Casting Design Guidelines


Aluminum Investment Castings

For electronic enclosures.

Documentation

  1. Drawing Notes.

  2. In the drawing notes shown below, specify either note 2A or 2B.
  3. Dimensioning of Castings.

  4. As shown in the linear tolerance table, the larger the distance the greater the tolerance range. The shortest distance to any given point of the casting feature is from the theoretical center point of the casting. Therefore it is recommended that castings be dimensioned from centerline datums as illustrated here.

Material Properties

The following material properties are what one might expect from the investment cast process. Because of the availability of purchasing (A) desgnated alloys, 356 should be used where ever possible.
Quality Aluminum Alloy Selector Chart
Courtesy of Uni-Cast, Londonderry, NH.
The following range of mechanical properties meet or exceed specifications: AMS 4260 series MIL-S-11866 and QQ-A-601.
AlloyConditionTensile
Strenght
Yield
Strength
ElongationRemarks
355 T-632,000 20,000 2% Good weldability/pressure thightness
356 T-633,000 22,000 3% Maximum cost reduction
Very good foundry characteristics
A356 T-640,000 30,000 3% Excellent foundry characteristics
on thin-walled applications
The following range of mechanical properties meet or exceed MIL-A-21180.
C355 T-641/44,000 31/33,000 2 to 3% Specify separately cast test bars
for maximum cost reduction.
A356 T-638/42,000 28/34,000 3 to 4%

Investment Casting Tolerances

Courtesy of Cercast, Inc., Quebec, Canada.
  1. Linear Tolerances:

    Tolerances are plus or minus.
    InchesMilimeters
    DimensionsToleranceDimensionsTolerance
    Up to .250 .005Up to 6 .12
    .250 to .500 .0066 to 12 .15
    .500 to .750 .00712 to 19 .18
    .750 to 1.250 .00819 to 31 .20
    1.250 to 1.750 .01031 to 44 .25
    1.750 to 2.500 .01244 to 62 .30
    2.500 to 3.500 .01562 to 87 .35
    3.500 to 5.000 .01887 to 125 .45
    5.000 to 7.000 .020125 to 175 .50
    7.000 to 10.000 .024175 to 250 .60
    Max. Var. .030Max. Var. .75
    Tolerances are plus or minus.
    InchesMilimeters
    DimensionsToleranceDimensionsTolerance
    Up to .250 .003Up to 6 .075
    .250 to .500 .0046 to 12 .10
    .500 to 1.000 .00512 to 25 .125

  2. Geometrical Tolerances:

    The geometrical tolerances (feature form variations) must be added to the
    linear variations.
  3. Other Tolerances:


  4. Size Limitations. Parts can generally be cast in sizes up to 15"x20"x45" (375mm x 1125mm). Consult your Foundry for their size limitations.