Section 44 of 50
38. Tolerance Allocation and Stack-Up Management
Stable section ID: S05-CON-012-SECTION-44 · 34 content blocks
System05 tolerances shall be allocated according to functional need, process capability, measurement capability, assembly behavior, and lifecycle variation.
Tolerance analysis shall address:
- Individual feature variation.
- Interface fit.
- multi-part stack-up.
- angular error.
- datum shift.
- coating thickness.
- thermal movement.
- moisture movement.
- elastic deformation.
- wear.
- installation adjustment.
Worst-case, statistical, or simulation-based methods may be used according to consequence and production knowledge.
Tolerance allocation shall distinguish:
- Manufacturing tolerance.
- assembly tolerance.
- inspection tolerance.
- functional tolerance.
- lifecycle tolerance.
- digital representation tolerance.
Tolerances shall not be tightened merely to resolve uncertainty in the design. Functional requirements shall first be clarified.
Where tolerance accumulation threatens assembly, the design should use:
- Self-alignment.
- adjustment.
- compliance.
- replaceable shims.
- controlled clearances.
- matched components.
- alternative datum strategies.
- Adjustment features shall have defined range, locking, inspection, and recording requirements.
Interface tolerance classes may support different production capabilities, but mating compatibility shall remain explicit.
Measurement uncertainty shall be included near acceptance limits. The acceptance rule shall identify how uncertainty affects conformity decisions.
Changes to a tolerance shall trigger evaluation of tooling, process capability, inspection, interchangeability, certification, and installed performance.