Analysis of crimp factors of ultra-fine Ni80Cr20 wire under cold drawing

The cold drawing of ultrafine Ni80Cr20 alloy wire often presents a regular three-dimensional helical crimp state. The effects of the drawing angle, working ratio, drawing speed and sizing section length on the curvature of NiCr alloy wire were studied. The NiCr ultrafine wire single-die cold drawing process was developed. The results show that with the increase of the drawing angle, the ultrafine wire curvature gradually increases; when drawing angle is 17, the curvature of the wire does not change significantly with increasing the working ratio, and it is about 0.56 mm-1. However，when the drawing angle is 0, its curvature gradually increases with the working ratio; when the drawing speed is less than 10 mmin-1, the curvature gradually increases, however, when the drawing speed is between 10 mmin-1 and 30 mmin-1, the increasing trend becomes slower; but it has a downward trend when the drawing speed is more than 30 mmin-1; meanwhile, with the sizing section length increases, the curvature value decreases. Analysis suggests that the reason why ultrafine wire crimp is that NiCr ultrafine wire surface additional shear deformation produced by cold drawing and flow rate inconformity of shear layer，meanwhile, the greater curvature, the greater residual stress. To reduce the inhomogeneous deformation of the ultrafine wire, the cold drawing process should use 0 to draw, the drawing speed should be 10 m min-1, the sizing zone length of diamond die should is 60% of diameter of die sizing area.