2022 年 61 巻 1 号 p. 349-353
In this study, in order to simulate the shape fixing heat treatment after twisting of ultrafine wires, we developed a test method that enables heat to be applied to the wire with a strain equivalent to that applied during twisting. Cu–Ag alloy wire (Ag：10 mass％) with an diameter of d=0.02 mm was used as the material. The test jig was U–shaped, consisting of a straight part and a curved part, to facilitate the measurement of the spring–back angle. A tube furnace with an inner diameter of 25 mm was used for heating, and the heating temperature was set at four levels：200°C, 300°C, 400°C and 500°C. The heating time was varied from about 30 s to 180 s. When a rigid punch was used, it was found that the wire moved in the jig and could not be held stably. Therefore, we devised a punch that can be flexibly deformed using stainless steel foil. We found that the punch could hold the wire stably. Following conclusions were obtained as a result of tests using the devised jig. (1) It was shown that it is possible to evaluate the shape fixability of ultrafine wires by small die and stainless steel foil and heating the entire jig. (2) The test conditions in this study are short and high temperature compared to the stress relaxation test of terminal materials, because the twisted wire processing is assumed. It was found that Larson–Miller parameter was also useful to summarize the results in this test range.
