Suryakumar S. - Research

Overview:

My primary area of research is Metal Additive Manufacturing, particularly of Large Sized Components. In achieving that broad theme, the following challenges are addressed: High Deposition rates, Shape complexity in fabricated parts, Residual Stresses and Distortion Control, Post-processing techniques suitable. Connected to this primary theme is work on Design for Additive Manufacturing, focusing on how to adopt AM specific constraints into Topology Optimization process. In addition to these, a few areas related to applications of AM for other spheres like Bio-Printing and Acoustics are also explored in collaboration. On the broader theme of Manufacturing/Fabrication, I have been involved with research related to Circular Manufacturing, Fluid Retriver System for Cervical Cancer Detection and Resuable Face Masks for COVID-19 protection.

Large Area Additive Manufacturing (LAAM)

With the growth of metallic Additive Manufacturing (AM), processes capable of producing large components (more than 1m in size) with high deposition rates have been of particular interest. On this front, arc based deposition processes stands out among the metallic AM processes with their high deposition rates, high material and power efficiency, lower investment costs, simpler setup and less demanding environment requirements. The essential weld-deposition AM system consists of a wire-based weld unit and a multi-axis motion system. The research focus has been to develop such system and addressing various related challenges. Various additional sub-systems including powder + laser system, deformation + deposition system, have also been built around this process. The following figures show some sample components built in our lab. As can be noted from the above figures, these components are much bigger in size than the usual AM produced components. The challenges in realizing them are also quite unique. Current work focuses on the various studies on building such system and addressing related challenges like shape complexity, residual stresses etc.

Functionally Gradient Materials through Twin-Wire Deposition

Functionally Gradient Materials (FGM) may have a controlled variation of the material matrix so as to obtain the desired distribution of the properties such as color, density, porosity, hardness, toughness etc. The objects built through Additive Manufacturing techniques are inhomogeneous or non-uniform, i.e., they are inherently anisotropic. When this inherent nature is carefully exploited, the anisotropy transforms into the desired distribution of the properties. Weld-deposition based Additive Manufacturing techniques offer unique advantages on that front due to their ability to control the properties of the deposited matrix through the control of process parameters like current, layer thickness etc. A wider control of material properties can be obtained with the help of tandem weld-deposition setup like twin-wire. In twin-wire weld-deposition, two filler wires (electrodes) are guided separately and it is possible to control each filler wire individually. This work focuses on obtaining a wide range of material properties by selecting filler wires with complementary properties and controlling the deposition rate of each of them separately to obtain desired Functional Gradience in properties.

Wire & Powder Hybrid Direct Energy Deposition

Amongst the Direct Energy Deposition (DED) processes, Powder and Wire are different forms of raw material that can be used. Powder-DED (of which LENS system from Optomec is the most common variant) comprises of a cladding head in which a laser fuses together powder particles sprayed from concentric nozzles. Wire – DED, also known as Wire Arc Additive Manufacturing (WAAM) builds on Arc welding to produce fully dense complex functional metallic objects with wire as feed stock. Amongst the Powder and Wire based processes, power offers better accuracy and feature resolution, wire based processes are capable high deposition rates. The objective of this work is to develop a Wire & Powder Hybrid Direct Energy Deposition (WP-DED) process bringing together the advantages of high deposition rate with high accuracy for large components. The system for WP-DED would involve three subsystems viz., weld-deposition system, laser cladding system and kinematic setup for controlling these deposition heads. Fronius make Cold Metal Transfer (CMT) and Twin-Wire are the two weld-deposition systems available with IIT Hyderabad for carrying out W-DED. A 2kW fiber laser from Coherent fitted together with an YC52 Precitec make cladding head is also available for P-DED. The need is to integrate these two into a single kinematic system for carrying out. The system integration will be accompanied by process planning for various types of features. While W-DED is capable of high deposition rates and useful for bulk deposition, finer aspects need P-DED. Hence, the CAD model has to be divided into features based on their size and resolution. This will be followed by the sequencing of these features before realization of the same on the individual deposition heads.

Variable Axis Deposition

To deposit an inclined features or overhanging features, supports or scaffolds are often needed. In some AM processes like Selective Laser Sintering (SLS), an easily breakable scaffold made of same material is deposited to realize the overhanging features. Even though a small overhang can be easily deposited in weld-deposition based AM processes by exploiting the inherent overhang capability of the weld bead. But the same cannot be applicable for complex geometries where the overhands are large. This work explores efficient way of depositing the overhanging features through weld-deposition, without use of support structures, based on inclined slicing and deposition. This approach uses higher order kinematics i.e. adding extra degrees of mobility to work piece for fabricating and/or repairing of fully dense functional metallic parts. While, this concept is implemented in the context of weld-deposition, it can be extended for any other deposition process as well.

Integrated Metal Additive and Formative Manufacturing System

The overall objective of the research is to develop a methodology for manufacture of complex metallic parts, combining the advantages of Additive and Formative methods. The primary aspect of the system is a wire-arc based direct energy deposition system for fabricating the desired shape in a layer by layer manner. The second feature is the deformation system to introduce necessary shape changes to that partial/completed geometry. These are aided by a focused heat source system and/or electric current for process simplification, load reduction and material property enhancement. This DED based additive manufacturing and deformation system is capable of manufacturing complex geometries without the need for support structures. By employing the deformation loads, this system can be used for material property enhancement, lowering the residual stresses developed and distortion.

