Ultrasonic reflection characteristics that vary with wrinkling enable the detection of wrinkles during press forming. In this study, we investigated the influence of wrinkles on ultrasonic reflection characteristics by Finite-Difference Time-Domain (FDTD) analysis and experiments with model specimens. The wrinkle shape on the model specimen was made into a trapezoid by electric discharge machining. FDTD analysis was performed using the analysis model that reproduces experimental situations. The first reflection wave occurring at the lower surface of the upper die affected the ultrasonic characteristics, which changed with wrinkle wavelength. The effective diameter of the ultrasonic probe and the irradiation diameter of the ultrasonic wave also affected the ultrasonic reflection characteristics. In the region where the ratio of the irradiation diameter of the ultrasonic wave to the wrinkle wavelength is 0.3 or more, the reflection intensity depends on the irradiation position of the ultrasonic wave. The irradiation position at the maximum reflection intensity varies depending on the fraction of the effective diameter of the ultrasonic probe and the wrinkle wavelength.
In cold forging processes, friction between a material and dies strongly influences the material flow, forging load, and damage to the dies. Therefore, several methods of evaluating friction have been proposed. However those methods are not well simulated for the severe conditions occurring in actual forging processes. In this study, a new method of evaluating friction coefficients is proposed. The method applies a developed die set with a rotating die in the ring compression test. The unique feature of the die set is a die rotating at a very slow angular velocity which makes it possible to measure both load and torque. By a combination of measured load and torque, friction coefficients can be monitored throughout the measurement process. Friction coefficients were measured for four types of lubrication: mineral oil, cold forging oil, dry-in-place, and bonderizing lubricants. These results confirm that the proposed method enables us to measure friction coefficients under cold forging conditions.
A processing technology for microholes in sheet metal is required for small electronic devices such as micropumps. Recently, hole processing by electromagnetic piercing has been considered. The flat-plate one-turn coil we use can generate high electromagnetic power, because a strong magnetic field of high frequency can be formed in a narrow linear region. In this report, the results of many simultaneous electromagnetic piercing experiments for different diameters (dh ) and different thicknesses (τ) of A1050-H24 are presented. The minimum energy of piercing (Wp ) and the characteristics of deformation are determined from the results. The relationship between Wp and dh /τ is indicated by one curve. A negligible amount of burr after piercing is observed, but the width of shear droop was 80% of the thickness. A method to determine the maximum magnetic pressure at piercing (Pm ) from the maximum current Im at Wp is described. Pm and Wp exhibit the same tendency with respect to dh . As mentioned above, the results are discussed with respected to both electrical and mechanical engineering.