Other Pattern Replication Methods

Since the late 1980s, there have been several pattern replication methods used to turn the weak “rapid prototypes” of those days into pieces with useful material properties. While the number of AM technologies has increased and the quality of the products they can manufacture has greatly improved, these processes of duplication are seeing less use as people choose to directly produce a functional component, if possible. Even with the multiplication of AM technologies and materials, however, pattern replication processes are commonly used by service offices and companies that need parts from different materials that cannot be processed directly in AM.

The most common pattern replication methods are probably RTV molding or silicone rubber molding. In RTV molding, as shown in Figure 9.13, the AM pattern is given visual markers (such as the use of colored tape) to show the parting line positions for the disassembly of the mold; the runners, risers, and gates are added; the model is placed in the mold box; and the rubber-like material is poured around the mold to encapsulate it. After cross-linking, the solid, translucent rubber mold is removed from the mold box, the rubber mold is cut into pieces by the parting line

FIGURE 9.13 RTV molding process steps.

marker, and the pattern is removed from the mold. The mold is reassembled and held together in a box, or by placing rubber bands around the mold to complete the replication process, and the molten material is poured into the mold and allowed to solidify. The mold is opened after solidification, the part is removed, and the process is repeated until there is a sufficient number of parts. This technique can be used to produce 10s or 100s of the same pieces using a single pattern. If the part formed in the RTV mold is a wax template then a metal part can be produced using it in an investment or plaster casting process.

Thus a single AM design can be repeated to a large number of metal parts at relatively modest cost by combining RTV molding and investment casting. Metal spraying processes were also used to reproduce geometry from part AM to part metal. In the case of a metal spray, the metal part is repeated only by one side of the pattern. It is most commonly used for tooling or sections where one side contains all the complexity of the geometry, and the rest of the tool or component consists of smooth edges. The AM pattern may be repeated using spray metal or electroless deposition processes to create an injection molding core or cavity which can then be used to mold other parts.