Characterization of bulk to thin wall mechanical response transition in powder bed AM

Abstract

Purpose In the development of powder bed additive manufacturing (AM) process parameters, the characterization of mechanical properties is generally performed through relatively large mechanical test samples that represent a bulk response. This provides an accurate representation of mechanical properties for equivalently sized or larger parts. However, as feature size is reduced, mechanical properties transition from a standard bulk response to a thin wall response where lower power border scans and surface roughness have a larger effect. Design/methodology/approach For this study, samples of wall thickness varying between 4.0 and 0.25 mm were built in 304L on the selective laser melting (SLM) platform and Ti-6Al-4V on the electron beam melting (EBM) platform. Samples were then mechanically tested, and fractography was performed for analysis. Findings This study experimentally identifies the threshold between bulk and thin wall mechanical properties for 304L SS on the SLM platform and Ti-6Al-4V on the EBM platform. A possible method for improving those properties and shifting the transition from bulk to thin wall response to smaller wall thicknesses by manipulation of scan pattern was investigated. Originality/value This study is a novel investigation into the effect of reduced wall thickness on the mechanical properties of a part produced by powder bed AM.

Additive manufacturing of cardiovascular CoCr stents by selective laser melting

“…The lattice structures obtained in macro components are similar to stent form and dimensions. The use of long pulsed (μs-ms) fiber lasers presents further benefits for high precision in lattice and fine structures, due to the more controlled energy input into the material and better control of pulse disposition over the scan geometry [18][19][20][21].…”

Material modelling and property mapping for structural FEA of thin-walled additively manufactured components

“…Young's modulus as well as Poisson's ratio can be directly determined in uniaxial tensile tests and thereof, a reasonable approximation of the shear modulus G ⊥ can be calculated (Faes et al 2017;Lindberg et al 2018) (see Section 2.4.2). Another characteristic of additively manufactured structures is the drastic dependency on local part thickness, which was reported not only for LS (Tasch et al 2018;Wörz and Drummer 2018;Sindinger et al 2020) but also for other polymer-based processes (Bell and Siegmund 2018) and common metal-based AM technologies including selective laser melting (Brown, Everhart, and Dinardo 2016;Barba et al 2020), electron beam melting (Algardh et al 2016;Wang et al 2020b) and laser powder bed fusion (Roach et al 2020). Tasch et al (2018) disclosed a distinct drop of almost 40 % in Young's modulus (E ⊥ ) from a thickness of 2 to 0.6 mm in LS Pa12 tensile coupons built in z-direction.…”

“…Explanations have been contributed to effects that are more negligible for thick parts but become critical as the cross-section decreases. These, to a minor degree, were attributed to a reduction of effective load bearing area, due to surface roughness and internal voids, as well as process condition-induced inhomogeneous microstructure over the cross-section, which is stipulated to play the principal role (Algardh et al 2016;Brown, Everhart, and Dinardo 2016;Wörz and Drummer 2018;Tasch et al 2018;Bell and Siegmund 2018;Sindinger et al 2020;Barba et al 2020;Roach et al 2020;Wang et al 2020b).…”

Structural Response Prediction of Thin-Walled Additively Manufactured Parts Considering Orthotropy, Thickness Dependency and Scatter

“…The described directional behavior of PBF structures is furthermore superimposed by a severe but often overlooked thickness dependency, whereby Young’s modulus, ultimate strength and failure strain are positively correlated to part thickness. Due to the relevancy for lightweight design that relies on the utilization of thin structural members, this effect has recently gained more attention and was reported in a multitude of studies for metal- [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ] as well as polymer-based PBF [ 29 , 30 , 31 ] and other processes like fused deposition modeling [ 32 ] and material jetting [ 33 ]. It appears plausible that the behavior is likewise inherent in laser-sintered short-fiber-reinforced polymers; however, no published articles were found addressing this issue.…”