What are the design rules for zinc die casting?

How thin can a zinc die-cast wall be?

Zinc fills thinner walls than any other common die-casting alloy, and the practical minimum depends mostly on how far the metal has to travel from the gate. Near the gate a wall can be well under a millimeter; far from it, plan on something closer to two.

The International Zinc Association gives the relationship directly: sections within about 50 mm of the ingate can run below 0.5 mm, while flow lengths of around 200 mm call for walls up to about 2 mm (IZA, design rules). The same page scales the typical minimum with the projected area of the part, from roughly 0.5 mm on a small casting to 1.5–2.0 mm on a large one. There is no hard upper limit, but the typical zinc casting rarely goes past 6 mm, because thick sections cool slowly and gather shrinkage porosity.

Uniformity matters more than the absolute number. IZA suggests an inscribed-sphere check: imagine the largest ball that fits in each section of the part and compare their diameters. A spread greater than 3:1 raises the risk of shrinkage porosity, and a spread beyond 6:1 costs a lot of strength. On a part converted from bar stock, that check usually finds the problem areas at once, because a machined part has no reason to keep its walls even.

NADCA adds the reason zinc goes thinner than aluminum: zinc alloys run in hot-chamber machines, cast at low temperature and fill fine detail, and precision features such as zero draft and press-fit diameters can often be held as cast (NADCA, alloy selection).

What fillet radius should a zinc die casting have?

Every inside corner should carry a fillet, and the only edge normally left sharp is the parting line. For zinc, IZA gives a small minimum radius and a larger common value for inside edges.

NADCA’s rule is simple: fillet all sharp corners and edges when you model the part, even the small ones, and leave the parting line sharp (NADCA, fillets). Fillets let the metal turn corners without turbulence, remove stress raisers from the finished part and make the die cheaper to cut and longer lasting. IZA recommends at least 0.4 mm and says 1.6 mm is common practice on inside edges (IZA, design rules). A small radius on outside corners also helps, because sharp outside edges chip and shed plating first.

Watch the fillet at a wall junction. A large radius where a rib meets a wall adds metal, and that local mass is exactly where the inscribed-sphere check from the wall section will flag porosity.

How deep can a cored hole or cast thread be in zinc?

Small cored holes are limited to shallow depths, and the allowed depth grows quickly with diameter; through holes can go deeper than blind holes. External threads can be cast when the parting line splits them, while internal threads are usually cheaper to machine or tap.

IZA’s core-depth guidance shows how fast the limit rises: a 3 mm blind hole is held to about 9 mm deep, a 6 mm blind hole to about 45 mm, and above 10 mm diameter the limit becomes a multiple of the diameter (IZA, design rules). Thin cores are fragile and overheat, so a deep small hole is normally cast as a shallow pilot and drilled, or drilled from solid.

For threads, IZA gives a smallest castable diameter of 8 mm and a finest pitch of 1 mm, and prefers the 8g external fit class, with 6e, 6g and 6h also possible (IZA, design rules). Below that size, or on any internal thread, plan to tap or machine after casting. Cast threads also carry a small flash line at the parting plane, so a thread that must gauge cleanly all the way around may need a chase anyway.

How do you convert a machined bar-stock part to Zamak 3?

Redesign the part for the die rather than copying the machined shape: even out the walls, add draft and fillets, core the heavy areas, and keep machining only for the few features that need it. Then confirm the alloy still suits the part’s service temperature and loading.

A practical checklist, in the order a design review usually runs:

• Pick the parting line first, at the part’s widest section and in a single plane if you can. Every other rule depends on which way the die opens.
• Hollow out the thick sections left over from bar stock and bring walls toward one nominal thickness, using ribs for stiffness.
• Add draft to every face parallel to the die opening, and list the faces that must stay square.
• Fillet every inside corner and soften outside corners, except at the parting line.
• Decide hole by hole: cast to size, cast a pilot and drill, or drill from solid.
• Move tight tolerances onto a small number of machined faces and datum features, and show the machining stock on the drawing.
• Specify the alloy by standard, for example “Alloy 3 (Zamak 3) per ASTM B86”, and the finish by standard and type.
• Specify raised rather than engraved lettering and logos, because raised text is cut into the die and is cheaper to make and change.

Check the service conditions before you commit. NADCA notes that the impact strength of zinc alloys falls off sharply below 32 °F (0 °C) and that zinc creeps under sustained load (NADCA, alloy selection), so a clamp that stays loaded for years, or a part that works outdoors in winter, may be better in aluminum. The ADC12 vs A380 guide covers that alloy family.

For buyers moving a program to Vietnam, the conversion review is also the moment to put the casting and the follow-on machining with one supplier, so one party owns the datum scheme from die to finished part. Saola Manufacturing sources Zamak 3 and ADC12 die castings from partner foundries and machines cast features on CNC turning and milling at its lead CNC plant; the quote names the production site and origin. Send the current bar-stock drawing and the annual volume, and ask for design-for- manufacturing notes with the quote.