• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.247-254
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• 1999

The effect of manufacturing parameters such as molding and curing conditions on friction characteristics of friction materials were studied using a pad-on-disk type friction tester. The optimal manufacturing rendition for the best friction characteristics were investigated using friction materials containing 15 ingredients employing Taguchi robust design experiment. The friction characteristics were strongly affected by pressing time, pressing temperature, pressing pressure, curing time, curing temperature.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.1
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• pp.102-107
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• 2006

This study investigates the properties as the difference friction welding area on SM25C steel rod. The tensile and bending strength and of welded joints, the hardness distribution of welds, the microstructure of welds and the tensile fracture surfaces were mainly investigated through this experiment. The fixed friction welding conditions were revolution 2000rpm, friction pressure 70Mpa, friction time 1.5sec, upset pressure 100Mpa, upset time 2.0sec, upset length 2.8mm and changeable friction welding parameter was friction welding area.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1145-1150
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• 2005

The aim of this paper is to investigate the effect of surface texturing on metal surface and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.57-62
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• 2000

An experimental study has been performed to investigate friction characteristics of pre-coated metals widely used in domestic appliances. Seven-coated sheet metals are tested by using three friction mechanism such as straight pulling, frictionless roller, and non-rotational roller with three kinds of cylindrical rollers. In this experiment, effects of friction mechanism, blank thickness, and roller diameter on friction coefficient, surface roughness, and scoring factor have been investigated From the experimental results, it has been found that tested pre-coated sheet metals have low friction coefficients ($\mu$ = 0.15~0.20) because films coated on sheets take a role of lubricants. Friction coefficients of pre-coated metals decrease with increasing roller-diameters. Surface of pre-coated metals can be improved by decreasing the blank thickness

• Tribology and Lubricants
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• v.14 no.4
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• pp.37-43
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• 1998

The friction loss between piston rings and cylinder liner is due to the tension of the piston rings. Lubricant is usually supplied to reduce the friction. However, the sliding speed of the piston varies during the reciprocating cycle and is very low near TDC(Top Dead Center)/BDC(Bottom Dead Center), where the hydrodynamic lubrication cannot be sustained. Since the lubrication regime is shifted from the hydrodynamic to the boundary lubrication near TDC/BDC, wear particles are easily generated so that the friction loss becomes bigger and bigger due to the plowing effect of wear particles. In this study, for the purpose of reducing the friction loss, an undulated surface is adopted to the cylinder liner to trap wear particles. The friction force variations, which are measured by strain gaged, show that the concept of undulated surface is one of the promising methods to effectively reduce the friction between piston rings and cylinder liner.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.24-27
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• 2001

Friction between the sheet and tools is one of the important factors affecting the sheet metal forming. Therefore, the clarification of the friction is essential to improve the formability of the sheet. In order to find the effect of material property and lubricant viscosity on the frictional characteristics, tensile test, surface roughness test and friction test are performed. The results showed that friction characteristics are mainly influenced by the surface roughness and lubricant viscosity. A mathematical model of the friction is developed for calculating friction coefficient in terms of surface roughness and lubricant viscosity. The validity and accuracy of the mathematical model of the friction are verified through the experiment and FEM analysis.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.328-334
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• 1998

In this work, friction materials with three different formulations containing different amounts of the solid lubricants were investigated to study the role of lubricants on the friction performance. The three friction materials contained graphite 10 vol. %, graphite 7 vol. % + MoS$_2$ 3 vol.%, and graphite 7 vol. % + $Sb_2S_3$ 3 vol. %, respectively, with the same amount of other ingredients. Results of this work showed that each formulation with different lubricants had unique advantages and disadvantages. The friction materials containing graphite 7 vol. % + MoS$_2$ 3 vol. % and graphite 7 % + $Sb_2S_3$ 3 vol. % showed better resistance to fading and improved friction stability compare to the friction materials containing graphite only as a lubricant. However, the friction materials with two lubricants (graphite + MoS$_2$ or $Sb_2S_3$) showed disadvantages on stick-slip phenomena, amplitude of torque, and rotor wear.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.47-52
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• 1997

Friction properties of two different types of automotive friction materials were studied. They were nonasbestos organic and semi-metallic friction materials. The two friction materials were tested using an inertia brake dynamometer to investigate friction stability, rooster tailing phenomena, temperature change of riction couples during drags and stops. Results showed that the level of the friction force is strong function of time, temperature, and speed regardless of the type of friction materials. The change of triction coefficient during braking (rooster tailing) was pronounced when the applied pressure was increased in the case of semi-metallic friction materials. This phenomena appears strongly dependent on the applied pressure, initial brake temperature and ingredients in the friction material.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.893-898
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• 2003

Coulomb friction is an important factor for precise position tracking control systems. The control systems with friction causes the steady state error because of being sensitive to the change of system condition and highly nonlinear characteristics. To overcome these problems, we use an estimation scheme of Coulomb friction to experiment for it's compensating. The estimated factor for Coulomb friction is used as a feed-forward compensator to improve the tracking performance of ball-screw systems. The tracking performance was improved by compensating the estimated friction torque in the feed-forward term. And, the sliding mode control which is derived from the Lyapunov stability theorem is applied for robust stability and reducing chattering. The experimental results show that the sliding mode controller with adaptive friction compensator has a good tracking performance compared with the friction uncompensated controller.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.799-804
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• 2003

Friction phenomenon can be described as two parts which are pre-sliding and sliding regions. In motion of the sliding region, friction forces depend on the velocity of the system and are known as Coulomb, stick-slip, stribeck effect and viscous friction. The pre-sliding region, which is before breakaway, depends on the position of the system. The motion of friction in the sliding region can be described as the LuGre model. But the pre-sliding motion of friction, which has hysteresis characteristics in general, is not known widely. Therefore, an improved friction model, which can describe the motion of friction in the pre-sliding region, is proposed in this paper. And simulation and experimental results show the effectiveness of the proposed friction model for precise tracking control systems.