A basic set of assembly tolerances is described, patterned after ANSI Y14.5 geometric feature controls, for specifying design requirements for a wide variety of applications. A complete computer-aided tolerancing system is described, which is tightly integrated with a commercial CAD system. Systematic modeling procedures and rules for creating vector assembly models are outlined. Vector assembly models are created graphically and analyzed for variation statistically in an interactive design environment. Closed vector loops describe the small kinematic adjustments that occur at assembly time.
Open loops describe critical clearances or other assembly features.
The DLM uses linearized assembly constraints and matrix algebra to estimate the variations of the assembly or kinematic variables, and to predict assembly rejects. A modified Monte Carlo simulation, employing an iterative technique for closed loop assemblies, was applied to the same problem set. The results of the comparison show that the DLM is accurate if the tolerances are relatively small compared to the nominal dimensions of the components, and the assembly functions are not highly nonlinear. Sample size is shown to have great influence on the accuracy of Monte Carlo simulation. When such feature variations occur on the mating surfaces between components of an assembly, they affect the variation of the completed assembly.