Effects of Energy Parameters on Dimensional Accuracy When Joining Stainless-Steel Powders with Heterogeneous Metal Substrates

Abstract

This work presents some breakthroughs for obtaining high dimensional accuracy and reliable geometrical tolerance in the joining of stainless-steel powders with heterogeneous substrates. In the laser melting process, the interfacial energy fractions and forces acting at the solid–liquid surface of the melting powders can effectively vary their geometrical shapes and positions before they turn into the liquid phase. When the interfacial free energy is low, the melting powders are near molten, thus the successive volumetric changes can alter the layered geometry and positions. This assumption was validated by a powder-bedding additive manufacturing process to consolidate stainless-steel 316L powders (SLM 316L) on a thin heterogeneous stainless-steel substrate. Experiments were carried out to reveal the effects of the process parameters, such as laser power (100–200 W), exposure duration (50–100 µs) and point distance (35–70 µm) on the resulting material density and porosity and the corresponding dimensional variations. A fractional factorial design of experiment was proposed and the results of which were analyzed statistically using analysis of variances (ANOVA) to identify the influence of each operating factor. High energy densities are required to achieve materials of high density (7.71 g/cm3) or low porosity (3.15%), whereas low energy densities are preferable when the objective is dimensional accuracy (0.016 mm). Thermally induced deflections (~0.108 mm) in the heterogeneous metal substrate were analyzed using curvature plots. Thermally induced deformations can be attributed to volumetric energy density, scanning strategy, and the lay-up orientation. The parametric optimizations for increasing in dimensional accuracy (Z1: ~0.105 mm), or in material density (~7.71 g/cm3) were proven with high conversion rates of 88.2% and 96.4%, respectively, in validation runs.

A Prediction Model for Additive Manufacturing of Inconel 718 Superalloy

“…The importance of this parameter can be attributed to the fact that the deviation in height of the sample can prevent uniform spreading of the powder, leading to failure in fabrication due to the collision between a part and the recoater. In this case, several studies investigated the effect of processing parameters on the dimensional accuracy; the height of the sample was considered as an important criterion [24,[47][48][49]. Similarly, in this study the sample height was selected as an output to represent the dimensional accuracy and the deviation from the designed value.…”

Surface morphology and dimensional accuracy of additively manufactured Ti-6Al-4V alloy: Effect of variable scanning speed with constant laser power in widespread energy density

“…4 The use of excessive energy density involves widening of scanning track leading to a balling effect on the fabricated layers. 5,6 Therefore, it is essential to identify the appropriate process window in the fabrication of defectless Ti-6Al-4V alloy parts.…”

“…Some researchers have observed variations in part dimensions from the target size fabricated with the use of the L-PBF process. 5,6,18 A difference in melt pool behaviour causes dimensional variations in fabricated samples related to several factors. During layer fabrication, the thermal expansion caused by VED leads to deviations from the targeted layer dimensions.…”