Scanning Manufacturing Parameters Determining the Residual Stress State in LPBF IN718 Small Parts

Abstract

The influence of scan strategy on the residual stress (RS) state of an as-built IN718 alloy produced by means of laser powder bed fusion (LPBF) is investigated. Two scan vector rotations (90 -alternation and 67 -rotation), each produced following two different scan vector lengths (long and short), are used to manufacture four rectangular prisms. Neutron diffraction (ND) and laboratory X-ray diffraction (XRD) techniques are used to map the bulk and surface RS state, respectively. The distortion induced upon removal from the baseplate is measured via profilometry. XRD measurements show that the two long scan vector strategies lead to higher RS when compared with the equivalent short scan vector strategies. Also, the 67 -rotation strategies generate lower RS than their 90 -alternation counterparts. Due to the lack of reliable stress-free d 0 references, the ND results are analyzed using von Mises stress. In general, ND results show significant RS spatial non-uniformity. A comparison between ND and distortion results indicates that the RS component parallel to the building direction (Z-axis) has a predominant role in the Z-displacement. The use of a stress balance scheme allows to discuss the d 0 variability along the length of the specimens, as well as examine the absolute RS state.

Diffraction-Based Residual Stress Characterization in Laser Additive Manufacturing of Metals

“…As Thiede et al [82] have concluded, a shift due to different local chemical segregation prevented the use of it as a reference (Figure 9b). Similar findings were made by Kolbus et al [103] and more recently Serrano-Munoz et al [107].…”

An Efficient Track-Scale Model for Laser Powder Bed Fusion Additive Manufacturing: Part 2—Mechanical Model

“…The S YY stress plots in Figure 14 shows layer-laminated structure for the 90 °and 45 °rotation patterns. This is due to the directional stresses and mismatches between the layers, resulting in a nonhomogenous stress distribution as discussed in (Kruth et al, 2012;Parry et al, 2016;Serrano-Munoz et al, 2021). The S YY component is significantly lower (>2X lower than Sxx) than the other directions due to the thin wall builds, as explained in Effect of Laser Power on Residual Stresses.…”

“…Past studies have shown that surface roughness significantly affects the residual stress measurements (Serrano-Munoz et al, 2021). Moreover, the residual stress of the final LPBF build layers is not essential as the free surface allows stress relaxation.…”

“…Laser printing patterns have been previously investigated by other researchers (Kruth et al, 2012;Setien et al, 2019;Serrano-Munoz et al, 2021). Generally, the scan strategy affects the final microstructure and part distortion more than the laser power (Xiao et al, 2020).…”

“…Laser path rotation reduces the directionality of the residual stresses and creates a more homogenous quasi-isotropic stress state (Parry et al, 2016;Setien et al, 2019). However, these studies focused mainly on "island" scanning patterns for thick part components (Cheng and Chou 2015;Serrano-Munoz et al, 2021). To the authors knowledge, there have been no studies on the effect of scanning patterns on thin-wall structures.…”