-loop fashion. The system is programmed from STL files (3D CAD) or grayshade pictures (surface patterns). Laser ablation appears to be a powerful method for building and texturing tools with fine detail and small features.

Lamination

The team observed some limited work going on in lamination whereby individual cross-sections of a part are first cut to shape with laser cutting and then bolted together to form a tool insert. The outer surface of each cross-section is cut in a 3D fashion. This is a crude technology (dating from the mid 1970s or earlier), but it has advantages for fast evaluation. The laser-cut sheet provides core and cavity at the same time.

Laser Bending

This is a process that bends sheet metal by laser-induced thermal stresses. No mechanical tooling or custom fixturing is required. Very large structures are possible, and part properties are similar to those parts built with conventional bending; no springback occurs. Sheet metal with thickness from 0.1-5.0 mm can be formed with an accuracy of 0.2 degrees.


1 Note from Michael Kauf of BLZ: "Lasercav® is a trademark of LCTec for all material removal technologies carried out by the laser. Today we talk about 'controlled laser ablation' and distinguish between three different processes: ablation by melting, sublimation, or oxidation, especially 'chip removal,' meaning the reactive ablation of ferrous materials."


Published: September 1996; WTEC Hyper-Librarian