Ali Akhavan Farid

Analysis of the influence of memory content of auditory stimuli on the memory content of EEG signal

One of the major challenges in brain research is to relate the structural features of the auditory stimulus to structural features of Electroencephalogram (EEG) signal. Memory content is an important feature of EEG signal and accordingly the brain. On the other hand, the memory content can also be considered in case of stimulus. Beside all works done on analysis of the effect of stimuli on human EEG and brain memory, no work discussed about the stimulus memory and also the relationship that may exist between the memory content of stimulus and the memory content of EEG signal. For this purpose we consider the Hurst exponent as the measure of memory. This study reveals the plasticity of human EEG signals in relation to the auditory stimuli. For the first time we demonstrated that the memory content of an EEG signal shifts towards the memory content of the auditory stimulus used. The results of this analysis showed that an auditory stimulus with higher memory content causes a larger increment in the memory content of an EEG signal. For the verification of this result, we benefit from approximate entropy as indicator of time series randomness. The capability, observed in this research, can be further investigated in relation to human memory.

Performance evaluation of carbide tools in drilling CFRP-Al stacks:

Composite-metal stack is an ideal combination of materials which unites the advantages of each dissimilar material in a substantial weight. However, drilling dissimilar materials has been a challenge since the composite-metal stacks are at demand in industries. It is important to choose the appropriate drill geometry regarding the stacking sequence and utilize proper machining parameters in order to achieve damage free and precession holes. This experimental study was conducted on dry drilling of CFRP/Al2024/CFRP (carbon fiber-reinforced plastic). Four types of twist drills with various geometries, both coated and uncoated, were utilized to study the effect of machining parameters on hole quality. It was observed that increasing feed rate entails an increase in entrance delamination, whereas exit delaminations and fiber fraying at 2nd CFRP exit diminished with increasing feed rate. It was also found that four facet tools performed better than two facet tools in terms of fiber delamination. Most accurate hole was attained on 2nd CFRP; however, it was found that increasing feed significantly affects the hole size on 1st CFRP.

A new hybrid model based on the radius ratio for prediction of effective cutting limit of chip breakers

Determination of accurate limit of cutting condition in order to obtain broken chips for various chip breaker geometries is essential to improve the machinability. This work presents a hybrid model based on the ratio of broken chip radius to the initial radius of chip to predict the type of chip regarding the characteristics of a chip breaker geometry and cutting parameters. An analytical geometrical model was developed to calculate the initial radius of chip. After running experimental tests for four types of chip breaker geometries and calculation of their chip ratio, type of chips and tool–chip contact were selected as two criteria for classifying chip ratio into three limits representing usable, acceptable, and unacceptable chips. Finally, the normalized data were used to train a neural network model to predict the type of chip which was verified by experiments carried out on a new chip breaker geometry. The trained network could predict the type of chip accurately by providing the geometrical details of the chip breaker and cutting parameters for the network.

Surface integrity study of high-speed drilling of Al–Si alloy using HSS drill

The motivation to replace steel and cast iron with Al–Si alloys for automotive components is part of the attempt to improve fuel economy and reduce emissions. In relation to that, the application of high-speed drilling is considered one of the most-used operations in hole making for automotive parts due to its ability to reduce lead time without sacrificing the hole quality. However, this advantage was offset by the creeping problems encountered during high-speed drilling. Although this issue is addressed accordingly, problems like uncontrollable surface integrity and poor hole quality still exist. Surface integrity studies involved the investigation of surface roughness, metallurgical changes and microhardness of the subsurface of the drilled hole. Significant alternations with respect to the loss of mechanical properties have been observed from the microhardness and microstructure analysis of the drilled hole. Results from this study showed that, in general, drilling parameters have significant effects on the surface quality and integrity of the drilled hole during high-speed drilling of Al–Si using an HSS drill.

Optimal flank wear in turning of Inconel 625 super-alloy using ceramic tool

Rapid tool wear is one of the major machinability aspects of nickel-based super alloys. In this article, the effect of cutting parameters on material removal rate and tool wear of a whisker ceramic insert in turning of Inconel 625 was examined. Optical microscope and scanning electron microscope were applied to measure and study tool wear mechanism. Response surface method was used to develop a mathematical model which confirmed by experimental tests. The statistical analysis done by analysis of variance showed that depth of cut is the most effective factor on the tool wear. Experiments showed that increment of feed rate had an insignificant effect on the progress of flank wear, and it is an important controlling factor when material removal rate is considered as a desired output. Finally, optimized cutting condition is presented in this work.

