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

Control of Laser Cladding Process

In this paper, a novel algorithm is proposed to develop a 3D transient finite element model of multilayer laser solid freeform fabrication (LSFF) process. The proposed model predicts the clad geometry as a function of time and process parameters including laser power, traverse speed, powder jet geometry, and material properties. In the modeling strategy, the interaction between the laser beam and powder stream is assumed to be decoupled, therefore, the melt pool boundary on the moving substrate is obtained in the absence of the powder stream. Once the melt pool boundary is calculated, a deposited layer is formed based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream. After the deposition of each layer, the effect of this geometrical change into the thermal distribution within the model is considered for thermal analysis of the next layer deposition. In the numerical simulation, the effects of a non-planar surface on the process parameters such as powder efficiency and absorption factor are taken into account. Geometrical aspects of a thin wall of steel AISI 4340 with four layers are numerically simulated by the developed modeling strategy. Numerical results show that with the growth of the number of layers in the wall, the powder efficiency increases while the absorption factor decreases. Experimental and numerical results are compared to verify the accuracy and reliability of the proposed model.Copyright © 2006 by ASME

Dynamic Geometrical Modeling of Deposited Material in Multilayer Laser Solid Freeform Fabrication Process

A State-of-the-Art Review on Fatigue Performance of Powder Bed Fusion-Built Alloy 718

This paper presents a coupled 3D transient numerical approach for modelling multilayer laser solid freeform fabrication process of heterogeneous structures. Using this model, temperature distribution and thermal stress field are dynamically obtained throughout the process domain assuming the interaction between the laser beam and the powder stream is decoupled. Once the melt pool boundary is obtained, the geometry of the multilayer deposited materials can be predicted based on the powder feed rate, elapsed time, and intersection between the melt pool and powder stream area. The main process parameters affected by the deposition on non-planar surfaces, such as powder catchment efficiency, are incorporated into the model. The proposed algorithm is used to simulate the fabrication of a heterogeneous structure of a thin wall. The effects of the multi-material depositions on the temperature and stress distribution patterns are investigated. Numerical results are experimentally verified by their experimental counterparts using a 1 kW fiber laser coupled with a five axis workstation.This paper presents a coupled 3D transient numerical approach for modelling multilayer laser solid freeform fabrication process of heterogeneous structures. Using this model, temperature distribution and thermal stress field are dynamically obtained throughout the process domain assuming the interaction between the laser beam and the powder stream is decoupled. Once the melt pool boundary is obtained, the geometry of the multilayer deposited materials can be predicted based on the powder feed rate, elapsed time, and intersection between the melt pool and powder stream area. The main process parameters affected by the deposition on non-planar surfaces, such as powder catchment efficiency, are incorporated into the model. The proposed algorithm is used to simulate the fabrication of a heterogeneous structure of a thin wall. The effects of the multi-material depositions on the temperature and stress distribution patterns are investigated. Numerical results are experimentally verified by their experimental co...

A time-dependent multiphysics simulation of laser solid freeform fabrication process for heterogeneous structures

In laser solid freeform fabrication (LSFF), the final microstructures and consequently the physical properties of the successive deposited layers of additive materials are determined through melting, solidification and solid state transformations caused by a moving laser beam. In this paper, temperature distribution and stress field induced during the multilayer LSFF process and their correlation with the local microstructure formation are studied throughout the fabrication of a four-layer thin wall of SS304L. For this purpose, parallel to the experimental investigation, a coupled 3D time-dependent numerical model is employed to simulate the process. The numerical and experimental results show that stress concentrations formed at the end points of the wall are the locations prone to potential delaminations and crack formations. Different types of microstructures, such as dendritic with and without secondary arm spacings, are observed at various locations within the same layer due to different cooling rates.

Ehsan Toyserkani

Papers

Control of Laser Cladding Process

Dynamic Geometrical Modeling of Deposited Material in Multilayer Laser Solid Freeform Fabrication Process

A State-of-the-Art Review on Fatigue Performance of Powder Bed Fusion-Built Alloy 718

A time-dependent multiphysics simulation of laser solid freeform fabrication process for heterogeneous structures

On the microstructure of a thin wall formed under thermal and stress fields induced in laser solid freeform fabrication process