Die Casting vs Gravity Casting - Process & Cost

High-pressure die casting and gravity casting both use metal molds, but they fill those molds in very different ways. High-pressure die casting injects molten metal into the die at high speed and pressure. Gravity casting fills the mold under gravity, sometimes with tilt assistance or low turbulence pouring.

The result is a major difference in wall thickness, cycle time, tooling cost, porosity behavior, heat treatment options, and production volume fit.

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Quick Answer

Choose high-pressure die casting (HPDC) for high-volume aluminum, zinc, or magnesium parts with thin walls, complex geometry, tight as-cast tolerances, and low unit cost.

Choose gravity casting for lower-volume aluminum parts, thicker walls, simpler geometry, improved heat treatment options, and applications where mechanical properties matter more than cycle time.

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Comparison Table

Factor	High-Pressure Die Casting	Gravity Casting
Mold fill method	High-speed injection under pressure	Gravity-fed pouring
Typical metals	Aluminum, zinc, magnesium	Mostly aluminum and copper alloys
Wall thickness	Thin walls possible, often 1.2-3.0 mm aluminum	Thicker walls, often 3.0 mm+
Cycle time	Very fast	Slower
Tooling cost	Higher	Lower to medium
Unit cost at volume	Lower at medium and high volumes	Higher at high volumes
Porosity risk	Gas porosity risk unless vacuum-assisted	Lower gas entrapment, but shrinkage still matters
Heat treatment	Limited for standard HPDC	Better suited to T6 heat treatment
Surface finish	Good as-cast surface	Good, but often less precise
Dimensional precision	Better as-cast repeatability	Moderate

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When HPDC Is Better

HPDC is usually the better choice when production volume is high and part geometry is complex.

Typical HPDC parts include:

• Electronics housings
• Motor end shields
• Heat sink housings
• Gearbox covers
• Pump and valve bodies
• Zinc lock and hardware components
• Thin-wall aluminum enclosures

The main advantage is production economics: fast cycle time, repeatable dimensions, and near-net-shape features reduce unit cost.

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When Gravity Casting Is Better

Gravity casting can be better when the part is lower volume, thicker, or requires heat treatment for improved mechanical properties.

Typical gravity casting applications include:

• Structural aluminum parts with thicker sections
• Lower-volume industrial components
• Parts requiring T6 heat treatment
• Components where tooling cost must stay lower
• Designs that do not need very thin walls or high-speed production

Gravity casting is slower, but it can be more forgiving for some alloy and heat treatment requirements.

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Porosity and Heat Treatment

Standard HPDC can trap gas because molten metal enters the cavity at high speed. This makes full T6 heat treatment risky, because trapped gas can expand during solution treatment and create blisters.

Gravity casting generally has lower gas entrapment, which makes it more suitable for heat treatment. However, gravity castings still need proper riser design and feeding to control shrinkage porosity.

Vacuum-assisted HPDC can reduce gas porosity and expand HPDC into more demanding applications, but it requires tighter process control.

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Buyer Decision Rule

If the part needs thin walls, high volume, tight repeatability, and integrated details, start with HPDC. If the part is lower volume, thick-walled, and needs stronger heat-treated aluminum properties, evaluate gravity casting.

KastMfg focuses on HPDC and can review whether your part is a good pressure die casting candidate before tooling.

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FAQ

Is gravity casting the same as die casting?

Gravity casting is sometimes called gravity die casting because it uses a permanent metal die, but it is not the same as high-pressure die casting. The key difference is that gravity casting fills the mold under gravity instead of injection pressure.

Which process is cheaper?

HPDC usually has a lower unit cost at medium and high volumes. Gravity casting can have lower tooling cost and may be better for lower-volume programs.

Can HPDC parts be T6 heat treated?

Standard HPDC parts are difficult to T6 heat treat because gas porosity can cause blistering. Vacuum-assisted HPDC can improve heat treatment feasibility on selected programs.

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Contact KastMfg: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China