There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

This study presents a unique melting strategy in electron beam-powder bed fusion of Alloy 718 to tailor the grain morphology from the typical columnar to equiaxed morphology. For this transition, a specific combination of certain process parameters, including low scanning speeds (400–800 mm/s), wide line offsets (300–500 μm) and a high number of line order (#10) was selected to control local solidification conditions in each melt pool during the process. In addition, secondary melting of each layer with a 90° rotation with respect to primary melting induced more vigorous motions within the melt pools and extensive changes in thermal gradient direction, facilitating grain morphology tailoring. Four different types of microstructures were classified according to the produced grain morphology depending on the overlap zone between two adjacent melt pools, i.e., fully-columnar (overlap above 40 %), fully-equiaxed (overlap below 15 %), mixed columnar-equiaxed grains, and hemispherical melt pools containing mixed columnar-equiaxed grains (overlap ~20–25 %). The typical texture was ; however, the texture was reduced significantly through the transition from the columnar to equiaxed grain morphology. Along with all four different microstructures, shrinkage defects and cracks were also identified which amount of them reduced by a reduction in areal energy input. The hardness was increased through the transition, which was linked to the growth of the γʺ precipitates and high grain boundary density in the fully-equiaxed grain morphology.

Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion

The influence of α precipitate morphology on the mechanical properties of additively manufactured Ti-5Al-5V-5Mo-3Cr (Ti-5553) is evaluated. Initially, Archimedes density measurements on cylindrical Ti-5553 samples printed using laser powder-bed fusion process were employed to determine the influence of parameters on the conduction melting band. The lowest and the highest volumetric energy densities (VEDs) identified in the conduction band were then selected for further characterization. X-ray Computed Tomography (XCT) was used to validate the expected high relative densities, the nature and distribution of defects in the samples printed at the two selected VEDs. Uniaxial tensile and impact tests were carried out on the samples printed at the two selected process parameter sets. The as-printed samples reached a notable fracture strain of 30 ± 5%. However, the impact-tested samples exhibited poor impact toughness. The results were compared and correlated with observed microstructural features. Electron backscatter diffraction, X-ray diffraction, and optical microscopy (OM) revealed the presence of non-lamellar α particles along the columnar grains in the building direction. The combination of outstanding ductility coupled with poor impact toughness was attributed to the presence of intragranular non-lamellar α particles. Fractured surfaces examined under scanning electron microscopy indicate a bi-modal fracture mode. Microhardness profiles and the corresponding OM images confirmed a grain size difference at the core-contour interface, which was attributed as a major contributing factor for the bi-modal fracture mode. 

Effect of non-lamellar α precipitate morphology on the mechanical properties of Ti5553 parts made by laser powder-bed fusion at high laser scan speeds

Mo(Si1-x,Alx)2 composites were produced by a pulsed laser reactive selective laser melting of MoSi2 and 30 wt.% AlSi10Mg powder mixture. The parametric study, altering the laser power between 100 and 300 W and scan speed between 400 and 1500 mm·s-1, has been conducted to estimate the effect of processing parameters on printed coupon samples' quality. It was shown that samples prepared at 150-200 W laser power and 400-500 mm·s-1 scan speed, as well as 250 W laser power along with 700 mm·s-1 scan speed, provide a relatively good surface finish with 6.5 ± 0.5 µm-10.3 ± 0.8 µm roughness at the top of coupons, and 9.3 ± 0.7 µm-13.2 ± 1.1 µm side surface roughness in addition to a remarkable chemical and microstructural homogeneity. An increase in the laser power and a decrease in the scan speed led to an apparent improvement in the densification behavior resulting in printed coupons of up to 99.8% relative density and hardness of ~600 HV1 or ~560 HV5. The printed parts are composed of epitaxially grown columnar dendritic melt pool cores and coarser dendrites beyond the morphological transition zone in overlapped regions. An increase in the scanning speed at a fixed laser power and a decrease in the power at a fixed scan speed prohibited the complete single displacement reaction between MoSi2 and aluminum, leading to unreacted MoSi2 and Al lean hexagonal Mo(Si1-x,Alx)2 phase.

Parametric Study on In Situ Laser Powder Bed Fusion of Mo(Si1-x,Alx)2.

A dual-parameter optical sensor having: a fiber optic cable; a fiber Bragg grating (FBG) section provided on the fiber optic cable; and a sleeve affixed to the fiber optic cable such that the sleeve encloses a predetermined portion of the FBG section, wherein the sleeve has a different thermal expansion co-efficient than the fiber optic cable. A method for manufacturing the dual-parameter optical sensor including selecting a fiber optic cable having a predetermined thermal expansion coefficient; forming a fiber Bragg grating (FBG) section on the fiber optic cable; selecting a sleeve having a predetermined thermal expansion co-efficient that is different from the thermal expansion co-efficient of the fiber optical cable; selecting a predetermined portion of the FBG section to be enclosed by the sleeve; and joining the fiber optic cable to the sleeve such that the sleeve encloses the selected predetermined portion of the FBG section.

Multi-parameter optical sensor and method for optical sensor manufacturing

In this work, the spreading properties of biomaterials, while a counter-rotating roller is used in rapid prototyping machines, are modeled and characterized. For modeling, the slab method is used in which biomaterial geometrical properties are incorporated into the model. A pressure dependent plasticity model is used as a constitutive model for biomaterial powders. In addition, the coulomb friction law for the powder-roller interface boundary is incorporated into the model. Size and shape of powder particles as well as roller rotational and linear velocities are considered within the friction coefficient. Powder bed parameters such as compaction pressure, stress distribution and relative density are predicted using the simulation.Copyright © 2007 by ASME

Ehsan Toyserkani

Papers

Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion

Effect of non-lamellar α precipitate morphology on the mechanical properties of Ti5553 parts made by laser powder-bed fusion at high laser scan speeds

Parametric Study on In Situ Laser Powder Bed Fusion of Mo(Si1-x,Alx)2.

Multi-parameter optical sensor and method for optical sensor manufacturing

Modeling and Characterization of Biomaterials Spreading Properties in Powder-Based Rapid Prototyping Techniques