Die Casting
High-pressure injection into hardened steel dies — fast, precise, high volume
Gravity Casting
Controlled gravity pour into permanent moulds — denser, stronger, heat-treatable
Die Casting vs Gravity Casting – Which Aluminium Casting Process is Right for Your Application?
Choosing between die casting and gravity casting is one of the most important decisions you'll make when specifying an aluminium component. Get it wrong and you'll face unnecessary costs, quality problems, or a component that simply doesn't perform as required. Get it right and you'll have a manufacturing process that delivers exactly the quality, volume, and cost-efficiency your project demands.
At RR Enterprises, Coimbatore, we have been operating both die casting and gravity casting processes since 2002 — giving us a unique, practical perspective on which process works best for each application. This guide lays out a clear, technical comparison to help you make the right decision.
Quick Answer: Choose die casting for high-volume, thin-wall, cosmetically important parts where speed and dimensional consistency matter most. Choose gravity casting for structural, pressure-tight, or heat-treated components where mechanical properties and low porosity are the priority.
What is Die Casting?
Die casting (also called high-pressure die casting or HPDC) is a process in which molten aluminium is injected into a hardened steel mould — called a "die" — under very high pressure, typically between 700 and 1,000 bar. The metal fills the die cavity in milliseconds and solidifies rapidly under continued pressure.
The result is a near-net-shape component with excellent surface finish, consistent dimensions, and the ability to produce very thin walls (as thin as 1.0–1.5mm). Because the cycle time is measured in seconds rather than minutes, die casting is ideally suited to high-volume production where thousands or tens of thousands of identical parts are required.
Key characteristics of die casting
- Injection pressure: 700–1,000 bar (high-pressure die casting)
- Cycle time: 30–120 seconds per shot depending on component size
- Typical wall thickness: 1.0–5mm
- Surface finish (Ra): 1.6–3.2 μm as-cast
- Dimensional tolerance (IT grade): approximately IT8–IT10
- Porosity level: higher — trapped air at high fill speeds
- Heat treatability: generally not recommended for standard HPDC
- Tooling cost: high — hardened H13 steel dies required
What is Gravity Casting?
Gravity die casting (also called permanent mould casting) pours molten aluminium into a steel or cast iron mould by gravity alone — no external pressure is applied. The mould is typically tilted or the metal poured from a ladle, and the slower, more controlled filling under gravity produces castings with significantly lower porosity than die casting.
The slower cycle time (measured in minutes rather than seconds) and lower injection energy mean gravity castings are generally better suited to low-to-medium production volumes, and to components that require heat treatment, pressure tightness, or superior tensile and fatigue strength.
Key characteristics of gravity casting
- Fill method: gravity pour — no external pressure
- Cycle time: 3–10 minutes per casting
- Typical wall thickness: 3–10mm (thinner walls are harder to fill)
- Surface finish (Ra): 3.2–6.3 μm as-cast
- Dimensional tolerance (IT grade): approximately IT10–IT12
- Porosity level: low — controlled slow fill reduces gas entrapment
- Heat treatability: T5 and T6 heat treatment possible
- Tooling cost: medium — permanent steel/cast iron moulds
Die Casting vs Gravity Casting – Head to Head Comparison
The table below gives a clear side-by-side technical comparison of the two processes across all the key parameters that matter to engineers and procurement teams:
| Parameter | Die Casting (HPDC) | Gravity Die Casting |
|---|---|---|
| Fill Method | High-pressure injection (700–1,000 bar) | Gravity pour – no external pressure |
| Cycle Time | 30–120 seconds | 3–10 minutes |
| Minimum Wall Thickness | 1.0–1.5 mm | 3–4 mm typical |
| Porosity Level | Higher – gas entrapment risk | Low – controlled fill |
| Dimensional Accuracy | Excellent – IT8–IT10 | Good – IT10–IT12 |
| Surface Finish (as-cast) | 1.6–3.2 μm Ra | 3.2–6.3 μm Ra |
| Tensile Strength (typical) | 220–280 MPa (as-cast) | 240–320 MPa (T6 heat treated) |
| Heat Treatability | Not recommended (standard HPDC) | T5, T6 possible |
| Pressure Tightness | Moderate – porosity risk | Excellent – low porosity |
| Typical Production Volume | High – 5,000+ parts | Low to medium – 500–10,000 parts |
| Tooling Cost | High – hardened steel dies | Medium – permanent moulds |
| Piece-Part Cost (high volume) | Lower | Higher |
| Typical Alloys | ADC12, A380, LM2 | LM6, LM25, A356, LM4 |
| Best For | Thin-wall, cosmetic, high-volume | Structural, pressure-tight, safety-critical |
Die Casting – Strengths
- Fastest cycle time – highest output per hour
- Thinnest wall sections achievable
- Best as-cast surface finish and dimensional accuracy
- Lowest piece-part cost at high volumes
- Complex external geometries in a single shot
- Consistent part-to-part repeatability
Gravity Casting – Strengths
- Lowest porosity – superior internal soundness
- Heat treatable to T6 for maximum strength
- Superior tensile and fatigue strength
- Pressure-tight for hydraulic & pneumatic applications
- Lower tooling investment for medium volumes
- More alloy flexibility including LM25 and A356
Not Sure Which Process is Right for You?
