In the press cutting of a square pipe, the effects of cutting parameters such as the top angle of the punch, tool clearance, wall thickness, side length and cut length on the distortion of the cut section and its surface decline towards the axis are discussed. The cutting force is also measured. The horizontal change in diagonal length is kept small, while the vertical one is increased with either decreasing cut length or increasing top angle of the punch. The higher the first peak force, which appears after cutting through the top corner thickness, the larger the distortion. For smaller distortion, the top angle should be smaller, the cut length should be longer and the thickness should be larger. The surface decline is affected by the ratio of the tool clearance to the wall thickness. To decrease the decline, it is suggested that the axial force applied during cutting work should be applied by 3% of the maximum cutting force.
An experimental method of applying in-plane combined tension-compression stresses to a sheet specimen is proposed. Comb-shaped dies are specially designed for the tension-compression test and are installed into a biaxial stress-testing machine developed by one of the authors [Kuwabara and Ikeda: J. JSTP, 40-457 (1999), 145-149]. To check the usefulness of the testing apparatus proposed in this study, we carried out biaxial stress experiments using a high strength steel with a tensile strength of 440MPa, and detailed measurements were made of the plastic work contours as below and the directions of the incremental plastic strain vectors at different levels of work-hardening for linear stress paths in the second and fourth quadrants of the principal stress space, as well as in the first quadrant. We found that the measured work contours are similar in shape, and that the directions of the incremental plastic strain vectors remain almost constant at each constant stress ratio. The work contours and the directions of the incremental plastic strain vectors are in close agreement with those predicted using the Hosford or Yld2000-2d yield function.
The split Hopkinson pressure bar test is numerically simulated, in which the assumed mechanical property of the specimen is compared with that calculated from the stress waves in incident and transmitted bars. The method of processing the stress waves in the bars is investigated to improve the accuracy of the stress-strain curve. The stress-strain curve of the specimen depends on how one determines the commencement time of stress pulse in the elastic bars. When the commencement time of stress pulse is determined using an appropriate threshold value of stress, both the elastic and plastic properties are close to the assumed ones. On the other hand, when the commencement time of stress pulse is determined by the speed of elastic wave propagation, the elastic modulus is considerably underestimated. Considering that both the elastic and plastic behaviors are well described quantitatively, the method using the threshold value of stress in determining the commencement time of stress pulse could be suitable for obtaining more accurate stress-strain curve.
Demands for personal digital assistants (PDA) require them to be of low profile, lightweight, and to have low power consumption. To fulfill these demands, it is necessary to develop a backlight unit that has features of low power consumption, high brightness, and high efficiency. The light source in a backlight unit has a light-guide plate with microreflection dots, which is a very important component. The smaller the microreflection dots and the higher the aspect ratio, the brighter the screen. The result of a simulation revealed that it is possible to improve the brightness of the light-guide plate by forming the shape of a truncated cone with a taper angle range of 68 to 78 degrees. However, by using the existing machining technology, it is difficult to form the microreflection dots into such a shape. Thus, we developed an innovative UV diffraction exposure method to fabricate tapered microstructure. We fabricated a light-guide plate using the UV-LIGA process by the UV diffraction exposure.
Recently, high-torque AC servomotors have been developed, and NC servo press machines equipped with these servomotors have started to become commercially available in Japan. The NC servo press machine has a programmable function to fully control the position and velocity of the slide on the machine. In this study, we experimentally examined the possibility of the burr-free shearing of an A5052 aluminum alloy sheet using such a press machine. As a result, it was clarified that burr-free shearing, which requires three processes using a conventional machining method, such as counter blanking, can be accomplished in one process using a common single-station die. The experiments also revealed that, when a punch or die, the edge of which is rounded with a radius range of 0.2-0.3 mm, is used, the range of conditions under which a sheared surface without burr generation can be obtained is wider than that for the case in which a sharp-edged tool is used.
In this paper, we gives a describe of the pushing shear process on a kraft paperboard. The cutting line force of a center bevel blade on the kraft paperboard was measured using a load cell and its cutting deformation was observed using a CCD camera to reveal the basic effects of the tip angle and tip thickness of the blade on the surface failures of the kraft paperboard. A deformation flow in the side view of the kraft paperboard was observed with respect to the indentation depth of the blade by varying the tip angle and tip thickness of the blade. From the experiment, the following results were obtained. 1) There are certain critical values of the tip angle αC and the tip thickness wC at which the inflection load response disappears and also the surface failures are restricted. 2) After the time when the surface layer of the kraft paperboard is cut off, lateral shear flow occurs in an in-plane layer of a laminated structure. The deformation flow and its resistance are strongly affected by the delamination and raised upper layer.