Simulation of Binder Infiltration in Additive Manufacturing of Sand Molds

This article proposes a computational fluid dynamics approach to simulate binder infiltration in 3D printing of sand molds using OpenFOAM facilitating the identification of suitable levers for application-specific material and process developments. A method for randomly generating powder bulks of designated powder size distributions (PSD) and procedures for automated analysis of the infiltration profile and volume are introduced. Simulation is utilized to investigate binder infiltration using different droplet spacings, representing different printheads’ resolutions. The apparent particle size at the exact location of the droplets’ impact, the droplets’ landing position in relation to the respective surface topography, and thus the statistical appearance of particle formations appear to be influencing the infiltration profile. High-speed camera observations show the plausibility of the predicted infiltration kinetics. An exemplary use case compares the predicted infiltration profiles to the compressive strength of specimens printed from silica sand with low binder contents. Simulation predicts an average infiltration of 250 μm that presumably achieves reliable bonding for layer thicknesses up to 365 μm. A decrease in strength with increasing layer thickness at constant binder contents can be found in the experiment – at layer thicknesses above 350 μm, only minor strengths are achieved.     

Ecological interface design and emergent users: Designing for small-scale trucking ecology in India

Effective on-road safety requires proper maintenance of vehicles. In the trucking sector in India, there is a need for supporting predictive maintenance to decrease downtime and improve safety. Improving maintenance in this sector involves certain challenges. First, most trucks are owned by small-scale fleet owners (trucks < 5). Second, maintenance is often handled by small-scale mechanic workshops. The fault diagnosis is very often limited to recognition by the driver and later reassessed by the mechanic by relying on the feel or the sound of the vehicle. Third, a majority of stakeholders in this sector—drivers, mechanics, and owners—have low levels of education. Despite these challenges, with the increase in the rate of digitalization, in the future, it will be easier to monitor the health of the parts of a truck. In addition, there is a developing trend of mobile phone and internet penetration in India that has leapfrogged a majority of Indians into becoming “emergent users” of information technology. Therefore, this article shows that sociotechnical approaches such as ecological interface design can be used to develop mobile interfaces for supporting predictive maintenance through health and usage monitoring of trucks for small-scale fleet owners in India. To develop the interface, a field study was conducted at several sites in the state of Tamil Nadu, India. The insights were used to develop scenarios and the abstraction hierarchy, which were later used creatively to develop the interface design for emergent users.     

Effect of milk protein standardisation using buffalo milk protein co-precipitates on the texture,composition and yield of paneer

Buffalo milk was utilised for preparing paneer samples after standardisation of protein:fat ratio to 0.68 with the addition of buffalo milk protein co-precipitates (BMPC). These paneer samples along with control paneer (from buffalo milk) were analysed for yield, composition, microstructure, sensory, texture profile and protein loss in whey during manufacture. Paneer prepared using BMPC was considerably higher in yield and recovery of total solids, protein and calcium content than control paneer and could withstand the frying conditions in terms of retention of shape and integrity. Texture profile analysis and microstructure evaluation revealed the differences in textural properties of paneer samples prepared using BMPC with control paneer.     

Drop breakage in a single-pass through vortex-based cavitation device: Experiments and modeling

Liquid–liquid emulsions are used in many sectors such as personal care, home care, and food products. There is an increasing need for developing compact and modular devices for producing emulsions with desired droplet size distribution (DSD). In this work, we have experimentally and computationally investigated an application of vortex-based hydrodynamic cavitation (HC) device for producing emulsions. The focus is on understanding drop breakage occurring in a single-pass through the considered HC device. The experiments were performed for generating oil-in-water emulsion containing 1%–20% rapeseed oil. The effect of pressure drop across the HC device in the range of 50–250 kPa on drop breakage was examined. DSD of emulsions produced through a single pass was measured using the focussed beam reflectance measurements. Comprehensive computational fluid dynamics (CFD) model based on the Eulerian approach was developed to simulate multiphase cavitating flow. Using the simulated flow, population balance model (PBM) with appropriate breakage kernels was solved to simulate droplet breakage in a vortex-based HC device. The device showed an excellent drop breakage efficiency (nearly 1% which is much higher than other commercial devices such as rotor–stators or sonolators) and was able to reduce mean drop size from 66 to ~15 μm in a single pass. The CFD and PBM models were able to simulate DSD. The presented models and results will be useful for researchers and engineers interested in developing compact devices for producing emulsions of desired DSD.     

