Mamilla Ravi Sankar

Tribo-mechanical and surface morphological comparison of untextured, mechanical micro-textured (MμT), and coated-MμT cutting tools during machining:

In machining process, cutting fluids are used to reduce the tool–chip interface temperature and forces, but it causes various health hazards to machine operators as well as increases the associated costs. To improve machining sustainability, researchers are trying to reduce or eliminate cutting fluid usage during machining by various other techniques (development of better tool material, bio-cutting fluids, use of vegetable oils, near-dry machining, process optimization, surface coatings, etc). In recent years, several researchers applied controlled surface modification (surface texturing/engineering) at the tool–chip interface to improve the tribological properties in the machining performance. In the present study, first mechanical microtextures (MµT) are created on the rake surface, and its structural stability is compared with an untextured/virgin cutting tool. The static structural analyses show a negligible effect of mechanical microtextures on the strength of the cutting tool. Afterwards, MµT cutting tools are coated using molybdenum disulphide (MoS2) solid lubricant (i.e. coated MµT, C-MµT). Subsequently, the machining performance studies of C-MµT were carried out to show its advantages over two other types of cutting tools (UC, MµT). Performance of C-MµT is improved by mechanical microtextures (due to the reduction in the actual contact area between tool–chip interfaces) and proper lubrication of the tool–chip contact area. Thus, due to the reduced contact area and formation of lubricant layer by MoS2 at the tool–chip interface, C-MµT experiences 23.75% lower tool–chip interface temperature, 41.06% reduction in the cutting force, and produces 14.37% less workpiece center line average surface roughness (Ra) compared to untextured cutting tool. C-MµT experiences 9.55% lower tool–chip interface temperature, 19.02% reduction in the cutting force, and produces 5.34% less workpiece center line average surface roughness compared to the MµT cutting tool. Hence, C-MµT cutting tools are the viable alternative to untextured cutting tools.

Mechano-tribological properties and in vitro bioactivity of biphasic calcium phosphate coating on Ti-6Al-4V

Biphasic calcium phosphate (BCP) consists of hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP). BCP is mainly used in artificial tooth and bone implants due to higher protein adsorption and osteoinductivity compared to HA alone. Although, many studies have been investigated on radio frequency (RF) magnetron sputtering of HA on Ti and its alloy, however, limited studies are available on BCP coating by this process and its bioactivity and adhesion behavior. Thus, in order to obtain a better understanding and applications of BCP films, RF magnetron sputtering is used to deposit BCP films on Ti-6Al-4V in the present study. The effect of film thickness on wettability, mechanical properties and in vitro bioactivity at a particular set of sputtering parameters are investigated. BCP film thickness of 400 nm, 700 nm and 1000 nm are obtained when sputtered for 4 h, 6 h and 8 h, respectively. Although the phase compositions are almost same for all films, the surface roughness values varies around 112-153 nm with rise in film thickness. This in turn enhances hydrophilicity in accordance to Wenzel relation as the contact angle decreases from 89.6 ± 2° to 61.2 ± 2°. It is found that the 1000 nm film possess highest micro-hardness and surface scratch resistance. No cracking of film up to scratch load of 2.3 N and no significant delamination up to load of 7.8 N are observed, indicating very good adhesion between BCP films and Ti-6Al-4V substrate. There is a great improvement in wt% apatite layer formation on all films when dipped in simulated body fluid (SBF) for 14 days. Among these, 1000 nm sputtered film results the highest increase in wt% apatite layer from 44.87% to 86.7%. The apatite layer possess small globular as well as elliptical structure are nucleated and grew on all the BCP films. Thus, sputtering of BCP films improves wettability, mechanical properties as well as bioactivity of Ti-6Al-4V, which can be applied for orthopedic implants.

