Choose pressure die casting for high volume production of small to medium, thin-walled components where dimensional accuracy, surface finish and low unit cost are the priorities. Choose gravity die casting for lower to medium volumes where better mechanical properties, lower porosity and the ability to heat treat are more important than production speed or minimum wall thickness. In both cases, critical tolerances are typically achieved by machining rather than as-cast, so the decision turns on volume, wall thickness, mechanical property requirements, and whether heat treatment is needed.
For: design engineers, manufacturing engineers, procurement leads and buyers at OEMs and Tier 1 manufacturers specifying non-ferrous metal components.
Answer: Pressure die casting forces molten metal into a hardened steel die under high pressure; gravity die casting pours molten metal into a permanent metal mould and relies on gravity alone to fill it.
Why: The method of filling the mould is the fundamental difference between the two processes and drives almost every other distinction – in wall thickness, porosity, surface finish, production speed and mechanical properties. Pressure die casting uses injection pressures of between 4,000 and 50,000 psi, producing rapid fill and fast cycle times. Gravity die casting fills slowly and without additional force, which reduces turbulence and gas entrapment but limits how thin walls can be and how fast the process can run.
How to decide:
When this advice may not apply: Low-pressure die casting – a variant not covered in this guide – sits between the two processes and may suit some applications at the boundary of volume or wall thickness.
Answer: Pressure die casting produces tighter dimensional tolerances and a better as-cast surface finish than gravity die casting.
Why: The high injection pressure forces metal into every detail of the die, producing very fine surface reproduction and dimensional consistency. Pressure die casting can typically achieve tighter dimensional tolerances, commonly around CT4-CT6 in accordance with the ISO 8062 tolerance grading system. Gravity die casting typically achieves around CT6-CT8, reflecting lower filling pressure and slightly greater variability in how the mould fills.
How to decide:
When this advice may not apply: In both processes, functional tolerances on critical interfaces – sealing faces, bores, mating surfaces – are typically achieved by machining rather than relying on as-cast accuracy alone.
Answer: Both processes are limited to non-ferrous alloys, most commonly aluminium, magnesium, zinc and copper alloys.
Why: The alloy ranges overlap significantly but the specific grades differ. Pressure die casting alloys are selected for fluidity under high injection pressure and fast solidification: commonly used grades include LM24, LM2, LM6, ADC12 and A380 for aluminium, AZ91 for magnesium, and Mazak for zinc. Gravity die casting alloys such as LM25 and LM4 are selected for good flow under gravity and, critically, suitability for heat treatment where required.
How to decide:
When this advice may not apply: Alloy availability varies by foundry and location. Always confirm with your sourcing partner before committing to a specification.
Answer: Gravity die casting typically produces better mechanical strength and internal integrity than pressure die casting, due to lower porosity from the slower, less turbulent mould filling process.
Why: High-pressure injection creates turbulence as metal fills the die at high velocity, trapping gas and creating porosity – small voids that reduce strength and make the component unsuitable for pressure-tight applications. Gravity die casting fills slowly without additional force, reducing gas entrapment and producing a denser casting with better fatigue resistance and higher tensile strength in equivalent alloys.
How to decide:
When this advice may not apply: Vacuum-assisted pressure die casting can reduce porosity significantly, potentially closing the gap with gravity die casting for some applications. Confirm availability if internal integrity is a priority.
Answer: Gravity die casting components can generally be heat treated to improve mechanical properties. Pressure die casting components generally cannot, because the porosity inherent in the process causes blistering during heat treatment.
Why: Heat treatment requires heating the component to elevated temperatures. In pressure die castings, trapped gas within the porosity expands when heated, causing surface blistering and internal damage that may render the component unusable. Gravity die castings, with their lower porosity, do not have this problem and can be heat treated using standard T5 and T6 temper processes to increase hardness, tensile strength and fatigue resistance. This is a fundamental process difference with significant implications for structural and safety-critical applications.
How to decide:
When this advice may not apply: Some specialist pressure die casting alloys and vacuum-assisted processes can support limited heat treatment – confirm with your sourcing partner if this is a requirement.
Answer: Pressure die casting is better suited to high volume production, with typical annual volumes of 5,000 to 1,000,000 parts. Gravity die casting suits lower to medium volumes, typically 100 to 50,000 parts per year.
Why: Pressure die casting is a highly automated, fast-cycle process with long tooling life and very low unit cost at high volumes. Gravity die casting is slower with a lower tooling cost, making it more economical at lower volumes where the tooling investment needs to be recovered over fewer parts.
How to decide:
When this advice may not apply: For high volume programmes where mechanical properties or heat treatment are critical, gravity die casting may still be the right process despite the slower cycle time.
Answer: Pressure die casting tooling is significantly more expensive than gravity die casting tooling and more costly to modify.
Why: Pressure die casting dies must withstand very high injection pressures over millions of cycles, requiring high-grade tool steel and precise engineering. Gravity die casting tooling operates at much lower stresses, is less expensive to produce and is more straightforward to modify. This difference in modification cost matters as much as the initial tooling cost for programmes where design changes are likely.
How to decide:
When this advice may not apply: Absolute tooling costs vary significantly by foundry, location and component complexity – confirm actual costs with your sourcing partner for your specific component.
