Misconceptions between design and mass production

Thomas Milnes, Industrial Design Consultancy Limited, highlights several misconceptions related to inspection processes during medical device development.

To keep up with the demand of high standards and fast time to market in medical device development, it is necessary to ensure development methods are optimized. Harnessing inspection processes during the development phase can ensure a smooth transition between design and production.

1. The more inspection, the better the components will be

It may seem logical to designers that including a more detailed component specification will lead to more thoroughly checked but taking this approach can lead to unwanted drawbacks:

Increased inspection time – The more dimensions / inspection points specified on the technical drawings, the longer the parts will take to inspect. Given some components can go through many samples before finalization, removing unwanted inspections should reduce development time.

Specification changes – Due to the complexity of production manufacturing processes and plastic materials, it may be that initial component samples are not completely accurate in all areas.

Prioritization of the specification – If the specification is over-extensive for each component, the manufacturers may not know which areas to prioritize. Even if critical dimensions are specified, the quantity can blur the importance, which means that aspects of the specification may get overlooked.

2. Widening tolerances and component specifications will reduce project costs

Designers will sometimes focus on loosening tolerances and reducing testing to try and speed up development and save money. Certain things should be considered before widening part specifications:

Design constraints – Considering the design inputs will set constraints for the design such as size and weight, when all these constraints are laid out, defining the individual component specifications should be easier. If defined correctly, there will be less chance that these specifications will need revisiting later.

Stack-up tolerance – If tolerances are loosened without consideration of the device’s intended function, the risk of device failures may increase. Tolerance stack-up calculations should help determine which can be loosened.

Manufacturing capabilities – Liaising with the manufacturer could determine where the tolerances can influence cost.

Material capabilities – For molding processes, the material itself can limit tolerance capabilities. Raw material suppliers are generally aware of the limitations of their materials, and they may have alternates available.

Ultimately, defining the component parameters well initially, should mean less component and specification modifications, this can directly improve overall product quality, reduce project cost and ensure the project is delivered on time.

3. Inspection is sufficient on its own, there is no need to test

There is a wealth of potential testing methods for many scenarios, and it should be evaluated whether there is a reason to test a device or individual components during early development. If inspection is the sole method of sample analysis during development, certain elements could be missed:

Unseen imperfections – Components may have imperceptible imperfections which influence their properties, such as contamination, pre-conditioning influences, moisture absorption etc.

Complex interactions – Inspection can be a vital tool in reviewing components, and engineering calculation combined with material research can help designers understand the interactions between parts. However, testing real part interactions could highlight any potential issues with interactions.

Complex properties – Plastics and their properties do not always easily translate to theory, these issues should be picked up by aging studies but may not be picked up by theoretical approaches.

Inexperienced medical device designers can rely too much on theory; inspection can provide information where testing does not, and vice versa, so using both inspection and testing methods helps give the device the best chance of moving quickly through the development phase.

Inspection can be an extremely useful tool to ensure successful development of medical devices when used correctly. Ensuring component specifications are realistically defined and with justification, and at the same time understanding the limitations to inspection, should translate into more successful projects.


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