• 한국안전학회지
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• 제15권3호
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• pp.7-13
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• 2000

Forming characteristics of tailored blank are mostly effected by the welding method. Recently, laser welding is widely used for the tailored blank. However, tensile and forming characteristics vary due to welding conditions such as welding speed, heat flux etc. The objective of this paper is to evaluate the effect of welding speed on the tensile and forming characteristics of laser welded tailored blank. For this purpose, tailored blank specimens with different welding speed were prepared and tensile tests were performed. Also forming tests such as LDH and OSU test, were performed to evaluate the effect of welding speed on the forming characteristics. Finally, forming limit diagrams were obtained for different welding speed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 제2회 박판성형심포지엄 논문집 박판성형기술의 현재와 미래
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• pp.121-130
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• 1998

In order to analyze the forming characteristics of laser welded tailored blanks, laser welded blanks of different thickness and strength combinations were prepared and tensile, stretching, stretch flanging and deep drawing tests were done. The tensile elongation perpendicular to the weld line, stretching and stretch flanging formability decreased with increasing the deformation restraining force (strength ${\times}$ thickness) ratio between two welded sheets. The tensile elongation along weld line reached a value above 90% of the single sheet's elongation. Stretch flanging formability was reduced to approximately 10% of the single sheet value when the deformation restraining force ratio between two welded sheets was increased to two. Weld line movement of deep drawing test specimens was also affected by the strength ratio of the combined sheets, the weld line location and forming conditions. In all forming modes of tailored blanks, excessive weld line movement resulted from strain concentrations at the weaker sheet and resulted in fracture of the weaker side.

• 한국레이저가공학회지
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• 제9권2호
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• pp.1-9
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• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range $({\Delta}K)$ region and faster in high${\Delta}K$ region than that of the base metal specimens. The slant crack angle slightly influenced the crack propagation of the TB specimen of 2.0+2.0mm thinkness.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.339-344
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• 1999

For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimen and base material was different, and it is increased by 25% when pre-strain was applied. The crack propagation rate was noticeable decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness.

• Journal of Welding and Joining
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• 제16권1호
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• pp.77-87
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• 1998

This paper deals with the effect of laser welding parameters on the weld formation. Thin steels for automotive application were prepared so as to be welded with high power carbon dioxide laser system. Major process parameters were position of focus and travel speed. The effect of shielding gas was also discussed by employing the high speed photometry. Test results showed that the optimal position of focus varied in accordance with the joint configuration; bead-on-plate, butt or lap welding. It was recommended that the position of focus for the lap welding be located at slightly inner part of the material to be welded. In this case, however, it was noticeable that the weld penetration ratio, d/t$_{0}$ dropped drastically at the critical region. Results also demonstrated that both the bead width and penetration reduced as the travel speed increased. The penetration ratio showed two distinct regions; stabilized zone at the lower range of the travel spped and sudden drop zone at the higher range of travel speed. Lower limit of the penetration for acceptable weld was proved to be about 90% of the parent metal thickness based on the physical properties of the weld. Mixed gas application for both the shielding of molten metal and laser induced plasma control was recommended as far as the penetration was concerned.d.