In this study to develop the process design of the extended forging process, the deformation behavior during flat-die forging has been investigated in detail. Regarding the square of the cross section, the relationships between forging conditions (initial forging shape, feed rate and reduction rate) and deformation are clarified on the basis of the results of 3D-FE analysis and the actual experiment. First, to improve the analytical accuracy, the laboratory equipment determined the sizes of the test bars that were heated. The cross section of the forging shape of the test bar was measured. Using this result, the coefficient of friction based on the analytical condition is determined. Using this analytical condition and an analytical model, in which the shape is the same as that of the actual specimen, the equation for predicting the forging shape is constructed, and it is confirmed that the prediction equation can be applied to actual forging. Using this relational expression, the equation for predicting the forging shape has been developed. The reduction of the next forging pass using the actual dimensions (thickness and width) can be calculated by employing the process design using this equation.

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Fine wires (with a diameter less than 0.4 mm) have been extensively used for precision machines and other devices. It is well known that finely drawn wires have a much higher tensile strength than thick drawn wires. In the drawing process, a large shear deformation zone with a hardened layer, known as the “additional shear strain layer”, is generated beneath the surface layer of the wire. It was clarified that the depth of this additional shear strain layer was about 0.04 mm for wires of various diameters. As the diameter becomes small, the area ratio of the additional shear layer increases. Hence, the additional shear strain layer is a factor contributing to the high tensile strength of fine wires. In this paper, the main purpose is to discuss the cause of the increase in the tensile strength of the additional shear strain layer metallurgically. Thus, the crystal orientation and microstructure was measured by the Electron Back-Scatter Diffraction (EBSD) method. It was ascertained that the crystal of the surface layer was subdivided more finely than the center, and then the tensile strength of the surface layer increased.

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Fine wires (with a diameter less than 0.4 mm) have been extensively used for precision machines and other devices. It is well known that finely drawn wires have a much higher tensile strength than thick drawn wires. One of the main factors for this characteristic has been determined to be an “additional shear strain layer”. The main purpose of this research is to clarify the relationship between the additional shear strain layer and the tensile strength of fine wire. In this paper, firstly the effects of the friction between the die and the wire and the die semiangle on the additional shear strain layer were investigated. It was ascertained that friction work was most effective for increasing the tensile strength of the additional shear strain layer and increasing in the tensile strength of the fine wire. Secondly, the additional shear strain layer generated in the multipass drawing was investigated. In the case of low-carbon steel, the increase in tensile strength of the additional shear strain layer was limited. On the other hand, the tensile strength of the additional shear strain continued to increase in high-carbon steel.

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Three aluminum alloy and steel sheets were joined with a self-piercing rivet. Self-piercing riveting can be applied to join steel and aluminum alloys having very different melting points because of plastic joining. The requisites for joining the three sheets are the driving of the rivet leg through the middle sheet, the flaring of the rivet leg in the lower sheet and the prevention of the fracture of the lower sheet. The joinability for various combinations of the three sheets was determined. When the thickness of the lower sheet is small and the total thickness is large, the rivet leg cannot be driven through the middle sheet owing to the relatively small length of the rivet leg. On the other hand, the lower sheet fractures for a small total thickness because of the relatively large length of the rivet leg. The joinability of three sheets can be evaluated as two sheets when the upper and middle sheets were made of the same material.

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