Optical CMM Gauge Capability Evaluation for Sub Millimeter Molded Features
Optical CMM capability on sub-millimeter molded features requires material-specific bias correction and telecentric backlighting to maintain GR&R under 20%.
Precision to Tolerance Ratio
Meaning
Quantitative standards measure the adequacy of a measurement system by comparing its inherent variability to the allowable engineering limits of a part. The precision to tolerance ratio indicates what percentage of the total error budget is consumed by the measurement tool itself.
Calculations Method
Calculation of this value involves dividing the six sigma width of the measurement variation by the total width of the specification. A low precision to tolerance ratio suggests that the measurement system is highly effective and adds little uncertainty to the inspection process. If this value exceeds ten percent, the system is generally considered borderline for critical quality control.
Meeting Standards
Acceptance of a measurement system in a production environment depends on meeting a specific target for this metric. When the precision to tolerance ratio is too high, it becomes impossible to tell if a part is truly out of spec or if the tool is simply giving a wrong reading. Manufacturers use this score to decide whether to invest in more accurate inspection hardware.
Constant Monitoring
Regular checks of the measurement system ensure that the equipment has not drifted or become damaged. Because the precision to tolerance ratio depends on the width of the part tolerance, a tool that is acceptable for one product might be completely inadequate for another. Continuous tracking of this ratio protects the integrity of the quality data.