Michiharu Narazaki

Deformation behavior of tubes with thickness deviation in circumferential direction during hydraulic free bulging

Abstract The influence of the initial thickness deviation of the tube wall on the deformation behavior during free hydraulic bulging was studied. The experimental study was performed with tubes that had an initial thickness deviation of approximately 1–4%. FEM simulation and theoretical speculation were also carried out in order to examine the experimental results. It was clarified that the cross sectional shape of the bulged tube maintained its circular shape until just before tube bursting. This tendency appeared independently of the amount of the initial thickness deviation. On the other hand, increase in thickness deviation during tube bulging depended on the degree of the initial thickness deviation, n -value and r -value. When the initial thickness deviation was large and n -value and r -value were small, the increase in thickness deviation was large.

Explanation of the origin of quench distortion and residual stress in specimens using computer simulation

Measurements of distortion and internal residual stresses after quenching in specimens (e.g., cylinders, disks, rings) have been performed for many years. As a result, patterns of distortion and stress distribution have been identified in the typical shapes, steels and cooling conditions. These experimental data were examined by pioneers of the heat treatment simulation for verifying their computer programs in the 1970s and 1980s. However, early researchers did not fully explain the mechanism of distortion and residual stress generation based on their simulated results. A way to explain the generation mechanism using simulated results, especially distributions of all types of strains, has been recently developed and successfully applied to some experimental works by the authors of this paper. Its concept is described briefly, and its applications for some specimens are summarised.

Metallo-Thermo-Mechanical Simulation of Carburized Quenching Process by Several Codes - A Benchmark Project -

As one of the activities carried out by our group of IMS-VHT (Virtual Heat Treatment tool for monitoring and optimising HT process), results of a benchmark project on the simulation of carburized quenching process is summarized. Several programs available for taking into account the metallo-thermo-mechanical coupling had been employed for the simulation for a cylinder, ring as well as a helical gear by use of common data of material properties and cooling characteristics. Comparison of the simulated values of distortion, residual stresses and profile of induced phases with the experimental data is made with some discussions.

Cooperative research to optimize heat treating process condition by computer based technology

The three-year activities of Japanese IMS-VHT (virtual heat treatment tool for monitoring and optimising heat treatment process) project are summarized in collaboration with international VHT program. A brief introduction of the developed code and the results of a simulation of the carburized-quenching process of a cylinder, ring, and helical gear are described by using accumulated databases of material characteristics and cooling conditions. A trial to optimizing the heat treatment (HT) process by using a database system is presented based on collected data of practical cases. The goal of this project is to optimize the process, such as gas-carburizing followed by quenching into oil, and to accumulate heat treatment data to create a knowledge-based database.

The Effect of Transformation Plasticity on Prediction of Tooth Distortion of Heat-Treated Helical Gear

The displacement profile in a shank and dedendum-addendum circle of helical gear made of through-hardened S45C carbon steel and carburized-hardened SCr420H low alloy steel by gas carburizing was measured and predicted using a finite element method of DEFORM-HT. Both gears were quenched into same oil quenchant. Heat Transfer Coefficient (HTC) was taken by measuring thermal history inside of firstly silver probe and secondly stainless steel SUS304 gear blank. Uniform HTC of silver probe was calculated by lumped heat capacity method, whereas zone-based HTC of SUS304 gear blank was calculated by iterative modification method. Transformation plasticity was included and excluded to predict the tendency of distortion. Simulation results were analyzed and compared to the experimental results to validate the influence of transformation plasticity on the prediction of distortion during the martensitic and bainitic/pearlitic transformation. However, more accurate distortion profiles require detailed HTC by taking thermal history on the surface of the tooth.

