details DESIGN
Castable cored holes and pockets are not limited by position or orientation.
As-cast features such as bosses, cylindrical clamp half and electronics card slots are cast to shape.
• T e determining factors for casting- in cored holes and slots in the investment casting process are the cored hole diameter, slot thickness, section thickness, ease of wax pat- ternmaking and assembly, ability to fl ow liquid slurry to make the shell/ mold, and fl uidity of the cast alloy.
• Well designed gating and risering allows metal to fl ow into intricate shapes with high defi nition, excellent surface fi nish, as-cast cored holes, pockets and thin- wall features, which eliminate secondary machining.
• Lower thermal gradients due to the preheated ceramic shell that is used as a mold in investment casting compared to conventional sand or metal molds provide better liquid metal fi lling to produce intricate shapes.
Investment casting offers multiple random parting plane orientations, allowing complex features to be cast along with the main shape.
• In investment casting, the complex shapes of a design, such as the card slots, cooling fi ns, mounting fl anges and half-cylinder clamp mount on the electronics housing, are broken down into individual wax shapes to build a pattern. T e wax pieces are drawn from the dies like in conventional sand casting and then assembled together.
• At times, loose pieces are used to accommodate stripping the wax shapes with re-entrant angles. T e design is not limited to a single parting plane or constrained by part- ing plane orientation.
MEDIA
RESOURCE Using the Actable App, scan this page
to see a video of Jiten Shah dis- cussing the part’s design details. For instructions on Actable, see p. 24. To watch online, go to
www.metalcastingtv.com.
Jiten Shah is president of Product Development & Analysis (PDA) LLC, Naperville, Ill., and a 25-year casting design and manufacturing veteran.
Sept/Oct 2013 | METAL CASTING DESIGN & PURCHASING | 17
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