Abstract:A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce full-density metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of the literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging and design-of-experiments), support structure optimization and overhang feature design; approximately 143 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs and potential future research directions are discussed in-depth in light of the present review.

Abstract:One of the most essential components of the fused deposition modeling (FDM) additive manufacturing (AM) process is the build plate, the surface upon which the part is constructed. These are typically made from aluminum or glass, but there are clear disadvantages to both and restrictions on which materials can be processed on them successfully. This study examined the suitability of heated aluminum-polycarbonate (AL-PC) composite print beds for FDM, looking particularly at the mechanical properties, thermal behavior, deformation behavior, bonding strength with deposited material, printing quality, and range of material usability. Theoretical examination and physical experiments were performed for each of these areas; the results were compared to similar experiments done using heated aluminum and aluminum-glass print beds. Ten distinct materials (ABS, PLA, PET, HIPS, PC, TPU, PVA, nylon, metal PLA, and carbon-fiber PLA) were tested for printing performance. The use of a heated AL-PC print bed was found to be a practical option for most of the materials, particularly ABS and TPU, which are often challenging to process using traditional print bed types. Generally, the results were found to be equivalent to or superior to tempered glass and superior to standard aluminum build plates in terms of printing capability.

A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce full-density metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion, and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization, and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging, and design-of-experiments), support structure optimization, and overhang feature design; approximately 140 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs, and potential future research directions are discussed in-depth in light of the present review.

Solid-propellant rockets are used for many applications, including military technology, scientific research, entertainment, and aerospace education. This study explores a novel method for design modularization of the rocket airframes, utilizing additive manufacturing (AM) technology. The new method replaces the use of standard part subsystems with complex multi-function parts to improve customization, design flexibility, performance, and reliability. To test the effectiveness of the process, two experiments were performed on several unique designs: (1) ANSYS CFX ® simulation to measure the drag coefficients, the pressure fields, and the streamlines during representative flights and (2) fabrication and launch of the developed designs to test their flight performance and consistency. Altitude and 3-axis stability was measured during the eight flights via an onboard instrument package. Data from both experiments demonstrated that the designs were effective, but varied widely in their performance; the sources of the performance differences and errors were documented and analyzed. The modularization process reduced the number of parts dramatically, while retaining good performance and reliability. The specific benefits and caveats of using extrusion-based 3-D printing to produce airframe components are also demonstrated.

Empirical studies have shown complexity metrics to be good predictors of testing effort and maintainability in traditional, imperative programming languages. Empirical validation studies have also shown that complexity is a good predictor of initial quality and reliability in object-oriented (OO) software. To date, one of the most empirically validated OO complexity metrics is the Chidamber and Kemerer Weighted Methods in a Class (WMC). However, there are many more OO complexity metrics whose predictive power has not been as extensively explored. In this study, we explore the predictive ability of several complexity-related metrics for OO software that have not been heavily validated. We do this by exploring their ability to measure quality in an evolutionary software process, by correlating these metrics to defect data for six versions of Rhino, an open-source implementation of JavaScript written in Java. Using statistical techniques such as Spearman's correlation, principal component analysis, binary logistic regression models and their respective validations, we show that some lesser known complexity metrics includingMichura et al.'s standard deviation method complexity and Etzkorn et al.'s average method * Correspondence to: Hector M. Olague, U.S. Army Space and Missile Defense Command,complexity are more consistent predictors of OO quality than any variant of the Chidamber and Kemerer WMC metric. We also show that these metrics are useful in identifying fault-prone classes in software developed using highly iterative or agile software development processes.

One of the fundamental characteristics of additively processed materials is that they are naturally anisotropic; this variance in mechanical properties is primarily generated through the formulation of patterned shell and in-filled regions within the material during processing. This paper describes the formulation and results of a study to ascertain the impact strength of various full–infill polymer-based materials processed in various orientations and angles via fused deposition modeling. Ten different materials were tested using seven different hatch angles and three print orientations. Seven different pure materials were tested, as well as three composites; these were acrylonitrile butadiene styrene, standard polylactic acid, high-temperature polylactic acid, high-impact polystyrene, nylon, polyethylene terephthalate + glycol, polycarbonate, aluminum polylactic acid, wood polylactic acid, and carbon–fiber polylactic acid. All experiments were carried out using ASTM IZOD Type E tests with a 2.7J pendulum. Five replications of each test combination were collected, for a total of 1050 tests. The results showed that the shell orientation and raster angle were primary drivers in determining impact properties, as they strongly influenced the crack length and path though the material during fracture. This was especially clear for the polycarbonate, nylon, and polyethylene terephthalate + glycol which underwent large plastic deformation during the tests. It was further observed that the impact toughness was inversely correlated with test repeatability, with the toughest materials having the highest variability between test replications.

A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce fulldensity metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion, and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization, and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging, and design-of-experiments), support structure optimization, and overhang feature design; approximately 140 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs, and potential future research directions are discussed in-depth in light of the present review.

This paper describes the collection of a large dataset (6930 measurements) on dimensional error in the fused deposition modeling (FDM) additive manufacturing process for full-density parts. Three different print orientations were studied, as well as seven raster angles ( 0 ∘ , 15 ∘ , 30 ∘ , 45 ∘ , 60 ∘ , 75 ∘ , and 90 ∘ ) for the rectilinear infill pattern. All measurements were replicated ten times on ten different samples to ensure a comprehensive dataset. Eleven polymer materials were considered: acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), high-temperature PLA, wood-composite PLA, carbon-fiber-composite PLA, copper-composite PLA, aluminum-composite PLA, high-impact polystyrene (HIPS), polyethylene terephthalate glycol-enhanced (PETG), polycarbonate, and synthetic polyamide (nylon). The samples were ASTM-standard impact-testing samples, since this geometry allows the measurement of error on three different scales; the nominal dimensions were 3 . 25 mm thick, 63 . 5 mm long, and 12 . 7 mm wide. This dataset is intended to give engineers and product designers a basis for judging the accuracy and repeatability of the FDM process for use in manufacturing of end-user products.