GPS - AN INCOMPLETE JOURNEY

"Navigation system" for geometrical product specifications

19 March 2012: Gunter Effenberger

Due to the hard work of ISO-TC 213 “Dimensional and geometrical product specifications and verification”, a total of 33 (!) new or revised standards were adopted in 2010 and 2011. It seems like you will need a navigation system to find your way through the maze of standards in order to reach the standard applying to your individual situation. This article starts to give an overview and illustrates some major changes in geometric dimensioning and tolerancing. You have to face this topic against the background of different capability indices including specification limits available in manufacturing (creation of characteristics) and in quality inspections (conformity assessment). Product developers and design engineers are even more affected by the field of geometrical product specifications. They use these standards to evaluate whether component geometry meets all functional requirements correctly. With the help of the information the standards provide, they avoid the risk of misinterpretation and are able to assess parts independent of where they are manufactured or where quality evaluation takes place.

General overview

As the title of the new global standard ISO 8015 already indicates, it provides fundamental assumptions for the reading of specifications on drawings. 13 principles help to relate the concept of the GPS standard to a company’s individual drawings and define fundamental rules for the interpretation of drawings. Some examples are that dimensions and tolerances are valid at 20°C, each workpiece is rigid or the tolerances of single geometrical characteristics apply independently. The duality principle brings together the specification of functional requirements, also referred to as specification operators, and the definition of the measurement and thus evaluation of the function (verification operator). You have to be acquainted with this global standard in order to understand the concept of geometrical product specifications and their single elements...


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