• 한국생산제조학회지
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• 제26권4호
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• pp.365-370
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• 2017

In this article, a 20 kHz Titanium (Ti) ultrasonic waveguide system for a nano-surface reformation process was designed and fabricated. First, finite element analysis using ANSYS software was performed to find the optimal dimensions. The obtained anti-resonance frequency for the Ti transducer with the piezoelectric device was 20.0 kHz, which value agreed well with the experiment result of 20.1 kHz (0.5% error). To test the system, chromium molybdenum steel (SCM) 435 was chosen as a test-piece. The result proved that the reformed depth was $36{\mu}m$. In addition, hardness was measured before and after the process. The value was changed from 14 HRC to 21 HRC, which is 50% increasing rate. Finally, the friction coefficient test result showed that the surface coefficient was reduced from 0.14 to 0.10 (28.6% reduction). Based on the results, the Ti ultrasonic equipment is regarded as a useful device for nano-scale surface reformation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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• pp.27-36
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• 2004

Contemporary objectives for steel rod rolling processing are increasingly complex and often contrasting i.e. obtaining a desired product with optimum combination of properties such as strength, toughness and formability at lower cost. Low-alloy steel rods have been produced with several heat treatments for drawing and forging processes at room temperature. In order to reduce these heat treatments much of the researches concerning of high temperature mechanical behavior of steel rods have been conducted at wire rod mill of POSCO. In this present work, optimizations of rolling temperature and cooling rate for JS-SCM435 are performed to eliminate softening heat treatment(Low Temperature Annealing) for drawing process. The results from the optimization changed the microstructure of rods after rod rolling from Bainite with high tensile strength of 1000Mpa to Pearlite and Ferrite with appropriate strength of 750Mpa that is equivalent tensile strength after softening heat treatment.

• 한국자동차공학회논문집
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• 제24권5호
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• pp.588-595
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• 2016

This paper is a study on head bolts that are used in A/C compressors to reduce production cost and solve leak problems on the head bolt seat area that causes massive intermittent malfunctioning during production. In this study, the pre-heat treated steel, which was used as a material in the head bolt, eliminated the heat treatment process after forging. The pre-heat treated steel head bolts, which have 10 % lower tensile strength than the conventional SCM 435 head bolts, were selected after considering the results of creeping rupture properties, axial force, and stress concentration per tensile strength variation. Then, the performance test and the durability test with the A/C compressor that was assembled with the pre-heat treated steel head bolts were performed and verified. Based on the results, the pre-heat treated steel head bolts developed in this study saved 7.3 % in production cost by eliminating the heat treatment process and the logistics process. Furthermore, the leak problem on the head bolt seat area in the A/C compressor was addressed significantly on the mass production assembly line.