• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.37-41
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• 1997

Tailored Blanks are defined as two or more separate pieces of sheet material having the same or dissimilar thickness and/or physical properties, joined together before forming. Its application is being increased especially in the automotive industrial area for the cost reduction, weight saving, and improvement of strength. In this paper, the deforming behaviour of the laser welded blanks with regard to different thicknesses and combinations are described through some experimental investigations on the formability of a door inner. To investigate how the combination of thickness and material property influences the movement of welding line, a series of laser welded T/B blanks are tested.

• Journal of Welding and Joining
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• v.18 no.3
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• pp.41-50
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• 2000

• Transactions of Materials Processing
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• v.9 no.5
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• pp.453-462
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• 2000

Tailor-welded blanks are used for forming of automobile structural skin components. The main objective of this study is to achieve weight and cost reduction in manufacturing of components. For successful application of tailor-welded blanks, design of initial welded blanks and prediction of the welding line movement are critical. The utilization of the backward tracing scheme of the finite element method shows to be desirable in design of initial welded blanks for net-shape production and in prediction of the welding line movement. First the design of the initial blank in forming of welded thick sheet with isotropy is tried, and it appears successful in obtaining a net-shape stamping product. Based on the first trial approach, the backward tracing scheme is applied to anisotropic tailored blanks. The welding line movement is also discussed.

• Transactions of Materials Processing
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• v.10 no.3
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• pp.193-199
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• 2001

Forming more than two parts of sheet metal in a single stamping operation lowers production costs, reduces weight, and heightens dimensional accuracy. The tailored blank (TB) is a laser-welded or mash-seam-welded sheet metal with different thicknesses, different strengths, or different coatings. Recently, automotive manufacturers have been interested in tailored blanks because of their desire to improve the rigidity, weight reduction, crash durability, and cost savings. Therefore the application to auto-bodies has increased. However, as tailored blanks do not behave like un-welded blanks in press forming operations, stamping engineers no longer rely on conventional forming techniques. Field try-outs are very important manufacturing processes for an economic die-making. In the field try-outs, the rounded geometries of tool and the drawbead shape and size in die face are generally modified when the forming defects can not be removed by the adjustment of forming process parameters. In this study, the field try-outs of tailored door inner panel are introduced and evaluated. The behaviours of laser tailored blank associated with different thickness combinations in the forming process of door inner panel are described focusing on terms of experimental investigations on the formability.

• Journal of the Korean Society of Safety
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• v.15 no.3
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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.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.17-23
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• 1997

A 3-D vision system is developed to evaluate blanks' line up and monitor gap and thickness difference between blanks in tailored blank welding system. A structured lighting method is used for 3-D vision recognition. Images of sheared portion in blanks are irregular according to roughness of blank surface, shape of sheared geometry and blurring. It is difficult to get accurate and reliable informations in the case of using binary image processing or contour detection techniques in real time for such images. We propoe a new energy integration method robust to blurring and changes of illumination. The method is computationally simple, and uses feature restoration concept, different to another digital image restoration methods which aim image itself restoration and may be used in conventional applications using structured line lighting technique. Experimental results show this system measuring repeatability is .+-. pixel for gap and thickness difference in static and dynamic tests. The data are expected to be useful for preview gap control.

• Journal of Welding and Joining
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• v.15 no.2
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• pp.54-63
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• 1997

For the purpose of establishing laser welding condition (laser power, welding speed and beam focus) and of evaluating tailored blanks for two kinds of thin steel sheets SPCC and SK5M using in the thin plate structure such as automobile, train, and so on, investigated their $CO^2$ laser weldability under various initial welding conditions. SPCC thin sheet showed good weldability under some welding conditions. But, high carbon steel sheet SK5M needed heat treatment after welding to obtain ductility of the welded joint. And next, tailored blank was tested through deep drawing to evaluate reliability of their obtained laser welding conditions. The forming depths by tailored blank were SPCC+SPCC=22-25mm and SK5M+SK5M=13-25mm.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.32-35
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• 1998

The material properties and forrnabilities of tailored blanks are evaluated by experimental tests. In the tensile test, the gradient of strength coefficients of the heat affected zone associated with the welded line width represents the quality of a welded part. In the hemispherical dome punching test, the plane strain state of the welded line is observed. In the squared cupping test, the thin side is stretched more than the thick side in the stretch mode, while both sides are similarly stretched in the draw mode. In the 2D draw test, FLCo is measured in a simple manner and the forming defects of the tailored blanks with the same thickness are found.

• Transactions of Materials Processing
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• v.8 no.1
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• pp.7-13
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• 1999

In this study, side panels were developed using the laser-welded tailored blank (T.B.) of both the same thickness and different thickness. At first, the formability of the same thickness T.B. was investigated to compare with one of the non-welded panel with respect to weldline movement and strain distribution in blank during the stamping process. Based on these results, we determined the weld line positions and the die step for T.B. forming of the blanks composed of different thickness combination. Then we made some stamping tryouts with selected types of blanks to investigate the formability of T.B. of the different thickness. During the tryouts, wrinkles were found in the a-pillar lower region which is under the deformation mode of the shrink flange. In the b-pillar region, fractures were also found. These defects have been reduced and corrected by controlling the blank design, the die faces and process parameters.