Chandra Nath | Georgia Institute of Technology (original) (raw)

Papers by Chandra Nath

Hard and brittle materials, such as Ni-and Ti-based alloys, glass, and ceramics, are very useful ... more Hard and brittle materials, such as Ni-and Ti-based alloys, glass, and ceramics, are very useful in aerospace, marine, electronics, and high-temperature applications because of their extremely versatile mechanical and chemical properties. One Ni-based alloy, Inconel 718, is a precipitation-hardenable material designed with exceptionally high yield strength, ultimate tensile strength, elastic modulus, and corrosion resistance with outstanding weldability and excellent creep-rupture properties at moderately high temperatures.

Micro-chipping via micro-cracks, due to rapid mechanical indentations by abrasive grits, is the f... more Micro-chipping via micro-cracks, due to rapid mechanical indentations by abrasive grits, is the fundamental mechanism of material removal during ultrasonic machining (USM) of hard–brittle materials like ceramics and glass. This study aims mainly to investigate the adverse effects of this inherent removal phenomena on the hole integrity such as entrance chipping, wall roughness and subsurface damage. It also presents the material removal mechanism happens in the gap between the tool periphery and the hole wall (called 'lateral gap').

Tool life has been a vital issue in machining titanium alloys. Recently, an atomization-based cut... more Tool life has been a vital issue in machining titanium alloys. Recently, an atomization-based cutting fluid (ACF) application has been found to be an effective approach for cooling and lubrication in micromachining operations. In this study, an ACF spray system is developed for macro-scale turning of Ti–6Al–4V. The spray system is designed to minimize interaction between the fluid droplets, and the gas nozzle to control the divergence of the fluid droplets.

In this thesis, conventional ultrasonic vibration cutting (CUVC) and ultrasonic elliptical vibrat... more In this thesis, conventional ultrasonic vibration cutting (CUVC) and ultrasonic elliptical vibration cutting (UEVC) methods are studied and applied to two difficult-to-cut materials. Firstly, theoretical study reveals that the CUVC mechanism is influenced by: 1) tool vibration frequency, 2) vibration amplitude and 3) cutting speed. The increase in first two and the decrease in third parameters improve CUVC performance.

The elliptical vibration cutting (EVC) technique has been found to be a promising technique for u... more The elliptical vibration cutting (EVC) technique has been found to be a promising technique for ultraprecision machining of various materials. In each overlapping EVC cycle, the thickness of cut (TOC) of work material, and the tool velocity get continuously varied. These two inherent phenomena, in fact, introduce transient characteristics into its cutting mechanics, which are considered to be different from the one applied for conventional cutting technique.

Ultraprecision machining of hardened steel by the conventional cutting (CC) technique using diamo... more Ultraprecision machining of hardened steel by the conventional cutting (CC) technique using diamond tools is impossible because of highly chemical affinity between carbon and iron at higher temperature during machining. An intermittently cutting technique, namely, ultrasonic elliptical vibration cutting (UEVC) technique has been being applied for high-quality machining of various difficult-to-cut materials for the last decade.

International Journal of Machine Tools and …, Jan 1, 2008

The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-... more The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-machine materials. It is found that the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force. However, the relation between the cutting force and these three parameters in the UVC is not clearly established. This paper presents firstly the mechanism how these parameters effect the UVC. With theoretical studies, it is established that the tool-workpiece contact ratio (TWCR) plays a key role in the UVC process where the increase in both the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life. This paper also experimentally investigates the effect of cutting parameters on cutting performances in the cutting of Inconel 718 by applying both the UVC and the conventional turning (CT) methods. It is observed that the UVC method promises better surface finish and improves tool life in hard cutting at low cutting speed as compared to the CT method. The experiments also show that the TWCR, when investigating the effect of cutting speed, has a significant effect on both the cutting force and the tool wear in the UVC method, which substantiates the theoretical findings. r

Journal of materials processing …, Jan 1, 2007

High quality mirror surface machining of hard and brittle materials such as glass, ceramics, tung... more High quality mirror surface machining of hard and brittle materials such as glass, ceramics, tungsten, Ni-based and Ti-based alloys has become more important in recent advanced technological applications; as these materials are widely used as aspheric shapes in optical and electronic devices, aerospace industries, household works etc. Much research has been conducted covering various cutting parameters to optimize machining conditions of such difficult-to-machine materials. Low alloy steel (DF2), a hardened steel, is a workhorse material in all industries, especially in chemical process industries due to its lower cost, good mechanical properties, weldability, and corrosion resistance at moderate temperatures. High quality surface finish is essential in most of the cases and this cannot be obtained by conventional turning (CT) process. Ultrasonic vibration cutting (UVC) has been applied to study the tool wear, cutting forces, chip formation and surface roughness under specified cutting conditions over a range. This paper investigates the effects of UVC in cutting of DF2 material, on abrasive wear and on the transition of low to high tool wear rate in the machining of the same material. Finally, it compares the UVC with CT in machining of DF2 for different cutting parameters. It is observed with photography that UVC process results in better surface finishes as compared to CT, and UVC requires lower cutting forces than in the CT process. It is also found that UVC has lower tool flank wear rate compared to CT under all cutting conditions.

