What is Robust Design?

In today’s automotive industry where simulation and virtual prototyping are increasingly used to reduce time to market, the design process has changed considerably since Taguchi invented the quality planning concept [1]. He found that it is often more costly to control the causes of manufacturing variation than making a process insensitive to these variations. By using simple experimental designs and loss functions, he often succeeded in greatly improving product performance by “building in” quality, in other words, implementing the quality-by-design idea.

Robustness analysis aims at providing an accurate estimation of the sensitivity of outputs to the variability on the inputs, described in terms of random variables characterized with probabilistic distributions. In general, standard deviation is used as a measure for the robustness of the outputs: the smaller the output standard deviation, the more robust the output.

The core ideas Taguchi elaborated on are still valid, although in a different design context. Today, product designers increasingly experiment using computer models instead of physical prototypes. These experiments typically involved Monte Carlo simulation, although robustness is suitable as a criterion for evaluating discrete-event simulation systems as well. Using simulation instead of experimenting with physical prototypes yields system performance improvements and cost savings, only when design robustness is evaluated properly. As a robust design optimization software solution, Optimus incorporates the Taguchi method  for robust design to deliver designs that are more robust with respect to manufacturing and geometric tolerances. 

Six Sigma Design wheel

In reality, robust design is rarely applied. In particular in the automotive industry, where time to market and cost control are crucial competitive aspects, calls for design methods that integrate design quality and safety in the design process. This process should be based on simulation-driven robustness assessment techniques that trained engineers can leverage to gain a deeper insight into the influence of real-world conditions and uncertainties on the functional performance characteristics of a vehicle. This is extremely important for critical vehicle design aspects, such as dynamics and safety. In fact, vehicle dynamics impact all aspects of vehicle drivability and performance, ranging from fuel emissions to comfort and NVH and to ageing and durability, whereas safety aspects represents an extremely sensitive attribute, for which crash simulations serves as the most effective design and analysis tool.

 

Taguchi, G., Introduction to quality engineering, UNIPUB/Krauss International, White Plains, New York, 1986.