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RAPID TOOL MANUFACTURING
This invention was made with Government support under Contract NOOO14-88-K-0642 awarded by the Department of the Navy. The Government has certain rights in this invention.
This is a continuation of copending application Ser. No. 07/562,386 filed on Aug. 3, 1990'.
FIELD OF THE INVENTION
The present invention is related to rapid tool manufacturing. More specifically, the present invention is related to rapid tool manufacturing using solid freeform fabrication, such as stereolithography, and thermal spray deposition.
BACKGROUND OF THE INVENTION
The capability to manufacture a wide variety of quality products in a timely and cost-effective response to 20 market requirements is a key to global competitiveness. The opportunities for improving manufacturing technology range across the entire spectrum of industries, materials, and manufacturing techniques. There is no single technological innovation which, by itself, will 25 significantly improve productivity; rather it is a systems issue which involves rethinking many manufacturing activities. One such activity is the manufacture of tooling (i.e., design, prototype, and fabrication) such as dies required for the high-volume production methods that 30 generate most of our manufactured products. Tooling manufacture is typically an expensive and time-consuming process. The reasons lie not only in the fabrication costs and time constraints imposed by conventional machining methods, but also in the organizational 35 framework. In most organizations, different groups employ different processes to design and manufacture tools and products, and the expertise in tool design and product design reside in different groups, impeding communications between them. The representational 40 and physical models used in design, prototyping, and manufacturing are often incompatible with one another, so that transitions between the stages are time-consuming and error-prone. Products often make several complete cycles through design, prototyping, and fabrica- 45 tion before reaching production. Thus, new product development or product modification implies a series of iterative changes for both product manufacturers and toolmakers. For all these reasons, a rapid and smooth transition from product concept to production remains 50 a challenge.
The present invention describes the development of a unified CAD/CAM tool manufacturing system. In this system, both prototyping and tooling fabrication are based upon compatible solid freeform fabrication, while 55 the underlying geometric and process models share a common representational scheme.
Solid freeform fabrication (SFF) builds three-dimensional shapes by incremental material buildup of thin layers, and can make geometrically complex parts with 60 little difficulty. These processes include selective laser sintering (Deckard, C. R. (1987). Recent Advance in selective laser sintering, in Fourteenth conference on production research and technology, NSF, Ann Arbor, Mich. October), laminated object manufacturing (Col- 65 ley, D. P. (1988). Instant Prototypes, Mechanical Engineering, July), ballistic powder metallurgy (Hauber, D. (1987). Automated fabrication of net shape microcrys
talline and composite metal structures without dies, in Manufacturing processes, systems and machines: 14th conference on production research and technology, S. K. Samanta, Ed., NSF, Ann Arbor, Mich., October), three-dimensional printing (Sachs, E. (1989). Three dimensional printing: rapid tooling and prototypes directly from a CAD model, in Advances in manufacturing systems engineering, ASME, Winter Annual Meeting, 1989), stereolithography, and near-net thermal spraying. The present invention incorporates commercially available technologies: stereolithography apparatus (SLA) and arc spray equipment. Stereolithography, which has been commercialized by 3D Systems, Inc. (Valencia, Calif.), is a new process which creates plastic prototype models directly from a vat of liquid photocurable polymer by selectively solidifying it with a scanning laser beam. In arc spraying, metal wire is melted in an electric arc, atomized, and sprayed onto a substrate surface. On contact, the sprayed material solidifies and forms a surface coating. Spray coatings can be built up by depositing multiple fused layers which, when separated from the substrate, form a free-standing shell with the shape of the substrate surface. By mounting the shell in a frame and backing it up with appropriate materials, a broad range of tooling can be fabricated including injection molds, forming dies, and EDM electrodes. For example, the cavities of injection molds can be fabricated by direct deposition of metal onto plastic SLA models of the desired part and backing the framed shell with epoxy resins. Relative to conventional machining methods, the sprayed metal tooling approach has the potential to more quickly and less expensively produce tools, particularly for those parts with complex shapes or large dimensions,. Thus, with stereolithography, an initial part shape or prototype is quickly created. Thermal spraying is then used to make tools based on the part shapes produced by stereolithography.
The potential effect of combining thermal spraying with stereolithography to build tooling is enhanced by integrating and automating these processes within a unified CAD/CAM environment. The goal of integration is to reduce the number of interactive cycles through design, prototyping, and fabrication. CADbased evaluation and modification tools can operate on design models to help the designer create manufacturable designs on the basis of requirements and limitations of the downstream processes. For example, there are certain shape features in thermally sprayed parts which are difficult to spray. The system should identify these features so that the designer may modify them before reaching the fabrication stage. Another example is to automatically critique ejectability by analyzing whether there is sufficient draft for part ejection from an injection mold or mold die. If drafts are not sufficient, the system should identify this geometric problem and bring it to the designer's attention.
Another step in the CAD/CAM approach is to automate the thermal spray process with robotics. Tooling manufacture by thermal spraying is currently a laborintensive artform. Shifting emphasis to robotic spraying, driven by an off-line trajectory and process planner, will improve tooling quality by achieving consistent and predictable performance of the sprayed metal shell.
Finally, the level of integration and the number of different models, in this CAD/CAM system requires geometric representations that can be abstracted at several levels and that can be manipulated over several