When moving into design development, you should have a feasible concept which can be developed into a product or a mechanism. This is where you might create an alpha prototype, where it should start to be made to look and work like the intended product. This will allow you to start thinking about soft tooling for example, injection moulding, vac casting or possibly CNC machined parts.

By this point, design changes should be for development and optimisation of the concept, rather than whole or significant conceptual changes. By applying and testing these smaller, incremental iterations, confidence in the design is built and progress in it’s development is more assured.

You could consider combining materials and manufacturing methods to build a prototype. For example, we are currently building 10 prototypes of a device. We had some of the external parts vac cast as we need clear components, with a high-quality look and feel. For some of the internal, functional parts we have used 3D printing, largely because elements of the design are still fluid so this will reduce development time. However, we are very aware that the material/mechanical properties of 3D printed components do not replicate those of our intended materials. Be aware that despite the best of modern prototyping techniques, that subtle design changes to suit the prototype process will usually be required to overcome inadequacies of 3D printed materials. It will then be necessary to make changes to suit the final production material. This is a particularly common requirement with clipped and flexible features.

The other benefit here is that prototypes can be physically tested to obtain data and user feedback to provide valuable insight. The prototype should appear, feel, and behave as closely as possible to the intended device otherwise, your feedback will be hindered. By presenting prototypes to users, it is possible to obtain crucial insight which allows for better design and development decisions to be made, and ultimately more user centred design solutions.

From here, you’re into beta prototypes and subsequently, design for volume manufacture – ideally, these should be components in production material and parts from real tooling. If not, you should be aware that prototype material properties will differ from production intent materials. At this stage, you would not typically use 3D printing to represent a part that is going to be injection moulded – it would not give a true reflection of the design or, final product. However, a 3D printed prototype of the final design is always a good idea and provides reassurance that there are no unforeseen clashes or issues that have crept in unexpectedly.

When prototyping, it is important to be aware of the process which you are intending to use and its limitations. If it is different from the production process, ask yourself what effect will it have on the part? If it’s too far removed, then it’s probably not worth making prototypes at this stage. You must really know why you are making them and what purpose it’s for – It’s then possible to design specifically to suit the manufacturing technique you will use to achieve the most from the prototypes created.

Some prototyping tips:

Take a look at prototyping during the initial design stages here.

Jack Dunkley CEng 19 February 2021

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Get in Touch with Jack Dunkley CEng

Lead Design Engineer

Jack is a chartered engineer who holds a Master’s degree in Mechanical Engineering from Cardiff University. He has experience working with design for injection moulding, machining and sheet metal as well as design for assembly and serviceability. Prior to HD, he worked at metrology company Renishaw for 6 years where he led several complex mechanical projects from initial concepts through to production. He has also worked at electrosurgical medical device manufacturer Olympus Surgical Technologies Europe (Gyrus ACMI).

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