Rakesh Sehgal

Estimation of cutting forces and surface roughness for hard turning using neural networks

Metal cutting mechanics is quite complicated and it is very difficult to develop a comprehensive model which involves all cutting parameters affecting machining variables. In this study, machining variables such as cutting forces and surface roughness are measured during turning at different cutting parameters such as approaching angle, speed, feed and depth of cut. The data obtained by experimentation is analyzed and used to construct model using neural networks. The model obtained is then tested with the experimental data and results are indicated.

Cryogenic Treatment of Tool Materials: A Review

Cryogenic treatment (CT) of materials has shown significant improvement in their properties. Various advantages like increase in wear resistance, reduced residual stresses, increase in hardness, fatigue resistance, toughness imparted by transformation of retained austenite to martensite, precipitation of carbides, eta-carbide formation, perfect distributed/homogenous crystal structure, better thermal conductivity, and reduced chemical degradation. Moreover, this technology is an eco-friendly, nontoxic, and nonexplosive. Different approaches have been applied for CT to study the effect on different types of steel and other materials. In recent years, researchers have tried to evaluate the process to optimize the parameters. This paper brings out the comprehensive analysis of the strategies followed in CTs and their significant effects on properties of materials by differentiating CT from cryogenic conditioning of the process. The final part of the paper discusses the developments and outlines the trends for further research in this field.

Reliability evaluation and selection of rolling element bearings

Abstract A procedure based on graph theory and matrix approach has been developed for the reliability evaluation and selection of a rolling element bearing for an application. The reliability of the bearing is evaluated considering reliability of its elements and their connections. This is modeled in terms of Reliability Graph of a Rolling Element Bearing. This graph is represented by an equivalent matrix called Rolling Element Bearing Reliability Permanent Matrix to obtain a matrix function-Reliability Permanent Function. This function is the characteristic of reliability of the rolling element bearing for the application. Reliability Index (RI) of the bearing is also defined. It is a numerical measure of the bearing reliability and is obtained by substituting reliability value of the bearing elements and their connections in the matrix function. The paper also suggests how to assess these reliability values to obtain the index. The proposed procedure is useful for designers and practicing engineers for selection of an optimum bearing for a given application. The methodology is illustrated by means of an example.

Fault location of tribo-mechanical systems—a graph theory and matrix approach

Abstract A procedure for the fault location of tribo-mechanical systems based on graph theory and matrix approach is presented. A component digraph which represents the failure propagation network of the tribo-mechanical system is developed for identification of fault location sources and failure paths. Starting from the nodes that indicate abnormal states, some nodes from the component digraph are selected as the probable candidates of failure origin by back-tracing. These candidates are further screened by using failure propagation probabilities and failure propagation time between adjacent nodes, and back-tracing. Finally, the failure propagation probabilities and failure rates of the devices are used to evaluate the ranking order among the screened candidates for fault location. The faults are located through pre-processing and alarm processing of the digraph. The methodology is applied to a journal bearing oil supply system for a thermal power plant.

Effect of tempering after cryogenic treatment of tungsten carbide–cobalt bounded inserts

Abstract.Cryogenic treatment is a recent advancement in the field of machining to improve the properties of cutting tool materials. Tungsten carbide is the most commonly used cutting tool material in the industry and the technique can also be extended to it. Although the importance of tempering after cryogenic treatment has been discussed by many researchers, very little information is available in published literature about the effect of multi-tempering after cryogenic treatment. In this study, an attempt has been made to understand effect of the number of post-tempering cycles during cryogenic treatment on tungsten carbide–cobalt inserts. Metallurgical investigations have been performed to observe the effect of such post-tempering on the inserts by analysing microhardness and micro-structural changes. The crystal structure and morphology were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Metallurgical investigations revealed a significant improvement in tungsten carbide inserts having three tempering cycles, after cryogenic treatment, with marginal differences for two cycles of tempered inserts, established by the study of wear behaviour in turning.