Three-dimensional printing of triply periodic minimal surface structured scaffolds for load-bearing bone defects

The porous and cellular architecture of scaffolds plays a significant role in mechanical strength and bone regeneration during the healing of fractured bones. In this present study, triply periodic minimal surface (TPMS)-based gyroid and primitive lattice structures were used to design the cellular porous biomimetic scaffolds with different unit cell sizes (4, 5, and 6). The fused filament fabrication-based 3D printing technology was used for the fabrication of polylactic acid scaffolds. The surface morphology and mechanical compressive strength of differently structured scaffolds were observed using scanning electron microscopy and a universal testing machine. The unit cell size of 4 showed higher compressive strength in both gyroid and primitive structured scaffolds compared to unit cell sizes 5 and 6. Moreover, the gyroid structured scaffolds have higher compressive strengths as compared to primitive structured scaffolds due to the higher bonding surface area at the intercalated layers of the scaffold. Hence, the mechanical strength of scaffolds can be tailored by varying the unit cell size and cellular structures to avoid stress shielding and ensure implant safety. These TPMS-based scaffolds are promising and can be used as bone substitute materials in tissue engineering and orthopedic applications.     

Hybrid Electrolyte Design for High-Performance Zinc–Sulfur Battery

Rechargeable aqueous Zn/S batteries exhibit high capacity and energy density. However, the long-term battery performance is bottlenecked by the sulfur side reactions and serious Zn anode dendritic growth in the aqueous electrolyte medium. This work addresses the problem of sulfur side reactions and zinc dendrite growth simultaneously by developing a unique hybrid aqueous electrolyte using ethylene glycol as a co-solvent. The designed hybrid electrolyte enables the fabricated Zn/S battery to deliver an unprecedented capacity of 1435 mAh g⁻¹ and an excellent energy density of 730 Wh kg⁻¹ at 0.1 Ag⁻¹. In addition, the battery exhibits capacity retention of 70% after 250 cycles even at 3 Ag⁻¹. Moreover, the cathode charge–discharge mechanism studies demonstrate a multi-step conversion reaction. During discharge, the elemental sulfur is sequentially reduced by Zn to S²⁻ (${\mathrm{S}}_8\to {\mathrm{S}}_{\mathrm{x}}^{2-}\to {\mathrm{S}}_2^{2-}+{\mathrm{S}}^{2-})$, forming ZnS. On charging, the ZnS and short-chain polysulfides will oxidize back to elemental sulfur. This electrolyte design strategy and unique multi-step electrochemistry of the Zn/S system provide a new pathway in tackling both key issues of Zn dendritic growth and sulfur side reactions, and also in designing better Zn/S batteries in the future.     

Flow physics of planar bistable fluidic oscillator with backflow limbs

Fluidic oscillators (FOs) are used in a variety of applications, including process control and process intensification. Despite the simple design and operation of FOs, the fluid dynamics of FOs exhibit rich complexities. The inherently unstable flow, jet oscillations, and resulting vortices influence mixing and other transport processes. In this work, we computationally investigated the fluid dynamics of a new design of a planar FO with backflow limbs. The design comprised of two symmetric backflow limbs leading to bistable flow. The unsteady flow dynamics, internal recirculation, jet oscillations, secondary flow vortices were computationally studied over a range of inlet Reynolds numbers (2400–12,000). The nature and frequency of the jet oscillations were quantified. The computed jet oscillation frequency was compared with the experimentally measured (using imaging techniques) jet oscillation frequency. The flow model was then used to quantitatively understand mixing, heat transfer, and residence time distribution. The approach and the results presented in this work will provide a basis for designing FO's with desired flow and transport characteristics for various engineering applications.     

A Study of Added SiC Powder in Kerosene for the Blind Square Hole Machining of CFRP Using Electrical Discharge Machining

Silicon - Carbon Fiber Reinforced Polymers (CFRPs) have been applied potentially for various application components owing to their lightweight and better mechanical properties. However, the...     

A novel approach for prediction of surface roughness in turning of EN353 steel by RVR-PSO using selected features of VMD along with cutting parameters

The abrupt changes in tool-workpiece interaction during machining process induce variation in the surface quality of work material. These interactions include built-up edge formation and their break-off, environmental conditions (use of coolant, rise of temperature etc.), material imperfections, improper structural fitness of machine & tool components, etc. This study presents prediction of surface roughness in turning of EN353 steel implementing the variational mode decomposition (VMD) for processing the vibration data, followed by estimation of the surface roughness using the relevance vector regression (RVR) optimized by particle swarm optimization (PSO). The raw vibration data has been decomposed in five discrete sets of frequency components known as variational mode functions (VMFs). A set of twenty-one statistical features in each three axes have been extracted for raw data and each VMF. The RVR has been trained using these 21×3 = 63 features and 3 cutting parameters — cutting speed, feed depth of cut. The RVR has also been trained separately using top 5 features selected through RreliefF algorithm. The optimal decomposition level has been determined to minimize the noise and predict the surface finish accurately. The results obtained in 1st VMF (high frequency, low amplitude) using its top 5 features for prediction have been found to be reliable with higher prediction accuracy.