Abstract: The relationships of process dimensions of a part can be described with the conventional method of process dimension chains, but the information of process of the part, the machining sequences and the datum of the process dimension of the elements of the part can not be reflected, which is not helpful to the concurrent design of process route and dimensional tolerance. The element of the part in machining process is marked by English letters with subscripts, the directed line segment is represented the procedure size between the reference and the process elements, then the path diagrams of process dimensions can be obtained by depicting with the tree graphic according to the machining sequences of the procedure size. The relations of dimensions are simple, visualized, and integrated in the path diagrams, it is easy to establish the full correlation of model of dimensions, The theoretical basis on reasonable labeling of the dimension of the black can be supplied with the substantial feature of the rough datum which can be obtained from the path diagrams. The improvement of the process route can be achieved by changing the position or sequences of the elements in the path diagrams. The path diagram of process dimensions is proved to effective to the reasonable establishment of the process route with an instance by optimizing it to improve the process route.

Key words: model of dimension;optimization of process route;tolerance calculation;blank dimension benchmark