Journal of manufacturing …, Jan 1, 2011

Journal of Materials …, Jan 1, 2011

Diamond tools cannot usually be applied for machining hardened steels while applying conventional... more Diamond tools cannot usually be applied for machining hardened steels while applying conventional cutting technique. As an alternative, ultrasonic elliptical vibration cutting (UEVC) technique was successfully applied for obtaining mirror surface on such steels using single crystal diamond (SCD) tools. In order to reduce production cost without compromising mirror surface quality, polycrystalline diamond (PCD) tools may be tested against highly expensive SCD tools. However, study on machining of hardened steel using PCD tools applying the UEVC technique has not yet been reported. The current research presents an experimental study on UEVC of hardened stainless steel (a typical Stavax, hardness 49 HRC) using the PCD tools. Face turning experiments were carried out to investigate the effects of three machining parameters: nominal depth of cut, feed rate, and nominal cutting speed on output performances such as cutting force, tool flank wear, surface roughness, and chip formation. Experimental results show that nominal cutting speed has very strong influence on the output performances, compared to the other two parameters. The surface roughness improves with a decrease in cutting speed. A mirror-like surface of approximately 804 mm 2 with a roughness value R a of 11 nm was achieved at a lower cutting speed. Theoretical explanations have been given to support the results drawn from the UEVC experiments. It can be concluded that, while applying the UEVC technique, the inexpensive PCD tools instead of the SCD tools can be effectively applied to obtain optical surface for producing precise molds from the hardened steel.

Key Engineering Materials, Jan 1, 2010

Structural SiC (α-type) is believed to be widely applied in hostile environments such as high-tem... more Structural SiC (α-type) is believed to be widely applied in hostile environments such as high-temperature, high-corrosive applications in the semiconductor industries due to its superior thermo-physical and mechanical properties. However, the extremely high hardness and brittleness of SiC makes hole drilling difficult by the conventional mechanical drilling (CMD) technique. Laser can be used to drill SiC; but the resultant holes are often tapered and uneven, with tendency for microcracks and thermal damage to occur at the hole entry due to the high thermal shock from the laser. This paper reports on the experimental results of a sequential laser-mechanical drilling (LMD) technique for drilling α-SiC. At first, an Nd:YAG laser was used to drill a series of pilot holes on a 3 mm thick SiC plate. Then a diamond-coated carbide drill was sequentially applied to these holes to obtain desired hole diameter of 0.5 mm. A number of through holes on SiC (aspect ratio: 6) were successfully obtained using this approach. The quality of the drilled holes were assessed in terms of the entrance and exit sizes and conditions, hole taper angle, hole edge shapes, and microcracks. Finally, comparisons of the LMD performances were also made against the holes predrilled by the laser itself and holes of the similar size drilled separately with the CMD technique. The experiment results show that the proposed drilling approach can effectively drill α-SiC ceramics.

Journal of Materials Processing Technology, Jan 1, 2009

The user has requested enhancement of the downloaded file. All in-text references underlined in b... more The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.

International Journal of Machine Tools and …, Jan 1, 2009

Sintered tungsten carbide (WC) is an extremely hard and brittle material extensively used in tool... more Sintered tungsten carbide (WC) is an extremely hard and brittle material extensively used in tool manufacturing industries. However, the current cutting technologies for shaping this typical hard-tomachine material are still cost ineffective. In this study, polycrystalline diamond (PCD) tools are used to study the machinability of sintered WC ($15% Co) by applying the ultrasonic elliptical vibration cutting (UEVC) technique. Firstly, it presents the UEVC principle and the effects of speed ratio (i.e. the ratio of the nominal cutting speed to the maximum tool vibration speed in the cutting direction) on the tool-workpiece relative motion as the cutting speed greatly influences the UEVC performance. Then UEVC experiments are carried out to analyze the cutting force, tool-wear progression, chip formation and surface quality against the cutting time at different speed ratios. The results show that when the speed ratio decreases, the resultant cutting force and the tool flank wear decrease while the surface finish improves. Average surface roughness, R a , in a range between 0.030 and 0.050 mm is achieved at speed ratios less than 0.107. The experimental findings suggest that the commercial PCD tools can be used to machine sintered WC to achieve ultraprecision surface by applying the UEVC technique, which will be cost effective for miniature cutting technologies in future.

Journal of Materials Processing Technology, Jan 1, 2009

… of Vacuum Science & Technology B: …, Jan 1, 2009

Precise machining or shaping of difficult-to-cut materials, such as tungsten carbide ͑WC͒, harden... more Precise machining or shaping of difficult-to-cut materials, such as tungsten carbide ͑WC͒, hardened steels, and optical glass, is always difficult to achieve by applying conventional cutting ͑CC͒ methods. Recently, the ultrasonic elliptical vibration cutting ͑UEVC͒ method has been successfully applied to machine some of such materials. However, this novel machining method has yet to be applied on WC using polycrystalline diamond ͑PCD͒ tools. This study aims to enhance the machining performance of commercial PCD tools for machining sintered WC by applying the UEVC method. First, the effects of cutting parameters on the cutting performance have been studied to establish a set of best cutting conditions. Then a case study has been carried out to justify whether the cutting performance in the UEVC method can further be improved by varying the related parameters but keeping the same machining rate. To substantiate the feasibility of UEVC method, a comparative performance of this method has been carried out with that of its CC counterpart. Experimental results have shown that the UEVC method results in better cutting performance with the decrease in the feed rate at the speed ratio of less than 1. A surface roughness of 0.027 m R a has been achieved on a machining area about 1257 mm 2 with the UEVC method. The findings reveal that the performance of PCD tools could be enhanced by the UEVC method for ultraprecision machining of hard-to-cut materials.

International Journal of Machine Tools and …, Jan 1, 2008

Journal of materials processing …, Jan 1, 2007

Journal of manufacturing …, Jan 1, 2011

Journal of Materials …, Jan 1, 2011

Key Engineering Materials, Jan 1, 2010

Journal of Materials Processing Technology, Jan 1, 2009

International Journal of Machine Tools and …, Jan 1, 2009

Journal of Materials Processing Technology, Jan 1, 2009

… of Vacuum Science & Technology B: …, Jan 1, 2009