The American Foundry Society’s C-9 Microfi nish Comparator shows surface fi nishes from 20 to 900 root mean square roughness.
sions that are held within close tolerances may be ineffective if the surface is not smooth enough for accurate measurement or proper positioning in a fixture. While a textured surface is desirable or even necessary for some finishing or coating procedures, a surface that is too rough can be detri- mental to finish quality and may require extra finishing with in- creased costs. Although a smooth surface on a cast part often is considered an aspect of its quality, this is not an accurate indicator of the overall quality of the casting. Finer finish requirements require special molding media or second- ary operations, such as grinding or machining and adds to costs.
cates how well the part meets the purchaser’s requirements and how consistently they are met during production. Consistent quality from order to order and from the fi rst to last casting of an order should be a major consideration in choosing a casting supplier. T e main parameters of cast
5
metal quality are: • Properties of the metal. • Soundness of the casting. • Accuracy and consistency of dimensions.
Quality Requirements and Assurance
“Quality” really indi-
specifications, such as those pub- lished by the American Society for Testing and Materials (ASTM) or the Society of Automotive En- gineers (SAE). Specifications are available for different alloys and for a wide range of quality levels required for differing applications.
Unnecessarily high quality
requirements increase the total costs. T e primary concern should be defi ning and meeting acceptable quality levels. At the same time, decreased cost is not a valid reason for purchasing castings that are below required standards. Any initial
Investment Casting Aluminum, Brass, Bronze & Al / SiC Metal Matrix Composite Alloys
“American Foundry Society / Metal Casting Design & Purchasing
2013 Casting of the Year”
• Smoothness of fi nish. Quality requirements often are detailed by reference to industry
Aluminum • Brass • Bronze • AI/SiC MMC • Turnkey Machining • Rapid Prototypes 600 Cannonball Lane O’Fallon, MO 63366
(636)272-6176
http://ofalloncasting.com
Jul/Aug 2014 | METAL CASTING DESIGN & PURCHASING | 29
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