Zinc is capable of being cast in small complex shapes with a fi ne surface fi nish, making the material ideal for toy cars.


that were impossible until recently. This capability should be uti- lized only as necessary to achieve performance or economic advan- tages. Uniform wall thicknesses are otherwise preferred.


2. Intersections of features, such as walls, ribs and gussets, should blend with transition sections and generous radii. This practice promotes metal flow and structural integrity and rarely creates a con- flict between casting requirements and product integrity.


3. Draft angles may be minimized where metal content is critical, such as thin sections oriented


parallel to die draw. Casting to zero draft may be specified in some cases to eliminate finish machining operations. These capabilities may be utilized as necessary to gain an economic advantage or to reduce weight. In all other cases, standard draft must be specified to facilitate ejection from the die and reduce die maintenance.


4. Sharp exterior corners can be spec- ified on appearance surfaces when crisp styling features are desired. Otherwise, sharp corners should be broken with radii or chambers to reduce die maintenance.


5. Undercuts should be avoided Table 2. Physical and Mechanical Properties of Zinc Pressure Diecasting Alloys


Physical Property Density (lb./cu. in.)


Solidifi cation Shrinkage (%) Solidifi cation Temp. Range (F) Thermal Expansion (in./in. –F)


Specifi c Heat Capacity (btu/lb.-F) Specifi c Heat Capacity (btu/cu. in.-F) Electrical Conductivity (%IACS) Electrical Resitivity (Micro ohm-in.) Ultimate Tensile Strength (ksi) Yield Strength (ksi) Elongation (%)


Hardness (Brinell-500 kg) Shear Strength (ksi)


Compressive Strength (0.1% offset) (ksi)


Impact Energy (unnotched bar 0.25 in. x 0.25 in.) (J) Fatigue Strength (5x108 cycles) (ksi)


2015 CASTING SOURCE DIRECTORY 2


0.24 1.25


734-715 15.2x10-6 0.1


0.024 25 —


48 — 2


98 46 93


6.8 8.5


3


0.24 1.17


728-719 15.2x10-6 0.1


0.024 27


2.5 35 — 16 72 31


60


55.6 6.9


5


0.24 1.17


727-717 15.2x10-6 0.1


0.024 26


2.6 39 — 13


80 38 87


54.2 8.2


Source: Engineering Properties of Zinc Alloys, International Lead Zinc Research Organization Inc. METAL CASTING DESIGN & PURCHASING 43


Alloy Designation 7


0.24 1.17


728-717 15.2x10-6 0.1


0.024 27 — 41 — 18


67 31


60


55.6 6.8


ZA-8 0.227


1.1


759-707 12.9x10-6 0.104 0.024 27.7 2.4 43 32 20 91


33 25 17 15


ZA-12 0.218


1.25


810-710 13.4x10-6 0.107 0.023 28.3 2.4 45 35 10 91


34 27 19 —


ZA-27 0.181


1.25


903-708 14.4x10-6 0.125 0.023 29.7 2.6 52 46


3.0 100 37 37


2.2 21


whenever possible because they require additional machin- ing operations or additional die members, such as retractable core slides. When core slides are used, the design should allow them to be located in the die parting plane.


6. Dimensions with critical toler- ances should relate to only one die member—either the ejector die half or the cover die half. Critical tolerances across the parting line are difficult to maintain. ■


This article was adapted from various bulletins and The Zinc Die Casting Process, published by the North Ameri- can Die Casting Association (NADCA).


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