Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Additive manufacturing (AM) of auxetic structure is gaining prominence for various fields ranging from structural material to biomaterials. This work proposes a novel design of the auxetic structure with regular honeycomb, i.e. hybrid auxetic structure. Additionally, a sharp corner of the auxetic structure is replaced with a fillet feature to stiffen the structure by suppressing the hinging mechanism. All models are fabricated in extrusion-based AM technique using Polylactic acid (PLA) material. A comparison study was carried out on 3D printed samples that were subjected to uniaxial tensile load. To understand the effect on functional and mechanical properties, a tool path strategy with single-pass and zigzag tool paths was proposed. Solid material properties were used in finite element analysis (FEA) to compare with experimental results. Experimental results indicate that hybrid structure takes more load than auxetic structure. The ultimate tensile strength (UTS) of the hybrid structure was 32% more than that of the auxetic structure. The finite element results are in good agreement with the experimental results. The observation reported in this article will help frame design rules and selection of AM processes for applications ranging from structural protection sandwich constructions with low-density cores to tissue engineering and regenerative medicine scaffolds.

Department of Manufacturing Engineering

School of Mechanical Engineering

Vellore Campus

Journal of Materials Engineering and Performance

Investigation on Mechanical Properties of Additive Manufactured Hybrid Auxetic Structure

Prosthetics are widely used to help people with permanent disabilities and provide a new chance to lead a normal and independent life. Prosthetics are customized for each individual, keeping in mind the use and physical attributes. However, the conventional prosthetics are heavier and the production is expensive and time consuming. The present study addresses this problem and proposes an alternative design for prosthetic foot and calf. The weight of the prosthetics is minimized with a hybrid optimisation approach using generative design and topology optimization. The proposed design has a <a href="https://www.sciencedirect.com/topics/materials-science/compliant-mechanisms">compliant mechanism</a> to minimize the load and it provides ease to the wearer. The designed prosthetic was simulated while walking to analyse the stress distribution. The study concludes that the wearer will feel comfortable with the new design, and will be able to walk naturally.

materials today proceedings

<a href="https://scholar.google.com/citations?view_op=view_citation&amp;hl=en&amp;user=Sm2CrvQAAAAJ&amp;citation_for_view=Sm2CrvQAAAAJ:KlAtU1dfN6UC">Optimization of Prosthetic Leg Using Generative Design and Compliant Mechanism</a>

Rapid casting gives the opportunity to develop a new casting in days, not in weeks or months. Evaporative Pattern Casting (EPC) process gives flexibility to produce complex geometries by integrating several parts in single casting. The lead-time and cost involved in designing and fabricating the metal tooling for Expanded Polystyrene (EPS) pattern making can be overcome by using the Segmented Object Manufacturing (SOM) machine. This hybrid system of pattern making is explored with all sub-systems and a complicated EPS pattern is produced by this Rapid Prototyping system. Conventional EPC process is more complicated due to coating development, vacuum assisted metal pouring and vibration system for filling the cavities by unbounded sand. In the present work, different mold-making processes are explored to avoid complications of conventional process. The Green sand, No-bake sand, and Plaster of Paris molds are prepared using Rapid Prototyped EPS pattern to produce the castings. The castings are characterized by comparing the surface roughness, dimensional accuracy, hardness, and surface morphology.

Advances in Additive Manufacturing and Joining.

<a href="https://scholar.google.com/citations?view_op=view_citation&amp;hl=en&amp;user=Sm2CrvQAAAAJ&amp;citation_for_view=Sm2CrvQAAAAJ:W7OEmFMy1HYC">Characterization of Rapid Foam Castings Produced by Different Mold Making Processes</a>

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. Copyright © SFF 2017.All rights reserved.

