• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.247-251
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• 2017

Titanium alloy has been widely used in the aerospace industry because of its high strength and good corrosion resistance. During cutting, the low thermal conductivity and high chemical reactivity of titanium generate a high cutting temperature and accelerates tool wear. To improve cutting tool life, cryogenic machining by using a liquid nitrogen (LN2) jet is suggested. In cryogenic jet cooling, evaporation of LN2 in the tank and transfer tube could cause pressure fluctuation and change the cooling rate. In this work, cooling uniformity is investigated in terms of liquid nitrogen jet pressure in cryogenic jet cooling during titanium alloy turning. Fluctuation of jet spraying pressure causes tool temperature to fluctuate. It is possible to suppress the fluctuation of the jet pressure and improve cooling by using a phase separator. Measuring tool temperature shows that consistent LN2 jet pressure improves cryogenic cooling uniformity.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.5
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• pp.865-870
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• 2013

In recent years, aluminum processing has been increasing in the aerospace, vehicle, airplane industries etc., because aluminum has abundant resources and has a high specific strength. Aluminum alloys have a high coefficient of thermal expansion therefore, it is necessary to consider the temperature problem in the cutting process. The objective of this research is to investigate the machinability of a hardened aluminum alloy Al7075-T6 by using cryogenic heat treatment. The machining test is conducted by comparing the cutting force and surface roughness, corresponding to various cutting conditions of depth of cut, cutting speed, and feed rate, with those of Al7075-T0.

• Journal of the Korea Safety Management & Science
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• v.4 no.2
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• pp.237-249
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• 2002

A cutting fluid can improve machining quality and tool life by maintaining the tool toughness and by providing a lubrication effect to reduce the friction between the chip and tool interface. Although liquid nitrogen as an environmentally safe coolant has been widely recognized in cryogenic machining, its function as a lubricant is plausible due to its chemical inertness, physical volatility and low viscosity. Since a reduced friction is a direct witness of the lubrication effect from a tribological viewpoint, this paper presents an evaluation of the apparent friction coefficient on the tool-chip interface in cryogenic cutting operations to prove and characterize the lubricity of LN2 in cryogenic machining. The mathematical approaches have been formulated to derive the normal and frictional forces on the tool-chip interface for the oblique cutting tests.

• Design & Manufacturing
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• v.13 no.1
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• pp.5-12
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• 2019

In this paper, we studied the micro tool deflection, micro cutting with low temperature, and deformation of micro ribs caused by cutting forces. First, we performed an integrated machining error compensation method based on captured images of tool deflection shapes in micro cutting process. In micro cutting process, micro tool deflection generates very serious problems in contrast to macro tool deflection. To get the real images of micro tool deflection, it is possible to estimate tool deflection in cutting conditions modeled and to compensate for machining errors using an iterative algorithm correcting tool path. Second, in macro cutting fields, the cryogenic cutting process has been applied to cut the refractory metal but, the serious problem may be generated in micro cutting fields by the cryogenic environment. However, if the proper low temperature is applied to micro cutting area, the cooling effect of cutting heat is expected. Such effect can make the reduction of tool wear and burr formation. For verifying this passibility, the micro cutting experiment at low temperature was performed and SEM images were analyzed. Third, the micro pattern was deformed by the cutting forces and the shape error occurred in the sidewall multi-step cutting process were minimized. As the results, the relationship between the cutting conditions and the deformation of micro-structure during micro cutting process was investigated.

• Proceedings of the Safety Management and Science Conference
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• 2002.05a
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• pp.221-225
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• 2002

Machinability improvement by the use of liquid nitrogen in cryogenic machining has been reported in various studies. This has been mostly attributed to the cooling effect of liquid nitrogen. However, No study has been found in discussion on whether liquid nitrogen possesses lubrication effect in cryogenic cutting. This paper presents lubrication mechanism related to chip microstructure. The friction reduction was further reflected In larger shear angle and less secondary deformation in the chip microstructures.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.3
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• pp.185-189
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• 2017

Recently, titanium alloys have been widely used in aerospace, biomedical engineering, and military industries due to their high strength to weight ratio and corrosion resistance. However, it is well known that titanium alloys are difficult-to-cut materials because of a poor machinability characteristic caused by low thermal conductivity, chemical reactivity with all tool materials at high temperature, and high hardness. To improve the machinability of titanium alloys, cryogenic cooling with LN2 (Liquid Nitrogen) and nanofluid MQL (Minimum Quantity Lubrication) technologies have been studied while turning a Ti-6Al-4V alloy. For the analysis of turning process characteristics, the cutting force, the coefficient of friction, and the surface roughness are measured and analyzed according to varying lubrication and cooling conditions. The experimental results show that combined cryogenic cooling and nanofluid MQL significantly reduces the cutting forces, coefficients of friction and surface roughness when compared to wet condition during the turning process of Ti-6Al-4V.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.381-383
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• 2005

This paper is concerned with the prediction of micro structural changes of Al alloys during cryogenic rolling using an Eulerian finite element analysis. The main objective of cryogenic rolling is to obtain ultra-fine grains by severe plastic deformation at the extremely low temperature. Thereby, this simulation focuses on micro structural developments - the texture development and the changes in the size and shape of grains. The former one may be modeled using a crystal plasticity theory while the other can be predicted by a streamline technique. Applications to three pass rolling are given.

• Journal of the Korea Safety Management & Science
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• v.4 no.2
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• pp.223-235
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• 2002

This paper presents some indirect physical evidences indicating that reduced friction occurs in an economical cryogenic machining process, in which LN2 is applied selectively in well-controlled jets to the localized cutting zone. These evidences include cutting force components, tool wear rate and chip morphology. LN2 reduced the tool wear rate to a great extent and elongated the tool life up to four times compared to emulsion cooling. The friction reduction was further reflected in larger shear angle and less secondary deformation in the chip microstructures. This study also found that the effectiveness of LN2 lubrication depends on the approach how LN2 is applied.

• Proceedings of the Safety Management and Science Conference
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• 2002.05a
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• pp.215-219
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• 2002

In this paper some physical evidences indicate that reduced friction occurs in an cryogenic machining process, in which LN2 is applied to the selected cutting zone. LN2 also reduced the tool wear rate to a great extent and elongated the tool life up to four times compared to emulsion cooling.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.32-37
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• 1994

We experimented on cutting characteristics - cutting force, behavior of cutting temperature, surface roughness, behavior of chips-under low temperature,which generated by liquid nitrogen(77K). The workpieces were freezed to -195 .deg. C and liquid nitrogen was also sprinkled on cutting area in order to increase the efficiency of machining in low temperature. The workpiece was became to -195 .deg. C in 5 minutes. In cooled condition(CC) surface roughness of workpiece was better than normal condition(NC). In addition, we investigated the possibility that surface roughness of workpiece and shear angle can be predicted analyzing cutting condititions by the trained neural network.