Search

Inconel 718 is widely used in many applications specifically in the aerospace and nuclear industry due to its superior properties in strength, hot hardness, and thermal and corrosion resistance. However, it is classified as difficult-to-cut material due to its extreme hardness that led to high cutting forces and temperature which further worsened by its strain hardening effect. Thus, it is crucial to analyze the different types of wear mechanisms and failure modes, to analyze causes, and also to understand how cutting parameters affect the wear mechanisms and failure modes. The study is conducted with PVD TiAlN-NbN coated inserts with varying cutting speeds (40, 60, and 80 m/min) and varying feed/tooth (0.7, 0.1, and 0.13 mm/tooth) under the wet condition of face milling. The flank wear progression and length of cut were measured and recorded to study the tool life against length of cut. The tool wear and failure modes of inserts were observed under the optical microscope and SEM/EDX. Results showed that cutting speed has a major effect on the tool failure as compared to feed/tooth. At low speed, the dominant tool failures were macro-chipping due to the severe BUE (built-up edge)/BUL (built-up layers) formation. At higher speeds, the dominant tool failures were flaking and notching which led to the sudden tool breakage. At low feed/tooth, the dominant failures were flaking and macro-chipping, but notching and tool breakage became dominant at higher feed/tooth. Moreover, it is found that the main wear mechanisms which contributed to the tool failures were adhesion, abrasion, thermal and mechanical cracks, diffusion and oxidation wear.

Optimization of flank wear width (VB) progression during face milling of Inconel 718 is challenging due to the synergistic effect of cutting parameters on the complex wear mechanisms and failure modes. The lack of quantitative understanding between VB and the cutting conditions limits the development of the tool life extension. In this study, a Gaussian kernel ridge regression was employed to develop the VB progression model for face milling of Inconel 718 using multi-layer physical vapor deposition-TiAlN/NbN coated carbide inserts with the input feature of cutting speed, feed rate, axial depth of cut, and cutting length. The model showed a root-mean-square error of 30.9 (49.7) µm and R2 of 0.93 (0.81) in full fit (5-fold cross-validation test). The statistics along with the cross-plot analyses suggested that the model had a high predictive ability. A new promising condition at the cutting speed of 40 m/min, feed rate of 0.08 mm/tooth, and axial depth of cut of 0.9 mm was designed and experimentally validated. The measured and predicted VB agreed well with each other. This model is thus applicable for VB prediction and optimization in the real face milling operation of Inconel 718.

Owning to the extremely abrasive silicon particles, low melting point of aluminum, and its susceptibility to adhere to the tool, high-speed drilling of aluminum alloys containing high silicon content becomes a challenging operation. Hence, the understanding of the tool wear mechanisms is essential in order to develop and select the efficient tool material. This paper reports on the investigation of performance and wear mechanism of uncoated and TiAlN and AlTiN-coated tools when high-speed drilling of Al-Si (A383) alloy. Drilling tests were conducted at various cutting parameters, while thrust forces were measured using a dynamometer. The wear mechanisms that contributed to the drill failure were assessed by analyzing the worn cutting edge and drill bit cross section; and by employing scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Results showed that feed rate has the highest effect on the primary wear stage; and flank wear at the outer cutting edge found to be dominant failure mode for all tools. Moreover, it is found that plastic deformation, diffusion, attrition, abrasion, and fracture are the main operating tool wear mechanisms. The longest tool life was recorded for AlTiN-coated tool, but more adhesion of Al was observed on this tool surface. At the end, TiAlN-coated drill was proposed as the tool with the best performance among the tool materials used in this study.

Load distribution has been studied extensively for ISO thread, but the load distribution on power screw threads, specifically ACME and Square threads, has not been studied yet. In this article, axisymmetric two-dimensional and three-dimensional Finite Element Analysis have been conducted on bolts with different sizes and thread geometries to examine the effect of the thread geometry on the load distribution. The thread geometries were studied with ISO, ACME, and Square threads attention. The sizes used are from the ISO coarse series. In order to investigate on the effect of bolt thread geometry, several simulations have been performed. The two-dimensional simulation results have shown reliable performance in determining the load distribution behaviour when the thread geometry is modified. Moreover, the results agreed with the three-dimensional simulation outcomes regarding the load distribution behaviour when the size is varied.

The curvature correction factor is an important parameter in the stress calculation formulation of a helical extension spring, which describes the effect of spring wire curvature on the stress increase towards its inner radius. In this study, the parameters affecting the curvature correction factor were investigated through theoretical and numerical methods. Several finite element (FE) models of an extension spring were generated to obtain the distribution of the tensile stress in the spring. In this investigation, the hook orientation and the number of coils of the extension spring showed significant effects on the curvature correction factor. These parameters were not considered in the theoretical model for the calculation of the curvature correction factor, causing a deviation between the results of the FE model and the theoretical approach. A set of equations is proposed for the curvature correction factor, which relates both the spring index and the number of coils. These equations can be applied directly to the design of extension springs with a higher safety factor.

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.

Control of continuous chips in turning operation is a very vital issue to enhance productivity and operator safety. A famous method to control the chip size is utilization of chip breaker. In this study, the influence of different aspects of chip breaker geometry on cutting force, chip shape, and bending moment was evaluated by using finite element and experimental approaches. Therefore, cutting tests were carried out on AISI 1045 steel using tungsten carbide inserts with various chip breaker geometries. The results indicated that the predicted cutting force and chip shape are in close agreement with the experimental ones. It is also observed that the bending moment generated by the upper level of breadth surface has the highest contribution in the development of combined and nonuniform state of stress at the root and body of deformed chip. Meanwhile, the chip breaker geometry had a significant effect on the cutting force value.

Chip formation during drilling operation is greatly influenced by the cutting parameters such as cutting speed, feed rate, and drill geometry. However, not many studies have focused on the direct observation of the chip formation during high speed drilling. This paper investigates the effect of cutting speed and feed rate on the chip morphology during high speed drilling of aluminum–silicon alloys using carbide drill. Observation on the multiview characterization of the chips was carried out which includes free surface, back surface, and cross-section of top surface. Structure and shape alterations of the free and back surfaces were analyzed using a scanning electron microscope. Finally, different geometrical parameters of chip cross-section were measured in order to study the effect of cutting parameters on chip compression ratio and thrust force. It was found that increase in cutting speed significantly affects the chip morphology especially on the structure of free surface and cross-section of the chips. Results also showed that built-up edge on the rake face of tool played an important role on the formation of irregular pattern on the chip back surface.

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.