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Mönchengladbach, November 20, 2017

High-purity, homogeneous metal powder for additive manufacturing

For use in additive manufacturing, SMS group is establishing an own pilot plant to produce high-purity metal powder.

  • Within the scope of Industrie 4.0 additive manufacturing is becoming the key technology. Its goal is automated production of customized products.
  • In a pilot plant for powder atomizing, SMS group is gaining practical experience to be able to offer its customers efficient and high-performance solutions in the future.
  • On this occasion, the process of atomizing is analyzed in detail and optimized, if so required.

Some decades ago, when SMS group started to gain experience in atomizing iron powder, as used in the processes of spray compacting, hot isostatic pressing and sintering, the vision of Industrie 4.0 was completely unknown. Hardly anyone could even guess or foresee, at that time, the future-oriented potential offered by metal powder. Today, this long-standing experience of SMS group is paying off, and so is the advanced metallurgical know-how of SMS Mevac as well as the vast expertise and competence of SMS in thermal process technology. All of these factors converge in a key technology that paves the way to the ultimate objective within the scope of Industrie 4.0, and that is automated manufacture of individualized products. SMS group is establishing an own pilot plant to produce metal powders for so-called additive manufacturing applications.

Metallic powder of highest quality and purity, consisting of microscopic spheres with a homogeneous size of approx. 15 to 45 micrometers, is the starting material to produce novel workpieces by laser, for instance in a powder-bed procedure. In the SLM (Selective Laser Melting) additive process, metal powder is deposited layer by layer in a closed laser facility and each of these micrometer-range layers is melted at certain spots according to a CAD model. Finally, the loose excess powder is removed and the melted structures remain. The result is complex, three-dimensional metallic components. The products made to this method may have geometrical structures that are not possible using conventional methods, as for example metal cutting.

Our pilot plant to produce additive metal powder marks the starting point of the process chain of future-oriented additive manufacturing. This means that the powder quality produced will determine all further process steps and also the final results. So, we will use our pilot plant also to develop and test new materials with regard to different alloys or the subsequent mixing of powders, for example. Using this fascinating technology, SMS group will enter new territory in every respect, and I am sure the industry involved will highly benefit from all developments. Markus Hüllen, Vice President Powder Metallurgy of SMS group
Using existing experience, establishing new know-how

SMS group decided to build its own pilot plant on an industrial scale. Contrary to experimental trial plants, this version provides the advantage of acquiring knowledge under real working conditions and offering potential customers a marketable solution based on reliable results. Norbert Gober, Head of Central Development at SMS group: “Thanks to our know-how in the design and process engineering of vacuum melting plants and due to the wealth of experience in metallurgy, we already have the core competences needed for the new process. By building and operating the pilot plant we will pool our technical and technological knowledge and enhance it to the benefit of our customers.” The essential components of the powder atomizing plant, which is about 13 meters high and has a footprint of 400 square meters, are a vacuum induction furnace (including crucible and tundish), an atomizing system in the powder tower and vacuum pumps, cyclones, gas coolers, bag filters and further assemblies such as air separators and screens for powder classification.

Main units and process sequence in powder production

To ensure maximum purity, the melting of metals and alloys is accomplished in an inductive process in a crucible under vacuum. Next is the tundish from where the melt flows to the crucial core component of the plant, a nozzle with a diameter of just a few millimeters. The liquid metal is atomized by means of pure argon in the absence of oxygen. This offers SMS group the greatest potential of development. Markus Hüllen comments: “Our pilot plant will provide us the opportunity of investigating the interaction of nozzle geometry, pressure, gas jet, temperatures and many other factors as well as the behavior of different metals under real-life production conditions. We will obtain a multitude of new metallurgical findings, acquire know-how and optimize the efficiency of such processes. To this end, SMS group has established cooperation with several research institutes and universities.”

