Machined vs Cast Molded Polyurethane
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CNC machining uses computer software to control machine tools that cut complex 2D and 3D shapes out of blocks of material. Usually, a CAD drawing or other digital representation of the desired part is created, and then the drawing is translated into instructions (e.g., speeds, locations, and coordination) for the CNC machine. The machining process may require multiple routers, lathes, and other tools to remove different layers and accomplish the final shape. In general, CNC machining is very fast, accurate, and repeatable, capable of achieving precise tolerances.
Cast molding – also known as casting, hand-poured molding, and clamshell molding – involves creating a tool in the desired shape and then pouring the liquid thermoset resin into the mold. The polyurethane expands to fill the cavity during the reaction and becomes polyurethane foam. After the foam cures and hardens, it is removed from the mold and the tool is prepared to make the next, identical part.
Casting is similar but has notable differences from injection molding. Injection molding involves injecting materials into the mold at high pressures, which means the injection molds require stronger materials, more time, and more cost to make. Casting relies on low pressure or gravity only to pour the blended reactants into the mold, therefore casting tools are generally faster and less costly to make. Also, setup and teardown for injection molding takes longer than casting, and may require the assistance of heavy lifting equipment.