Direct laser sintering (DLS) is seeing rapid uptake in the construction of unmanned aerial vehicles. DLS is an additive manufacturing (AM) technique that can produce some of the most durable high-quality products around. Aerospace manufacturers -- along with numerous users in the medical sector -- are taking advantage of AM to produce low volumes of complex products requiring high precision.
"We're seeing a growing interest in DLS for aerospace," Andy Snow, EOS regional director for North America, told us in an interview.
The process can be used to make parts as simple as basic clips that hold harnesses. Some typical applications include components of engines and turbines, as well as parts for cabin interiors. Manufacturing gas turbine engines for use on commercial aircraft -- a use of DLS that's accelerating quickly -- is one high-value application. More manufacturers are identifying many components within the engine that can be laser sintered.
A wing fuel tank for an Arcturus T-20 UAV made with EOS laser sintered plastic (PA 2201) by Northwest Rapid Manufacturing (part of the Northwest UAV Propulsion Systems family of companies).
Photo courtesy of Northwest Rapid Manufacturing
EOS DLS systems process different materials, including polymers and metals. Part of the reason for using laser sintered parts is to reduce part counts and simplify assembly procedures. Another is the speed and cost-effectiveness with which fully operative parts with complex geometries and aerodynamic properties can be made available. Other factors include material and weight savings, which can reduce fuel consumption. In addition, manufacturers get fully integrated parts faster and reduce costs. They can also produce small batches and make manufacturer-specific modifications, such as in the cabin.
But the fastest-growing demand in aerospace is from makers of UAVs for lightweight components. Northwest UAV Propulsion Systems’ Northwest Rapid Manufacturing business, for example, uses EOS laser sintering systems to produce polyamide and polystyrene UAV components. Laser sintering melts materials at high temperatures and lays them down one at a time in thin layers, making it possible to create complex and unusual shapes.
In North American automotive applications, EOS is still focused primarily on rapid prototyping. "But we have some low-volume manufacturing applications for specialty, limited-series, custom-made automotive designs and luxury vehicles using DLS," said Snow. Those production runs are around 2,000 vehicles per year. Car manufacturers and their suppliers are also using EOS processes in the Formula 1 industry for very small quantities.
Medical and dental uses for DLS are growing rapidly. The materials that have been developed for these applications, such as EOS PEEK HP3, are biocompatible and capable of being sterilized, since they withstand very high temperatures.
Laser sintered parts made of EOS PEEK HP3 have a continuous use temperature of 180°C for mechanical dynamic, 240°C for mechanical static, and 260°C for electrical. One of the highest-volume uses for making end-products is dental copings and crowns. Another is patient-matched cutting and drilling guides, such as for knee and hip replacements, which have been used in hospitals for the past three years. "In one hospital, surgeons reduced the number of operating trays per surgery from a dozen to one or two," Snow said.
Curious how expensive this process is. You mention aerospace, medical and dental, where high costs can presumably be absorbed. Given the durability and ease of assembly (by aggregating more subassemblies into one piece), DLS seems like it should have huge uptake in automotive, but I'm guessing at this point that it's just too expensive.
Direct Laser Sintering technologies as a means to help Unmanned Aerial Vehicles has definitely been on Design News' radar screen for a while and is a great application for this technology. We wrote about one of the first UAVs built with this method taking flight this summer--SULSA,the Southampton University Laser Sintered Aircraft, which was printed using the EOS EOSINT P730 nylon laser sintering machine.
The materials have been costly, but the earlier machines were, too. Added to that, because items are produced one at a time the per unit cost tends to be higher than unit costs of a high-volume manufacturing process. And that's exactly why this technique is still limited mostly to specialty and race cars, not volume automotive manufacturing.
I think some of the parts being produced by this method are replacing parts that were previously produced by forging with secondary machining. If this is the case, how do the final parts stand up without the grain structures of the forgings? Aren't sintered parts produced from powdered metals fused together with heat and pressure. It would therefore have no grain and be lacking the inherent strength generally associated with that feature. While that would be immaterial on dental crowns and similar items not subjected to torque requirements, engine parts may be problematic. This is akin to plywoood being replaced by particle board. If that is not the case, I wish someone would explain why or why not.
From what I've read, metal parts made by direct laser sintering are typically not fully dense. They can be infiltrated with a copper alloy to help fill some of the porosity, or treated by hot isostatic pressing (HIP'ing) to increase the density. But I would not expect them to have the mechanical properties of castings or forgings. I would expect them to be closer to powder metallurgy (P/M) parts in terms of properties. That being the case, I would be very careful about putting them in any application which sees significant amounts of tension, torsion, or bending. Does anyone have any numbers for mechanical properties of laser sintered metal powders?
Some sintered parts are then forged, which does produce an oriented grain structure, and in addition does increase the density. The ultimate success would be to create a means to do laser forging. I have no ideas on how to do that, but when such a macine is invented I will buy one and go into the laser forged parts business.
@William: There's no reason why you couldn't powder forge a laser sintered part - except that you'd have to build a forging die, which would tend to negate the whole "rapid" aspect of laser sintering. I agree that anyone who could figure out how to make a net shape part with wrought properties through a rapid process with no tooling would probably become a multi-gazillionaire overnight. This would be the Holy Grail of rapid manufacturing. However, like you, I don't have the slightest idea of how this could be done.
I think at some point in the not-too-distant future, laser sintering might become competitive with investment casting for small production volumes - basically, where the production volume is too small to justify the tooling investment. Of course, investment casting foundries could stay competitive by using the same technology to make rapid wax patterns - and, in fact, they already are. In terms of mechanical properties, I would expect an investment casting to be superior to a laser sintered part.
To be fair, investment casting technology has had about a five thousand year head start compared to laser sintering.
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