Die Casting parameters tolerances
Die casting is a manufacturing process that injects molten metal at high pressure into a steel mold (die). The pressure allows filling complex cavities with high precision and excellent surface finish. It is widely used to produce components made of aluminum, zinc, magnesium, and copper in large volumes, with two main variants: hot chamber (for low melting point metals such as zinc) and cold chamber (for aluminum, magnesium, and copper alloys).
Applicable materials
Section titled “Applicable materials”| Material | Representative alloys | Density (kg/m³) / (lb/in³) | Pouring temperature (°C / °F) | Key characteristics |
|---|---|---|---|---|
| Aluminum | AA 380 (A03800), AA 384, AA 386, AA 390 | 2640 / 0.0953 (alloy 360) | 650 / 1200 | Lightweight, high dimensional stability, good corrosion resistance, retains strength at moderate temperatures. |
| Zinc | Zamak 3, Zamak 5 | 7135 / 0.2577 (pure zinc; alloys around 6600 kg/m³) | 425 / 800 | Excellent fluidity, high ductility and impact resistance, easy to chrome plate, very thin walls possible, long mold life. |
| Magnesium | AZ91D | 1770 / 0.0639 (AZ31B) | 650 – 680 / 1200 – 1256 | Lightest of structural metals, excellent strength-to-weight ratio, good machinability. |
| Copper / Brass | Silicon brass, bronze | 8400 – 8700 / 0.303 – 0.314 (cast brass) | 900 – 1000 / 1650 – 1830 | High mechanical and wear resistance, excellent dimensional stability, corrosion resistance, properties close to steel. |
Operating parameters
Section titled “Operating parameters”The injection pressure in die casting typically ranges between 10 MPa (1,450 psi) and 210 MPa (30,500 psi). Temperature, minimum wall thickness, and draft angle parameters depend on the material, as summarized in the following table.
| Material | Pouring temperature (°C / °F) | Minimum wall thickness (mm / in) | Minimum draft angle (°) | Typical tensile strength (MPa / ksi) |
|---|---|---|---|---|
| Aluminum (AA 380) | 650 / 1200 | 0.9 / 0.035 | 0.5 | 324 / 47 |
| Aluminum (AA 384) | 650 / 1200 | 0.9 / 0.035 | 0.5 | 331 / 48 |
| Aluminum (AA 386) | 650 / 1200 | 0.9 / 0.035 | 0.5 | 317 / 46 |
| Aluminum (AA 390) | 650 / 1200 | 0.9 / 0.035 | 0.5 | 283 / 41 |
| Zinc | 425 / 800 | 0.6 / 0.025 | 0.25 | 280 – 330 / 40 – 48 (typical) |
| Copper / Brass | 900 – 1000 / 1650 – 1830 | 1.25 / 0.050 | 0.7 | 350 – 550 / 50 – 80 (typical) |
Note: Tensile strength of zinc and copper alloys may vary depending on exact composition. The values given for aluminum correspond to the listed AA alloys.
Typical tolerances
Section titled “Typical tolerances”Die casting achieves dimensional accuracy of up to ±0.2% of the nominal dimension, allowing complete elimination of subsequent machining in many parts. For example, on a 100 mm dimension, a tolerance of ±0.2 mm (±0.008 in) can be maintained. Typical surface roughness obtained is between 1.6 µm and 3.2 µm (63 µin to 126 µin). Geometric tolerances vary depending on part size; the most relevant design limitations are minimum wall thickness and draft angle, whose values by material are found in the operating parameters table. Additionally, it is recommended to keep maximum section thickness below 13 mm / 0.5 in to avoid shrinkage voids.
