Ni-plated steel wire used for springs in electrical appliances and other devices has good corrosion resistance. It is demanded as an alternative to stainless steel wire in a mildly corrosive environment. However, surface gloss is required for this material. To achieve surface gloss in wire drawing, die wear can be a problem. It is common knowledge that drawing with back tension is effective in improving die wear. Tandem pass drawing, the method of drawing continuously through two dies, is expected to improve die wear because of the back tension provided by the drawing force in the first die. There have been several reports on wire diameter in the tandem pass drawing, but only a few reports on surface gloss. This research has been conducted to investigate the relationship between tandem pass drawing conditions and surface gloss. In addition, friction coefficients and die pressures that affect die lifetime have been calculated by the finite element method. It is found that surface gloss, as-processed by single pass drawing, can be attained by tandem pass drawing with a low maximum shear stress at the meeting point.
Recently, smooth bar and wire surfaces for office automation and automobile industry have been required to achieve high fatigue strength. In a conventional process, the drawn bar surfaces are smoothed by additional processes, such as grinding and polishing. However, these processes results in a higher production cost and a lower productivity. To produce ultrasmooth bars by only drawing, a new die was developed and evaluated. The new die had protrusions with hights of 20 - 60 μm in the bearing area. The protrusion die induced high contact pressure and shearing strain on the surface of the drawn bar. In this research, the carbon steel and aluminum bars were drawn using the new die. As a result, surface roughness under the maximum height of irregularities 1 μm was achieved using the new designed die.
We investigate the effect of drawing conditions on the drawn diameter in cold wire drawing by Finite Element Method. The mechanism of diameter variation was elucidated including the elastic deformation of the die, undershoot, diameter thickening during drawing and unloading springback. Undershoot was caused by the separation of the bar from the die at the beginning of the bearing zone during drawing, and it was the main reason for the variation in the drawn diameter. The undershoot was induced by the plastic deformation at the surface of the bar. We considered that it is caused by the tensile virtual residual stress and drawing stress at the surface of the bar in the axial direction. Thus, applying a low-approach semiangle to reduce the diameter of the second die is an effective method to reduce the diameter variation in tandem pass drawing.
A superplastic dieless drawing process that uses no dies or tools is applied to the drawing of a Zn-22Al superplastic alloy for fabricating micro-noncircular tubes such as square, rectangular and noncircular multicore tubes combined with inner square and outer rectangular section tubes. In this study, the effects of heating conditions such as heating length and the use or nonuse of a cooling device on deformation behavior are investigated. As a result, a micro-square tube with a 0.58mm side and a micro-rectangular tube of 0.75×1.3mm were fabricated after 3-pass superplastic dieless drawing. In addition, the fundamental deformation behavior of noncircular tubes combined with square and rectangular tubes during the dieless drawing process has been clarified experimentally. The cross-sectional shape of the noncircular tubes after the superplastic dieless drawing process tends to be maintained on basis of the similarity law in the case of a large heating condition compared with a narrow heating condition. Furthermore, a micro- noncircular tube, which has inner square tubes with a 335μm side, and an outer rectangular tube of 533×923μm were fabricated successfully after a 4-pass superplastic dieless drawing process. Consequently, it is found that superplastic dieless drawing for the fabrication of noncircular multicore tubes is quite effective.