Die Casting Service — Aluminum, Zinc & Magnesium Alloys
Manufacturing Guide
Die Casting Service: Alloys, Dies, Tolerances and Post-Processing — The Complete Guide
Table of Contents
- What die casting is and why it matters
- Hot chamber vs cold chamber die casting
- Die casting alloys: aluminum, zinc and magnesium
- Die design and die life
- The die casting process step by step
- Die casting tolerances and surface quality
- Post-processing: deburring, CNC, plating and coating
- Die casting vs injection molding vs CNC machining
- Applications: automotive, electronics, industrial
- Cost drivers and minimum order quantities
- Frequently asked questions
What die casting is and why it matters
Die casting is a metal casting process in which molten metal — typically aluminum, zinc or magnesium alloy — is forced under high pressure into a hardened steel die (mold). The die is a “negative shape” of the part, pressed together hydraulically; the molten metal fills the cavity, cools, and the part is ejected. The die survives the process and makes the next part, which is what separates die casting from sand or investment casting, where the mold is destroyed to remove each part (Xometry: xometry.com/resources/casting/die-casting/).
The result is a metal part with:
- Complex, thin-wall geometry that would be expensive to machine.
- Excellent dimensional repeatability across thousands of parts.
- A smooth, fine-grained surface ready for finishing.
- Production rates that make it economic at high volume.
For buyers sourcing metal housings, brackets, connectors and enclosures, die casting is often the answer between “machine it” (too slow/expensive at volume) and “fabricate it” (too imprecise). A one-stop supplier adds value by running the die, casting, CNC finishing and plating under one roof.
MOLDITQUICK (Dongguan Guohong Precision, 东莞国宏精密) provides one-stop custom die casting: in-house die making, die casting, CNC machining and post-processing for aluminum, zinc and magnesium alloy programs, inside a 10,000 m² plant with 280 employees and IATF 16949, ISO 13485 and ISO 9001 certifications. Die casting complements our core injection molding, CNC, stamping (20 Aida presses), overmolding and LSR capabilities.
Hot chamber vs cold chamber die casting
The machine configuration is decided by the alloy’s melting point and reactivity:
| Feature | Hot chamber | Cold chamber |
|---|---|---|
| Metal source | Furnace attached to the machine; plunger immersed in molten metal | Metal ladled into the shot sleeve for each shot |
| Alloys | Zinc, magnesium (low melt point), tin, lead | Aluminum, and higher-melt alloys |
| Melt temperature | ~380–450 °C (zinc) | ~600–700 °C (aluminum) |
| Cycle speed | Faster (no ladling step) | Slower (ladle + inject per cycle) |
| Machine size | Smaller tonnages typical | Larger tonnages (58–800 T and beyond) |
| Typical parts | Small zinc parts: locks, gears, nameplates, toys | Aluminum housings, engine brackets, electronics |
Zinc’s low melting point is why zinc parts are die cast on hot chamber machines with very fast cycles. Aluminum requires cold chamber because molten aluminum would attack the steel plunger/gooseneck of a hot chamber machine. FirstMold, a leading China die casting service, publishes 58–800 T die casting machine capability and a >98% pass rate in full-scale inspections (firstmold.com/die-casting-service/) — the 58–800 T band covers small zinc parts through large aluminum housings.
Die casting alloys
Aluminum alloys (most common)
Aluminum die casting is the workhorse of the industry — lightweight, corrosion-resistant, strong, and castable into thin sections. Common grades:
| Alloy | Key properties | Typical applications |
|---|---|---|
| ADC12 (A383 equivalent) | Good castability, strength, thermal conductivity | Electronics housings, auto parts, 5G equipment |
| A380 | Excellent casting + mechanical properties balance | Engine brackets, housings, pumps |
| A383 | Better corrosion resistance and castability for thin walls | Complex thin-wall housings |
| A360 | Superior corrosion resistance | Marine, food-contact, high-corrosion duty |
| A413 | Excellent pressure tightness | Pressure-tight housings, valve bodies |
Zinc alloys
- Zamak 3 / ZA-8 / Zamak 5: the classic zinc die casting family.
- Extremely accurate, thin walls down to ~0.5 mm, excellent surface for plating/painting.
