Ramesh Raghavendra

Waterford Institute of Technology | WIT · School of Engineering

This current work evaluates the efficacy of a co-flow nozzle for cold spray applications with the aim of mitigating nozzle clogging issues, which can occur during long-duration operations, by replacing the solid wall of a divergent nozzle section with an annular co-flow fluid boundary. Simulations were conducted on high-pressure nitrogen flowing th...

Injection moulding (IM) tools with embedded sensors can significantly improve the process efficiency and quality of the fabricated parts through real-time monitoring and control of key process parameters such as temperature, pressure and injection speed. However, traditional mould tool fabrication technologies do not enable the fabrication of compl...

The current work numerically evaluates the efficacy of a co-flowing nozzle for cold spray applications with the aim to mitigate nozzle clogging by reducing the length of its divergent section. The high-pressure nitrogen flow through convergent-divergent axis-symmetric nozzles was simulated and the particle acceleration is modelled using a 2-way Lag...

The clogging, a frequent gas passage deformation phenomenon because of powder accumulation on inner nozzle wall, is a major issue in long duration Cold Spray (CS) operations and a major challenge for Cold spray technology to be adopted for additive manufacturing. This study aims to design and integrate new nozzle design in Cold Spray operations for...

Additively manufactured (AM) metal parts are usually post-processed by mechanical surface finishing to attain desired surface roughness. Simulation of AM chain provides means to effectively optimize the final product's quality characteristics in the design stage. The present study developed theoretical models for simulation of surface topography an...

The use of additive manufacturing (AM) has grown exponentially in recent years and has many advantages, including feasibility, over other conventional processes in many current applications. The use of a second process, for example, machining, improves the surface finish and in this case, the use of two processes is known as hybrid manufacturing. H...

WE43 magnesium alloy is a low density, biocompatible material that has been identified as a viable option for temporary orthopaedic implants due to its favourable mechanical and biodegradation properties. This bioresorbable material eliminates the requirement for an invasive second surgery to remove a traditional bioinert temporary implant after th...

Recent scientific achievements in the area of printed electronics allow the production of electronic devices with enhanced performances and versatility at a relatively low cost. The transfer from a single to multi-material applications, advances in the sequential deposition of insulators, conductors or semiconductors enable the progress from uncomp...

Metal additive manufacturing (AM) processes, viz laser powder bed fusion (L-PBF), are becoming an increasingly popular manufacturing tool for a range of industries. The powder material used in L-PBF is costly, and it is rare for a single batch of powder to be used in a single L-PBF build. The un-melted powder material can be sieved and recycled for...

Laser-based powder bed fusion (L-PBF) of AlSi10Mg is used to fabricate complex, light-weight structures with high thermal conductivity. Much effort has gone into investigating the mechanical behavior of L-PBF components; however few studies investigated their thermal properties. This investigation characterizes the effect of process parameters on t...

In this study, the effect of as-built and heat-treated additively manufactured 316L stainless steel at different temperatures was examined on the electrochemical corrosion performance. The corrosion was investigated by Tafel polarization and electrochemical impedance spectroscopy methods in a 3.5% NaCl solution. For this purpose, the as-built and h...

Metal Additive Manufacturing (AM), viz, laser powder bed fusion (L-PBF), processes are becoming an increasingly popular manufacturing tool for a range of industries. L-PBF allows for the manufacture of complex and often critical components in the medical device, medical implants, aerospace, and automotive industries, to name a few. The powder mater...

With the proliferation of metal additive manufacturing (AM) as a production technique in industry, the need to effectively and efficiently inspect components with free-form shapes and internal geometries is constantly increasing. X-ray micro-computed tomography is a natural inspection partner for this production technology; however, metallic sample...

This paper presents a methodology for the embedding of a sensor in a 316L stainless steel component during the laser powder bed fusion process. The aim of this study is to overcome the drawbacks of traditional sensor attachment to the surface of a component via placing sensors into a part during the manufacturing process. A methodology for the embe...

This paper presents the embedding of a temperature Surface Acoustic Wave (SAW) sensor in an additively manufactured 316L stainless steel part during the Laser Powder Bed Fusion (L-PBF) process. The embedding of sensors and integrated circuits in additively manufactured (AM) parts is an important step towards the development of smart components; how...

This paper presents a comparative study on the effect of multi-machine laser powder bed fusion manufacturing on the quality of 316L stainless steel parts. Within industry, often the same additive manufacturing machines are used for research and development of components as are used for production. However, there is a challenge in terms of determini...

Despite the recent progress in additive manufacturing (AM) process and technology, challenges in the repeatability and reproducibility of AM parts still hinders the adoption of this technique in many industries. This is particularly difficult when a part is qualified on a particular part on a certain machine using optimised parameters. If a manufac...

