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Plasma assisted machining (PAM) is a method to improve machinability of hard turning. The process of plasma assisted machining for turning applications utilizes a high-temperature plasma arc to provide a controlled source of localized heat, which softens only that small portion of the work material removed by the cutting tool. The goal of this study is to present a methodology for determination cutting force during plasma enhanced turning of hardened steel AISI 4140. In this regard, a finite differential model was made to estimate the uncut chip temperature under different plasma currents, cutting speeds and feeds during PAM. A mechanistic model developed to estimate cutting force under different PAM conditions by considering shear stresses in the primary, secondary shear zones and force on the tool edge. The proposed model was calibrated with experimental hard turning data, and further validated over practical PAM conditions. Mean errors of predicted values and experimental data is lower than 10 percent. It is shown that PAM can decrease main cutting force in comparison to convectional to 40 percent in turning of hardened steel at high levels of uncut chip temperature due to softening the material.

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One of the new lubrication methods in machining processes is Minimum Quantity Lubrication (MQL). In this method, a very small amount of fluid by compressed air creates a spray and is used as lubricant. One of the advantages of this method compared to conventional (wet) lubrication is the reduction of environmental pollution and undesired effects on operator health. In the present study, the effect of minimum quantity lubrication on surface roughness in hard turning of 100Cr6 bearing steel has been investigated and compared with dry and wet machining methods. To perform MQL, some equipment have been added to the lathe machine. The tool used for material removal of 100cr6 steel is Nano-CBN that is a new generation of CBN tools with Nano technology. All experimental tests performed in dry, wet and MQL conditions. For investigation of surface roughness, each of cutting parameters include cutting speed, feed rate and cutting depth were selected in three different levels and all possible combinations of these parameters has been tested. According to experimental results and analysis of variance, feed rate 68%, lubrication method 14%, cutting speed 4% and cutting depth less than 1% affected on the surface roughness. The obtained results showed that the surface roughness in MQL method has been averagely decreased 42% and 30% in comparison with dry and wet machining, respectively.

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Machining of hard steels has it’s own problems. According to the recent advances in implementing of new cutting tools, the machining of hard steels with operations such as turning and milling is possible and it can replaced with some of grinding operations. Turning of workpieces with 45 HRC or upper hardness, is said hard turning. The aim of this article is the investigation of the effect of workpiece hardness and cutting speed and feed rate parameters on surface roughness in hard turning of cold work tool steel X210Cr12 or SPK in dry condition. For achieving this goal, the workpieces of X210Cr12 steel where hardened with different heat treatments cycles such that their hardnesses lie in the hard turning range. Then the workpieces were machined with different cutting parameters using CBN tool and the resulted surface roughness were compared. Experimental tests designed with full factorial method and totally 36 tests have been done. According to obtained results of experimental tests and analysis of variance, the effect of feed rate and workpiece hardness on surface roughness was 90.4% and 8.3%, respectively. The effect of cutting speed on surface roughness is negligible. Increasing the feed rate results in the upper surface roughness. Increasing the workpieces hardness to 50 HRC, decreases surface roughness and increasing workpieces hardness from 50 to 65 HRC, increased surface roughness.

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The effect of texturing the tool rake surface on the surface quality in hard turning of 1191/1 steel with a surface hardness of 45 HRC was studied in this research. The pattern parameters including, cavity diameter, pitch, and depth, as well as the pattern distance from the main cutting edge were changed in 3 levels, assuming the cutting tool with regular cavity texture. Nine tests were designed using the Taguchi DOE and conducted in dry and lubricated conditions with 2 repeats. Machining forces during the tests and surface roughness of the machined workpieces were measured in machining under lubricated and dry conditions. The results showed that in turning with a textured tool under lubrication, changing the parameters of the texture pitch and the distance from the cutting edge increased the surface roughness of the workpiece by 57.6% and 39.2%, respectively. This is while the increase in the diameter of the tissue cavity, due to the reduction of the contact area in the tool-chips interface and better lubrication near the cutting region, improved the surface roughness up to 40.7%. The cavities depth of also did not have a significant effect on improving lubrication and reducing the roughness of the final surface. In dry turning, increasing the cavities diameter in texture and decreasing the pattern pitch, reduced the surface roughness by 10.6% and 29%, respectively. Examining the SEM images also indicated the production of the workpiece surface with smoothed texture when turning using optimized textured tool.