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The importance of powder quality in additive manufacturing

Additive manufacturing, or AM, is the term given to describe the technologies that construct 3D objects through a material layering technique. 3D printing is one form of additive manufacturing, and the two terms are often interchangeable. Materials used can differ, but the one we will focus on here is metal. Specifically, we will consider why it is so important that the powders used are of the required quality.

Firstly, it is important to establish just how additive manufacturing works. Typically, it involves 3D modelling software, along with the layering material, such as a powder. The software is used to produce a computer aided design, or CAD, from which the AM equipment reads, allowing it to lay down the powder. Additional layers of the powder are then introduced, added in a layer-by-layer fashion to ‘build up’ the 3D object.

The powders used are predominantly metal alloys that are combined with heat – delivered via laser – to fuse the powders into a solid form. Other additives may also be used, helping to catalyse the formation of the process and alter the properties of the finished product.

Powders have to be used because it is not possible to ‘spray’ a molten metal accurately. Additive manufacturing powders are said to offer a range of benefits over current methods of manufacturing metals, such as forging or casting from a metal stock. These techniques can limit the potential shapes and structures that can be produced because of the physical restrictions imposed by the moulds. 3D printing of either plastics or metals may largely remove these constraints as the structure is built up in layers, enabling an increase in the range and complexity of the items that can be produced.

The quality of the powders used in additive manufacturing is incredibly important because these powders will impact on the physical properties of the finished product. For instance, the powder will play a crucial role in shaping the product’s tensile strength/brittleness, impact resistance, heat tolerance and resistance to corrosion.

As the process requires the combination of multiple powders, a precise understanding of the chemical composition of the finished product is required. The carbon, sulphur, oxygen, nitrogen and hydrogen composition will impact on the physical properties of the final product – importantly, however, some of these elements may be lost under the heating process. This means that even though the elemental composition is known at the beginning of the process, it may be altered in the finished product.

For this reason it is important to be able to analyse the final product to compare its elemental composition. By comparing ‘good’ and ‘bad’ products, it is possible to understand what differences there are in elemental composition between the two.  

Another important point to consider is that the powders used in additive manufacturing can oxidise over time. That being the case, it is vital to gain a firm understanding of how quickly this will likely occur, and to discover more about how this oxidisation will affect the finished item. For instance, analysis will be required to determine the shelf-life of the product.

How the future of additive manufacturing shapes up remains to be seen. However, the benefits of using powders – especially the removal of physical limitations of products – should mean them playing a hugely important role as the industry evolves and develops. There is a significant amount of research and development currently being carried out in this area, with manufacturers keen to establish new ways for better performing products to be made. At present, 3D printed metal products are in their infancy and, as understanding of the process of printing the products improves and the processes are refined, the number of items that can be manufactured using these methods will increase exponentially. 

Similarly, improvements in the quality of the powders used will help to increase the number of products that can be made. “The current barriers to successful additive manufacturing are the physical properties of the alloys formed,” said Peter Morgan, product specialist at Elementar UK, which manufactures the Inductar product line – a range used to determine the elemental compositions of an inorganic material, such as the powders used in additive manufacturing. “They are currently brittle and so they cannot take the stress of a cast/forged metal item. When the technique is refined it will be possible to produce bespoke items cheaply. This is very expensive currently due to the cost of the moulds that need to be created for the production of the piece. This is common with other items, such as plastics.

“Ever wondered why some seemingly simple parts are disproportionately expensive? Normally it’s because they will not sell in large number and so are produced in small batches. This means the cost of making the moulds, for example, cannot be spread over a large number of items. This therefore, has more of an impact on the final prices of the item.”

Morgan explained that if it is possible to make custom parts cheaply, then bespoke products will become more affordable. He gives the example of a classic car: “If you have a classic car and need a new part for the engine, but the part is no longer produced, rather than trying to track down a part in the scrapyard you may be able to print a new one. Another example concerns medical care. If a person breaks a bone and requires a plate to support the break, might it be possible in the future to print a bespoke part from an MRI scan?”

With powders being vital to a 3D printing industry with such incredible potential, one that could help to revolutionise many other industries, including the medical world, the importance of using powders of the required standard is clear. Additive manufacturing could play a crucial role in metal production in the years ahead – as such, it is imperative that the materials used, can be properly tested and analysed. With the right equipment, any fears can be allayed that a powder is unsafe or unsuitable, and that it is of the required standard to produce items that can make a real difference.