We still do MD internal validation every year, including external calibration/verification and daily monitoring every hour during production. If the MD breaks down and requires external services, MD validation is carried out right after the repair before use in production.
Our MD validation is done by the following:
1. Passing all test pieces (we have 2, 2.5 & 3mm) multiple times on the MD in different locations (left, right, centre), ensuring that each pass of test piece is rejected
2. Passing different finished products we produced (w/ different sizes, w/ diff components) multiple times with the test pieces on multiple locations (left, centre, right), ensuring that each pass of finished products with test piece is rejected
3. Passing different metal objects (rejected by MD throughout the years) on the different finished products, placing on varying locations in the product (top, bottom, left, right), ensuring that each metal object is rejected.
Ours maybe a bit excessive, but this works for us and every auditor have accepted this MD validation without question.