Influence of chip serration frequency on chatter formation during end milling of Ti6Al4V

This paper includes the findings of an experimental study on instabilities of the chip formation process during end milling of Ti6Al4V alloy and the influence of these instabilities on chatter formation. It has been identified that the chip formation process has a discrete nature, associated with the periodic shearing process during machining. The chip formed during machining of titanium alloy Ti6Al4V is found to be mainly with primary serrated teeth appearing in the main body of the chip. Secondary serrated teeth resulting from the coagulation of a certain number of primary serrated teeth also happen to appear at the free or constrained edge of the chip, especially when the system enters into chatter. In order to identify the interaction of these chip instabilities with the prominent natural vibration of the machine tools system components, the different mode frequencies of the vibrating components of the system have been identified using experimental and finite element modal analyses, and vibration responses during actual cutting have also been recorded using an online vibration monitoring system. The vibration signals in frequency domain (fast Fourier transform) have been analyzed to identify the chatter frequencies and the peak amplitude values. Chatter was found to occur at two dominant mode frequencies of the spindle. These mode frequencies at which chatter occurred have been compared with the chip serration frequencies in a wide cutting speed range for different conditions of cutting. It has been concluded from these findings that chatter occurs during end milling due to the resonance of the machine tools system component when the frequency of primary serrated teeth formation is approximately equal to the "prominent natural frequency" modes of the system components, which are the two mode frequencies of the VMC machine spindle in this particular case

Probiotics as Alternative Therapy for Psychometric Disorders in Hepatic Encephalopathy

Aim: To identify whether probiotics have the same effectiveness as lactulose in improving the results of psychometric testing in patients with hepatic encephalopathy.Method: Literature Searching were performed on Pubmed, EBSCOhost, Scopus, and Cochrane databases to obtain an randomized controlled trial (RCT) or a systematic review. Searches were made with the keywords "hepatic encephalopathy", "probiotic", "lactulose" and number connection test  ("NCT").  Search is continued by excluding the literature through abstract and full text.Results: Two studies were found to be relevant according to the criteria. The study by Mittal showed that probiotics were better than lactulose in improving NCT-B with a risk ratio (RR) of 0.88 (95% CI: 0.54-1.44; p = 0.62) but not better for improving NCT- A with RR 1.43 (95% CI: 0.62-3.24; p = 0.40). In the Sharma study, lactulose was better in improving NCT score with the mean difference (MD) 6.7 (95% CI: 0.58-12.82) and in the Li study, there was no significant significance between MD 3.93 (95% CI: -0,72-8,58)Conclusion: In conclusion, Probiotics cannot replace lactulose as a standard therapy for hepatic encephalopathy. There is not enough evidence that proves probiotics are better than lactulose

Response surface methodological approach for the prediction of tangential cutting forces in end milling of stainless steel

The present paper discusses a response surface methodological approach for the prediction of tangential cutting force produced in end-milling operation of Stainless steel (SS304). It is difficult to predict accurately the cutting forces encountered in end milling operations due to large number of independent variables involved. In this work, an approach was undertaken to develop mathematical model based on RSM design for predicting the average tangential cutting force in end milling of SS304 in terms of cutting parameters cutting speed, feed rate, and axial depth of cut. All the individual cutting parameters affect on cutting force as well as their interaction are also investigated in this study. The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated. The adequacy of the predictive model was verified using ANOVA at 95% confidence level. This paper presents an approach to predict cutting force model in end milling of stainless steel using coated TiN insert under dry conditions and full immersion cutting

PCD inserts in end milling of Aluminum Silicon Carbide (AlSiC)

