Direct energy deposition DED puts final touch to part surfaces

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Direct energy deposition is also suitable for surface finishing — in contrast to powder bed processes. Listemann wants to start using this method and later manufacture entire components additively.

Listemann commits to its first 5-axis machine. The service provider from Liechtenstein specialises in surface finishing, or more precisely in optimising and combining materials. This year, the company plans to add Directed Energy Deposition (DED) to its existing processes, more precisely a Modulo 400 from Beam. The new version will be delivered worldwide for the first time in September 2021 and installed directly at the Listemann plant. In the DED process, a melt pool is usually generated by a laser, and at the same time metal powder or wire is fed in and melted. The Modulo 400 works with powder that reaches the application nozzle via a powder conveyor. Beam uses the second generation of its Medicoat vibrating feeders as conveyors, which supply both application nozzles developed in-house. The five simultaneously moving axes ensure that components can be built up from many different angles during the process.

Listemann is not new to additive manufacturing — and yet somehow they are. The subsidiary IQ Temp emerged from a cooperation with Renishaw, so it has experience with selective laser melting (SLM). But for Listemann, powder bed and DED are worlds apart. On the one hand, their work is limited by the small installation space of the powder bed machines. On the other hand, “we decided in favour of the DED process because of its flexibility and deposition performance,” says Dr Manfred Boretius, CEO of the Listemann Group. In addition, an inert gas atmosphere can also be purchased from Beam. With this inert gas it is also possible to process reactive metals like titanium or to work with higher capacities. Another important point is that Listemann can do more with the process than just additively manufacture components. They can carry out repairs on an existing component or modify it. For example, Listemann could weld cams onto a pipe — in any geometry and size. But Listemann will start with coating as the first application. Up to now they have refined surfaces by vacuum brazing or thermal spraying, now they will add laser processing.

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Selection from Listemann's portfolio

Once the Modulo 400 has arrived at Listemann in Liechtenstein, they first want to familiarise themselves with the machine and establish a sound know-how before accepting the first customer orders. “As a service provider, we have to master the machine and the process 100 percent and obtain flawless results with it before we go to market,” says Boretius. He estimates that they will have fully implemented coating by mid-2022. For more complex applications, they are taking more time to train.

Programming skills and welding experience

They are excited because the Modulo 400 will be their first 5-axis machine. “This is completely new for us,” says Boretius. “We need to build up skills in DED design and programming a 5-axis machine.” For the time being, IQ Temp will take care of the design for additive components, but Listemann has no experience in programming such a machine. “For machine operators who programme NC programs of a 5-axis milling machine, there is hardly any difference,” assures Jörg Oster, Beam's Account Manager Germany and Austria. This is because the design of the Modulo 400 corresponds to that of a standard 5-axis or gantry machine. “But you have to be aware,” Oster interjects, “that material is not being removed but built up! That's why, as the building process progresses, the component can suddenly be in the way. This is something the programmer has to take into account. “Actually, you only have to change the prefixes. Where you put a minus sign in milling, you add a plus in DED,” says Oster, putting the difficulty into perspective. Experience in welding is also a good basis for working with DED machines. Because here, classic welding knowledge is required: Which materials go together? How much does the material to be applied mix with the base material? Where do you insert a cooling pause so that distortion does not occur?

Investment paid off through high-quality coating

First, however, the machine has to be purchased — for about three times the price of a modern 5-axis milling machine. Oster puts the following costs into perspective: since the grain sizes of the metal powders are 45 to 100 µm, they are usually somewhat cheaper than those of powder bed processes and also not as lung penetrating, which increases the safety of the employees. Boretius is also relaxed regarding the high investment: “If I coat a cheap base material with a high-quality one and thus achieve a 10-fold service life, then it has paid off very soon.” In addition, the coating layers are not just a few µm thick, as is usual in toolmaking, but between one and 10 mm. “If we build up a 3 mm thick coating, the customer can sand it down three times without having to apply a new coating,” adds Oster. Moreover, the Liechtenstein company does not want to go into the mass market. They focus on niches and want to serve customers who are looking for specific material design, highest quality and innovative material solutions.

Developing new alloys during the printing process

Especially for tool and mould making, Beam is in the process of developing four universally applicable stainless and tool steels, with more in the pipeline. Everyone should find the right material for their applications. “It probably won't be exactly the material you use in conventional processes, because it's very difficult to prepare them as powders for additive manufacturing,” explains Oster, “but there will be a suitable equivalent.” The materials are to be available in hardnesses ranging from hard to tough. Users can also expand the material portfolio themselves. Because developing new material alloys in the printing process is one of the advantages of the DED process. Boretius is also looking forward to this: “We can take several powder conveyors, mix these powders with different compositions, feed them into the process and thus create customised materials or transitions from material A to material B.” The powders come together in the laser head and are fused with the component in the laser beam.

Improving tools with material transitions

Material transitions are useful for cutting punches, for example. They should be hard at the cutting edge so that they can easily pass through the material to be machined and are not worn out after only 1000 cycles. But if you make a cutting punch so hard that the wear is low, there is a risk that it will break. So a compromise between hardness and toughness is currently being applied. “With DED, we can build up a material that is soft or tough — perhaps also shock-absorbing — and use an ultra-hard material for the last 5 or 10 mm at the tip. This significantly extends the tool life in production,” says Oster. But what happens to the residual powder? According to Oster, there is very little residual powder because the material is applied directly to the relevant processing point and not spread over a larger area.

Minimal post-processing required

A component that comes out of a 3D printer is ready for post-processing. Except for heat treatment, Listemann outsources all post-processing work. So the customer can choose whether he wants to post-process the coated part himself or leave it to a Listemann partner. Oster notes that the 5-axis movement during assembly means that support structures are usually not needed. It is also a near net shape process. This means that the parts straight from the printer are already very close in geometry and contour to the final dimensions of the desired part.

The two companies are currently working on further developing the Modulo 400 and the DED process for tool and mould making. But the cooperation has a future: because potential customers of Beam who do not want to buy a machine right away can order parts from Listemann and thus be persuaded by the quality.

This article was written in cooperation with our partner portal Mission Additive.

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