BITS Faculty Publications
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Item Additive Manufacturing of Complex Shapes Through Weld-Deposition and Feature Based Slicing(ASME, 2016-04) Sharma, Panchagnula JayaprakashFabricating fully dense and functional metallic components is one of the important challenges in Additive Manufacturing (AM). Additive Manufacturing is a technology in which functional components can be fabricated rapidly and efficiently from their CAD models. It is also referred as Layered Manufacturing (LM) as the object is created by slicing the CAD model into layers and realizing each layer at a time. These layers are thin and stacked or glued together to get the physical shape of the CAD model. However, realizing overhanging features is a difficult task due to deficiency of support mechanism for metals. A separate support structure has to be deposited to build overhanging structures. Although, use of a distinct support material is quite common in non-metallic AM processes, such as Fused Deposition Modelling (FDM), and the same for metals is not yet available. The various techniques in AM process for fabricating metal parts can be mainly classified as laser based, electron beam based and arc based processes. While some Additive Manufacturing processes like Selective Laser Sintering (SLS) employ easily-breakable-scaffolds made of same material to realize the overhanging features, the same approach cannot be extended to deposition processes like laser or arc based direct energy deposition processes.Item Inclined slicing and weld-deposition for additive manufacturing of metallic objects with large overhangs using higher order kinematics(Taylor & Francis, 2016-04) Sharma, Panchagnula JayaprakashThis paper presents an automated tool path planning for deposition of overhanging features using GMAW-based weld-deposition. Overhanging features, although possible to a certain extent in power-bed process like SLS, remain a challenge in deposition-based processes. Deposition processes like weld-deposition-based AM realised smaller overhangs by exploiting the inherent overhang capability of the weld bead; but the same cannot be applicable for complex geometries with large overhangs. This paper explains an efficient way of depositing the overhanging features through weld-deposition, without use of supports, based on inclined slicing and deposition. This approach uses higher order kinematics, that is, adding extra degrees of mobility to workpiece. The methodology used for realising these inclined slices based on an in-house MATLAB code has also been presented. While this concept is implemented in the context of weld-deposition, it can be extended for any other metallic deposition processes as well.Item Manufacture of complex thin-walled metallic objects using weld-deposition based additive manufacturing(Elsevier, 2018-02) Sharma, Panchagnula JayaprakashGas Metal Arc Welding (GMAW) based weld-deposition process is one of the deposition-based Additive Manufacturing (AM) processes with the ability to produce fully dense complex functional metallic objects. Due to its high deposition rates, high material and power efficiency, lower investment costs, simpler setup and work environment requirements it is slowly becoming a viable metallic AM method. Amongst various geometrical features that can be realized in weld-deposition based AM, the thin-walled features (i.e., features with one single deposition pass) are the toughest as the process has to overcome the bead-over-bead complexity. Based on geometric modelling and experimentation, this paper presents an efficient technique for producing the thin-walled metallic structures, including objects with undercut features. This is possible by adding extra degrees of freedom or by using higher order kinematics to the work piece and/or to the deposition head by suitably aligning the overhanging feature in-line to the deposition direction. An in-house MATLAB code was developed to slice the CAD model and generate the tool path for inclined deposition of a given layer of a thin-walled model. A geometrical model proposed to predict the layer thickness of a given layer during such bead-on-bead deposition showed good correlation with experimental data. Some illustrative complex thin-walled components successfully fabricated using this model have also been presented.Item Feature based Weld-Deposition for Additive Manufacturing of Complex Shapes(Springer, 2016-08) Sharma, Panchagnula JayaprakashFabricating functional metal parts using Additive Manufacturing (AM) is a leading trend. However, realizing overhanging features has been a challenge due to the lack of support mechanism for metals. Powder-bed fusion techniques like, Selective Laser Sintering (SLS) employ easily-breakable-scaffolds made of the same material to realize the overhangs. However, the same approach is not extendible to deposition processes like laser or arc based direct energy deposition processes. Although it is possible to realize small overhangs by exploiting the inherent overhanging capability of the process or by blinding some small features like holes, the same cannot be extended for more complex geometries. The current work presents a novel approach for realizing complex overhanging features without the need of support structures. This is possible by using higher order kinematics and suitably aligning the overhang with the deposition direction. Feature based non-uniform slicing and non-uniform area-filling are some vital concepts required in realizing the same and are briefly discussed here. This method can be used to fabricate and/or repair fully dense and functional components for various engineering applications. Although this approach has been implemented for weld-deposition based system, the same can be extended to any other direct energy deposition processes also.Item A new approach for attaining uniform properties in build direction in additive manufactured components through coupled thermal-hardness model(Elsevier, 2019-04) Sharma, Panchagnula JayaprakashThe theme of the investigation is to strategize uniform build direction properties in additive manufactured components. A computationally efficient