The continued evolution of rapid manufacturing is dependent on two basic elements: processes and materials.
“Processes have to become faster and more reliable, and distinguish between polymers and metals,” said Hans-Joachim Schmid, Chairman of the Mechanical and Environmental Process Engineering faculty at the University of Paderborn, Germany. “One of the issues with polymers is the inability to get reliable and repeatable mechanical properties because there are sometimes large variations caused by powder recycling. A lot of powder has to be recycled because of the cost. That affects the end product because you see some variation in the degradation of mechanical strength.
“With metals, you can in general get mechanical properties that are often better than cast metals. But you struggle with large internal stresses that can cause deformation of your part.”
That’s the process side. The problem with materials is different, particularly for high-performance polymers designed for aerospace applications.
“The number of materials on the polymer side is limited,” said Schmid. “You need either high-temperature- or low-temperature-resistant polymers. You also want to address flammability of polymers, and even the toxicology of polymers.”
The industry answered some of those concerns this past December, when Germany’s EOS introduced a new laser-sintering machine at the EuroMold show in Frankfurt, Germany.
The EOS P 800 is the first high-temperature system for laser-sintering high-performance polymers, according to EOS. The company’s polyaryl ether ketone polymer, PEEK HP3, has a tensile strength of up to 95 MPa and a Young’s modulus of up to 4400 MPa—values up to 100% above those attained by the PA 12 and PA 11 materials currently available.
Depending on the field of application, the continuous operating temperature is between 180° and 260°C, leading to acceptable application-specific properties such as flame retardancy and biocompatibility. Suitable for process temperatures of up to 385°C, the high-temperature system is the first equipment worldwide to make use of this material group for laser-sintering technology, says EOS.
An EOS P 800 prototype was purchased by Toyota for its Formula One racing team, said Jim Fendrick, Vice President of EOS North America. The prototype was a P 700 machine that was modified to handle higher heat in the build chamber, he explained. Since building the prototype, EOS has sold one $1 million P 800 machine to an unnamed company in the U.S., Fendrick said.
The development of high-temperature polymers for rapid manufacturing means that OEMs can use them for applications that heretofore have been off-limits, such as in the cockpit where stringent flammability requirements are in place.
The machine is the vessel in which the part grows, but its DNA is in the polymer or powder from which it is made. Industry observers have always acknowledged that the primary limiting factor in rapid manufacturing has been the unavailability of powder versions of commonly used aerospace materials such as nickel-based super alloys.
The same is true in the polymer world, but EOS’ PEEK HP3 material is expected to change that. Now the same has to happen with metals.
"We're beta testing Inconel 718 and 625 powders [with EOS],” said Greg Morris, founder and COO of Morris Technologies, which specializes in metals technology. Inconel 718 and 625 are nickel-based alloys for high-temperature applications in turbofan engines, for example. Once testing is complete, Morris expects “design engineers [to] be able to immediately use those alloys.”
Fendrick expects additional modifications to the machines will be necessary before powdered metal alloys can be made ready for aerospace components.
“With high-temperature alloys, you need better temperature control in the build chamber and might have to introduce heating elements,” he said. “You also might have to shift from a nitrogen atmosphere to an argon atmosphere for titanium. With argon, you can create a more inert atmosphere, which you need because of the contamination issues with titanium.”