Gravity Die Casting: Real Production Experience, Tolerances, and a Practical Case Study

If you are searching for a gravity die casting supplier, you are likely not interested in marketing slogans.
What really matters is whether the manufacturer understands tooling design, process control, dimensional tolerance, and secondary machining—and whether they have real production experience, not just theory.

Below is a real-world gravity die casting case, including materials, tolerances, defect control methods, and inspection data, to help you judge whether we truly know how to produce gravity cast parts.

What is Gravity Die Casting (Brief but Practical)

Gravity die casting is a permanent mold casting process where molten metal fills the mold only by gravity, without high-pressure injection.

Compared with:

• High-pressure die casting (HPDC) → higher porosity, thinner walls

• Sand casting → rougher surface, lower dimensional accuracy

Gravity die casting sits in the middle:

• Lower porosity than HPDC

• Better mechanical properties than sand casting

• Suitable for structural aluminum parts requiring machining

Typical applications:

• Automotive & EV housings

• Industrial motor covers

• Medical & optical equipment frames

• Heat-dissipating structural parts

Real Customer Case: Aluminum Gravity Die Casting Housing

Project Background

• Customer industry: Industrial automation equipment

• Part function: Structural aluminum housing with internal ribs

• Annual volume: ~8,000 pcs

• Critical requirement:

  • Stable mechanical strength

  • Machinable reference surfaces

  • Tight flatness after machining

The customer originally tried sand casting, but failed due to:

• Excessive porosity

• Unstable wall thickness

• Large machining allowance and scrap rate

Part Specifications (Actual Production Data)

Dimensional Tolerance & Machining Strategy

Gravity die casting alone cannot achieve final precision—machining is designed into the process from day one.

As-Cast Tolerance (Controlled)

• Linear dimensions: ±0.3 mm / 100 mm

• Wall thickness variation: ≤ ±0.4 mm

• Casting flatness (raw): ≤ 0.6 mm

After CNC Machining

• Critical bore tolerance: ±0.02 mm

• Flatness on mounting face: ≤ 0.05 mm

• Parallelism: ≤ 0.03 mm

• Surface roughness (machined): Ra 1.6–3.2 μm

Key point: We intentionally leave 1.0–1.5 mm machining allowance only on functional areas, not the entire part—reducing cycle time and cost.

Mold Design Details (Where Most Problems Are Solved)

This project succeeded mainly due to correct gravity die mold design, not luck.

Mold Design Highlights

• Multi-point bottom gating to reduce turbulence

• Overflow wells at rib ends to trap oxide

• Local chills added at thick sections

• Controlled solidification direction (no random shrinkage)

Defects We Actively Controlled

• Shrinkage porosity at rib intersections

• Cold shuts on thin ribs

• Gas entrapment near mounting bosses

Final X-ray inspection result:

• No porosity in machined zones

• ASTM Level ≤ 2 (internal standard)

Inspection & Quality Control

Every batch follows the same QC flow:

1. Chemical composition verification (spectrometer)

2. Visual & dimensional check (as-cast)

3. T6 heat treatment hardness test

   • Typical result: HB 80–95

4. CNC machining inspection

   • CMM report on critical dimensions

5. Random X-ray inspection (per lot)

This is why dimensional repeatability stayed stable across 12+ months of production.

When Gravity Die Casting Is the Right Choice

Gravity die casting is suitable if:

• You need stronger mechanical properties than HPDC

• You will machine functional surfaces

• Wall thickness is ≥4 mm

• Annual volume is 1,000–50,000 pcs

It is not suitable if:

• Ultra-thin walls (<3 mm) are required

• Cosmetic Class-A surfaces are critical

• Extremely high volume with minimal machining is needed

What This Case Proves

This project is not a lab example—it shows that we:

• Understand gravity die mold design

• Control porosity and solidification

• Know how to combine casting + machining

• Can deliver repeatable tolerances, not just samples

If you have a gravity die casting project and want:

• A DFM-based feasibility review

• Clear tolerance expectations

• Honest feedback on whether gravity casting is suitable

You can start by sharing your drawing.
We prefer to solve problems before tooling, not after scrap happens.