Ultrasonic impact treatment （UIT） is recently being used in several manufacturing processes. UIT is a process in which ultrasonic vibration is used to throw pins onto a metal surface. In order to clarify the mechanisms of deep compressive residual stress in UIT, the effects of the pin tip radius on residual stress distributions are analyzed by the dynamic explicit finite element method. The sonotrode vibration amplitude is 25 μm and its frequency is 20 kHz. The pin velocity accelerated by the sonotrode is about 4. 6 m·s-1 at the first impact. The depth of residual compressive stress stays nearly constant for pins of various tip radius （1. 5, 3, 8, 12mm） after the first impact. During 10 ms, eleven impacts occur between the pin and the metal surface in the case of using an 8 mm-tip-radius pin. The pin velocities depend a great deal on the sonotrode velocity in the collision range from 4 m·s-1 to 16 m·s-1. The depth of residual compressive stress increases with increasing impact number. After 10 ms, the depth of residual compressive stress is about 2. 5 mm when using an 8 mm-tip-radius pin and it increases with increasing tip radius.
The typical sliding conditions at the fracture-risk positions in press forming of automotive parts were identified by FE analysis and laboratory-scale sliding tests. The investigated sliding conditions fall into three categories：the inflow sections of a steel sheet （group A）, the punch shoulders in drawing （group B）, and the stretch sections （group C） . The frictional properties of group A and group B could be evaluated by measurement of the dynamic coefficient of friction in the flat sliding tests under a high contact pressure and at low sliding speed in each group area. The frictional properties of group C could be evaluated by the static coefficient of friction, which is measured as the primary peak in a coefficient of friction – stroke curve under the specific sliding test conditions （contact pressure：7MPa, sliding speed：10mm/min, tool length：10mm） .
Welding is widely used for constructing many structures. Residual stress is generated near the bead. Tensile residual stress degrades the strength of a structure. The authors have proposed a method of reducing residual stress using vibration during welding and applied it during the welding of thin plates. Residual stress is reduced more when a larger amplitude of the vibration is used. In this paper, repair welding of the mold is considered, and the surface of a thick plate is welded. Two ultrasonic vibrations are used to realize large amplitude and the reduction of residual stress is examined. Residual stress is reduced more than when using one ultrasonic vibration. Next, experimental results are examined by a simulation method. An analytical model that takes plastic deformation into consideration is proposed because the yield stress immediately after welding is very low. It is demonstrated that residual stress is reduced more when two ultrasonic vibrations are used. Finally, the advantage of the method using two ultrasonic vibrations is examined statistically. The reduction probability of residual stress is obtained. The reduction probability of the method using two ultrasonic vibrations is very high. By the t-test, it is demonstrated that the method using two ultrasonic vibrations is more effective than that using one ultrasonic vibration for the reduction of residual stress.
The application of T-bars in shipbuilding has recently increased. Slim T-bars having a web height of at least twice the flange width are generally required in ships. Because the dimensions of existing hot-rolled T-bars are unsuitable, T-bars fabricated by welding two plates are currently used in shipbuilding. To manufacture slim T-bars by hot rolling, we devised a new T-bar rolling process using two universal mills and an edging mill. The two universal mills have different roll shapes. The horizontal roll width of the first mill is wider than the web height of the T-bar, whereas that of the second mill is narrower than the web height in order to reduce the web height with a vertical roll. Multi-pass rolling experiments with pure lead were performed using the new process, and a T-bar having an excellent cross section was obtained. Finite element analyses of universal rolling were also carried out to investigate rolling deformation behavior in detail. Following these investigations, a T-bar hot rolling test was carried out at an actual structural steel mill. As a result, steel T-bars with an excellent cross section were successfully produced, and the capability of the new T-bar rolling technology was clearly demonstrated.
In this paper, a basic investigation of rotary forging was carried out by experiment and FEM analysis to clarify the mechanism of surface hardening by rotary forging. We used columnar low-carbon steel as a workpiece. As a result, we found rotary forging produces a hard surface because of surface expansion and submicron fine grains. Ratio of minimum principal stress to von Mises stress is less than-1. 2 was proposed as the new criterion for surface on the basis of the result of the minimum principal stress distribution in a hourglass-shaped workpiece. We applied this criterion to a rotor and confirmed that the results correspond with those of FEM analysis.
First, back-up rolls for rolling require toughness, particularly in the shaft portion, and high-hardness in the sleeve portion. The back-up rolls are classified into two types; one is a single-solid type, and the other is a shrink-fitted construction type consisting of a sleeve and an arbor. The shrink-fitted back up roll has several advantages, for example, different materials can be chosen and the arbor can be reused by replacing the damaged sleeve. Therefore, the shrinkfitted back-up rolls are economical. However, residual deflection becomes a major problem for the shrink-fitted back-up roll. Elucidating the mechanism of the occurrence of residual deflection and devising countermeasures are important issues. Unfortunately conducting a real experiment is difficult because of much time and huge cost. In this paper, we reproduce this phenomenon by elastic FEM analysis, establish a simulation method, and elucidate the mechanism behind underlying residual deflection.
In this study, a new microtube hydroforming （THF） system utilizing ultrahigh pressure to fabricate cross-shaped microcomponents is designed and developed. The micro-THF die assembly employs a new type of split die and has a die housing with a flow channel of fluid medium to apply ultrahigh pressure into a tube through micro notches on an axial punch. A phosphorous-deoxidized copper tube with an outer diameter of 500µm and thickness of 100µm is used for cross-shaped micro THF experiment. Finite-element analysis is carried out to confirm and clarify the deformation characteristics, forming limit, and suitable forming conditions inoder to enhance the protrusion height of cross-shape forming. Consequently, a cross-shaped microcomponent with an outstanding bulge height of 1. 6 times the outer diameter is successfully fabricated experimentally.