فهرست مطالب سلمان خانی

In this study, the effect of microtextures parallel to the cutting edge on the rake face of cutting tools during the turning process of 17-4PH steel was investigated. The depth, width, and distance of micro-textures were studied. Turning tests were performed with the created tools and the cutting force was measured by a dynamometer. The results showed that by increasing the width of microgrooves, the cutting force first decreases and then increases. This trend shows that the width of the microgrooves has an optimal value in which the cutting force during the turning process is minimal. Also, the cutting force is reduced by increasing the depth of microgrooves. By increasing the distance of microgrooves, it was found that the cutting force has increased. Based on the optimization results, the optimal values of the parameters of width, depth, and distance of the microgrooves are 126 µm, 15 µm, and 200 µm, respectively. The calculated error percentage for optimization validation was 5.81%, which indicates the high accuracy of the optimization process in the Design-Expert software. The deflection of the workpiece was achieved with a tool with an optimal microgroove of 30 µm and with a plane tool equal to 62 µm, which shows a 51.6% reduction with a textured tool. In fact, the accuracy of the machined part was improved with microtextured tools.

17-4PH stainless steel is a martensitic precipitation hardening stainless steel that provides an outstanding combination of high strength, good corrosion resistance, good mechanical properties, good toughness in both base metal and welds, and short time, low-temperature heat treatments that minimize warpage and scaling. This valuable alloy is widely used in the aerospace, nuclear, chemical, petrochemical, food processing, power generation, and naval industries; however, 17-4PH stainless steel is categorized as hard to machine materials due to low thermal conductivity and high toughness. Tool wear in traditional machining of 17-4PH stainless steel is high; hence, low tool life causes high tooling cost. In this paper, indirect cryogenic machining was used, in order to improve machinability of 17-4PH stainless steel in turning operation with TiN coated carbide insert tool. Pressurized-liquid-nitrogen (LN) was used as a cryogenic coolant. Nitrogen gas applied on the liquid nitrogen to pressurize it. A specific tool holder was designed and manufactured for cryogenic turning. Cryogenic machining decreases temperature-dependent tool wear and increases tool life by keeping tool temperature low. Cutting force, tool flank wear and maximum tool temperature have been studied as machinability parameters. Cutting force was measured by the Kistler 9121 piezoelectric dynamometer. The Dino-Lite digital microscope with 20-200X magnification was used to measure tool flank wear. The experimental results showed that cryogenically enhanced machining decreases cutting force and tool flank wear by 22 and 23 percent, respectively, compared with dry turning. Predicting of tool life using linear extrapolation showed that tool life in cryogenic turning improved by 39% over dry turning. In addition, cutting force in cryogenic machining became more stable than the force in dry condition. Thermal analysis of the carbide tool performed in the ANSYS Software using experimental data. Thermal analysis showed that the maximum temperature of cutting tool in cryogenic machining is 75 percent lower than dry condition.