3D printing has also long been established with metallic materials. Filigree and complex structures can be produced much more easily and cost-effectively than with conventional metalworking methods. Reliable quality control in the form of material testing is also essential for 3D-printed components. The manufacturer of 3D metal printers, SLM Solutions from Lübeck, develops, assembles and sells printers and system solutions for the selective laser melting (SLM) process. The company uses a testing system from ZwickRoell for strength tests.

Qualify production parameters

Companies usually use the SLM process to produce prototypes or small series. Based on CAD data, a laser is used to create the desired homogeneous structures from a metal powder using the melting process. The starting metals for the powder can be aluminum, tool steel, stainless steel, nickel-based alloys, cobalt-chrome or titanium, for example. The process parameters for 3D printing, such as laser power, scanning speed and layer thickness, must be adjusted separately for each of these materials.

At the end of a parameter qualification, a tensile test is performed to check whether the print with the selected parameters meets the required mechanical characteristics. SLM Solutions relies on a materials testing machine from ZwickRoell's ProLine series with a maximum test load of Fmax = 100 kN. "The robustness, high quality and simple operation of the testing machine convinced us," says Daniel Brück from the Material and Process Development department at SLM.

Test systems in research

Another example of material testing in the 3D printing environment is in the field of research: The Institute for Materials and Application Technology Tuttlingen (IWAT) at Furtwangen University has been cooperating with ZwickRoell for years as part of research and final theses. The institute carries out mechanical tests in ZwickRoell's testing laboratory to determine the strength characteristics of additively manufactured metal components.

One test was carried out as part of the master's thesis "Design and additive manufacturing of various porous components and their characterization using X-ray computed tomography methods" and was used to determine the mechanical properties of additively manufactured porous components under uniaxial compressive loading. The investigation was carried out on porous titanium components with different lattice structures. Three samples were tested in each case to determine the mechanical properties using an AllroundLine testing machine (Fmax = 250 kN).

3D printing on the moon

In order to send manned space missions to Mars in the future, space organizations are working on planning a lunar station as a base. Transporting materials to the moon is very complex and expensive. This is why the Vienna-based company Lithoz, a specialist in technical ceramics in 3D printing, has developed a process for the European Space Agency (ESA) to produce building materials, spare parts and tools from synthetic moon dust using a 3D printer with LCM technology (Lithography-based Ceramic Manufacturing-Technology). "Our LCM technology is the leader in ceramic LCM 3D printing, if you look at the quality of the results," says Johannes Homa, Managing Director of Lithoz.

For an ESA project, Lithoz is researching how tools and building materials can be produced on site from moon dust using 3D printing. The material is being tested using ZwickRoell machines. © ZwickRoell

ZwickRoell could also be involved in the construction of a base station on the moon, as the company tested samples of synthetic regolith - artificially produced moon dust - for Lithoz. The material contains metals such as aluminum and iron and can be additively processed in a similar way to metal powder. The question was: Is the material suitable for producing the required materials on the moon using 3D printers in the future? To this end, ZwickRoell test engineers examined the samples produced using the sintering process at 1100 °C and 1200 °C. These were subjected to compression and 3-point bending tests to determine their special properties in terms of load-bearing capacity. The material had previously been tested in Vienna. "A second examination is always very helpful in such cases and helps us to continuously improve the process," explains Homa, adding: "There are around 400 kilograms of moon dust on Earth from previous lunar missions. However, this is now contaminated by the air and moisture. It has also lost its chemical reactivity and is therefore unusable for today's experimental purposes." However, the artificially produced regolith has "almost 100 percent identical chemical, mechanical or technical properties and characteristics to real moon dust."

"The material tests with Regolith were a first for us, but we were able to carry them out very well in line with the customer's specific requirements," says Tobias Ebner, the materials engineer responsible for the sample tests for the "Moon Dust" project. "Our client is now responsible for evaluating the test results to determine whether and to what extent the material is suitable for the construction of a moon station or whether it needs to be adapted." The results and findings of the two-day quality tests are currently being analyzed by Lithoz, discussed with ESA and then published.

Testing for the aerospace industry at -269 °C

3D printing is also interesting in other areas of aerospace, as additive manufacturing processes such as laser melting offer outstanding design freedom and therefore great potential for minimizing weight. This manufacturing process can also be used cost-effectively due to the low quantities that are common in aerospace.

KRP Mechatec, based in Garching near Munich, uses a testing machine from ZwickRoell to test additively manufactured aluminum and titanium structures at low temperatures down to -269 °C, for example. The company specializes in the development and analysis of materials and structures for the aerospace industry. In space travel, liquid hydrogen at a temperature of -253 °C is used as a fuel in combination with liquid oxygen. The tanks are exposed to very high loads at these low temperatures. The aim of the test program at KRP is to exploit the lightweight construction potential of additive manufacturing in this special application. To this end, the company produces material specimens from the aluminum and titanium alloys used and tests them in an individual test setup with an AllroundLine Z250SW materials testing machine (Fmax = 250 kN) from ZwickRoell.

To this end, KRP has developed a special device that allows various material tests such as tensile, compression, shear and hole expansion tests to be carried out in a cryostat. In this, specimens and assemblies are cooled to -196 °C using liquid nitrogen or to -269 °C using liquid helium and tested at this temperature. "As a German manufacturer, we receive the support we need from ZwickRoell to carry out our special testing tasks. The testing machine and the software enable flexible use in the research and development environment," says Dr. Christoph Zauner, Technical Manager at KRP Mechatec.