Metal matrix composites (MMC) falls under the category of potential engineering materials applicable to the automotive and aerospace industries. This is become their excellent properties, such as the capability to resist elevated temperature, improved strength, higher stiffness, low density, improved wears and creep resistance and higher elastic modulus. Among these materials aluminum alloys reinforced with silicon carbide found most attentions [1]. AlSiC is preferred over ceramics materials because of their higher combination of properties such as high strength, ductility and high temperature resistance, compared to ceramics [2]. Li et al [3] found that aluminum alloys reinforced with silicon carbide particles are almost three times more efficient than the un-reinforced aluminum alloys in destroying tungsten projectiles at 1.2 km/sec. AlSiC has been considered for use in automobile brake discs and various components in internal combustion engines. Aluminum silicon carbide (AlSiC) is also being widely used in the electronic packaging industries. Though the properties of this new engineering material are quite attractive, the machinability of AlSiC is very poor. Poor machinability is associated with abrasive wear, which make it a class of difficult-tomachine advanced materials [4]. The hardness in the range the silicon carbide phase is comparable with that of tungsten carbide (WC), and is mainly responsible for the high abrasive wear of the tool. Consequently the cutting edge of the tool which in course due to abrasion wear results in the formation of poor surface finish during turning [5]

Artificial neural network chip serration frequency model in end milling of medium carbon steel

In this research, an Artificial Neural Network (ANN) model was developed for the investigation and prediction of the relationship between cutting parameters and chip serration frequency during high speed end milling of medium carbon steel (S45C). The input parameters of the ANN model are the cutting parameters: cutting speed, feed and axial depth of cut. The output parameter of the model was chip serration frequency. For this interpretation, advantages of statistical experimental design technique, experimental measurements, artificial neural network were exploited in an integrated manner. Cutting experiments are designed based on statistical central composite design experimental design technique. A predictive model for chip serration frequency was created using a feed-forward back-propagation neural network exploiting experimental data. The network was trained with pairs of inputs/outputs datasets generated, when end milling steel with TiN coated carbide inserts. A very good predicting performance of the neural network, in terms of concurrence with experimental data was attained. The model can be used for the analysis and prediction for the complex relationship between cutting conditions and the chip serration frequency in metal-cutting operation

Investigations of the causes of chatter in computer aided manufacturing process during end milling operation

Chatter is an unwanted but sometimes unavoidable phenomenon in computer aided machining. The term defines the self-excited violent relative dynamic motion between the cutting tool and workpiece. Experimental investigations have been conducted on the chips and common types of discreteness in the form of serrated saw teeth have been identified. It has been identified that the chip formation process has a discrete nature, associated with the periodic shearing process of the chip during machining of Ti6Al4V. Apart from the primary serrated teeth, a typical instability of periodic nature, in the form of secondary saw/serrated teeth, which appear at the free edge of the chip, has been identified. Mechanism of formation of these teeth has been studied and the frequency of their formation has been determined. The different modes of the vibrating components have been extracted by modal analysis and the vibration responses during cutting conditions have also been recorded using an online monitoring data acquisition system. The most vibrating components during computer aided milling machine operation have been identified. It has been found that chatter appears in the system as a resonance during cutting when the chip serration frequency is equal or any integer multiple of the prominent natural frequency of the system components like spindle, tool holder

Enhanced combined assimilative and bound phosphorus uptake in concurrence with nitrate removal in pre-anoxic cyclic sequencing batch reactor

Needless to specify, controlling nitrogen and phosphorus discharge from wastewater treatment plants is synonymous with the prevention of eutrophication of surface waters, as one of the major issues related to water security. The present study investigates the performance of a pre-anoxic sequencing batch reactor (SBR) working on the basis of intermittent aeration, operated at varied carbon (bCOD) to nitrogen (C/N) ratio of 3, 7.5, and 10, and readily biodegradable (rbCOD) to slowly biodegradable (sbCOD) ratio of 0.1, 0.25, and 0.5. The findings revealed that an enhanced nitrogen removal was observed, together with higher C/N and rbCOD to sbCOD ratios. The results also show a consistent increase in total phosphorus removal with an increase in nitrogen removal. The phosphorus uptake of sludge varied from 0.02 – 0.045 mgP/mgVSS (avg. 0.031 ± 0.004), which resulted in enrichment levels of 0.88 – 1.68 times the stoichiometric value of 0.0267 mgP/mgVSS (avg. 1.45 ± 0.14). On an average basis, the assimilative total phosphate (TP) content was increased by 0.008 gTP/gNO -/3 -N removal rate. The excess phosphorus removal was due to the formation of poorly soluble polyvalent phosphate compounds, which was found based on dry analysis, which persisted as bound phosphate in the sludge

Global wealth disparities drive adherence to COVID-safe pathways in head and neck cancer surgery

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