Identification of the constitutive equation and the failure points locus based on the mechanics of orthogonal metal cutting.

Peer reviewed: YesNRC publication: Ye

Laser Powder Bed Fusion of Unalloyed Tungsten: A Review of Process, Structure, and Properties Relationships

Tungsten (W) as a structural component has grown roots in many special applications owing to its radiation-shielding capabilities and its properties at elevated temperatures. The high ductile-brittle transition temperature (DBTT) and the very high melting point of tungsten however have limited its processability to certain technologies such as powder metallurgy. Laser powder bed fusion (LPBF) has been introduced in recent years as an alternative for manufacturing tungsten parts to overcome the design limitations posed by powder metallurgy technology. A review of the literature shows significant improvements in the quality of tungsten components produced by LPBF, implying a strong potential for manufacturing tungsten with this technology and a need for further research on this subject. This review paper presents the current state-of-the-art in LPBF of unalloyed tungsten, with a focus on the effect of process parameters on the developed structure/properties and identifies current knowledge gaps

Negative Thermal Expansion Metamaterials: A Review of Design, Fabrication, and Applications

Most materials conventionally found in nature expand with an increase in temperature. In actual systems and assemblies like precision instruments, this can cause thermal distortions which can be difficult to handle. Materials with a tendency to shrink with an increase in temperature can be used alongside conventional materials to restrict the overall dimensional change of structures. Such structures, also called negative-thermal-expansion materials, could be crucial in applications like electronics, biomedicine, aerospace components, etc., which undergo high changes in temperature. This can be achieved using mechanically engineered materials, also called negative thermal expansion (NTE) mechanical metamaterials. Mechanical metamaterials are mechanically architected materials with novel properties that are rare in naturally occurring materials. NTE metamaterials utilize their artificially engineered architecture to attain the rare property of negative thermal expansion. The emergence of additive manufacturing has enabled the feasible production of their intricate architectures. Industrial processes such as laser powder bed fusion and direct energy deposition, both utilized in metal additive manufacturing, have proven successful in creating complex structures like lattice formations and multimaterial components in the industrial sector, rendering them suitable for manufacturing NTE structures. Nevertheless, this review examines a range of fabrication methods, encompassing both additive and traditional techniques, and explores the diverse materials used in the process. Despite NTE metamaterials being a prominent field of research, a comprehensive review of these architected materials is missing in the literature. This article aims to bridge this gap by providing a state-of-the-art review of these metamaterials, encompassing their design, fabrication, and cutting-edge applications

Process–Structure–Property Relationships of Copper Parts Manufactured by Laser Powder Bed Fusion

The process–structure–property relationships of copper laser powder bed fusion (L-PBF)-produced parts made of high purity copper powder (99.9 wt %) are examined in this work. A nominal laser beam diameter of 100 μm with a continuous wavelength of 1080 nm was employed. A wide range of process parameters was considered in this study, including five levels of laser power in the range of 200 to 370 W, nine levels of scanning speed from 200 to 700 mm/s, six levels of hatch spacing from 50 to 150 μm, and two layer thickness values of 30 μm and 40 μm. The influence of preheating was also investigated. A maximum relative density of 96% was obtained at a laser power of 370 W, scanning speed of 500 mm/s, and hatch spacing of 100 μm. The results illustrated the significant influence of some parameters such as laser power and hatch spacing on the part quality. In addition, surface integrity was evaluated by surface roughness measurements, where the optimum Ra was measured at 8 μm ± 0.5 μm. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were performed on the as-built samples to assess the impact of impurities on the L-PBF part characteristics. The highest electrical conductivity recorded for the optimum density-low contaminated coils was 81% IACS

The Effect of MQL on Tool Wear Progression in Low-Frequency Vibration-Assisted Drilling of CFRP/Ti6Al4V Stack Material

