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Here, the effect of thermal annealing (TA) on the stability of solution‐sheared thin films of the semiconducting polymer poly[2,5‐bis(2‐octyldodecyl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione‐3,6‐diyl)‐alt‐(2,2′;5′,2′';5′',2′"‐quaterthiophen‐5,5′"‐diyl)] (PDPP4T) against the original coating solvent is studied, and it is shown that TA significantly improves the solvent resistance of semiconducting polymer films. Specifically, after the thin films are annealed at or above a critical temperature, the thin film thickness is largely retained when exposed to the original solvent, while for lower annealing temperatures material loss occurs, i.e., the thin film thickness is reduced due to rapid dissolution. The results of various techniques including grazing‐incidence wide‐angle x‐ray scattering (GIWAXS), atomic force microscopy (AFM), and ultraviolet‐visible‐near infrared (UV–vis‐NIR) absorption spectroscopy suggest physical changes as the cause for the increased solvent resistance. Such annealed films also show stable electrical characteristics in bottom‐gate, top‐contact (BGTC) organic field‐effect transistors (OFETs) even after solvent exposure. In initial tests, a multitude of technologically relevant polymers show such behavior, underlining the potential impact of such temperature treatments for the fabrication of multi‐layer polymer devices. [ABSTRACT FROM AUTHOR]

Abstract Here, the effect of thermal annealing (TA) on the stability of solution‐sheared thin films of the semiconducting polymer poly[2,5‐bis(2‐octyldodecyl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione‐3,6‐diyl)‐alt‐(2,2′;5′,2′’;5′’,2′’’‐quaterthiophen‐5,5′’’‐diyl)] (PDPP4T) against the original coating solvent is studied, and it is shown that TA significantly improves the solvent resistance of semiconducting polymer films. Specifically, after the thin films are annealed at or above a critical temperature, the thin film thickness is largely retained when exposed to the original solvent, while for lower annealing temperatures material loss occurs, i.e., the thin film thickness is reduced due to rapid dissolution. The results of various techniques including grazing‐incidence wide‐angle x‐ray scattering (GIWAXS), atomic force microscopy (AFM), and ultraviolet‐visible‐near infrared (UV–vis‐NIR) absorption spectroscopy suggest physical changes as the cause for the increased solvent resistance. Such annealed films also show stable electrical characteristics in bottom‐gate, top‐contact (BGTC) organic field‐effect transistors (OFETs) even after solvent exposure. In initial tests, a multitude of technologically relevant polymers show such behavior, underlining the potential impact of such temperature treatments for the fabrication of multi‐layer polymer devices.

Wire-arc additive manufacturing (WAAM) is increasingly popular for the low-cost and rapid manufacture of large and complex metallic components due to its high deposition rate and material efficiency. However, its insufficient manufacturing precision impedes a wide application of this process. In order to improve the geometric accuracy of beads deposited by WAAM, a feedback control system based on the multiple model approach is developed. Different local models are identified to characterize the complex dynamics between the process parameter travel speed and the bead geometry. The developed control system is tested in the manufacturing of three different parts with variable geometry. It is demonstrated that the system effectively compensates for geometric errors (both width and height), and the three tested parts' mean error is reduced by 78%. The system can also increase the productivity of deposition by avoiding requirements of low interlayer temperatures. [ABSTRACT FROM AUTHOR]

Heat accumulation is a critical problem in continuous multi-layer laser aided additive manufacturing (LAAM) process, resulting in inhomogeneous mechanical properties and non-uniformity in the deposited height which can deteriorate the deposition process. This work presents a new integrated finite element (FE) simulation and machine learning approach to select a multi-layer laser infill toolpath planning strategy for fabricating quadrilateral parts to minimise localised heat accumulation during the deposition process. After one layer deposition simulation, the approach employs a Temperature-Pattern Recurrent Neural Networks (TP-RNN) model to predict the temperature field after the next layer deposition for each of the candidate infill toolpaths, and a process parameters inspired thermal field evaluation method to select the best candidate toolpath. The approach would significantly improve the computational efficiency of the laser infill toolpath planning, which was validated by improving the flatness of the 20-layer cube deposition samples with two dimensions (20 mm × 20 mm and 30 mm × 30 mm).

