Assembly Tolerance Analysis Including Flatness: Using Virtual Mating Plane

Fits of flat surfaces is one of the most popular ways for parts assembly. In order to take the flatness into account during the assembly tolerance analysis process, a virtual mating plane (VMP) is established. With micro-motion plane, a mathematical definition of the VMP using three various parameters to describe its characteristics is presented. Based on the VMP, the flatness could be decomposed into translation and rotation of the part to assemble in the following step under the reference coordinate system (RCS). The translation is defined by the flatness tolerance and the rotation by the flatness tolerance and the mating plane size. Then the global coordinate system (GCS) of the assembly is established, the rotation matrix (RM) is used to represent the parts' position. And a vectorial dimension chain is constructed to finish the assembly tolerance analysis. Finally, an aircraft wing sub-assembly is chosen to validate the methodology.