Simulation and experimental investigations into abrasive flow nanofinishing of surgical stainless steel tubes

ABSTRACT Surface roughness is one of the critical properties that affect the performance of biomedical devices and human implants functions. Higher surface roughness leads to the comparatively higher probability of body fluid retention in the surface valleys. Surface roughness peaks can easily obstruct the flow of body fluid and drug. Abrasive flow finishing (AFF) is an advanced finishing process, which can produce nano-level surface finish in complex components. In this paper, experimental investigations, including parametric study on nanofinishing of surgical stainless steel 316L tubes using AFF process has been reported. Indigenous multiple polymers blended base medium was developed to perform the nanofinishing experiments. Based on the experimental results, statistical model has been presented. To understand the AFF process in depth, finite element approach has been implemented to determine the finishing forces generated during the AFF experiments. Initial surface roughness on the internal surface of the workpiece varies in the range of (0.67–0.50) µm. The best surface finish of 48 nm with a percent improvement (% ΔRa) of 92.20% has been achieved after processing the workpiece with AFF process. Simulated results are validated with the experimental results and the deviations are in the acceptable range.

Experimental investigations of nanosecond-pulsed Nd:YAG laser beam micromachining on 304 stainless steel

Abstract The demand for miniaturized components is increasing day by day as their application varies from industry to industry such as biomedical, micro-electro-mechanical system and aerospace. In the present research work, high-quality micro-channels are fabricated on 304 stainless steel by laser beam micromachining process with nanosecond Nd:YAG laser. The laser pulse energy (LPE), scanning speed (SS) and scanning pass number (SP No.) are used as the process parameters, whereas the depth and width of the kerf as well as the surface roughness are used to characterize the micro-channels. It is found that the kerf depth, width and surface roughness decrease with increase in the SS. The kerf depth sharply increases with increase in the SP No. The kerf width is minimum at 30 mJ LPE, 400 µm s‒1 SS and 10 SP No. The minimum surface roughness is observed at 30 mJ LPE, 500 µm s‒1 SS and 10 SP No. The oxygen content is found to gradually decrease with the distance from the centre of the micro-channel. Based on the experimental results, optimized input parameters can be offered to control the micro-channel dimensions and improve their surface finish effectively on stainless steel.

Sustainable Cutting Fluids: Thermal, Rheological, Biodegradation, Anti-Corrosion, Storage Stability Studies and its Machining Performance

