Sculptured surface tolerance verification with design datums

Sculptured or free-form surfaces are widely used in many fields with extensive applications. Once such surfaces are manufactured, surface inspection compares the manufactured surfaces with the surface design specifications to verify conformance. Although significant research and development efforts have been devoted to the design and manufacturing of products consisting of partial or sole free-form surfaces, the inspection of these surfaces is still a difficult task. For many engineering applications, a free-form surface is assigned a profile tolerance with reference to design datums for assembly, functionality and other manufacturing requirements. The paper discusses developments of surface inspection techniques for profile tolerance of free-form surfaces. The concept of datum direction frame is proposed to find the transformation information that localizes measurement data to design model. The technique consists of two major steps: localization of measurement data to the design system, based on the datum reference information; and further localization based on the information from free-form surfaces. Testing examples were carried out to validate the developed techniques. The new method does not need corresponding points from the datums of the design model and measured surfaces. Therefore, it is simpler, yet more robust. It can also be used conveniently in manufacturing processes.