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Browsing Conference Proceedings and Journals by Author "Aboud Gatrell, Bernice"
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Item Expert Survey to Understand and Optimize Part Orientation in Direct Metal Laser Sintering(University of Texas at Austin, 2017) Hoelzle, David; Peng, Hao; Ghasri-Khouzani, Morteza; Gong, Shan; Attardo, Ross; Ostiguy, Pierre; Aboud Gatrell, Bernice; Budzinski, Joseph; Tomonto, Charles; Neidig, Joel; Shankar, M. Ravi; Billo, Richard; Go, David B.The additive manufacturing (AM) process Direct Metal Laser Sintering (DMLS) uses a layer-by-layer workflow to build complex architecture metal structures in low-volumes. The primary process failure mechanism is a thermal stress driven thermal distortion that yields out-of-tolerance manufacture or complete process failure. However, DMLS design experts have developed heuristic rules to optimize the part orientation and support structure to reduce the likelihood of failure. We believe that experts innately attempt to minimize the design metrics of support volume (V), support-to-part surface area (A), maximal cross-sectional area of the slicing planes (X), parallelism of part faces with the recoater blade (P), and part height (H); however, it is unclear what relative weighting of each metric the expert uses. This manuscript details an interactive expert survey, the statistical analysis of the survey responses, and the synthesis of an automatic algorithm for part orientation based on survey data. We received responses from 18 experts and 151 total part orientation responses. The median survey respondent had greater than four years of DMLS experience. Our analysis shows that the expert attempts to minimize metric V the most, metric X the second most, and metric H the third most; experts put essentially no weight on metrics A and P. The manuscript concludes with two orientation design studies where the expert survey responses are used in a least squares minimization algorithm to automatically orient the part for DMLS manufacture. As a comparison set, novice users were instructed to orient the parts for best DMLS printing success without using the tool and required multiple attempts to successfully print the test parts. The automatically oriented parts failed on our first iteration of the code. The manuscript concludes with our proposed modifications to the code to improve results.Item Optimization of Build Orientation for Minimum Thermal Distortion in DMLS Metallic Additive Manufacturing(University of Texas at Austin, 2017) Peng, Hao; Ghasri-Khouzani, Morteza; Gong, Shan; Attardo, Ross; Ostiguy, Pierre; Aboud Gatrell, Bernice; Budzinski, Joseph; Tomonto, Charles; Neidig, Joel; Shankar, M. Ravi; Billo, Richard; Go, David B.; Hoelzle, DavidThe additive manufacturing (AM) process direct metal laser sintering (DMLS) can quickly produce complex parts. However, thermal stress in DMLS may induce thermal distortion and cause build failure. This manuscript presents an optimization algorithm for the build orientation in DMLS to minimize thermal distortion. The algorithm is built on the foundation of two coupled thermal and thermo-mechanical models developed in our previous work. The DIRECT search method and a universal objective function for thermal distortion were used. Constraints were included to rule out build orientations resulting in overheating or excessive oxidation. The optimization algorithm was tested on a rectangular bar and a complex, contoured part. Both parts were printed using an EOS M290 machine, and measured by a coordinate measuring machine. In comparison to build orientations chosen by two novice operators, the optimized build orientations gave significant reduction in the thermal distortion and number of print trials before print success.Item Part-Scale Model for Fast Prediction of Thermal Distortion in DMLS Additive Manufacturing Part 2: A Quasi-Static Thermomechanical Model(University of Texas at Austin, 2016) Peng, Hao; Go, David B.; Billo, Rick; Gong, Shan; Ravi Shankar, M.; Aboud Gatrell, Bernice; Budzinski, Joseph; Ostiguy, Pierre; Attardo, Ross; Tomonto, Charles; Neidig, Joel; Hoelzle, DavidThe direct metal laser sintering (DMLS) additive manufacturing process can quickly produce complex parts with excellent mechanical properties. However, thermal stress accumulated in the layer-by-layer build cycles of DMLS may induce part distortion and even cause the failure of the whole build process. This paper is the second part of two companion papers that present a part-scale model for fast prediction of temperature history and part distortion in DMLS. In this paper, a quasi-static thermomechanical (QTM) model is built to estimate the thermal distortion of entire parts in DMLS. Firstly, the thermal contraction in each build cycle is modeled as a quasi-static loading process; the final thermal stress accumulated in the parts is the superposition of thermal stress generated in each build cycle. Secondly, the stress relaxation process after the parts are cut off from the substrate is modeled, and final distortion of the parts is predicted with thermal stress calculated from the thermal contraction processes. In comparison to existing transient thermomechanical models, the QTM can predict thermal distortion in DMLS with much faster computational speed, and a comparison against experiment shows less than 10% error.