World University root node

Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2017

Rapid prototyping of EPS pattern for complicated casting

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. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

Virtual and Physical Prototyping

Investigation of ablation studies of EPS pattern produced by rapid prototyping

Purpose: The support structures of sacrificial material are built in deposition-based additive manufacturing (AM), which are later removed either by breaking or dissolving. Such a sacrificial material is not feasible in metal AM. The purpose of this study is to find a suitable method for eliminating the need of support mechanism. In this work, the authors use the tilting of the substrate to alleviate the need for the support mechanism altogether. Design/methodology/approach: As in the traditional AM, the object is grown in horizontal layers. However, wherever undercuts are encountered, the substrate is tilted appropriately to capture the droplets. Such a tilt involves two rotary axes invariably. To conform to the slice geometry, these two tilts are accompanied by the three linear movements. Thus, the object with undercuts is grown in planar layers using five-axis deposition without any support structure. Each pair of the corresponding top and bottom contours of any slice defines a ruled surface. The axis of the deposition head will be aligned with the rules of this surface. Findings: The need for the support mechanism was eliminated using five-axis deposition. This was experimentally demonstrated by building an aluminum impeller using a metal inert gas cladding head. Research limitations/implications: In the proposed methodology, the objects with an abrupt change in the geometry are not possible to realize. Originality/value: This manuscript proposed a novel method of eliminating the support mechanism through continuous five-axis deposition. © 2018, Emerald Publishing Limited.

Rapid Prototyping Journal

Elimination of support mechanism in additive manufacturing through substrate tilting

Hybrid Layered Manufacturing (HLM) is a Rapid Manufacturing (RM) process of metallic objects, which combines the best features of additive and subtractive manufacturing techniques. Similar to other RM processes, HLM also proceeds in the layer by layer manner. 3D CAD model is sliced into thin 2D layers and the tool pathsaregenerated for each layer. The deposition of metal according to the generated tool path can be done using a Metal Inert gas (MIG), Tungsten Inert gas (TIG) and LASER cladding process. The different characteristics of these three cladding methods such as speed, precision and cost, make them useful for different applications. After the deposition of near net shape, the machining process is used to provide the final dimensional accuracy. So far Aluminium, Mild steel and Tool steels have been used for HLM process andother super alloys such as Titanium and Inconelwill be explored soon. The process parameters such as cladding current, stepover and torch speed have been optimized to achieve the desired thickness of the layers and spatter free cladding. Several build strategies have been developed and incorporated through an in-house build software. One of the strategy called integrated substrate method, found its application in the manufacturing of turbine blades, ribs, and spar/bulkhead structures of aircrafts. In this work this strategy has been explained and its capability has been proved through the manufacturing of turbine blade as a case study. © 2017 Elsevier Ltd.

Materials Today: Proceedings

Hybrid Layered Manufacturing of Turbine Blades

Purpose-In additive manufacturing (AM) process, the physical properties of the products made by fractal toolpaths are better as compared to those made by conventional toolpaths. Also, it is desirable to minimize the number of tool retractions. The purpose of this study is to describe three different methods to generate fractal-based computer numerical control (CNC) toolpath for area filling of a closed curve with minimum or zero tool retractions. Design/methodology/approach-This work describes three different methods to generate fractal-based CNC toolpath for area filling of a closed curve with minimum or zero tool retractions. In the first method, a large fractal square is placed over the outer boundary and then rest of the unwanted curve is trimmed out. To reduce the number of retractions, ends of the trimmed toolpath are connected in such a way that overlapping within the existing toolpath is avoided. In the second method, the trimming of the fractal is similar to the first method but the ends of trimmed toolpath are connected such that the overlapping is found at the boundaries only. The toolpath in the third method is a combination of fractal and zigzag curves. This toolpath is capable of filling a given connected area in a single pass without any tool retraction and toolpath overlap within a tolerance value equal to stepover of the toolpath. Findings-The generated toolpath has several applications in AM and constant Z-height surface finishing. Experiments have been performed to verify the toolpath by depositing material by hybrid layered manufacturing process. Research limitations/implications-Third toolpath method is suitable for the hybrid layered manufacturing process only because the toolpath overlapping tolerance may not be enough for other AM processes. Originality/value-Development of a CNC toolpath for AM specifically hybrid layered manufacturing which can completely fill any arbitrary connected area in single pass while maintaining a constant stepover. © Emerald Group Publishing Limited.