August 10, 2022

Misconceptions between design and mass production

Thomas Milnes, Industrial Design Consultancy Limited, highlights several misconceptions related to inspection processes when developing medical devices.

To meet the demand for high standards and fast time to market in medical device development, it is necessary to ensure that development methods are optimized. Leveraging inspection processes during the development phase can ensure a smooth transition from design to production.

1. The more inspection, the better the components

It may seem logical to designers that including a more detailed component specification will lead to more thorough verification, but taking this approach can lead to undesirable drawbacks:

Increased inspection time – The more dimensions/inspection points specified on the engineering drawings, the longer the parts will take to inspect. Since some components may 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, initial component samples may not be completely accurate in all areas.

Prioritization of the specifications – If the specification is too extensive for each component, manufacturers may not know which areas to focus on. Even if critical dimensions are specified, the quantity can cloud the importance, meaning that aspects of the specification can be overlooked.

2. Expanding Component Tolerances and Specifications Will Reduce Project Costs

Designers sometimes focus on loosening tolerances and reducing testing to try to speed up development and save money. There are a few things to consider before expanding part specs:

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

Tolerance report – If tolerances are loosened without considering the intended function of the device, the risk of device failure may increase. Tolerance stack-up calculations should help determine what can be loosened.

Manufacturing Capabilities – The liaison with the manufacturer could determine where the tolerances can influence the cost.

Hardware Capabilities – For molding processes, the material itself may limit tolerance capabilities. Raw material suppliers are generally aware of the limitations of their materials and may have alternatives available.

Ultimately, setting component parameters well at the start should mean less component and specification changes, this can directly improve overall product quality, reduce project cost, and ensure the project is delivered on time.

3. Inspection is self-sufficient, no need to test

There are a multitude of potential test methods for many scenarios, and it should be assessed whether there is a reason to test a device or individual components early in development. If inspection is the only method of analyzing samples during development, some things might be missing:

Invisible imperfections – Components may have imperceptible imperfections that influence their properties, such as contamination, influences from preconditioning, moisture absorption, etc.

Complex interactions – Inspection can be an essential tool in examining components, and engineering calculation combined with materials research can help designers understand the interactions between parts. However, testing real part interactions could highlight any potential interaction issues.

Complex properties – Plastics and their properties do not always translate easily into theory, these questions should be addressed by aging studies but may not be by theoretical approaches.

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

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