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BN 첨가된 AISI P20 금형강의 밀링 가공에서 공구 마모와 표면거칠기 특성에 관한 연구
황성국,이정환,류시형 한국기계기술학회 2018 한국기계기술학회지 Vol.20 No.4
As product diversity increases and product life cycle gets shorter, lead time reduction and manufacturing cost saving of die & mold are getting important in machinery, automotive, and electronics industries. To develop a novel free-machining die & mold steel, we try to modify the chemical compositions of AISI P20 mold steel by adding boron, nitride, and sulfur. After making three types of mold steels which are base metal of AISI P20 mod., boron and nitrogen added, and boron, nitrogen, and sulfur added to the base metal. Milling tests are carried out using TiN, TiCN, and TiAlN coated WC end-mills under various cutting conditions. Boron and nitrogen added steel machined by TiN coated tool shows the most excellent tool wear and surface roughness characteristics. The results might come from BN inclusions in base metal acting as a stress concentration source and lowering strain resistance during cutting process. The relationship between tool wear and surface roughness are also discussed including feed rate effects.
황성국,Sang-Pill Lee,Jin-Kyung Lee,Dong-Su Bae,이문희,Seunghoon Nam 한국산업융합학회 2019 한국산업융합학회 논문집 Vol.22 No.1
This study dealt with the tensile strength characteristics of stainless steel 304L steel by hydrogen charging. Especially, the effect of hydrogen charging time on the tensile strength and ductility of 304L stainless steels was evaluated, in conjunction with the observation of their fracture surfaces. The tensile properties of hydrogen-charged 304L stainless steels were also investigated with the variation of tensile loading speeds. The hydrogen amount of 304L stainless steels obviously increased with the increase of hydrogen charging time. The tensile properties of 304L stainless steels were clearly affected by the short term charging of hydrogen. In particular, the elongation of 304L stainless steels decreased with increasing hydrogen charging time, due to the hydrogen embrittlement. It was also found that the tensile properties of hydrogen-charged 304L stainless steels were very sensitive to the crosshead speed for tensile loading.
AISI 1536.V와 AISI 4330 재질별 제조 공정에 따른 잔류응력에 관한 연구
황성국,문정수,김한주 한국기계기술학회 2018 한국기계기술학회지 Vol.20 No.4
To improve life time of machine components, higher alloy grade materials are used by adding more metal alloy components and content. Also production processes are further complicated and subdivided such as the forging, preliminary heat treatment, quality heat treatment, rough machining and finished machining process. Those reasons become major cause of large stress in the materials, and the residual stress generated during the manufacturing process causes fatal defects, such as crack, surface tear, warping and deformation of the products. It is necessary to evaluate the residual stress on the entire processes, from forging process to final finished machining process. Also in order to avoid those problems caused by residual stresses, it is necessary to know in advance what process is important to be controlled and what parameters affect residual stress. By the hole drilling method, residual stress was measured in each manufacturing process step. In this study, the hardness of the surface, the cutting force test and the metal analysis were performed to clarify the influence of manufacturing process parameters.
제조공정에 따른 강종별 잔류응력 특성에 관한 연구; AISI 1536V, AISI A387
황성국(Sung-Kug Hwang),문정수(Jeong-Su Moon),김한주(Han Joo Kim) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.9
This study analyzes the residual stress of AISI 1536V for an engine shaft of the shipbuilding industry and AISI A387 for a reactor shell of the chemical refining industry by the hole drilling method with a strain gauge rosette, which transforms fine mechanical changes into electrical signals. Tensile residual stress is generated in the forging and heat treatment process because specimens are affected by thermal stress and metal transformation stress. In the heat treatment process, the residual stress of AISI A387 is almost 170% the yield strength at 402 MPa. Since during the machining process, variable physical loads are applied to the material, compressive residual stress is generated. Under the same condition, the mechanical properties greatly affect the residual stress during the machining process. After the stress-relieving heat treatment process, the residual stress of AISI A387 is reduced below the yield strength at 182 MPa. Therefore, it is necessary to control the temperature, avoid rapid heat change, and select machining conditions depending on the mechanical properties of materials during manufacturing processes. In addition, to sufficiently reduce the residual stress, it is necessary to study the optimum condition of the stress-relieving heat treatment process for each material.
항공 무기체계 초가속수명시험 최적 시험방안 적용을 위한 산업군 별 초가속수명시험 시험 절차 비교
황성국(Seongguk Hwnag),김무영(Mooyoung Kim) 항공우주시스템공학회 2019 항공우주시스템공학회 학술대회 발표집 Vol.2019 No.5
최근 초가속수명시험(HALT)을 포함한 신뢰성 시험의 중요성과 그 효과에 대한 인식이 점점 높아지고 있는 추세이다. 자동차, 생활가전, 국방 등 다양한 산업군에서 신뢰성 시험을 통한 제품의 신뢰성 및 품질 향상을 요구하고 있으며 국내/외 일부 완성차 업체에서는 신뢰성 시험을 강제 요구 규격으로 제시하기도 한다. 특히 HALT는 개발단계에서 비교적 짧은 시간에 제품의 품질 확보를 할 수 있는 신뢰성 시험으로 개발 초기 단계에 짧은 시간, 적은 비용으로 고신뢰성 설계에 용이하다. 본 연구에서는 초가속수명시험에 대한 각 산업군 별 수행 사례 및 기준을 비교분석 함으로써 국방 항공 무기체계의 초가속수명시험 최적 시험방안을 연구해 보고자 한다.