Fevzi Bedir

Effect of tool coating materials on surface roughness in micromachining of Inconel 718 super alloy

Surface roughness is an important parameter that determines the post-manufacturing product quality. In this study, effect of cutting parameters, coating material and the built-up edge phenomenon on the surface roughness were investigated in micro end milling process of Inconel 718 using a white light interferometer and scanning electron microscopy. A micro end mill with a diameter of 768 µm coated with five separate coating materials (AlTiN, AlCrN, TiAlN + AlCrN, TiAlN + WC/C and diamond-like carbon) was used in this study. According to the results obtained, mean surface roughness values of surfaces machined with a diamond-like carbon-coated and AlTiN-coated cutting tool were lower than for other coatings. However, surface roughness values of surfaces obtained with tools coated with TiAlN + AlCrN and AlCrN were higher. Specifically, the formation of built-up edge causes chips to be smeared on machined surfaces, which has a negative impact on the surface quality. As can be expected, wear occurs faster on uncoated tools. As a result of this, the edge radius may increase excessively, and the mean surface roughness value may decrease. Also in this study, multivariate analysis of variance was carried out and the parameter that was most effective on surface roughness was established.

Fabrication of two-layered Al-B4C composites by conventional hot pressing uuder nitrogen atmosphere and their characterization

In this study, we describe the conventional hot pressing (CHP) of layered Al-B4C composites and their characterization. The matrix alloy A1-5 wt.%Cu was prepared from elemental powder mixtures. The metal and B4C powders were mixed to produce either Al-Cu-10vol.%B4C or Al-Cu-30vol.%B4C combinations. Then, these powder mixtures were stacked as layers in the hot pressing die to form a two-layered composite. Hot pressing was carried out under nitrogen atmosphere to produce 30×40×5 mm specimens. Microstructural features and age hardening characteristics of composites were determined by specimens cut longitudinally. The flexural strength of both layered composites and their monolithic counterparts were investigated via three point bending tests. In the case of layered specimens of both 10vol.%B4C and 30vol.%B4C containing layers were loaded for three-point test. The results show that a homogeneous distribution of B4C particles in the matrix alloy which is free of pores, can be obtained by CHP method. The ageing behavior of the composites was found to be influenced by the reinforced materials, i.e. higher hardness values were reached in 8 hrs for the composites than that for the matrix alloy. Flexural strength test showed that two-layered composites exhibited improved damage tolerance depending on layer arrangement. Microstructural investigation of the fracture surfaces of the bending specimens was performed by means of scanning electron microscope (SEM). While layer with lower reinforcement content exhibited large plastic deformation under loading, the other with higher reinforcement content exhibited less plastic deformation.

Finite element modeling of micro-milling: Numerical simulation and experimental validation

ABSTRACT In this study, micro-milling of Inconel 718 was investigated. For this purpose, cutting tests were conducted by using uncoated tools and taking four different feed rates (1.25, 2.5, 3.75, and 5 µm/flute) and a constant cutting velocity (48 m/min) into account. In numerical modeling, thermomechanical behavior was modeled using the modified Johnson–Cook material model. Analyses were also conducted for different cutting tool edge angles (+8°, 0, and −8°). In the numerical analyses, cutting force, tool stress, and cutting temperature values were estimated depending on tool rotation and cutting tool edge type and compared with experimental results. When the results obtained from the study are considered, it is seen that the experimental cutting force and temperature values are in harmony with the numerical results. Moreover, it is seen that there is an increase in cutting force, cutting temperature, and stress values depending on the feed rate. In addition, in the numerical analyses for different cutting tool edge geometries it was observed that cutting force temperature and tool stress values varied depending on the edge geometries.

The effect of minimum quantity lubrication and cryogenic pre-cooling on cutting performance in the micro milling of Inconel 718

In this study, the effects of different cutting conditions on the cutting performance were investigated in the micro milling of Inconel 718. In this context, dry cutting, minimum quantity lubrication and cryogenic pre-cooling were considered as the cutting conditions. Tool wear, surface roughness and burr formation were determined as performance criteria in the cutting processes carried out using an AlCrN-coated tool. At the end of the study, cryogenic pre-cooling led to increased tool wear. In contrast, a significant reduction in surface roughness as well as burr formation was observed in the cutting process with cryogenic pre-cooling. However, the minimum quantity lubrication process increased tool life, but it was not seen as the clear effect for decreasing surface roughness and burr formation.

Safety Rules and Measures to Be Taken Where Hydrogen Gas Is Stored

Hydrogen is much safer than other energy sources. Hydrogen is nontoxic, not easily flammable and the products of oxygen water released during energy production are harmless to the natural environment. For pressurized tanks, the higher the pressure of the gas is, the smaller the tank volume needed, and the higher the operating cost. Safety regulations on high-pressure gas storage (including the compression process), utility, and transportation are strict, and complying with the regulations costs more than the hydrogen generators and storage equipment. Cryogenically cooling hydrogen into a liquid state is a well-established technology and considered the comparative benchmark for storing hydrogen. But the technology requires substantial energy to liquify the hydrogen, including continual “boil off” of hydrogen during storage and it requires very costly storage tanks and handling. Chemical or physically combined storage of hydrogen in other materials has potential advantages over other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. Metal-hydride–based chemical hydride and rechargeable hydride technologies offer storage efficiency and storage safety while providing the cost-saving advantage of being able to use the existing fossil fuel infrastructure to deliver and store a pumpable and nonexplosive hydride slurry as future hydrogen fuels. In this study we compare hydrogen storage methods, and show their advantages and disadvantages.