Characterisation of the thermal ageing effects on the mechanical properties when reusing polyamide 12 in the selective laser sintering process

Additive manufacturing is one of the key technologies for future production complex and individualised components. One most challenging questions to minimize cost reuse powder leftover after building process. This study investigates influence on mechanical properties when reusing out process chamber up four times. Tensile test specimens are produced investigated. The results show a decreasing in ultimate tensile strength with repeated powder. After times increases again. cannot be explained by literature has verified further investigations. investigations reveal high anisotropy as highly depends component orientation chamber. particle shape does not any differences between virgin aged under scanning electron microscope. Die additive Fertigung zählt zu den Schlüsseltechnologien für die zukünftige Produktion komplexer und individualisierter Bauteile. Eine der größten Herausforderungen, um Produktionskosten minimieren, ist Wiederverwendung des nach dem Bauprozess übrig gebliebenen Pulvers. In dieser Studie wird Einfluss auf mechanischen Eigenschaften bei mehrmaliger nicht aufgeschmolzenen Pulvers untersucht. Es werden Zugproben hergestellt Ergebnisse zeigen eine Abnahme Zugfestigkeit wiederholter Restpulvers. Nach viermaliger steigt Festigkeit wieder an. Der Anstieg lässt sich abschließend begründen muss weiteren Untersuchungen verifiziert werden. hohe Anisotropie, da stark von Orientierung Komponenten Prozesskammer abhängt. Unter Rasterelektronenmikroskop können keine Unterschiede zwischen Neupulver thermisch belasteten Pulver festgestellt processes have already been use over 25 years field prototyping (rapid prototyping) industry research 1. Due increasing need products, well possibility producing geometries integration functions, series 2. area polymer selective laser sintering that currently at transition stage from prototype tooling 1-4. For this reason, particularly important generative plastics 5. Even though become plastic production, there only rather small amount materials, which used industries 1, 6. A part some exceptions like polypropylene polyetheretherketone special application, materials based semi-crystalline thermoplastic polyamide 11 12 1-3, 6, 7. It estimated 95 % 12, underlines predominating market position polyamides process, base material manufacture parts. successively applied thin layers construction area, so-called bed then melted locally help carbon dioxide laser. molten solidifies forms layer fragments component. melt solidified, lowered thickness, new next bonded its surroundings melting solidifying 8. until produced, layer. order reduce warpage caused fast cooling required energy so temperature increase necessary plastic, preheated set just below 2, 9, 10. achieved heaters. These temperatures (around 175 °C 12) lead thermal ageing unsintered powder, limited reusability. aims evaluate effects samples made different qualities terms their state compared each other. Mechanical sintered parts investigated several authors 11, 12. studies carried virgin, mixed investigate manufacturers or orientations build chamber, whereas following more focused hence defined material. Additionally morphology particles analysed aid fabricated sinter system Vanguard HS company 3D-Systems Inc. equipped 100 W investigation study, volume 380×330×275 mm3 used. As mostly industries, built DuraForm PA manufacturer dimensions chosen according DIN EN ISO 527-2 Type 1 A, Table l1 [mm] l2 l3 b1 b2 h 80 110 170 10 20 5 states material, cycles. first cycle performed using step, reused fabricate another sample set. cycles left used, no addition other guarantees ageing, parameter kept same. To ensure clear proper dataset At end will off sets Additionally, mixture 60 40 common refreshing rate industries. ten were fabricated. Five placed along x-direction, parallel application direction five y-direction, perpendicular that, Figure produce components, thickness μm chosen. Each starts warm 12.5 mm total height, followed 2 ends cool down 2.54 mm. All 177 °C. Orientation im Bauraum. characterize changes regarding Zwick 1445–02, kN universal testing machine. obtain accurate values strains modular sensor arm extensometer least three tested receive assessment properties. reserve case an invalid run. Furthermore, grains investigated, Schottky emission microscope JSM-7200F Jeol GmbH. non-conductive sputtering investigation. realise microscopy prepared sputter coating gold. gold serves conductive without influencing grains, range nm–15 nm. Specimen holder extensometer. Probenhalter mit Fühler-Extensometer. Investigating room indicates decrease 3. stress-strain curves exemplarily sequence x-direction. evident specimen, 60/40 roughly middle all results. resulting 36.8 MPa differs 0.6 overall median (37.4 MPa), (y-direction) reached can components 4. striking again, Evaluating complete confirms behavior, fourth clearly seen also (y-direction). Although clear, behaviour confirmed must series. Stress-strain positioned (x-direction). Spannungs-Dehnungs-Diagramm Zugproben, entlang Pulverauftragsrichtung (x-Richtung) angeordnet sind. Ultimate data Zugfestigkeiten unterschiedliche thermische Alterungszustände Grundwerkstoffs. elongation break (6.08 %) higher than entire specimen lie around value %, same behavior obtained allocated y-direction. stiffness, literature. Comparing y-direction those x-direction shows mean average 24 importance positioning manufacturing, characteristic 13, 14. Contrary expectations, images resolution 1’000. change size due degradation was expected. Both, exhibit potato-like shape, Figures 5, Since section, should information about possible distribution. Scanning Rasterelektronenmikroskopische Aufnahmen Neupulvers. strong anisotropy. significantly application. When direction, where lower. general, observed Reusing time could clarified finally Analysing did particles, distribution examined diffraction. author acknowledge staff laboratory technology kind support experiments. Many thanks 4D Concepts providing specimens. Project supported Federal Ministry Economic Affairs Energy (BMWi) basis decision German Bundestag. cooperative project companies GmbH M.J. Open access funding enabled organized Projekt DEAL.