Thermal Balancing Approaches for Residual Stresses & Distortion Control

The Additive Manufacturing (AM) of metal components involve sequential and selective deposition of molten metal. A significant amount of heat spread in a non-uniform manner results in residual stresses and distortion. In this study, innovative approaches for control of residual stresses and distortion in AM are proposed. The experiments are conducted with two approaches for thermal management - passive and active. The passive approach of experiments is performed by variation of the selected process parameters to study their effect on residual stresses and distortion. The chosen parameters are current, torch speed, geometry, continuous or delay in the deposition, and cooling arrangement. Based on the understanding from the passive set of experiments, further experiments are conducted to study the effect of an active approach. This was implemented by insulating the substrate with and without adaptive current and heating the substrate. For a better understanding of the process, the experimental results were corroborated with the simulation of the process. A comparative study for hardness is made based on the T8/5 extracted from simulation. These experiments and simulations endorse thermal management, both passive and active, as an effective tool that can alter the distortion and residual stress pattern and the mechanical properties in an AM component.

Microstructure Evolution along Build Direction

In WAAM, the near-net shape is manufactured through layer-by-layer weld-deposition on a substrate. However, as a result of this sequential weld-deposition, different layers are subjected to different types of thermal cycles and partial re-melting. The resulting microstructural evolution of the material may not be uniform. Hence, the aim of this study has been to assess microstructure variation along the lamination direction (or build direction). The study was carried out for two different boundary conditions viz., (1) Isolated condition and (2) Cooled condition. The microstructural evolution across the layers is hypothesized based on the measurements involving microhardness, SEM imaging and EBSD analysis and subsequently collaborated with the help of thermal modelling of the process. Results indicate that while the last set of layers have columnar grains due to rapid solidification, the bulk of the layers across have uniform grains due to the remelt-resolidification phenomenon. This transition is happening around 3 mm to 4 mm from the top surface, after which a uniform grain can be observed across the layers. This study can provide foundation for adaptive control of the process parameters to tailor the local properties.

Post-Processing of Metal AM Parts

Advancements in metal AM can provide parts with higher part performance comparable and often better than wrought/as cast materials. However, issues like anisotropy, surface finish, porosity, residual stresses etc remain to be addressed. Material property enhancement of metal AM heat treatment and other secondary processing such as machining will accelerate the widespread adoption of metal AM. Post treatments, and specifically heat treatments are the most common methods used to provide coarsening and the homogenizing the grains in the microstructure in order to enhance the properties. In most of the cases studied, heat treatments improved the ductility. On the other hand, the strength was often reduced. Thus, the importance of developing different material property enhancement methods will lead to the broader adoption of metal AM. This work, which is in its nascent phase aims to look into a few such solutions.

Design for Additive Manufacturing

Additive manufacturing (AM), known for its ability to manufacture complex shapes, is becoming an essential companion of topology optimization (TO) to optimize the structure. However, the topology-optimized structure may result in suboptimal performance or even have features, which are difficult to manufacture in a given AM process. This study attempts to refine the outcome from TO with AM-specific considerations, like minimum feature resolution and material continuity related constraints by introducing a neighborhood density function. The four different cases have been studied to demonstrate the effectiveness of the presented approach yielding better results when compared with conventional TO under three-point bending test. The current study provides optimized geometry with the decreased number of voids and ensuring the minimum feature size without substantial loss in the structural behavior and becomes the basic framework to integrate manufacturability into structural TO for AM process.

Additional Research Ventures (in Collaboration)

In additional to the above discussed research theme focused around Metal AM, I have been active in a few connected research themes in the broad areas of Manufacturing along with some specific applications of Additive Manufacturing. The following is a brief summary of the ventures:

AM for Tissue Engineering Applications: Additive Manufacturing method with its ability to add material at desired location to make a component is best suited for creating such a scheme for cell culture in Tissue Engineering applications. It has a unique ability to precisely control of the matrix architecture like size, shape, interconnectivity, branching, geometry and orientation. Due to these reasons, Additive Manufacturing is increasingly becoming a powerful tool for the realization of tissue engineering applications. . The current work develops an idea to export a 3D CAD model to a Fused Deposition Modeler (FDM) to produce scaffolds of biocompatible materials like Polylactic acid (PLA) & Hydrogel (Sodium Alginate + Calcium Chloride) with varying pore structures. A study on the feasibility and methodology of fabricating biocompatible materials for tissue engineering has been done. Effect of different printing parameters has been studied, which is of interest in Tissue Engineering technology.
AM for Acoustics Applications: This work studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used to fabricate the integrated honeycomb structures with a perforated face sheet. Technique and methodology presented in the current study gives an alternative way to design and fabricate honeycomb structures with perforations for acoustic applications such as aircraft cabins, ship structures and building acoustics.
Circular Manufacturing: Circular manufacturing such as product remanufacturing, refurbishment, and repair is a key element in promoting a circular economy. This research work, part of Norway-Japan-India project aims to address issues like advancement of process automations, design for restoration, quality enhancement of metal 3D printing-based restoration, and cost reduction of the process applications centred around this theme.
Fluid Retriever Device for Cervical Cancer Screening: The main objective of this research is to develop a detection kit which could collect the cervical fluid sample that would be analyzed for immediate results. This device would be both easy to use and interpretation of results will be color based. The proposed project would allow the women, irrespective of their social and economic backgrounds to get the diagnosis for cervical cancer and other common vaginal infections instantaneously.
Re-usable Face Masks for Covid Protection: The objective of this work is design and production deployment of reusable face masks. These PPE (personal protection equipment) face masks aim to provide better protection than cloth masks and are autoclavable and reusable by changing the filter. The focus of the work in ensuring that the design is suitable for high volume, high speed and cost effective production and allows for complete local manufacture.

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