QUICK-TURN CASTINGS
Rapid manufacturing bridges the gap from prototype to production. DENISE KAPEL, SENIOR EDITOR
O
riginally devel- oped to produce models in the product design and develop- ment stage, rapid
prototyping (RP) and rapid manu- facturing techniques offer a fast and economical solution to reduce lead times on cast products. RP is highly suited to casting orders
of one or two pieces, and it provides designers with a flexible option for testing a cast part before production, allowing them to make any required changes before the final tooling and molds are created. Te process has evolved from pro-
totyping to the manufacture of tooling used in full-run production for larger volumes of cast parts. Sand molds and cores can be produced from RP patterns as well as “printed” directly on the latest RP equipment. Rapid prototypes often are used for diecast tooling to get a leg up on production while the hard tooling is being created. In the investment casting process, rapid prototypes are used as patterns to produce castings. Machining is another RP option, for both metal tooling and sand molds and cores. Te common denominator among
the many RP methods is the 3D CAD data used to fabricate the parts. In traditional RP, that data is converted into an .STL file and the pattern is “printed” on a machine that employs stereolithography (SLA), selective
laser sintering (SLS) or fused depo- sition modeling (FDM) to build a plastic prototype in layers. Depend- ing on the method, photopolymer, thermopolymer, polystyrene or another material is used. Metalcasters, design engineers and equipment suppliers are continuously developing new RP pro- cesses, enhancing the capabilities and potential of the available technology to evolve beyond the plastic “prototypes.” RP material costs are low due to the elimination of hard tooling. Plastic patternmaking is used mainly for smaller cast parts, within one cubic foot. Some niche suppliers can take RP patterns to a larger size, at a greater cost, but RP printers gener- ally have a limited size capacity. Te protoypes can be assembled into a larger pattern for casting. Frequently, multiple small prototype parts are built, side by side, at the same time.
Investment Casting Options For the investment casting pro-
cess, RP patterns often are produced as plastic models on SLA, SLS and FDM equipment. RP prototypes produced on SLA or SLS equipment can be attached to a gating system and run through the typical investment casting process. Plastic tooling offers a significant cost savings and reduces the setup required to produce shells for the final cast metal parts. Te equipment used for SLA builds layers on a platform that is submerged in
a vat of liquid polymer, employing laser technology to cure one layer at a time. Vertical support is needed for products that incorporate horizontal overhangs. Te “steps” between layers are smoothed, and any details are added in post-cure processing. Among the additive meth- ods, SLA is considered the fastest and offers the best surface finish. Coming in at a close second in total speed of production, SLS offers more flexibility as it incorporates powders cured with a laser to sinter the thin layers that compose a finished pattern. Its surface finish is not as smooth as what can be achieved with SLA, and both methods have limitations in terms of the prototype piece’s durability over time.
Te FDM method applies a
continuous filament of thermoplastic polymer or wax through an extruding head, constructing the pattern layer by layer with no required supporting structure for horizontal overhangs. Te result is a stronger pattern than those created through other RP methods. But as the steps between wider layers are larger, the finish quality is not as high. FDM machines are quiet and
ONLINE RESOURCE
For more information about rapid tooling for diecasters, read “Rapid Tooling Opens New Diecasting Doors” at
www.moderncasting.com.
January 2013 MODERN CASTING | 37
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