SMS group simulations, too, will be used to advance the atomizing technology. Norbert Gober: “Simulations help cut development periods substantially and indicate optimization potential in a very early stage. But it is equally vital to verify and refine the simulation models under real-life conditions. Based on reliable models, we will be able in the future to predict by computer calculation options to increase yield, for example.” After atomization, the droplets solidify to form tiny spherical particles in the micrometer range. This is followed by a treatment in cyclones and bag filters to separate gases. The fine metal powder is collected in containers arranged underneath the cyclones. Screens and air separators make sure the metal powder selected as high-quality additive powder consists of spheres in a defined and homogeneous size. Markus Hüllen explains: “Our target is a highly efficient facility. The pilot plant will support our ambition to considerably minimize the share of by-products, which are powder particles that are too small or too big, and optimize powder quality in terms of grain shape, grain size distribution, flowability and further properties.”

Focus on 3D technology

The powder grades produced from different high-quality metallic materials and alloys are the basic materials used in additive manufacturing which was developed in 1995. The precursor to this process was 3D printing with plastics. This method was born at the beginning of the 1980s and has meanwhile become established in the industry. As a rule in a 3D printing process, heated thermoplastics are extruded through a nozzle layer by layer to form an object. SMS group, too, uses this manufacturing method to produce complex single-part bodies for cameras to monitor strip processing lines or for flow-optimized cooling tubes made from a plastics- aluminium compound as used in wire rod mills for groove cooling.

The focus of the metal producing and processing industry, including SMS group, is however on 3D processes using metal materials. In the aviation sector in particular, but also in the automotive area, bionic honeycomb structures permit high-strength, crash-proof but clearly lighter components to be manufactured. This means an increase in safety, energy efficiency and environmental protection. Another aspect is that there are no expensive special machines or special processes needed to make such parts.

SMS group takes advantage of additive manufacturing also for inhouse mechanical engineering applications. “We have established a group of experts who have studied the multitude of possible optimizations, and have already designed concrete parts and manufactured them in small series. The results are more than promising,” says Norbert Gober. One example out of many is a new sealing element for bright-steel drawing mills. This element is monolithic and must not be assembled from many components as usual in the past. It can be manufactured in less time, substantially shortens the replacement period at the customer’s site and, last but not least, increases the sealing effect.

Norbert Gober: “Based on the newly designed parts we can manufacture to the additive method by now we are able to optimize the processes of our plants and machinery. An illustrative example hereof is the quick-action safety valve for our plate stretchers. Due to its light structure and flow-optimized channels, the part reacts within milliseconds, which is a crucial advantage in an emergency.” Further, the innovative lightweight design of valves permits processes and cycles in other plants to be accelerated, respectively the required rating and performance of hydraulic equipment or motors to be reduced, which helps save investment costs. The result is an increase in energy efficiency paired with a reduction in operating costs.

We are building a plant on an industrial scale since we want to demonstrate our customers the new opportunities under real-life conditions and to jointly develop processes for new applications. Dr. Guido Kleinschmidt, Member of the Managing Board of SMS group
Benefits for the global service

All plant operators around the world know the problem: Shall they keep expensive spare parts on stock or shall they save this capital commitment and instead accept extended downtimes? This conflict may soon be a thing of the past. Additive manufacturing has brought the production of spare parts on demand within reach. Norbert Gober: “For the future, we can imagine to have defined spares within the scope of the SMS group service manufactured by the additive method in the country of the respective plant operator. And that according to our engineering and in OEM quality. This would help plant operators cut their costs and, in addition, free them from laborious and time-consuming logistics and customs formalities.”

The pilot plant is just the start

With the pilot plant SMS group is going to produce high-purity metal powders from different metallic materials and alloys in application-related grain sizes. Jointly with customers, research institutes and the inhouse product managers, SMS group will explore the new technological options of the pilot plant together with the related possible applications and will advance them towards marketability. “The pilot plant is not only the starting point in the additive manufacturing process chain, but also the origin of many further innovations. We at SMS group are looking forward to significantly contributing to advancing these developments,” says Markus Hüllen. Future powder atomizing plants will be marketed by SMS Mevac.