R. Krishnamurthy

Microwave processing of sprayed alumina composite for enhanced performance

Abstract To meet the challenging in-service requirements, surfaces of many mechanical components need to be modified. This can be achieved by altering the surface properties through deposition technique followed by suitable post processing. Apart from the conventional methods, laser treatment is the most popular post processing technique. Of late, microwave heating is emerging as one of the potential post processing sources. Microwave processing of materials is fundamentally different from traditional techniques. In microwave processing, energy is directly transferred to the material through interaction of electromagnetic waves with molecules leading to volumetric heating. However, for processing of transparent (to microwaves) materials, a technique known as microwave hybrid heating (MHH) can be used. In this study, MHH is used for post processing of plasma deposited alumina–titania ceramic composite coatings on steel substrate; resulting properties of the post processed coatings are evaluated. Results show reduction in porosity, enhancement in microhardness, and wear resistance of the irradiated coatings owing to microstructural changes and densification. Results are discussed with suitable illustrations.

In-process tool wear and chip-form monitoring in face milling operation using acoustic emission.

Abstract This paper discusses the need for on-line tool condition monitoring and chip-form identification during metal machining. Acoustic Emission (AE) analysis was applied to study the effect of tool wear and corresponding change in chip-form in face milling. The AE parameters and flank wear were measured at fixed interval. Also chips were collected simultaneously at same interval. The results indicate that the AE parameters namely ringdown counts, rise time increase with progressive tool wear; however number of events and event duration are sensitive to chip-form. These results may be readily used for in-process monitoring of chip status and consequently tool condition.

In-process monitoring of grinding burn in the cylindrical grinding of steel

Abstract While moving towards complete automation of the grinding process in order to be able to realise unattended manufacturing, it becomes mandatory to closely monitor the process in order to detect any malfunction at the earliest moment with high reliability. In the grinding process, a proper estimate of the life of the grinding wheel is very useful. When this life expires, redressing is necessary. Generally, chatter marks, surface roughness, burn marks, etc. are considered as the tool-life limit in grinding. In this paper, the occurrence of burn marks on the work surface is adopted as a criterion of the wheel life; accordingly, the time of the occurrence of grinding burn during the cylindrical plunge grinding of steel is studied under different conditions of grinding. The data thus collected is used for the prediction of the time to burn using an artificial neural network.

Machining performance of phase transformation toughened alumina and partially stabilised zirconia composite cutting tools

Abstract Phase transformation toughened zirconia (TTZ) doped with yttria or ceria has excellent properties such as higher order fracture toughness, thermal shock resistance and moderate hardness. With these qualities, they are able to exhibit machining performance comparable to cold-compacted Al 2 O 3 cutting tools. With an addition of 20% aluminium oxide to TTZ, i.e. the composites of alumina and partially stabilised zirconia (PSZ) exhibit improved toughness, enhanced thermal shock resistance and hardness. The alumina and PSZ composite ceramic tools exhibit cutting performance better than TTZ tools and comparable to zirconia toughened alumina tools.

Modeling and optimization of process parameters for defect toleranced drilling of GFRP composites

Drilling is a frequently practiced machining process for fiber-reinforced plastics (FRP) in industry owing to the need for component assembly in mechanical structures. Drilling experiments are performed on a (0/±45/90)2s 3-mm-thick glass fiber-reinforced laminate using 4-, 6- and 8-mm-diameter HSS drills. The machining response of the quasi-isotropic laminate was studied by monitoring the thrust and torque. The performance of the HSS drills for different cutting conditions was studied by measuring the tool wear. Delamination due to drilling is a major concern in machining a composite laminate and is analyzed by using linear elastic fracture mechanics, classical plate bending theory, and the mechanics of composites. A mechanical model for evaluating the critical thrust at which delamination is initiated at different ply locations has been used, and the critical thrust force at the onset of delamination has been found to be 70 N. The present work analyzes data on the thrust force, torque, and tool life by using a group method data handling (GMDH) algorithm. An optimization algorithm using simulated annealing with a performance index is then applied to search for the optimal process parameters for delaminatien constrained drilling.

