The JTEC/WTEC panel visited 11 sites in Europe that have RP tooling applications (all are in Germany, except as noted):1
Seven Fraunhofer institutes, with financial support from the German government, are cooperating in a rapid prototyping network to speed up the development, advancement, and dissemination of rapid prototyping technologies to improve the competitiveness of the German manufacturing industry. (The main emphasis of this network is metallic prototypes; see Chapter 6.) The seven Fraunhofer institutes are the four listed above, and the following three (not visited by the panel):
What the JTEC/WTEC panel learned in its interviews at the Fraunhofer Institutes is that they are all very well prepared. The Fraunhofer Institutes have a broad knowledge base, a lot of experience, and a lot of shop-smart expertise. The developments underway at their facilities should not be underestimated.
Although there are various cooperative arrangements between them, each of the Fraunhofer Institutes focuses on a different issue: one takes software, another material development, still another focuses on applications, etc. The JTEC/WTEC panel found that by using this approach, the institutes are building a comprehensive infrastructure for rapid prototyping. The Fraunhofer labs are pristine, with brand new equipment. However, they had few parts at the time of the panel's visit, because they are just developing their infrastructure. The panel expects that once the laboratories are fully in place, they will be a strong force. Their integrated information model for rapid prototyping as shown in Fig. 11.1 is very impressive and worthy of note. There is nothing comparable in the United States.
There is continued work at IPA on reverse engineering, or the use of physical models as computer input data. Some of this work was initiated during the Intelligent Manufacturing Systems IMS test case program of 1993. Here, laser scanning, optical and tactile measurement systems, X-ray computer tomography, and 3D ultrasonic sensors are applied for the shape digitizing of models to create a point cloud, which is then fed back into a CAD system to generate a CAD model for further evaluation. In an interesting development, IPA researchers are now working on integrating that process with software tools for surface segmentation, point cloud management, and curve fitting to virtual prototyping and physical prototyping. See Figs. 11.2a and 11.2b.
Fig. 11.2a. Scanned point cloud model.
Fig. 11.2b. Solid model from scanned data.
Researchers at IPA are also investigating coating technologies by applying metallic coating to stereolithography plastic parts for applications like EMI shielding and tooling. The coating processes include PVD, electroplating, and electrolysis plating. One benefit of coatings is that when an otherwise fragile component is coated with a metal, it acquires new characteristics and can be capable of withstanding harsher environments for downstream applications. This allows the part, component, or tool to be useful in new applications. Another benefit of coatings is that they can fill in the staircasing of the part, providing a smoother surface.
Another useful development at IPA is in the area of information and organization. IPA uses a quality function deployment (QFD) approach (Fig. 11.3) for selecting the most appropriate rapid prototyping technology.
Although this work is not being done in the area of tooling at the present time, it certainly can be, with potentially very beneficial results. If the tooling industry can have an intelligent selector based on a tool's features and other requirements, designers will be able to very quickly determine what best fabrication approach to use for tooling or for casting, as well as what materials to use, and so forth. This could be one of the measures that could tie into a STEP application protocol, as discussed in Chapter 8. There are numerous potential applications and implications for IPA's QFD approach.
At ICT, the JTEC/WTEC panel found an example of rapid prototyping being used to make the cavity and core of a plastic injection mold. ICT researchers are making the mold inserts to go into a steel mold set. In this case, the mold is for an electrical receptacle. Using the 3D Systems stereolithography SLR-5180 epoxy resin, they were able to process some 200 parts in a variety of materials, including the following:
Their next step is to try to find ways to integrate the use of additional core pulls or slides so that they can mold more complex geometric features. Fig. 11.4 shows the mold cavity.
Researchers at IFAM are using the Stratasys Fused Deposition Modeling (FDM) process to make substrates. This process is akin to making the reverse of the desired part. Using an electroplating process that does not provide stress or heat, metal is applied on the back side of the part. After building a certain amount of metal on the back side of the part, it is back-filled with an epoxy material, aluminum shot material, or some other material to hold it so that it can be used as an injection mold, which has a 3 mm thickness of metal cladding interface between the mold and the back filling. Using the EOSINT laser sintering process, IFAM researchers are making molds with the Electrolux powder and infiltrating with PbAg2Sn2. This allows for a greater number of parts to be produced from the tool. Over 300 parts were processed from a single mold made from an ABS glass-filled nylon. Fig. 11.5 shows a sample tool and part.
Chapters 2 and 6 discuss the laser-generated rapid prototyping under development at IPT. There, researchers are integrating the powder deposition approach with the use of a laser, followed by NC machining of the top surface and the periphery in a layer-by-layer fashion. IPT is now working with a die-casting company to commercialize this technology.
