Drawing of Ni–Ti shape-memory-alloy fine tubes used in medical tests

The utilization of shape-memory-alloy fine tubes in catheters and injection needles for medical tests and treatments is expected, since they do not react with organisms, and their torque transfer feature can be increased at the time of medical treatment and tests, facilitating easy clinical application, while reducing the patient’s discomfort. In this study, using Ni–Ti shape-memory-alloys, we investigated the optimal drawing conditions for the sinking and plug drawing of fine tubes. Ni–Ti alloys are excellent functional materials with ultra-elasticity and the characteristics of shape-memory-alloys; however, they are inferior with respect to ease of formability compared with practical alloys. Therefore, we conducted studies on the selection of an easy-to-draw lubricant, the improvement of drawing conditions including die angle and reduction of area, the clarification of drawing limits, the determination of shape-recovery percentages after drawing as well as after thermal treatment, and the determination of the inner- and outer-surface roughness of drawn fine tubes. We also discussed theoretically the distributions of stress and strain during drawing using a finite element method.