Effect of the surface morphology of solidified droplet on remelting between neighboring aluminum droplets

Good metallurgical bonding between neighboring droplets is essential in droplet-based 3D printing. However, although the mechanism of remelting has clearly been mastered, cold laps are still common internal defects of formed parts in uniform aluminum droplets deposition manufacturing, which is due to the overlook of the surface morphologies of solidified droplets. Here, for the first time, the blocking effect of ripples and solidification angles on the fusion between droplets is revealed. To investigate the detailed process of remelting, a 3D numerical model was developed, basing on the volume of fluid (VOF) method. Experiments and simulations show that the remelting process between neighboring droplets can be divided into two stages according to the transient contact between the second droplet and the substrate. In the first stage, a non-intuitive result is observed that cold laps can also be formed even if the remelting conditions are satisfied in theory. Ripples on the surface of previously-deposited droplet block its direct contact with the new-coming droplet. In the second stage, cold laps on bottom surface are formed due to incomplete filling of liquid metal when the solidification angle is greater than 90°. Furthermore, these cold laps are difficult to be completely avoided by improving the temperature parameters. To address this problem, a novel strategy of decreasing the thermal conductivity coefficient of the substrate is proposed. This method effectively promotes remelting between droplets by eliminating ripples and decreasing solidification angles

Direct fabrication of unsupported inclined aluminum pillars based on uniform micro droplets deposition

In order to investigate forming directly complex parts without support materials or structures by uniform micro droplets deposition technique, the present work focus on fabricating the unsupported inclined aluminum pillars through offset deposition. An experimental system is developed to produce and deposit uniform molten aluminum droplets. A model is introduced to describe the inclined angle of the droplet deposition at different offset ratios. A one dimensional heat transfer model is proposed to help select the initial temperature parameters of the impinging droplet and the previous solidified droplet to ensure that the fusion occurs. No melting, partial melting and excessive melting region at different offset ratios are determined. The correspondence between offset ratio and inclined angle is considered to be a simple cosine function, and the hypothesis is verified by experiments. The influence of deposition error on an inclined angle of pillars is studied. Internal microstructure of droplet fusion is observed in order to ensure good metallurgical bonding. All of these studies show the feasibility of fabricating directly unsupported inclined aluminum pillars in the limited angle range by using uniform micro droplets

Technologies of Coatings and Surface Hardening for Tool Industry

The innovative coating and surface hardening technologies developed in recent years allow us to obtain practically any physical–mechanical or crystal–chemical complex properties of the metalworking tool surface layer. Today, the scientific approach to improving the operational characteristics of the tool surface layers produced from traditional tools industrial materials is a highly costly and long-lasting process. Different technological techniques, such as coatings (physical and chemical methods), surface hardening and alloying (chemical-thermal treatment, implantation), a combination of the listed methods, and other solutions are used for this. This edition aims to provide a review of the current state of the research and developments in the field of coatings and surface hardening technologies for cutting and die tools that can ensure a substantial increase of the work resource and reliability of the tool, an increase in productivity of machining, accuracy, and quality of the machined products, reduction in the material capacity of the production, and other important manufacturing factors. In doing so, the main emphasis should be on the results of the engineering works that have had a prosperous approbation in a laboratory or real manufacturing conditions

Volume-conservative modeling of structures manufactured by molten drop-on-drop deposition

An improved analytic model to accurately determine the geometry of structures manufactured by molten drop-on-drop deposition is presented. This deposition mode allows quasi-spherical deposited droplets to be achieved and precise control over the geometry of the final manufactured structures. The model exactly conserves the volume of the deposited material and matches the solidification contact angle between consecutive deposited droplets, providing a precise geometrical description of the manufactured structures. The proposed model is validated using results of experiments performed with several materials for the deposited droplets and substrate, and droplet radii ranging from 40 to 800 m. A good degree of agreement was found between theoretical and experimental results. A comparison with the well-established Gao&Sonin model shows that the proposed model represents a major improvement, and may be of great practical interest in industrial applications.The authors gratefully acknowledge the joint support of the Spanish Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación and FEDER through projects DPI2017-87826-C2-1-P and DPI2017-87826-C2-2-P, and the Spanish Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (MCIN/ AEI/ 10.13039/501100011033) through projects PID2020-120100GB-C21 and PID2020-120100GB-C22

