Sealing the deal on AM parts

11 Dec 2018

Engineering capacity news posted by Andy Sandford

Solving porosity problems has allowed a breakthrough in additive manufacturing applications and quality at Graphite AM

In a few short years, additive manufacturing has evolved from a revolutionary technology into a mainstream process. Enabling the fast and cost-effective production of complex high-quality components in a range of materials, it’s helping revolutionise manufacturing in an increasing number of industries. But for all its state-of-the-art advantages, it can also be subject to a more traditional and well recognised manufacturing problem: porosity. In a quest to resolve this challenge, leading additive manufacturer Graphite AM turned to the porosity sealing specialist Ultraseal International. The result is a breakthrough in both applications and quality.

In recent years, additive manufacturing – often referred to as 3D printing – has seen a significant growth in applications. It’s easy to understand why. The process is clean and simple, and produces high-quality components on demand, all without the need for expensive tooling or machining. 3D printing enabled the quick development of prototypes, while small and intricate parts could be cost-effectively produced as one-offs or in low volumes. For these reasons, the process was quickly adopted by cutting edge and hi-tech industries including motorsport and aerospace. As the technology has become more familiar however, its benefits have been more widely recognised. Today, additive manufacturing is becoming an increasingly viable manufacturing option across all sectors, and a new breed of companies has emerged to meet the demand.

One such is Graphite Additive Manufacturing, a 3D printing consultancy specialising in complex designs and high-performance components in tailored materials. Reflecting the growth of the process, Graphite AM’s original customer base was almost exclusively hi-tech sectors including automotive, motorsport, aerospace and defence. While the company still serves these sectors, it has seen a real growth in other industries. Says Jonathan Warbrick, Sales & Marketing Manager of Graphite AM: “Additive Manufacturing is no longer a revolutionary process for prototyping and limited production runs. The cost and turnaround mean it’s of huge benefit for low-mid volumes – typically 250-500 component runs and tooling. Manufacturers have seen this and are turning to 3D printing for the fast and reliable supply of high quality parts. It’s an area of huge potential, and has become a strategic focus of our work.”

Working to a 3D model, Graphite AM primarily uses SLS (selective laser sintering), an additive manufacturing process which deploys lasers to sinter powdered material, binding it together to create a solid structure. While the majority of 3D Printing Bureaus use standard or Glass filled Nylon materials - such as PA11 and PA12 - Graphite AM has developed its own range of unique SLS blends, including the use of fine graphite particles. As well as having impressive anti-static properties, the use of graphite also improves impact and thermal resistance (up to 170°C), meaning it is particularly suited to lightweight applications where strength and performance are critical factors. Combined with the ability to produce complex shapes and highly detailed designs without the need for metal tooling dies, Graphite AM is now supporting a wide range industry. These include components for automotive applications, turbo system components, plenum chambers, oil and water pipework and manifolds, fuel cells and EV battery cooling systems. They also produce components for mission critical applications including environmental monitoring systems and unmanned aerial vehicles (UAVs). “For manufacturers, the potential is huge,” says Warbrick,

Yet while the manufacturing technology has changed, a familiar old challenge remains: porosity, something which has long been recognised as a major issue with die-cast components. While the cause might be different, the end result is the same. During additive manufacturing, microscopic holes are formed within the body of a part. Though invisible to the eye, these reduce the overall density of the component, potentially leading to cracks, leaks and fatigue. In applications with pressure differentials or which need to be air or fluid tight - for example in cooling systems – this can be an especially critical issue.

In 3D printing, this porosity is typically caused either by the printing process itself, or by the powder used in the process. Either way, it’s a long-recognised problem, transposed to state-of-the-art technology. Which is why, to help minimise this issue, Graphite AM began the search for a specialist porosity sealing partner. Explains Warbrick: “To make sure our customers capitalised on the very best product quality, we needed to find a consistent, reliable solution to porosity. And for that, we needed expertise and experience.” 

Their choice of partner was Ultraseal International, a global leader in the development, manufacture and supply of porosity sealing chemicals, impregnation equipment and services – and one that, like Graphite AM, has a proven track-record in the automotive industry. Says Dr. Mark Cross, Commercial Sales Director at Ultraseal: “Ultraseal has unrivalled experience and understanding of the component impregnation process and a proven track record of developing the highest quality solutions to the problem of porosity in die-casting and electronic component manufacture. Though the technology is different, the challenge is similar, and we’ve been able to use our knowledge to create an effective solution. It’s pleasing to see that our technology will continue to have a key role to play in sealing components manufactured from new materials and processes such as additive manufacturing.”

Ultraseal’s solution involves sealing the component using vacuum impregnation, a process which uses three key stages.

First, components are placed into an autoclave containing Ultraseal PC504/66 resin, a high performance thermocure methacrylate sealant. The sealant is applied to the component under vacuum in an autoclave. Once components are immersed in sealant the vacuum is released, allowing the sealant to penetrate into the micro-porosities and leak paths within the 3D printed part through the resultant change in pressure, which draws the sealant into any micro-porosities and leak paths.

Second, a cold wash module removes excess sealant from external component surfaces and tapped holes.

The third process stage is a hot cure cycle. This exposes components to heat for a predetermined time period using a hot water bath which polymerizes the sealant, changing it from a liquid state to solid polymer by applying heat. As a further quality test, the components are pressure tested to ensure they are leak free.

Approached initially as a consultant and solutions provider, Ultraseal now delivers an end-to-end sealing service for Graphite AM from its UK Service Centre in Slough. This has added real value to Graphite AM, explains Warbrick: “Our customers rely on quality components, and we rely on Ultraseal to ensure they’re sealed effectively against the problems of porosity. Our partnership means we’re able to deliver reliable and leak free components, an essential characteristic in high performance parts. Ultraseal also deliver reliable and rapid turnaround. I’ve been impressed both the with service, and product quality.”




Picture - Graphite AM produces additive parts for UAVs