Site: Fockele und Schwarze
Alter Kirchweg 34
W-33178 Borchen-Alfen, Germany

Date Visited: 25 October 1995

JTEC/WTEC Attendees: J. Beaman (report author), R. Brown, B. Kramer

Hosts:

Dieter Schwarze, Principal
Matthias Fockele, Principal

BACKGROUND

Fockele und Schwarze was founded in late 1991 by two solid state physics PhD graduates from the University of Paderborn, Matthias Fockele and Dieter Schwarze. They obtained DM 180,000 in financing from a required (Westphalia) government program, DM 210,000 in bank loans, and DM 60,000 from personal investment. This DM 450,000 seed money allowed them to construct an experimental system, which was operational in June 1992. The company consists of the two principals, one full-time employee, and a part-time software person. It is located in Dr. Fockele's home. In 1992, Fockele and Schwarze began commercial operations by selling parts as a service bureau. Their commercial plan is to sell machines to industry. They sold their first machine to the Fraunhofer IPA in 1994 and their second machine to the University of Magdeburg also in 1994. Both of these buyers are research organizations, which will use the machines for studies in rapid tooling, machine optimization, etc. At the time of the JTEC/WTEC team's visit, the company had recently received an order from an industrial company.

RESEARCH AND DEVELOPMENT ACTIVITIES

Laser Research (Machine Design & Methodology)

Fockele and Schwarze are experimenting with a 2 W Nd:YAG solid-state laser supplied by Coherent Atlas. This laser provides 1.06 mm wavelength, which is then frequency-tripled. Pumping for the laser is provided by two laser diodes. This laser has a number of potential advantages over the existing Ar ion laser:

Software (CAD)

One of the unique capabilities of this company is its software, which is based on HPGL graphics language in conjunction with a ProEngineer solid modeler. A typical software sequence of events to produce a part would entail five steps:

  1. create ProEngineer solid model (or modify from IGES file)

  2. slice ProEngineer solid model into HPGL formatted layers

  3. sort HPGL data for connectivity and identify inner and outer regions

  4. generate support structure both inside and outside of part contours (part skin) using Materialise CONTOOLS

  5. generate scan style by sorting scan regions by geometric position

During the procedure, the skin contours are scanned last, and support structure regions can be scanned in an interlaced fashion to reduce stress and curl. The line-scanning technique differs greatly from those of other companies. Fockele and Schwarze have found cure procedures that significantly reduce curl and simultaneously give full control of cure depth and line width at any point on the surface.

The advantage of the Fockele and Schwarze direct slicing approach over standard STL methods lies in its ability to incorporate true geometric representation (not linear tessellation) with smaller files. Another advantage to this approach is its ability to have greater software control of the process. This would be invaluable in an R&D environment. The system also appears to require far fewer parameters than a 3D machine to control the process.

Machine Research (Machine Design)

Electrostatic (dynamic) recoating

This company has invented an electrostatic (dynamic) recoating blade and curved blade shape. The electrostatic blade moves 1 mm above the surface of the bath and attracts the photopolymer up to the blade and spreads it over a layer without any necessity for "deep dip." This system works best with the Allied Signal Exactomer low-viscosity resin.

Capacitive level sensing

A capacitive level-sensing device provides more accurate and robust detection of the photopolymer liquid level in the vat. This noncontact sensor is positioned approximately 4 mm above the bath and has an accuracy of ~ 5 µm.Piston-driven vat

The Fockele and Schwarze machine has a photopolymer vat that is driven from the bottom by a lead screw and a stepper motor. The advantages of this approach are the ease of changing resin (by changing out the entire vat) and the elimination of liquid level changes due to elevator support dripping into the bath. The machine also has a simple mechanical rod fixed to the platform to compensate for height changes due to volume reduction by platform down-movement.

SUMMARY OF DISCUSSION

Dieter Schwarze and Matthias Fockele were very open about their system and shared many technical issues with the JTEC/WTEC team. One issue that they repeatedly brought up was that of the photopolymer resin. Their greatest success has been with the Allied Signal Exactomer resin, which has a low viscosity, but customers complain about the "sticky" feel to the parts made from this material. They found the DuPont resin too susceptible to humidity (hydroscopic). For business reasons, they have not been able to test any of the Ciba-Geigy resins. They gave the team a thorough hands-on review of their machine, including the results of their experiments with the Nd:YAG solid-state laser. They successfully incorporated this laser into their system in the short period of ~ 1_ weeks. The machine's technical specifications include the following:

After Fockele and Schwarze gave the team a detailed review of their software, there was a short discussion of the company's strengths, which lie in its technical development of SLA technology. They see four important future SLA issues:

  1. production of stereolithography machines with Nd:YAG lasers

  2. development of materials for ease of use and functionality

  3. fabrication of small (micro) intricate parts

  4. reduction of price to encourage midsize German companies to invest in the technology

In closing, they mentioned a technical development that initially they found interesting. This was a polygon mirror scanning system for high speeds. On closer analysis, they found the technology lacking due its inability to compensate for internal stresses. They also mentioned work by J. J. Clair in France in 1993 on a two-laser system that is similar to the work by Swainson in the United States. They believe this work has been discontinued.

Overall Assessment: Fockele and Schwarze are good developers of SLA technology but have limited marketing resources.


Published: September 1996; WTEC Hyper-Librarian