- Low melt temperature = long die life (hundreds of thousands of shots) and fast cycles.
- Used for: locks and hardware, nameplates, gears, brackets, decorative parts, toys.
- Cheap to cast; often the low-cost answer for small precision metal parts (Xometry notes zinc is used where strength isn’t the priority, being affordable and easy to work with — xometry.com/resources/casting/die-casting/).
Magnesium alloys
- AZ91D is the dominant magnesium die casting alloy.
- Lightest structural alloy (about 2/3 the weight of aluminum), excellent strength-to-weight.
- Magnesium’s low-viscosity melt allows some of the thinnest sections possible in die casting (Xometry: xometry.com/resources/casting/die-casting/).
- Used for: laptop/phone frames, automotive components, power tool housings, 3C accessories.
- Watch-outs: flammability control during melt/casting, and galvanic corrosion when coupled to other metals.
Alloy selection cheat-sheet
- Weight reduction is the goal → magnesium (AZ91D).
- Best overall casting economics at volume → aluminum ADC12/A380.
- Small precision parts with plated finish → zinc (Zamak).
- Corrosion or pressure tightness → A360 / A413.
Die design
The die (mold) is the heart of die casting economics. Key design elements:
- Parting line: where the two die halves meet; placed to minimize flash and optimize ejection.
- Draft angles: typically 1–3° on side walls so the casting releases; zinc can use less, magnesium more.
- Wall thickness: 1.0–3.0 mm typical for aluminum; thin walls possible with proper gating.
- Ribs and bosses: add stiffness without thickening walls; boss cores need sufficient clearance for ejector pins.
- Slides and cores: side features and undercuts require moving die members — each adds cost.
- Runner/gate system: metal flows from the shot sleeve through runners and gates; gate design controls fill and turbulence.
- Cooling channels: water lines remove heat to set the cycle time; die temperature management is critical for quality.
- Ejector system: pins push the cooled casting off the core.
Die life
Die life depends on alloy (melt temperature = thermal fatigue), die steel (typically H13 for aluminum), and process control:
| Alloy | Typical die life (shots) |
|---|---|
| Zinc | 500,000 – 1,000,000+ |
| Magnesium | 100,000 – 300,000 |
| Aluminum | 80,000 – 150,000 (with maintenance) |
A well-maintained H13 die for aluminum with controlled die temperature and regular inspection hits the top of its band; die life is a cost line item you should ask about when comparing quotes.
The die casting process step by step
- Die preparation: die faces cleaned, release agent sprayed, inserts checked, die heated/controlled to operating temperature.
- Clamping: the two die halves are closed and clamped under hydraulic pressure — the closure faces seal the cavity (Xometry: xometry.com/resources/casting/die-casting/).
- Injection: molten metal is forced into the cavity at high pressure (cold chamber: ladled into the shot sleeve first). High pressure is what allows fine features and thin sections to fill completely (same Xometry source).
- Solidification: the part cools inside the die; cooling channels set the rate.
- Ejection: the die opens and ejector pins push the casting out.
- Cycle repeat: typically 30 seconds to a few minutes per shot depending on part size and wall thickness.
Optional advanced routes: vacuum die casting (reduces porosity for high-integrity parts) and semi-solid / thixotropic casting for improved mechanical properties (RapidDirect covers these in its die casting guide: rapiddirect.com/blog/what-is-die-casting/).
Tolerances and surface quality
Die casting holds tighter tolerances than sand casting or permanent mold casting because the hardened die is dimensionally stable and the high pressure packs the metal against the cavity.
| Feature | Typical die casting tolerance |
|---|---|
| General dimensions (zinc) | ±0.05–0.10 mm |
| General dimensions (aluminum) | ±0.10–0.20 mm (tight features ±0.05 mm) |
| Wall thickness | ±0.10 mm typical |
| Draft-affected dimensions | Add draft-angle component |
| Parting-line dimensions | ±0.10–0.25 mm (flash-dependent) |
Surface finish as-cast is typically Ra 1.6–3.2 µm — smoother than sand casting, and ready for plating or powder coating after light treatment. Tight tolerances on machined features (bores, mounting faces, seal surfaces) are achieved with post-casting CNC machining.