Grey-Based Taguchi Analysis for Optimization of Multi-Objective Machining Process in Turning

In the present experimental study, Taguchi method and the GRA grey relation analysis technique were used to optimize a multi-objective metal cutting process to yield maximum performance of tungsten carbide-cobalt cutting tool inserts in turning. L18 orthogonal array was selected to analyze the effect of cutting speed, feed rate and depth of cut using cryogenically treated and untreated inserts. The performance was evaluated in terms of main cutting force, power consumption, tool wear and material removal rate using main effect plots of S/N signal to noise ratios. This study indicated that grey based Taguchi technique is not only a novel, efficient and reliable method of optimization, but also contributes to satisfactory solution for multi machining objectives in turning process. It is concluded that cryogenic treated cutting tool inserts performed better. However, the feed rate affected the process performance most significantly.

Failure cause identification of tribo-mechanical systems using fault tree—a digraph approach

A procedure for the failure cause identification of tribo-mechanical systems is presented based on fault-tree using a digraph approach. A variable-event system digraph for a tribo-mechanical system is suggested which takes into account structure of the system. A top event or undesirable event for the system is then defined and the fault-tree for this top event is deduced from the digraph by back-tracking it. The analysis of the fault-tree aids the design and practising engineers in design and development of reliable, safe and productive tribo-mechanical systems. The methodology is applied to journal bearing oil supply system in a power plant application.

Wear Evaluation and Ranking of Tribomaterials Using a Hasse Diagram Approach

A procedure is developed to evaluate and rank tribomaterials based on wear parameters using a vectorial approach. The method known as the Hasse Diagram approach allows one to graphically compare tribomaterials based on a large number of wear parameters or test results which might otherwise be very confusing. The inclusion of uncertainty and a provision to include weighting factors so that the ranking scheme does not change when additional tribomaterials are added have also been discussed. An example of eight tribo-materials has been presented for ranking based on five wear parameters.

Experimental study of friction and wear characteristics of titanium alloy (Ti-6Al-4V) under lubricated sliding condition

Purpose – In the present study, an attempt has been made to examine friction and wear behaviour of Ti-6Al-4V alloy sliding against EN-31 steel under lubricative media of common commercial grade oil (hydrol-68). The paper aims to discuss these issues. Design/methodology/approach – Tribological properties of Ti-6Al-4V under hydrol-68 as lubricative media are measured using multi-tribo tester. Lubricating oil samples at different normal loads have also been analysed with the help of laser net fines (LNF) as per ISO 4406:1999. Experiments have been designed by two level full factorial method. Findings – Experimental results indicate that the wear rate of Ti-6Al-4V alloy decreases as sliding speed increases. But it shows typical transition characteristics as the normal load increases; till 30 N wear rate decreases then it increases from 30 to 50 N. Also for all loads and at every speed, the average wear increases as the sliding distance increases. The average coefficient of friction of the Ti-6Al-4V alloy decr...

Effect of Iron on Microstructure of Al-12Si-1Cu-0.1Mg Alloy

Iron is generally considered harmful as an element in Al foundry alloys due to its adverse effect on the mechanical properties, and the same is attributed to formation of brittle Fe-rich intermetallic compounds formed with combination of different alloying elements present in the alloy, e.g., Al5FeSi (β phase). The present article describes the results of an experimental work to study the effect of Fe on microstructure and hardness of Al-12Si-1Cu-0.1Mg alloy. Microstructure characterization was performed by using image analyzer, scanning electron microscope (SEM), and electron probe microanalysis (EPMA). It was found that increase in wt% of Fe leads to significant increase in area fraction and aspect ratio of Fe-rich intermetallics and decrease in Al–Si eutectic area fraction. Hardness remains steady up to 0.6 wt% Fe at 86 Hv, and increases significantly afterwards to 105 Hv. Secondary as well as Primary dendritic arms spacing reduces significantly with an increase in Fe content. Increase in porosity was observed above 0.6 wt% Fe.