Deposition-Based Additive Manufacturing Research Articles

Elimination of support mechanism in additive manufacturing through substrate tilting

PurposeThe support structures of sacrificial material are built in deposition-based additive manufacturing (AM), which are later removed either by breaking or dissolving. Such a sacrificial material is not feasible in metal AM. The purpose of this study is to find a suitable method for eliminating the need of support mechanism. In this work, the authors use the tilting of the substrate to alleviate the need for the support mechanism altogether.Design/methodology/approachAs in the traditional AM, the object is grown in horizontal layers. However, wherever undercuts are encountered, the substrate is tilted appropriately to capture the droplets. Such a tilt involves two rotary axes invariably. To conform to the slice geometry, these two tilts are accompanied by the three linear movements. Thus, the object with undercuts is grown in planar layers using five-axis deposition without any support structure. Each pair of the corresponding top and bottom contours of any slice defines a ruled surface. The axis of the deposition head will be aligned with the rules of this surface.FindingsThe need for the support mechanism was eliminated using five-axis deposition. This was experimentally demonstrated by building an aluminum impeller using a metal inert gas cladding head.Research limitations/implicationsIn the proposed methodology, the objects with an abrupt change in the geometry are not possible to realize.Originality/valueThis manuscript proposed a novel method of eliminating the support mechanism through continuous five-axis deposition.

Model Development in OpenFOAM for Laser Metal Deposition-based Additive Manufacturing Process

Laser metal deposition (LMD) process is an additive manufacturing process that uses a high-power laser to melt the metal powder supplied coaxially to the focus of the laser beam through a deposition head. The LMD process involves various interconnected physical phenomenon that are challenging to model numerically. It includes laser–material interaction, fall of molten droplets in a melt pool and the associated heat, momentum and mass transfer, free surface flow, bubble formation and air entrapment, and rapid solidification. A numerical solver in open-source platform OpenFOAM® using the VOF approach is developed for the spot LMD process. Flows due to natural and Marangoni convection are modelled by adding source terms in momentum equation. Energy addition in the substrate due to laser irradiation is added as a source term in energy equation. Enthalpy-porosity technique is used to model the melting and solidification phase change. Mass and energy addition due to falling droplets are modelled by adding molten droplets in the melt pool. The role of melt pool convection on heat transfer and melt pool geometry is established by an analysis using relevant dimensionless numbers. Ratio of Marangoni number and Grashof number suggest that the fluid flow within the melt pool during laser heating stage is mainly driven by Marangoni force.

On the influence of laser defocusing in Selective Laser Melting of 316L

Despite its many benefits, Selective Laser Melting's (SLM) relatively low productivity compared to deposition-based additive manufacturing techniques is a major drawback. Increasing the laser beam diameter improves SLM's build rate, but causes loss of precision. The aim of this study is to investigate laser beam focus shift, or “defocus”, using a dynamic focusing unit, in order to increase the laser spot size. When applied to the SLM process, focus shift can be integrated into a “hull-core” strategy. This involves scanning the core with a high productivity parameter set using defocus while enabling return to the focused smaller spot size position for hull scanning. To assess the process stability, single line scans were made from 316L stainless steel powder. The consolidated melt pool morphology was analyzed and correlated with the process parameters comprising laser power, scanning speed and defocus distance. In order to link the melt pool morphology with the heat input, Volumetric Energy Density, Normalized Enthalpy and Rosenthal equation were considered. The suitability of using the Normalized Enthalpy as a design parameter to predict the melt pool depth and Rosenthal equation to predict its width was highlighted. This study shows that within a single laser setup, implementing defocus can lead to a potential productivity increase by 840%, i.e. to 18.8 mm3/s.

An experimental study of pneumatic extruding direct writing deposition-based additive manufacturing

A pneumatic extruding direct writing deposition process is proposed in this paper. Compressed high-purity nitrogen was selected as a driving force to squeeze a liquid metal out of a nozzle. Combining this step with movement of the underlying substrate enabled the formation of metal patterns. Four nozzles with different structures were employed in this research, and the effect of the structural design of the nozzle on the flow of the liquid metal was analyzed both theoretically and experimentally. The influence of the distance between the nozzle and the substrate on the deposited metal lines was also investigated. To demonstrate a practical application, several metal patterns were successfully fabricated, each with a uniform and continuous metal line. Furthermore, three-dimensional objects were also fabricated. The results of a morphological analysis of the deposited metal lines show that the throttle channels added to the nozzle significantly decrease the flow of the metal fluid; as a result, nozzles with throttle channels produce thinner metal lines. The distance between the nozzle and the substrate influences the outline of the cross section of the deposited metal lines without significantly decreasing the outflow of the liquid metal.

Manufacture of complex thin-walled metallic objects using weld-deposition based additive manufacturing

Gas Metal Arc Welding (GMAW) based weld-deposition process is one of the deposition-based Additive Manufacturing (AM) processes with the ability to produce fully dense complex functional metallic objects. Due to its high deposition rates, high material and power efficiency, lower investment costs, simpler setup and work environment requirements it is slowly becoming a viable metallic AM method. Amongst various geometrical features that can be realized in weld-deposition based AM, the thin-walled features (i.e., features with one single deposition pass) are the toughest as the process has to overcome the bead-over-bead complexity. Based on geometric modelling and experimentation, this paper presents an efficient technique for producing the thin-walled metallic structures, including objects with undercut features. This is possible by adding extra degrees of freedom or by using higher order kinematics to the work piece and/or to the deposition head by suitably aligning the overhanging feature in-line to the deposition direction. An in-house MATLAB code was developed to slice the CAD model and generate the tool path for inclined deposition of a given layer of a thin-walled model. A geometrical model proposed to predict the layer thickness of a given layer during such bead-on-bead deposition showed good correlation with experimental data. Some illustrative complex thin-walled components successfully fabricated using this model have also been presented.

Laser Additive Manufacturing of Magnetic Materials

While laser additive manufacturing is becoming increasingly important in the context of next-generation manufacturing technologies, most current research efforts focus on optimizing process parameters for the processing of mature alloys for structural applications (primarily stainless steels, titanium base, and nickel base alloys) from pre-alloyed powder feedstocks to achieve properties superior to conventionally processed counterparts. However, laser additive manufacturing or processing can also be applied to functional materials. This article focuses on the use of directed energy deposition-based additive manufacturing technologies, such as the laser engineered net shaping (LENS™) process, to deposit magnetic alloys. Three case studies are presented: Fe-30 at.%Ni, permalloys of the type Ni-Fe-V and Ni-Fe-Mo, and Fe-Si-B-Cu-Nb (derived from Finemet) alloys. All these alloys have been processed from a blend of elemental powders used as the feedstock, and their resultant microstructures, phase formation, and magnetic properties are discussed in this paper. Although these alloys were produced from a blend of elemental powders, they exhibited relatively uniform microstructures and comparable magnetic properties to those of their conventionally processed counterparts.