Dimensional metrology and CAD - Normative language and models

The era of industrialization coincides with the emergence of quality. Products have to meet various cost and quality requirements in order to be competitive. In the aeronautics industry, for example, airplanes have to meet stringent specifications before they can be marketed and flown. The emergence of quality is precisely linked to these certifications, which are synonymous with compatibility with standards. Standardization is a fundamental tool. It enables specification rules to be defined and generalized. The ISO 9000 family of standards is the best-known in the industrial sector for integrating quality assurance policies. It ensures the efficiency and, above all, the traceability of information between different stages in a product's life cycle. Quality assurance applies to all the physical quantities surrounding an element (dimensions, temperature, pressure, etc.). We are interested here in the study of geometric characteristics, also known as dimensional physical quantities, and their dimensional metrology.

The geometry of parts encompasses several aspects: the definition of surfaces, the relative position of surfaces for the constitution of parts, the tolerancing of parts and then their assembly, as well as the dimensional metrology of physical parts by verifying their conformity with the theoretical toleranced part.

In a very short space of time, geometric definition has moved away from the stage of the "épure" and towards the culture and definition of the digital, through two-dimensional and then three-dimensional geometric models in the world of computer-aided design (CAD). This acceleration of events necessitated profound changes in know-how. Sketches were made on paper, and CAD geometric models forced users to manipulate digital tools.

Computerized systems have made it possible to evolve in the field of quality. Nominal geometry is produced by design-aid tools, increasingly in line with the specifications defined in tolerancing standards. Today, however, a digital definition of geometry still coexists with a "paper definition" of tolerancing specifications. Tolerancing or (functional) dimensioning too systematically leads to the drawing of part definitions, which to this day, despite all the possibilities offered by CAD/CAM (computer-aided design and manufacturing), remains the most widely used means of technological communication between the different players in the company. Underlying the concept of tolerance is the notion of quality. Tolerances determine the permitted variations in the material. These conditions guarantee the assembly of physical parts.

The concept of quality is present throughout a product's life cycle. Its objective is to guarantee optimization of this cycle, through correctly defined...