GR&R: Consistent Noncontact Inspection

Quantitative/qualitative profile analysis for GR&RFor years, optical comparators coupled with overlays have been an accepted inspection method for products produced in the medical industry. However, in today’s tighter tolerance environment, especially the inspection of profiles, this method is no longer viable. Gage repeatability and reproducibility (GR&R) testing has proven that operator variability/subjectivity can be greater than the entire tolerance allowed. Essentially, the problem occurs with the overlay charts, not the use of the comparator.

Forgoing Go/No-Go
At best, overlays give a basic Go/No-Go result. Coupled with other overlay-associated problems, such as traceability, storage and calibration, the industry is searching for newer restriction-free methods with many advantages to improve product quality and increase manufacturing throughput.

With overlays, operator subjectivity is a significant factor. There are fine nuances to contend with, such as on-screen placement, imprecise mylars, magnification, complex part shapes, and especially, the lack of detailed, variable data. Such issues force an inspector into the realm of judgment, which varies from operator to operator. Fatigue and data accuracy also come into play.

Functional fit gages also present their share of challenges. The gage development process is usually lengthy and expensive, with limited flexibility when parts change – and again, no variable data is attainable.

GR&R
Ultimately, the goal in any inspection program should be to attain acceptable GR&R, and in the process, provide comprehensive, documentable data for statistical process control (SPC) and traceability.

Reliable GR&R is 100% possible with today’s non-contact video and multisensor systems and their advanced software. Current QC readout and measuring technology software provides full qualitative/quantitative profile analysis functions where an inspector can compare a part profile against a nominal CAD model and obtain an actual graphic representation of any deviation from the CAD file.

The system automatically finds and tracks the edge, continuously comparing it to a profile or measured geometric features, and superimposes them on to a CAD model. An operator quickly, easily and automatically collects tremendous amounts of data that are all archived and documented with date, time, lot number, job number and so on, removing operator error from the equation. In addition to realizing 100% inspection, inspection speed and throughput dramatically increases due to automated measurement routines, and depending on the application, palletized multi-fixture inspection tables. Indeed, today’s technology offers far more than error-prone conventional methods.

The L.S. Starrett Co.
Athol, MA
starrett.com