Numerical Investigation of Pileup Process in Metal Microdroplet Deposition Manufacture

This paper presents a systematic numerical investigation of the transient transport phenomenon during the pileup of molten metal droplets on the substrate. The physical mechanisms of the pileup process, including the bulk liquid, capillarity effects at the liquid-solid interface, heat transfer, and solidification, are identified and quantified numerically. The droplet diameter is 100 μm, and the impact velocities are 1–3 m/s. These conditions correspond to Re = O(100), We = O(1). The initial substrate temperature is 350 K. The initial droplet temperature of aluminum alloy molten droplets is 960 K. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of impacting velocity and relative distances between two successive molten droplets on the end-shapes of impact regime are examined. This investigation is essential to implement effective process control in metal microdroplet deposition manufacture

Jetting of multiple functional materials by additive manufacturing

The rise and consolidation of Additive Manufacturing (AM) as a technology has made possible the fabrication of highly customised and complex products in almost every industry. This not only allows the creation of objects that were impossible just a few decades ago but also facilitates the production of small runs of products at a reasonable cost, which reduces the design-prototyping cycles and boosts product innovation. However, to produce truly functional parts it is desirable for these systems to be able to deposit multiple complex materials in a single process to locally embed controllable properties such as electrical conductivity or sensing capabilities into the produced geometries. Consequently, a review of current AM technologies capable of depositing conductive materials is performed in this PhD and discussed to find the most suitable approaches. Similarly, existing multi-material set-ups are studied to find limitations and common practices to create a system that is capable of fulfilling the objectives of this work. Piezo-activated inkjet printing (PIJ) is identified as an appropriate technology for multi-material applications due to its non-contact nature, high spatial resolution, capability of mixing and digitally grading materials and simple scale-up of the process. Furthermore, in the last decade it has been shown that jetting can be used for the accurate deposition of a wide range of functional materials. However, upon detailed review of this method, the limitations that it imposes on the compositions of the inks are identified as its main drawback. Specifically, the solid content and molecular weight of the fluids that can be jetted are restricted by the viscosity of the final ink, typically under 40 mPa·s. This is problematic in the case of jetting conductive materials, since it forces the solid content to be very low, therefore yielding very thin and often inhomogeneous layers. Additionally, all the organic components on the inks added to facilitate its ejection need to be removed, which typically means longer and more aggressive post-processes before rendering the printed tracks conductive. For this reason, drop-on-demand micro-dispensing valves were chosen as a high viscosity jetting (HVJ) approach in this work, with the intention of assessing their capability as a suitable tool for multi-material AM of functional inks. However, since their resolution and speed are lower than conventional inkjet, a hybrid approach is presented including micro-dispensing valves and inkjet printheads capable of depositing a wide range of viscosities in a single process. A comprehensive description of the hybrid set-up is given, discussing its main elements including the printing heads, the custom design printer assembly, the ultraviolet (UV) and infrared (IR) lamps installed for in-situ processing, the monitoring system and the set-up to measure the evolution of the electrical resistance in printed tracks in real time during post-processing. Additionally, the printing strategy and process flow is discussed. The investigated set-up was used to study the printability and performance of several functional materials ranging from UV-curable polymers to conductive formulations such as carbon paint, a silver nanoparticle-based paste and a dispersion of PEDOT:PSS. Each material was thoroughly characterised prior to printing with a special focus on viscosity. Their drop formation and deposition processes were studied at different printing settings using high speed imaging and footprint analysis of the deposited drops. These tests were used to obtain sets of working parameters that allow reliable printing and were used to produce 2D patterns with different resolutions to find the drop spacing that results in flat homogeneous films. Later, these films were post-treated according to the requirements of each material and multilayer structures were produced and analysed with an optical profilometer. The cross-section of these 3D tracks was used together with the measured resistance to obtain the electric conductivity of the materials under the printing conditions used. Finally, the accumulated information during the previous stages of printing was used to produce 3D multi-material demonstrators with incorporated conductive tracks, electric components and electroluminescent elements. These proof-of-concept samples were used to discuss limitations of the approach and showcase future possibilities of the system

