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 processes such as 3D printing use time-consuming, stepwise layer-by-layer approaches to object fabrication. We demonstrate the continuous generation of monolithic polymeric parts up to tens of centimeters in size with feature resolution below 100 micrometers. Continuous liquid interface production is achieved with an oxygen-permeable window below the ultraviolet image projection plane, which creates a "dead zone" (persistent liquid interface) where photopolymerization is inhibited between the window and the polymerizing part. We delineate critical control parameters and show that complex solid parts can be drawn out of the resin at rates of hundreds of millimeters per hour. These print speeds allow parts to be produced in minutes instead of hours.

http://science.sciencemag.org/content/sci/347/6228/1349.full.pdf

Continuous liquid interface production of 3D objects

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

The metallurgy and processing science of metal additive manufacturing

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing

Three-dimensional printing of viscoelastic inks to create porous, elastomeric architectures with mechanical properties governed by the ordered arrangement of their sub-millimeter struts is reported. Two layouts are patterned, one resembling a “simple cubic” (SC)-like structure and another akin to a “face-centered tetragonal” (FCT) configuration. These structures exhibit markedly distinct load response with directionally dependent behavior, including negative stiffness. More broadly, these findings suggest the ability to independently tailor mechanical response in cellular solids via micro-architected design. Such ordered materials may one day replace random foams in mechanical energy absorption applications.

Three-Dimensional Printing of Elastomeric, Cellular Architectures with Negative Stiffness

3D x-ray computed tomography (CT), using conventional laboratory-based 	x-ray sources, has been used in the past to image multiple levels of interconnects in 3D microelectronic packages. These conventional x-ray sources can provide high resolution images with throughput times (TPT) of several hours. However, this can only be performed on localized areas of about 	1–2 mm2, which gravely limits the application of 3D x-ray CT in the field of microelectronic packages with sizes usually in the range of 100–3600 mm2. An alternative to laboratory-based x-ray sources is synchrotron radiation, which can produce large area collimated beams for high flux x-ray imaging over a much larger field of view (FOV) than conventional sources. Synchrotrons can potentially image an entire 3D stacked chip package at high resolutions in less than an hour. Here, we present results using the micro-CT line at the advanced light source synchrotron to image an entire 16 × 16 mm system in a package in times as low as 3 min, demonstrating several orders of magnitude increase in the ratio of FOV to TPT as compared to laboratory-based x-ray methods.

Synchrotron Radiation Microtomography for Large Area 3D Imaging of Multilevel Microelectronic Packages

The recent applications of 3D X-ray computed tomography (CT) in microelectronic packages, including nondestructive failure analysis, defect monitoring in solder joints and Cu vias, and progressive reliability study of solder voids, electron migration induced void nucleation in solder joints, and void evolution in Cu vias are reviewed. The high resolution and non-destructive 3D X-ray CT data has proven to be highly valuable in package assembly process development, quality control and reliability risk assessment; however, the field of view of current lab-scale 3D X-ray CT technology is limited to about 1-2mm 2 localized area at micron level resolution, due to its low brightness and nonparallel X-ray beam resulting in long data acquisition time. Synchrotron X-ray sources, on the other hand, can provide large area collimated beams with high brightness, which allows imaging within 3-20 minutes an entire 3D package, including Si, underfill, multiple levels of solder joints, and dielectric layers, Cu vias as well as through holes in multiple substrates. The limitation of current 3D X-ray CT techniques as well as directions for next generation 3D X-ray CT techniques provided by the synchrotron X-ray study of 3D packages are discussed in this paper.

Holly D. Barth

Papers

Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing

Three-Dimensional Printing of Elastomeric, Cellular Architectures with Negative Stiffness

Synchrotron Radiation Microtomography for Large Area 3D Imaging of Multilevel Microelectronic Packages

High resolution and fast throughput-time X-ray computed tomography for semiconductor packaging applications

Cellular Solids: Three‐Dimensional Printing of Elastomeric, Cellular Architectures with Negative Stiffness (Adv. Funct. Mater. 31/2014)