Shape measurement in sheet metal forming. Requirements and solutions

Basically, optical profilometry has a wide spread application potential in sheet metal forming starting at the design stage when models have to be digitized, followed by needs for shape aquisition in tooling technology, and finally in on-line testing during mass production. In particular, deep-drawing of car body components and surface structures of aircrafts put high demands on metrology. In the past, a number of restrictions caused application limits of optical 3d sensing in this field. The paper will show, that object size > 1 m, measuring time < 15, vertical resolution < 1/10.000 of object size and the capability to work on shining, oil-covered metallic surfaces are key criteria for industrial applications. New approaches are described addressing these practical needs. Based upon high brightness, high contrast pixel by pixel projection equipement (Digital Micromirror Device of Texas Instruments Inc.), algorithmus have been developed and tested that meet the objectives named above. Mutilevel adaption generates near- to- perfect sinnsoidal fringes across the field of view and advanced phase analysis improves both, measuring accuracy and reliability of operation. Fast data aquisition has been obtained by developement of sophisticated synchronisation hardware. An application example will be given showing surface structures on a large sheet metal part at two different scales of height.