1. Precision Requirements (usually reaching the micron or even nanometer level)

1.1 Dimensional accuracy

The tolerance of key components such as turbine blades and combustion chamber parts is often controlled within ±0.005 mm, and the roundness error of aero-engine rotor shafts needs to be less than 0.001 mm.

1.2 G&D tolerance

Aircraft structural parts (such as wing ribs and frames) have extremely high requirements for flatness and coaxiality.

1.3 Fit accuracy

The fit clearance between the valve core and valve body of the hydraulic system is only 1-3 μm, which needs to avoid leakage or jamming.

2. Surface Quality Requirements

2.1 Surface roughness: Ra≤0.8μm is the foundation, and key parts need to reach Ra0.02μm

• The surface roughness of the engine blade body must be ≤Ra0.4μm: A rough surface will increase air resistance (for every 0.1μm increase in Ra, the aerodynamic efficiency decreases by 1%~2%)
• The tooth surface roughness of precision transmission parts (such as helicopter reducer gears) must be ≤Ra0.08μm. The ultra-smooth surface can reduce frictional wear during meshing, extending the gear life to 5~10 times that of ordinary industrial gears

2.2 Mechanical properties of the surface layer: Strict control of residual stress and hardness

• Load-bearing components such as landing gears need to introduce -500~-800MPa surface compressive stress through processes such as shot peening: The compressive stress can offset the alternating tensile stress during flight, increasing the fatigue life by 3~5 times. If tensile stress is generated during processing (such as overheating during grinding), it may cause the landing gear to break suddenly under the impact of takeoff and landing
• The tenon surface of the turbine disk needs to be carburized, with a hardness of HRC58~62: Insufficient hardness at high temperatures (600~1000℃) will cause the connection between the tenon and the blade to loosen, causing severe vibration

2.3 Surface integrity: Zero defect requirement

• Any microcracks are prohibited: Surface cracks on the engine combustion chamber wall (even with a depth of only 5μm) will expand rapidly under the scouring of high-temperature and high-pressure gas, leading to combustion chamber explosion
• Strict control of surface contamination: Surface oil stains or oxide layers on spacecraft parts (such as satellite solar wing brackets) will affect the outgassing performance in a vacuum environment, causing contamination of optical components

3. Cases of Precision and Surface Quality Requirements for Typical Parts

3.2 Integral aircraft structural parts (such as wing spars)

• Precision: The straightness of deep holes with a length-diameter ratio >50 (used for oil pipes) is ≤0.1mm, and the positional tolerance of the hole system is ≤0.03mm to avoid increased fuel flow resistance caused by pipeline bending
• Surface: The roughness of the milled wall panel surface is Ra≤1.6μm, and the machining burrs must be removed (burr height ≤0.02mm) to prevent burrs from falling off and damaging other components under air flow scouring