Making Design Validation Effective

Mar 01, 2005

The purpose of design validation is to demonstrate that a product performs as intended. The usual route to this goal is showing that every item on the specification has been achieved, but it is not an easy path. The specification itself can create difficulty if it includes statements like "as long as possible" or the real horror "to be decided." Verification tests can reveal so many problems that the design must change to such an extent that earlier tests are no longer relevant. And there is also the practical difficulty of obtaining sufficient samples to test when the manufacturing engineers have not completed their standard operating procedures, the product design is not fixed yet, the component suppliers are late, and the marketing department has taken all the samples to show to prospective customers.

Design validation is not just a test tacked on to the end of development. It is most successful when it is an integral part of an effective design and development process. Thorough design validation combines effective testing with a well planned development strategy. As with other types of validation, design validation is associated with jargon and technical terms that have different meanings for different people. This introduction explores general principles that must be adapted to the needs of a company, product, or team.

Product Specification The product specification is the foundation of design validation. It is vital that it is clear and well-structured since the validation must show that everything it contains has been achieved. A hierarchical, top-down specification that begins with the needs of the users and ends with process tolerances is recommended.

Benefits to the user. The specification should contain a statement that the product delivers the right amount of drug in the right form to the right place. It also often includes statements about ease of use, environmental conditions, labeling, and cleaning. The critical issue is quantifying these statements; otherwise it is not possible to validate them. For example, "easy to use" is no help at all. Strict validation requires that customers (or at least representative people) attempt to use the product and their success and opinions are documented.

Table 1. Design Validation and the Development Process
Performance. Product performance specifications begin to convert the user needs into engineering values. For example, specifications for a self-injection device would include the depth of penetration of a needle, the toughness and hardness of the skin, and the delivery time for the drug.

Reliability. Reliability is a huge topic in its own right and a difficult one. A product that is used over a long period will have an expected lifetime, a failure rate during use, and a failure proportion for early-life defects. A one-shot device is characterized by a success probability after a given storage time. Environmental conditions for use, storage, and transport affect reliability. Some products can use the "Martini specification" — any time, any place, any where.

4. How it works. This part of the specification describes the product's specific characteristics and defines the engineering parameters that ensure the product meets its performance specification. During the design and development process, this part of the specification grows to include details of critical components, dimensional tolerances, and process conditions.

The Design Validation Process Prevention of problems. Failure modes and effects analysis (FMEA) is a standard tool for risk assessment. It should be used early in the development process at the system level to try to foresee problems such as those a user might experience.

FMEA should also be used during development to anticipate design errors that could have serious consequences but which are unlikely to be discovered before manufacture commences. Critical factors could be the choice of plastic for a component, corrosion resistance of a spring, or estimates of mechanical loads on a specific part.

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