Heat accumulation is a critical problem in continuous multi-layer laser aided additive manufacturing (LAAM) process, resulting in inhomogeneous mechanical properties and non-uniformity in the deposited height which can deteriorate the deposition process. This work presents a new integrated finite element (FE) simulation and machine learning approach to select a multi-layer laser infill toolpath planning strategy for fabricating quadrilateral parts to minimise localised heat accumulation during the deposition process. After one layer deposition simulation, the approach employs a Temperature-Pattern Recurrent Neural Networks (TP-RNN) model to predict the temperature field after the next layer deposition for each of the candidate infill toolpaths, and a process parameters inspired thermal field evaluation method to select the best candidate toolpath. The approach would significantly improve the computational efficiency of the laser infill toolpath planning, which was validated by improving the flatness of the 20-layer cube deposition samples with two dimensions (20 mm × 20 mm and 30 mm × 30 mm). [ABSTRACT FROM AUTHOR]

The metal droplets deposition method (MDDM) is a rapid prototyping technology, implemented via metallurgy bonding within droplets. The anisotropy of heat transfer and re-melting is caused by an asymmetric deposition process. A lattice Boltzmann method (LBM) model is established to predict the heat transfer and phase change in the multi-layer deposition. The prediction model is verified by the experimental temperature profiles in existing literature. The monitoring points are set to compare the temperature profiles, and decoupling analyze the heat transfer mechanism in different positions. The negative relationships between the re-molten volume of the temperature difference, as well as the influence of the dispositive position and the relative position of the adjacent component are observed and analyzed under the heat conduction. This work is helpful to choose the appropriate temperature conditions and the optimal dispositive method. [ABSTRACT FROM AUTHOR]

Powder spreading precedes creation of every new layer in powder bed additive manufacturing (AM). The powder spreading process can lead to powder layer defects such as porosity, poor surface roughness and particle segregation. Therefore, the creation of homogeneous layers is the first task for optimal part printing. Discrete element methods (DEM) powder spreading simulations are typically limited to a single layer and/or small number of particles. Therefore, results from such model configurations may not be generalized to multiple layer processes. In this study, a computationally efficient multi-layer powder spreading DEM simulation model is proposed. The model is calibrated experimentally using static Angle of Repose measurements. The adhesion model parameter, cohesive energy density is related to adhesive surface energy and strain energy release rate parameters. The model results show that interaction between particle and the powder spreading rake leads to noticeable variation in packing density, surface roughness, dynamic angle of repose (AOR), particle size distribution, and particle segregation. The powder model is experimentally validated using a recoater spreading rig to measure the dynamic AOR at spreading speeds consistent with recoating speeds and layer heights used in AM processes. [ABSTRACT FROM AUTHOR]

Variation in process parameters and deposition strategies has produced different thermo-mechanical characteristics in a part fabricated by a wire feeding type directed energy deposition (DED) process. The purpose of this paper is to select a proper deposition strategy to fabricate a straight wall part using a wire feeding type DED process. The deposition strategies include different deposition directions, deposition patterns and interpass time. In order to investigate the influences of deposition strategies on thermo-mechanical characteristics of fabricated part, three-dimensional finite element analyses (FEAs) have been proposed. A volumetric heat flux has been applied to simulate the transient heat transfer phenomena of the DED process. Influences of different deposition strategies on thermo-mechanical characteristics of fabricated part have been discussed. From the result of residual stress distribution, an appropriate deposition strategy has been selected for the multi-layer deposition. Results of FEAs have been verified through comparison of vertical displacements between estimated results from FEAs and those of experiments. [ABSTRACT FROM AUTHOR]