model for prediction of layer-wise thermal cycle is developed using control volume approach. The thermal model is coupled with a hardness model to predict the hardness variation in the component. The predicted results are validated with hardness measurement and microstructure observation for a thin walled component of 60 layers produced by wire arc additive manufacturing. The experimental results strongly corroborate the computed cooling rates. The results show how the dynamic control of external conditions (e.g. substrate temperature) can be a very effective measure to attain uniform hardness in the build direction. An optimal strategy is presented for a candidate component. The investigation discloses new strategic steps to achieve uniform mechanical properties vis-à-vis in contrast to the conventional practice of cooling the substrate; the investigation suggests that heating the substrate to a pre-determined temperature and then cooling at a controlled rate during the deposition of layers helps to manage the properties in build direction.Item Influence of Various Tool Path Patterns on Hardness Used in Weld Deposition-Based Additive Manufacturing(Springer, 2019-10) Sharma, Panchagnula JayaprakashIdentification of optimal tool path is critical for successful fabrication of bulk metallic parts using weld deposition-based additive manufacturing (AM). The various features of tool path, i.e., the number of starts and stops, convolutions, and continuity, have a significant effect on the geometric as well as physical properties of manufactured parts. Ideally, an optimised tool path is a continuous path with no self-intersecting pattern, with a minimum of starts and stops and minimum convoluted patterns. The tool paths available in the literature are unable to achieve all the listed requirements. Further, there are no one-to-one comparisons of these tool paths in detail in the literature. The present work aims in comparing various tool path techniques based on flatness achievable by minimum material skinned out during face milling (thickness of the deposited layer) and the hardness achieved. Experiments are performed using the in-house developed weld-based metallic AM workstation (weld deposition torch is retrofitted with a CNC).Item Enhancement of mechanical properties and corrosion resistance of friction stir welded joint of AA2014 using water cooling(Elsevier, 2017-01) Sinhmar, SunilAn investigation on the microstructure, mechanical properties, and corrosion behavior of friction stir welded joint of AA2014 in natural cooled (NC) and water cooled (WC) conditions have been reported. Optical microscopy, field emission scanning electron microscopy (FESEM) with Energy dispersive X-ray spectroscopy (EDS), Vicker's microhardness, tensile testing, X-ray diffraction (XRD), and electrochemical potentiodynamic polarization corrosion test (Tafel curve) were carried out to characterize the friction stir weld joints in both the cooling conditions. Water cooling resulted in higher strength and microhardness of friction stir weld joint compared to the natural cooling. The width of heat affected zone was reduced by the use of water cooling during friction stir welding (FSW) and minimum hardness zone was shifted towards weld center. The corrosion test was performed in 3.5% NaCl solution. Corrosion resistance of water cooled joint was found higher than natural cooled FSW joint. The precipitation behavior of weld nugget and heat affected zone impacts the corrosion resistance of FSW joint of AA 2014. Hardness, tensile, and corrosion properties of FSW joints produced under NC and WC conditions have been discussed in the light of microstructure.Item A study on corrosion behavior of friction stir welded and tungsten inert gas welded AA2014 aluminium alloy(Elsevier, 2018-04) Sinhmar, SunilThe present study comprises the comparison of the electrochemical behavior of friction stir weld (FSW) joint and tungsten inert gas (TIG) weld joint of AA2014 using immersion test, potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). Weld thermal cycles and microhardness were correlated with corrosion behavior of the weld joints. TIG weld joint showed lower corrosion resistance than FSW joint. Heat affected zone was the most corrosion susceptible region in both type of weld joints. Optical microscopy, FESEM, TEM and XRD analysis were performed to discuss the corrosion behavior in light of the microstructure.Item Effect of weld thermal cycle on metallurgical and corrosion behavior of friction stir weld joint of AA2014 aluminium alloy(Elsevier, 2019-01) Sinhmar, SunilFriction stir welding of AA2014 aluminium alloy was performed at seven different speed combinations. Weld thermal cycles were measured at all the speed parameters and corresponding peak temperatures were observed at higher tool rotation speed and lower welding speed. Hardness and tensile tests were performed to study the mechanical properties of the weld joints. Corrosion behavior was studied using immersion, Tafel and electrochemical impedance spectroscopy tests. Optical microscopy, FESEM, XRD and transmission electron microscopy were used to investigate the metallurgical behavior of the weld joints. Microhardness and corrosion resistance were found higher at low rotation speed and high traverse speed. Corrosion behavior has been discussed in light of microstructure.Item Friction Stir Processing of AA 7039 Alloy(2014-12) Sinhmar, SunilFriction stir processing (FSP) is an effective solid state surface modification technique used to improve the surface properties of metals like aluminium, and titanium controlled structural refinement. In present work, friction stir processing of 5 mm thick plate of Al-Zn-Mg alloy (AA 7039) was carried out using a conical pin and overlap of 50%. Modified surfaces were characterized in respect of macrostructure, microstructure, hardness and tensile properties. It was observed that friction stir processing refined the microstructure of AA 7039 alloy and increased the ductility (%elongation). However, tensile strength and hardness were found to be adversely affected. Hardness has been found to be increased with number of passes during friction stir processing.