We have recently developed a novel processing method for enlarging the diameter of a hollow shaft locally through the combination of cyclic torsional load with axial compressive load. First, experiments were conducted under various processing conditions to measure the deformation in the part with an enlarged diameter. Next, numerical simulation was performed using the finite element method to investigate the distributions of stress and strain in the processed part. The effects of axial-compressive load and twist angle on deformation behavior in the enlarged part were characterized through the above experiment and analysis. In addition, the cracking mechanism in the processed part was also investigated.
A new upsetting-extrusion type tribometer has been developed to investigate the performance of lubricant coatings coated on the side surface of steel wire for cold forging. In this tribo-test, a lubricant coating is first destroyed by an upsetting process due to the free expansion of the material surface and then evaluated on the basis of extrusion. The frictional shear factor of the lubricant coating can be obtained by plotting the measured forging load and the position after forging of a centerline drawn on the billet in advance on the calibration curve obtained by Finite Element Method. A series of experiments was carried out using two types of bonderized coating and an applied alternative coating. It was revealed that the bonderized coating provides much better performance than the alternative coating when the lubricant coating is thinned by a large surface expansion during the extrusion.
A series of experiments has been carried out using an upsetting-extrusion type tribometer to investigate the effect of tool surface roughness on the friction behavior of lubricant coating. Experiments using a typical conversion lubricant coating and three types of alternative lubricant coating showed that the reduced peak height Rpk is a more appropriate parameter than the maximum height of the profile, Rz, to express the effect of tool surface roughness on seizure generation in cold forging. When Rpk is larger than the critical Rpk, the generation of seizure becomes more striking for the alternative lubricant coating than for the typical conversion coating. In this experiment, the critical Rpk changes with the type of lubricant coating and is in the range of 0.045-0.056 μm. When no seizure occurs, frictional shear factor hardly varies with the type of lubricant coating and surface expansion ratio.
The effects of forming conditions on wrinkling in the neck of stainless-steel pipes were investigated by experiments and three-dimensional finite element simulations. The materials used in this study are pipes used for automotive exhaust parts. When the axial or radial forming pitch of the rollers is large, the outside of the pipe is subjected to considerable compressive stress in the peripheral direction by the contact with the rollers. Simultaneously, the inside of the pipe is subjected to considerable tensile stress in the peripheral direction. Thus, the pipe is subjected to excessive localized forming, which causes the curvature to become uneven in the peripheral direction, thereby resulting in wrinkling. The number of contact points with the rollers was determined. It was shown that the optimum forming conditions could be easily determined to achieve short forming times and high dimensional accuracy.
An experiment with the aim of developing a technology for reducing noise during blanking was carried out using the advantages of an NC servo press machine. Results indicate that a reduction in blanking noise by approximately 10 dB is possible for mild steels, such as SS330, by adopting low-speed blanking, compared with the case of conventional blanking. In addition, blanking noise can be reduced by approximately 14 dB by slide-motion blanking, in which the speed of descent of a slide is reduced immediately before material separation, compared with the case of conventional blanking. Furthermore, when blanking is carried out while applying a counter pressure with a magnitude equivalent to the maximum shearing load at an appropriate timing such that neither a sharp decrease in load nor an increase in maximum shearing load is caused by the breakthrough phenomenon, a significant noise reduction of 24 dB becomes possible even for a 2-mm-thick SUS304 plate, for which blanking noise reduction has not been achieved by conventional methods.