Minimum Quantity Lubricated Grinding of Inconel 751 Alloy

Minimum Quantity Lubrication (MQL) results a better cooling effect than the boundary lubricated and dry environment, besides being environmental friendly. Very few investigations have been carried out on the influence of MQL parameters, such as oil flow rate and air pressure on grinding performance. Since grinding comprises both cutting and sliding, it is necessary to provide a balanced environment of heat extraction and lubrication. Thus it requires a controlled grinding environment such as MQL. The current study is an experimental investigation on the significance of the MQL parameters on grinding performance of Inconel 751. Inconel is an ideal material for high temperature applications although it poses difficulties during machining, especially grinding. It was found that better results were obtained for the optimal MQL condition in grinding in terms of reduced grinding force, temperature, and roughness. Also it was found that there is hardly any crest flattening on the surface being ground with minimum quantity lubrication. Induction of MQL facilitates considerable reduction in the grinding forces, temperature, and roughness, apart from the absence of visible grinding burns.

Development of alumina and Ce-TTZ ceramic-ceramic composite (ZTA) cutting tool

Zirconia toughened aluminas (ZTAs) with their enhanced transverse rupture strength and fracture toughness are more widely applicable and more productive than plain alumina ceramics and cermets in metal cutting applications. The development of Ce-transformation toughened zirconia (TTZ) based alumina ceramic-ceramic composite (ZTA) for machining applications has resulted in a cutting tool which can be used in a finishing operation even at relatively low cutting speeds, which is usually the range for carbide cutting tools.

Effect of processing parameters on the laser glazing of plasma-sprayed alumina–titania ceramic ☆

Abstract An Nd-YAG laser beam has been employed to glaze the surface layer of atmospheric plasma-sprayed alumina–titania (AT) ceramic composite deposited on a low carbon steel substrate. The effect of laser processing parameters such as power intensity, traverse speed, and beam focussing distance on microstructure and processing defects have been evaluated. Experimental study yielded a shiny glazed surface of plasma-sprayed AT ceramic composite by choosing an appropriate range of parameters. The working range of process parameters is illustrated. XRD analysis has been carried out for determining possible phase changes with different processing parameters. XRD analysis showed that there was only marginal variation in the phase change when glazing with parameters within the working range. Monitoring of AE was observed to closely indicate the response of the ceramic to the glazing process.

Efficient grinding of Ce-TZP with SiC wheels

Abstract Transformation toughened zirconia has been widely studied. Most of the reports on zirconia deal only with the transformation behaviour in various environments. However, for the effective use of any ceramic, information on processing is essential. In spite of stabilized zirconia being an important material for various technical applications, details on how it can be processed by grinding is lacking. The present paper reports on the grindability of ceria-stabilized zirconia with various grinding wheels. Based on the grinding forces, specific grinding energies, phase structure and grinding induced surface cracks, it is shown that SiC grinding wheels can grind Ce-TZP efficiently.

Micro-Grooving Studies on Alumina Ceramic Material

Sintered alumina (99.8%) was subjected to grooving at different conditions using a diamond indenter. The process parameters considered for the study are normal load, inclination angle of the indenter and grooving speed of the grooving. The parametric influence on the grooving process indicators such as groove geometry, horizontal cutting force, specific cutting energy and size of the plastic zone were studied. Ceramics are prone to median and lateral cracking during sliding indentation, and hence it is meant to evaluate the conditions facilitating ductile mode of grooving. It was found that at some conditions controlled grooving has taken place with ductile mode of material removal. Fine grooving occurred at a normal load of 10 N, with angle of inclination 5–10 deg. and at a grooving speed of 18 mm/sec, which favors ductile mode of grooving.