Hit print: The benefits and restrictions of 3D printing

Ian Matthew, Owen Mumford 3D Printing, explains how to harness the benefits and identify the restrictions of this technology.

According to a new market research report, published by Credence Research, the global 3D printing in healthcare market is estimated to expand at a CAGR of 17.5% from 2016 to 2023. But does the 3D printer present those designing and manufacturing medical devices with any restrictions?

The rise in healthcare IT solutions is the most significant factor spreading the adoption of 3D printing technology in the medical sector.

At Owen Mumford, we’ve harnessed 3D printing as a valuable tool for early design developments. It contributes to proving a design principle and assessing part assembly and geometry for new devices. 3D printing allows us to improve our understanding of a concept and inform early development decisions, as well as highlight fundamental problems that can be quickly rectified.

However, it’s important to understand the output required when producing a prototype, as this will affect the 3D method chosen or justify a decision to use a different prototyping method entirely. This means firstly understanding what the restrictions are, and then developing methods to overcome them. 

There are multiple 3D printing techniques that can be deployed for different requirements, including:

• Fused Deposition Modelling (FDM) - an additive manufacturing technology commonly used for modelling, prototyping and production applications.

• Stereolithography (SLA) printing - a technique or process to create aesthetic prototypes to present to customers and exhibit at trade shows.

• Polyjet - used for iterative designs, this is the predominant medium of 3D prototyping. Due to the brittle nature of polyjet, this technique can’t be used for any loading or creep testing.  

Alongside these forms of 3D printing there’s another set of techniques, which are required to create more production representative parts:

• Injection moulding – we’ve developed a dedicated bolster set which uses 3D printed inserts, positioned correctly into an injection moulding machine. This technique enables a developmental injection moulding process to be used, across different plastics and grades of material, making the entire prototyping process more efficient and accurate.

• Soft tooling – we use an external company to provide soft tooling options for injection moulding parts at much higher volumes. These are particularly beneficial for early usability studies and functional testing in which we need a representative manufacturing process, along with higher volumes compared to rapid prototyping. 

While our 3D printing machines are extremely relevant, there are still some restrictions to consider, including:

• Structural integrity of printed parts – the layered printing process causes structural weakness, resulting in failures that don’t occur in moulded parts.

• Mechanism functionality - the material chosen impacts the surface finish and the resulting friction, directly impacting on the mechanical functionality of the design.  

The limited range of materials available from 3D printing doesn’t allow detailed incremental design changes, which can be the difference between a working and non-working design.

• Wear of material over time restricts intensity of testing – a substantial amount of testing is required to ensure the product is capable of achieving its life requirements. It’s often the case that printed parts will cause a failure, which would not be seen with a moulded part.

• Dimensional accuracy – the process of making a part, its geometry and its material are the main factors affecting dimensional accuracy.

These factors all contribute to the capability of the manufacturing process, which is critical to understand when defining dimensional tolerances. Components must be designed to function throughout the entire tolerance range; the range achieved by a 3D printed part will not reflect the moulded tolerance.

• Response under impact loading – impact testing is limited with 3D parts. These parts can demonstrate an area of weakness due to geometry. Any further resolution of performance under loading requires representative material and manufacturing processes.

We’re striving to use more materials in our production environment, including engineering grade polymers to further develop devices and comply with updated regulations. 3D printing allows the use of generic materials groups (such as ABS) but to optimise designs we require specific grades of material groups. Material properties of different grades can have a significant effect on the performance of a part or assembly. This level of resolution and adjustment is not possible with rapid prototype techniques.

As we continue to see more technological advancements in the way in which we design and manufacture medical devices, we’re able to assess more concepts at a much lower cost - meaning we can continue to be truly innovative at a much lower risk. Companies must continue to keep abreast of design to manufacturing - and allow themselves to harness the benefits of 3D printing.