Shiv Sharma

Bio: Shiv Sharma is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Machining & Microstructure. The author has an hindex of 2, co-authored 2 publication(s) receiving 11 citation(s).

Microstructure attributes and tool wear mechanisms during high-speed machining of Ti-6Al-4V

Abstract: The present study is mainly focused on the influence of microstructure attributes such as grain size, phase fraction and grain morphology on the machining characteristics and its correlation with the tool wear mechanisms during high-speed machining of Ti-6Al-4V under dry cutting environment. The thermo-mechanical loading at the cutting zone was analyzed in terms of the cutting forces and machining-induced sub-surface microstructure and its microhardness. The SEM-EDS analysis has been performed to correlate the microstructure characteristics with the deformation process and their consequent tool wear mechanisms. Study of built-up edge shows its substantial effect on the cutting force at higher cutting speed. Grain morphologies at the machined sub-surface depicted the severity of the deformation and explain the machining characteristics. It has been observed that the machined surface/sub-surface deformation depth increases with an increase in tool wear considering microstructural attributes. The obtained results revealed a significant correlation between microstructure attributes, cutting forces, machining-induced sub-surface microstructure and tool wear mechanisms.

Microstructure Induced Shear Instability Criterion During High-Speed Machining of Ti–6Al–4V

Abstract: The microstructure attributes are responsible for the deformation mechanism of material which induces shear instability primarily in difficult-to-machine material like Ti6Al4V. Consequently, the dynamic cutting force yields serrations in the chip morphology. Therefore, microstructure induced shear instability has been investigated in the present work using an analytical tool to unveiled the deformation behaviour in correlation with microstructural characteristics (grain sizes, phase fractions and microhardness) and process parameters; temperature, strain and strain rate. The combined effect of feed rate and high cutting speed was found to enhance the strain localization phenomena, which leads to a more pronounced cracking, inducing dynamic cutting force. Segmentation frequency and force-frequency correlation imply that there is a significant transition exhibit from static to dynamic nature of cutting force. The segmentation frequency of the equiaxed microstructure is lowest among the rest at lower cutting speed, which reveals the shear instability dependency on the microstructure. Grain size effect restricts the dislocation movement at the higher cutting speed which led to a larger strain in as-received microstructure followed by equiaxed and fully lamellar microstructure.

Tool wear and machined surface characteristics in side milling Ti6Al4V under dry and supercritical CO2 with MQL conditions

Abstract: Ti6Al4V alloy is a typical difficult-to-cut material In order to improve its machinability and realize cleaner production, eco-friendly cooling/lubrication techniques are applied Therefore, this study aims to investigate the tool wear, surface topography, cutting torque, and surface profile in side milling Ti6Al4V under four sustainable conditions, ie, dry, supercritical carbon dioxide (scCO2), scCO2 with antifreeze water based minimum quantity lubrication (scCO2-WMQL), and scCO2 with oil-on-water based MQL (scCO2-OoWMQL) conditions A theoretical model of flank wear width VB with average prediction error 1587% is established scCO2-OoWMQL reduces VB by 672% compared to scCO2 alone due to improved lubricity Detailed characteristics of machined surface profile are investigated using continuous wavelet transform The performance of scCO2-OoWMQL as a new sustainable and efficient cooling/lubrication technique is superior to scCO2 alone

Advancements in material removal mechanism and surface integrity of high speed metal cutting: A review

Abstract: The research and application of high speed metal cutting (HSMC) is aimed at achieving higher productivity and improved surface quality. This paper reviews the advancements in HSMC with a focus on the material removal mechanism and machined surface integrity without considering the effect of cutting dynamics on the machining process. In addition, the variation of cutting force and cutting temperature as well as the tool wear behavior during HSMC are summarized. Through comparing with conventional machining (or called as normal speed machining), the advantages of HSMC are elaborated from the aspects of high material removal rate, good finished surface quality (except surface residual stress), low cutting force, and low cutting temperature. Meanwhile, the shortcomings of HSMC are presented from the aspects of high tool wear rate and tensile residual stress on finished surface. The variation of material dynamic properties at high cutting speeds is the underlying mechanism responsible for the transition of chip morphology and material removal mechanism. Less surface defects and lower surface roughness can be obtained at a specific range of high cutting speeds, which depends on the workpiece material and cutting conditions. The thorough review on pros and cons of HSMC can help to effectively utilize its advantages and circumvent its shortcomings. Furthermore, the challenges for advancing and future research directions of HSMC are highlighted. Particularly, to reveal the relationships among inherent attributes of workpiece materials, processing parameters during HSMC, and evolution of machined surface properties will be a potential breakthrough direction. Although the influence of cutting speed on the material removal mechanism and surface integrity has been studied extensively, it still requires more detailed investigations in the future with continuous increase in cutting speed and emergence of new engineering materials in industries.

