Scaling up to meet the PPE challenge
Additive Manufacturing vs Injection Molding

Paul Holt, Managing Director of Photocentric, explains how the inventor of LCD 3D printing was able to print 1 million parts a month and then compare the process to moulding in mass manufacture volumes.

3D Printing Face Shields

As the Covid crisis took hold of the UK in the Spring of 2020, there was a massive shortage of PPE, exacerbated by a combination of restrictions of exports from China and increased domestic demand. 3D printing using FDM (Fused Deposition Modelling) printers arose as an immediate actionable solution, and companies such as Prusa[1] released open-source designs to be created with the technology. In the UK, a Slack group of hundreds of users combined their FDM printers and managed to make a maximum of 500 a day. Face shields were being assembled in homes, it was uncontrolled and unscalable. Crowd printing PPE like this would subsequently be banned by the Government.

In response to demand, Photocentric decided to design a scalable face shield to provide in large volume, aiming to deliver value, manufacturing consistency and optimal performance for those on the frontline during the pandemic. At the same time, we also ran a parallel process of laying down tooling to create a real-time comparison between an identical part made by Additive Manufacturing and Injection Molding. This enabled us to examine the difference in performance, time to market and cost between the two manufacturing technologies in scaled up quantities.

[2] Guidance for new high volume manufacturers of COVID-19 Personal Protective Equipment
[3] BS EN 166:2002

The Design for Additive process

On the 25th March 2020, Ed Barlow, one of our 3D Engineers, designed our first face shield in CAD. He printed it, attached a laser cut polyester sheet to it and a strip of rubber to tension on his head. He was wearing our first face shield, only a few hours after designing it. We had started our road to product optimisation.

Figure 1: Design iterations of the face shields separator chronologically from top left to bottom right

Using our LC Magna printer harnessing LCD light, we were able to position 110 of the face shield separators (the part that keeps the plastic visor away from the face) on the platform of the printer. This was in contrast to only four of the FDM’s design, speeding up production. We wore our shields around the office and started to optimise their performance from personal experience, looking at comfort and curvature of the shield around the sides of the face. We obtained medical feedback, made improvements, and met the newly issued Government PPE standard under derogation[1]. We would subsequently get the product approved to the full eye protection standard[2].

The design for additive (DFA) process aims to achieve optimised user performance and optimised print performance with minimum material used, and this became our goal. Open structures were initially designed, as they used less material and were still structurally rigid. This open structure facilitated very fast printing. However, there was a conflict with product performance, as the shield was then open to droplets falling in front of the face, so the holes were closed off in the design.

The relative movement in the part’s centre of gravity (COG) throughout the print was also assessed. By orientating the part at different angles and adjusting its shape, we could maintain the COG in each layer in the same vertical line. This prevented the part from undergoing sideways (x:y plane) forces during the print, eliminating the need for external 3D print supports and significantly reducing causes of print failure.

Figure 2: Design iterations of the face shields separator chronologically from top left to bottom right

The first layers of the print that attached the separators to the platform were designed to snap off cleanly, leaving a completely clean platform with no residual artefacts. Removing non-functional supports significantly increased our process efficiency. This base support was repurposed as a clip retaining the PET shield to become a functional aspect of the design. it was then mirrored on the other side of the design at the top of the print.

We were able to increase the number of parts per platform even more by rotating them 90°. We ended up with 210 on each platform, and each one was made in less than a minute.  This compared to the original FDM print time of 8 hours, and our original LC Magna print time of 20 minutes – a two orders of magnitude improvement delivered by DFA. We had managed to achieve two things: invent a high-quality product and make its production scalable. In the first two months, we worked hard to create 200,000 of them with a lot of manual intervention, but in the following month we made 1 million face shields in a production environment.

Scaling up the production floor

We cleared out a warehouse in our building in Peterborough and installed power, lighting, drainage, extraction, water and benches. We designed packing systems, Standard Operating Procedures and post-processing machines and constructed the 45 Photocentric LC Magna printers to fill the space. Designs for the floor layout were conceived in CAD to flow product from liquid resin with 1 tonne IBCs of resin delivered from the vessel room next door to the printers, creating parts that travelled through washing, post processing, QC and into face shield assembly and dispatch.

Additive Manufacturing compared to Injection Molding

When compared to injection moulding, we found that the most significant gain that the LCD printing process provided over moulding, was time, enabling us to fulfil a market need in a matter of a handful of days. Time to market has huge value to any business but proved critical when supplying PPE in a pandemic.

Performance of both parts in the face shield was identical. Both processes (AM and IM) required modifications from the initial design to optimise them for their respective manufacturing processes. The greatest factor affecting the cost of the printed part is material cost, and this remains the main battle that must be overcome for additive manufacturing projects of this nature. The reduction in material prices will continue to unlock more widespread and innovative volume applications as an alternative to injection moulding.

To run 1 million parts a month by printing took just 10 days, in comparison the time to run it with injection moulding took 156 days. Tooling costs of £83,000 were amortised over the order quantity and added to the molded unit cost of 6p, this compares to the total printed cost of 36p. The cost-break-even-point in parts in moulding compared to printing was 320,000 units.

This project demonstrated that additive manufacturing can be used effectively beyond prototyping to deliver mass manufacturing applications at scale and speed.