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AISI 4340 steel is a low alloy steel with high tensile strength that has numerous applications in industry. Machinability of this alloy steel has difficulties due to its low heat conduction and high heat concentration in cutting zone. Therefore, use of cutting fluids in machining of this steel is inevitable. On the other hand, environmental problems of using mineral lubricants lead industries into use of biodegradable oils such as Vegetable based cutting fluids. The aim of this study is to investigate the drilling of AISI4340 alloy steel in presence of semi-dry lubricant and using soybean vegetable-based oil. For this purpose, drilling parameters including feed rate and cutting speed at three levels and workpiece hardness at two levels were chosen. Totally 18 experiments were carried out using coated carbide drill. Results revealed that vegetable-based oil can effectively be used in drilling using a semi-dry lubrication method. In addition, feed rate was the most effective parameter on cutting force and surface roughness and by increasing it, the cutting force increased, and the surface quality deteriorated. Also, workpiece hardness showed significant effect on surface roughness.

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AISI4340 hardened steel have a vast functionality in industries. Hard machining of this steel have several benefits such as, higher productivity, lower production cost and improved workpiece properties. In machining operation, ultimate surface roughness is the most important characteristic of machined surface and plays an important role in workpiece life. One of the effective factors on surface integrity is cutting fluid used in machining operation, which have health and environmental problems is spite of positive effects. As a result, using minimum quantity lubrication is considered as an alternative method. In present study, relations between milling parameters and final surface quality in milling of AISI4340 hardened steel, in the presence of lubrication systems including; dry, wet and minimum quantity lubrication have been investigated. Cutting speed, feed rate, axial and radial depth of cut have been considered as main parameters of milling operation. Totally, 90 experiments have been done using response surface method to analyze the effects of process parameters on surface roughness. Results revealed that feed rate and cutting speed have the most Influences on surface roughness. Also higher values of cutting speed and lower values of feed rate are necessary to reduce surface roughness. In addition, compared to other lubrication methods, minimum quantity lubrication have the best performance in surface quality, especially in high cutting speed and depth of cut.

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The productivity of a part is assessed based on factors such as dimensional and geometrical tolerances. In fact, tolerance features are the most important factors in shop drawing of an industrial part. The aim of present study is to empirically investigate the precision of holes created by helical milling method on AISI 4340 alloyed steel. This method refers to create the hole using milling tool, which moves along a helical path. By using helical milling, a high quality hole has been produced and there is no need for boring. Taguchi design of experiment was used to study the effects of process parameters including; cutting speed, feed rate, axial depth of cut and workpiece hardness on dimensional and geometrical tolerances of created hole. In addition, effect of minimum quantity lubrication method with two different oils and dry milling methods was studied. Results showed that the helical milling can be a suitable replacement for conventional drilling. In addition, cutting speed as the main parameter had significant effect on quality improvement of the created hole. On the other hand, in the helical milling, minimum quantity lubrication method using vegetable-based oil showed the best performance compared to mineral oil or dry cutting.

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Helical milling has been known as an innovative method for making high quality holes. In this method, milling tool generates efficiently a high quality hole by moving along a helical path. The hole diameter can be adjusted through the diameter of this helical path. Regarding accuracy of hole in industrial parts, it is necessary to compare this method with conventional hole drilling. Therefore, in this study helical milling and conventional drilling, have been compared with each other. Eight experiments were conducted considering two levels of cutting speed and feed rate on the samples made of AISI 4340 steel at 45 HRC. Minimum quantity lubricant system with two nozzles was used. 100 ml/h of Behran-11 mineral oil at air pressure of 4 bar was employed in this system. Machining forces, surface roughness, nominal diameter, roundness, and cylindricity were output parameters. According to the obtained results, cutting speed was the only one with positive effect on all qualitative parameters of the machined holes. On the other hand, independency of cutting parameters, helical milling lessened machining forces, surface roughness, and geometrical tolerances in compare with conventional drilling.

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Superhydrophobic surfaces have gained significant attention as a promising approach for drag reduction of submerged objects. Accurate evaluation and prediction of drag reduction induced by these surfaces require expensive experimental measurements, numerical simulations, or the development of reliable models and correlations. In this paper, a model is proposed for calculating the skin friction coefficient and drag reduction of superhydrophobic flat surfaces. Utilizing previous data on the skin friction coefficient of flat surfaces under no-slip boundary conditions, a model is developed to estimate the skin friction reduction and skin friction coefficient of these surfaces after applying superhydrophobic coatings. The validity of the model is verified by comparing its results with those of computational fluid dynamics (CFD) simulations of flow over a flat plate at different velocities. The results of the model and simulations indicate that for inlet velocities of 1, 5, and 25 m/s and a slip length of 50 μm, drag reductions of 15%, 41%, and 77%, respectively, are expected. Additionally, the skin friction reduction increases with increasing flow Reynolds number. The developed model is validated for flat surfaces and its ability to accurately estimate the skin friction coefficient and drag force of these surfaces is thoroughly examined. However, further investigations are required to assess the model's validity for curved surfaces and variable slip lengths.