Jetting of multiple functional materials by additive manufacturing

The rise and consolidation of Additive Manufacturing (AM) as a technology has made possible the fabrication of highly customised and complex products in almost every industry. This not only allows the creation of objects that were impossible just a few decades ago but also facilitates the production of small runs of products at a reasonable cost, which reduces the design-prototyping cycles and boosts product innovation. However, to produce truly functional parts it is desirable for these systems to be able to deposit multiple complex materials in a single process to locally embed controllable properties such as electrical conductivity or sensing capabilities into the produced geometries. Consequently, a review of current AM technologies capable of depositing conductive materials is performed in this PhD and discussed to find the most suitable approaches. Similarly, existing multi-material set-ups are studied to find limitations and common practices to create a system that is capable of fulfilling the objectives of this work. Piezo-activated inkjet printing (PIJ) is identified as an appropriate technology for multi-material applications due to its non-contact nature, high spatial resolution, capability of mixing and digitally grading materials and simple scale-up of the process. Furthermore, in the last decade it has been shown that jetting can be used for the accurate deposition of a wide range of functional materials. However, upon detailed review of this method, the limitations that it imposes on the compositions of the inks are identified as its main drawback. Specifically, the solid content and molecular weight of the fluids that can be jetted are restricted by the viscosity of the final ink, typically under 40 mPa·s. This is problematic in the case of jetting conductive materials, since it forces the solid content to be very low, therefore yielding very thin and often inhomogeneous layers. Additionally, all the organic components on the inks added to facilitate its ejection need to be removed, which typically means longer and more aggressive post-processes before rendering the printed tracks conductive. For this reason, drop-on-demand micro-dispensing valves were chosen as a high viscosity jetting (HVJ) approach in this work, with the intention of assessing their capability as a suitable tool for multi-material AM of functional inks. However, since their resolution and speed are lower than conventional inkjet, a hybrid approach is presented including micro-dispensing valves and inkjet printheads capable of depositing a wide range of viscosities in a single process. A comprehensive description of the hybrid set-up is given, discussing its main elements including the printing heads, the custom design printer assembly, the ultraviolet (UV) and infrared (IR) lamps installed for in-situ processing, the monitoring system and the set-up to measure the evolution of the electrical resistance in printed tracks in real time during post-processing. Additionally, the printing strategy and process flow is discussed. The investigated set-up was used to study the printability and performance of several functional materials ranging from UV-curable polymers to conductive formulations such as carbon paint, a silver nanoparticle-based paste and a dispersion of PEDOT:PSS. Each material was thoroughly characterised prior to printing with a special focus on viscosity. Their drop formation and deposition processes were studied at different printing settings using high speed imaging and footprint analysis of the deposited drops. These tests were used to obtain sets of working parameters that allow reliable printing and were used to produce 2D patterns with different resolutions to find the drop spacing that results in flat homogeneous films. Later, these films were post-treated according to the requirements of each material and multilayer structures were produced and analysed with an optical profilometer. The cross-section of these 3D tracks was used together with the measured resistance to obtain the electric conductivity of the materials under the printing conditions used. Finally, the accumulated information during the previous stages of printing was used to produce 3D multi-material demonstrators with incorporated conductive tracks, electric components and electroluminescent elements. These proof-of-concept samples were used to discuss limitations of the approach and showcase future possibilities of the system

GSI Scientific Report 2009 [GSI Report 2010-1]

Displacement design response spectrum is an essential component for the currently-developing displacement-based seismic design and assessment procedures. This paper proposes a new and simple method for constructing displacement design response spectra on soft soil sites. The method takes into account modifications of the seismic waves by the soil layers, giving due considerations to factors such as the level of bedrock shaking, material non-linearity, seismic impedance contrast at the interface between soil and bedrock, and plasticity of the soil layers. The model is particularly suited to applications in regions with a paucity of recorded strong ground motion data, from which empirical models cannot be reliably developed