Effects of process approaches and process parameters on assembly precision

In this thesis, a comparative study of different assembly processes and different process parameters is conducted to analyse their impact on assembly precision and dimensional variation of the final products. In particular, we are investigating how different mechanical alignment methodologies, part fixture locating layouts and part-to-part joining geometries affect the assembly precision in the presence of form and surface errors of the workpieces.; Due to the complexity and difficulty of building a multiple-station monitoring system for assembly processes, theoretical modelling is used for the study.; To date, relatively little attention has been paid to the design of alignment systems and how the parts should be located with respect to the mechanical alignment system in the assembly process. The effect of using various part surfaces as datums for making the parts and assembling the parts is investigated in this thesis. Our analysis shows that if the MAS is not properly selected, the form errors as well as surface waviness and roughness of the workpieces to be assembled can badly limit the level of accuracy achievable. Such cases are common, where fabrication operations are done on parts before they are assembled. The study shows that if the workpieces are aligned with the same orientation, using similar or identical MAS for the fabrication processes and assembly processes, then the effect of the form errors as well as surface waviness and roughness of the workpieces can be greatly suppressed. The precision level can be readily improved from hundreds of microns to several microns and there is almost a two-orders-of-magnitude difference in the assembly precision between the good assembly case and the bad assembly case.; Different types of part fixtures locating layouts and part-to-part joint geometries can significantly affect the assembly precision. In this thesis, we investigate the effects of three types of part-to-part joint geometries on assembly precision in the presence of part dimensional error, surface roughness and waviness. We confirm that fixture error, workpiece dimensional error, surface roughness and waviness can have significant effects on assembly precision. In addition, our analysis shows that the selection of joint and joining process can fairly affect the dimensional accuracy of part-against-part joints.; Industrial case studies of front rail and rear gate opening assemblies during the automotive body manufacturing process have been investigated. Some of the potential impacts of the typical assembly approach and error sources have been identified. (Abstract shortened by UMI.)...