Post-processing is one of the main ways to improve mechanical and microstructural characteristics of stainless steel 316L fabricated by the laser-based powder bed fusion (LPBF) process. In this study, optimized LPBF parameters were used to manufacture SS316L bars. For the post-processing, two main heat treatment strategies have been used, quenching...

Laser-Powder Bed Fusion (L-PBF) of metallic parts is a highly multivariate process. An understanding of powder feedstock properties is critical to ensure part quality. In this paper, a detailed examination of two commercial stainless steel 316L powders produced using the gas atomization process is presented. In particular, the effects of the powder...

With the increasing popularity of metal additive manufacturing, in particular the powder bed fusion (PBF) process for the production of end-use components in a wide range of industries, the ability to recycle un-melted powder increases the attraction of PBF. Previous research has characterised the effects of recycling the powder on both the powder...

Lipoyl-apocynin and lipoyl-sesamol are bio-active conjugates of thioctic acid (also known as alpha-lipoic acid), synthesized by benign chemical approach by the combination of thioctic acid and powerful bio-phytonutrients, apocynin and sesamol respectively. Encapsulation is done for chemically modified thioctic acid conjugates within liposome struct...

In this study, selective laser melting (SLM) was investigated for the manufacturing of 316L stainless steel press-fit joints. The accuracy of selective laser melting technique in fabrication of texture profile in shape, pitch and height of microsurface texturing was examined. The resulting insertion and removal forces achieved from the produced tex...

Manufacturing-induced defects are a key source of crack initiation and component failure under high temperature cyclic loading. In this work, 3D X-ray micro-computed tomography and microstructural analysis of manufacturing-induced defects is presented for forged and cast MarBN martensitic-ferritic steel, along with high temperature, low cycle fatig...

free access to the paper: https://rdcu.be/b32vL The objectives of this study are: 1) to verify whether using linear heat input alone is sufficient to predict the resulting microstructure. 2) to demonstrate the potential of single-step process of functionally graded material using powder bed fusion. In laser powder bed fusion, linear heat input is...

Recycling metallic powders used in the additive manufacturing (AM) process is essential for reducing the process cost, manufacturing time, energy consumption, and metallic waste. In this paper, the focus is on pore formation in recycled powder particles of stainless steel 316L during the selective laser melting process. We have introduced the conce...

Lipoyl-apocynin and lipoyl-sesamol are bio-active conjugates of thioctic acid (also known as alpha-lipoic acid), synthesized using a benign chemical approach via the combination of thioctic acid and the powerful bio-phytonutrients, apocynin and sesamol, respectively. Encapsulation was performed for chemically modified thioctic acid conjugates withi...

Direct metal laser sintering (DMLS) is a powder bed fusion (PBF) additive manufacturing process commonly used within the medical device and aerospace industries where regulations drive the requirement for stringent quality control. Using in-situ monitoring, the identification of defects, as well as the geometric and dimensional measurement of the l...

Additive manufacturing, viz. powder bed fusion (PBF), processes are becoming increasingly more applicable to a range of industries. Direct metal laser sintering (DMLS) is a PBF process commonly used within the medical and aerospace industries to produce complex and often critical components. Powder material used in the DMLS process can be costly an...

The tensile mechanical properties and anisotropy levels of identical test-coupons, fabricated from maraging steel 300 (MS300) using two alternative EOS EOSINT M280 Additive Manufacturing (AM) systems, have been examined. The mechanical performance variations resulting from process differences between the two suppliers and the part's build volume or...

This experimental study investigates the combined effect of the three primary Additive Manufacturing (AM) build orientations (0, 45, and 90deg) and an extensive array of heat treatment plans on the plastic anisotropy of maraging steel 300 (MS1) fabricated on the EOSINT M280 Direct Metal Laser Sintering (DMLS) system. The alloy's microstructure, har...

The research presented here compares the weight and structural strength of several lightweight 3D metal printed fractal antennas to the equivalent metal-coated polymer 3D printed antenna. Lattice structures are recognized for their advantages in providing lightweight, stiff and shock-resistant structures. In this work, they are used to create a str...

Direct metal laser sintering (DMLS) is a powder bed fusion (PBF) process commonly used within the medical device and aerospace industries to fabricate high value, complex components. Powder material used in the DMLS process can be costly and it is rare for a single build to require a full batch of powder. The un-melted powder, which differs in part...

Interim Results Presentation

Additive manufacturing, viz. powder bed fusion (PBF), processes are becoming increasingly more applicable to a range of industries. Direct metal laser sintering (DMLS) is a PBF process commonly used within the medical and aerospace industries to produce complex and often critical components. Powder material used in the DMLS process can be costly an...