In this paper, the tool wear mechanisms for low-frequency vibration-assisted drilling (LF-VAD) of carbon fiber-reinforced polymer (CFRP)/Ti6Al4V stacks are investigated at various machining parameters. Based on the kinematics analysis, the effect of vibration amplitude on the chip formation, uncut chip thickness, chip radian, and axial velocity are examined. Subsequently, the effect of LF-VAD on the cutting temperature, tool wear, delamination, and geometrical accuracy was evaluated for different vibration amplitudes. The LF-VAD with the utilization of minimum quantity lubricant (MQL) resulted in a successful drilling process of 50 holes, with a 63% reduction in the cutting temperature. For the rake face, LF-VAD reduced the adhered height of Ti6Al4V by 80% at the low cutting speed and reduced the crater depth by 33% at the high cutting speed. On the other hand, LF-VAD reduced the flank wear land by 53%. Furthermore, LF-VAD showed a significant enhancement on the CFRP delamination, geometrical accuracy, and burr formation

Z-list based modeling of cutting geometry and cutting forces in 5-axis machining of complex surfaces.

Peer reviewed: YesNRC publication: Ye

Influence of Shot Peening on AlSi10Mg Parts Fabricated by Additive Manufacturing

The additive manufacturing (AM) of aluminum alloys promises to considerably enhance the performance of lightweight critical parts in various industrial applications. AlSi10Mg is one of the compatible Al alloys used in the selective laser melting of lightweight components. However, the surface defects obtained from the as-built parts affect their mechanical properties, and thus represent an obstacle to using them as final products. This study aims to improve the surface characteristics of the as-built AlSi10Mg parts using shot peening (SP). To achieve this goal, different SP intensities were applied to various surface textures of the as-built samples. The SP results showed a significant improvement in the as-built surface topography and a higher value of effective depth using 22.9 A intensity and Gp165 glass beads. The area near the shot-peened surface showed a significant microstructure refinement to a specific depth due to the dynamic precipitation of nanoscale Si particles. Surface hardening was also detected and high compressive residual stresses were generated due to severe plastic deformation. The surface characteristics obtained after SP could result in a significant improvement in the mechanical properties and fatigue strength, and thus promise performance enhancement for critical parts in various industrial applications

Chip Morphology and Delamination Characterization for Vibration-Assisted Drilling of Carbon Fiber-Reinforced Polymer

Carbon fiber-reinforced polymers (CFRP) are widely used in the aerospace industry. A new generation of aircraft is being built using CFRP for up to 50% of their total weight, to achieve higher performance. Exit delamination and surface integrity are significant challenges reported during conventional drilling. Exit delamination influences the mechanical properties of machined parts and, consequently, reduces fatigue life. Vibration-assisted drilling (VAD) has much potential to overcome these challenges. This study is aimed at investigating exit delamination and geometrical accuracy during VAD at both low- and high-frequency ranges. The kinematics of VAD are used to investigate the relationship between the input parameters (cutting speed, feed, vibration frequency, and amplitude) and the uncut chip thickness. Exit delamination and geometrical accuracy are then evaluated in terms of mechanical and thermal load. The results show a 31% reduction in cutting temperature, as well as a significant enhancement in exit delamination, by using the VAD technology

The Effect of Selective Laser Melting Process Parameters on the Microstructure and Mechanical Properties of Al6061 and AlSi10Mg Alloys

Additive manufacturing (AM) offers customization of the microstructures and mechanical properties of fabricated components according to the material selected and process parameters applied. Selective laser melting (SLM) is a commonly-used technique for processing high strength aluminum alloys. The selection of SLM process parameters could control the microstructure of parts and their mechanical properties. However, the process parameters limit and defects obtained inside the as-built parts present obstacles to customized part production. This study investigates the influence of SLM process parameters on the quality of as-built Al6061 and AlSi10Mg parts according to the mutual connection between the microstructure characteristics and mechanical properties. The microstructure of both materials was characterized for different parts processed over a wide range of SLM process parameters. The optimized SLM parameters were investigated to eliminate internal microstructure defects. The behavior of the mechanical properties of parts was presented through regression models generated from the design of experiment (DOE) analysis for the results of hardness, ultimate tensile strength, and yield strength. A comparison between the results obtained and those reported in the literature is presented to illustrate the influence of process parameters, build environment, and powder characteristics on the quality of parts produced. The results obtained from this study could help to customize the part’s quality by satisfying their design requirements in addition to reducing as-built defects which, in turn, would reduce the amount of the post-processing needed