A thermo-mechanical finite element simulation model to analyze bushing formation and drilling tool for friction drilling of difficult-to-machine materials

Abstract: In metallurgical view point, difficult-to-machine materials are named as materials which have high work-hardening, low thermal conductivity, and great toughness. Since recently special attention has been paid to the difficult-to-machine materials in different applications, an excellent potential for product fabrication is proposed by friction drilling. However, the main problem is encountered when friction drilling of difficult-to-machine materials are poor machining performance and short tool life. Due to the wide range of applications for difficult-to-machine materials AISI304, Ti-6Al-4 V, and Inconel718 in different industries, this paper is concerned with thermo-mechanical modelling of friction drilling process on these materials using drilling tool of WC which contributes to gain an in-depth understanding of how friction in workpiece-tool interface generates the heating. It can help to find out effects of frictional heat generation on bushing formation and drilling tool, and how to improve quality of bushing formation and prolong tool life. In order to verify the numerical simulated results and evaluation of surface quality and required thrust force, an experimental validation is also conducted. A comparison of the predicted and experimental results reveal that the main reasons of uniform bushing formation quality and low tool degradation for friction drilling of Inconel718, and non-uniform bushing formation quality and high tool degradation for friction drilling of Ti-6Al-4 V are high work hardening of Inconel718 and low thermal conductivity of Ti-6Al-4 V. Moreover, the bushing formation cycle time, where the maximum contact between drilling tool and bushing hole-wall occurs, is the most critical step time in friction drilling process that causes maximum tool wear.

Influences of machining parameters on tool performance when high-speed ultrasonic vibration cutting titanium alloys

Abstract: Tool performance is a key factor in evaluating machining processes. To improve machining productivity and part quality, researchers have conducted numerous studies on improving tool performance, such as tool design, coatings, functional micro textures, cooling/lubrication conditions, cutting parameter optimization, and intermittent cutting. Focusing on materials that are difficult to cut (i.e., Ti alloys), this paper explores a high-speed ultrasonic vibration cutting method that combines intermittent cutting, cooling, and lubrication. Through theoretical analysis and experiments on tool wear, cutting force, temperature, etc., the influence of machining parameters on tool performance is investigated. The results show that a large separation effect coupled with good cooling and lubrication conditions is key to improving tool performance. Among these, the feedrate and phase shift resulting from the rotary (spindle) speed are the core machining parameters. On this basis, the choice of machining parameters is summarized to provide a reference for the high-efficient machining of Ti alloys for scholars and engineers. First, cooling and lubrication conditions, such as dry machining and fluids, are determined. The duty cycle is then set from 0.5 to 0.6 via a relatively small feedrate value (i.e. 0.005 mm/r) and a π phase shift. Finally, the cutting speed and depth of cut are chosen according to the requirements of machining efficiency and cost.

A physically based constitutive model of microstructural evolution of Ti6Al4V hard machining under different lubri-cooling conditions

Abstract: The metallurgical phenomena taking place during machining processes affect the thermo-mechanical properties of the severely deformed materials, influencing, consequently, the process behavior. The microstructural modifications are difficult to be evaluated when the material is subjected to high speed deformations that are typical of material removal processes. Therefore, the microstructure-based numerical simulations can represent a useful tool able to properly predict their mechanics. Hard turning experiments were conducted on Ti6Al4V alloy, involving different process parameters and lubri-cooling conditions. The worked samples surfaces were assessed in terms of resulting microstructural changes and microhardness. The obtained results (cutting forces, temperature, and surface metallurgical modifications) were considered to develop and validate a physics-based model able to describe the microstructural phenomena occurring under large deformation processes, taking into account the influence of the physical phenomena that accommodate the material plastic strengthening and their resulting effects on the process variables. The dislocations reciprocal influence and their interaction with the material lattice were considered to understand the material viscoplastic flow. Moreover, also the recrystallization phenomena influencing the grain size related strengthening were considered to formulate the model. Then, the developed material model was implemented via user sub-routine in a commercial finite element (FE) software. The FE model was used to in-depth analyze the inner evolution of the processed material and to predict the variables of industrial interest. A good agreement was shown between the experimentally measured variables and the numerically predicted results. Moreover, the model was employed to investigate additional machining conditions via finite element analysis (FEA), demonstrating a huge capability to improve the manufacturing process performances, leading to a deeper knowledge of microstructural evolution and the material machinability under various process conditions.