Iterative Modification of Lumped Heat Capacity Method on Predicting Residual Stress and Distortion of Still-Quenched S45C Steel Cylinder

Computer simulation can be utilized to predict the property and quality of heat-treated products. The prediction accuracy depends upon the thermal boundary condition and the thermal history from which surface heat transfer coefficient (HTC) is derived. Variables studied are thermal boundary and the surface HTC. Zone-based thermal boundary is set with and without edge effect. Lumped heat capacity method is used to predict HTC of silver probe (1st step), then iterative modification method is applied to the prediction of HTC of SUS304 cylinder (2nd step) and S45C cylinder itself (3rd step). Using FEM tool of DEFORM-HT combined with lumped heat program LUMPPROB, this research is intended to obtain the number of thermal boundary and iterative modification step. The higher accuracy is obtained by employing the edge effect of thermal boundary. The 2nd step significantly increases the prediction accuracy of radial distortion and residual stress distribution. However, 3rd step does not significantly increase the prediction accuracy.

Residual Stress Measurement and Verification of Quenched Steel Based on Neutron Diffraction Method

The purpose of this paper is to deal dealing with residual measurement of quenched steel based on neutron diffraction method and its verification by finite element analysis on the stresses induced by phase transformation. The initial interplanar spacing do and elastic constant were measured with rotating specimen method, the residual stress in quenched carbon steel S45C was obtained by means of neutron diffraction. Then a micromechanical approach and simulation based on metal-thermal-mechanical theory were carried out to estimate the microstructure in the steel due to phase transformation during quenching process. Finally the measured results of XRD, neutron diffraction as well as calculated value were compared and discussed.

Basic Property of High-Precision Metal Flow Joining Method without the Need for Any Specialized Punch

Several metal flow joining methods have been developed since 1980 aimed at low cost and high productivity. In this study, we examine a new metal flow joining method that enables a shaft and ring to be combined without the need for any specialized punch. In this experimental study, 20-mm-diameter solid shafts and 40-mm-outer-diameter rings having a 20-mm-inner-diameter step at the 18.5-mm-inner-diameter center hole were used. The material combinations of the shaft/ring were S45C/SKD11, A5056/S45C, and S45C/A5056. The experiment was performed as follows. The shaft was inserted into the ring and pressed. Then, metal flowed between the contact faces. The gap between them was filled with the flowing metal, and then, they were joined by the high clamping pressure. The primary results were as follows. This joining method caused small amounts of metal flow because of the highly precise fitting between the shaft and ring. Therefore, they could be joined by small pressing strokes. In this experiment, the maximum joining efficiency (shaft return proof load/joining load) ranged from 25% to 35%. This new metal flow joining method appears to be highly useful in terms of low cost, high productivity, and non-mass production.

Influence of axial feeding on the growth of circumferential thickness deviation in free hydraulic bulging

Loading paths (hereafter referred as LPs) that consist of internal pressure and axial feeding are important manufacturing conditions in tube hydroforming. Among the factors that affect LP design, friction between the forming die and tube causes the most difficulty due to its complicated characteristics. Although there is no friction, a number of issues with LP design remain. In this study, free hydraulic bulging (hereafter FHB) with internal pressure and axial feeding is investigated. In FHB, tubes are freely expended without friction. It has been shown that axial feeding affects the circumferential thickness distribution in the tube periphery. The tubes in this study are straight seamless tubes. Seamless tubes typically have predictable thickness deviations resulting from their manufacturing processes. In general, the degree of thickness deviation will increase as the tube expands. A FEM simulator is used to analyze the mechanism of the growth of thickness deviation.

Verification of distortion characteristics in water quenched cylinders by computer simulation

Few measurements of both internal residual stresses and distortions in quenched cylinders are found, although many individual measurements have been performed for many years since the 1920s. A water quench test of steel cylinders was carried out for evaluating length and diameter changes, as well as axial residual stress distributions in the 1940s. The effects of carbon content to quench distortions and residual stress distributions were identified from the test results. However there was no explanation of the relationship between distortions and stress distributions. Here, measurements of both stress and distortion in this test were referred to, and evaluated by, computer simulation. Simulated results verified measured distortion and stress characteristics in cylinders, and explained their relationship and generation mechanism.