Fig. 2. This fi gure shows two fi xture locating points off the parting line in the drag (bottom) side of the sand mold. Note that the part has been turned over for picture clarity.
Begin With the Middle in Mind
Every designer knows what the
end product will look like, but a savvy designer will take into account the manufacturing steps and methods that will be required to reach the desired end result. Well-designed cast-on locators
will give a common point of refer- ence for all suppliers throughout the production process. T ese locators are designed into the initial casting for reasons that include: • Giving the metalcasting facility solid inspection points.
• Providing consistent fi xture loca- tions for the machine shop.
• Providing a uniform set of refer- ences for inspection.
• Providing a set of reliable align- ment points for fi nal assembly personnel.
T ese factors are geared toward
increasing repeatability and accuracy in inspection and manufacturing. T is means an opportunity for greater dimensional precision and lower costs due to scrap.
Freedom of Casting Design The cast-on locators do not
have to look like out-of-place lugs stuck on the side of your organically flowing casting design. The casting process gives designers the freedom to put material only where they need it. This concept applies to locator design as well. A machining locator can look like many things as long as
Fig. 4. The three fi xture point types with suffi cient draft are used to reduce the possibil- ity of sand tears are shown.
Fig. 3. This illustrates the use of three fi xture points on a part with an irregular shape. The three points locate the part in accordance with the three-datum plane system.
Fig. 5. Shown are fi ve examples of fi xture tabs and divots that can remain in the part or be easily removed during a subsequent machining operation.
May/Jun 2016 | METAL CASTING DESIGN & PURCHASING | 41
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