Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

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

The current national consensus standard for laser safety in the United States is the American National Standard for Safe Use of Lasers (ANSI Z136.1). Over the past few years, a comprehensive rewrite of this standard has been conducted. The updated version of the standard (Z136.1-2000) incorporates a wealth of new bioeffects data and establishes a number of new maximum permissible exposure (MPE) limits for laser safety. The updated standard also includes new procedures for the computation of MPE values, which must be understood by health physicists, laser safety officers, and others in the field of occupational safety. Here we present the first in a series of tutorial articles to clarify laser safety analysis procedures under this new standard. This article deals with the proper application of three rules for determining the appropriate MPE values for repetitively pulsed lasers or repeated exposures from laser beams.

A procedure for multiple-pulse maximum permissible exposure determination under the Z136.1-2000 American National Standard for Safe Use of Lasers

Numerical simulation of the laser welding process in butt-joint specimens

Inelastic effects on springback in metals

An earlier model of deep-penetration laser welding has been simplified in order to provide a useful model of process analysis. This work involves the modelling of the various energy-absorption mechanisms which determine the keyhole shape and thus the dimensions of the melt pool. The penetration depth and weld width (top and bottom) predicted by the model are shown to be in close agreement with experimental results. The widening of the top of the weld seam as a result of Marangoni flow is accurately modelled by introducing an artificially enhanced value for the workpiece's thermal conductivity towards the top of the weld. The model allows analysis of the dependence of the weld profile on the process parameters.

https://iopscience.iop.org/article/10.1088/0022-3727/30/9/004/pdf

An analytical thermodynamic model of laser welding

The oxidation dynamics of laser cutting of mild steel and the generation of striations on the cut edge

This article examines the factors that effect the efficiency of the CO2-laser powder cladding process. By theoretical calculation and experimental work it has been possible to identify how much of the original laser energy contributes to the cladding process and how much is lost to the surrounding environment by reflection, radiation, convection, etc. Every aspect of energy redistribution has been analyzed and quantified and this has led to a deeper understanding of the process. The article concludes with a number of suggestions for improving the efficiency of blown powder laser cladding.

Energy redistribution during CO2 laser cladding

It is important to know how sheet metals behave under complicated loading conditions, since yielding and hardening of a metal are actually dependent upon the stress state and deformation history. A ...

The Bauschinger effect in compression-tension of sheet metals

This paper gives the results of a detailed examination of the particles ejected from the cut zone during CO2 laser cutting of mild and stainless steels. Cuts were carried out over a range of material thickness at the optimum speed for each at a laser power of 900 Watts. Particles ejected from the cut zone were collected and analyzed to establish their chemical and physical characteristics. Analysis techniques included Scanning Electron Microscopy, wet chemical analysis, optical microscopy, metallography and particle sizing. The results from this extensive analysis have enabled the authors to estimate the heat generated by the oxidation process during cutting of both mild and stainless steels.

Claes Magnusson

Papers

An analytical thermodynamic model of laser welding

The oxidation dynamics of laser cutting of mild steel and the generation of striations on the cut edge

Energy redistribution during CO2 laser cladding

The Bauschinger effect in compression-tension of sheet metals

The Role of Oxidation in Laser Cutting Stainless and Mild Steel