Fabrication Process for Ni-Ti Shape-Memory-Alloy Fine Tubes Used in Medical Tests

形状记忆合金细管不与生物体发生反应，可以在医疗和测试时增加扭矩传递特性，便于临床应用，同时减少患者的不适感，因此有望用于医学试验和治疗的导管和注射针。在本研究中，我们研究了镍钛形状记忆合金用于细管拉拔的最佳拉拔条件，镍钛合金是一种具有超弹性和形状记忆合金特性的优良功能材料，但与实际合金相比，它们的易成形性较差。为此，我们对易拉拔润滑剂的选择、拉深条件的优化(包括模具倾角和缩小面积)、拉深极限的确定、拉拔后和热处理后形状回复率的确定以及拉拔细管内外表面粗糙度的测定进行了研究。并用有限元方法从理论上讨论了拉拔过程中的应力应变分布。在此基础上，阐明了细管截面积减小约20%的单拉拔法和塞拔法是可行的，所获得的基础数据可有效地用于实际生产。

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 sing 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 optimization 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. Based on the results obtained, we clarified that sing and plug drawing with a reduction in the cross-sectional area of the fine tube of approximately 20% was possible; the basic data obtained could be effectively utilized in actual production.