Design iteration

Design iteration is a cycle in which an existing design is reviewed, tested or evaluated and then modified based on what was learned. The process repeats until the design meets all requirements or until an acceptable trade-off is reached.

In product development, iteration is both unavoidable and desirable. The first version of a design is only a hypothesis that has to be proven in practice. Each iteration brings new information: what works, what does not and what the customer actually needs. That is why agile and lean development approaches put iteration at the center of the development process.

Rapid prototyping has dramatically shortened iteration cycles. A single iteration used to take weeks or months, because fixtures or tooling had to be made first. Today, 3D printing typically delivers a first physical prototype within 1 to 3 days of finishing the CAD model. Many fast iterations usually teach you more than a few slow ones.

The key to effective iteration is a clear definition of what each iteration tests and which decisions it will enable. Prototyping "just to be safe" without a clear test plan is waste. Every prototype should answer a specific question or test a specific hypothesis.

An iterative approach fits wherever the requirements cannot be fully described or calculated in advance: the ergonomics of handheld products, mechanisms with latches and springs, parts with cosmetic requirements, products tested by users, or designs whose behavior in real-world use is uncertain.

It usually starts with rough, inexpensive models that prove the concept, continues with functional prototypes and ends with pre-production samples made with a process close to the one used in series production.

Iteration without a goal leads to endless development. Before each round, define what is being tested, what the success criteria are and who decides on the result. Document the changes between iterations (revision number, reason for the change, test result); otherwise, after a few rounds nobody remembers why the part is designed the way it is.

Another risk is iterating for too long on a process that will not be used in production. Properties fine-tuned on a 3D-printed part can change once you switch to injection molding. Plan for at least one iteration made with the production process, or with one close to it.