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Abstract3D printing opens up new possibilities for the production of polymeric structures that would not be possible with injection molding. However, it is known that the manufacturing method might have an impact on the mechanical properties of manufactured components. To this end, the mechanical behavior of test specimens made of thermoplastic polyurethane is compared for two different manufacturing methods. In particular, the SEAM technology (screw extrusion additive manufacturing) is compared to a conventional injection molding process. Uniaxial tension test specimens from both manufacturing methods are analyzed in two testing sequences (multi-hysteresis tests to analyze inelastic properties and uniaxial tension until rupture). To get as less perturbation as possible, the 3D-printed samples are printed with only one strand per layer. Moreover, a correction approach based on optical measurements is applied to determine the true cross-sectional area of the test specimens. The mechanical tests reveal that the inelastic material behavior is the same for both manufacturing methods. Instead, 3D-printed specimens show lower maximal stretch values at rupture and an increased variance in the results, which is related to the surface structure of 3D-printed specimens.

The Screw Extrusion Additive Manufacturing (SEAM) technology provides output rates up to 10 kg/h, a melt pressure up to 350 bar and temperatures up to 400 °C as well as strands with an adjustable bead width between 1-8 mm. Due to a bypass nozzle, position jumps without material extrusion, local wall thickness reduction, and the control of the volume flow (0-100 %) are made possible. Further, the extruder is able to process fiber-reinforced as well as highly filled plastics and integrates a regranulation system to return bypassed material into the process. The hexapod parallel kinematic meets the process requirements, as it generates a rapid movement of the workpiece (up to 1 m/s) in 6 degrees of freedom within a large printing workspace (1100 × 800 x 600 mm3), where an additional Z-axis carries the extruder and realizes the part height. Eccentric joints provide high accuracy and stiffness while being cost-efficient at the same time. The commercial Beckhoff TwinCAT control allows G-code processing and provides an HTML based GUI for machine and extruder control. Consequently, high accuracy is achieved, which is verified by the use of a double-ball-bar measuring device and by producing a test workpiece.

Der 3-D-Druck ist ein sehr stark wachsender Markt, welcher für Kunden und die Industrie völlig neue Produkt- und Fertigungsansätze eröffnet. Neue innovative Ansätze für die additive Fertigung von Kunststoffbauteilen entwickelt das Fraunhofer-Institut für Werkzeugmaschinen und Umformtechnik (IWU) in Zusammenarbeit mit der BMW Group. Auf Basis einer extrusionsbasierten Plastifiziereinheit zur Verarbeitung von Kunststoff-Standardgranulaten erfolgt in Kombination mit einer Pentapod 5-Achs- Parallelkinematik einer METROM-Werkzeugmaschine das 3-D-Drucken von Kunststoffbauteilen. Dabei werden bestehende Verfahrensgrenzen überschritten und eine neue Generation von 3-D-Druckverfahren mit deutlich gesteigerter Prozessgeschwindigkeit geschaffen.

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