Theory On The Shortest Path Tree Of Dimension In Mechanical Manufacturing Process And Its Application

Dimension references,dimensions and tolerances are correlated with each other and are existed in mechanical design and manufacture process,whether rationality of dimension references and dimensions and tolerances of parts directly affect the quality and cost of products.Studies on the properties of reference and influences on tolerance in each step of design and manufacture are essential to scientifically determine dimensions and tolerances in design and manufacture process.The corresponding functional dimensions in machine assembly and parts machining and blank produce have respective formative paths,while difference of path will directly affect the precision and cost of functional dimension.The formative paths of all kinds of dimensions based on graph theory are studied,related rules of all kinds of dimensions,obtains the shortest path tree of dimensions are established,rational dimension references and dimension paths from the shortest path of dimensions are extracted,and dimension model for rational design of dimensions and tolerances are provided in this paper.Several following studies have been carried out.(1)Study on dimensioning mode of partsAccording to the relationship between the structure of assembly and parts in the assembly,the relationships between the formative path of the functional dimension and dimensions and references of parts are established.By starting the requirement of assembly functions,taking the shortest formative path of functional dimension as target,and based on the problem of the shortest path,the shortest spanning tree of functional dimensions is obtained,which determines the rational dimensioning mode of parts in assembly.(2)Establishment and solution of dimension modelsRelationships between functional dimensions and all design dimensions of parts in assembly are contained in the shortest spanning tree of functional dimension,sometimes dimension models of functional dimensions and all design dimensions of parts can be established and dimensions and tolerances of parts can be solved by the shortest spanning tree of functional dimension.(3)Study on optimizing of processing technologyAccording to study on machining processing technology of parts,tree graph is introduced to express machining reference,machining sequence and process dimensions of parts in machining process,and the process dimension tree of parts can be established.Based on process dimension tree,study is carried on optimizing of processing technology of parts.(4)Establishment of process dimension models and solution of dimensions and tolerancesAccording to study on process dimension tree,relationships between dimensions of parts,process allowance and process dimension are contained in the process dimension tree.Based on the process dimension tree,dimension models between all dimensions of parts and process allowances and process dimensions are established,and process dimensions and tolerances can be solved.(5)Study on blank dimensioning referenceBased on process dimension tree of parts,influences of rough reference of parts in machining process on tolerance of blank dimension allowances and machining precisions of parts are explored;especially plane blank dimension reference is conducted in-depth study and general selection principle of blank dimension reference is established.The study in this paper provided a new approach on dimension references,dimensions and tolerances in mechanical manufacture process,which has strong theoretical value and engineering value for research on precisions of mechanical manufacturing.