Site: Fraunhofer Institute for Manufacturing Engineering and Automation (IPA)
Nobelstrasse 12
D-70569 Stuttgart, Germany

Date Visited: 26 October 1995

JTEC/WTEC Attendees: L. Weiss, A. Lightman (report co-authors)

Hosts:

Dr.-Ing. Wilhelm F. X. Steger
Dipl.-Ing. Thomas Haller
Dipl.-Phys. Martin Geiger

BACKGROUND

(See the ICT site report for a brief general introduction to the Fraunhofer Institutes and the Fraunhofer Rapid Prototyping Network.)

The Fraunhofer Institute for Manufacturing Engineering and Automation (FhG-IPA or simply, IPA) has an R&D staff of 250 and a budget of DM 50 million per year. The IPA's Rapid Product Development Group, which started in 1988-89, is part of the Department of Information Processing. The department has a staff of 35 (70% from FhG and 30% from the University of Stuttgart). The RPD group has a technical staff of 6 and an annual budget of DM 5.5 million. IPA is one of the seven Fraunhofer institutes that participate in the Fraunhofer Strategic Alliance in Rapid Prototyping. Work related to RP Network projects represents 20% of the IPA's rapid prototyping efforts.

THE RAPID PRODUCT DEVELOPMENT GROUP

IPA's Rapid Product Development Group is conducting research and development in three areas pertinent to this JTEC/WTEC study: reverse engineering, generative manufacturing and conversion technologies, and information and organization.

Reverse Engineering

This effort involves first scanning surfaces (e.g., clay models, existing parts, etc.) with high-speed, commercially available, optical and tactile digitizing apparatus. Software tools, which IPA staff have developed, are used to support digitizing and to mathematically describe the shapes. These interactive software tools, which are implemented in CATIA, perform several functions, such as surface segmentation for curve fitting. The resulting models can then be used as input to both virtual prototyping environments (which is being done in another group at IPA) and physical prototyping apparatus.To drive the physical prototyping apparatus, the Rapid Product Development staff have done extensive work developing corrective slicing strategies that help account for process limitations (such as overcuring in stereolithography) and post-processing requirements (such as sanding and assembly). Rules for defining layer boundaries in relationship to the 3D CAD model (i.e., the location of the stair-step relative to the actual part boundary) determine whether each layer boundary region is located outside or inside the original 3D CAD model or "best-fit." Since these corrections must be made after slicing, they cannot be done after storing the slice information in a standard published format such as CLI or SLC; by then, the necessary information is lost. The "LEAF" format (Layer Exchange ASCII Format) permits corrections to be applied after slicing. IPA intends to commercialize its slicing software, which was developed with André Dolenc (Helsinki) and follows generalization efforts from SLI and CLI. It provides both border and process information, including the direction of surface normals. Use of the software will provide the experience needed to guide the development of a de facto standard for layer manufacturing. It could help to determine the application protocol (AP) for rapid prototyping that will be part of STEP. The format and results will be published.

Generative Manufacturing and Conversion Technologies

Multiphase jet solidification (MJS)

MJS is an extrusion-based process, similar to Fused Deposition Modeling methodology, which is being jointly developed by IPA (software) and IFAM (materials). There are currently three machines, one each at IPA and IFAM, and one sold by an industrial partner (Logeto GmbH) to an institute. MJS extrudes metal or ceramic slurries using metal injection molding technology. The slurry is contained in a heated vessel and pumped through an attached nozzle with a screw-activated plunger. The feedstock cannot be reloaded without stopping, so build volume is limited. Typical powder sizes are ~50 (m in diameter with a plastic or wax binder. The resulting green preforms are about 30-33% dense (volume) and very homogeneous. Final sintered parts are claimed to be ~99% dense. The developers assume isotropic shrinkage ("better than metal injection molding") of 20-40%. Parts have been made with stainless steel, titanium, and alumina, and examinations have been conducted with other materials. IPA is looking at infiltration with copper.

Models that the JTEC/WTEC team saw had fairly rough surface appearances. The process appears to require significant work to improve overall accuracy and surface quality. IPA is upgrading the software, and IFAM is upgrading the hardware with the goal of commercializing the next-generation system (discussions are being conducted with Fockele and Schwarze and there are contacts with other partners as well). IPA and IFAM have a German patent for MJS and is applying for a U.S. patent. Since the basic methodology of depositing 3D shapes by extrusion, in layers, is considered public domain, the patent pertains to the feedstock composition, the heated material supply (up to 200°C to liquefy the binder and obtain the desired viscosity), and the extrusion nozzle.

Stereolithography

IPA has the first Fockele and Schwarze (F&S) machine. The institute is working with F&S to modify the machine for greater commercial acceptance. (See also the F&S site report, pp. 14-16.) IPA staff believe that this machine has many advantages, such as its ease of reconfigurability, and they are investigating implementation of the diode-pumped frequency-tripled Nd laser in place of the argon laser they currently use. Interchangeable vats allow for quick changeover of resins and for testing of small quantities of experimental material.

Coating technologies

IPA's work in coating technologies includes developing, testing, and installing processes to apply metallic coatings to stereolithography parts for applications like tooling and EMI shielding. Coating processes include physical vapor deposition (PVD), electroplating, and electroless plating. Coatings are applied to help parts withstand the harsh environments of follow-on processes, and coatings can also fill in the part's stair-casing to provide a smoother border.

IPA is also starting a project with the University of Stuttgart on process simulation (applicable to all processes) to help select process parameters. The goal is to develop a VR presentation showing the material buildup and the associated stresses (augmented reality), dimensional errors, material strengths, etc. One objective is to be able to display to engineers the results of their selection of geometry, process, etc., and to provide an environment in which they can get rapid feedback on the impact of modifications. Another aspect will be product evaluation by the design team within this virtual environment. The project is currently in the conceptualization phase. This special project is funded by the government through the university. There are other groups at the IPA that provide high-speed computer capability for process simulation.

Information and Organization

Of particular interest is IPA's use of Quality Function Deployment (QFD) methodology to help select the best rapid prototyping technology for fabricating a part, given a set of design features. There is a system selector based on similar methods from BIBA (Bremen) and a materials selector from IKP. IPA is looking to integrate these selectors because the global processing has many steps, and evaluation becomes complex. The institute is also investigating the potential for doing rapid prototyping via the Internet. To this end, IPA researchers are studying STEP and LAN and WAN requirements. There is an interest in business product and process reengineering, in particular to determine if new technologies are needed for competitive advantage and, if so, how should the business be restructured to apply the new technology to maximum advantage. They are also looking at implementing EDI to form manufacturing alliances. They are studying networks (ISDN) and communication protocols such as Euro File Transfer Protocol (EFTP) for arbitrary partners and ODETTE File Transfer Protocol (OFTP) for the automotive industry and suppliers.


Published: September 1996; WTEC Hyper-Librarian