Rapid Tooling Techniques

DSPC (Direct Shell Production Casting)

DSPC (Direct Shell Production Casting) produces the actual ceramic molds for metal castings directly from 3-D CAD designs. No tooling or patterns are required. DSPC uses Three Dimensional Printing technology to produce the ceramic casting molds using a layer-by-layer process.

PROCESS DESCRIPTION

The CAD file of the designed part is transferred via modem or magnetic tape to the Shell Design Unit (SDU) of the DSPC system. The SDU operator then designs the ceramic mold for casting the metal part by adding the gating system to the part geometry and converting the updated file into a cavity file in CAD space. This is a one time process after which many identical ceramic mold could be generated. The cavity file for the ceramic mold is then used to automatically generate the ceramic casting mold.

The ceramic mold is created in layers. The fabrication process involves three steps per layer. First, the ceramic shell model is "sliced" to yield a cross-section of the ceramic mold. Second, a layer of fine powder is spread by a roller mechanism. Third, a multi-jet printhead moves across the section, depositing binder in regions corresponding to the cross-section of the mold.

The binder penetrates the pores between the powder particles and adheres them together to form a rigid structure. Once a given layer is completed, the ceramic shell model is sectioned again, at a slightly higher position, and the process is repeated until all layers of the mold are concretized. The DSPC mold is then cleaned of excess powder, fired and poured with molten metal.

A DSPC mold may contain an integral ceramic core, producing a hollow metal part. Virtually any molten metal can be cast in DSPC molds. Automotive parts have already been manufactured in aluminum, magnesium, ductile iron, and stainless steel.

The DSPC machine is like a three dimensional printer that uses the designer’s Computer Aided Design to create the actual ceramic casting molds. Consequently, it expedites the design and the functional testing of new automotive components such as engines, transmissions and turbochargers. First article parts, made directly from the customer’s CAD, are delivered in days. Importantly, any design change is easily incorporated in CAD space, which provides the ultimate configuration control and assures that all design changes are properly documented.

With DSPC, production tooling (dies, patterns and core boxes) are cast as net shape tools from the CAD file of the approved part. This tooling is now created only once, guaranteeing a smooth and cost effective transition from the first article part to production. The need for temporary (prototyping) tooling is eliminated, and so are the huge monetary outlays associated with prototype tooling that previously had to be considered. With DSPC, an indefinite number of design iterations, including testing the design with different alloys, can be created without the costly and time consuming need to produce tooling with each step.