Site: Fraunhofer Institute for Chemical Technology (ICT)
Joseph von Fraunhofer Strasse 7
D-76327 Pfinztal (Berghausen), Germany

Date Visited: 27 October 1995

JTEC/WTEC Attendees: P. Fussell (report author), C. Atwood, R. Aubin

Hosts:

Dr.-Ing. Peter Elsner

Dipl.-Ing. Dietmar Völkle

Lothar Merz

BACKGROUND ON THE FRAUNHOFER RAPID PROTOTYPING NETWORK

There are currently 46 Fraunhofer Institutes (FhGs) in Germany employing a total of 8,000 people. In addition, there are 3 Fraunhofer Resource Centers (not Fraunhofer Institutes per se) in the United States, headquartered in Ann Arbor, and there are several others worldwide. All the Fraunhofer Institutes are independent with a common administration in Munich. The Fraunhofer Institutes derive approximately 20-30% of their annual budgets from the German federal government through the Fraunhofer Society, 40-50% from industry, and 30% from other government sources. The institutes are enjoined from directly competing with industry; rather, they are intended to assist in the development and transfer of technology to industry. (They are interested, in fact, in working with U.S. industry as partial fulfillment of their charter.) There are three integrated Fraunhofer programs that involve several of the institutes: rapid prototyping, environment, and energy.

Seven of the 46 FhGs have allied themselves in a Strategic Alliance for Rapid Prototyping: the Institute for Chemical Technology (ICT) in Berghausen, the Institute for Applied Materials Research (IFAM) in Bremen, the IGD in Darmstadt, the ILT in Aachen, the Institute for Manufacturing Engineering and Automation (IPA) in Stuttgart, the IPK in Berlin, and the Institute for Production Technology (IPT) in Aachen. The Fraunhofer RP network is currently funded entirely by the government. Preceded by a half-year case study, it is a 3-year effort to develop software and prototype processes and then sell them back to industry to achieve industry funding equal to 1.5 times the government funding level. (There is a schedule for performance, and penalties apply if the milestones are not met.) This alliance has received DM 5 million from the Fraunhofer Society as start-up funds. The network started operation in September 1994 and was expected to spend two years to start up and align its efforts. The group meets at least once every three months. There is also industrial interaction and guidance and the expectation that industrial contracts greater than DM 5 million will be signed by September 1997.

At the time of the JTEC/WTEC team's visits, there were 3 joint projects on-going in the Fraunhofer Rapid Prototyping Network:

The JTEC/WTEC team visited four of the Fraunhofer Institutes in the Rapid Prototyping Network: the Institutes for Chemical Technology, Applied Materials Research, Manufacturing Engineering and Automation, and Production Technology.

BACKGROUND ON THE ICT

The Fraunhofer Institute for Chemical Technology (ICT) was created in 1959 to provide research and expertise to the German military for chemically based explosives ("highly energetic materials"). With the end of the Cold War, the mission for this group was expanded to include industry-related problems while maintaining a core expertise for the military mission. The intent is to balance 50/50 the funding for the military work and the commercial work. Total personnel number about 280 workers, about 120 of whom are scientists, and 29 have PhDs. ICT has a budget of about DM 30.3 million.

Prof. Dr.-Ing. P. Eyerer is the head of the institute. He is also the director of the Institute for Polymer Testing and Polymer Science (IKP) at the University of Stuttgart. The Fraunhofer ICT is in close association with the IKP, especially in projects related to polymer engineering and rapid prototyping. This institute is divided into five areas: Energetic Materials, Energetic Systems, Applied Electrochemical Systems, Environmental Engineering, and Polymer Technology. Dr. Schmitt oversees the Energetic Materials and Energetic Systems groups, and Dr. Elsner oversees the Applied Electrochemical Systems, Environmental Engineering, and Polymer Technology groups.

