In the press forming of various small-quantity products used in social infrastructure products, the increase in forming cost and die adjustment based on expert know-how have become issues. For these reasons, the development of flexible forming technology has been promoted. In this study, from the application viewpoints of high accuracy and cost reduction for the impeller used in the pump and the compressor, we have developed an incremental method that sequentially repeats bend and twist forming accomplished with a pair of straight punches and a pair of clamps. Since this method incrementally forms the material, the shape error of the final shape becomes the accumulation of forming errors in each forming element. Thus, in the forming of each element, in-process shape evaluation and feedback to the forming conditions are performed. To achieve this, we constructed a process control system with shape correction and a condition database, using the amount of bending and twisting, and the spacing between the two linear punches as process control factors. In addition, we developed new forming equipment with the process control system and verified its use in the forming of impeller blades (approx. overall length 210 mm). As a result of the shape evaluation of the formed blades, while an error of 0.5 to 1.0 mm occurred at the edges of the segment line, the error in almost regions of the formed blades was within ± 0.5 mm. Thus, it was confirmed that forming can be performed flexibly without using a pair of punches and clamps.

The small diameter bending of thin-walled copper tubes which are used for heat exchanger is desired to reduce the size and weight of products. In this study, a series of experiments were conducted to investigate appropriate tool shapes, such as that of a mandrel, for preventing wrinkling, cracking and flattening in rotary draw bending. A C1220 tube with a diameter of 7 mm and a thickness of 0.21 mm was used in the experiments. The bending radius was twice the tube diameter. Plug and ball mandrels were used. The effects of the mandrel position, the mandrel shape, and the clearance between the tube and the mandrel were investigated. As a result, moving the mandrel position forward prevented wrinkling and flattening, but moving the mandrel position excessively caused cracking. The mandrel position at which the wrinkle and crack occurred varied depending on the mandrel shape and clearance. By optimizing the tool shape, wrinkling and cracking were prevented, and flatness was reduced to less than 15% for the plug mandrel and 5% for the ball mandrel.