General state of the art. Most companies overlook the uncertainty of coordinate measurement in their routine inspections of manufactured products: as evaluating the uncertainty is difficult and time-consuming in coordinate measurements, this is very often not done at all, or is very coarse. The consequence is that not only are the requirements of the EN ISO 14253-1 not fulfilled, but also the decisions made on the basis of inspections are unreliable. This is particularly dangerous for critical parts, whose functional failure may result in serious or even catastrophic failure of the overall product, e.g. an aircraft falling down because of a faulty turbine blade. The uncertainty of measurement is key in supporting reliable decision-making. Coordinate measurements suffer from the lack of recognised viable methods for evaluating the uncertainty. This has large economic impact on EU manufacturing because the lack of reliable information on part conformity may induce designers to over-specify tolerances to ensure product functionality, thus increasing the manufacturing cost unnecessarily. The prevailing guidance for users is given in the EN ISO 15530 series of standards. However as valuable as this guidance is to industry part 1, albeit very informative and tutorial, it is not intended to provide operative evaluation tools, and the methods described in Part 3 and Part 4 are often impossible to apply in practical cases. The EN ISO 14253-2 also provides guidance in uncertainty evaluation, but it addresses dimensional measurements at large with no focus on coordinate measurements: in fact, the tutorial examples given in Annexes A, B, C cover simple measurements compared with those done with coordinate measuring machines (CMMs). The EN ISO 14253-5 as well as its specialisations for CMM, ISO/TS 17865 and ISO/TS 23165, are about the uncertainty evaluation in the special case when an indicating measuring instrument, and a CMM in particular, is being tested. This is useful in acceptance and reverification testing of CMMs, but it is not useful for the intended CMM use, i.e. the inspections of parts.
Beyond the state of the art. The project will provide specific guidance on the evaluation of coordinate measurement uncertainty, in a form suitable for an intake in international standards. Specifically, it targets two missing Parts of the ISO 15530 series: Part 2 on a repetition and reversal method, and Part 5 on a method based on prior information and expert judgement. This aligns with the ISO/TC213/WG10’s original plan formulated when designing the ISO 15530 series: two Parts on similar subjects were conceived but abandoned for a lack of resources in that particular Working Group. In addition to that, these methods will be disseminated to industry by means of a set of industrial EUCoM seminars spread in 10 different countries. This will provide early impact, given that the average time to publish ISO/TC213/WG10 standards is on the scale of several years.
