Tolerance & Time margin

Abstract This paper deals with production variabilities and their formalization: Geometrical variability that affects the product quality and Time variability that affects the productivity. Due to the manufacturing imperfections, the manufacturing system faults, the human factors, ... it is not possible to attain the theoretical dimensions and the theoretical time in a repetitive manner. This causes degradations of the product & production system performances. In order to ensure the desired behavior and the performance of the engineering system in spite of uncertainty, the system features are assigned a permissible tolerance or a margin. Time margin allocation consists in establishing a certain level of work flexibility, which gives the operator the possibility to develop different ways of working to meet production targets, without having adverse effects on his or her health. The concepts of geometric tolerance and time margin are very similar; they directly have an impact on the Overall Equipment Effectiveness (OEE): An OEE of 100% means that only good parts are produced (100% quality), at the maximum speed (100% performance), and without interruption (100% availability). The human or manufacturing system fatigue and reliability affect directly the respect of the time margin and indirectly the product conformance. There exists a strong link between tolerance and time margin.