Cold working of austenitic stainless steel results in the formation of α⁰-martensite (ferromagnetic) within the host material (paramagnetic). The role of α⁰-martensite and carbide precipitation in the reverse transformation mechanism during the heat treatment of AISI 304 is presented. A magnetic Barkhausen noise (MBN) measurement technique was empl...

This research relates to the design, modelling and fabrication of 3D metal printed heat sinks. The heat sinks presented in the research are the commonly used longitudinal fin solid heat sink (LFSHS) and three LFSHS lattice structure designs, differing only in their lattice sizes, fabricated using the Direct Metal Laser Sintering (DMLS) technique, o...

This research presents the impact on surface roughness of build orientation in the fabrication of a 3D metal printed X-band horn antenna (8.2-12.4 GHz). Build orientation is investigated by printing the antenna at three different orientations of 45,̊ 90̊ and 180̊, with respect to the building platform. The results indicate that the build orientatio...

An overview of literature and the work carried out by the authors in 3D metal printed microwave components is presented. Components produced include a conventional horn antenna, Sierpinski gasket antenna, waveguide antenna array, a monocone antenna with an integrated feed and horn antenna with inbuilt periodic structures. In addition, antenna with...

Irish Research Council (IRC) awardees showcase their research to the IRC Board members

The research presents a 3D metal printed X-band (8.2-12.4 GHz) horn antenna with side-lobe reduction, achieved by printing pyramidal periodic structures on the inner faces of the antenna’s E-plane. The 3D pyramidal periodic structures result in the suppression of the surface current and hence reduce the side-lobes of the horn antenna. The placement...

In this work, a 3D monocone antenna for wideband applications, with an integrated N-type feed, is created via Additive Manufacturing (AM). AM permits the production of complex RF components with ease, in this case in realizing both the monocone structure and the integrated feed. Integrating the feed as part of the antenna reduces the assembly requi...

In this research, the design, simulation, and fabrication of the first ever 3D metal printed Sierpinski gasket antenna, with multiple resonance characteristics is reported. The antenna is fabricated from Titanium alloy Ti-6Al-4V, using the Direct Metal Laser Sintering (DMLS) technique. Mechanical considerations like Rumsey’s principle and the suppo...

The research presents the performance evaluation of a 3D metal printed antenna, as the inherent surface roughness is gradually reduced using different surface treatment techniques. In this work, surface treatment is performed on a complex shaped, 3D metal printed Sierpinski gasket antenna, fabricated from Ti-6Al-4V using a Direct Metal Laser Sinter...

In this research, the post-processing steps and their importance is highlighted for 3D printed microwave components. The components created so far include various antennae and a waveguide fabricated with Titanium alloy (Ti-6Al-4V), using the Direct Metal Laser Sintering (DMLS) technique. The variations in performance after each post-processing step...

For many years there has been considerable research from both an academic and industrial perspective into the monitoring and control of CNC machining processes, and progress has been well documented. It is widely acknowledged within the CIRP community that collection of information into the performance of material cutting processes is a worthwhile...

Etoricoxib (ECB) is a large, lipophilic molecule that is practically insoluble in water and exhibit an exceedingly slow dissolution rate making it a Class II compound in Bio pharmaceutics Classification System. In the present article, the higher solubility advantage of ECB in solid dispersion is explored. More specifically, solid dispersion of ECB...

The aim of present study was to develop conventional and PEGylated (long circulating), liposomes containing anastrozole (ANS) for effective treatment of breast cancer. ANS is a third-generation non-steroidal aromatase inhibitor of the triazole class used for the treatment of advanced and late-stage breast cancer in post-menopausal women. Under such...

The properties of porous silicon make it a promising material for a host of applications including drug delivery, molecular and cell-based biosensing, and tissue engineering. Porous silicon has previously shown its potential for the controlled release of pharmacological agents and in assisting bone healing. Hydroxyapatite, the principle constituent...

In precision engineering, tool wear affects the dimensional accuracy and surface finish of machined components. Currently, errors associated with tool wear remain uncompensated for and are usually only detected at the end of the machine cycle, by which time the product may be scrap. If real-time, accurate monitoring were available, machine paramete...

ZnO based varistors are widely used for overvoltage protection in many electrical and electronic circuits, at voltages ranging from a few to over a million volts. By careful control of the microstructure, through nano-structuring by chemical routes, it should be possible to produce varistors with high breakdown voltage (Vc), as this is proportional...

Microwave sintering of multilayer capacitor/varistor-based integrated passive devices (IPDs) has been investigated for the first time. The sintered samples were characterized for density, microstructure, composition, and electrical performance. It was found that IPDs with varistor/capacitor formulations could be microwave sintered to fully dense de...

This paper was published in Ceramic Engineering and Science Proceedings [© The American Ceramic Society] and details of the definitive version are available from: http://ceramics.org/acers-bookstore/cesp-ceramic-engineering-and-science-proceedings/ The feasibility of employing the microwave methodology for the processing of integrated passive devic...

