AM: Keeping it Clean

Article by Pierre Forêt

How atmospheric gases will be key to future additive manufacturing

ADDITIVE manufacturing (AM), or the process of creating a product or component part layer-by-layer instead of using traditional moulding or subtractive methods, is leading a transformation in manufacturing technology.

“AM” is often used interchangeably with the term 3D printing, but this is a misnomer. While AM may have 3D printing at its heart, the process consists of much more, with both pre- and post-production treatments being integral to the overall manufacturing approach. And there are multiple approaches – from laser powder-bed fusion, directed energy deposition (using a laser or an arc), electron beam melting, to material jetting. But behind these various production methods – and the ancillary processes at either end – are the vital atmospheric gases and gas technologies which are fundamental enablers of this manufacturing revolution.

New technology for atmospheric control

Inert gas –  typically argon or nitrogen –  is central to the core printing process in addition to pre- and post-production processes such as metal powder production and storage.

As is well understood, the core AM process takes place within a closed chamber filled with high-purity inert gases such as argon and nitrogen. What is less well understood is that even after the atmosphere is purged, impurities can remain present in the chamber due to incomplete purging, via access through loose connections or within the metal powder itself. Even extremely small variations in oxygen can impair mechanical or chemical properties of alloys like titanium or aluminium, affecting composition of the end product and resulting in negative physical characteristics such as discolouration and even 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. Linde Gases has, over the past 4 years, developed new technology to overcome atmospheric impurities to give manufacturers optimal printing conditions. The result – ADDvance O2 precision – continuous analysis of the gas atmosphere, detecting oxygen levels with high precision without cross-sensitivity. Recognising O2 concentrations as low as 10 ppm, the unit automatically initiates a purging process to maintain the atmosphere as pure as needed. 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 partners, both industrial and academic.

Precision: Continuous analysis of the gas atmosphere, down to 10 ppm

Metal powder: the beginnings

The mechanical properties of a finished product are not only highly dependent upon the AM process itself, but also the characteristics of the powder used in that process. The quality of metal powders 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. Powder quality also plays a vital part in consistency and production repeatability – a key focus area for AM which looks to ultimately apply stringent uniformity for more series-based production. For the delivery of necessary powder excellence, atmospheric gases play an essential role.

Article by Pierre Forêt

Senior Expert, Additive Manufacturing, Linde

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