• 한국정밀공학회지
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• 제27권5호
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• pp.75-84
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• 2010

The aim of this paper is to design the blank shape of SPFH 590 high strength steel for stamping of the center hinge of automotive via numerical analyses and experiments for multi-stages transfer forming process. Three-dimensional elasto-plastic finite element analyses for the transfer forming process with six stages were performed using a commercial code AUTOFORM V4.2. The influence of the blank shape on the formability and the shape conformity were quantitatively examined through the FE analyses. From the results of the FE analysis, a feasible shape of the blank and the forming load were estimated. Stamping experiments were carried out using the proposed blank shape. The results of experiments were shown that the center hinge parts with the desired shapes can be manufactured successfully as the proposed blank shape is used. Through the comparison of the results of the experiments with those of the analyses, it was shown that the estimation of blank shape using the FE analysis is a proper methodology to create a feasible shape of the blank for the center hinge of automotive.

• Design & Manufacturing
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• 제17권2호
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• pp.55-61
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• 2023

With femtosecond (fs) laser pulse irradiation on metals, various types of nano- and micro-scale structures can be naturally induced at the surface through laser-matter interaction. Two notable structures are laser-induced periodic surface structures (LIPSSs) and cone/spike structures, which are known to significantly modify the optical and physical properties of metal surfaces. In this work, we irradiate fs laser pulses onto various types of metals, cold-rolled steel, pickled & oiled steel, Fe-18Cr-8Ni alloy, Zn-Mg-Al alloy coated steel, and pure Cu which can be useful for precise molding and imprinting processes, and adjust the morphological profiles of LIPSSs and cone/spike structures for clear structural coloration and a larger range of surface wettability control, respectively, by changing the fluence of laser and the speed of raster scan. The periods of LIPSSs on metals used in our experiments are nearly independent of laser fluence. Accordingly, the structural coloration of the surface with LIPSSs can be optimized with the morphological profile of LIPSSs, controlled only by the speed of the raster scan once the laser fluence is determined for each metal sample. However, different from LIPSSs, we demonstrate that the morphological profiles of the cone/spike structures, including their size, shape, and density, can be manipulated with both the laser fluence and the raster scan speed to increase a change in the contact angle. By injection molding and imprinting processes, it is expected that fs laser-induced surface structures on metals can be replicated to the plastic surfaces and potentially beneficial to control the optical and wetting properties of the surface of injection molded and imprinted products.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.202-203
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• 2014

금형 내부의 마모를 줄이기 위한 경질 박막의 안정성 향상과 표면에 인가된 압축 잔류 응력이 고주기 피로 특성에 미치는 영향을 연구하기 위해 정밀 플라스틱 사출 금형강에 주로 사용되는 Fe-3.0%Ni-0.7%Cr-1.4%Mn-X강에 스크린 질화처리와 DLC 코팅을 시간과 단일, 복합처리의 변수를 두어 코팅하였다. PAPVD법으로 DLC($3{\mu}m$), 스크린 질화(3h, $50{\mu}m$)/DLC($3{\mu}m$) 코팅 후 고주기 피로 시험을 행하여 고주기 피로 특성을 평가하였다. 스크래치 시험, 마모 시험, 잔류응력 측정을 통해 질화 처리 여부에 따른 코팅의 안정성을 평가하였다. DLC, 스크린질화/DLC 코팅한 경우 압축 잔류 응력의 영향으로 모두 피로 수명이 향상되었고 스크린질화/DLC 코팅한 경우 그 향상폭은 더 컸다. 질화 처리 후 DLC 코팅한 경우 질화층은 버퍼레이어로 작용하여 코팅의 박리를 억제함을 확인하였다.

• Tribology and Lubricants
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• 제31권4호
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• pp.157-162
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• 2015

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si₃N₄) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.

