Selective laser sintering/melting (SLS/SLM) of pure Al,Al–Mg,and Al–Si powders: Effect of processing conditions and powder properties

Selective laser sintering/melting (SLS/SLM) processing difficulties of aluminium powders had been attributed to issues associated with laser–materials interaction only while neglecting the role of powder properties. This study provides a wholistic understanding of factors that influence the development of SLS/SLM processing window, densification, and microstructure of pure Al, Al–Mg, and Al–Si powders, fabricated in single and multiple layer parts by exploring the roles of processing and material parameters. It was demonstrated that similarities existing in the SLS/SLM processing maps of the powders could be attributed to similarities in their packing densities with the alloying addition of magnesium and silicon having no predominant effect on their processing maps’ boundaries. Rather, alloying addition has significant effect on the nature of the evolved surface morphology of SLS/SLM processed aluminium powders in their processing windows. In addition, the flow and solidification behaviour of the melt pool of the powders during single layer scan was strongly influenced by the particle morphology and oxygen content of the powders as well as applied energy density. The energy density in the range of 12–16 J/mm² was found to be the threshold below which SLS was predominant and above which SLM occurred for the investigated powders. Moreover, successful oxide disruption phenomena which is necessary for inter-particulate coalescence in multi-layered SLS/SLM processed aluminium powders are found to be mainly controlled by the amount of oxide in the as-received powder, the degree of the uniformity of the distribution of the surface oxide film covering the aluminium particles, the nature of thermal mismatch existing between the oxide film and the parent aluminium particle which was dependent on the phase present in the oxide film. Al–12 wt% Si powder is hereby affirmed as a suitable candidate material for SLS/SLM process due to its low thermal expansion and uniform distribution of its surface oxide films as well as the mullite phase in its oxide film.     

Effects of Daniella oliveri Wood Flour Characteristics on the Processing and Functional Properties of Wood Polymer Composites

The effects of particle sizes/distribution and contents on the processing, changes in microstructure and functional properties of wood polymer composites (WPCs) prepared from virgin high-density polyethylene (vHDPE) and sodium hydroxide (NaOH) treated Daniella oliveri wood flour via compression molding have been explored. Findings from this study suggested that an appropriate choice of wood flour characteristics could improve the interactions between the wood flour and the vHDPE matrix by eliminating incomplete wetting, segregation, and agglomeration of wood flour particles during processing while enhancing mechanical and thermal properties of the composites. Properties of the WPCs were optimized when wood flour of particle sizes/distribution and contents of +210–300 µm and 35 wt%, respectively, were blended with vHDPE matrix.     

Optimization of the Quality Characteristics of Laser-Assisted Cold-Sprayed (LACS) Aluminum Coatings with Taguchi Design of Experiments (DOE)

This study employs Taguchi design of experiments to identify optimal process parameters (deposition temperature, transverse speed, powder feed rate, and operating pressure) associated with quality characteristics (porosity and hardness) of laser-assisted cold-sprayed (LACS) pure aluminum coatings. Optimal quality characteristics of the coatings were obtained by setting deposition temperature at 450°C, transverse speed at 5 mm/s, operating pressure at 30 bar, and powder feed rate at 25 rev/min. This study helps in improving the yield and stability of pure aluminum coatings produced via LACS process while it also reduces its variability which results in high rejection, rework, and warranty costs.     

Deposition Mechanism and Microstructure of Laser-Assisted Cold-Sprayed (LACS) Al-12 wt.%Si Coatings: Effects of Laser Power

Surface treatment is one of the most costly processes for treating metallic components against corrosion. Laser-assisted cold spray (LACS) has an opportunity to decrease those costs particularly in transportation systems, chemical industries, and renewable energy systems. This article highlights some of those potential applications. In the LACS process, a laser beam irradiates the substrate and the particles, thereby softening both of them. Consequently, the particles deform upon impact at the substrate and build up a coating. To circumvent the processing problems associated with cold-spray (CS) deposition of low-temperature, corrosion-resistant Al-12 wt.%Si coatings, a preliminary investigation detailing the effect of laser power on its LACS deposition mechanism and microstructural properties is presented. The deposition efficiency, the microstructure, and the microhardness of the LACS-deposited coatings produced by a 4.4-kW Nd:YAG laser system were evaluated. The outcome of this study shows that pore- and crack-free Al-12 wt.%Si coatings were deposited via softening by laser irradiation and adiabatic shearing phenomena at an optimum laser power of 2.5 kW.     

Applications of imaging systems for the assessment of quality characteristics of bread and other baked goods: A review

One of the most widely researched topics in the food industry is bread quality analysis. Different techniques have been developed to assess the quality characteristics of bakery products. However, in the last few decades, the advancement in sensor and computational technologies has increased the use of computer vision to analyze food quality (e.g., bakery products). Despite a large number of publications on the application of imaging methods in the bakery industry, comprehensive reviews detailing the use of conventional analytical techniques and imaging methods for the quality analysis of baked goods are limited. Therefore, this review aims to critically analyze the conventional methods and explore the potential of imaging techniques for the quality assessment of baked products. This review provides an in-depth assessment of the different conventional techniques used for the quality analysis of baked goods which include methods to record the physical characteristics of bread and analyze its quality, sensory-based methods, nutritional-based methods, and the use of dough rheological data for end-product quality prediction. Furthermore, an overview of the image processing stages is presented herein. We also discuss, comprehensively, the applications of imaging techniques for assessing the quality of bread and other baked goods. These applications include studying and predicting baked goods' quality characteristics (color, texture, size, and shape) and classifying them based on these features. The limitations of both conventional techniques (e.g., destructive, laborious, error-prone, and expensive) and imaging methods (e.g., illumination, humidity, and noise) and the future direction of the use of imaging methods for quality analysis of bakery products are discussed.     

Conceptual Design Framework for Setting Up Aluminum Alloy Powder Production System for Selective Laser Melting (SLM) Process

JOM - Documentation on the correct process and component requirements for setting up efficient aluminum powder production systems capable of manufacturing powder that meets the requirements for the...     

Densification mechanism and microstructural evolution in selective laser sintering of Al-12Si powders

The role of processing parameters on the densification mechanism and microstructural evolution in laser sintered Al-12Si powder has been explored. It was established that both the densification mechanism and microstructural evolution in laser sintered Al-12Si powder were controlled by the specific laser energy input. Analysis of the cross-section of laser sintered microstructures of Al-12Si powders indicated that the tops of the grains in the previous layer are partially re-melted and then undergo epitaxial growth in the next layer where the heat affected zones (HAZ) grain boundaries and solidification grain boundaries (SGBs) are continuous along the fusion boundary.