The demand for energy is increasing day by day due to ever-going development, modernization and industrialization. The energy consumption by world is estimated to increase by 33.5% from 2010 to 2030 (Saidur et al., 2011). Fossil fuels are one of the most commonly used sources of energy. In general, fossil fuels are used in the form of fuel and lubricant to fulfil worlds soaring energy demand. Survey estimation says that 30–40 million tons of lubricants are used every year. Out of these, 20 million tons come back to the environment after usage (Mang and Dresel, 2017). Most of these lubricants (over 95%) that end up in the environment are based on petroleum products (Schneider, 2006). Petroleum-based cutting fluids are subdivided into two categories; straight oils and neat oils. Both consists performance enhancer additives to improve its various properties. Additives such as fatty material, free sulphur, chlorinated paraffin, sulphurized oils and phosphorus compounds are present in petroleum-based cutting fluids (Dixit et al., 2012). At higher temperature these additives react with work material and form metal chloride, phosphates as well as sulphides, which are hazardous and harmful to the environment (Trent, 2000; Gajrani and Sankar, 2017a). In long run, inappropriate disposal of used petroleumbased cutting fluids can cause serious damage to environment. Moreover, prolong exposure to emissions of the cutting fluids causes several types of cancers as well as respiratory diseases (Sankar and Gajrani, 2017). Also, petroleum-based lubricants are nonrenewable. A global concern has aroused due to environmental hazard and gradual depletion of petroleum source. Nowadays to minimize these concerns, several alternative measures such as development of environment friendly cutting fluids and green energy systems are focused (Nagendramma and Kaul, 2012; Bart et al,., 2013; Somashekaraiah et al., 2016). Therefore, bio-based cutting fluids or bio-cutting fluids (BCF) are derived using bio-based raw materials such as animal fats, vegetable oils, unsaturated acids, etc., (Salimon et al., 2010). From recent past, BCF production is growing with agricultural advancement. As per the estimation of United States Department of Agriculture (USDA), 185.72 million metric tons vegetable oil will be produce in 2016/17 (USDA, 2016). Most BCF have almost similar molecular structure. They mainly consist of triglycerides. Triglycerides have number of long unsaturated fatty acids chains (Fox and Stachowiak, 2007; Mongkolwongrojn and Arunmetta, 2002), which are renewable and readily biodegradable. In addition, BCF have high viscosity index and high flash point than that of petroleumbased mineral oils (MO) (Soni and Agarwal, 2014). High viscosity index of BCF ensures better stable lubricity, which means with the increase in temperature viscosity of BCF drops slowly as compared to petroleum based MO (Woods, 2005). Also, high flash point of BCF reduces possibilities of fire hazard and smoke formation. Moreover, BCF have higher boiling point and heavier molecular weight that reduces vaporization and mist formation (Khan and Dhar, 2006). Further, BCF is capable of reducing friction and wear between two mating surfaces. It is due to ability of polar and long carbon unsaturated acid chain to strongly interacting with intermetallic surface. Apart from above mentioned characteristics, BCF is sustainable, biodegradable and highly renewable source. Therefore, BCF can be a viable alternative to petroleum-based cutting fluids. Fig. 1 illustrates life cycle of renewable resources based products (Willing, 2001). In spite of numerous merits, usage of BCF is still limited today. It is due to major issues regarding their cost and performance. However, most of the researchers have used BCF with minimum quantity lubrication (MQL) also known as minimum quantity cutting fluid (MQCF) technique to reduce cost by minimizing its consumption (Boswell et al., 2017; Khandekar et al., 2012; Heinemann et al., 2006). As per the performance is concern, these insufficiencies can be improved by the addition of proper additives and chemical modifications. These additives and modification changes the properties of BCF. With proper knowledge, BCF properties can be altered and controlled in a desired way. Therefore, it is necessary to investigate various properties of BCF. Furthermore, constant activities among government organizations, environmental agencies and manufacturer will results in development of procedures for the implementation of bio-technologies that can benefit ecological, social and economic aspects. In long run, there hard work can lead in sustainable environmental management and assessment (Walters, 1986). In this study, physical properties of BCF are characterized. Also, thermal, rheological, apparent activation energy, biodegradable potential, anti-corrosion and storage stability characteristics of BCF are investigated. For comparison, similar studies are also conducted with MO. Afterwards, machining experiments using minimum quantity cutting fluids (MQCF) technique are carried out to examine the relative machining performance of both cutting fluids in terms of cutting force, feed force, coefficient of friction and surface roughness.

Sustainable Machining With Self-Lubricating Coated Mechanical Micro-Textured Cutting Tools

