When discussing the key elements of 3D printing, the first things that come to mind are software, hardware and materials. In later years operators have begun to increasingly understand the key value of other elements such as new design ideas, workflow automation and post-processes. It was not until very recently that the AM industry and gas manufacturers fully realized the importance – and thus the potential business opportunity – behind the gas supply. In this segment, even global companies like Linde Gases now see great opportunities for future growth.
It’s not only about keeping metal 3D printers from blowing up (although that is a big part of it): inert gas, typically argon or nitrogen, is central to the function of metal AM as well as peripheral AM processes including atomization as well as pre- and post-production activities. Gas is also used for quenching during the vacuum heat-treating process. Abundant, colorless, odorless, tasteless, and non-toxic, argon is 38% denser than air and it can displace the oxygen in an enclosed area.
Argon and Nitrogen gas is used in several AM processes such as laser powder-bed fusion as well as Laser Directed Energy Deposition (Laser DED), Selective Laser Sintering (SLS) and other AM processes using gas-metal arc welding and plasma welding techniques. It creates the perfect environment for the process. A major challenge in metal AM is building components in a controlled environment and minimizing the introduction of any possible impurities. Inerting is also critical for proper management of the combustible dust which from the powder metal and printing process when using reactive metals such and aluminum and titanium.
Because it is so important, as the AM industry grows, gas suppliers have come to view it as a key area for business development. One of these companies is Linde Gases. The industrial gases giant has dedicated the past 3 years to developing its gases along with pioneering technologies to overcome atmospheric impurities in order to give manufacturers optimal printing conditions.
3dpbm recently had the opportunity to speak with one of the people leading Linde’s AM activities, Pierre Forêt, 37. He is currently Senior Expert Additive Manufacturing and oversees the Global Development Center for Additive Manufacturing in Munich, leading a team developing new solutions – from powder production to laser powder-bed fusion/wire-arc to post processes.
“I lead the AM development team at Linde,” says Dr. Forêt. “Our group was established in 2015 and we’ve grown to ten dedicated people. Our goal is to develop technologies using gas for customers that use it in additive manufacturing. As a gas company, we have seen quite an interest in this technology. Although volumes are still small we believe there is a huge potential that it will grow. From the data, we see that the growth in AM is significant year on year. In addition, gas is not used only in the AM processes but in the entire value chain, from atomization to post-processing.”
Pioneering technology for atmospheric control
The core AM process takes place within a closed chamber filled with high-purity inert gases such as argon and nitrogen. However, even after the atmosphere is purged, impurities can remain present in the chamber. Even extremely small variations in oxygen content can impair the mechanical or chemical properties of alloys sensitive to oxygen like titanium or aluminum and can affect the composition of the end product, resulting in negative physical characteristics such as poor fatigue resistance. For industries at the forefront of AM adoption such as aerospace, automotive and medical, such negative production outcomes are critically important to avoid.
“For Linde, it’s all about gas molecules,” says Dr. Forêt. “Gases have been a business for over a hundred years but we need to always work to make a difference in the market with new technologies. Our idea is not not limit ourselves to the gas molecules but to develop the eco-system around it to support our customers”.
Over the last year, Linde introduced three products tailored for AM. One of them is part of a project called “adventure to precision”. It was developed two years ago by engineers working to have more precision in the measurement and control of the oxygen levels within the printer.
The result is the ADDvance O2 precision, a system that provides continuous analysis of the gas atmosphere, detecting oxygen levels with high precision without cross-sensitivity. Recognizing O2 concentrations as low as 10 parts per million (ppm), the unit automatically initiates a purging process to maintain the atmosphere as pure as needed. This means that the user can monitor anything that happens, including leakages or defects in the atmosphere, and be alerted by a warning if parameters are incorrect. The technology is already in use at companies at the vanguard of AM including Liebherr Aerospace in France, leading car manufacturers in Germany as well as other Linde partners – both industrial and academic.
The mechanical properties of a finished product are not only highly dependent upon the AM process itself but the initial characteristics of the powder used in that process. The quality of metal powders used in AM is critically important as it can impact on the physical properties of the finished product, including tensile strength, brittleness, impact resistance, heat tolerance and resistance to corrosion. For delivery of much-needed powder excellence, atmospheric gases play an essential role. It is essential to maintain the correct atmosphere during storage in order to avoid humidity. Humidity will lower the flowability of the powder and will increase the amount of O2 during printing. Thus Linde’s AM solutions now also include Linde’s ADDvance® powder cabinet to ensure optimal conditions for powder storage.
“Our customers told us they need to store sensitive aluminum and titanium powders in order for it to avoid aging and deterioration,” says Dr. Forêt. “This powder cabinet acts like a fridge with an inert gas on the inside and no humidity drop. You can store powder inside of it and reuse it directly afterward. Now we are looking at new, larger size options”
The third product is used clean AM parts. During any of the AM processes, blast powder residue or unfused powder can build up on the part being printed. Removing particles from holes and cavities can represent a particular challenge in the case of small, elaborate parts and components with complex geometries, especially as melting metal residue requires potentially damaging high temperatures. This product is mainly tailored for niche medical applications, where you don’t want any impurities on your part,” says Forêt: “It hits the surface and goes away with everything that is un-fused. It doesn’t leave any contaminants because it just evaporates after use.
The first new products in the Linde’s pipeline will focus on another key area of AM: powder manufacturing by gas atomization.“Powder manufacturers are the biggest users of argon in the entire AM value chain. They use as much as a truck a day,” Dr. Forêt explains. The new products will enable increased Argon recycling to reduce consumption of Argon in gas atomization processes.
In the longer term future, we may see the development of new gases and new gas hybrids, specifically for different AM materials and processes. “Take welding as an example,” says Dr. Forêt. “In the very beginning it used a single inert gas and today you have a different gas for each material. Each application has a specific recipe of weld gas that has been developed by the gas companies. In the future – Dr. Forêt continues – you may choose a gas mixture for high-performance parts and other gases for lower cost parts. It’s an extremely complex topic and also extremely interesting. One of the tests we conducted was on a mixture base from argon and helium for titanium. For now, we just ran some tests with positive results but in order to actually introduce it to the market, we need to do many modifications to the process itself, to the machines and to the process parameters.
There are many reasons to continue developing gases for AM. They can be used to reduce fumes and particles in the air, and also to increase the scanning speed thus increasing system productivity.
Binder jetting enhanced post-processing: the final touch
Most AM components require a heat treatment step to reduce stress with atmospheric gases at the heart of the process – either via hot isostatic pressing (HIP) – an advanced material heat treatment process utilising elevated temperatures in a contained high-pressure atmosphere to eliminate internal porosity and voids within cast metal materials and components or sintering after the binder jetting process. In binder jetting technologies gas are used during the sintering post-process phase with the part being fed slowly through a special high-temperature furnace to bond the metal particles together. For this process, an inert gas such as argon or even a special reactive gas mixture including some hydrogen or methane is needed.
Dr. Forêt agrees that this AM process is ideal for the automotive industry. “They are under a huge cost pressure, so they want to reduce costs. On our part, we can So look at how we can reduce the cost of the gas for that process while still improving productivity. We feel that after aerospace has led the way, larger production segments such as automotive and energy are going to be the drivers for the next phase of AM growth. Our role in the AM industry is enabling us to reach out to many new companies and potential clients that we have never worked with before. And, at the moment, we’re leading the industry with the gas technologies we offer. It helps our clients and it also helps us to win their business.