Development of Forming Technology for Circumferentially Tailored Thickness Structures by Multi-Directional Forced Lubrication Hydroforming

Motoki Sasaki･Hiroki Tsutsumi･Yunosuke Asahina･Hiroaki Kubota (Tokai University)

Differential thickness structures with circumferential thickness distribution were formed using multi-directional forced lubrication hydroforming, and bending-compression behavior was evaluated through FEM analysis. Under three-directional and four-directional lubrication conditions, both the maximum load and absorbed energy were improved compared with conventional hydroforming. The results indicate that controlling the circumferential thickness distribution by forced lubrication can effectively enhance crash performance. Furthermore, the proposed method demonstrates the potential to achieve both lightweight structures and improved crash safety performance in automotive structural members.

Study on the Prediction Accuracy of Outer Panel Distortion Caused by Bead-Applied Stiffeners

Tkashi Iwama･Yoichiro Onishi･Toyohisa Shinmiya (JFE Steel)･Ayaka Honda･Yujiro Mitsui (SUBARU)

The application of bead-applied stiffening materials has been investigated to improve the panel stiffness of automotive outer panels. However, panel distortion caused by material shrinkage during the paint baking process is a critical issue. For vehicle implementation, it is necessary to determine appropriate bead dimensions (width and thickness) that do not induce distortion, but no reliable prediction method has been available. Through prototype testing of an actual vehicle door, it was found that incorporating material property changes during thermal curing significantly improves distortion prediction accuracy.

Quantitative Evaluation of the Effects of Single Blowhole Size and Through-Thickness Location on Stress State in Aluminum Alloy Welded Joints

Sogo Takuno･Eita Niisato･Kazumi Otake (Toyota Motor)

The application of aluminum alloys in automotive body structures has increased in recent years to achieve vehicle weight reduction. However, welded joints in aluminum alloys often exhibit lower strength than the base material, making the weld zone a potential structural weak point. As a result, manufacturing defects such as blowholes can significantly influence joint strength and remain a critical issue for quality assurance. Conventional evaluations have primarily focused on defect size and porosity. However, even defects of identical size can produce different stress states depending on their position within the cross section. This study aims to quantitatively clarify the combined effects of blowhole size and location on joint strength. Linear finite element analysis was conducted on aluminum alloy welded joints with varying blowhole diameters and positions to evaluate stress at crack initiation sites. In addition, machine learning was applied to efficiently analyze trends across multiple conditions. Experimental validation was performed through static and fatigue tests using specimens with artificial defects introduced by drilling. The results indicate that defect position has a greater influence on stress concentration than defect size. The combined evaluation of size and position enables a more systematic assessment of blowhole effects on joint strength.

Efforts to develop door deformation prediction technology in the paint drying process

Kazuki Shouyama (TOYOTA Auto Body)･Shinich Takezoe (TOYOTA AUTO BODY R&D)

In vehicle manufacturing, the fit of the body and doors is a crucial control item for ensuring exterior quality. Regarding the phenomenon of door shape change (hem misalignment) before and after the paint drying process, which is an influencing factor, we have conducted verification of the occurrence mechanism using component evaluation and developed a prediction technology using simulation, which we will now introduce.

Development of Gears with Low Heat Treatment Distortion

Yuudai Ookawa･Gou Katou･Makoto Maeda (JATCO)

Drivetrain gears acquire high strength and wear resistance through heat treatment, but the resulting thermal distortion necessitates a subsequent deformation correction step. Hollow-structured internal gears for planetary gear systems are particularly susceptible to severe deformation. To address this challenge, we have developed a novel combination of materials and processing methods that achieves both high strength and low distortion. This approach enables the production of high-precision gears while entirely eliminating the correction process.