Stable formation of powder bed laser fused 99.9% silver

This is an accepted manuscript of an article published by Elsevier in Materials Today Communications on 11/05/2020, available online: https://doi.org/10.1016/j.mtcomm.2020.101195 The accepted version of the publication may differ from the final published version.Additive manufacture (AM) of metals and alloys using powder-bed fusion (PBF) often employs a 400 W (1060–1100 nm wavelength) fibre laser as the primary energy source for Selective Laser Melting (SLM). Highly reflectie and thermally conductive materials such as pure silver (Ag) offer significant challenges for SLM due to insufficient laser energy absorption at the powder bed. Accordingly, this work pioneers the processing, analysis, and fabrication of 99.9% (pure) atomised Ag using PBF AM featuring a 400 W fibre laser system. The atomised pure silver powder is characterised for its morphology, size, shape, distribution and compared to current AM sterling silver. Laser-powder interaction is then investigated through single track fabrication to assess the feasibility of laser melting pure Ag. Varied process parameter single laser pass and single-track fabrication on both copper and steel build substrates are conducted and analysed with optical and scanning electron microscopy (SEM) techniques. The resulting SLM process parameters are then used to create pure Ag 3D structures and the effects of laser power, scan speed, hatch distance and layer thickness on material density is evaluated. Furthermore, SEM analysis of the 3D structures was conducted to identify optimum laser power, scan speed, hatch distance and layer thickness required to create dense pure Ag structures. The results of this study show that SLM processing of pure Ag utilising PBF AM is feasible. The optimum process parameters required for the generation of controlled track formation and 3D fabrication of pure Ag at a 97% density is reported.Accepted versio

Influence of laser beam profile on the selective laser melting process of AlSi10Mg

Selective laser melting (SLM) offers great potential to manufacture customized and complex metallic parts. Major drawbacks that limit its industrial application are the high cost of the process that is related to low process speeds and issues with reproducibility. One important process parameter that has the potential to increase the reproducibility and speed of the process is the laser beam intensity profile. Since its influence has not been sufficiently investigated, the goal of this study is to analyze the effect of the beam profile on the SLM process of AlSi10Mg. Single tracks and density cubes are manufactured with different process parameters and two beam profiles (standard Gaussian and Donut beam profiles) and analyzed with respect to appearance, the size of melt tracks, porosity, and the types of defect. The results reveal several advantages of the Donut beam profile such as fewer defects and a significantly broader process window that promises a more robust process

Measurement of actual powder layer height and packing density in a single layer in selective laser melting

For a detailed numerical analysis of lasermaterial interactions and melt pool dynamics in selective laser melting (SLM), it is important to consider correct powder layer height and packing density in a single layer. Thus far, most experts assume that the powder layer height, which is equal to the leveling height of the build platform divided by the packing density of the powder bed, reaches a steady state after several layers. However, this assumption neglects the fact that a certain amount of powder is deposited (e.g., by spatter), and therefore, does not contribute to the molten powder layer height and that the packing density in a single layer is smaller than in bulk. To determine the actual powder layer height and packing density in a single layer, experiments are conducted using two different materials (SS 17-4 PH and Ti6Al4V)and layer heights (30 and 50 μm). The results reveal that the powder layer height is between 4 and 5.5 times the leveling height of the build platform and is, therefore, significantly larger than that assumed thus far. This is an important finding to consider when one investigates the details of the lasermaterial interaction and melting process in SLM, e.g., by numerical simulations. The measured packing density varied between 44% and 56%

Influence of Process Parameters on the Quality of Aluminium Alloy EN AW 7075 Using Selective Laser Melting (SLM)

AbstractSelective laser melting (SLM) is an additive manufacturing process, forming the desired geometry by selective layer fusion of powder material. Unlike conventional manufacturing processes, highly complex parts can be manufactured with high accuracy and little post processing. Currently, different steel, aluminium, titanium and nickel-based alloys have been successfully processed; however, high strength aluminium alloy EN AW 7075 has not been processed with satisfying quality. The main focus of the investigation is to develop the SLM process for the wide used aluminium alloy EN AW 7075. Before process development, the gas-atomized powder material was characterized in terms of statistical distribution: size and shape. A wide range of process parameters were selected to optimize the process in terms of optimum volume density. The investigations resulted in a relative density of over 99%. However, all laser-melted parts exhibit hot cracks which typically appear in aluminium alloy EN AW 7075 during the welding process. Furthermore the influence of processing parameters on the chemical composition of the selected alloy was determined

Biomimetic design and laser additive manufacturing - A perfect symbiosis?

Biomimetics as well as additive manufacturing have prominently produced novel design approaches for parts and products independently from each other. The combination of both has resulted in numerous innovative part designs that were unseen before. However remarkable the marketing impact of individual 3D printed biomimetic parts has been, a widespread industrial application is missing to date. This publication, therefore, takes a closer look at how biomimetic design in additive manufacturing is currently pursued and evaluates the different design approaches based on their suitability for industrial application. The assessment reveals that algorithms and thesaurus tools should be preferred in an industrial biomimetic design process. From the various additive manufacturing methods, laser additive manufacturing today is a dominating industrial application when it comes to metal parts. Thus, several case studies of biomimetic designs produced with laser additive manufacturing are presented. On the basis of the selected examples, the added value through biomimetic design is discussed and reviewed critically, raising the question of when a biomimetic design approach is promising compared to conventional design approaches. Based on the review of current use cases and the potentials that the combination of biomimetics and additive manufacturing offer, recommended fields of research are concluded. Finally, the road to industry for biomimetic additive manufacturing design is outlined, taking into account the findings on existing biomimetic design methodologies and tools