Development of Laser Welding Pressed-frame for Small Scooters Considering High Production Efficiency

摘要

The laser-welded pressed-steel frame made of the high-tensile-strength steel sheet and suitable for high efficiency production has been developed for small scooters. In majority of the conventional designs, the frame of small scooters is composed of a large number of steel pipes and stamped parts complexly welded together, requiring a number of welded joints. As a result, since the welding length increase and the dimensional error of the frame body after welding tends to be large, a correction operation in a post process is required. This has been one of the factors preventing further enhancement of production efficiency. In an attempt to cope with this issue, we have chosen to apply the pressed-steel frame construction using the high-tensile-strength steel sheet, which has been applied to small motorcycles, to small scooters. In addition, we replaced the spot welding with more efficient laser welding to further enhance productivity. The optimum cross section design taking advantages of the pressed-steel frame construction permits more gradual changes of cross sectional area than the conventional steel pipe frame, allowing dispersing of stresses in the frame. Consequently, the frame reinforcement members are reduced while maintaining the same or higher strength as the steel pipe frame, realizing a 39% reduction of number of parts and 10.7 kg reduction of frame weight. The torsional stiffness is also increased by 4% from the conventional design, contributing to the riding comfort and the steering stability. The production time per frame is reduced by 43% from the conventional steel pipe frame.