| Material | Minimum wall thickness (mm / in) | Minimum draft angle (°) |
|---|---|---|
| Aluminum | 0.9 / 0.035 | 0.5 |
| Zinc | 0.6 / 0.025 | 0.25 |
| Copper / Brass | 1.25 / 0.050 | 0.7 |
Advantages and limitations
Section titled “Advantages and limitations”| Advantage | Description |
|---|---|
| High dimensional accuracy | Up to ±0.2% of dimension, reducing or eliminating secondary machining. |
| Excellent surface finish | Smooth and uniform surfaces, suitable for coatings and paint. |
| High productivity | Short cycles (a few seconds) suitable for mass production of thousands of parts. |
| Complex geometries | Possibility to mold intricate shapes, thin walls, and ribs. |
| Material versatility | Applicable to aluminum, zinc, magnesium, copper, and lead/tin. |
| Limitation | Description |
|---|---|
| High initial tooling cost | Hardened steel molds require high investment and long manufacturing lead times. |
| Exclusion of ferrous metals | Cannot process steel or iron due to their high melting point and reactivity with the mold steel. |
| Part weight limits | Typical maximum weight: aluminum ~32 kg / 70 lb, zinc ~35 kg / 77 lb, magnesium ~20 kg / 44 lb, brass ~4.5 kg / 10 lb. |
| Porosity | Air and gas entrapment can create porosity, mitigable with vacuum casting or careful design. |
| Limited thicknesses | Sections larger than 13 mm / 0.5 in can cause shrinkage and voids. |
Material selection guide
Section titled “Material selection guide”| Material | Recommended applications | Key advantages |
|---|---|---|
| Aluminum AA 380 | Engine components, housings, utensils, general purpose parts | Balance between cost, strength, and filling fluidity. |
| Aluminum AA 384 | Parts with complex shapes and high filling ease | Very good castability. |
| Aluminum AA 386 | Marine components, corrosive environments | Excellent corrosion resistance. |
| Aluminum AA 390 | Engine blocks, pistons, high-wear applications | High wear resistance due to high silicon content (17%). |
| Zinc | Gears, racks, connectors, precision and decorative parts | Excellent fluidity, high ductility, easy to coat, very thin walls. |
| Magnesium | Transmission cases, portable housings, aerospace components | Lightest of all, high specific stiffness. |
| Copper / Brass | Valves, electrical connections, marine hardware | High mechanical and wear resistance, good corrosion resistance. |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum pressure in die casting?
Section titled “What is the maximum pressure in die casting?”Injection pressure can reach up to 210 MPa / 30,500 psi in cold chamber machines, while hot chamber processes typically operate between 10 and 35 MPa / 1,450 and 5,000 psi.
What dimensional accuracy is achieved in die casting?
Section titled “What dimensional accuracy is achieved in die casting?”An accuracy of ±0.2% of the nominal dimension is achieved, which is equivalent to ±0.1 mm (±0.004 in) on 50 mm parts, often eliminating subsequent machining.
What is the pouring temperature of aluminum and zinc?
Section titled “What is the pouring temperature of aluminum and zinc?”Aluminum is poured at a temperature of 650 °C / 1200 °F, while zinc is processed at 425 °C / 800 °F, allowing shorter cycles for the latter.
What minimum wall thickness is possible in die casting?
Section titled “What minimum wall thickness is possible in die casting?”With zinc alloys, a minimum thickness of 0.6 mm / 0.025 in is possible; for aluminum, the minimum is 0.9 mm / 0.035 in, and for copper alloys, 1.25 mm / 0.050 in.
Why can’t ferrous metals be die cast?
Section titled “Why can’t ferrous metals be die cast?”Steels and irons have melting points above 1150 °C / 2100 °F and chemically react with the mold steel, drastically reducing its service life; therefore the process is limited to non-ferrous metals with lower melting points.
How much can die cast parts weigh?
Section titled “How much can die cast parts weigh?”Typical maximum weights are 35 kg / 77 lb for zinc, 32 kg / 70 lb for aluminum, 20 kg / 44 lb for magnesium, and 4.5 kg / 10 lb for brass; in modern automotive applications, aluminum parts over 100 kg / 220 lb have been achieved using advanced technology.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html
- efunda.com: https://www.efunda.com/processes/metal_processing/die_casting.cfm