MIM dimensional reports classify each dimension on the drawing into one of three categories. This classification determines how tightly it is controlled, how often it is inspected, and what CpK is required.
The three classifications:| Classification | Symbol | Definition | Inspection Frequency | CpK Requirement | Example |
|---|---|---|---|---|---|
| Critical | CC or ⚠️ | A dimension whose failure could cause safety issues or complete function loss | 100% inspection or CpK-based sampling (highest frequency) | ≥ 1.67 | Hole diameter for pressure seal, press-fit dimension |
| Significant | SC | A dimension whose failure would significantly affect fit, function, or assembly | Regular sampling (per control plan) | ≥ 1.33 | Mounting hole center-to-center, critical clearance |
| General | — | All other dimensions — minor impact on function | Minimal sampling; periodic audit | ≥ 1.00 | Overall length, non-critical radii |
- A typical MIM part drawing has 1-2 critical characteristics, 3-8 significant characteristics, and 10-30 general characteristics
- The cost of inspection is heavily weighted toward the critical characteristics (may require CMM or 100% vision inspection)
- Design engineers should carefully choose which dimensions are critical — designating too many dimensions as critical unnecessarily increases inspection cost without improving quality
| Column | What It Shows |
|---|---|
| Dimension # | References the drawing callout |
| Classification | CC, SC, or general |
| Nominal ± tolerance | The specification per drawing |
| Measured average | Average of all parts measured |
| Min / Max measured | Range of measurements |
| CpK | Process capability for this dimension |
| Pass/Fail | Conformance to specification |
A MIM dimensional report lists all measured dimensions on a part, classified as critical (CC), significant (SC), or general. Critical dimensions require CpK ≥ 1.67 and the highest inspection frequency. Significant dimensions require CpK ≥ 1.33. General dimensions require only CpK ≥ 1.00. The report shows the specification, measured values, range, and CpK for each dimension.