Additive manufacturing of metallic components – Process, structure and properties

Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

Laser additive manufacturing of metallic components: materials, processes and mechanisms

Laser-based additive manufacturing (LBAM) processes can be utilized to generate functional parts (or prototypes) from the ground-up via layer-wise cladding – providing an opportunity to generate complex-shaped, functionally graded or custom-tailored parts that can be utilized for a variety of engineering applications. Directed Energy Deposition (DED), utilizes a concentrated heat source, which may be a laser or electron beam, with in situ delivery of powder- or wire-shaped material for subsequent melting to accomplish layer-by-layer part fabrication or single-to-multi layer cladding/repair. Direct Laser Deposition (DLD), a form of DED, has been investigated heavily in the last several years as it provides the potential to (i) rapidly prototype metallic parts, (ii) produce complex and customized parts, (iii) clad/repair precious metallic components and (iv) manufacture/repair in remote or logistically weak locations. DLD and Powder Bed Fusion-Laser (PBF-L) are two common LBAM processes for additive metal part fabrication and are currently demonstrating their ability to revolutionize the manufacturing industry; breaking barriers imposed via traditional, ‘subtractive’ metalworking processes. This article provides an overview of the major advancements, challenges and physical attributes related to DLD, and is one of two Parts focused specifically on DLD. Part I (this article) focuses on describing the thermal/fluidic phenomena during the powder-fed DLD process, while Part II focuses on the mechanical properties and microstructure of parts manufactured via DLD. In this current article, a selection of recent research efforts – including methodology, models and experimental results – will be provided in order to educate the reader of the thermal/fluidic processes that occur during DLD, as well as providing important background information relevant to DLD as a whole. The thermal/fluid phenomena inherent to DLD directly influence the solidification heat transfer which thus impacts the part's microstructure and associated thermo-mechanical properties. A thorough understanding of the thermal/fluid aspects inherent to DLD is vital for optimizing the DLD process and ensuring consistent, high-quality parts.

An overview of Direct Laser Deposition for additive manufacturing; Part I: Transport phenomena, modeling and diagnostics

Ti-based alloys are finding ever-increasing applications in biomaterials due to their excellent mechanical, physical and biological performance. Nowdays, low modulus β-type Ti-based alloys are still being developed. Meanwhile, porous Ti-based alloys are being developed as an alternative orthopedic implant material, as they can provide good biological fixation through bone tissue ingrowth into the porous network. This paper focuses on recent developments of biomedical Ti-based alloys. It can be divided into four main sections. The first section focuses on the fundamental requirements titanium biomaterial should fulfill and its market and application prospects. This section is followed by discussing basic phases, alloying elements and mechanical properties of low modulus β-type Ti-based alloys. Thermal treatment, grain size, texture and properties in Ti-based alloys and their limitations are dicussed in the third section. Finally, the fourth section reviews the influence of microstructural configurations on mechanical properties of porous Ti-based alloys and all known methods for fabricating porous Ti-based alloys. This section also reviews prospects and challenges of porous Ti-based alloys, emphasizing their current status, future opportunities and obstacles for expanded applications. Overall, efforts have been made to reveal the latest scenario of bulk and porous Ti-based materials for biomedical applications.

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New Developments of Ti-Based Alloys for Biomedical Applications

The direct metal deposition (DMD) laser process is a novel technique, well adapted for aeronautical applications, that allows the building of complex 3D geometries through the interaction between a powder nozzle system and a continuous laser beam. A three-step analytical and numerical approach was carried out to predict the shapes of manufactured structures and thermal loadings induced by the DMD process. First, powder temperature was calculated using a recent analytical model, then the geometry of walls was predicted by a combined numerical + analytical modelling using a discretization of the physical interaction domain, and finally, a finite element calculation was carried out on COMSOL 3.3 Multiphysics software to describe thermal behaviour during DMD of a titanium alloy.Our thermal model takes into account the moving interface during metal deposition with a specific function κ (t, x, y, z) allowing the conductivity front to move simultaneously with the moving laser source (with an appropriate spatial energy distribution), thus representing rather precisely the DMD process. This allowed us to provide an adequate representation of temperatures near the melt-pool, and to reproduce with a good accuracy thermal cycles and melt-pool dimensions during the construction of up to 25-layer walls. This was confirmed by comparisons with experimental thermocouple data T = f(t), and fast camera melt-pool recording.