Post-processing
Most die castings need at least one secondary operation:
| Operation | Purpose |
|---|---|
| Deburring / trimming | Remove flash at parting line and gates |
| Shot blasting / sand blasting | Clean surface, uniform texture, remove die lube residue |
| CNC machining | Precision bores, threads, mounting faces, holes not castable |
| Vibratory finishing | Deburr small features, smooth edges |
| Impregnation (sealing) | Fill micro-porosity for pressure-tight parts |
| Electroplating | Decorative chrome/nickel on zinc; conductivity |
| Anodizing | Hard/colored oxide on aluminum |
| Powder coating / painting | Durable finishes for housings and frames |
| Tapping/threading | Threaded holes, often machined post-cast |
A one-stop supplier that does die + casting + CNC + surface finishing in-house removes three hand-offs, three sets of logistics, and three chances for quality drift. This is exactly the model we run.
Die casting vs injection molding vs CNC machining
| Criterion | Die casting | Injection molding | CNC machining |
|---|---|---|---|
| Material | Aluminum, zinc, magnesium | Plastics (incl. engineering grades) | Any metal or plastic |
| Tooling cost | High (steel die) | High (steel mold) | None |
| Unit cost at volume | Low | Very low | High |
| Part strength | Metal, strong, heat-resistant | Polymer, lower strength/heat | Strongest (wrought properties) |
| Weight | Heavy (aluminum) to light (magnesium) | Lightest | Depends on material |
| Complexity | High, thin walls | Highest, most design freedom | Medium (tool access limits) |
| Electrical conductivity | Yes | No | Yes |
| Typical volume | 10,000+ | 5,000+ | 1–500 |
Selection logic: need a metal part at volume with complex shape → die casting. Need a lightweight plastic part → injection molding. Need a metal part in small quantities or with extremely tight tolerances → CNC. See our die casting vs injection molding deep-dive for the full comparison.
Applications
Automotive
- Engine brackets, transmission housings, alternator housings, steering column components, seat frames.
- New energy vehicle (NEV) parts: battery housings, motor housings, charging components — the fastest-growing die casting segment (FirstMold lists NEV parts among its aluminum and magnesium die casting applications: firstmold.com/die-casting-service/).
- Magnesium saves up to ~30% weight versus aluminum for the same structure.
Electronics and 3C
- Laptop/tablet/phone frames and chassis (magnesium, aluminum).
- 5G communication equipment housings and heat-dissipating shields.
- Camera bodies, LED housings, connectors, nameplates (zinc).
- Die cast housings double as heat sinks — a real advantage over plastic.
Industrial and consumer
- Power tool housings, gear boxes, pump housings, valves, lock bodies, hardware, furniture fittings, track light castings, appliance components.
Cost drivers and minimum order quantities
| Cost driver | Impact |
|---|---|
| Alloy | Zinc cheapest to cast; magnesium material expensive; aluminum mid |
| Part size & weight | Material + machine tonnage scale with part |
| Die complexity | Slides/cores/inserts add die cost |
| Wall thickness & gating | Thinner walls need better gating design, can raise die cost but cut cycle |
| Secondary machining | Each machined feature adds cost |
| Finishing | Plating and coating add cost per part |
| Volume | Die amortization dominates at low volume |
Die casting is a high-volume process — die cost and setup make small runs uneconomic versus CNC. Practical MOQ for die casting is typically in the thousands of parts; for smaller quantities, CNC machining or a combination (CNC prototype → die casting at volume) is the smart path. Prototype the design with CNC first — it validates geometry before you commit to a die — then scale into die casting.
