1. Ph.D Theses
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Item Investigations on Machinability Characteristics of EN47 Spring Steel using Optimization Techniques(National Institute of Technology Karnataka, Surathkal, 2019) Vasu, M.; Nayaka, H Shivananda.Challenge of any manufacturing industry to give a better quality of products to society with minimum manufacturing cost, low manufacturing time and less consumption of raw material. Manufacturing involves various processes to convert raw material into finished products and hence meet demands with high-quality products. Selection of process parameters plays a significant role to satisfy all demands to ensure the quality of the product, increased production rate, and reduced operating cost. For such cases, optimization is essential to represent manufacturing process. Process parameters have been optimized by chosen best possible optimization techniques. Before conducting any experiments, selection of workpiece and tools it is necessary, to explore the literature to know, what has happened in earlier days. A literature survey has been done thoroughly existing statistical techniques are understood and implemented to optimize speed, feed, and depth of cut. EN47 spring steel has been chosen as work material which has a hardness of 45-48HRC. Hard turning process eliminates grinding process, and EN47 steel possesses low thermal conductivity and suitably oil hardened and tempered. Hardened spring steel offers excellent toughness and shock resistance, and are considered as suitable material for automobile applications. Other applications involve such as manufacturing of die, leaf spring for a heavy vehicle, crankshaft, spindles, pumps and steering knuckles and many general engineering applications. Experiments were performed using two different techniques, namely, one factor at a time (OFAT) approach and Design of Experiments (DOE). Cutting tool inserts are commercially available in the form of PVD coated TiAlN German make and are used during machining. Cutting forces, surface roughness, tool tip temperature, and material removal rate are estimated experimentally. From the experimental work, it is known that with an increase in nose radius, cutting forces, tool tip temperature, and material removal rate are increased, but surface roughness is decreased. Further, a tool with 0.8mm nose radius exhibits nominal performance in all output performances. 0.8mm nose radius tools are used to work in three different cutting environments, namely dry, wet and cryogenic. From the analysis, cryogenic machining showed better quality of the machined surface, tool wear also reduced and tool tip temperature decreased.viii Experiments were performed and analyzed using design of experiments (DOE) technique L27 full factorial design. A second order regression model was developed to know the interaction effect of output responses. Tool wear was analyzed by confocal microscope and SEM, with varying cutting time. ANOVA was used to identify the significant factor and percentage contribution for a particular output. Results from machining reveal that cutting force is mainly influenced by feed rate and depth of cut. Surface roughness was influenced by cutting speed and feed rate. Tool tip temperature was influenced by cutting speed and depth of cut. Material removal rate was influenced by speed, feed, and depth of cut. 3D response surface plots show interaction effect on each output response. Main effects plots show optimum condition for each output performance. Normal probability plots showed that the developed models are adequate by observing normal error distribution. Determination coefficient (R2) value should be in between 1 or 100% in the model. Multi-objective optimization was identified by Desirability Approach (DA) and Particle Swarm Optimization (PSO). Also, Artificial Neural Network (ANN) is used to predict experimental results and compared with RSM model, as well as, experimental value. Statistical analysis was done by Minitab and Design Expert Software. Validation was performed by ANN. MATLAB is used to develop artificial neural network model, as well as; codes are developed for PSO. From the experimental analysis, the developed model showed a significant and good agreement between the experimental value and predicted value.Item Machinability Studies on Carbon and Alloy Steels using Face Turning(National Institute of Technology Karnataka, Surathkal, 2014) Shankar, Lalbondre Rajshekhar; Mohan Kumar, G. C.; Krishna, PrasadThe present study is an experimental investigation on the machinability of carbon and alloy steels by face turning method. This study finds its usefulness in economic machining solution to fulfil the local objectives of knowing, in advance, the machinability of selected carbon and alloy steel material of grade: AISI-1050, AISI- 51100, AISI-52100, AISI-4320 and AISI-9320. The face turning method makes use of cylindrical steel bar specimen as test pieces for testing the machinability of the steels. The technical effectivity of the face turning method is assessed by studying: the cutting time required for the tool to reach flank wear upto 0.3mm (tool life criterion); tool wear development and wear mechanisms involved in machining; tool life studies and machinability indices of the work-material; surface roughness and microhardness investigations (SEM) of the machined surfaces; and chip morphology and crater wear studies. These aspects are further tested and verified for its repeatability and reproducibility. The tests are being carried according to some of the guidelines laid in the international standards, ISO 3685:1993(E) and American Foundry Society (AFS) standard machinability tests. The results presented here demonstrate