In-Situ Preheating in Hybrid Layered Manufacturing for Tooling Elements

Solidification cracking of hard materials such as H13 tool steel is one of the major problems in metal based Additive Manufacturing (AM) processes. Hybrid Layered Manufacturing (HLM) is one of the metal based AM process which uses Metal Inert Gas (MIG) cladding for addition and CNC milling for subtraction of material. In this work, an in-situ induction heating based preheating system has been developed to solve the solidification cracking problem. The Tungsten Inert Gas (TIG) and Induction heating methods are compared and it has been found that the induction based preheating system can produce better microstructure and sound products. In the experimental procedure, before deposition of a layer the prebuild layer is preheated up to 350-5000C. Also the effect of in-situ preheating on the microstructure of the deposited layers have been studied using Scanning Electron Microscope (SEM).Mechanical Engineerin

Challenges in path planning of high energy density beams for additive manufacturing

As there are no cutting forces in High Energy Density (HED) beams like lasers and Electron Beam (EB), their speeds are limited only by their positioning systems. On the other hand, as the entire matrix of the 3D printed part has to be addressed by the thin beam in multiple passes in multiple layers, they have to travel several kilometers in tiny motions. Therefore, the acceleration of the motion system becomes the limiting factor than velocity or precision. The authors have proposed an area-filling strategy for EB to fill the layer with optimal squares to exploit analog and hardware computing. 3D printing requires uniform intensity slanged as flat hat shape whereas the default is Gaussian. The authors have proposed an optimal algorithm that takes into account the maximum velocity and acceleration for achieving a flat hat without any compromise on productivity

Tailoring coil geometry for secondary heating of substrate towards the development of induction heating-based wire additive manufacturing

Induction heating (IH), a clean energy source, is potentially used to develop wire additive manufacturing (AM) system. The optimised parameters that simultaneously melt the mild steel wire and raise the substrate temperature is established. A fully coupled thermal-electromagnetic model of AM system is developed to perform numerical experiments on temperature development. The proposed hybrid helical-pancake coil with circular cross-section melt the metallic wire and raise the substrate temperature to 1490 K. The hybrid coil provides rapid heating to the wire (2819 K) and substrate together by enhancing magnetic field strength. The experiments using high-frequency IH system (550 A and 353 kHz) with a 3-turn helical coil is validated with model results for 2 mm mild steel wire.</p

Investigation of ablation studies of EPS pattern produced by rapid prototyping

Expanded Polystyrene (EPS) patterns are used in Evaporative Pattern Casting (EPC). The cost of EPS pattern-making through moulding cannot be justified for small batch production. As 3D printing or Additive Manufacturing (AM) is suitable for small volumes, several efforts have been made to develop these machines for EPS including Segmented Object Manufacturing (SOM) of the authors. EPS is typically processed through ablation or traditional machining, the former using hot tools in the form of profiled axisymmetric shapes, blades or wire. The efficacy of SOM machine relies on the performance of the individual sub-systems, so in the present work, the ablation studies of hot wire slicing of the machine is performed. The kerfwidth and surface roughness determine the quality of the pattern produced by ablation. The objective of the paper is to investigate the ablation process by introducing novel mathematical model to predict the kerfwidth for different power inputs and feedrates, which is further validated with experimental data. Subsequently, an empirical relationship is established to predict the surface roughness (Ra) of the sliced surface by performing regression analysis of collected experimental data. The different cutting zones have also been classified, which gives an overall understanding of slicing mechanism. The average error in surface roughness prediction is found to be around ±10%. With the help of these models, the SOM machine can produce better quality EPS patterns in terms of kerfwidth and Ra value, which finally depicts the quality of final casting produced by EPC process

Retrofitment of a CNC machine for omni-directional tungsten inert gas cladding

Metal inert gas (MIG), Tungsten INERT GAs (TIG), laser and Electron beam (EB) cladding processes are used in cladding-based Additive manufacturing (AM). Only in the case of MIG, the raw-stock is fed axially into the molten pool resulting in the omni-directional cladding. In other processes, the raw-stock is fed off-axially into the molten pool resulting in deviation in the bead geometry from its actual trajectory and varying bead cross-section along the path. As the trajectories vary widely in cladding-based AM, it is required to maintain a consistent raw-stock feeding condition (namely, front, back or sides). Therefore, an auxiliary wire orienting mechanism has been developed which can be easily retrofitted with a conventional TIG cladding torch and CNC machine. The wire orientation angle is computed on-the-fly and hence the NC programme need not provide this information. Although this implementation was demonstrated for TIG, the same methodology holds good for laser and EB too

