Control gap analysis in an assembly system using remote laser welding

Dimensional variations of zinc coated sheet metal parts is a relevant problem in manufacturing process, especially during the joining operation with a Remote Laser Welding system. This issue requires a tight part-to-part gap control to ensure a good quality of final product. The remote laser technology needs of constricted tolerance limits in the gap between overlapped parts: in fact the lower tolerance is aimed to avoid porosity problem, caused by the zinc vapour escape during the welding, meanwhile the upper limit must be respected to obtain the metal fusion between parts. This work presents a methodology about the Selective Assembly, in which parts are previously selected and coupled, in order to reduce the gap problem. The proposed approach to evaluate the goodness of part-to-part joining is mainly based on a criterion to determine the easiness of parts' fitting. A Similarity Analysis is a valid solution to find the best predictor of a good joining. After a robust assessment about a set of indicators chosen for the analysis, the best one is applied to classify parts in different groups; the obtained clusters will be used for the selective assembly strategy. The research about the similarity analysis has been carried on in the International Digital Laboratory of Warwick University (UK). A typical sector affected by this matter is the Automotive: remote laser welding is deeply used in car components assembly line. A collaboration with Fiat-Comau and CRF (Centro Ricerche Fiat) allowed the real case treatment through a development of the complete approach on Cassino assembly line.