the ability of the face turning method to assess the tool wear development while machining different work-materials; to evaluate the tool life for each of the work-material under consideration; to differentiate very distinctly and rank these materials according to their machinability; to investigate surface finish due to tool wear and micro-hardness of the machined surface generated after the tool wear reached its tool life criterion; to analyse the chip morphologies with crater wear; and to overall characterize the machinability of steels under consideration. The face turning method used here is simple and effective for the given tool-work material pair.Item Machinability Studies on 17-4 PH Stainless Steel Under Cryogenic Cooling Environment(National Institute of Technology Karnataka, Surathkal, 2017) Sivaiah, Potta; Chakradhar, D.17-4 precipitated hardened stainless steel (PH SS) is widely used in various areas including nuclear reactor components, marine constructions, jet engine parts, aircraft fittings, missile fittings, oil field valve parts and rotors of the centrifugal compressors owing to excellent properties like high corrosion resistance, high strength and good ductility. Productivity improvement while machining of 17-4 PH SS is a difficult work due to the limitation of higher cutting conditions. 17-4 PH SS material is treated as difficult to cut material due to formation of built up edges (BUE) on the cutting tool during machining and difficulty in chip control, which causes for poor surface quality as well as increases the number of tools required for machining. One of the methods to overcome above mentioned problems is to use of conventional coolants. But, in the recent years, environmental conscious regulations have became stringent in terms of disposal of chemically contaminated conventional coolants from the health and environmental safe prospective. Because of these reasons, nowadays, metal cutting industries are looking towards new sustainable machining method to reach the target set by the environmentally conscious regulations in terms of usage and disposal of chemical contaminant conventional coolants without sacrificing the productivity. Hence, the present work, focused on cryogenic machining which is recently developed eco-friendly as well as efficient cooling technology. The present work is divided into three phases while machining of 17-4 PH SS. In the first phase, experiments were conducted based on the one factor at a time approach to study the individual effect of process parameters like cutting velocity, feed rate and depth of cut on performance characteristics like cutting temperature, tool flank wear, material removal rate (MRR), chip morphology and surface integrity (surface topography, surface finish, microhardness, white layer thickness) under various cooling environments like cryogenic (liquid nitrogen), minimum quantity lubrication (MQL), wet machining and dry conditions. It was found that as the cutting velocity, feed rate and depth of cutincreases, response like cutting temperature, flank wear and MRR were increased respectively under all the cooling environments. Whereas, in the case of surface roughness, decreasing trend was observed at the cutting velocity variation and increasing trend was found for feed rate and depth of cut variations conditions respectively. In overall, it was also evident from the experimental results that cryogenic machining significantly improved the machining performance and product performance all the cutting conditions. From result, it was found that cryogenic machining is selected as a best feasible machining method for 17-4 PH SS and it was selected for next phases of the work. On the other way machining efficiency, quality of the product and machining cost highly depending on the selection of optimum machining conditions. In the second phase, Taguchi L9 orthogonal array experimental design has been used for optimization of cutting conditions for single and multiple objective responses under the cryogenic cooling environment. Taguchi method was used for single response optimization and ANOVA was used to find the most influenced process parameters on each response. Gray relational analysis (GRA) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) optimization techniques have been applied for multi response optimization, best multi optimization tool which suits for the current study have been selected through conformation tests. From the conformation test results, it was observed that Taguchi determined optimum cutting conditions significantly improved the turning performance characteristic during machining of 17-4 PH SS. Whereas, in the case of multi response optimization condition, GRA technique substantially improved the turning performance characteristic when compared to the TOPSIS technique. In the third phase, correlation models were developed for modeling of cryogenic turning process by finding out the relation between the input process parameters and output responses using Response Surface Methodology (RSM) for cost effective research methodology. In additions to this, interaction effects of process parameters on turning performance characteristics were studied using 3D surface plots. From the modelingconformation test results, it was observed that close agreement was found between the actual and predicted values. From interaction plots of surface roughness, it was observed that the high level of cutting velocity and low levels of feed rate and depth of cut could be contributed to generate lower surface roughness respectively. Whereas, from interaction plots of flank wear and MRR, it was found that the highest levels of process parameters could produce high flank wear and maximum MRR respectively.