• Design & Manufacturing
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• 제16권2호
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• pp.1-6
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• 2022

As environmental regulations are strengthened, automobile manufacturers continuously research lightweight structures based on carbon fiber reinforced plastic (CFRP). However, it is difficult to see the effect of strength reinforcement when using a single CFRP material. To improve this, a hybrid laminate in which CFRP is mixed with the existing body structural steel was proposed. In this paper, CFRP patch reinforcement is applied to each compression/tensile action surface of a 22MnB5 metal sheet, and it was evaluated through a 3-point bending experiment. Progressive failure was observed in similar deflection on bending deformation to each one-sided reinforced specimen. After progressive failure, the tensile reinforced specimen was confirmed to separate the damaged CFRP patch and 22MnB5 sheet from the center of the flexure. The compression reinforced specimen didn't separate that CFRP patch and 22MnB5, and the strength reinforcement behavior was confirmed. In the compression reinforced specimen, damaged CFRP patches were observed at the center of flexure during bending deformation. As a result of checking the specimen of the compression reinforcement specimen with an optical microscope, It is confirmed that the damaged CFRP patch and the reinforced CFRP patch overlapped, resulting in a concentrated load. Through the experimental results, the 22MnB5 strength reinforcement characteristics according to the reinforcement position of the CFRP patch were confirmed.

• 생물환경조절학회지
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• 제8권4호
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• pp.257-264
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• 1999

세라믹의 종류와 두께 그리고 소성온도를 달리하여 제작한 세라믹 자동점적센서의 점적성능을 비교 분석하였다. 자체제작 세라믹센서에 가장 많이 함유된 조성성분은 $SiO_2$로 54.17~71.62wt.%였으며 다음이 A1$_2$O로 15.42~33.79 wt.%였다. 두 성분의 합계는 백자토 92.34 wt.%, 옹기토 89.18 wt.%, 미립분청토 88.17 wt.%, 세립분청토 87.96 wt.%, 대조구(시판수입제품) 87.04 wt.%였다. $SiO_2$：A1$_2$O의 비율은 백자토 73.2：26.8, 옹기토 80.2：19.8, 미립분청토 68.9：31.1, 세립분청토 61.6：38.4, 재조구 82.3：17.7이었다 기타 Fe$_2$ $O_3$, CaO, MgO, $Na_2$O, $K_2$O, Ti $O_2$, P$_2$ $O_{5}$ 등이 10wt.%내외 함유되어 있었다. 공극율은 세립분청토에서 가장 높았고 백자토, 옹기토 순이었으며 소성온도가 높을수록 두께가 두꺼울수록 공극율이 높았다. 두께 2.5mm로 성형한 세라믹의 점토종류에 따른 공극율은 세립분청토 37.47%, 세립분청토와 옹기토의 혼합토 34.82%, 백자토 34.71%, 옹기토 32.5% 순이었다. 세라믹의 점토종류, 소성온도에 관계없이 자동점적이 가능하였으나 점적센서의 반응주기와 점적량의 집중도는 차이가 있었으며, 세라믹의 두께나 상부 플라스틱 개폐장치의 탄력성에 따라서도 점적패턴과 점적량의 집중도에 큰 차이가 있었다. 세립분청토나 백자토에서는 점적지속시간이 짧았으며 백자토의 경우 점적량의 증가가 급격하지만 감소는 서서히 이루어졌다. 또한 세라믹의 두께가 두꺼울수록 점적지속시간이 짧았으며 점적량의 증가는 급격하였고 감소는 완만하였다. 그러나 두께 1mm로 얇은 경우는 백자토를 제외하고는 정상적인 급액이 이루어지지 못하였다. 세라믹 센서를 50$0^{\circ}C$에서 소성한 경우 점적지속시간이나 단위시간당 점적량이 불안정하였으며 $600^{\circ}C$ 및 $700^{\circ}C$에서는 비교적 안정된 양상을 보였으나 점적지속시간이 길어졌으며 80$0^{\circ}C$ 또는 90$0^{\circ}C$에서 소성한 경우는 점적지속시간이 짧은 반면 단위시간당 점적량이 커지면서 점적의 개시와 종료가 뚜렷하였다.