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.
