Good zinc parts start with good design. That means uniform walls, practical draft, smart coring, and clear thinking about what to cast and what to machine. We cast zinc every day and we keep the advice simple. Design to help metal flow. Design to help the die eject. Design to protect the faces your customers see.
- If you want a quick refresher on the process itself, start with Zinc Die Casting 101.
- If you are still choosing between material families, see zinc vs aluminum die casting.
- For precision features we machine in house, visit CNC machining.
- Our inspection and documentation approach is outlined on quality.
- Want fast feedback. Request a DFM review.
Key takeaways
- Uniform walls and smooth transitions control flow and shrink. This reduces porosity and improves cosmetics.
- Draft is not optional. Add more on deep internal features. This protects finish and extends die life.
- Core smart. Remove heavy masses, add ribs for stiffness, and support cores so they stay put.
- Place the parting line and ejectors to protect visible faces. Plan trim and any post‑cast finishing.
- Cast what is practical to cast. Machine what must be perfect. Use measurement plans that focus on functional features.
- Lock the finishing sequence early. Cast, seal if needed, machine, then plate or coat.
What are we solving in design
Die casting is fast, but it is still physics. Metal must fill, vent, solidify and release without surprises. Your design choices make that easier or harder. We stack the deck by keeping thickness uniform, rounding intersections, adding draft and moving the parting line where it does the least harm. Then we decide what to machine.
If you need a quick comparison of zinc and aluminum before you dive in, read zinc vs aluminum.
Wall thickness and transitions
Uniform sections set up even flow and even shrink. That is the simplest way to reduce porosity and distortion. If a region must be thicker for strength, taper into it with gentle transitions. If you need stiffness, prefer ribs over bulk. Smooth intersections help cosmetics and tool life.
- Target one nominal wall. Blend into local changes with ramps and fillets.
- Use ribs to add stiffness without heavy masses. Space and fillet ribs to avoid pockets that trap gas.
- Core bosses and heavy features. This saves cycle time and reduces shrink voids.
For public design context and illustrations, see NADCA’s high‑level design guidance and IZA’s zinc design primers:
NADCA design considerations and
IZA zinc die casting.
Draft that matches the feature
Draft is a small taper that lets the part leave the die without scraping. It protects finish, lowers ejection force and extends die life. Add more draft as depth increases. Internal walls usually need more draft than exterior walls. Textured surfaces need more draft than polished surfaces.
- Set a base draft for general faces. Increase for deep pockets and internal cores.
- Texture, logos and matte faces need extra draft. Plan that early.
- Do not hold zero draft on blind features. That turns ejection into a scrape event.
NADCA’s public note on draft is a good baseline:
NADCA draft guidance.
Radii, fillets and stress relief
Sharp corners block flow and concentrate stress. They also raise finishing effort. Add fillets and blends everywhere you can. Round internal corners more than external corners. This helps flow, reduces turbulence and avoids sink marks that show under plating or paint.
- Blend wall intersections with fillets. Avoid knife edges.
- Use consistent radii to keep the tool strong and easy to maintain.
- Fillet the base of ribs and bosses. This reduces cracks in the die and surface tears on parts.
Ribs and bosses that work
Ribs are a lightweight way to add stiffness. Bosses provide fastening and alignment. Both need smart proportions and support. Design ribs to guide flow, not block it. Design bosses with cores to avoid heavy masses. Tie them into surrounding walls with generous fillets.
- Use ribs to move metal where it helps stiffness. Avoid ribs that form sealed pockets.
- Core bosses to keep section thickness even. Support cores with prints so they stay aligned.
- Consider gussets at the base of tall bosses. This adds strength without a large mass.
Cored holes, windows and core support
Cores remove material where solid stock would create thick sections and long cooling times. They also create holes and windows without drilling. Core placement affects flow, venting and ejection. Give every core a clear support plan so it does not shift under pressure or heat.
- Support long cores with prints and guide features. Keep them rigid and easy to service.
- Leave room for vents and overflow pads near complex cores. This helps gas escape.
- Avoid thin, unsupported steel in the die. It breaks and it marks parts.
For process fundamentals and defect prevention context, see NADCA’s introduction and defect guides:
NADCA introduction and
NADCA defect resources.
Parting line, ejectors and cosmetics
The parting line is where the die opens. It decides gate routing, venting, trim, and most cosmetic outcomes. Ejector placement decides where you can accept small marks. We place both to protect the faces your customer will see and touch.
- Place parting lines on hidden edges when possible. If the line must cross a visible face, plan a trim or polish step.
- Lay out ejectors on non‑critical faces. Use sleeves or polished pins where marks must be small.
- Plan for flash control and trim access. Do not trap flash in a corner that is hard to reach.
Realistic tolerances and capability
Start with public NADCA tolerance ranges for zinc. Then tune by feature size, location and distance from the gate and ejectors. Small zinc castings can hold tight repeatability when the process window is stable. The best results come when we set capability targets on the few dimensions that drive function and assembly.
- Do not tighten every dimension. Tighten only where function needs it.
- Call out datum schemes that are easy to access and measure.
- If a face or bore must be near perfect, plan a light machining step.
Public references many engineers use as a starting point:
NADCA tolerance tables (archived).
Threads, bores and what to machine
Cast threads can work for certain sizes and loads. Precision threads and tight bearing bores run best when cut after casting. That approach is fast when we plan clamp points and tool access into the casting. It also protects cosmetics and reduces risk.
