Spot welding is a representative process in automotive welding and the application of intelligent systems is accelerating. In particular, in the case of welding electrode management, the timing of electrode wear and dressing was determined by continuous spot welding evaluation, however there is concerned that errors in welding equipment or processes may work in a complex manner. In this study, a dynamic resistance waveform sensing and image measurement system that greatly affects the nugget formation, which is important to the quality of spot welding, was fabricated and used. Based on the experimental data of the galvanized steel sheet, an electrode life prediction algorithm for electrode wear was derived through CNN(Convolutional Neural Network) model of machine learning training.

Hydrogen evolution on a steel surface and subsequent hydrogen diffusion into the steel matrix are evaluated using an electrochemical permeation test with no applied cathodic current on the hydrogen charging side. In particular, cyclic operation in the permeation test is also conducted to clarify the corrosion-induced hydrogen evolution behavior. In contrast to the conventional perception that the cathodic reduction reaction on the steel in neutral aqueous environments is an oxygen reduction reaction, this study demonstrates that atomic hydrogen may be generated on the steel surface by the corrosion reaction, even in a neutral environment. Although a much lower permeation current density and significant slower diffusion kinetics of hydrogen are observed compared to the results measured in acidic environments, they contribute to the increase in the embrittlement index. This study suggests that the research on hydrogen embrittlement in ultra-strong steels should be approached from the viewpoint of corrosion reactions on the steel surface and subsequent hydrogen evolution/diffusion behavior.

In order to expand the application of oxide dispersion-strengthened (ODS) steel, a composite material is manufactured by adding mechanically alloyed ODS steel powder to conventional steel and investigated in terms of microstructure and wear properties. For comparison, a commercial automobile part material is also tested. Initial microstructural observations confirm that the composite material with added ODS steel contains i) a pearlitic Fe matrix area and ii) an area with Cr-based carbides and ODS steel particles in the form of a Fe-Fe3C structure. In the commercial material, various hard Co-, Fe-Mo-, and Cr-based particles are present in a pearlitic Fe matrix. Wear testing using the VSR engine simulation wear test confirms that the seatface widths of the composite material with added ODS steel and the commercial material are increased by 24% and 47%, respectively, with wear depths of 0.05 mm and 0.1 mm, respectively. The ODS steel-added composite material shows better wear resistance. Post-wear-testing surface and cross-sectional observations show that particles in the commercial material easily fall off, while the ODS steel-added material has an even, smooth wear surface.

In this study, the cold rolled DP590 FSW joints were obtained by the position control type of the FSW machine and examined. The FSW weldability was investigated using the Si3N4 tool specially made by Cold Isostatic Press (CIP). Defect-free joints were formed at 180-300 mm/min at 800 rpm. However, a groove-like defect was observed along the joint line of the advancing side due to the insufficient material flow. In addition, the life of the Si3N4 tool was compared to that of the polycrystalline cubic boron nitride (PCBN) tool for the durability. The SI3N4 tool that was broken in which tool reached a length of 5 m and around half of the performance level of the PCBN tool.

The flat type automotive cross members with high strength steel have advantages in light weight and fewer parts compared to the hump type cross members. But the complex part shape of the flat type cross member and the poor formability of high strength steel make it difficult to form the parts without forming defects, such as splits and wrinkles. The purpose of this study is to develop the flat type automotive cross member with high strength steel. For that purpose, drawing processes are evaluated using PAM-STAMPTM and proper draw die and blank designs are proposed. Using the proposed die and blank design, the flat type upper and lower cross member could be formed successfully without forming defects.

본 연구는 산업부산물인 제철 산업의 전기로 산화슬래그골재를 이용하여 천연골재를 대체하고 자동차 산업에서 발생하는 폐유리를 분쇄하여 채움재로 활용하는 연구로써, 환경친화적인 아스팔트 포장 재료를 개발하였으며, 폐PVB로 아스팔트 바인더의 물리적 성능을 개선하여 현장적용성을 검토하였다. 최적의 공극률을 결정하기 위한 반복적인 배합설계를 거쳐서 13-5mm(40%), 5-0mm(57%), 폐유리미분말 채움재(3%), 아스팔트(4.1%)의 투입량을 결정하였으며, 마샬안정도는 약 10,000N의 강도를 발현하였으며, 간접인장강도는 1.00~1.16 MPa의 범위를 나타내고 있었다. 혼합 및 다짐온도 조건은 실내 최적 배합설계에서 적용한 결과를 동일하게 적용하였다. 현재 전기로 산화슬래그는 제철 인근의 토목현장에 사용되고 있으며, PVB 필름과 차량 폐유리는 토목·건축용 자재로 일부 사용되고 있으므로 향후 도로현장이 추가 수요처로 안정된 소비가 기대된다. 본 연구에서 더욱 기대되는 것은 PVB 필름으로 개발될 중온형 아스팔트 바인더에 전기로 산화 슬래그 골재의 높은 강성과 고분말 폐유리 미분말의 충진성이 조화되어 기존 제품과 차별화된 친환경 고내구성 포장체의 한 분야를 개척할 수 있을 것으로 기대된다.