Papers by Author: Kenichi Manabe

Abstract: A novel microforming process - Micro Cross Wedge Rolling (MCWR) has been developed, which is promising for fabricating micro stepped components used in micro electro-mechanical systems. Numerical simulations have been established and the effect of geometrical and process parameters such as forming angle α, stretching angle β and reduction ΔA have been studied. Micro stepped components have been fabricated successfully on a MCWR testing rig by adopting flat wedge tools. The effects of initial surface roughness of tool, grain size and cross section area reduction on surface morphology have been assessed quantitatively.

Abstract: The newly proposed rotating bending process of metal tubes is a novel kind of Severe Plastic Deformation (SPD) process, which is expected to refine and control the microstructure of metallic tubular materials. The stress distribution and accumulated equivalent plastic strain of deformation part have a significant influence on the microstructure refinement and control of metal tubes during the rotating bending process. The present study focused on the analysis of stress and strain of deformation part during rotating bending process of metal tubes. The model of the deforming metal tubes was proposed. The formulas for determining the stress and accumulated equivalent plastic strain were successfully achieved by analyzing the deformation of metal tubes during rotating bending process.

Abstract: Dieless bellows forming using local heating technique is an advanced flexible forming technology to produce bellows from straight tube without the use of dies. The deformation is induced by applying continuous compression, and local heating. Advantages of these processes are the absence of dies, applicability for various materials, suitability for flexible forming process including low batch production, flexibility on workpiece sizes and output geometries. However, the implementation of these processes is still low owing to the low quality, reproducibility, and production speed. The limitation of these dieless forming processes using local heating is caused by the absence of dies required to form the desired profile. Therefore deformation depends on temperature, length of heating zone, processing speed, speed ratio of feeding to fabrication speeds. In order to enhance the product quality in these dieless forming with local heating, real-time monitoring are necessary to identify deformation progress. Machine vision based on image processing technique was selected to monitor deformation behavior on dieless bellows forming process. The present paper describes real-time monitoring using image processing approach to monitor dimensional profile and temperature distribution during the process. The results show that machine vision is effective and efficient to monitor dynamic deformation of dieless bellows forming proces and able to identify abnormal process condition.

Abstract: Micro metal forming with metal foils is one of the promising approaches to fabricate micro parts. In this study, a finite element (FE) model for metal foil considering material inhomogeneity due to different flow stresses for each crystal grain to predict free surface roughening and necking behavior is suggested. Material used is pure copper C1020-O, pure aluminum 1N30-O and pure titanium TR270C-O with thickness of 0.05mm. Material inhomogeniety parameter of variation in α value is determined by parameter fitting between uni-axial tensile test and FE analysis considering material inhomogeneity under uni-axial tensile state. Standard deviation σ_sd of variation in α value of 0.28 for C1020-O is obtained by parameter fitting process. In addition, free surface roughening behavior is observed by FE analysis considering material inhomogeneity and confocal laser microsope. As a result, the increase in surface roughness with uni-axial tensile deformation can be observed for both FE analysis and experiment. In addition, it is considered that the generation of concave parts in free surface roughening is due to grains with low flow stress by quantitative measurement of FE analysis and confocal laser microscope. Surface roughening behavior of FE analysis considering material inhomogeneity is in good agreement with that of experimental results. Thus, the validation of FE model considering material inhomogeniety for metal foils can be verified. Furthermore, the effect of material properties for metal foils such as grain size, material inhomogeneity parameters and strain hardening sensitivity on necking behavior is investigated. As a results, it is found that the ratio of surface roughening to thickness strongly affects necking behavior for metal foil. In particular, in case of large n-value, the concave part generated by surface roughening during plastic deformation would cause the onset of necking for metal foils. Therefore, it is found that the factor of surface roughening is very strong in micro metal forming with metal foils.