Main purposes of cutting fluids are to cool and lubricate machining region as well as to flush away the chips produced. Cutting fluids have various merits over dry machining. During machining, use of cutting fluids improves machined surface finish and reduces cutting tool wear. In general, cutting fluids also have anti-corrosion properties, which protect machined surfaces from corrosion. Cutting fluids also save power consumption by reducing the machining forces. In few applications, the associated costs of cutting fluids are higher than tool related costs (Astakhov, 2008). However, apart from merits, cutting fluid also possess various detrimental effects on the environment and health hazard to the operators (Gajrani and Sankar, 2017a). Cutting fluid associated diseases to operators are mainly caused due to direct contact or inhalation of its fumes, which produces during machining. Dermatitis, skin irritation, folliculitis and allergic reaction are caused due to direct contact of cutting fluids. However, hypersensitivity pneumonitis, bronchitis and asthma are few examples of diseases caused due to inhalation of cutting fluids fumes (Sankar and Gajrani, 2017). Most of the chemicals present in petroleum-based cutting fluids are suspected carcinogens (Dixit et al., 2012). Moreover, due to prolonged exposure to cutting fluids; machine and materials are also affected. For example, water-based cutting fluid emulsions cause corrosion and stains on machined surface. Disposal of cutting fluids after its usage is a major concern. In general, waste cutting fluids are dumbed either in water bodies or landfill. Thus, it can pollute groundwater, surface water as well as can cause soil contamination, which ultimately affects agriculture and contaminate food (Dixit et al., 2012). Therefore, use of cutting fluids need to be minimized or eliminated. Few researchers have reduced amount of cutting fluid usage by adopting minimum quantity cutting fluids (MQCF) (Gajrani et al., 2017a). In MQCF, a combination of pressurized air is mixed with cutting fluids to form a mist, which is directly injected at the tool-chip interface to reduce heat and to lubricate sliding interface (Gajrani et al., 2017b). However, due to mist nature of MQCF mixture, cutting fluid mix with atmospheric air and easily inhaled by operators working in its vicinity, which may lead to indirect diseases caused by cutting fluids. Thus, it is recommended to totally avoid usage of cutting fluids. Keeping in mind the safety of environment and operators, one of the viable solutions is dry machining (Sreejith and Ngoi, 2000). Dry machining has several merits such as safety of operators and environments as well as no issue of cutting fluid disposal. However, alternatives to the function of cutting fluids need to explore to reduce heat from machining region and to lubricate toolchip interface. Researchers have tried various different methods to reduce heat from machining zone such as the use of heat pipe (Jen et al., 2002), internal cooling (Sanchez et al., 2011), cryogenic cooling (Yildiz and Nalbant, 2008), thermoelectric refrigeration (Sreejith and Ngoi, 2000). Researchers have also tried to lubricate machining zone during dry machining using various techniques such as trilayer and multilayer hard coating of various substances on the surface of cutting tools (Kustas et al., 1997; Koshy, 2008). One such technique to enhance tribological properties in-between tool-chip interface is to fabricate controlled surface textures on the rake of cutting tools (Gajrani et al., 2016; Gajrani and Sankar, 2017b). Controlled engineered modification of surfaces by fabricating micro to nano patterns using various techniques is known as surface textures. Surface textures have the ability to reduce friction between two sliding pairs due to which it is getting wide attention. Optimized textures can improve various functions of surfaces. Engineered surface textures have the variety of applications in industries such as medical implants, to create hydrophobic surfaces, microfluidics, MEMS components, piston rings, bearings, acoustics, etc., (Coblas et al., 2015). Micro-textures can be fabricated using a variety of techniques including both conventional and unconventional methods in varying geometry, shape and size (micrometre to nanometre level). Unconventional texturing methods such as laser (Li et al., 2014), electrical discharge machining (Wenlong et al., 2011), focused ion beam (Kawasegi et al., 2017), etc. have been employed to fabricate micro-textures on the number of various previous studies. In past decade, surface textures are introduced on the tool rake and flank surface to reduce frictional heating at the machining region. Due to the presence of micro-textures, the actual contact length of tool-chip interface reduces, which in turn reduces sliding friction (Jianxin et al., 2009). Another study reported lesser tool-chip contact length up to 30% due to the presence of microtextures (Lei et al., 2009). This also favours lesser workpiece material adhesion on the surface of the cutting tool, which leads to stabilize the built-up edge formation (Kummel et al., 2015). Sugihara and Enomoto (2012) have also reported the reduction in adhesion of aluminium workpiece on the tool surface due to the presence of nano/micro textures. Sharma and Pandey (2016) have filled surface textures using calcium fluoride (CaF2) solid lubricant. Result shows that CaF2 was able to reduce friction heat generation from machining zone. Deng et al. (2013) carried out machining experiment using molybdenum disulphide (MoS2) coated micro-textured cutting tools and it was found that cutting temperature and cutting force was reduced as compared to machining with convention tool. As discussed above, surface textured cutting tools have several benefits; however, in most of the studies, thermal-based texturing techniques have been used to fabricate micro-textures. There are several issues with thermal-based texturing techniques such as the formation of recast layer, formation of heat affected zone, development of thermal stress and formation of cracks (Gajrani et al.,

