Robust Design of a Light Weight Flush Mount Roof Rack 2011-01-1274

Roof racks are designed for carrying luggage during customers' travels. These rails need to be strong enough to be able to carry the luggage weight as well as be able to withstand aerodynamic loads that are generated when the vehicle is travelling at high speeds on highways. Traditionally, roof rail gage thickness is increased to account for these load cases (since these are manufactured by extrusion), but doing so leads to increased mass which adversely affects fuel efficiency.

The current study focuses on providing the guidelines for strategically placing lightening holes and optimizing gage thickness so that the final design is robust to noise parameters and saves the most mass without adversely impacting wind noise performance while minimizing stress. The project applied Design for Six Sigma (DFSS) techniques to optimize roof rail parameters in order to improve the load carrying capacity while minimizing mass.

The analysis model consisted of a finite element model of a roof rack system. The numerical simulation runs were made on LS-Dyna software. Taguchi's orthogonal array was used to build factorial response plots for signal to noise ratio and main effects. Load carrying capacity and mass were considered as two primary responses and the optimum design was determined by maximizing load capacity while minimizing mass. Some of the important parameters being considered were part thickness, material selection, hole size, hole spacing, hole to attachment interface, and crossbar location. Based on response plots, these parameters were rank ordered for best performance. The results provided guidelines and enormous benefits to engineers for designing light weight flush mounted roof racks in current and future vehicles.