It is important to use reusable plant resources effectively from the viewpoint of the reduction in carbon-dioxide emission and the sustainable use of resources in the future. In this study, injection molding using only steamed bamboo powder by means of an industrial machine was carried out as a basic study of the formation of wood plastic composites (WPC) and natural fiber reinforced plastics (NFRP) of high wood ratio. First, as an injection feature, pressure behavior in injection was investigated and the effects of the temperatures of the nozzle and cylinder and injection speed were examined. Secondly, injection molding was attempted, and the effects of nozzle temperature and injection speed on injection molding properties and the bending strength of the products were examined. The results show that the injection molding properties improved with increasing temperature of the nozzle and cylinder, and that it was possible to inject materials by adjusting the temperature of the material to 150℃ or more. Moreover, it was possible to realize good product filling into a mold perfectly under appropriate conditions. Also, it was possible to realize products with a bending strength exceeding 40MPa.
Various global environmental problems are caused by the volume consumption of fossil resources. As a solution to these problems, the development of wood plastic composites (WPC) and natural fiber reinforced plastics (NFRP) as substitutes for oil-based plastic is being furthered. However, the investigation of the environment resistance of injection molding products made from only wood-based material as a basic study of WPC and NFRP has not been carried out. In this study, a basic examination of resistance to water, heat-drying and light was performed on injection molding products made from only steamed bamboo powder. The results show that the products did not deteriorate after soaking in water for two weeks. Sectional area and weight increased after soaking in water, but they decreased by more than 10% after air-drying. Vickers hardness decreased after soaking in water, but it recovered after air-drying. Heat-drying at 80℃ for two weeks did not change the appearance of the products markedly. However, shrinkage between 4% and 8% was observed and weight decreased by about 5%. On the other hand, Vickers hardness and bending strength increased. By irradiation with ultraviolet rays, the color and shape of the products did not change markedly, but brightness markedly increased.
In this paper, we propose a new method of suppressing the wrinkle and torsional springback in sheet metal forming by FE simulation. The key technique is the determination of the optimum shape and height of drawbeads by an optimization technique. To demonstrate this technique for the forming of a Stepped-shape beam using a high-strength steel sheet, we show a new approach to evaluating the degree of wrinkle based on the curvature distribution in wrinkle areas. The optimization problem, where the objective function to be minimized is the degree of wrinkle and the design variables are geometric parameters of drawbead shape, is solved under several constraints on torsional springback, fracture, sheet thickness and so on. Using the thus-determined drawbeads, we have succeeded in reducing wrinkle and torsional springback markedly, which was confirmed in a Stepped-beam forming experiment.
Numerical simulation by a finite element method investigated the mechanism of roughness improvement in pierced holes using a press working (PW) punch. Two types of simulation, i. e. piercing and crack conjunction, were performed. Piercing simulation suggested that the PW punch suppresses both the generation and propagation of a crack in a sheet material around the punch edge because of the suppression of plastic strain localization, but promotes the generation and propagation around the die edge because of the high stress triaxiality induced. This result implies the suppression of the mismatch of the two cracks by the dominant crack from the die edge. Crack conjunction analysis based on bifurcation and stress triaxiality showed that crack mismatch increases the unevenness of a fracture area of pierced surfaces.
Products formed using a conventional cold-roll forming machine have cross-sectional profiles constrained to a single width along the longitudinal axis. Products with cross-sectional profiles varying in width in the longitudinal direction, namely, flexible cross sections, cannot be formed using a conventional cold-roll forming machine. In recent years, research and development of a flexible cold roll forming machine controlled by a Progressive Logic Controller (PLC) Unit to form products with flexible cross sections has been carried out in Japan and Europe. In 2011, we presented a forming method for several flexible channel sections and shape defects such as swell distortion, and edge buckling occurred during forming with this machine. In this study, the deformation process of strips in forming a flexible channel section with different widths using a four tandem flexible cold roll forming machine has been experimentally investigated from the relationship between the shape of blank sheets and the strain produced during passage through rolls. A flexible channel section is formed from a blank steel sheet of 0.5 mm thickness with the flexible edge lines. Moreover, the distribution of membrane strains and principal strains occurring at the flange and the web part during the forming of the flexible product are measured using a strain gauge. From these measurements, the mechanism of the occurrence of the swell distortion is clarified.
“Orowan's ω-function" in the theory of rolling is defined by a definite integral, and the general method of computing it is a time-consuming numerical integration. An alternative method is “zero-degree approximation" in the gradient of the roll surface, because, according to Orowan, the error in the ω-function is less than 0.01. However, this is inconsistent with the aim of his theory to “avoid all mathematical approximations," and the resulting error in overall rolling analysis has not yet been examined. In the present paper, we elaborate on the effects of the approximation by comparing it with numerical integration and second-degree approximation. The error of the latter in the ω-function is 0.0002 at the largest. Since errors in the roll force, torque, and forward slip are much smaller than the error in the ω-function itself, the error could be regarded as negligible even with zero-degree approximation in practical situations. The two equations of second-degree approximation provide reference values in place of numerical integration from the viewpoint of accuracy, and the computing time is sufficiently short for online use.