Nanofinishing of Microslots on Surgical Stainless Steel by Abrasive Flow Finishing Process: Experimentation and Modeling

Miniaturization of components is one of the major demands of the today’s technological advancement. Microslots are one of the widely used microfeature found in various industries such as automobile, aerospace, fuel cells and medical. Surface roughness of the microslots plays critical role in high precision applications such as medical field (e.g., drug eluting stent and microfilters). In this paper, abrasive flow finishing (AFF) process is used for finishing of the microslots (width 450 lm) on surgical stainless steel workpiece that are fabricated by electrical discharge micromachining (EDlM). AFF medium is developed in-house and used for performing microslots finishing experiments. Developed medium not only helps in the removal of hard recast layer from the workpiece surfaces but also provides nano surface roughness. Parametric study of microslots finishing by AFF process is carried out with the help of central composite rotatable design (CCRD) method. The initial surface roughness on the microslots wall is in the range of 3.50 6 0.10 lm. After AFF, the surface roughness is reduced to 192 nm with a 94.56% improvement in the surface roughness. To understand physics of the AFF process, threedimensional (3D) finite element (FE) viscoelastic model of the AFF process is developed. Later, a surface roughness simulation model is also proposed to predict the final surface roughness after the AFF process. Simulated results are in good agreement with the experimental results. [DOI: 10.1115/1.4039295]

Experimental, Theoretical, and Simulation Comparative Study of Nano Surface Roughness Generated During Abrasive Flow Finishing Process

Abrasive flow finishing (AFF) is one of the advanced finishing processes used mainly for finishing of complex surface features. Nano finishing of aluminum alloys is difficult using conventional finishing processes because of its soft nature. So, in this work, aluminum alloys are finished using AFF process. Since the finishing is carried out using polymer rheological abrasive medium (medium), the finishing forces on aluminum alloy workpieces are too low compared to conventional finishing processes. Thus, this process generates nano surface roughness on aluminum alloy. By using the theoretical model, change in surface roughness (DRa) with respect to various AFF input parameters is studied. A new simulation model is proposed in this paper to predict the finishing forces and DRa during AFF process. Modeling of finishing forces generated during the AFF process is carried out using ANSYS POLYFLOW. These forces are used as input in the simulation model to predict DRa. Medium rheology decides the magnitude of the generated finishing forces in AFF process. Therefore, to predict the forces accurately, rheological properties of the medium are measured experimentally and used as input during modeling. Further, to make the simulation more realistic, abrasive particle bluntness with respect to extrusion pressure and number of strokes is considered. Because of considering these realistic conditions, simulation and experimental results are in better agreement compared to theoretical results. [DOI: 10.1115/1.4035417]

SURFACE ALLOYING OF ALUMINUM WITH COPPER USING CO 2 LASER

Aluminium and its alloys have high demand in manufacturing and service industries due to their high specific strength. Addition of different metals like Cu, Mg, Ni, Cr, and Zn provides enhanced service life. In this work, commercially available 99 % pure aluminium was alloyed with copper powder of 10 μm particles size, which was melted by CO2 laser . Three different methods were used for uniform placing of 95 % copper powder and 5 % aluminium powder on the aluminium substrate. The result was examined by Vickers hardness test. SEM and FESEM were used for studying surface and subsurface defects. Defect free aluminium alloy with improved microstructure and enhanced mechanical properties was obtained.