- Design cast threads with blunt starts and adequate draft. Validate torque targets.
- Plan machining pads and clearance for tools. Avoid cutting across cosmetic faces.
- Define thread seal and gasket surfaces early. This affects sequence and masking.
We machine critical features in house. Details on our
CNC machining page. Our inspection plans live on
quality.
Porosity prevention you control in design
Porosity comes from trapped gas, shrink during solidification and blocked venting. Tooling and process choices matter, but design is the first lever. Uniform walls, radiused intersections, and smart core layouts reduce turbulence and shorten the path for air to leave. Keep heavy masses in check. Leave room for vents and overflow pads near complex features.
- Uniform sections and smooth transitions reduce hot spots and gas pockets.
- Core to avoid thick masses. Place cores so gas can escape to vents.
- Agree on a vent and overflow plan at tool design review. Design must allow it.
If your part must be leak‑tight, vacuum impregnation can seal micro‑porosity in otherwise good castings. See neutral primers on
vacuum methods and this accessible overview from
Godfrey & Wing.
Designing for plating and powder
Zinc is finish‑friendly. Design for the finish you want and plan the sequence. If you want bright decorative chrome, put polish access on the faces that matter and keep the wall structure uniform to avoid sink and waviness. If you want powder, plan masking for threads and grounding, and choose textures that support your gloss level.
- Place parting and ejectors away from primary cosmetic faces. Plan trim.
- Call out cosmetic classes on the print. Define samples at PPAP or first article.
- Masking plans and rack contact points belong in the drawing package.
Neutral resources on plating and prep:
IZA polishing and plating overview and
Products Finishing on zinc plating.
Process sequence that protects quality
Sequence matters. It protects adhesion, dimensions and leak‑tight performance. Here is a simple pattern that works on many parts.
- Cast and trim. Confirm fill and basic dimensions.
- Seal if required. Vacuum impregnation on parts that must be leak‑tight.
- Machine critical bores, threads and faces. Keep cutter paths off cosmetic areas.
- Plate or coat. Control masking and rack points. Inspect against cosmetic class.
We run this with a documented plan under our
ISO 9001:2015 quality system. Secondary ops live under
CNC machining. If you want us to map this to your part,
request a DFM review.
One‑page DFM checklist
- Environment. Temperature, fluids, UV, shocks.
- Alloy. Start at ZAMAK 3; consider ZAMAK 5, ZAMAK 7 or ZA‑8 based on features and finish.
- Walls. One nominal wall. Blend transitions. Use ribs for stiffness.
- Draft. Set base draft. Increase on deep internal features and textured faces.
- Radii. Fillet all intersections. Avoid knife edges.
- Cores. Core heavy masses. Support cores with prints and allow venting.
- Parting and ejectors. Protect cosmetic faces. Plan trim.
- Tolerances. Use NADCA ranges as a start. Tighten only where function demands it.
- Machining. Decide which features must be cut. Provide pads and tool access.
- Finish. Pick plating or powder early. Add masking and rack notes.
- Sequence. Cast, seal if needed, machine, then finish.
Want a fast markup of your model.
Request a DFM review.
FAQ
How much draft do I need
Enough to release without scraping and to protect the finish. Deep internal features and textured faces need more. NADCA’s public draft guidance is a good baseline. See
NADCA draft.
What wall thickness should I target
Use one nominal wall where you can. Blend into local changes with ramps and fillets. Avoid isolated heavy masses. NADCA and IZA design notes show patterns that work. See
NADCA design and
IZA zinc die casting.
Can I cast threads
Yes for certain sizes and loads. Precision threads and tight bearing fits are better machined. We cut those in house and protect cosmetics while we do it. See
CNC machining.
How do I design for chrome or premium cosmetics
Keep walls uniform. Plan polish access. Hide parting and ejectors from primary faces. Define cosmetic class and samples. IZA’s finishing primer helps:
polishing and plating.
When should I plan for vacuum impregnation
When a good casting still needs leak‑tight performance. Plan it before machining and finishing. Neutral overviews here:
Henkel and
Godfrey & Wing.
Where do I set tolerances
Start with public NADCA ranges. Tighten only where function needs it. For a quick reference many engineers use, see the
NADCA tolerance tables.
For a bigger picture of alloy choice before you lock details, read our
zinc alloys selection guide.
If you want live feedback from our team,
request a DFM review.
References
- NADCA — Introduction to Die Casting: https://www.diecastingdesign.org/introduction/
- NADCA — Design considerations and defects: https://www.diecastingdesign.org/industry/knowledge-center/knowledge/design-considerations/ & defects
- NADCA — Draft guidance: https://www.diecastingdesign.org/draft/
- NADCA — Tolerance tables (archived): https://www.paceind.com/wp-content/uploads/2016/02/NADCA-Tolerances-2009.pdf
- International Zinc Association — Zinc Die Casting: https://diecasting.zinc.org/
- IZA — Polishing and plating notes: https://diecasting.zinc.org/properties/en/finishing/eng_prop_f_polishing-and-plating/
- Products Finishing — Plating zinc die castings: https://www.pfonline.com/articles/zinc-plate-on-zinc-die-castings
- Henkel — Vacuum impregnation overview: https://next.henkel-adhesives.com/us/en/articles/vacuum-impregnation.html
- Godfrey & Wing — What is vacuum impregnation: https://www.godfreywing.com/vacuum-impregnation/
