How to Inspect Aluminum Die Castings: Complete Quality Control Process

In aluminum die casting, quality control is not a single checkpoint—it’s a complete verification chain. Every stage, from verifying alloy purity to the final dimensional report, determines whether a part performs reliably in the field.
This article walks through the entire QC process used in professional aluminum foundries—showing how suppliers like Yongzhu Casting ensure traceability, precision, and long-term stability for every production batch.

Step 1 – Material Certification and Alloy Verification

Supplier Certification and COA Verification

Quality control begins with raw materials. Each aluminum ingot, recycled return, or billet arrives with a Certificate of Analysis (COA) that lists chemical composition, supplier lot number, and smelting date.
Before storage, inspectors check labeling, oxidation, and moisture content.
Factories maintain a traceability chain linking every shipment to its melt batch and final product lot—so if a defect appears, the origin can be traced back within minutes.

Alloys Commonly Used

While A380, ADC12, and AlSi10Mg are the most common, other alloys like A360, A383, and AlSi9Cu3 are often selected depending on strength, ductility, or corrosion resistance.

Spectrometer Analysis

Before pouring, a spectrometer tests molten aluminum for Si, Cu, Mg, Fe, Mn, and Zn content. The device excites a small sample with plasma and compares emission spectra to certified standards.
If readings fall outside tolerance (e.g., excessive Fe or Cu), the melt is refined or discarded—preventing porosity or brittleness in casting.

Mold Sampling and First Article Approval

Each new mold undergoes First Article Inspection (FAI) before mass production.

• A trial part is die-cast, trimmed, and dimensionally measured against CAD drawings.
• If issues such as shrinkage, cold shut, or misalignment occur, engineers adjust die temperature, injection pressure, or venting.
• Only after a Golden Sample is approved and archived does serial production begin.

Example: During the first A380 trial, porosity appeared near the corner ribs. The engineer increased die temperature by 20 °C and extended holding time by 0.2 s, which eliminated trapped air and stabilized flow.

Step 2 – In-Process Casting Inspection

High-pressure die casting requires continuous process monitoring to prevent defects before they spread.

Visual Inspection at Demolding

Operators visually check each casting for flash, short fill, or incomplete edges.

• Flash/Burrs: Removed by trimming press or manual deburring; excessive flash may signal mold mismatch.
• Cracks or cold shuts: Immediately rejected and logged for die temperature or pressure review.

Dimensional Sampling During Production

At least 3–5 samples per batch are measured with gauges and micrometers to verify tolerance control. Any deviation triggers machine parameter review (pressure curve, shot speed, lubrication).

X-Ray or CT Inspection

Internal porosity and shrinkage cannot be seen from the outside. X-ray or CT scanners reveal voids or inclusions inside cast walls.

• Common causes: trapped gas, low metal pressure, or contaminated melt.
• Prevention: degassing tablets, vacuum casting, and improved vent design.

Leak and Pressure Testing

For sealed housings or fluid components, parts undergo air-pressure testing (0.5–1 MPa). Any bubbles in a water tank indicate leakage and immediate rejection.

Step 3 – Machining and Surface Verification

Machining Accuracy Check

After CNC machining, critical features such as holes, threads, and sealing surfaces are re-checked.
If any dimension exceeds ±0.05 mm tolerance, the batch is isolated for rework or tool offset adjustment.

Surface Quality and Coating Tests

Surface inspection ensures both function and appearance.

• Visual check: scratches, pinholes, stains.
• Roughness test (Ra): ensures sealing faces below Ra 1.6 µm.
• Adhesion test (ASTM D3359): verifies coating bonding strength.
• Salt-spray test (ASTM B117): evaluates corrosion resistance (500–1000 h for outdoor parts).

Example: A batch of ADC12 covers failed adhesion test; root cause was residual lubricant on surface. The cleaning bath temperature was increased by 10 °C and the curing cycle extended, achieving full adhesion.

Step 4 – Final Dimensional Verification: Why CMM Testing Is the Industry Standard

Why CMM Reports Are Trusted

In die-cast manufacturing, the Coordinate Measuring Machine (CMM) report is considered the highest standard of dimensional accuracy.
Unlike manual gauges, a CMM captures the true 3D coordinates of every feature and compares them directly with the CAD model.
Each measurement and deviation is stored digitally, producing a traceable, repeatable record suitable for ISO 9001 or IATF 16949 audits.
For this reason, many OEM and Tier-1 clients require CMM reports as part of the FAI (First Article Inspection) and PPAP documentation.

Why the Equipment Is So Expensive

A professional CMM system costs from US $50,000 to over $300,000 because it combines:

• a thermally stable measuring platform (granite or composite stone) that minimizes vibration and expansion,
• high-precision linear guides and sensor probes with 2–5 µm resolution, and
• a temperature-controlled inspection room (20 ± 1 °C) to prevent drift.
  This precision hardware allows repeatable micro-level accuracy even on complex die-cast geometries.

How the Measurement Works

The aluminum part is clamped securely on the CMM measuring table or fixture platform to prevent movement.
The probe moves along the X, Y, Z axes, recording points on critical planes, holes, and edges.
The software automatically compares these points to the CAD nominal data and generates a CMM dimensional report, showing any deviation beyond tolerance.

Different Products, Different Accuracy Requirements

Not all parts demand the same precision:

• Decorative covers or non-critical housings: ±0.1 mm tolerance—verified with gauges.
• Sealing or mechanical interfaces: ±0.03 mm tolerance—verified by CMM.
• Motor housings or optical frames: ±0.01 mm or better—verified by high-precision bridge-type CMM.

In short: CMM testing provides the final, unbiased confirmation that every aluminum die-cast component meets its CAD-defined geometry and fits perfectly during assembly.

Step 5 – Documentation and Traceability

A professional factory links every quality record digitally:

Each file is attached to the batch barcode, ensuring full end-to-end traceability.

Step 6 – Common Defects and Corrective Actions

Step 7 – Final Audit and Shipment

Before shipment, QA supervisors perform a comprehensive audit:

• Visual review under 500 lux lighting
• CMM dimensional conformity check
• Label, weight, and packaging verification

Only after all checkpoints are signed off and documented can a lot be released for export.

Conclusion

A complete aluminum die casting QC system combines scientific testing, traceable documentation, and disciplined inspection.
From supplier COA to CMM verification, each checkpoint prevents hidden defects and builds customer trust.
For OEM and distributor buyers, this process guarantees that every delivered component meets its design, tolerance, and performance requirements — consistently, batch after batch.