3D-printing of polymers is a hub to Additive Manufacturing (AM) of...

3D-printing of polymers is a hub to Additive Manufacturing (AM) of metals

Klaus Ahlborn & Thorsten Müller, Mgr. in R&D and Sourcing, Deutz AG, Cologne, Germany [FWB: DEZ]

Klaus Ahlborn & Thorsten Müller, Mgr. in R&D and Sourcing, Deutz AG, Cologne, Germany [FWB: DEZ]

Looking to my “Wohlers Reports” on Rapid Prototyping (RP) dating back into 19983D-printing has been economically overestimated for decades. Nevertheless, bearing manifold unseen technological solutions and with the help of digitalization, Additive Manufacturing quietly overcame barrier by barrier, Computer Aided Design and Finite Element Analysis opening the door. Ever since 3D-printing is sneaking behind new software, capacity-growth of memory and ever accelerated computing now stipulating the question: Will there ever be a limit? For an answer let us have a look to the past, the state of art and the perspectives for a renowned engine maker.

While testing carbon-fiber coil-structures back in 1986,we first could imagine, what the 3D-printing will offer and what is called “bionics” today: FE-analyzing the layer structure of trees and bones with respect to their loads we understood the necessity to place fiber by fiber three dimensionally. But how to manufacture? We were limited to filament winding.

In 2002 I started 3D manufacturing using laser for photo polymerization of Epoxies (SLA) and got subsequently involved in printer development, mostly in use for dental applications then.

Polymer printing is common for RP and manufacturing equipment

Today inhouse RP with polymers for R&D is common, as well as adaption components, specific fixtures, repair or optimizing modifications of equipment for our manufacturing lines. In house printing created a common understanding foreach process step and their interlinking: 3D adequate design, availability and type of raw materials, their properties, printing software, printer capabilities, reworking, post processing. What is hindering a mass production?

Achilles heel of polymers are temperature and creep resistance. Plus having a good thermal conductivity makes metals the selected material for combustion engines. However, selective laser sintering (SLS), selective laser melting(SLM) or binder jetting (BJ) starting from metal powders are relatively new and lack validation under fatigue load at elevated temperatures.

Additive Manufacturing of metals on the way to serial production

Alike any new technology when entering its market, AM starts, were small lot sizes are required. How small is small? Once the digital dataset is generated a lot size =1 is possible. That was the go for individualized personal dental applications. For an engine maker it means: We are ready to market on spare parts, cutting storage costs for parts and molds, and opening JIT-availability worldwide without transport. With this experience the market will open for customer driven individual adaptions to our standard power units.

There are manifold options of further optimization, as can be seen from the spare part shown. SLM-printed to save a molding tool, the airduct fits for purpose. However, micrographs reveal a heterogenic layered structure resulting from melting seam of the laser and a high ratio of pores. How can a printed spare part comply with the requirements then? Since the low-cost aluminum-alloy AlSiCu3 had to be replaced with AlSi10Mg for availability, the imperfections are overcompensated by a doubled fracture strength.

The example not only shows potential to optimize function and costs (AM-compatible redesign with reduced wall-thickness based on FEA, finer and slower SLM, post-homogenizing heat treatment, development of low-cost raw materials). Not being able to envision the full scale of this very versatile technology we here barely “copy the design of the past.” Why not investigate the “toolbox of developments” to enlighten the future?

Advanced materials for Additive Manufacturing to come

As well starting from powders ceramics are coming into focus next. Imagine we would send a robotic printer to Mars which uses nothing else than lenses and pure sunlight to melt marsian sand according transmitted design data. Will it be possible to build shelters for astronauts before arrival? Together with Royal Colage of Art, London the product designer Markus Kayser has successfully AM-manufactured sculptures from Sahara sands, achieving some 2.000°C from sunlight with his equipment. Did you recognize? Another barricade is breaking: Limits in size!

What if we lay our material norms into the drawer and ask ourselves: What new type materials compositions make AM-techniques possible?

Where brittleness is a weakness of ceramics, their toughness increases with decreasing grain size. Using LED-light and a fine Silicium-Carbide-powder can be AMed to a green compaction. By a thermal post-treatment, a fine grained polycrystalline and thus tough SiC is backed, achieving a performance near to Diamond. Similar for nanoscale Yttriumoxids (Y2O2).

Why not taking advantage from themelting and cooling cycles following the laser beam to modify the structure of materials? Fraunhofer- and Max-Planck-Gesellschaft have lifted the hardness of “Maraging Steels” by 50% by thermally influencing the intermetallic phases. And AM is the only technique ever to consolidate metallic gears in amorphous (= non-crystalline) state by fast cooling.

Summarizing for Deutz AG,AM bears a great outlook to meet our demand for durable components at high temperatures.

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