冷拉拔超细Ni80Cr20合金丝卷曲因素分析

Ni80Cr20超细丝经冷加工后呈规则的三维螺旋卷曲状态。实验研究了拉拔角度、变形量、拉拔速度和模具定径区长度对超细丝材曲率的影响，制定了NiCr合金丝单模冷拉拔工艺。结果表明:随拉拔角度的增加，丝材曲率逐渐增加；变形量增加，拉拔角度为17时，丝材曲率没有明显规律，基本在0.56 mm-1左右，但拉拔角度为0时，丝材曲率逐渐增加；拉拔速度小于10 mmin-1时，曲率逐渐增加，大于10 mmin-1时，曲率增加趋势变缓，大于30 mmin-1曲率又有所下降；定径区长度越长丝材曲率越小。分析认为，NiCr丝材表面产生的附加切变形及切变层的流动速度的不一致性是丝材产生卷曲的原因，且曲率越大残余应力越大。为减小不均匀变形，冷拉拔工艺采用0拉拔、拉拔速度10 mmin-1、模具定径区长度为模具定径区直径的60%。

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.