Redesign of an Exhaust Manifold Outlet Fastener Using Robust Design Techniques

An L₁₆ orthogonal array parameter Design of Experiment (DOE) evaluated six design parameters of the mating thread interface between the exhaust manifold outlet flange and jointing stainless steel fastener. The objective of this study was to identify optimal parameters for the redesign the thread interface by ensuring 100% seating of the fastener into the manifold flange (here after referred to as stud seating). Since the current fastener and manifold outlet flange interface threads do not always achieve the design objectives, due in part to a form of abrasive wear, consideration was given to develop a testing strategy that would quantify the amount of remaining thread engagement for a given stud length. This testing strategy ensured that the control parameters considered in this experiment would reveal main effects and interactions between the stud and tapped hole threads thus providing the necessary parameters for the redesign on the joint threads. It will be shown that significant interaction between stud out-of-round and fastener coating lead to improved stud performance when used with certain manifold materials while other thread features and fastener coating lead to other results. The previously mentioned findings provided the necessary information to the redesign of the manifold outlet flange and joining fastener threads.