Rapid Prototyping of EPS Pattern for Complicated Casting

In Rapid Prototyping (RP) process the 3D object is approximated into several 2D slices. All these slices are of a uniform thickness hence called uniform slicing of zeroth order approximation. Such a system always suffers with the staircase defects. Very thin slices have to be used to minimize these defects, which increase the production time. In this work, a RP system called Segmented Object Manufacturing (SOM) is used to produce the Expanded Polystyrene (EPS) pattern, which uses adaptive slicing with higher order approximation. This system uses the concept of visible slicing in which a complicated object is produced by converting it into the accessible (visible) segments. This is a hybrid system for producing EPS patterns which utilizes the advantages from subtractive and additive processes. These EPS patterns found their application in Evaporative Pattern Casting (EPC). EPS bracket is produced by SOM machine to prove the capability of the system.Mechanical Engineerin

Feasibility Study of Heat Transfer Enhancement in Solar Photovoltaic-Thermal Systems Using FDM Generated Novel Curved Thermal Absorbers

Global warming and climate change are the major global concerns in the recent past as far as power generation is concerned. Renewable energy power generation is extensively promoted for the reduction of harmful gas emissions resulting in global warming. Among all the renewable energy technologies solar energy has greater global potential as the sun’s radiation is received uniformly everywhere. Solar thermal and solar photovoltaic (PV) are the two prominent routes of converting sunlight into usable forms wherein PV technology is more accessible for domestic and commercial deployment of solar energy. With higher intensity radiations, PV systems experience 0.45% efficiency loss per degree rise in solar cell temperature. To address this difficulty, solar photovoltaic-thermal (PV/T) collectors are proposed. PV/T is a promising technology where the simultaneous generation of both electrical and thermal energy generation is possible. The present study addresses the current challenges associated with the existing PV/T collectors or absorbers. The problem of heat transfer rate enhancement consistently persists because of low surface area exposure and less cooling uniformity of thermal absorbers. PVT thermal absorbers which have been designed by existing curves or patterns like Raster, Spiral or Rectangular spiral, etc., fail to deliver the optimum outcomes because of the raised issues. The alternative novel type of curves has the potential to overcome these problems, categorized as space-filling curves and have a significant role in mathematical analysis. Spacefilling curves usually include the Hilbert curve, Peano curve, Grosper curve, Sierpinski curve, Z-curve, etc. with features like complex shapes or multiple turns and higher space-filling ratio, which will be favourable for designing a better PV/T thermal absorber. So, the proposed work will focus on the feasibility study of these space-filling curves as PV/T thermal absorbers for heat transfer enhancement, wherein investigation and identification of suitable novel space-filling curves as PV/T thermal absorbers have been performed for higher thermal and electrical efficiency. The investigation formulated an analytical and computational analysis for finding the best suitable curve. The results of this analysis are compared to the existing curves as PV/T thermal absorbers to find a better alternative. The Hilbert curve is found to accommodate a larger tube length at the back of the PV panel, which facilitates a higher surface area and exhibits 9.676%, 35.237% and 14.576% increase in total surface area compared to Raster, Rectangular spiral and Peano curves respectively for heat transfer. Furthur, the time taken to extract the available heat to reach steady state condition from the specified PV panel surface by the Hilbert curve pattern is the comparatively minimum from other available curve patterns, showing its ability of maximum heat transfer rate. Thus, the Hilbert curve is better than available space-filling curves, exhibiting Higher surface area and heat transfer rate superiority. The fabrication of such novel curved metal absorbers becomes costly and needs sophisticated instruments like 3D printing technology due to its intrigued pattern, which has a maximum number of turns in its single pathway. Thus, Prototype models were prepared by Fused Deposition Modelling (FDM) using PLA as filler material, showing the practicability of these novel curves as PV/T thermal absorbers. Hence, to optimize efficiency, some novel types of space-filling curves, like the Hilbert curve, can be considered for full-scale PV/T thermal absorbers