A lightweight stamped frame with high production efficiency was developed for application in small motorcycles produced in large numbers. This development was motivated by the challenge to produce the lightest frame in this category of 150 cm3 displacement motorcycles, and weight reduction was pursued by the application of thin plate material for its production. To ensure the necessary strength and stiffness, high-tensile steel plates were used and the suitable cross-sectional profiles of the frames were newly devised. In the production using high-tensile steel plates, there exist rigorous restrictions in the orientation of parts partitioning, because they are highly resistible against the extension force and the press-forming of the parts with a large depth is considerably difficult. To cope with those restrictions, the forming parts were designed to have limited depths by employing the structure having flanges for welding at the upper and the lower portions of the parts enabling the coupling-type assembly along their horizontal direction while achieving enhancement of the strength, along their cross-sections, in the direction of the main load application. Moreover, the manufacturing time was shortened by normalized manufacturing processes and the simplified parts correction process brought by the application of the separated structure of the frame, which formerly was a mono-bone structure. However, when the stamped frame was constructed with the front-rear separation structure, the yield rate of the parts per plate went down and became an issue because of the complexity of the parts shapes. To cope with this issue, multiple parts blanking, in which multiple parts are cut out at one time, was introduced by adjusting the thicknesses of the yielding plate parts into a few standardized thicknesses. Consequently, the weight reduction was achieved while minimizing the increase in the manufacturing processes and the decrease of the yield rate, even though the frame parts were downsized and divided into a larger number of parts. Through these measures, a 30% reduction in weight and 30% reduction in process time were realized compared to the current stamped frame manufacturing processes, while maintaining the equivalent strength and stiffness of the frame.
Article of Honda R&D Technical Review Vol.25 No.2 (73 - 84)