Castings possess many inherent advantages that have long been accepted by the design engineer and metal parts user. In terms of component design, casting offers the greatest amount of flexibility of any metal forming process. The casting process is ideal because it permits the formation of streamlined, intricate, integral parts of strength and rigidity obtainable by no other method of fabrication. The shape and size of the part are primary considerations in design and in this category; the possibilities of metal castings are unsurpassed. The flexibility of cast metal design gives the engineer wide scope in converting ideas into an engineered part. The freedom of design offered through the metalcasting process allows the designer to accomplish several tasks simultaneously. These include the following:
• Freedom of design to optimize functionality and manufacturability.
• Net or near-net shape design.
• Intricate components can be produced as single cast part.
• Few restrictions on part weight or size
• Almost all metals and alloys can be cast.
• Optimal appearance.
CASTING  WELDMENT
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Cost Effective Casting Design |
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Structural design engineers who work successfully with castings commonly design in a narrow group of casting types poured from familiar alloys (like the family of irons or the 300 series of aluminum) and molded from familiar metalcasting processes (like green sand or nobake). Rules of thumb have been developed over the years for common design situations.
Close inspection of these rules reveals that they sometimes recommend conflicting geometries. For example, the use of gusseting instead of mass for stiffness might be labeled “recommended” in one set of design rules and “poor” in another.
Further, when a design engineer leaves a familiar casting design realm for an unfamiliar one, unexpected trouble may result. For example, let’s say we are moving from ductile iron to aluminum bronze while staying in a familiar metalcasting process, nobake molding. No alarms are sounded among the “rules of thumb,” but there’s likely trouble in the usual “ductile iron-style” geometry. Good aluminum bronze geometry is different than typical ductile iron geometry, and the molding process may need to supplement the different geometry with heat transfer techniques. Not suspecting this, the design engineer’s new casting design may suffer from “no-quotes,” or higher-than-expected prices and requests for design changes.
How are design engineers supposed to know that successfully casting geometry for aluminium bronze should somehow be different? And if a design engineer did know that, what would be the proper course of design action?
The answer lies in a better understanding of the relationship among geometry, various metalcasting alloys and structure.
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How to Design