Characterization of various coatings on wear suppression in turning of Inconel 625: A three-dimensional numerical simulation

Applying cutting tool with longer functioning time is a vital issue in machining of the nickel-based super alloys. However, the experimental analysis of this problem is quite expensive. Thus, three-dimensional numerical simulation of tool wear propagation in turning of Inconel 625 super alloy is taken into account, in this study. The cutting insert with complex geometry is modeled by using a reverse engineering method. Based on the cutting tool and workpiece material, Usui wear rate model is exerted to estimate the tool wear rate. In the first section, characterization of TiAlN-coated carbide tool, which is suggested by catalogue, on wear resistance is evaluated and then simulation results are validated with experiments. As a result, increment of depth of cut is the most effective factor on the generation of temperature and stresses on the tool faces resulting in wear rate acceleration. In the second section, different commercial coatings with multicompositions are applied in the simulation to find the best performance against wear. Finally, TiCN coating outperformed other coatings in turning of Inconel 625.

Statistical Analysis, Modeling and Optimization of Thrust Force and Surface Roughness in High Speed Drilling of Al-Si Alloy

The needs to rapid manufacture of automotive components have led to the extensive uses of high-speed drilling in hole-making operation. However, issues such as uncontrollable thrust force and hole quality need to be addressed effectively in order to have full benefit of high-speed machining. Modeling the effect of drilling parameters on the machining responses can be a useful approach in controlling the thrust force and surface quality of the hole. This article reports on the development of mathematical models for thrust force (Ft) and surface roughness (Ra) during high-speed drilling of Al–Si alloy using uncoated carbide tools. Central composite design coupled with response surface methodology was used to predict the Ft and Ra values in relation to the primary machining variables such as cutting speed and feed rate. Second-order polynomial models were developed for both responses, and the adequacy of models was verified by analysis of variance. Results show the goodness of response surface methodology in the development of mathematical models in explaining the variation of thrust force and surface roughness by relating them to the variations of cutting parameters. In the developed models, linear effects of cutting parameters have the highest contribution to the thrust force model, while their quadratic effects are the significant terms influencing the surface roughness. Consequently, the optimum cutting condition was predicted at the high and low levels of cutting speed and feed rate, respectively.

Effect of Machining Parameters and Cutting Edge Geometry on Surface Integrity when Drilling and Hole Making in Inconel 718

Superalloys such as Inconel 718 have high strength at elevated temperatures, which make them attractive towards various applications in aerospace industry. However, these materials are considered difficult to machine materials. The state of a workpiece surface after machining is definitely affected by cutting parameters, such as cutting speed, feed rates, drill types and drill geometries. Drilling tests, at different spindle-speed, feed rates, drills and point angles of drill, were conducted in order to investigate the effect of the above parameters on the quality of machined holes and surface integrity of Inconel 718. The quality of machined holes was evaluated in terms of the geometrical accuracy and burr formation. Surface integrity involved the aspect of surface roughness, metallurgical alterations and microhardness of the substrate of the hole surface. High hole quality was observed even at holes produced using worn tools, in relation to dimensions, surface roughness and burr height. However, microhardness measurements and microstructural analysis of work-piece showed significant microstructural changes related with a loss of mechanical properties. In general the cutting parameters have significant effects on the surface quality and surface integrity when drilling Inconel 718 using uncoated carbide drill.

Effects of Cutting Condition on Surface Roughness when Turning Untreated and Sb-Treated Al-11%Si Alloys Using PVD Coated Tools

Surface roughness is an important output in different manufacturing processes. Its characteristic affects directly the performance of mechanical components and the fabrication cost. In this current work, an experimental investigation was conducted to determine the effects of various cutting speeds and feed rates on surface roughness in turning the untreated and Sb-treated Al-11%Si alloys. Experimental trials carried out using PVD TIN coated inserts. Experiments accomplished under oblique dry cutting when three different cutting speeds have been used at 70, 130 and 250 m/min with feed rates of 0.05, 0.1 and 0.15 mm/rev, whereas depth of cut kept constant at 0.05 mm. The results showed that Sb-treated Al-11%Si alloys have poor surface roughness in comparison to untreated Al-11%Si alloy. The surface roughness values reduce with cutting speed increment from 70 m/min to 250 m/min. Also, the surface finish deteriorated with increase in feed rate from 0.5 mm/rev to 0.15 mm/rev.

Tool life prediction model of uncoated carbide tool in high speed drilling of Al-Si alloy using response surface methodology

This paper reports on the development of a mathematical model for tool life of uncoated carbide tools during high speed drilling of Al-Si alloys. Central composite design (CCD) of experiment, coupled with response surface methodology (RSM) were used to predict the tool life in relation to the machining variables such as cutting speed and feed rate. The adequacy of the predictive model was verified by analysis of variance (ANOVA). Results show that effect of feed rate on the predicted tool life model was very significant as compared to cutting speed. It was evident that chipping at the outer cutting edge was the dominant failure mode at the highest level of feed rate employed. However, with decreasing feed rate and increasing cutting speed, non-uniform flank wear was observed to be the dominant failure mode of the uncoated carbide tool during high speed drilling of Al-Si alloy.