tooling, molds and cores. RP equipment manufacturers have
developed systems that print sand molds and cores, rather than plastic patterns, offering a significant opportunity to produce small-quantity casting orders without tooling. Sand mold printing machines can produce numerous small molds and cores side by side, just as plastic prototype equipment does. Tey either fuse polymer-bonded sand to- gether or use inkjet technology to bond the sand. Te technology also allows for greater design flexibility, as the elimina- tion of the tooling step removes some limitations from the process of achiev- ing the desired geometry. Production-wise, sand printed cores and molds are available in a variety of molding materials and binders, includ- ing organic and inorganic, and can be used with most metals, including aluminum, magnesium, copper-base, iron and steel. Suppliers of sand printing technology continue to research new materials and binders to use. For producing patterns, sand casting
is one area where SLA does not shine as brightly as the other additive meth- ods, due to the patterns’ lack of rigidity. Tis has been improved in recent years, however. SLS parts offer a surface finish that interlocks with sand grains, but these patterns also have limited du- rability. FDM parts withstand repeated use, but defects are a concern due to their porosity. Additional additive methods used to
produce patterns for molds and cores in- clude solid ground curing and laminated object manufacturing. Solid ground cur- ing involves building incremental layers of liquid photopolymer that are covered by a photomask and cured with a 2kW ultraviolet lamp. No support structure or post curing is necessary. Laminated object manufacturing offers a relatively low-cost, quick method using sheets of material, such as paper, plastic or com- posites, thermally bonded with a laser that scans the contours of each layer. Te excess material is later removed. Another rapid manufacturing
approach for molds and cores is to computer numerical control (CNC) machine them from a block of bonded sand. It skips the patternmaking step for prototyping and short production runs, and allows designers to test a casting before creating the permanent tooling. Tis method offers a particular benefit for larger parts that cannot be produced in one piece using additive RP equip- ment. In addition, robotically automated
2015 CASTING SOURCE DIRECTORY Many rapid tooling methods are based on laser printing technology.
production lines can produce machined molds quickly.
A Diecasting Difference For diecasting, the options for rapid
manufacturing are machined tooling, laser-based die insert fabrication and plaster molding. Te rapid manufacturing method
most often employed for diecasting production is plaster molding.
Depending on the required surface finish and accuracy of a diecast part, an RP-generated pattern can be used to create a rubber mold, which is then filled with plaster to form a mold the metal is poured into to produce a casting. Plaster castings often are used to eliminate hard tooling costs for parts with tolerances suited to this method, as well as for prototyping or testing. They also are employed as a tempo- rary substitute while the hard tooling is prepared. Rapid tooling for diecasting can
be created through the application of direct metal deposition technol- ogy, which is similar to fused deposi- tion modeling. It uses a laser to melt injected powder metal and deposit it in a precise location. For die inserts, more methods have been developed, including direct metal laser sinter- ing (DMLS), electron beam melting (EBM) and laser engineered net shap- ing (LENS). CNC machining also can be used to
A die insert formed by the LENS process shows the complex designs possible. This insert features curved, irregularly shaped cooling channels.
create individual dies, as well as metal parts and tooling. And rapid solidifica- tion process tooling (RSP) begins with an RP part or machined prototype,
METAL CASTING DESIGN & PURCHASING 13
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