Answer: Pressure die casting achieves thinner minimum wall thicknesses than gravity die casting and is better suited to intricate geometries. Gravity die casting requires thicker walls and suits simpler, die-friendly shapes.
Why: High injection pressure forces metal into fine features and thin sections, achieving minimum wall thicknesses of around 0.5mm. Gravity die casting relies on metal flowing under gravity alone, requiring walls of typically 3 to 5mm minimum to ensure complete fill. Gravity die casting does support the use of sand or metal cores for internal features, which adds some geometric flexibility, but die constraints still limit complexity compared with pressure die casting.
How to decide:
When this advice may not apply: Complex geometries in either process may require a design-for-manufacture review before tooling is committed, regardless of wall thickness.
Answer: Choose pressure die casting when you need high volume production of small to medium, thin-walled non-ferrous components with tight dimensional tolerances, good surface finish and low unit cost, and heat treatment is not required.
Why: Pressure die casting delivers its strongest combination of advantages when volumes are high, the design is stable, walls are thin, tolerances are tight, and the alloy does not need to be heat treated. In these conditions, no other casting process matches the unit cost, production rate and dimensional consistency of pressure die casting.
How to decide:
When this advice may not apply: If mechanical strength, pressure tightness or heat treatment are required alongside high volumes, vacuum-assisted pressure die casting or gravity die casting should be evaluated before committing to standard pressure die casting tooling.
Answer: Choose gravity die casting when volumes are low to medium, mechanical properties and internal integrity are important, heat treatment may be required, and wall thickness allows for the thicker sections the process requires.
Why: Gravity die casting delivers its strongest combination of advantages when volumes are in the range of 100 to 50,000 parts per year, the component is structural or subject to load and fatigue, and the design is stable enough to justify the tooling investment. The lower porosity and heat treatability of gravity die castings make it the preferred route for components where internal integrity is specified, pressure tightness is required, or mechanical properties need to be enhanced after casting.
How to decide:
When this advice may not apply: For very low volumes – typically below 100 parts per year – or highly complex geometries with significant internal features, sand casting may offer a lower-risk and more cost-effective alternative. Discuss with your sourcing partner if volumes are at the lower end of the range.
The core difference
Pressure die casting injects molten metal under high pressure; gravity die casting pours it in and lets gravity do the work. That single difference in filling method drives almost every other distinction between the two processes.
Volume and unit cost
Pressure die casting is the high-volume option: 5,000 to 1,000,000 parts per year, fast cycle times, and very low unit cost once tooling is recovered. Gravity die casting suits 100 to 50,000 parts per year, with moderate tooling cost and slower cycle times. At low to medium volumes, gravity die casting’s lower tooling investment often makes more financial sense.
Wall thickness and geometry
Pressure die casting achieves minimum wall thicknesses of around 0.5mm and handles intricate, complex geometries well. Gravity die casting requires walls of 3 to 5mm minimum. If your component has walls below 3mm, pressure die casting is the only viable die casting option.
Mechanical properties and porosity
Gravity die casting produces denser castings with lower porosity and better mechanical strength than pressure die casting in equivalent alloys. For structural components, load-bearing parts, or anything that must be pressure-tight, gravity die casting has a clear advantage.
Heat treatment
Gravity die casting components can be heat treated to improve mechanical properties. Pressure die casting components generally cannot – the porosity inherent in the process causes blistering at elevated temperatures. If heat treatment is specified, gravity die casting is the required route.
Tooling cost and design stability
Pressure die casting tooling is significantly more expensive and more costly to modify than gravity die casting tooling. If your design is not yet finalised, gravity die casting reduces the financial risk of iteration.
The decision in summary
Choose pressure die casting for high volume, thin-walled components where surface finish, dimensional accuracy and low unit cost are the priorities and heat treatment is not required. Choose gravity die casting where mechanical properties, pressure tightness, heat treatability or lower tooling commitment matter more than production speed or minimum wall thickness.
| Factor | Pressure die casting | Gravity die casting |
|---|---|---|
| Filling method | Molten metal injected under high pressure | Molten metal poured under gravity |
| Typical annual volume | 5,000 to 1,000,000 parts | 100 to 50,000 parts |
| Tooling cost | High | Moderate |
| Tooling modification cost | High | Moderate |
| Minimum wall thickness | 0.5mm | 3 to 5mm |
| Dimensional tolerance | CT4 (tightest) | CT6 to CT8 |
| Surface finish | Excellent | Good |
| Porosity | Higher (turbulent fill) | Lower (gravity fill) |
| Mechanical strength | Good | Better in equivalent alloys |
| Heat treatment | Generally not suitable | Yes – T5 and T6 temper available |
| Common alloys | Aluminium (LM24, LM2, LM6, ADC12, A380), magnesium (AZ91), zinc (Mazak) | Aluminium (LM4, LM25, LM6), copper alloys, magnesium, zinc |
| Geometry complexity | High – thin walls, intricate detail | Moderate – thicker walls, die-friendly shapes |
| Internal features | Limited by die design | Sand or metal cores available |
| Production speed | Fast – short cycle times | Slower |
| Best for | High volume, complex thin-walled components, tight tolerances, cosmetic finish | Structural components, pressure-tight parts, heat-treatable applications, lower volumes |
Not sure whether pressure die casting or gravity die casting is right for your component? Talk to Investacast’s engineering team about the best process for your project. Get in touch
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