Designing Miniature Parts

Zinc die casting technology has evolved significantly in recent years, especially in the area of miniaturization. Very small, geometrically complex parts can now be die cast with great precision, including numerous features such as contoured shapes, very thin walls, flash-free sculpted shutoffs, and multiple cored through-holes.

At Fielding Manufacturing, we have made miniature zinc die casting our specialty. With our high-speed, four-slide, microprocessor-controlled machines, we offer in-house capabilities in engineering, rapid prototyping, and tool design, manufacturing, and maintenance. And, we guarantee our tools for the life of the part.

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Very small parts require a much more integrated approach to design and engineering. As a designer, you need to put all your disciplines together: part design, tooling, and processing, in order to successfully make miniature parts.

Ten Things To consider When Designing Miniature Parts For Zinc Die Cast Production

1. Minimum wall thickness is dependent on overall part geometry. However, as a rule of thumb, keep to a .014" minimum.
2. Match tool layout with part geometry to assure:
   • Proper gating and fill to meet cosmetic requirements.
   • The ability to overflow thin wall sections for solid fill and finish.
   • Proper tool half registration and control since tolerances on tiny parts are usually tighter.
   • The ability to consistently eject the part. Determine KO pin size and locations (or unique methods such as the KO pin forming a part feature and stripping the part from the KO pin after ejection from the die).
   • The ability to degate runners and overflows quickly without distorting the part, and the ability to sort/separate parts from runners and overflows.
   • Optimal location of parting lines that support part function.
   • Proper cavitation: due to the unique challenges associated with tiny parts, single cavity tooling is usually recommended. High volume parts may allow multi-cavity tooling based on part geometry.
   • Analyze downstream secondary operations and sequencing of operations for maximum productivity (e.g., tap small parts on the runner system to facilitate handling).
3. Analyze downstream secondary operations and sequencing of operations for maximum productivity (e.g., tap small parts on the runner system to facilitate handling).
4. Post-cast forming operations must be disclosed to die caster to assure success.
5. If parts require plating for corrosion protection or cosmetics, consider the effect of plating on features and tolerances.
6. Consider material handling vwhereas very tiny parts can be more difficult to handle than big, heavy parts.
7. Allow sufficient draft for internal features and tool surface finish to facilitate low force ejection or stripping.
8. Incorporate corner or edge radii/fillets to improve material flow and avoid turbulence, and reduce stress concentrations in die steel and core pins.
9. Ensure tool lubrication and control to facilitate low force ejection and avoid material adhesion.
10. After casting, avoid secondary machining whenever possible, as this takes away the skin of the casting which is the strongest part. Castings have inherent porosity, but the skin (.006" to .010" thick) is the strongest part.

On micro-miniature parts, involve your die-cast supplier/partner early on in the design process. This will help to develop parts that are castable and trouble free. Also, early designs can be rapid prototyped and tested to assure form, fit, and function - and help you get customer feedback and involvement early! And the die caster can often suggest ways to consolidate parts, facilitate assembly, or eliminate potential failure modes.

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