Auto supplier Rheinmetall Automotive (Neckarsulm, Germany) is increasing its use of Selective Laser Melting (SLM) technology to create prototype parts and components in short time and in intricate shapes and designs that cannot be achieved through conventional methods.
SLM, which began in rudimentary form in 1995 at the Fraunhofer Institute ILT in Aachen, Germany, is an additive manufacturing process that utilizes three-dimensional computer-aided design data as an information source, and energy in the form of a high-power laser beam to create three-dimensional metal parts by fusing layers of aluminum powder. The laser energy is intense enough to permit full melting of the particles to form solid metal.
The extremely fine powder is deposited on the build platform of the SLM machine in layers 20–100 µm thick, or half as thin as a sheet of paper. The exposed layers are fused by a high power-density laser beam with hundreds of watts directed in the X and Y directions with two high-frequency scanning mirrors. After one layer has solidified, the process is repeated several thousand times. Once the process is completed, any support structures are removed and the finished component is ready for use.
This takes place inside a chamber containing a tightly controlled atmosphere of inert gas, either argon or nitrogen, at oxygen levels below 500 parts per million.
“When we put the first machine into operation in 2012, we had to contend with several malfunctions,” said Frank Junker, responsible for business development, sales, marketing and quality at Rheinmetall 3D TechCenter GmbH (Neuss, Germany), a recently established unit within Rheinmetall Automotive focusing on 3D printing.
To address the issues, a number of refinements were made to both the machine technology and actual production process with the support of the in-house mechanical engineering staff.
“The challenge lies in producing the component in the desired quality quickly and economically,” Junker said.
Quality is primarily determined by the density of the component, which is reliant on the grade of the raw aluminum powder used in the process. Rheinmetall 3D TechCenter utilizes pulverized aluminum without a binding agent that only a few manufacturers globally can atomize to the required quality from a solid substance.
“Finding the right powder takes real detective work,” Junker said, noting the finely ground powder allows his company to achieve a component density of 99.9%, which ensures the mechanical characteristics largely correspond to the base material.
Greater efficiencies in the process also can be realized by adjusting the placement of the component within the SLM machine and optimizing laser exposure time in relation to the layering of the material.
Utilizing SLM results in a number of benefits, including reducing the manufacturing time from six weeks to two days, minimizing material waste, and improving subcomponents and assembly performance. Further, its ability to create intricate designs and shapes that traditional processes can’t replicate opens the door to new possibilities.
To date, Rheinmetall 3D TechCenter has used the technology to produce hollow structures to reduce inertia, as well as conduits that can be used for cooling lubricants.
Today, six machines run automatically a total of 5000 hours per year, including weekends. During operation they are monitored by a team of qualified engineers with extensive knowledge of SLM technology.
The 3D TechCenter also lends its SLM capabilities to other Rheinmetall divisions.
“The SLM process is a success story for us,” Junker said. “With our know-how, we are pioneers in a technology that is actually still in its infancy. This has advanced the production of complex sample parts and, as a consequence, promoted the entire development process.”
Edited by Yearbook Editor Bill Koenig from information supplied by Rheinmetall Automotive
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