Dynamic mechanical properties of AMmanufactured stainless steel material CIRP STC-E Paris, 27.01.2012 A.B. Spierings, G. Levy, K. Wegener Inspire institute for rapid product development irpd St. Gallen, Switzerland 1
Agenda Background & Motivation Mechanical properties of stainless steel Dynamic material qualification Case study Spierings, Adriaan 01/2012 inspire AG 2
Background & Motivation AM technologies, especially Beam Melting Technologies such as SLM, offer an interesting way to highly improved functional & structural parts for Aerospace applications Automotive Machine industry Medical applications (implants, instruments) www.botzeit.de Inspire-irpd Inspire-irpd Spierings, Adriaan 01/2012 inspire AG 3
Background & Motivation However, the success of AM-technologies in industry requires a further development in different areas: «Lab environment» / first applications R&D driven Material knowhow Process knowhow & development Affordable machines - AMproduction environment --- Exemplary applications Inspire-irpd is involved in all fields Production environment Spierings, Adriaan 01/2012 inspire AG 4
Background & Motivation Focus on material properties and integrity Static mechanical properties Widely investigated / known Dynamic mechanical properties Only partially investigated Fracture behaviour (da/dn, K I,II,C, ) Almost no results available General material integrity Many investigations and analysis Internal stresses available / R&D topic of high interest Microstructure Korrosion behaviour Industrial applications Mechanical properties: static, dynamic, fracture behaviour, Microstructure Internal stresses Porosity Spierings, Adriaan 01/2012 inspire AG 5
Mechanical properties We know that mechanical properties are different to «conventionally» processed materials, due to Fine grained, columnar microstructure anisotropy Viewing direction F 90 F Main grain orientation F 0 Viewing direction F Build direction z Main grain orientation / dendrits Internal stresses BRINKSMEIER, E., LEVY, G., MEYER, D. & SPIERINGS, A. B. 2010. Surface Integrity of Selective-Laser-Melted Components. CIRP Annals - Manufacturing Technology, 59, 601-606. Some porosity SPIERINGS, A. B. & LEVY, G., 2009. Comparison of density of stainless steel 316L parts produced with selective laser melting using different powder grades. In: BOURELL, D. L., ed. Proceedings of the Annual International Solid Freeform Fabrication Symposium, August 3-5 2009 Austin, Texas. 342-353. Spierings, Adriaan 01/2012 inspire AG 6
Mechanical properties Static mechanical properties R m 30um - 0 45um - 0 30um - 90 45um - 90 For many materials known Typically good static properties (Hall-Petch!) Many materials meet the requirements for static applications. (MPa) 900 800 700 600 500 400 300 200 100 0 Literature Type 1 Type 2 Type 3 Powder Types 900 800 700 600 500 400 300 200 100 0 Spierings, A.B. et.al; Influence of the particle size distribution on surface quality and mechanical properties in additive manufactured stainless steel parts; Rapid Prototyping Journal, 2011. 17(3): p. 195-202. Dynamic mechanical properties Partially analysed Typically lower strength compared to conventionally processed materials Is this dramatic and hindering a use of AM-materials in more dynamic (industrial) applications? Spierings, Adriaan 01/2012 inspire AG 7
Dynamic material qualification Analyse of dynamic properties of AM-processed stainless steel Machines & Materials Material: SS-316L ConceptLaser - M1 100 W v = 425 mm / s Layer thickness 30 µm Hatch 0.13 mm Build direction: vertical Powder - D 50 15 µm SLM machine @ Inspire-irpd Spierings, Adriaan 01/2012 inspire AG 8
Dynamic material qualification Analyse of dynamic properties of AM-processed stainless steel Test setup S-N specimens Surface finishing - as-built - machined - polished Testting (ASTM-E739) at - R = 0.1 («severe») - 50 Hz 50 samples for SS 316L Spierings, Adriaan 01/2012 inspire AG 9
Dynamic material qualification Results As-built & Machined & polished Spierings, Adriaan 01/2012 inspire AG 10
Dynamic material qualification Conclusions Values are comparable to conventional materials, depending on the specific conditions (annealed or not, ) polished as-built machined As-built samples: Lower endurance strength compared to machined, polished Only small differences in fatigue range between as-built machined polished samples! Spierings, Adriaan 01/2012 inspire AG 11
Dynamic material qualification Open questions Surface quality Interestingly, the surface quality did not play a highly significant role. conventional machining (grooves)!! other factors play a more important role. This behaviour was also shown on other materials! Differences in S-N curves: z- versus xy-direction The grain size plays an important role in fatigue, especially during crack initiation ( K th for d ). Crack growth in the current (z-direction) specimens: load acting to the long axis of the grains for cracks: «coarse grained structure» Expectation for xy-built specimens: Lower values compared to z-built specimens «fine grained structure» Z-specimens (left), xy-specimens (right) Spierings, Adriaan 01/2012 inspire AG 12
Dynamic mechanical properties Challenges: Are the dynamic mechanical properties sufficient for industrial applications? We need to qualify the materials Material database We can optimise the part-design Design Geometry Joints Material selection Surface condition Topological optimisation Stress Optimization of stress flow distribution We need to optimise the processes Reduction of porosity Reduction of internal stresses Design Optimization Material Static Dynamic da/dn Fracture toughness Qualification of materials Optimise d Application processe s Leightweight Functionally optimised Answer Spierings, Adriaan 01/2012 inspire AG 13
Case study Formula student car 2011 Production of heavily loaded brackets for the Formula Student Cars 2010 & 2011, ETH Zurich Bracket development (leightweight) Dynamically loaded Exemplare case study: Motivation for an industrial use of SLM for functional, load-bearing parts. AMZ Formula Student Car 2010 & 2011, 1st place winner in Silversone 2010. Spierings, Adriaan 01/2012 inspire AG 14
Formula student car of ETHZ Version 2011: Brackets, produced by inspire-irpd Different brackets (Version 2011) SPIERINGS, A. B., et.al, 2011. Production of functional parts using SLM Opportunities and limitations. In: BÀRTOLO, P. J., ed. Virtual and Rapid Manufacturing: Advanced Research in Virtual and Rapid Prototyping, September 28-October 1 2011, Leira, Portugal. CRC Press, Taylor & Francis, London, 785-790. Spierings, Adriaan 01/2012 inspire AG 15
Dynamic material qualification Outlook («Materials») Analyse more materials S-N measurements done 316L 1.4313 Some measurements on 1.4542 Process development & Simulation Materials SLM machine equipment Analyse not only S-N curves, but also Crack propagation curves (da/dn) K I,C Applications Planned: Measurements on Aluminium (S-N, da/dn) SLM fields of activity @ inspire-irpd Spierings, Adriaan 01/2012 inspire AG 16
Dynamic material qualification Participation of inspire-irpd in CWG proposal «Laser in Production» Spierings, Adriaan 01/2012 inspire AG 17