What is the maximum allowable tolerance for airframe cast parts?

What Is the Maximum Allowable Tolerance for Airframe Cast Parts?

Industry Tolerance Standards for Airframe Castings

For aluminum die cast components used in airframe structures, the maximum allowable dimensional tolerance depends on the part’s size, complexity, and criticality. Generally, per NADCAP, AMS 2175, and SAE AS specifications, the maximum standard tolerance for non-critical dimensions in aerospace-grade aluminum castings (e.g., A356, AlSi10Mg) is:

• ±0.25 mm for dimensions under 25 mm

• ±0.40 mm for dimensions between 25 mm – 100 mm

• Up to ±0.75 mm for large, non-critical sections over 300 mm

For critical features on airframe parts (e.g., mounting points, mating surfaces, or aerodynamic control housings), tolerances as tight as ±0.05 mm to ±0.10 mm may be required. These are typically achieved through post-casting processes like CNC machining, rather than as-cast.

Factors Influencing Tolerance Capabilities

Achieving precise tolerances in aerospace castings is affected by several variables:

• Alloy shrinkage behavior: Alloys like A360 and AlZn10Si8Mg offer more predictable solidification and less distortion.

• Tool and Die Precision: Tolerances depend heavily on tool and die accuracy and thermal management during production.

• Casting Process Control: Consistent injection pressure, mold temperature, and cycle time are essential for repeatable dimensional accuracy.

• Inspection Techniques: Use of CMM and X-ray inspection validates dimensional compliance and identifies internal defects.

Compliance with Aerospace Standards

To be used in airframe assemblies, cast parts must comply with AS9100 and often with Boeing (BAC), Airbus (ABR), or MIL-STD-2175 specifications. These standards define tolerance classes, casting integrity levels, and inspection protocols. Castings that don’t meet critical tolerance thresholds are often post-machined to specification.

Recommended Services to Ensure Tolerance Control in Airframe Castings

Neway supports tight-tolerance aerospace casting with:

• Tool and Die Making: High-precision mold creation for dimensional consistency.

• Post-Machining Services: Achieve tight tolerances on critical features.

• Dimensional and NDT Inspection: CMM and radiographic inspections to ensure compliance with aerospace tolerance requirements.

These services enable consistent quality and dimensional reliability for airframe-grade cast parts under demanding aerospace standards.