ICT has expertise in the subject areas of measurement, new battery technology, environmental technology (such as using supercritical water as a means to decompose hazardous chemicals), and conductive polymers. ICT plans to leverage its previous work in extruding and processing of highly loaded (~90 wgt %) polymers to commercial applications. It also plans to integrate expertise from several areas and to combine processes in order to create unique products and processes. The institute also seeks to avoid labor-intensive solutions, preferring automated approaches to assure work will stay on German soil.

Because different polymers are available in Europe than in the United States and are generally more costly, ICT is studying ways of using, for example, polycarbonate rather than polystyrene, and is looking for other cheaper polymer and polymer processing solutions to engineering problems.

NEEDS, GOALS, OBJECTIVES, AND PLANS

The main focus of the Polymer Technology group is tooling, with the following goals:

The overarching goal is to produce the right material for the application and the process used to make the tool; the group does not concentrate on a particular fabrication method, but rather expends effort on the material-process interaction. ICT's goal for stereolithography-related work, using the SLA 500 device, is to optimize the use of the machine for tooling technology, and specifically for prototype tooling. The goal for sintering-related work is to make the best material.

While the prototype applications are interesting, the longer-term focus is on tooling for complicated small parts. ICT researchers believe that such tooling cannot be made quickly using conventional methods: they compare making complex small parts to a watchmaker's craft as opposed to that of a traditional machinist. They believe that tooling for complicated large parts will be made using subtractive methods such as ECM, EDM, or milling.

In the area of ceramic systems, ICT researchers speculate that medical applications are the only profitable areas for high technology. The first application will be fabrication of teeth.

EQUIPMENT AND FACILITIES

The institute has an SLA 500, an EOSINT P 350, and an experimental sintering device using a YAG laser for high-power experimental work. The SLA 500 was installed in 1994 and had been used about 1,350 hours over the course of a year. It is filled with CibaTool 5180. Institute staff control the humidity as well as the temperature of the device. The SLA operation had apparently been successful in the sense that ICT was providing parts to industry as needed (the large working volume of the SLA 500 is appealing for some of industry's problems). The team saw a display of well-made and well-processed SLA parts. The EOSINT P 350 has a working volume of 350 mm x 350 mm x 600 mm. This EOSINT device was only used for sintering polystyrene material at the time of the JTEC/WTEC visit. The device has some of the additions needed for polyamide materials, but ICT researchers have not been successful with other materials. They believe they can operate the EOSINT device to produce polystyrene (PS) parts that are 90% dense. They have enclosed the EOSINT device in a room on the shop floor to help control odor and dust.

The high-power sintering machine uses a Nd:YAG laser with 100 W at the powder bed. The focus point is inside of a commercial oven for environmental temperature control. The experiments ICT had most recently conducted at the time of the team's visit were based on using PS-coated iron particles. ICT was performing coating experiments using a commercial fluidized bed coating device obtained from the pharmaceutical industry.

ICT's injection molder is an Arburg 270M, suitable for metal injection molding and ceramic injection molding, as well as for conventional plastic injection molding.

MATERIALS

Materials work is the center of this institute's efforts. ICT researchers are working on applying as thin a coating as possible to metal or ceramic powders, and using this system as feedstock for laser sintering devices. They are now developing parameters with a polyethylene glycol coating. It is easy to apply and photograph so they can quickly understand the effects of parameter changes. Their model metal is 45 - 90 µm vanadium steel. The polystyrene coating is the system they have the most immediate experience with.

They hope to develop a system where they are not only able to provide a very thin coating on the particles, but perhaps also to provide a controlled texture to the coating. Apparently one goal is to use the texturing to minimize the amount of coating needed for creating green parts. One area of interest is inorganic coatings: they would like to add a coating of carbon to iron particles -- after sintering they hope to show a steel structure with near full density. Their coating goals are about 1 wgt %.

The steel alloys of long-term interest are those of the current tooling industry: H13, P20 types. They wish to focus on materials they can harden, polish, and weld.

