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Article history:A cowl cross is a part of the car's instrument panel used to maintain the rigidity of the vehicle body side. The application of laser welding has the benefits of speed and thermal deformation compared to arc welding. An ultra-high strength steel sheet is used to reduce the weight of the vehicle body parts. Generally, formability of such a steel sheet is poor because its elongation is very low. For this reason, a method for cold forming of an ultra-high strength steel sheet is required. This paper describes how to improve the formability and weldability of the ultrahigh strength steel sheet. Mechanical tests of this material were also performed to evaluate the welding properties of CO 2 (GMAW) and those of laser welding.

[3,4] . [6,7] . 본 연구에서는 Journal of the Korean Society of Manufacturing Technology Engineers 26:1 (2017) 59~65https: //doi.org/10.7735/ksmte.2017.26.1.59 J. Korean Soc. Manuf. Technol. Eng. ISSN 2508 ARTICLE INFO ABSTRACTArticle history:A seat track product is a car seat part that provides a base for vehicle seats. An ultra-high strength steel sheet is used to reduce the weight of vehicle body parts. However, the formability of an ultra-high strength steel sheet is poor because of its very low elongation and very high elastic deformation. For this reason, a new forming technology of an ultra-high strength steel sheet is required. The influence of spring-back of seat track parts on the shape freeze in forming processes was investigated to be solved by adjusting the appropriate tool design such as minus clearance between punch and die, and punch angle. This paper describes how to apply the spring-back prevention technique for improving shape freeze by using the ultra-high strength steel sheet with 980MPa to develop lightweight seat tract parts.

FIGURE 1. Two conventional arrangements of AC-LEDs for AC-direct LED driver: (a) Anti-parallel string configuration (anti-parallel LEDs) and (b) Bridge-rectifier configuration (rectifier LEDs).

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