Megacasting involves molding large cast parts such as one-piece battery enclosures that eliminate seams. A new battery case, which traditionally consists of more than 60 parts, has been reduced to only five parts, making it possible to produce a high-quality, thin and light enclosure.

3D Friction Stir Welding (FSW) is being applied to two processes in the manufacturing of battery cases. The first is the process of joining parts made by megacasting to form the case enclosure, and the second is the process of joining the water jacket cover, which is necessary to provide the battery with cooling. The technology uses only the frictional heat between the rotating rod-shaped tool and the joint to soften and join the aluminum parts. 

“We believe that FSW is an important way to increase the flexibility and productivity of our products,” says Atsushi Yoshida, a Honda engineer working on the project. “As there is less damage to the base material from heat than with conventional welding, joints can easily be maintained at a high quality, making the entire battery case thinner and lighter while ensuring joint strength and airtightness.

“With battery case manufacturing, we focused on shortening the processes,” explains Yoshida. “By setting the joining conditions according to characteristics such as strength that vary by material and optimizing tool movements and other factors according to the shape of the joints, we were able to stabilize the quality of the joints while minimizing the amount of preprocessing required.”

Honda is also experimenting with a flex-cell production system where all assembly tasks are performed by one person in a fixed location. The revolutionary production system avoids stoppages of the entire line by arranging multiple identical facilities in parallel, stabilizes production volume, improves production efficiency by eliminating waiting time for product transfer, and realizes more efficient capital investment.

“Furthermore, it can accommodate future changes and evolution of production lines,” says Rikki Ito, a body production engineer at Honda. “Since each process has to be connected in order to build a flex-cell production system, communication among [operators] was the most difficult aspect of the project. We were able to realize this system by building good human relationships….”

When joining body parts, it is often difficult to join ultra-high tensile strength steel plates and decorative exterior plates (thin soft steel plates) using conventional spot welding, due to spatter and loss of strength which occurs because of the difference in thickness and materials.

To address this problem, Honda engineers have developed constant DC Chopping (CDC) welding technology that uses inverter-controlled current. “Conventional spot welding could not be used with light and strong materials, leading to an increase in the weight of body components, while CDC welding technology has improved material efficiency and weight reduction,” explains Xihao Tan, a Honda engineer who specializes in metal joining processes.

“At first, welding machine manufacturers said this technology was impossible, because of its very short time control of approximately 10 microseconds,” says Tan. “But, ‘if it doesn’t exist, we make it’ is Honda’s way. We did not give up, but worked out how to make it real.”