JTEC/WTEC panelists feel that IPT scientists, by combining their RP expertise with their extensive knowledge and capabilities in tooling, conventional laser and ultrasonic machining, and advanced grinding techniques, have great potential to develop new RP processes that overcome many current limitations.
IKP researchers are not particularly interested in investigating the various mold conversion techniques; they prefer to directly fabricate the mold using EOS stereolithography. As at ICT, researchers at IKP are fabricating the mold inserts directly from the computer model, but then putting them into a steel mold set reinforced with aluminum shot and epoxy. They have produced about 200 parts with this technique for Mercedes-Benz. The parts, however, show signs of deterioration and mold flash. For low-volume production this has proven to be efficient in terms of both time and cost.
BLZ conducts a variety of development efforts with lasers. Among the BLZ projects is one on laser sintering of EDM electrodes, as shown in Fig. 11.6. The process uses an EOS machine and Electrolux bronze alloy for the electrode material. The electrodes will be used for injection mold tooling and for forge dies. By creating some of these electrodes directly, using the laser sintering process, and then using these electrodes in EDM machines, it is possible to burn the shape into the forge die that is then used to forge parts.
BLZ researchers are also developing a laminated process for sheet metal, where the laser cuts sheet metal layers that are then bolted together to form a tool insert. In addition, BLZ researchers are working on a process that uses the heat from a laser to selectively heat sheet metal to form and shape the sheet metal. In another project, BLZ researchers are continuing development on a metal-removal process called lasercaving, which was originally invented by Maho (see also Sites 1996, 1-3). It appears that BLZ is investigating ways to integrate rapid manufacturing and sintering of tools and parts, using the lasercaving process to do the finish machining. The JTEC/WTEC team and the BLZ representatives had a lot of discussion about such "hybrid processes," where the rapid manufacturing processes of making components are integrated with the removal processes to do final finishing, in order to achieve both the accuracy and the surface finish required.
A large variety of molding applications are under development at KU Leuven, in conjunction with its spin-off service bureau, Materialise. Most of these applications are quite well known to those in the fields of vacuum casting of polyurethanes in silicone rubber molds and spin casting of zinc die casting alloys in vulcanized rubber molds. KU Leuven and Materialise researchers are conducting research on including reinforcing fibers and woven glass mats that are transparent to the laser energy into the stereolithography resin, which make parts or tools more wear-resistant. Additional development is underway in selective laser sintering of metals for parts and tools and in rapid production of polymer injection molds and metal casting dies by 5-axis NC machining.
The EOSINT M (for metal) machine was developed to make metal molds using the Electrolux bronze powder. Some EOS customers are finding that they do not have to infiltrate the green sintered mold inserts for low-volume plastic injection molds with the solder. They can sinter the mold directly: it is strong enough to be used for some plastic injection mold parts, and the mold insert porosity does not prohibit molding. It is a fast and easy way to make tools that will suffice for a limited number of applications.
Although Cubital did not have any direct applications for tooling at the time of the JTEC/WTEC panel's visit, company representatives acknowledged in discussions with panelists that the company has a program underway to develop epoxy materials that will accommodate tooling.
The cooperative work of these two French companies has produced very positive results. They have two programs that apply RP to tooling. The first is direct fabrication of a mold cavity using glass-filled resin, 70% of which consists of glass microspheres. These are used to make aluminum sand-casting mold halves for Dassault air-conditioning ducts (Fig. 11.7).
Laser 3D's second cooperative tool-making program with Dassault is the use of a stereophotolithography (SPL) master pattern in a 3D hydrotel tracing machine, where a control stick for the Mirage 2000 Fighter was machined in aluminum by tracing the SPL master pattern. The control stick had complex and ergonomic features. In this Laser 3D/Dassault SPL example, the hydrotel machine scans a plastic SPL part while it machines an aluminum replica. A hydrotel has a stylus and a milling cutter. The stylus motion on the part being traced also controls the motion of the milling cutter that is machining the duplicate of the scanned part. According to Dassault, this process has realized a three-fold cost savings compared to CNC machining.
Dassault provided a photo of a mold that was generated from Laser 3D master patterns (Fig. 11.8).
At Daimler-Benz, tooling is considered the most important application area for use of rapid prototyping technologies. This company is aggressively pursuing ways to make tools. Daimler-Benz participated in a study with IKP, noted previously, where an injection molding tool was fabricated directly from a 3 mm-thick stereolithography shell that was later backfilled with aluminum shot and epoxy resin. This tool produced about 200 injection-molded automotive parts. The mold inserts showed signs of wear, chips on corners, and some pitting. Nevertheless, in cases where only a few parts are needed for design verification of a new component under development, this process is a viable way to make a tool directly from a computer model at a reasonable cost.