with this method most often, but rap- id tooling technology advances have made shorter runs—between 500 and 2,000 pieces—more economical while also signifi cantly reducing lead times to one to four weeks (Fig. 1). Because of the shot chamber meth-


DIECASTING


od of introducing metal into the mold, metal loss in diecasting is usually low.


Why Permanent Mold? Casting size for permanent mold


ranges from less than a pound to more than several hundred pounds.


Surface finish varies between 150 to 400 RMS, basic linear tolerances are about +/-0.01 sq. in. and minimum wall thickness is 0.1 in. In the permanent mold process, molten metal is poured into a mold made in two halves either directly by


PERMANENT MOLD CASTING


Suitable for: • Aluminum, magnesium and zinc alloys. • Simple to moderate complexity. • Very small to medium casting sizes (ounces to 30 lbs.).


• Quantities in the medium to very large range.


Features: • Thicknesses down to 0.025 in. • Draft of 0.5-3 degrees. • Base tolerance of +/- 0.002 in. • High tooling lead time. • Surface fi nishes between 32-90 RMS. • Low casting cost. • High tooling cost ($5,000-$500,000). • Low fi nishing cost. • Low to moderate casting lead time.


Suitable for: • Aluminum, copper-base, magnesium and zinc alloys.


• Simple to moderate complexity. • Small to medium casting sizes (ounces to more than 100 lbs.).


• Quantities in medium to large ranges.


Features: • Thicknesses down to 0.125 in. • Base tolerance of +/ -0.015 in. • Surface fi nishes between 150-250 RMS. • Draft of 2-4 degrees. • Moderate tooling lead times. • Moderate tooling cost ($5,000-$20,000). • Low to moderate casting lead times. • Low to moderate casting cost. • Moderate fi nishing cost.


42 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2014


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