In this study, the 3D-FEM (finite element method) code “DEFORM 3D” was applied to the simulation of RR forging. RR stands for the initials of Mr. Roederer (President of Cresot-Loire Ltd.) and Mr. Ruget (the inventor). To estimate the deformation and load accurately, analytical conditions such as the strain rate and temperature dependency of flow stress, the temperature distribution of the material and volume decrement caused by the oxidation scale were taken into consideration. As a result, it was found that numerical results such as the shape of arms and the positions of flash and underfill showed a good agreement with those measured. Moreover, using this method, we built and verified an empirical equation for predicting the maximum forging load by estimating the effect of the restraint depending on each die's mode. Using this equation, the optimum forging shape was designed and used in the actual forging process. By this new designed process, successful yields have been obtained.
The mechanism of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes was examined. Free bulging hydroforming experiments of steel tubes under oscillating and constant inner pressures were performed. For a high constant pressure, round bulging with local reduction in wall thickness was observed, whereas wrinkling occurred for a low constant pressure. The occurrence of these defects was prevented by oscillating the internal pressure in the pulsating hydroforming. In the pulsating hydroforming, uniform expansion without local reduction in wall thickness was obtained, and thus the formability is improved. It was found from an observation of deformation behavior using a video camera that the uniform expansion is attained by repeated small wrinkling and bulging. The cause of the uniform expansion for the pulsating hydroforming was also evaluated from the variation of stress components. In addition, a similar deference in deformation behavior between the oscillating and constant inner pressures was obtained from finite element simulation. The pulsating hydroforming is effective in improving the formability of tubes.
Flexible shaft backing assemblies (FSBAs) which have a series of slots in the area of the saddles of backup rolls have been introduced into an actual 20-high Sendzimir mill to extend the shape control quantity of the AS-U crown adjustment, and shape control technology using FSBAs has been investigated. To begin with, a simulation model for predicting the shape of cold-rolled strips in the 20-high Sendzimir mill was developed considering the distribution of geometrical moment of inertia in the roll body length direction in order to analyze the deflection characteristics of FSBAs. The calculated values were in good agreement with the experimental values in experiments using FSBAs in the 20-high Sendzimir mill. From simulations carried out using this analysis model, it was found that the effect of the slot angle of the assembly shaft on strip shape was large. It was also found that the shape control range was doubled by the introduction of FSBAs and that it was mainly extended toward the quarter buckles side and edge waves side.
Flexible shaft backing assemblies (FSBAs) have been introduced into an actual 20-high Sendzimir mill and shape control technology using FSBAs has been investigated. In our previous paper, it was found that the shape control range was extended by the introduction of FSBAs, mainly toward the quarter buckles side and edge waves side. Thus, shape control technology with the combination of FSBAs and the first intermediate rolls given a concave profile partially (concave rolls) was investigated to improve quarter buckles. From simulations carried out using the analysis model which was described in the previous paper, it was found that quarter buckles were improved by optimizing the concave roll profile. In experiments using rolls with the concave profile in the 20-high Sendzimir mill, it was confirmed that quarter buckles were improved under extensive rolling conditions. It was also confirmed that better strip shape was obtained by combining FSBAs and concave rolls than using only concave rolls. FSBAs and concave rolls have been applied to commercial production and have contributed to the improvement of strip shape.
In the multistage deep drawing processes of a beta titanium alloy sheet, the formability and the improvement of surface roughness have been investigated. The beta titanium alloy sheets have sufficient ductility at room temperature, whereas a seizure tends to occur during deep drawing due to high reactivity with other materials. To prevent the seizure, the beta titanium alloy sheet was treated by oxide coating heating, because the coated sheet was not in direct contact with the die during deep drawing due to the existence of the oxide layer. The blank used was the commercial beta titanium alloy Ti-15V-3Cr-3Sn-3Al. The effects of the coating conditions and lubricants on the formability in the multistage deep drawing processes were examined. Long drawn cups with a height sixfold that of the diameter were successfully formed by oxide coating heating. To improve the surface roughness of drawn cups, deep drawing and ironing as well as the grain refining by thermomechanical treatment were also attempted. It was found that the methods of ironing and grain refining were effective for improving the surface roughness of drawn cups.
With the recent advances in the semiconductor industry, the demand for gold, copper and aluminum bonding wires has been increasing. Wire diameter has been decreasing due to the market demand for small and highly functional products. Also, a high degree of wire straightness is required to prevent short-circuit defects caused by contact between looped wires. Although methods of improving the straightness of superfine wires by tensile straightening have been examined, the number of such studies is limited and the mechanism of improving the straightness of wires has not yet been clarified. In this study, tensile straightening was carried out for superfine gold wires to examine the change in wire straightness under various conditions. We proposed a residual stress measurement method that allows us to quantitatively measure the residual stress in a wire specimen, which obtained by removing a part of the wire using a focused ion beam (FIB). We also demonstrated the relationship between straightness and residual stress. Furthermore, the effect of tensile strain on the crystalline structure was examined to clarify the effect of the tensile strain on the straightness of the wire and the crystal orientation rate.
