Die Casting Process

Aluminum Die Castings, Zinc Die Castings

• Lowest per part piece price of all casting processes.
• Thin walls, .080 / .125 thick
• The ability to cast many features into the casting, eliminating the need for machining
• Surface finish as cast 63 to 125 RMS
• Finishes that can be applied to aluminum, zinc & magnesium die castings are painting, powder coating and anodizing.
• Repeat ability of dimensions from part to part is .001 / .003
• Cast letters, numbers & logos into parts

Types of Die Casting Dies
There are various types of die casting dies and each serves a critical need for the customer.  The choice of which type of die casting die the customers requires is usually determined by the following:

• Size of the part to be cast
• Volume of parts required
• Requirement for “family” sets of parts
• Desirability of core slides
• Requirements for cast-inserts
  

1. The geometry of the part is not physically moldable.
2. The necessary draft & radii are not incorporated.
3. Line & surface geometry are not connected within .001”.

PROPERTIES OF ZINC AND ALUMINIUM DIE CASTINGS

TYPICAL MECHANICAL PROPERTIES

• Linear dimensions
• Dimensions across parting lines
• Dimensions formed by moving die components (MDC)
• Angularity
• Draft
• Flatness
• Cored holes for threads

• Concentricity
• Parting Line Shift

Standard Tolerances
Standard Tolerances cover expected values consistent with high casting cycle speeds, uninterrupted production, reasonable die life and die maintenance costs, as well as normal inspection, packing and shipping costs.

Linear Dimensions: Standard Tolerances
The Standard Tolerance on any of the features labeled in the adjacent drawing, dimension “E1” will be the value shown in table S-4A-1 for dimensions between fea­tures formed in the same die part. Tolerance must be increased for dimensions of features formed by the parting line or by moving die parts to allow for movement such as parting line shift or the moving components in the die itself. Linear tolerance is only for fixed components to allow for growth, shrinkage or minor imperfections in the part.
Tolerance precision is the amount of varia­tion from the part’s nominal or design feature.
For example, a 5 inch design specifica­tion with ±0.010 tolerance does not require the amount of precision as the same part with a tolerance of ±0.005. The smaller the tolerance number, the more precise the part must be (the higher the precision). Normally, the higher the precision the more it cost to manufacture the part because die wear will affect more precise parts sooner. Production runs will be shorter to allow for increased die maintenance. Therefore the objective is to have as low precision as possible without affecting form, fit and function of the part.

Example: An aluminum casting with a 5.00 in. (127 mm) specification in any dimension shown on the drawing as “E1”, can have a Standard Tolerance of ±0.010 inch (±0.25 mm) for the first inch (25.4 mm) plus ±0.001 for each additional inch (plus ±0.025 mm for each additional 25.4 mm). In this example that is ±0.010 for the first inch plus ±0.001 multiplied by the 4 additional inches to yield a total tolerance of ±0.014. In metric terms, ±0.25 for the first 25.4 mm increments plus ±0.025 multiplied by the 4 additional 25.4 mm to yield a total tolerance of ±0.35 mm for the 127 mm design feature specified as “E1” on the drawing. Linear dimension tolerance only applies to linear dimensions formed in the same die half with no moving components.

Mr. Palmer may be reached by calling toll free: 888.494.0414 or email: (dick@castingreps.com)