Send RR Enterprises your drawings and component requirements — our casting engineers will recommend the optimal process and provide a detailed quote within 24 hours.
Porosity – The Critical Difference
Of all the technical differences between die casting and gravity casting, porosity is the most significant — and the one that most determines which process is appropriate for a given application.
In high-pressure die casting, molten aluminium is injected at high velocity. This fast fill can trap air and gas within the casting cavity before the metal solidifies — resulting in microscopic gas pores distributed throughout the casting. This porosity:
- Reduces tensile strength and fatigue life relative to a pore-free casting
- Makes components unable to hold pressure (for hydraulic or pneumatic applications)
- Prevents T6 heat treatment — the trapped gas expands at heat treatment temperatures, causing blistering and surface defects
- Can be problematic for components that are later welded or braised
In gravity die casting, the slower, laminar fill under gravity allows gas to escape more easily from the mould vents, producing castings with significantly lower porosity that can be heat treated, pressure tested, and used in structurally demanding applications.
Important Note: Vacuum-assisted die casting (VADC) and squeeze casting are variants of die casting that significantly reduce porosity — making heat treatment and higher mechanical properties possible while retaining some of die casting's speed advantage. RR Enterprises can discuss these options where your application demands both volume and low porosity.
Alloy Selection for Die Casting vs Gravity Casting
The casting process you choose also determines which aluminium alloys are available to you:
| Alloy | Die Casting ✓ | Gravity Casting ✓ | Why |
|---|---|---|---|
| ADC12 / A383 | ✓ Ideal | ✗ Not typical | High fluidity at die casting speeds; poor gravity flow |
| A380 | ✓ Most common | Limited | Excellent die castability; good general properties |
| LM2 | ✓ Good | Possible | Good fluidity, adequate properties for general use |
| LM6 (Al-Si12) | Possible | ✓ Excellent | Best gravity flow; excellent corrosion resistance |
| LM25 / A356 | ✗ Rarely used | ✓ Preferred | Lower Si; excellent properties after T6 heat treatment |
| LM4 | Possible | ✓ Good | Good all-round casting alloy; heat treatable |
| A356 T6 | ✗ Not suitable | ✓ Best in class | Highest tensile strength after T6; aerospace standard |
Which Process Should You Choose? A Decision Guide
Choose the Right Casting Process for Your Component
Choose Die Casting When…
- Production volume exceeds 5,000 parts per run
- Wall thickness is below 3mm
- Surface finish and cosmetic appearance are important
- Tight dimensional tolerances without post-machining
- Heat treatment is not required
- Component does not need to hold pressure
- Alloy: ADC12 or A380
Choose Gravity Casting When…
- Component is structural or safety-critical
- T5 or T6 heat treatment is required for strength
- Pressure tightness is essential (hydraulic, pneumatic)
- Wall thickness is 3mm or greater
- Volume is low to medium (under 5,000 parts)
- Welding or brazing is required post-casting
- Alloy: LM25, A356, LM6
Applications – Die Casting vs Gravity Casting in Industry
Typical Die Casting Applications
- Automotive — gearbox casings, engine brackets, air-conditioning compressor housings, electric vehicle battery housings, door handles, seat belt components
- Electrical & Electronics — heat sinks, motor housings, connector bodies, LED lamp housings, switchgear enclosures
- Consumer products — power tool housings, furniture hardware, handles, decorative components
- General engineering — instrument cases, valve bodies (non-pressure), mounting brackets
Typical Gravity Casting Applications
- Aerospace & defence — structural brackets, instrument housings, armament components, UAV structural parts
- Automotive safety systems — brake callipers, steering knuckles, suspension components, wheel hubs
- Pumps & compressors — pump casings, impellers, valve bodies for hydraulic systems
- Oil & gas — pressure-tight housings, metering bodies, manifolds
- Marine & offshore — corrosion-resistant structural castings using LM6 alloy
Cost Comparison – Die Casting vs Gravity Casting