With the ability of layer-by-layer fabrication, eliminating solidification challenges, friction stir surfacing-based additive manufacturing is of potential interest for bulk fabrication of structural components. However, the thermal cycling effect of proceeding layers has a significant influence on the mechanical and microstructural properties of prior depositions, which demands an in-depth investigation. This paper presents a novel and effective method for investigating the intra-layer mechanical and metallurgical effect in multi-layer friction stir surfacing-based additively manufactured aluminum structures with high deposition capability. Mechanical investigations involving tensile and hardness tests demonstrated the in-plain isotropic behavior of deposited material with out-of-plane hardness downscaling of pre-deposited layers. Insignificant variation of mechanical strength by ± 0.49 MPa demonstrated the effectiveness of multilayered deposited structure as a homogeneous bulk material. Variation of hardness from one layer to other and at the interface has been correlated with microstructural characterizations such as grain size increment opposite to build direction and dissolution of strengthening Mg 2 Si precipitates. With a high joining efficiency of 81.01% and an enhanced deposition rate of 169 cm3/h, the presented innovative deposition methodology meets the potentiality for industrial practice of large structures. [Display omitted] • Friction stir surfacing-based metal additive manufacturing. • Effects of multi-layer deposition on the formerly deposited layer. • Variation of mechanical and microstructural properties along the building direction. • No significant directional dependency of tensile properties in deposited structure. • Comparatively high deposition efficiency (average 65.5%) achieved for multi-layer. [ABSTRACT FROM AUTHOR]

The hot cracking sensitivity dramatically increases because of the longitudinal macro-segregation of craters and the transverse macro-segregation of welding center in pre-layers. Statistical analysis of the total area, average size and Nb concentration of interdendritic low-melting point Laves phase, the Nb concentration of the γ phase in the dendritic core, and the arm spacing of different sub-regions was used to explore the effects of macro- and micro-segregation of Nb. Solidus and liquidus curves were used to determine the temperature at which solid and liquid phases coexist in different sub-regions, which were combined with Scheil equation curves to identify Nb sources and interlayer transfer, so as to develop a model for the molten pool of subsequent layers. This model explains the effect of transversal and longitudinal macro-segregation in the pre-layer on the Nb concentration of the melt pool of subsequent layers, the dynamic balance of the solidification interface and the relative area of Laves phase in the macro-segregated sub-region of the solidified metal. [ABSTRACT FROM AUTHOR]

Direct Metal Deposition (DMD) is becoming increasingly attention-attracting technology for new component manufacture and repair. However, fundamental process understanding is not yet comprehensive. Without considering the realistic spatial distribution of powder flow, some important process conditions have been neglected in layered deposition, such as the initial stand-off distance of nozzle, scanning direction (orientation of nozzle), change in stand-off distance through process and stability of multi-layer deposition. This then limits the efficacy of deposition strategies which serves to limit the industrial uses of DMD. In this paper, a realistic model was built for the simulation of multi-layer deposition, using real spatial powder flow concentration. Then, the influences of the orientation of nozzle, the stand-off distance of nozzle and single-step rise on geometric characteristics are investigated. It is showed that the stand-off distance of nozzle significantly affects the geometric characteristics of the deposited layer thickness, while the influence of the orientation of four-tip nozzle on deposition can largely be neglected. Furthermore, the stability of multi-layer deposition was discussed, and the steady condition was obtained by analyzing relation among single-step rise, maximum deposited layer thickness and stand-off distance of nozzle. This also allows a deposition strategy to be optimized for the purpose of manufacturing given procedure. The approach taken here is also verified by experiments with the strategies proposed by simulation. [ABSTRACT FROM AUTHOR]

Abstract: Electro-spray deposition (ESD) was applied to fabricate solution processed donor–acceptor bulk heterojunction organic photovoltaic devices with multi-layer structure. Solvent effect was observed when using different organic solvents. Power conversion efficiency (PCE) of the devices prepared from dichlorobenzene increased dramatically comparing to the ones from chloroform, owing to improved homogeneity of the films. ESD enabled us to fabricate solution processed multi-layer (donor/donor:acceptor/acceptor) devices with simple successive deposition steps. Energy Dispersive X-ray Reflectometry analysis confirmed distinct three layered structure of the active layers. Solar cell device parameters of the trilayer devices were compared to single layer devices and those of spin coated devices with the same donor:acceptor ratio and film thickness. Post-thermal treatment results showed that after annealing at 125°C, trilayer devices exhibited best performance with the maximum PCE of 2.17%. [Copyright &y& Elsevier]