METAL CASTING PROCESSES Metal Casting Principles Metal Casting Metal Casting Operation Effect Of Gases On Metal Casting Metal Casting Design Expendable Mold Casting Plaster Mold Casting Ceramic Mold Casting Shell Mold Casting Vacuum Casting or V-process Expanded Polystyrene Casting Investment Casting Permanent Mold Casting Basic Permanent Mold Casting Slush Casting Pressure Casting Vacuum Permanent Mold Casting Die Casting Hot Die Casting Cold Die Casting True Centrifugal Casting Semicentrifugal Casting Centrifuge Casting Ingot Casting Continuous Casting MANUFACTURING PROCESSES Metal Forming Metal Rolling Metal Forging Metal Extrusion Metal Drawing Sheet Metal Powder Processes
Sand casting is the most widely used metal casting process in manufacturing. Almost all casting metals can be sand cast. Sand castings can range in size from very small to extremely large. Some examples of items manufactured in modern industry by sand casting processes are engine blocks, machine tool bases, cylinder heads, pump housings, and valves, just to name a few.
Most sand casting operations use silica sand (SiO2). A great advantage of sand in manufacturing applications is that sand is inexpensive. Another advantage of sand to manufacture products by metal casting processes, is that sand is very resistant to elevated temperatures. In fact, sand casting is one of the few processes that can be used for metals with high melting temperatures such as steels, nickel, and titanium. Usually sand used to manufacture a mold for the casting process is held together by a mixture of water and clay. A typical mixture by volume could be 89% sand, 4% water, 7% clay. Control of all aspects of the properties of sand is crucial when manufacturing parts by sand casting, therefore a sand laboratory is usually attached to the foundry.
When planning the manufacture of a particular casting, remember some properties of a sand casting mold mixture are contradictory to each other. Tradeoffs in different properties are often needed to achieve a compromise that provides a sand casting mold mixture with adequate properties for the specific part and casting application. There are some things to consider when selecting a sand mixture for a manufacturing process. Small grain size enhances mold strength, but large grain size is more permeable. Sand casting molds made from grains of irregular shape tend to be stronger because of grain interlocking, but rounder grains provide a better surface finish. A sand casting mold mixture with more collapsibility has less strength, and a sand casting mixture with more strength has less collapsibility.
In industrial sand casting processes a gating system, (not shown), is often incorporated as part of the pattern, particularly for a cope and drag pattern. Patterns can be made of different materials, and the geometry of the pattern must be adjusted for shrinkage, machine finish, and distortion. Pattern basics are covered in detail in the patterns section.
Of specific interest to sand casting would be; the effect and dissipation of heat through the particular sand mold mixture during the casting's solidification, the effect of the flow of liquid metal on the integrity of the mold, (mold sand mixture properties and binder issues), and the escape of gases through the mixture. Sand usually has the ability to withstand extremely high temperature levels, and generally allows the escape of gases quite well. Manufacturing with sand casting allows the creation of castings with complex geometry. Sand casting manufacture, however, only imparts a fair amount of dimensional accuracy to the cast part.
After the sand casting is removed from the sand mold it is shaken out, all the sand is otherwise removed from the casting, and the gating system is cut off the part. The part may then undergo further manufacturing processes such as heat treatment, machining, and/or metal forming. Inspection is always carried out on the finished part to evaluate the effectiveness and satisfaction of its manufacture.
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