https://iopscience.iop.org/article/10.1088/0022-3727/41/2/025403/pdf

Analytical and numerical modelling of the direct metal deposition laser process

The coaxial laser cladding process is the heart of direct metal deposition (DMD). Rapid materials processing, such as DMD, is steadily becoming a tool for synthesis of materials, as well as rapid manufacturing. Mathematical models to develop the fundamental understanding of the physical phenomena associated with the coaxial laser cladding process are essential to further develop the science base. A three-dimensional transient model was developed for a coaxial powder injection laser cladding process. Physical phenomena including heat transfer, melting and solidification phase changes, mass addition, and fluid flow in the melt pool, were modeled in a self-consistent manner. Interactions between the laser beam and the coaxial powder flow, including the attenuation of beam intensity and temperature rise of powder particles before reaching the melt pool were modeled with a simple heat balance equation. The level-set method was implemented to track the free surface movement of the melt pool, in a continuous las...

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Numerical simulation of heat transfer and fluid flow in coaxial laser cladding process for direct metal deposition

Breinan and Kear first reported fabrication of three-dimensional metallic components via layer by layer laser cladding in 1978 and subsequently a patent was issued to Brown et al. in 1982. Recently, various groups are working world wide on different types of layered manufacturing techniques for fabrication of near net shape metallic components. Integration of lasers with multi-axis presently available CNC machines, CAD/CAM, sensors and powder metal delivery through co-axial nozzles along with the laser beam are the main innovations for fabrication of 3-Dimensional components. Continuous corrective measures during the manufacturing process are necessary to fabricate net shape functional parts with close tolerances and acceptable residual stress. The closed loop Direct Metal Deposition(DMD) System, using an optical feedback loop along with a CNC working under the instructions from a CAD/CAM software, indicate that it can produce three dimensional components directly from the CAD data eliminating intermediate machining and reduces final machining considerably. This technology is now being commercialized.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fabrication of 3D components by laser-aided direct metal deposition

Three-dimensional additive manufacturing or solid freeform fabrication (SFF) techniques, originated in the rapid fabrication of non-functional physical prototypes in polymers (Rapid Prototyping), have matured to the manufacture of functional prototypes, short-run production products, and now even advanced engineering designs. Laser-based material deposition or laser cladding has been used as a SFF technique, in which a laser beam is used as a precise high-energy thermal source to melt preplaced or pneumatically delivered metal powders and make solidified deposits on a substrate. By using laser cladding techniques, three-dimensional fully dense components can be built line-by-line and layer-by-layer directly from a CAD model with tailored material properties. Laser cladding is essentially a fusion and solidification (thermal) process, which involves complicated interactions between the laser beam, metal powders, the base material (substrate), and processing gases. Maintaining a stable and uniform melt pool during laser cladding is critical to produce dimensional accuracy and material integrity. An effective control of energy (laser power) spatial and temporal distributions in either an open-loop or closed-loop laser cladding process is essential to achieve the high quality results. This paper reviews, from a laser-material interaction point of view, various laser cladding based SFF processes, and particularly the direct metal deposition technique.© 2006 ASME

Huan Qi

Papers

Numerical simulation of heat transfer and fluid flow in coaxial laser cladding process for direct metal deposition

Fabrication of 3D components by laser-aided direct metal deposition

Laser Cladding Based Solid Freeform Fabrication and Direct Metal Deposition