Satoshi Kajino

Effect of Additional Shear Strain Layer on Microstructure and Tensile Strength of Fine Wire

The mechanical and electrical applications of fine wires (D = 0.1 mm) has become more widely spread. In general, it is well known that fine drawn wires have high tensile strength while maintaining ductility. It has been determined that a hardened layer of around 0.04 mm in depth, referred to as the “additional shear strain layer,” is generated beneath the surface layer of the wire, and this additional shear strain layer affected the tensile strength of the fine wire. As an origin of this phenomenon, it was ascertained that the microstructure of surface layer was finer than that of center layer. The purpose of this paper is to investigate the effect of die angle on the microstructure and the tensile strength of the additional shear strain layer. The tensile test was performed as the surface layer was thinned by electro-polishing, and the crystal orientation and the crystal grain were measured via EBSD. As a result, it was ascertained that die angle affected the tensile strength and crystal grain refinement of the additional shear stray layer.

Development of Shearing with Torsion for Restricting Work Hardening by Torsion

Shearing is a commonly used method of cutting materials for former from bars or wires. However, the cut face shape of a material after shearing is poor because droop is formed at the edges of the cut face. It is necessary to alter the cut face shape after shearing for use in former. In this research, we developed a new shearing method in which shearing is combined with twisting to achieve a short cutting time with a length high accuracy and a cut surface without droop. Annealed low-carbon steel bars (diameter: 1.96 mm) were used for the experiment. The specimens were twisted after a static shear force was applied to the bar. As a result, the droop height decreased markedly. In addition, to restrict the work hardening area by applying torsion, the bar was twisted after shear stress, which was slightly less than the yield stress, was generated at the clearance with the loading of a large static shear force. The equivalent stress at clearance exceeded the yield stress, when the torsion was small because the shear stress was large. Therefore, the twisted area became narrow, and work hardening was restricted.

Improvement of Straightner in Tension Annealing and Rotational Blade Straightner for Superfine Wire

Higher straightness of superfine wires of 0.1 mm or less in diameter is in demand for recent development of electronic devices.A rotational blade straightener is effective for straightening superfine wires. It is particularly effective for straightening coiled wires because the straightener can bend wires along the longitudinal and circumferential directions. We found that a higher rotational speed of blades, lower feeding velocity, and gradual decrease in curvature ratio during straightening were very effective in producing excellent straightness in rotational blade straightening.Tension annealing is also one of the popular methods to straighten superfine wires. The tension annealing has a higher level of straightening effect without surface damage. The phosphor bronze and the tungsten superfine wires are used in this study. We observe that the initial radius of curvature, roundness and work hardening exponent are very important factors to make excellent straightness in tension annealing.