Assembly Tolerance Analysis Method Based on the Real Machine Model with Three Datum Planes Location

An assembly tolerance analysis method based on the real machine model is proposed, aiming to investigate the effect of the geometric errors of datum feature on the result of tolerance chain. The real parts are simulated by the variation of the geometric features, which are represented by the control point variation model and generated by the Monte Carlo simulation. The investigated objective is the assembly success rate of pin-hole assembly at the location with the three datum planes, the assembly clearance or interference is calculated according to the assembly requirements and assembly process. The part coordinate system in assembly is constructed firstly by the datum embodiment principles, then the position of the junction planes are determined according to the assembly requirements, and finally, the position of the parts relative to machine are determined by the coordinate transformation. The assembly success rate is represented by the probability distribution of clearance or interference between pin and hole, and the influences of the datum errors on the assembly result are discussed by the example assembly.