Abstract: In this study a cyclic rotating bending process for microstructure control of metal tubes was newly proposed. The AZ31 magnesium alloy tube was conducted to investigate the effect of the rotating bending process on the microstructure and mechanical properties of metal tubes. The rotating bending process was carried out with rotation speed of 20r/min for 10min at the temperature of 150, 200, 250, 300 and 350°C. The rotating bending processes carried out with various conditions show that the grains in cross-section and longitudinal section of magnesium alloy tube were refined for all samples by the rotating bending process with rotation speed of 20r/min for different rotation numbers and temperatures. The rotating bending temperature shows a various effects on the mechanical properties. When the temperature was 200°C, the highest strength as well as ductility was obtained.

Abstract: The effect of drawing speed and heating length on deformation behavior was investigated by numerical approach for AZ31 magnesium alloy tubes to realize high speed dieless drawing process. The length of deformation zone expands with increasing the feeding speed. The increase in heating length leads to expanding length of deformation zone. The mean strain rate increases with increasing the feeding speed firstly, and then rate of increase in the strain rate becomes gradual under condition of any length of heating band. Based on these results, a limiting reduction in area of 52.5% under higher speed and larger heating length conditions can be realized experimentally.

Abstract: In this study, we evaluated the characteristics of 3D finite element (FE) model considering material inhomogeneity for prediction of free surface roughening. Free surface roughening behavior can be observed by this model. The variation in material inhomogeneity parameter value has a strong correlation with the rate of increase in the surface roughness. macroscopic strength coefficient K value does absolutely not affect the rate of increasing surface roughness. Strain hardening sensitivity index n value slightly affects the free surface roughening behavior. The true stress – true strain curve of the inhomogeneous FE model is in good agreement with those of the homogeneous FE model and the experimental result. As a result, the characteristics evaluation of suggested model considering material inhomogeneity is conducted.

Abstract: In this study, the effects of isothermal bainite treatment (IBT) holding time on the microstructure of transformation induced plasticity (TRIP) seamless steel tube were studied via optical microscopy, TEM and XRD. Its mechanical properties and hydroformability were evaluated by tensile test and flaring test, respectively. The results revealed that the volume fraction of retained austenite (RA) increased at first then decreased with IBT holding time for a particular set of intercritical annealing (IA) temperature, IA holding time and IBT temperature. It was also demonstrated that high tensile strength of 618MPa, total elongation of 35.5%, n-value of 0.23 and better hydroformability could be successfully produced in this TRIP steel tube at IA temperature of 800°C, holding for 10 min, and IBT of 410°C for 4 min holding time.

Abstract: In this study, non-uniform heating approach in warm T-joint forming process is attempted for the AZ31 magnesium alloy tube. For this purpose, finite element simulation is performed to analyze the appropriate temperature distribution. The validity of the finite element(FE) model of T-joint tube hydroforming(THF) is verified by comparing the FE simulation and experimental results. Using this FE model, appropriate temperature distribution was suggested. In addition, it was showed that the wall thickness could be more uniform by optimizing the temperature condition.

Abstract: Grain refinement processing by severe deformation, combined equal-channel angular extrusion (ECAE) processing and conventional tube extrusion, is applied to AZ31 magnesium alloy. By a combination of ECAE processing and tube extrusion, a fabricated tube, with outer and inner diameters of 2 mm and 1 mm, respectively, has fine, homogeneous, and equiaxed grain structure with an average grain size of 1.5m. Tensile test results indicate that the fine-grained tubes exhibited a superplasticity potential m value of 0.55.The maximum elongation (688%) is obtained at a temperature of 673K. Furthermore, the tubes fabricated by combined ECAE/extrusion process is applied to dieless drawing process without using any tool and die.As a result, dieless drawing limit is enhanced due to high m value achieved by combined ECAE/Extrusion process. From these results, the effectiveness of new grain refinement processing for fabricating fine-grained tubes and its application for dieless drawing process to fabricate the fine tubes was demonstrated experimentally.