Cost is always a critical factor. Understanding the cost structure of each process helps you choose the most economical option for your volume and requirements:
| Cost Component | Die Casting | Gravity Casting |
|---|---|---|
| Tooling / Mould Cost | High (₹3–15 lakhs for complex dies) | Medium (₹0.5–4 lakhs) |
| Piece-Part Cost (low volume) | Higher – tooling cost not amortised | Lower |
| Piece-Part Cost (high volume) | Much lower – fast cycle time | Higher per piece |
| Secondary Machining | Less – near-net-shape | Slightly more |
| Heat Treatment Cost | Not applicable | Additional (T6: ₹20–50/kg) |
| Break-even Volume | Typically die casting becomes cost-competitive above 3,000–5,000 parts/run | |
RR Enterprises Cost Tip: For volumes below 2,000 parts, gravity casting almost always offers a lower total cost of production despite the higher cycle time — because the tooling investment is significantly lower. For volumes above 5,000 parts, die casting typically wins on piece-part cost. Between 2,000–5,000 parts, the choice depends on mechanical property requirements and alloy specification.
How RR Enterprises Selects the Right Process for You
At RR Enterprises, we don't prescribe a process before reviewing your requirements. Our casting engineers evaluate each project against a structured set of criteria:
- Component geometry — wall thickness, complexity, draft angles, and features that favour one process over the other
- Mechanical property requirements — tensile strength, yield strength, fatigue life, hardness targets
- Post-processing requirements — does the component need T6 heat treatment? Will it be welded? Must it hold pressure?
- Production volume — current volume and projected annual requirement
- Alloy preference — customer-specified or recommended based on application environment
- Total budget — balancing tooling investment against unit cost over the expected production life
This systematic approach means our clients get the process that genuinely best suits their component — not the process that happens to be most convenient for us.
Frequently Asked Questions
Die casting injects molten aluminium under very high pressure (700–1,000 bar) into a hardened steel die, producing thin-wall, high-volume components with excellent surface finish. Gravity casting pours molten aluminium into a permanent mould under gravity alone — no external pressure — producing denser, lower-porosity castings with superior mechanical properties that can be heat treated to T6.
Gravity casting with T6 heat treatment typically delivers better mechanical properties — particularly tensile strength, yield strength, and fatigue resistance — because the lower porosity and heat treatment produce a finer microstructure. Standard die castings (untreated) have lower porosity tolerance but cannot be heat treated, limiting their achievable strength. T6 gravity-cast A356 alloy, for example, can achieve tensile strengths of 280–310 MPa vs 240–280 MPa for as-cast ADC12 die castings.
Die casting has higher tooling costs (hardened steel dies) but lower piece-part costs at high volumes due to fast cycle times. Gravity casting has lower tooling costs but higher piece-part costs per component. For volumes below 3,000–5,000 parts, gravity casting is typically more economical in total. Above that volume, die casting usually becomes the more cost-effective option.
Standard high-pressure die castings are generally not heat treated because trapped gas pores expand during the high-temperature solution treatment cycle, causing blistering and dimensional distortion. Vacuum-assisted die casting (VADC) and squeeze casting variants can sometimes be T5 heat treated. Gravity castings, with their lower porosity, can typically be T5 or T6 heat treated without issue.
It depends entirely on the component's function and volume requirements. For high-volume automotive brackets, housings, and covers where cosmetics and tight dimensions are key — die casting with ADC12 or A380 alloy. For safety-critical components like brake callipers, steering parts, or structural brackets where T6 strength and pressure tightness are required — gravity casting with LM25 or A356 alloy and T6 heat treatment.
Get a Quote for Aluminium Castings
Whether you need die casting or gravity casting, RR Enterprises has the expertise, equipment, and alloy knowledge to deliver the right component — from Coimbatore, to India and the world.
Related Articles
