جستجوی مقالات مرتبط با کلیدواژه "عمر ابزار" در نشریات گروه "مکانیک"

Nowadays, due to the increasing need of various military, aerospace, automotive, etc. industries for materials with high strength-to-weight ratio, good resistance to wear and fatigue, etc. the use of composite materials, especially metal-based composites, has increased significantly. Machining to achieve high dimensional accuracy is an integral part of the production process of products made with metal-based composites. Due to the presence of reinforcing materials such as silicon carbide, etc. the machining of this category of materials always faces many challenges, including tool wear, increased machining forces, decreased surface quality, etc. Therefore, it is to study the parameters affecting the machining of metal composites. Many studies have been done in this field by different researchers. In this article, by reviewing the most important articles published in this field, comprehensive and at the same time summary information on the influencing factors in conventional machining processes such as turning, milling, etc. or non- conventional machining processes such as electrical discharge, electrochemical machining, etc. has been tried to be available to the readers. Also, the performance of different types of tools during the machining of metal composites was investigated. In the end, the existing gaps and new and studyable topics for researchers were pointed out.

Machining of hard workpieces is one of the most important challenges of the manufacturing industry. Hence, new methods were added to traditional machining. Ultrasonic vibration machining is one of these methods. The advantages of using ultrasonic vibrations compared to traditional machining include reducing machining forces, reducing tool wear and friction, increasing tool life, creating intermittent cutting conditions, increasing surface quality, and so on. To vibrate the tool, a horn with a resonant frequency of 20,633 Hz was analyzed by Abacus software. In this study, the effects of cutting speed, feed rate, conventional machining conditions, and vibration machining conditions at three different hardness of 15, 30, and 45 Rockwell C for the workpiece on surface roughness and tool wear were evaluated. The experiments were designed at full factorial, and a total of 54 experiments were performed. The results showed that at higher workpiece hardness by applying vibration the surface roughness was reduced. The surface roughness (Ra) in machining by means of ultrasonic vibrations is up to about 36% less than conventional machining in various machining parameters. In addition, the temperature in vibration machining is lower about 15% at higher stiffness of the workpiece. Also, with the increase in the hardness of the workpiece, the tool wear was increased, which is less by applying ultrasonic vibrations. Also, by applying vibrations, tool wear was reduced in total, which can be minimized by selecting cermet tools and applying vibrations in 4140 AISI steel machining.

Selecting tool materials, tool sizes and determining the cutting parameters presents a great challenge in machining operations especially in high speed machining processes. In this study effect of feed rate which is one of the important machining parameters and tool size on tool life in high speed machining of Ti-6Al-4V alloy were investigated. Fixed cutting speed of 200 m/min, feed rate of 0.03 and 0.06 mm/tooth together with axial cutting depth of cut 5.0 mm, and radial cutting depth of cut 1.5 mm were employed as the cutting parameters. TiAlN TiN coated tungsten cemented carbide insert in two different size was used during machining operations. Flank wear land measurement was taken by using a toolmakers’ microscope and recorded accordingly throughout machining processes. The results showed during the machining employing both feed rate and using smaller tool size chipping occurred on the tool nose along with gradual tool flank wear. Also by increasing the feed rates utilizing the smaller size of tool highly affected tool life compared to employing the larger one during the high speed machining operations. Reduction the feed rate by 50 percent increased the tool life of smaller tool size by 200 percent.

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.

The aim of this research work is to evaluate the effects of coolant including nano- powder material for the cooling purpose in milling process and comparing the results with the conventional coolant. Generation heat and weak heat transfer reduces the tool life and also deteriorate surface roughness during milling operation. To overcome this problem, it is necessary to use coolant for cooling as well as lubrication purposes. Due to limited heat removal rate from the work piece through the conventional coolant, some nano powder material is added to coolant, to improve the heat transfer coefficient. The added nano powder also increases machinability, decreases production time and improve surface roughness. In this paper nano fluid of copper with 99 percent purity added to Z1 coolant for machining of St37 work piece in milling machine. In this research, some factors such as rotational speed, feed and depth of cut in the three states of machining, with different coolant including Z1 and nano fluid and dry condition were investigated and finally temperature of machined work piece and its surface quality were evaluated. By comparing the obtained results it is evident that the heat removal rate and surface quality in the case of nano fluid are improved and furthermore the tool life as well as machining efficiency increases.