• 한국자동차공학회논문집
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• 제18권5호
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• pp.25-30
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• 2010

The authors have studied on the corrosion resistance of the hot stamped steel sheets for the application to automotive parts. Recently automotive companies have focused on the hot stamped parts to meet the light weighting needs and the safe reason. Because of the cost reduction of the hot stamped parts, automotive companies increase the usage of the coated steel sheets, especially Al-Si coated steel sheets. The coated layer of Al-Si coated steel sheets contains up to 50% of Fe, which was diffused from the steel sheet, after hot stamping. The hot stamped steel sheet was not phosphated due to the oxidation layer of the coating, however, the result of the water resistance test is similar to that of the conventional GA steel sheets. The pitting depth and the weight reduction of the coated layer of hot stamped steel sheets are less than those of GA steel.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.39.2-39.2
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• 2010

Recently, hot stamping process has been paid attention greatly by automobile makers in accordance with the fuel efficiency and environmental issues as well as crash safety issue. The hot-stamped parts, however, demand extreme mechanical properties such as tensile strength of over 1470 MPa or equivalently Vickers hardness of around 450. In this work, to meet the demand efficiently, a method to predict mechanical property of hot-stamped parts based on numerical phase transformation scheme has been proposed associated with the thermo-mechanical coupled finite element analysis. This work deals with various phase transformation equations and validates them to select appropriate model for 0.2C-0.1Si-1.4Mn-0.5Cr-0.01Mo-0.002B steel sheet. The authors show that an efficient method saving time and cost to develop hot-stamped automobile parts ensuring suitable mechanical properties such as Vickers hardness and strength.

• 소성∙가공
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• 제24권5호
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• pp.354-360
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• 2015

AHSS (Advanced High Strength Steels) has been increasingly employed by global automotive OEMs in order to satisfy strengthened regulations and reduce weight for fuel efficiency. Hot stamping using boron steels in AHSS increases not only formability but also strength. The typical hot-stamped automotive part is the center pillar that is critical for vehicle side impact. However, the hot-stamped part can be risky for the passenger safety caused by brittle fracture under a vehicle collision. The high power diode laser is suitable for the heat treatment giving AHSS increased elongation that prevents brittle fracture in car crash. Therefore, local softening by laser heat treatment for energy absorption area on the hot-stamped part improves crash-worthiness.

• 대한기계학회논문집A
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• 제39권1호
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• pp.89-94
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• 2015

본 연구의 목적은 열처리 전 후의 보론강 레이저 용접성을 비교하는 것이다. 일반적으로 보론강이 핫스탬핑 공정에 사용되고 있으며, 핫스탬핑 공정은 강판을 오스테나이트 온도까지 가열한 후 성형과 동시에 냉각하는 방법이다. 열처리후 보론강은 1500 MPa 이상의 고강도를 가진다. 따라서 본 연구에서는 보론강 및 핫스탬핑강의 레이저 용접성을 조사한 후 비교하였다. CW 디스크 레이저를 이용하여 레이저 출력 및 용접속도를 변화시켜가며 맞대기 및 겹치기 용접을 실시하였다. 맞대기 용접 결과, 핫스탬핑강에서 완전 용입을 얻을 수 있는 임계냉각속도가 보론강보다 낮았으며, 겹치기 용접결과 완전 관통이 일어난 용접 조건에서는 접합부 폭은 용접속도와 관계없이 거의 유사하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.7-12
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• 2008

A hot stamping technology of vehicle door impact beam made of thin sheet steel has been developed, with the aim of ensuring occupant safety in a side collision. This technology has been implemented to increase the strength of vehicle body parts and to reduce not only the weight of door impact beam but also the number of work processes. Mechanical tests were performed to obtain material properties of hot-stamped specimen and those were used as input data in stamping and structural simulation for optimal design of door impact beam. Strength of hot-stamped door impact beam increased to the value 102% higher than that of conventional pipe-shaped door impact beam and structural simulation showed that hot-stamped door impact beam achieved 28% weight reduction.

• 한국정밀공학회지
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• 제28권1호
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• pp.63-72
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• 2011

In recent years, hot-stamped components are more increasingly used in the automotive industry in order to reduce weight and to improve the strength of vehicles. In hot stamping process, blank is hot formed and press hardened in a tool. However, in hot stamping without cooling channel, temperature of the tool increases gradually in mass production thus cannot meet the critical cooling rate to obtain high strength over 1500MPa. Warpage occurs in the hot stamped component due to non-uniform stress state caused by unbalanced cooling. Therefore, tools should be uniformly as well as rapidly cooled down by the coolant which flows through cooling channel. In this paper, optimal design method of cooling channel to obtain uniform and high strength of the component is proposed. Optimized cooling channel is applied to the hot press V-bending process. As a result of measuring strength, hardness and microstructure of the hot formed parts, it is known that the design methodology of cooling channel is effective to the hot stamping process.

• 소성∙가공
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• 제21권3호
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• pp.186-194
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• 2012

Hot stamping is a forming method that offers various advantages such as superior mechanical properties, good formability, and very small springback. However, relatively large-sized parts, such as front pillars, exhibit poor formability when hot stamped due to the limited material flow and thickness reduction imparted by the process. This reduction in thickness can also lead to cracks. One of the reasons is the relatively high friction between the sheet and the die. In this study, in order to obtain the optimal conditions for hot stamping of front pillars, various process parameters were studied and analyzed using the sheet forming software, J-STAMP. The effects of various parameters such as the die structure, blank shape, blank holding force, punch speed, clearance(upper and lower dies) and distance block were analyzed and compared.

• 소성∙가공
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• 제23권6호
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• pp.357-362
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• 2014

The purpose of the current study is to predict the hardness distribution in steel products after hot stamping using a quench factor analysis(QFA) coupled with FE-simulations. QFA is a method to predict properties such as hardness and tensile strength based on time-temperature-property(TTP) curves and can determine properties based on the temperature histories. The constants($K_1{\sim}K_5$) of QFA were determined using hardness data obtained after various cooling rates. In the current study, a rear side member was selected for evaluation and FE-simulations were performed to obtain the temperature histories during hot stamping. The predicted temperature data were imported into the QFA to calculate the hardness distribution of the hot stamped parts. A hot stamping experiment of the rear side member was conducted to verify the predicted hardness. The simulation results show good agreement with the experimental measurements.

• 소성∙가공
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• 제20권8호
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• pp.540-547
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• 2011

Recent years have seen advent of hot stamped parts made from laser-welded blanks of boron steels for structures requiring high crash energy absorption. However, the presence of Al-Si coating interfered with satisfactory mechanical characterizations after laser butt welding. In this study, laser ablation technology was considered in order to facilitate adequate mechanical characterization of the final hot-stamped panels.

• 소성∙가공
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• 제32권3호
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• pp.160-165
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• 2023

As the supply of eco-friendly vehicles increases, the application rate of hot stamping components is rising to reduce vehicle weight and improve safety. Although Al-Si coated steel sheets are commonly used in hot stamping processes, their manufacturing costs are elevated due to process patents and royalties. Various hot stamping studies have been conducted to reduce these production costs. In this study, we derived a process control method for suppressing the oxide layer of hot stamping parts using uncoated boron steel sheets. Firstly, hat-shaped parts were hot stamped under atmospheric conditions to analyze the tendency of oxide layer formation by location. Then, the Gleeble system was used to observe oxide layer formation based on oxygen content under various atmospheric conditions. Finally, the oxide layer thickness was quantitatively measured using SEM images.