P.P. Bandyopadhyay

Effects of cryo-cooling in grinding steels

Abstract The grinding process is inherently characterised by high specific energy and high temperature, which are responsible for high wheel loading, increased grinding forces, reduced metal-removal rate, rapid wheel wear and deterioration in the quality of the ground surface through oxidation, the induction of tensile residual stress and micro-cracks. These problems become more acute when the product is of HSHR material and subjected to dynamic loading while functioning. Therefore, in industry the user should pay special attention to control and optimise all the significant parameters for minimising the afore-said problems, aiming at higher grindability, productivity and overall economy in grinding. The basic principles of controlling such high temperature are: (i) proper selection and optimisation of wheel and process parameters; (ii) the removal of heat from the grinding zone by the application of proper grinding fluid. Profuse cooling with conventional grinding fluids, even in the form of mist or jet, is virtually unable to solve the problem. However, cryogenic cooling by agents such as liquid nitrogen is expected to meet this challenge. In the present work, specimens of different steels, namely MS, HCS, cold- and hot-die steel and HSS, have been surface ground at different infeeds under dry conditions and with soluble oil and liquid nitrogen. The effects of such cryo-cooling relative to soluble oil and dry grinding have been investigated in respect of chip formation, grinding forces, specific energy, burning and surface characterisation. The experimental results indicate that the grinding temperature and burning decreased remarkably under cryo-cooling. Thermal damage of the ground surface has been reduced substantially by cryo-cooling, but to different degree in different steels. Cryo-cooling also enables retention of the wheel sharpness for a longer period and results in less force and specific energy being required.

Neural-networks-based tool wear monitoring in turning medium carbon steel using a coated carbide tool

Abstract Appropriate on-line tool condition monitoring is essential for sophisticated and automated modern machine tools for aiding better tool management. It enables higher productivity and safety to the machine-fixture-tool-work system. This paper presents a neural-networks-based system for on-line assessment of TiN-coated carbide inserts. The wear estimates by the system are observed to have very close agreement with the directly measured flank wear.

Modeling of input-output relationships for a plasma spray coating process using soft computing tools

To automate any manufacturing process, its input-output relationships are to be known in both forward and reverse directions. The present work aims to correlate input process parameters with various responses of a plasma spray coating process. Statistical regression analysis had been carried out previously for this process based on the data collected through central composite design of experiments to establish input-output relationships in forward direction. However, the said relationships could not be accurately determined in reverse direction using the obtained regression equations due to the presence of a non-square transformation matrix. Soft computing-based approaches had been developed to model the process in both forward as well as reverse directions. The performances of the developed approaches had been tested on different cases obtained through real experiments. A comparative study had been made of these developed approaches in terms of accuracy in predictions.

Hierarchical adaptive neuro-fuzzy inference systems trained by evolutionary algorithms to model plasma spray coating process

A novel architecture of hierarchical adaptive neuro-fuzzy inference systems was developed, which was tuned using a genetic algorithm and particle swarm optimization algorithm, separately. It was used to establish input-output relationships of a plasma spray coating process. The parameters, namely primary gas flow rate, stand-off distance, powder flow rate and arc current were considered as inputs of the process and the quality of coating was represented using three responses, such as its thickness, porosity and microhardness. Particle swarm optimization-based approach was found to perform better than the genetic algorithm-based approach on some test cases.

Fabrication of Optical Components by Ultraprecision Finishing Processes

The demand of ultraprecision optical components is increasing extensively with the rapid development of the modern optics. The optical components used in X-ray microscopy and extreme ultraviolet lithography (EUVL) demand surface roughness of about 0.1 nm rms, a figure accuracy about 1 nm peak-to-valley (p–v) and no induced subsurface crystallographic damage. Furthermore, an aspherical surface is gaining more interest over the past few years for its favourable properties, and many new optical materials are also being developed. Fabrication of ultraprecision optical components became a great challenge to the optical fabrication industry. Aspheric optical components are generally fabricated by shaping methods followed by precision finishing processes. Near net shape of the component can be accomplished by the shaping methods (e.g. single-point diamond turning, deterministic micro-grinding, etc.). The application of optical components fabricated by this method is limited to the infrared (IR) optics owing to the presence of high-spatial-frequency surface irregularities which lead to the possibility of scattering for shorter wavelength applications. Desired surface finish, figure accuracy and surface integrity can be attained by precision finishing techniques to make it suitable for shorter wavelength applications. In the recent years, ion beam figuring, elastic emission machining, nanoparticle colloid jet machining and magnetorheological finishing are extensively used for fabrication of ultraprecision optics. In this chapter, principle mechanism of material removal and applicability of aforementioned ultraprecision finishing processes to different materials are discussed.

Review of several precision finishing processes for optics manufacturing

Abstract The ultrasmooth optical components with atomic-order surface roughness and nanometre-level shape accuracy are in immense demand with the rapid advancement of modern optical technology. In recent years, aspherical and free-form surfaces are gaining more interest for its favorable properties. Moreover, the new optical materials with immensely enhanced mechanical properties are being developed to meet the stringent requirements of modern optics. Fabrication of complex-shaped ultrasmooth optical components becomes a significant challenge as conventional finishing techniques are unable to machine aspherical or free-form surfaces precisely. This situation demands some highly deterministic finishing processes. Mostly, the optical components are fabricated by shaping or pre-finishing methods followed by final finishing processes. In the shaping or pre-finishing methods, the rigid abrasive tools are used to remove the material at an enhanced rate and near net shape of the elements can be attained. Surface finish and shape accuracy can also be improved to some extent. Owing to the presence of residual finishing marks generated by shaping methods, the application of the components is limited to the infrared (IR) optics. Final finishing processes include more deterministic and flexible polishing techniques that can achieve desired surface finish, figure accuracy and surface integrity to make it suitable for shorter wavelength applications. In recent years, single point diamond turning, precision grinding, plasma chemical vaporization machining and magnetorheological fluid-based finishing are widely used for fabricating ultrasmooth optics. In this article, principle, mechanism of material removal and applicability of the aforementioned precision finishing processes to different materials are discussed.

Plasma-Sprayed Titania and Alumina Coatings Obtained from Feedstocks Prepared by Heterocoagulation with 1 wt.% Carbon Nanotube

Properties of plasma-sprayed ceramic coatings can be improved significantly by reinforcing such coatings with carbon nanotube (CNT). However, it is difficult to disperse CNT in the plasma spray feedstock owing to its tendency to form agglomerate. A colloidal processing technique, namely heterocoagulation, is effective in bringing about unbundling of CNT, followed by its homogeneous dispersion in the ceramic powder. This report deals with the mixing of micro-sized crushed titania and agglomerated alumina powders with CNT using the heterocoagulation technique. Heterocoagulation of titania was attempted with both cationic and anionic surfactants, and the latter was found to be more effective. Mixing of the oxides and carbon nanotube was also accomplished in a ball mill either in a dry condition or in alcohol, and powders thus obtained were compared with the heterocoagulated powder. The heterocoagulated powder has shown a more homogeneous dispersion of CNT in the oxide. The coatings produced from the heterocoagulated powder demonstrated improvement in hardness, porosity, indentation fracture toughness and elastic modulus. This is attributed to CNT reinforcement.