The CAD fi le of a pattern is programmed into a machining center. The patterns then are machined in layers to suit the lengths of the cutters.
RP methods. But as the steps between wider layers are larger, the fi nish quality is not as high. FDM machines are quiet and off er an environmentally friendly option, without the volatile organic com- pound emissions present in the resins used for other methods.
Sand Casting Solutions For sand casting, the plastic pro-
toypes created using additive methods of rapid manufacturing can be used as tooling to produce molds and cores, as well. Techology exists to “print” sand molds and cores directly, eliminating the patternmaking step. Machining is another commonly used RP method for sand tooling, molds and cores. For producing patterns, sand casting
is one area where SLA does not shine as brightly as the other additive methods, due to the patterns’ lack of rigidity. T is has been improved in recent years, how-
ever. SLS parts off er a surface fi nish that interlocks with sand grains, but these pat- terns also have limited durability. 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 off ers 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. T e excess material is later removed. RP equipment manufacturers have
developed SLS equipment that prints sand molds and cores, rather than
Nov/Dec 2012 | METAL CASTING DESIGN & PURCHASING | 27
plastic patterns, off ering a signifi cant opportunity to produce small-quantity casting orders without tooling (see a case study about the rapid manufacture of sand tooling on page 49). Sand printing machines can produce numerous small molds and cores side by side, just as plastic prototype equipment does. T ey either fuse polymer-bonded sand to- gether or use inkjet technology to bond the sand. T e technology also allows for
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ONLINE RESOURCE
Some metalcasters have developed unique ways to produce temporary tooling for short-run production. See “Alternative RP Methods,” at
www.metalcastingdesign.com.
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