The team's hosts briefly discussed their understanding of the glass-filled photopolymer work done at Stuttgart. They understood from that effort that viscosity, density, and segregation issues make this approach quite problematic, especially with a recoating method (doctor blade) similar to that of the stereolithography system.

One technique ICT researchers are pursuing is the use of nanoparticles of either a single composition or a mixture, and agglomerating them to form the material needed for sintering. Another route is to produce reactive systems, silicate systems in particular, that will require no organic binder, thus avoiding the problems of gas production and carbon black contamination during sintering. They are also interested in making particles of altered morphology in the 5-360 µm range, working with spheroidal slurry systems in the above range, and trying to maximize density with bimodal and trimodal mixtures. They hope to reach 90% dense, yet flowable, powder systems.

Finally ICT researchers are looking at novel particle production techniques, including thermal spray processes, fluidized bed techniques, and crystallization methods. They are also beginning to study the possibility of placing hollow sphere particles into a liquid system, and particularly of adding the particles to the polymer during the gelation phase -- that is, shoot the particles into the material during gelation.

APPLICATIONS

The applications of primary interest at ICT are those of sintering. One route under investigation is using a sinter device to create the green part, using supercritical fluids to remove a portion of the binder, and then post sintering to achieve the desired strength and density.

The supercritical fluid approach is now commonly used in industrial practice (to decaffeinate coffee and tea, for example). The notion of ICT researchers is to partially debind the laser-sintered green part and then complete the final sintering. In an interesting variation, they also believe that it would be possible to add a second material to the porous structure by running the supercritical system in reverse. Their current experimental equipment will remove about 75% of the binder from a 4 mm x 5 mm x 60 mm part (fairly porous to start) in one hour. There are researchers studying and using this technology in the United States at Modell and the University of California at Berkeley.

The basic sequence is as follows:

The choice of solvents is highly dependent on the required chemistry. ICT does not have a "general" solvent and does not expect to have one.

In SLA direct tooling, ICT researchers have experimented with making an SLA-plastic injection molding tool (that is, the tool is made directly in SLR 5180 epoxy material). They showed the JTEC/WTEC team their first experiment, a wall outlet 2 in. by 2 in. with wall thicknesses of 0.125 inches. The 5180 epoxy tool had made about 200 parts (we saw parts #117 and #150) in polystyrene and ASA (acrylnitryl styrene acrylic copolymer). The tool had been used to make 100 of each material. The operating parameters were

ASA: Material at 240°C, 1000 bar, 40 sec cycle time PS: Material at 210°C, 900 bar, 40 sec cycle time

Researchers had run the ASA material in a series of 20 parts, then cooled the die, then 40 parts, then cooled the die, then 20 parts.

The SLA part is assembled into a typical metal mold base. The sprue is fed through the cavity half (the nozzle fits against the metal base), and the ejectors are in the core half. The tool was still in one piece, although chipping and surface defects were visible in both the tool and the parts.

ICT's next step in this area is to build a tool with a core pull or slide. The initial idea was to make the slide of steel, but the researchers now believe that a 5180 slide may behave adequately. For reactive polymer systems, the team's hosts observed that copper will frequently have a very detrimental affect on the reaction system. As a consequence, ICT staff were not interested in using the copper-infiltrated tooling now becoming available for RIM, etc., tooling.

MISCELLANEOUS OBSERVATIONS

The Polymer Technology group at ICT is interested in working on high-speed machining. Its researchers are experimenting with ion-implanted hardened tooling, altering the tooling geometry (changing the angle of the cutting face), and using atomized mist coolant sprays. The hosts noted that the coolant flow rates were greatly reduced from traditional machining, but they didn't describe no-coolant experiments. They are attempting to turn hard materials (hardened tool steels), and they are investigating the use of 30 nm diameter nanocrystalline diamond-coated tooling (spherical diamond particles).


Published: September 1996; WTEC Hyper-Librarian