R. Krishnamurthi

Bio: R. Krishnamurthi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Surface integrity & Ultrasonic machining. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

Ultrasonic machining—a comprehensive review

Abstract: Ultrasonic machining (USM) is a mechanical material removal process used to erode holes and cavities in hard or brittle workpieces by using shaped tools, high-frequency mechanical motion, and an abrasive slurry. The fundamental principles of stationary ultrasonic machining, the material removal mechanisms involved, proposed models for estimation of machining rate, the effect of operating parameters on material removal rate, tool wear rate, and workpiece surface finish, research work reported on rotary mode USM, hybrid USM, process capabilities of USM have been extensively reviewed in this article. The limitations of USM, gaps observed from the literature review, and the directions for future research have also been presented. Overall, this article presents a comprehensive review of USM process for advancement of the process through fundamental insights into the process.

Investigating the Machining Characteristics of Titanium Using Ultrasonic Machining

Abstract: Titanium has been known as the ‘metal of the future’ for last few decades owing to its ever increasing applications in aerospace; marine; defense; nuclear energy; missiles; chemical production; hydrocarbon processing; power generation; desalination; nuclear waste storage and processing; metal recovery; offshore; marine deep sea applications; anodes; automotive components, food and pharmaceutical processing, medical implants and surgical devices and many other emerging fields of science and technology. Titanium is branded as difficult-to-machine metal as the conventional machining processes are unable to provide cost-effective solution for its commercial machining. Titanium is machined commercially by non-traditional methods such as Electric Discharge Machining (EDM) and Laser Beam Machining (LBM), but the surface quality obtained is not satisfactory from the prospect of surface integrity as well as surface finish. Ultrasonic Machining (USM) is another non-traditional machining process that is widely used in commercial machining of hard and brittle materials such as ceramics, refractory materials and precision stones. USM is a process known for its capabilities in providing excellent surface finish without any significant alterations is surface integrity or structure of the work material. Moreover, the compressive stress induced in the sub-surface as a result of repeated impacts of abrasive grains contributes in improving the fatigue strength of the machined components; which is a very important aspect especially for a material like titanium. Hence, the study was aimed to investigate the machining characteristics of titanium using different tool materials in ultrasonic machining and to model these characteristics for their application in the concerned manufacturing industry. The machining characteristics investigated are material removal rate (MRR); tool wear rate (TWR) and surface roughness. In the present investigation, the work has been limited to commercially pure titanium (ASTM Grade-I) as work material, in combination with five different tool materials (High carbon steel; High speed steel; titanium; titanium alloy and cemented carbide) for experimentation. The results showed that the response variables were strongly influenced by control factors (input parameters).

14 – Fatigue Wear

Abstract: Publisher Summary The fundamental characteristics of fatigue wear and ways of controlling it are discussed in this chapter. During sliding a consistent pattern of events relating to subsurface plastic deformation, crack formation and subsequent release of wear debris is evident. The role of material properties in determining wear rates involves factors influencing crack initiation and propagation. A material with the minimum of microscopic flaws and inclusions will usually give low fatigue wear rates. The lack of relative motion among contacting asperities in rolling contacts ensures that wear during rolling is relatively slow compared to sliding wear. Wear under dry rolling is sufficiently slow to allow many mechanical components to operate without lubrication or other forms of wear protection for a certain limited period of time. The application of lubrication further reduces the level of wear during rolling, so that a considerable period of rolling must elapse before the first wear particle is produced. Fatigue-based wear is inevitable for all sliding and rolling contacts so that the onset of delamination or spalling could be considered as an acceptable limit to the working life of the component provided that only gradual failure occurs.

Modelling of ultrasonically assisted micro drilling

Abstract: Micro drilling has been applied in the interconnection and precision manufacturing industries extensively As a promising machining technique, Ultrasonically Assisted Drilling (UAD) has become increasingly popular in both academia and industry in recent years In this thesis, modelling techniques and experiments for Ultrasonically Assisted Micro Drilling (UAMD) are investigated Representative work on modelling of micro drills and UAD has been documented and categorised Existing gaps in the literature are identified and the aims of this research are formulated Using the Finite Element (FE) technique, a hybrid model is developed to realise modelling for the whole drill bit without compromising the computation efficiency, even when the drill has a complicated geometry (small diameter flute, multiple step shanks, etc) A specific drill model (Φ03 mm diameter, 2 step shanks) is chosen for a case study in order to evaluate the model The hybrid tool shows sufficiently accurate results and impressive computation efficiency in the evaluation For vibration modelling, force modelling and experimental work, a standard Φ1 mm drill with 1 step shank is used across the chapters First of all, FE analysis is conducted on the whole drill and normal modes are solved with boundary condition as fixed simply supported A 2 Degree-of-Freedom (DOF) model is then built considering rotation and the ultrasonic excitation to solve the transverse vibration with boundary conditions consistent with the FE model The asymmetric geometric characteristics of the drill bit are taken account of through using the first two fundamental modes in the FE model Potential parametric resonances are discussed in the numerical simulation Other vibration characteristics are also discussed with varying parameters such as ultrasonic frequency, ultrasonic amplitude and rotational speed In order to extend the vibration model, a nonlinear thrust force model has been developed for incorporation into the 2 DOF model The force model considers ultrasonic parameters, feed rate, material properties and the nonlinearity of the UAMD process Force reduction during the UAMD process is explained qualitatively with the model and a full range of feed rates have been simulated to study their effect on the force reduction The limitations of this model have also been explained A high speed UAMD system was designed to examine the effects of key parameters Experiments with different ultrasonic frequencies, amplitudes and rotational speeds were conducted and the influences of these parameters on thrust force were investigated With the thrust force data from these experiments, a correlation study to the simulation results based on the force model is carried out The study identifies the limitations on the current one dimensional force model and leads to recommendations for the further development of the force model Further work is identified for both modelling and experiments, and the present models can be expanded to suit the research and development of UAMD techniques

Comparative analysis of ultrasonic drilling process using static and rotary tools

Abstract: Ultrasonic drilling (USD) is widely used for drilling of glass. A comparative study of USD for 2.0 mm diameter hole in 3.0 mm thick soda lime glass has been performed using static (USD-ST) and rotary tool (USD-RT) of mild steel. To make the process more cost effective and productive, statistical models of material removal rate (MRR), hole circularity at entry and exit (HCentry, HCexit) and hole taper (Ht) have been developed using Box–Behnken approach of response surface methodology. The effect of abrasive size, frequency, ultrasonic power and tool rotational speed have been investigated and it was observed that abrasive size is the most significant factor to control MRR during USD-ST. In USD-RT, MRR, HCentry, HCexit and Ht are significantly affected by frequency. The combination of low frequency and small grain size produces high MRR in USD-RT. Increase of frequency from 22 to 24 kHz increases HCentry by 4.3% in USD-ST, whereas for rotating tool the increase of frequency from 22 to 25 kHz decreases the value by 2%. HCentry increases with the rise of frequency at constant ultrasonic power, USD-ST provides 7.14% more circular hole at entry compared to USD-RT for a combination of frequency and grit size. In multi-objective optimization of USD-ST, a desirability value of 0.8589 was obtained at ultrasonic power of 90%, frequency 23.47 kHz and abrasive grit no 60, whereas for USD-RT the desirability value of 0.8499 were correspondingly obtained at 78.48%, 25.5 kHz, 770.20 rpm and 60.