Flow stress and microstructure for two commercial AZ31 magnesium alloy sheets with different grain sizes of 12μm and 5μm have been investigated in warm tension tests at temperatures from 448K to 523K and at strain rates from 1x10-3/s to 1x10-1/s. The formula σ = Fεn(ε/ε0)m for flow stress was successfully established with F, n and m values obtained experimentally. F was calculated from the equation F = -3.673T + 2170 (MPa) for both materials. Grain refinement by continuous dynamic recrystallization significantly occurred at a large strain of 0.8∼0.9 and at a temperature of 523K for both materials. The effect of grain size on F was very small. n, however, decreased and m increased with decreasing grain size in the experimental ranges of temperature and strain rate.
FeMnSi-based shape memory alloy (SMA) has already been used practically as steel pipe joints. In most cases of the applications, it is possible to estimate the reduction of diameter from the present data measured on the shape recovery for a uniaxial stretch of FeMnSi-based SMA. However, to promote the extensive practical application of FeMnSi-based SMA, investigations of shape recovery characteristics for biaxial stretch are significant. In this study, shape recovery characteristics for uniaxial tensile stretch, biaxial tensile stretch, and the stretch of the transition field from simple tension to biaxial tension are investigated. In addition, microstructures of FeMnSi-based SMA are observed, and the mechanism of stress-induced martensitic transformation which controls shape recovery actions is interpreted. Shape recovery strain after biaxial tensile stretch is markedly smaller than that of simple tensile stretch. The relationship of shape recovery characteristics to orientations of the ε-phase is clarified from microstructural observations. The technical data and interpretation presented in this study should be useful in forming design guidelines for promoting the extensive application of FeMnSi-based SMA.
Microtube is commonly used and required, particularly as micro components in micro-system technologies (MST) and micro electro-mechanical systems (MEMS). In this paper, fabrication process of microtube using superplastic dieless tube drawing is studied experimentally. Superplastic material used is Al-78Zn alloy tube with outer diameter of 2mm and wall thickness of 0.5mm. A high-frequency induction heating apparatus with air cooling nozzle is used for the dieless drawing. In the experiment of single pass dieless drawing, the effect of drawing condition such as forming temperature, distance between heater and cooler and tensile speed on deformation profile is clarified. Furthermore, in three-pass dieless drawing, a microtube with outer and inner diameters of 343μm and 161μm respectively can be fabricated successfully. In addition, from the experimental results and fundamental principles, it is confirmed that the ratio of inner to outer tube diameters maintains a constant value in the dieless drawing. In other words, the geometrical similarity with the minimization of dimension is satisfied in this process. Finally, it is found that the surface roughness of microtube maintains a constant value in the dieless drawing process.
In the production of cast iron powder containing dispersed ultrafine graphite particles in excess content, powder mixtures of machined cast iron (FC30) chips and graphite (Gr) powder with 5∼20mass%Gr were mechanically alloyed (MA) for up to 36ks. Ferrite-phase particles in the MA powder become crystals of nano-order size upon long-time milling and the solubility limit of carbon in the ferrite phase reaches 0.18mass%. The remaining graphite becomes amorphous and it is dispersed in the vicinity of the ferrite phase. Polypropylene (PP) and paraffin wax (WAX) as binders were mixed with the MA powder and then compacted by a pressure of 15MPa during the debinding treatment at 873K. The compact was sintered at 973∼1273K in an argon atmosphere. The amorphous carbon becomes graphite through crystallization during sintering, but the crystalline size of the ferrite phase not changed by sintering. The vickers hardness and the bending strength of the sintered MA compact increase with increasing sintering temperature, but they decrease at a sintering temperature of 1273K. The rupture strength of the MA alloy during bending is extremely low because of the cast iron with high graphite contents.
In this paper, we describe the tip crushing of a center bevel blade that has a quenched tip. The push testing on a steel blade, the wedge angle of which was 42 degrees, was carried out experimentally and numerically. By varying the height of the quenched tip and the applied line force, the crush profile and stress distribution of the blade tip were investigated by elastoplastic finite element analysis. The following results were obtained : (1) The sinking phenomenon of a quenched tip into a base material is a primary deformation characteristic of quenched center bevel blades. (2) The critical line force, which changes the deformation mode of tip crushing, is estimated using the yielding strength of the base material and the effective length of the quenching hazard zone. (3) When the quenched tip begins to sink into the base material, that is, when the applied line force is larger than the critical line force, concentrated tensile stress occurs at the cross points of the hazard boundary line and the surface lines of the blade.
In this study, a simple and effective piercing method using ultrasonic vibration is newly developed to produce small holes with a fine sheared surface. This method uses two independent units : a vibration unit and a piercing unit. In the piercing unit, a coil spring is placed between the punch and the guide-bush to support the punch in a floating state. The punch is pushed into the target material by an ultrasonic vibration horn at a constant speed. When the ultrasonic vibration is transferred to the punch by the horn, the punch extends out and hits the material, and then rebounds to collide with the horn. This back-and-forth shuttling motion of the punch is repeated until the material is penetrated. Commercial stainless steel thin sheets are used as the test material. By optimizing the experimental conditions in the shuttle piercing process, the fractured zone on the sheared surface is almost eliminated. It has been experimentally determined that the punch shuttling motion effectively suppresses crack initiation and produces microholes with an almost straight-line profile in an axial direction around the hole exit portion.