Mandrel drawing and plug drawing of shape-memory-alloy fine tubes used in catheters and stents

Drawing technology used to fabricate tubule catheters and stents for medical use, in which shape-memory and superelastic characteristics are applied, was studied. Processing conditions, improvement of dimensional accuracy and reduction of the roughness of the inner surface of the tube, which are required for the fabrication of small-diameter and thin-walled tubes, were examined by drawing experiments and using a finite-element method. Since the plastic formability of the shape-memory-alloy is extremely low, the possibility of fabricating high-quality fine tubes by mandrel drawing and plug drawing was examined. We determined an optimal shape for the plug, with which breakage frequency during plug drawing is suppressed to as low as possible, using a finite-element method, and fabricated plugs used in the experiments, based on the obtained optimal shape. For mandrel drawing in which a copper wire was used as a mandrel, drawing formability, change in the wall thickness of the drawn tubes was examined. We clarified that the fabrication of fine tubes used in catheters and stents is possible by means of plug drawing and mandrel drawing.