Additive Manufacturing: Qualification and Certification: Process and Control
Sponsored by: TMS Additive Manufacturing Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomaterials Committee
Program Organizers: Faramarz Zarandi, RTX Corporation; Jacob Hochhalter, University of Utah; Douglas Wells, NASA Marshall Space Flight Center; Richard Russell, NASA Kennedy Space Center; Mohsen Seifi, ASTM International/Case Western Reserve University; Eric Ott, GE Additive; Mark Benedict, Air Force Research Laboratory; Craig Brice, Colorado School Of Mines; J Hector Sandoval, Lockheed Martin

Tuesday 2:00 PM
November 3, 2020
Room: Virtual Meeting Room 8
Location: MS&T Virtual

Session Chair: Craig Brice, Colorado School Of Mines; Hector Sandoval, Lockheed Martin


2:00 PM  Invited
Reducing Heat Buildup and Regularizing Melt Pool Dimensions in Laser Powder Bed Fusion through a “Powder Moat” Scan Strategy: Evan Diewald1; Christian Gobert1; Nicholas Jones1; Jack Beuth1; 1Carnegie Mellon University
    The stochastic nature of the laser powder bed fusion (LPBF) process results in undesired defects such as porosity, residual stress, and inconsistent microstructure. Many flaws are related to erratic thermal conditions caused, in part, by suboptimal infill scanning strategies. This article presents an approach for reducing heat buildup in metals additive manufacturing (AM) that can be implemented within the bounds of most commercial machines. The “Powder Moat” strategy, where a thin wall is built outside the boundaries of the intended part, eliminates in-plane hotspots by inducing a predictable delay after each raster. A semi-analytical model is used to generate process maps of delay times and moat thicknesses as a function of laser power and velocity, and the approach is validated through high speed imaging. By standardizing melt pool dimensions and thermal distributions, the strategy serves the broad goal of process qualification and is a practical step toward increasing AM’s reliability.

2:30 PM  Invited
Ensuring Build Quality thru Physics-based Support Design Optimization for Residual Stress: Albert To1; Lin Cheng1; Qian Chen1; Xuan Liang1; 1University of Pittsburgh
    A new design optimization method based on fast process simulation is proposed for the design of support structure for reducing residual stress and distortion in laser powder bed fusion (LPBF) processed metallic components. First, a modified inherent strain method is proposed for fast prediction of the stress and deformation. Second, a projection scheme is proposed to map the domain of support structure for a given solid component, in which the minimum support area is found for the next step. Third, lattice structure topology optimization is applied to minimize the mass consumption of support structure subjected to yield stress constraints. This not only prevent failure of the LPBF builds by limiting the residual stress below the yield strength, but also reduce material required for support structure. Both numerical simulation and experiments prove that the proposed method can ensure success of metal LPBF builds.

3:00 PM  Invited
Unveiling the Relationships between Powder Bed Conditions and Materials Quality during Selective Laser Melting: Tan Phuc Le1; Matteo Seita1; 1Nanyang Technological University
    All powder bed additive manufacturing processes involve spreading a thin layer of powder feedstock that is selectively consolidated, either thermally or chemically. The characteristics of this powder layer—such as its packing density, thickness uniformity, and contamination level—strongly affect the quality of the resulting parts. In this work, we demonstrate the capability of acquiring this information in-situ—layer by layer—using a “powder bed scanner” (PBS). The PBS consists of a re-coater that integrates a contact image sensor to image the entire powder bed at high spatial resolution. We use the PBS during selective laser melting of stainless steel 316L and correlate site-specific powder bed features to the porosity and microstructure of 3D printed samples. These results provide insights into the relationships between powder bed conditions and part quality, and open a new pathway to in-line monitoring of powder bed additive manufacturing processes.

3:20 PM  
Recyclability of Ti-6Al-4V Powders Used in Additive Manufacturing: Nicholas Derimow1; Nikolas Hrabe1; 1National Institute of Standards and Technology
    Titanium alloys are widely used in industry for their high strength-to-weight ratios and good corrosion resistance. However, titanium’s affinity for oxidation leads to costly processing environments to maintain purity of the finished product. The lifetime of a Ti-6Al-4V powder batch is determined by how many times it can be recycled across builds, as oxygen pickup will increase to a level that is no longer acceptable and will need to be discarded. The source of oxygen is often assumed to be water vapor trapped in the powder during exposure to atmosphere during powder handling outside the AM machine. However, other potential sources of oxygen have not been investigated despite the potential to have an equivalent magnitude effect. This example knowledge gap, and others presented in this talk, will demonstrate significant opportunity to further optimize this process to achieve increased powder batch lifetime and reduce overall process cost.

3:40 PM  
CT Based Analysis of Generation and Characterization of Parameter- and Process-induced Defects in Powder Bed Fusion Additive Manufacturing: Brett Diehl1; Abdalla Nassar1; David Corbin1; 1The Applied Research Laboratory
    Post-build detection, in-situ sensing, and prevention of defects in powder bed fusion additive manufacturing (PBFAM) are of significant interest to both researchers and end-users of the technology. However, these efforts have been stifled by a lack of an ability to reliably produce voids which are characteristic of natural ones. The goal of our work is to develop and implement control methods for producing defects characteristic of lack of fusion, keyholing, and spatter particles becoming entrained in the meltpool. These methods are implemented on a laser powder bed fusion machine, as it builds Ti-6Al-4V components, with otherwise optimized (default) processing parameters. After the build, the size, distribution, and morphology of the purposefully induced defects are confirmed with high-resolution X-ray computed tomography, demonstrating the ability to produce defects of known size and morphology at known locations.