MECHANISM OF CHIP FORMATION IN HIGH-SPEED TURNING OF INCONEL 718

The mechanism of serrated chip formation during high-speed turning of Inconel 718 using PCBN cutting tools has been investigated with the aid of scanning electron microscopy and optical microscopy. A conceptual model of chip formation has been developed knowing the chip morphology. It is followed by the analysis of chip segmentation frequency and the chip forms. Further, the chip segment forms and geometry were quantitatively characterized as a function of machining parameters and the cutting edge geometry using statistical methods. The chip morphology has been correlated with the cutting forces, specific shearing energy and the resultant roughness of the machined surfaces

Experimental Investigation into the Effect of Ball End Milling Parameters on Surface Integrity of Inconel 718

In machining of Inconel 718, various difficulties such as increased tool wear and poor machined surface quality are frequently encountered due to its high temperature strength and poor thermal properties. This work considers the effect of number of passes and the machining environment on the machined surface quality in ball end milling of Inconel 718, which hitherto has not been adequately understood. To this effect, extensive experimentation has been carried out to analyze machined surface quality and integrity in terms of surface roughness, surface damage, and microhardness variation in the machined surfaces. The machined surfaces show formation of distinct bands as a function of instantaneous machining parameters along the periphery of cutting tool edge. A distinct variation is also observed in the measured values of surface roughness and microhardness in these regions. The minimum surface roughness is obtained in the stable cutting zone and it increases toward the periphery of the cutter on band #2 and band #3. Microhardness of depth beneath the machined surface shows that the machining affected zone varies from 60 to 100 A mu m in ball end milling under various machining conditions

Effect of machining parameters and cutting edge geometry on surface integrity of high-speed turned Inconel 718

Stringent control on the quality of machined surface and sub-surface during high-speed machining of Inconel 718 is necessary so as to achieve components with greater reliability and longevity. This paper extends the present trend prevailing in the literature on surface integrity analysis of superalloys by performing a comprehensive investigation to analyze the nature of deformation beneath the machined surface and arrive at the thickness of machining affected zone (MAZ). The residual stress analysis, microhardness measurements and degree of work hardening in the machined sub-surfaces were used as criteria to obtain the optimum machining conditions that give machined surfaces with high integrity. It is observed that the highest cutting speed, the lowest feedrate, and the moderate depth of cut coupled with the use of honed cutting edge can ensure induction of compressive residual stresses in the machined surfaces, which in turn were found to be free of smeared areas and adhered chip particles. (C) 200

An analytical model to predict specific shear energy in high-speed turning of Inconel 718

Machining of Inconel 718 at higher cutting speeds is expected to provide some relief from the machining difficulties. Therefore, to understand the material behavior at higher cutting speeds, this paper presents an analytical model that predicts specific shearing energy of the work material in shear zone. It considers formation of shear bands that occur at higher cutting speeds during machining, along with the elaborate evaluation of the effect of strain, strain rate, and temperature dependence of the shear flow stress using Johnson-Cook equation. The model also considers the 'size-effect' in machining in terms of occurrence of 'ploughing forces' during machining. The theoretical results show that the shear band spacing in chip formation increases linearly with an increase in the feedrate and is of the order of 0.2-0.9 mm depending upon the processing conditions. The model shows excellent agreement with the experimental values with an error between 0.5% and 7% for various parametric conditions. (C) 200

Spinal anesthesia with an indwelling catheter reduces the stress response in pedaiatric open heart surgery

BACKGROUND: Extreme stress and inflammatory responses to open heart surgery are associated with increased morbidity and mortality. Based on both animal and adult human data, it was hypothesized that spinal anesthesia would be more effective at attenuating these responses than conventional high dose intravenous opioid techniques in infants and young children undergoing open heart surgery. METHODS: A prospective randomized controlled clinical trial was performed in 60 children aged up to 24 months undergoing open heart surgery. Patients were randomly assigned to receive either high-dose intravenous opioid or high-dose intravenous opioid plus spinal anesthesia. Spinal anesthesia was administered via an indwelling intrathecal catheter. RESULTS: Spinal anesthesia significantly reduced the stress responses as measured by plasma norepinephrine and epinephrine concentrations (both P < 0.05). Spinal anesthesia reduced plasma lactate concentrations (P < 0.05), but increased fluid requirements during the first postoperative day (P < 0.05). There were no differences in other cardiovascular parameters. CONCLUSIONS: Continuous spinal anesthesia reduces stress responses in infants and young children undergoing cardiac surgery with cardiopulmonary bypass more effectively than high-dose intravenous opioids alone

Enhancement of surface integrity in cryogenic high speed ball nose end milling process of inconel 718

Surface integrity of machined subsurface in any machining process has become an important aspect because of increased quality demands especially in high accuracy demand industries like aerospace, automotive, defense and medical applications. The attention of these industries is to achieve a good surface roughness, avoid plastically deformed layer and most cases increasing the hardness at the subsurface area for robust application. As is known, Inconel 718 is a difficult-to-machine material and it is often used in the manufacture of turbine gas and jet engines for aerospace applications. In most cases, Inconel 718 machining will be resulting an excessive heat generated at the cutting zone. This can cause in a variety of problems during machining such as rapid tool wear, damage on machined surface and microstructural defects. Hence, various cooling methods have been made to address these problems and improve the quality of machined surface. In this study, a cryogenic cooling technique using nitrogen liquids (LN2) was developed to cool the tool-chip interface during milling Inconel 718. The goal of this paper is to presents a comparison study on surface roughness, machined surface microhardness and subsurface microstructure changes between cryogenic cooling and dry techniques. The experiments conducted using a PVD coated with TiAlN/AlCrN ball nose tungsten carbide for varying cutting speeds ranging between 140–160 m/min, a feed rate of 0.15-0.20 mm/tooth, and radial depth of cut of 0.2-0.4 mm. The results revealed that the cryogenic cooling technique is more effective than dry cutting for improving surface roughness and lessening deformation of microstructure changes underneath the machined surface. However, machining in dry technique has produced a high microhardness for machined surface compared to cryogenic cooling technique. Overall, the utilization of the cryogenic technique has improved the surface roughness to a maximum of 88% and reduced the plastic deformation layer, while dry machining can improve the surface microhardness up to 5%