An artefact for traceable freeform measurements on coordinate measuring machines

The present paper describes an artefact based approach to obtain traceability of freeform measurements on coordinate measuring machines. First, the requirements for the traceability of freeform measurements and a strategy for the development of a feasible solution are presented. A new concept of artefact, called the "Modular Freeform Gauge" (MFG) has been developed. It is based on physical modeling of a given freeform surface by a combination of items with regular geometry, well calibrated on their dimensions and form. The relative position is accounted for during the procedure. this information is used to generate a "calibrated" CAD model as reference for freeform measurements. The architecture of the artefact. its collocation in the traceability chain, and the calibration procedure are described. Finally. a procedure for the uncertainty assessment of actual freeform measurements is presented. The work here described has been focused on implementation of the uncertainty assessment procedure for freeform measurements on turbine blades. A task-specific Modular Freeform Gauge was developed for this application.