Young Shik Pyoun

Nano Structured Surface Modification of Tool Steel and its Beneficial Effects in Mechanical Properties

The industrial beneficial effects of nano-structured surface modification of tool steel (SKD 61) have been studying. Ultrasonic cold forging technology (UCFT) is one of severe plastic deformations for the improvement of mechanical properties by making nano-structure on surface. The basic mechanism of UCFT and experimental device for treatment of trimmer knives (SKD 61) are presented. Test results of UCFT treated knives in cold steel milling line and analysis why the improved service life is achieved are explained.

TRIBOLOGICAL CHARACTERISTICS OF RADIAL JOURNAL BEARINGS BY ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION TECHNOLOGY

Ultrasonic nanocrystal surface modification (UNSM) has applied to a radial journal bearings made of bearing steel SUJ2. Mechanical characteristics are compared between UNSM treated and untreated bearings. Friction torque is measured at the boundary lubrication condition, the mixed lubrication condition, and the full hydrodynamic lubrication condition. The peak torque at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM treated samples are reduced. These effects are very useful to improve the service life of journal bearings. The Stribeck curve at the mixed and full hydrodynamic lubrication is derived and compared. The friction coefficient at these two regimes is reduced by more than 50%, which will do effective role for improvement of energy efficiency. The major effects for this reduction at three lubrication regimes could be explained in the terms of micro dimple surface.

Study of Inner Micro Cracks on Rolling Contact Fatigue of Bearing Steels Using Ultrasonic Nano-Crystalline Surface Modification

The purpose of this study is to analyze the effect of ultrasonic nano-crystalline surface modification (UNSM) treatment on rolling contact fatigue (RCF) characteristics of bearing steels. It was found that severe plastic deformation occurred at surface by over 100 µm after UNSM treatment. The micro surface hardness was increased by 18%, and the measured compressive residual stress was as high as -700~-900MPa. The polymet RCF-2 roller type RCF test showed over 2 times longer fatigue lifetime after UNSM treatment under Hertzian contact stress of 425.2kg/mm2 and 8,000 rpm. And SEM study showed a spalling phenomenon at the samples which went through the RCF test after UNSM treatment. Samples before UNSM treatment produced surface initiated spalls and multi shear lips by progressive spalling at the end along the rolling direction, but sub-surface initiated spalls were formed without multi shear lips after UNSM treatment. The spalling occurred at once, and the size and depth of spalls were larger than those before UNSM treatment. And micro cracks were found to form within the spallings after UNSM treatment, and stress distribution at the maximum Herzian shear stress through these micro cracks is thought to improve the fatigue lifetime of bearing materials.

Friction and Wear Characteristics of SUS304 and SUS630 after Ultrasonic Nanocrystal Surface Modification

Owing to the superior properties of stainless steel it is pertinent to make use of it in various applications of automotive, aerospace, nuclear, chemical and cryogenic products. This paper describes a study of friction characteristics of SUS304 and SUS630 stainless steel disk specimens against silicon nitride Si3N4 ball in dry, grease-, and oil-lubricated conditions and wear characteristics in dry condition in sliding contact. The ultrasonic nanocrystal surface modification (UNSM) technology was applied to those disk specimens and its friction and wear properties were compared with polished one. The experiment was conducted with a pin-on-disk tribo tester using ball-on-disk contact geometry at room temperature. The experiment results show that in dry, greased- and oil-lubrication conditions the coefficient of friction of UNSM-treated specimens was lower and constant than polished specimens and in dry condition the wear rate was also smaller than polished one. Micro dimples made by UNSM treatment contribute those effects.

Flexibility Value as a Tool for Improving Decision-Making in Flexible Automation

ABSTRACT To narrow the discrepancy between the benefits of investment in flexible automation of manufacturing systems promised by financial evaluation tools and the benefits realized in practice, we distinguish the potential flexibility of a system from its realizable flexibility. A classification is given of the realizable flexibility in automated manufacturing systems in mass, mid-variety and mid-volume, and multi-variety and small-volume production systems. A systematic procedure for quantifying the realizable flexibility in monetary terms and integrating this value into a Financial evaluation model is proposed and applied to a test case with significant results. Comparisons are also made with typical previous studies.