When I need a flexible part how do I choose which process to use?

Your requirement will be unique to you and various factors will influence the decision including aesthetics, functionality, environment, porosity, hardness, and time.

Aesthetics 

Rapid Prototyping processes work in layers and usually in proprietary materials. Dressing layers out of a flexible part is not viable, thus if we are looking for a 'step free' part, possibly colour matched, our options are between silicone tooling and PU, or tooling and injection moulding. 

There is a large cost and lead-time difference between these solutions, so the decision usually depends upon the maturity of the design. Small runs of PU parts (say 1 – 40) can frequently be achieved in around 10 – 15 days. Injection moulding will take between 12 – 30 days depending on complexity. The properties of PU will not match those of injected grades like Santoprene, but it remains a very valuable prototyping option.

Functionality 

Clearly the ultimate is the injected moulded production material and this can sometimes be viable via a prototype tool – timescales permitting. Usually we are forced to compromise and this gives us two options: silicone tooling and PU parts or 3D printed parts.

Laser Sintered (SLS) materials such as Duraform Flex or TPE210S are available, but tend to be run infrequently. PU has the advantage that it can meet aesthetic requirements, whilst 3D Printing has the speed advantage. Properties such as elongation and hardness can be varied by selection of PU grade and material in the case of 3D Printing.

Environment 

If the part is to be exposed to specific fluids, this must be considered as some materials will dissolve and others soften. There are too many combinations to cover here so please contact Plunkett Associates for more information.

Porosity 

No problems have been recorded with 3D Printing, PU or moulded parts when processed correctly.

Hardness 

There is often uncertainty about the exact hardness required for an application during the prototyping stage. Therefore, processes that offer the ability to bridge the predicted hardness have an advantage. Silicone tooling and PU parts and 3D Printing can achieve this. PU is typically available from around 35 – 90 Shore A and 3D Printing from 27 Shore A upwards.

Time

The quickest solution is 3D Printing. Parts are produced directly in a flexible material, simultaneously in a range of hardnesses. Typical lead-times are 3 – 4 days. PU parts typically take 10-15 days.