Die casting design rules: wall, draft, ribs and bosses
Good die-cast geometry is the cheapest quality insurance you can buy. The design rules below are industry-standard practice — and they directly map to how the melt behaves in the die.
| Feature | Aluminum | Zinc | Magnesium | Why it matters |
|---|---|---|---|---|
| Typical wall thickness | 1.5–4 mm | 0.8–3 mm | 1–3 mm | Thinner = faster cycle, lighter part |
| Minimum wall | ~1 mm | ~0.5 mm | ~1 mm | Below this, fill is unreliable |
| Draft angle (walls) | 0.5–2° | 0.5–1° | 0.5–2° | Required for ejection without scoring |
| Draft angle (deep cores) | 2–3° | 1–2° | 2–3° | Deep features need more draft |
| Internal radii | ≥ 1 mm | ≥ 0.5 mm | ≥ 1 mm | Radii avoid hot spots and cracking |
| Rib thickness | 0.6–1× wall | 0.6–1× wall | 0.6–1× wall | Ribs stiffen without thick sections |
| Boss height | ≤ 2.5× diameter | ≤ 3× diameter | ≤ 2.5× diameter | Tall bosses trap air and sink |
Porosity: the honest technical limit
Every die casting has some porosity — the question is how much and where. Porosity types:
- Gas porosity — trapped air from injection. Mitigation: vacuum die casting, better venting, slower plunger start.
- Shrinkage porosity — solidification contraction in thick sections. Mitigation: uniform walls, directional solidification, intensification pressure.
- Flow porosity — turbulence during fill. Mitigation: gate design, overflow wells.
If a part will be pressure-tested, welded, or machined to reveal internal surfaces, call it out in the RFQ. The supplier then plans for vacuum casting, HIP (hot isostatic pressing), or resin impregnation — all of which cost money but prevent catastrophic field failures.
Textures and logos
- Draft for texture: textured surfaces need 1–3° extra draft, depending on texture depth.
- Logos and part numbers: use raised (embossed) features on the die — they read better and are cheaper than recessed ones.
- As-cast lettering: keep minimum feature height ~0.25 mm and avoid fine serif fonts.
Post-processing and secondary operations
Raw castings rarely ship to assembly. The typical finishing chain:
| Operation | Purpose | Notes |
|---|---|---|
| Trimming / deburring | Remove flash and gate stubs | Automated trim dies for high volume |
| Shot blasting | Clean surface, uniform matte | Also improves paint adhesion |
| Vibratory finishing | Deburr edges, radius small features | For threaded and fine features, less aggressive |
| CNC machining | Precision faces, holes, threads | Casting near-net-shape + CNC = best of both |
| Tumbling | Polish and compact | Cosmetic |
| Chemical conversion (chromate) | Corrosion protection, paint base | Standard for aluminum |
| Anodizing | Hard, wear-resistant surface | Class II or Class III per spec |
| Painting / powder coating | Cosmetic + protective | Primer + top coat for exterior parts |
| Electroplating | Decorative or functional | Nickel, chrome, zinc on zinc alloys |
| Pressure testing / impregnation | Seal porosity | For leak-tight housings |
| Assembly | Insert nuts, gaskets, fasteners | One-stop delivery |
The key insight: die casting + CNC is the standard industrial combination. The casting provides near-net shape at low cost; CNC provides the ±0.05 mm precision faces that casting alone cannot hold. Most automotive housings, pump bodies and electronic enclosures ship through exactly this two-step chain.
Die casting vs injection molding vs CNC machining
Buyers often compare three processes for the same part. Here is the honest decision matrix:
| Criterion | Die casting | Injection molding | CNC machining |
|---|---|---|---|
| Material | Aluminum, zinc, magnesium | Thermoplastics, LSR | Any machinable metal/plastic |
| Part strength | High (metal) | Moderate (plastic) | Highest (wrought metal) |
| Wall thickness | 1–4 mm typical | 0.5–5 mm | Limited by tool reach |
| Electrical conductivity | Yes | No (unless filled) | Yes |
| EMI shielding | Natural | Requires coating | Natural |
| Tooling cost | High | Medium-high | None |
| Per-part cost at volume | Very low | Lowest | High |
| Best volume range | 5k–millions | 1k–millions | 1–1,000 |
| Complexity | High (with slides/cores) | Highest | High |
| Typical lead time (tooling) | 25–45 days | 25–30 days | 1–10 days |
Selection rule of thumb: metal performance at volume → die casting. Plastic at volume → injection molding. Anything under ~1,000 pieces or needing tight tolerances today → CNC. Our die casting vs injection molding guide and CNC vs injection molding guide go deeper on the trade-offs.
