How Avicena re-invented the wheel

Award-winning WA company Avicena was quick to recognise the contribution 3D printing could make to the manufacture and ongoing operation of its ground-breaking Sentinel Biosecurity Platform, an accurate, rapid and scalable molecular diagnostic instrument capable of detecting diverse pathogens, including COVID-19.

In the company’s West Perth offices there is an alcove called the Print Room –but this is a print room with a difference. Alongside a traditional laser printer, busily churning out Avicena’s correspondence and documentation, are two Markforged 3D printers The smaller Mark Two printer has a footprint roughly the size of the laser printer. The second, an X7, is only slightly larger. markforged.com avicenasystems.com

Despite their diminutive size Avicena’s CEO, Tony Fitzgerald, says these two leading edge machines play a “small but significant” role in the company’s operations. More than 100 components of the Sentinel system were designed – and are now produced – inhouse on the two printers.

“In the early iterations of Sentinel, most small components were made of aluminium, and many were sourced as ready-made items. As we progressed, we redesigned many of the parts to improve functionality, and in many cases upgraded the materials we used to increase component strength,” said Fitzgerald.

“A good case in point is the small bearing wheels on the Sentinel instrument, about the size of a ten cent piece, which we bought ‘off the shelf’ and used by the hundreds. We found these wore relatively quickly, requiring regular maintenance and unwanted down-time.

To overcome this problem we literally ‘reinvented the wheel’, using a composite material including a percentage of carbon fibre, producing wheels that, after months in use, show no discernible signs of wear. “This is just one of the reasons we regard our 3D printers as an important part of our supply chain,” he said.

Wet blasting

The role of wet blasting in the post-processing of AM parts. Colin Spellacy, the Head of Sales at Rosler in the UK describes the processes which are taking place in the traditional manufacturing paradigm.

Additive manufacturing continues to disrupt the traditional manufacturing paradigm, and every day secures a more robust foothold as a production technology. The reason for this is driven by advances in build processes that promote increases in speed, accuracy, and repeatability of production, and therefore increased yield ratios.

As is now well-known and accepted, AM is important as it facilitates the creation of geometrically complex parts and components. AM reduces waste, and allows for the creation of lighter structures with an obvious importance in the automotive, aerospace, and medical sectors. AM also allows for the simple production of replacement parts impossible or uneconomical to replace using traditional processes, meaning that machines can be repaired not replaced. All such advantages along with AM’s ability to democratise and localise manufacturing with all that implies in terms of shortened and domestic supply chains means that as a technology, its future is assured.

AM and post processing

One area where significant issues reside in AM parts is in the surface finish as they come out of the build chamber or off the build plate. Whether plastic or metal, AM produced parts require primary postprocessing processes to remove powder or physical supports. But even then, AM parts are characterised by relatively poor look and feel, layer steps often being obvious, and surface roughness often being significantly high, which can affect aesthetics as well as functional performance. This means that in most instances, they require secondary post-processing to enhance surface form and finish.

With a significant part of the cost of a finished end-use AM part being the cost of post processing, the fight is on to develop efficient, repeatable, and automated AM post processing techniques. A number of mass finishing technologies are already used such as vibratory finishing, tumble finishing, and shot blasting, and shot peening and chemical smoothing technologies all maintain a foothold.

Wet blasting is a clean, reliable, repeatable, and accurate process which creates parts with a consistently superior surface finish than alternative processes, and which is ideal for parts made using direct metal laser sintering (DMLS) and selective laser sintering (SLS). Wet blasting is when water and abrasives media work together, and is particularly well suited for the finishing of delicate, precisionproduced parts. The process is characterised as being dust free, can use very fine abrasives, and uses very low volumes of abrasives due to the protective water layer. It also produces what is perhaps the most important AM post-processed part characteristic, superior surface finish.

Wet blasting typically sees a mix of between 10-40% abrasive media to water. The slurry is pumped to the blast gun and then accelerated to a high velocity using compressed air through a blast gun nozzle that is directed at the part. The blast media impact on the work piece creates the desired effect, be that cleaning, surface smoothing, coating preparation, cosmetic surface texturing, or peening.

Advantages of wet blasting

Wet blasting has benefits for the characteristics of the work piece itself, but also for the processing environment. The over-riding advantage is its gentleness, but also the process produces no dust, which prevents electro-static issues and therefore removes the need to consider regulations concerning explosive atmospheres. There is also no media impingement using wet blasting, an ever present problem with dry blasting where media particles can embed in the work piece surface compromising surface integrity. solutions-for-am.com

Dry blasting generates significant heat during post processing which when combined with high impact energy of the media on the work piece can lead to warping and bending of delicate parts. Wet blasting by contrast is a cooler gentler process that immediately washes away anything that is adhering to the work piece.

In terms of surface finish, wet blasting promotes smoother finishes while being more precise, consistent, and repeatable. Finishes are fine and uniform, with low surface roughness of 100µm Ra being easily attainable.

When looked at through the prism of exacting tolerance attainment, superior surface finish, applicability to delicate and geometrically complex parts, and repeatability, wet blasting is a compelling technology for the post-processing of AM parts and components while remaining adaptable and cost effective.