The co-firing characteristics of ZnO varistor and NiZn ferrite thick films were investigated, the objective being to create an integrated passive device. Bismuth oxide additions were used to increase the shrinkage of the ferrite during sintering. Dilatometry analysis proved that well-matched shrinkage characteristics could be obtained for bismuth o...

An industrially viable solution-based processing route using minimal amounts of solvent has been used to prepare bulk quantity nanopowders (average particle size 15 +/- 3 nm) for the fabrication of ZnO varistors. The xerogels, calcined powders and sintered materials were fully characterised. The preparation of varistors from nanopowders has been op...

ZnO varistor materials were prepared by a sol gel route with subsequent drying and calcination. Varistor discs fabricated from these materials were subjected to a two step sintering schedule. Therefore in a typical experiment, the samples were heated to 1000 degrees C, then allowed to cool for over 30 min to 900 degrees C and held there for 6 h. Th...

In this paper design, modeling and characterization of single and double coils, which consist of conductive layer embedded in the soft ferrite material, are described. These surface-mount components, comprising of a cofired multilayered ferrite and coil, have been developed in the ceramic coprocessing technology. A simple analytical model of propos...

This paper describes the design, modeling, simulation and fabrication of zig-zag and meander inductors embedded in low- or high-permeability soft ferrite material. These microinductors have been developed with ceramic coprocessing technology. We compare the electrical properties of zig-zag and meander inductors structures installed as surface-mount...

Thirteen glasses of the general formula (M1, M2)9.33Si14Al5.33O41.5N5.67 where M1=La or Nd and M2=Y or Er have been prepared with M1/(M1+M2) fractions of 1, 0.75, 0.5, 0.25, and 0. Data for molar volume (MV), glass compactness (C), Young's modulus (E), microhardness (H), glass transition temperatures (Tg), and dilatometric softening temperatures (T...

Nucleation and crystallization studies were conducted on a YSiAlON glass that contained 17 equiv.% nitrogen (7.5 at.%) by using a two-stage nucleation-and-growth treatment. Classical and differential thermal analysis (DTA) techniques were both used to study the crystallization process, to ensure that the optimum heat-treatment schedule that yielded...

This letter describes the design, modeling, simulation, and fabrication of novel integrated passive devices (IPDs). These IPDs, comprising of a cofired multilayered varistor and inductor, have been developed in the ceramic coprocessing technology. The equivalent model of the new structures is presented, suitable for design and circuit simulations....

ZnO nanoparticles were prepared by a solid state pyrolysis reaction of zinc acetate dihydrate and oxalic acid dihydrate at 500degreesC. The course of reaction at various temperatures was followed by XRD. Subsequently varistors were fabricated from this nano-ZnO material by solid state mixing with various oxide additives and sintering to 1050degrees...

The purpose of this work was to co-fire crack-free varistor-ferrite ceramic multilayers fabricated via a dry pressing route. Multilayers were sintered using a standard industrial grade varistor sintering regime. Sinter shrinkages of both varistor and ferrite materials were measured using dilatometry and showed that the varistor shrunk significantly...

Linear arrays of ZnO nanoparticles have been successfully prepared by a simple sol - gel condensation reaction involving chemical modifiers, followed by drying (80 degreesC) and calcination (500 degreesC). The calcined material (nanoarray ZnO) is composed of approximately spherical nanoparticles of average diameter 21 +/- 3 nm, self-assembled to fo...

Nanoparticles of ZnO were prepared by the reaction of ethanolic solutions of zinc acetate and oxalic acid followed by drying (80 °C) and calcination (500 °C). Subsequently varistor materials were fabricated from this nanoparticular ZnO via two separate routes:- a) from a “core shell” material using metal salts as additives; b) by using a convention...

Nanoparticles of ZnO were prepared by the reaction of ethanolic solutions of zinc acetate and oxalic acid followed by drying (80degreesC) and calcination (500degreesC). Subsequently varistor materials were fabricated from this nanoparticular ZnO via two separate routes:- a) from a "core shell" material using metal salts as additives; b) by using a...

Mixed lanthanide cation oxynitride glasses have been prepared in the Ml - M2 - Si-Al-O-N systems where Ml = La or Nd and M2 = Y or Er. The densities (p), Young's moduli (E), microhardnesses (Hv), glass transition temperatures (Tg), dilatometric softening temperatures (Tdil) and coefficients of thermal expansion (CTE) of 13 glasses were determined....

Glasses containing up to 20% (e.o.) nitrogen were prepared in Nd-Si-Al-O-N system. Compositions, which crystallise in single and multiphase materials, were heat-treated under various conditions, and oxynitride glasses were found to be self-nucleating. The crystalline phases formed depend on both the composition of the parent glass and the heat-trea...