It is presently thought that, in riveting, plates are fastened by the rivet head, as well as by the pressure between the rivet axis side and plates in the rivet hole as a result of the spreading of the rivet axis. However, the fundamental characteristics of these joint forces have not been clarified yet. Therefore, to set guidelines for obtaining a high joint strength in riveting, we examined the fastening force for plates by the rivet head and the joint force between the rivet axis and plates by carrying out experiments such as separation and rotation tests on joined plates, push-out tests on the rivet axis side, and the elastic-plastic FEM simulation of riveting in the case in which the rivet material is much softer than the riveted plate. The results show that, in such a case, the fastening force for the plates by the rivet head is very small, so that the plates are primarily joined on the rivet axis side. The relationships of punch shape with springback of rivet and joint force on the rivet axis side were also obtained from these results.
The relationship between the mechanical properties and microstructure of an extrafine high-speed steel wire has been studied. The microstructure of the extrafine wire mainly consists of a ferrite parent phase, MC and M6C carbides. From the results of tensile tests, some of the wires indicate a discontinuous yielding behavior. These wires with a discontinuous yielding behavior indicate superior elongation compared with typical yielding wires. The occurrence of discontinuous yielding is strongly affected by the volume fraction of the carbides as well as size distribution. The discontinuous yielding appears in the case of a small volume fraction (<30%) of the carbides, or a small volume fraction of the finer carbides (<2μm). This implies that the carbon content in the matrix phase is higher in the material that shows the discontinuous yielding behavior. That is, the dissolution of the carbides leads to a higher carbon content in the ferrite matrix; thus, carbon solute atoms pin the dislocations, which contribute to the typical yielding behavior. Therefore, the productivity and the drawing process of the extrafine high-speed steel wire can be expected to have an improvement by controlling carbide size as well as volume fraction.
The mechanisms responsible for the formation of rectangular and trapezoidal bars by an extrusion process in which dies are inclined at various angles were investigated using numerical simulations. The greater the die inclination angle or the aperture exit angle, the smaller the radius of curvature of the extruded bar. The calculated radius of curvature agreed well with the radius observed in experiments. The particle flow pattern, one of the outputs of the simulation, was used as a basis for investigating the mechanisms of curvature generation. When the die inclination angle was increased in the case of the extrusion of rectangular bars, the volume of dead metal increased, causing material flow in the plane perpendicular to the extrusion direction. This material flow gave rise to curvature of the extruded bar. It was also found that when the cross section was trapezoidal, the asymmetry of the container aperture caused differences in material flow velocity between the top and bottom portions; these differences affected the curvature.
A cold deep drawing process for commercial magnesium alloy (AZ31) sheets was developed. The commercial sheets were successfully formed into circular cups using cold deep drawing by optimizing the annealing temperature of the sheets, i.e. a limiting drawing ratio of 1.7 was attained for an annealing temperature of 500 °C. The increases in elongation, n-value and r-value, and the decrease in flow stress effective in the improvement of drawability were obtained for the annealing. The apparatus for cold deep drawing operation without heating becomes much simpler than that for the conventional warm operation. The effects of the lubricant, the clearance between the die and the punch and the corner radius of the punch on the drawability were examined. The limiting drawing ratio was increased by applying force onto the edge of a blank through the die corner. In addition, cold deep drawing of magnesium alloy square cups was performed. It was found that comparatively shallow magnesium alloy cups are satisfactorily formed at room temperature without heating.
The objective of this investigation is the forming of a flange with grooves similar to that of a V-belt pulley or a cogged-belt pulley by a new method of applying reverse redrawing. The first step of the survey is a finite element analysis of individual forming processes. Next, the relationship between experiment and simulation is examined in terms of the load-stroke curve and the shape of the product. This method is composed of four processes. The first process is deep drawing, the second process is compressing the end of the drawn cup, the third process is embossing to make a groove at the end of the cup, and the fourth process is forming a flange with grooves by reverse redrawing. Furthermore, each process is simulated, and the condition that makes possible, "formable area", can be attained.
The deformation behavior in superplastic dieless tube drawing is studied numerically by the finite element method (FEM). The FEM with coupled thermo-mechanical analysis is conducted considering strain rate sensitivity to clarify the effect of dieless tube drawing conditions such as tensile speed and material properties on the deformation behavior of the tube. In the calculation, the material properties were dealt with as a function of temperature in a special subroutine, whose constitutive equation considering strain rate sensitivity and strain hardening was used, and was linked to the solver. FEM results for both heat transfer and the deformation profile are in good agreement with experimental results. Therefore, the validity of FE modeling of superplastic dieless drawing is demonstrated. In addition, the effect of material properties m and n values on the deformation profile is demonstrated numerically. As a result, a higher m value constrains the local instability deformation. In cases where the m value is high, the n value has little effect on the deformation profile. Consequently, it is found that analysis considering strain rate sensitivity is important for the prediction of the deformation profile in the dieless drawing process.
Three kinds of extrusion-type friction tests were performed to evaluate friction shear factors at different kinds of extrusion dies, or at the backward extrusion punch. The first kind is a forward rod-backward can extrusion type friction test for evaluating friction at a taper die. The second kind is a new friction test based on forward rod-backward can extrusion with a conical die providing projections. The third kind is a friction test based on combined forward- backward straight can extrusion. The third kind was modified to evaluate friction at the bearing of a backward extrusion punch quantitatively. The lubricity of conversion coating lubricant for low-carbon steel, the lubricities of conversion coating lubricant and various viscosity mineral oils for aluminum alloy were evaluated. The lubricities of the different lubricants were compared for each extrusion type. Surface expansion ratio does not always affect friction shear factor directly. The lubricity of conversion coating is almost the same for each extrusion type. On the other hand, the lubricity of mineral oils is markedly affected by the extrusion type. In the case of extrusion in which oil is difficult to retain, the lubricity decrease, and adhesion occurred.
In this study, the effect of tool modeling accuracy on finite-element simulation of a square cup deep-drawing process is examined. First, the accuracy of tool modeling by a conventional approach, in which polyhedral surfaces are used, is compared with that of an alternative one, in which the quadratic parametric surfaces proposed by Nagata (Nagata patch) are used. It is clear that the Nagata patch yields a much more accurate tool model than the polyhedral surface in terms of tool shape and tool normal vector. Next, the simulations of the square cup deep-drawing process are carried out for various numbers of tool elements. It is clarified that a polyhedral tool with at least 10 patches at the die shoulder is required to carry out appropriate simulations. The simulated result of the Nagata patch tool with two patches at the die shoulder corresponds well to that of the polyhedral tool with more than 10 patches. From this point of view, it is concluded that the number of tool elements can be markedly decreased by using the Nagata patch tool. In the present case, the number of tool elements can be reduced to about 10% that of the polyhedral tool.
Joining two or more parts by forming is an economical method of manufacturing complex-shaped products. In this study, we discuss a form-joining process to provide high torsional strength for shaft products. Experiments to join a shaft of quenched steel and a thick flange of mild steel were carried out. Joining was achieved by forming a hole in the flange with a serrated shaft. The formed serrations had fill-up ratios of 50∼70 % and were 1.4∼1.8 times harder than the machined serrations due to work hardening. The distribution of hardnesses agreed well with those of the fill-up ratios. As a result of torsion tests, the maximum torque increased in proportion to joining length. Torsional strength was estimated using the shear strength of the flange material. Furthermore, the joint was compared with a mechanically fitted joint having the same shape and joining area, which proved that the joint created by forming had higher torsional strength than that created by fitting.