Examining multiple alternatives during the styling activity is an example of set-based concurrent engineering. Toyota considers a broad range of alternatives and systematically narrows the sets to a final, often superior, choice.

Set-based concurrent engineering considers the different design perspectives proposed by different parties, a phenomenon that can best be graphically illustrated by Venn diagrams. Each party has some acceptable range of alternatives – a solution space that will work from its own perspective. Front-loading finds where the sets overlap and, in the process, identifies the winning design solution.

Toyota’s approach has essentially eliminated a great deal of waste while achieving a superior solution.

Toyota’s process does not focus on the speedy completion of individual component designs in isolation, but instead looks at how individual designs will interact within a system before the design is compete. In other words, they focus on system compatibility before individual design completion. The principle of compatibility before completion is fundamental to the set-based approach and is a major contributor (along with standard architecture and processes) to Toyota’s extremely low number of engineering changes.

To get at the root of “set-based thinking”, however, requires an understanding that it is more than a specific set of tools or methods. Companies can adapt structural aspects of this culture to their own PD by using the following:

1. Intentionally identifying multiple solutions to design problems before selecting just one.
2. Encouraging engineers (both upstream and downstream) to discuss alternatives early before a fixed decision has been reached on a single design from one perspective.
3. Using set-based tools such as trade-off curves to identify the trade-offs of various solutions from different perspectives.
4. Capturing past knowledge in checklists in the form of graphs and equations that show the effects of different alternatives.
5. Using system methods like parametric design that quickly show system impacts when parameters are changed.
6. Having structured time early in this front-end period for participants with diverse perspectives to work out solutions when the broadest set of alternatives is still available.

Source: Liker, J.K and Morgan, J.M, The Toyota Product Development System: Integrating People, Process and Technology, Productivity Press, 2006