Die casting cost drivers and how to control them
Die casting prices are transparent once you know the levers:
- Die (tooling) cost — driven by part size, cavity count, sliders/cores, steel grade and finish. First cost, amortized over the program.
- Alloy choice — zinc alloys cost more per kg but cast thinner and faster; aluminum is the volume-price sweet spot; magnesium is premium.
- Cycle time — wall thickness and cooling design set the cycle; thinner walls win.
- Secondary operations — machining, plating and painting often cost more than the casting itself. Design them in early.
- Volume — die casting rewards volume; the die amortizes and cycle efficiencies compound.
- Tolerance band — as-cast tolerances are cheap; machined precision costs machine time.
Cost control checklist: consolidate secondary ops, combine parts into one casting where possible, standardize on one alloy family, and let the supplier DFM the part before quoting — a good DFM routinely cuts 10–20% off the as-quoted cost.
Quality control and inspection for die castings
Serious buyers audit casting quality the same way they audit molds:
- Dimensional: CMM first-article, key characteristics per drawing.
- Chemical: alloy composition certificate per heat.
- Mechanical: tensile/hardness sampling per lot where specified.
- Visual: surface defect standards (paint-ready vs. structural faces).
- Leak testing: air-under-water or pressure decay for housings.
- X-ray / dye penetrant: internal porosity checks for safety-critical parts.
Under IATF 16949, automotive castings additionally demand PPAP, control plans and capability studies. Ask which of these a supplier provides by default — the answer tells you how they’ll behave on your program.
FAQ
1. What is die casting? A manufacturing process where molten metal (aluminum, zinc or magnesium alloy) is injected under high pressure into a reusable steel die to make precise, complex metal parts at high volume.
2. What is the difference between hot chamber and cold chamber die casting? Hot chamber machines keep the melt in the machine (used for zinc/magnesium); cold chamber machines ladle metal per shot (required for aluminum, which would attack hot chamber parts).
3. Which alloys can be die cast? Aluminum (ADC12, A380, A383, A360, A413), zinc (Zamak family), magnesium (AZ91D), plus tin, lead and copper alloys in special cases.
4. What is the strongest die casting alloy? Aluminum alloys like A380 offer the best balance of strength, castability and cost for structural parts; magnesium wins on strength-to-weight.
5. What tolerance can die casting hold? General dimensions ±0.10–0.20 mm for aluminum, ±0.05–0.10 mm for zinc; tight features ±0.05 mm; machined features tighter via post-CNC.
6. How long does a die casting die last? Zinc: 500k–1M+ shots; magnesium: 100k–300k; aluminum: 80k–150k with proper maintenance (H13 steel).
7. Is die casting cheaper than CNC machining? At volume (thousands+ of parts), yes — the die cost amortizes and cycle time is seconds. Below ~500 parts, CNC machining is cheaper.
8. Is die casting cheaper than injection molding? At comparable volume, plastic injection molding has lower unit cost, but die casting produces metal parts with strength, conductivity and heat resistance plastic cannot match. Compare on function, not just price.
9. What is the minimum wall thickness for die casting? ~1.0 mm typical for aluminum, ~0.5 mm for zinc; magnesium can cast some of the thinnest sections in the industry (Xometry: xometry.com/resources/casting/die-casting/).
10. Can die castings be plated? Yes — zinc castings are commonly chrome/nickel plated; aluminum can be anodized or powder coated.
11. What is die casting porosity and can it be fixed? Porosity is trapped gas in the casting, a natural die casting characteristic. It’s controlled by gating design, vacuum die casting and impregnation sealing for pressure-tight parts.
12. What machines do you use for die casting? The 58–800 T band is the industry standard for custom die casting (FirstMold: firstmold.com/die-casting-service/); we quote by part envelope and alloy.
13. Can you do die casting and CNC in one place? Yes — MOLDITQUICK provides one-stop die casting with in-house die making, casting, CNC finishing and plating/coating.
14. Do you provide die casting for automotive? Yes, including NEV components, under IATF 16949 documentation and process control.
15. What is the MOQ for die casting? Typically thousands of parts — for smaller runs, CNC machining or CNC prototype + die casting scale-up is recommended.