Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.43 no.503 December 2002)
Cross-sectional Shapes of Corner Zones of Hexagonal Steel Pipes
Formed by Extroll-Forming Mill with Expanding Inner Idler Rolls
Takuo NAGAMACHI,Yoshitomi ONODA,
Sadao KIMURA and Takeo KITAWAKI
(Received on October 17, 2001)
To improve the cross-sectional shapes (outer curvature, wall thickness change) of the corner zones of hexagonal steel pipes (168.0, 170.0 and 173.0mm wide, STK400) formed by an extroll-forming mill, an expanding-type forming tool with six idler rolls is introduced into the groove of No.1 grooved rolls to impose peripheral bending on the portions of the round pipes (outer diameter D0=190.7mm, wall thickness t0=4.6mm) that correspond to the corner zones of the finished products. Characteristics of the cross-sectional shapes of the corner zones of the hexagonal pipes are investigated with respect to the nose radius of the inner roll and the degree of corner bending by the inner rolls, and compared with the results obtained by conventional extroll-forming. The results show that a hexagonal steel pipe with a small outer radius at each corner zone can be manufactured using a pair of inner idler rolls with small nose radius.
Key words : roll forming, tube forming, extroll-forming, round welded steel pipe, hexagonal pipe, non-driven grooved rolls
Development of Database and FEM Assisted Intelligent Control Press Forming System
Hiroshi KOYAMA, Ken-ichi MANABE and Shoichiro YOSHIHARA
(Received on November 19, 2001)
In order to realize a highly flexible and efficient process design system, a database and FEM assisted concept for developing an intelligent control press forming system is proposed. In the system, all the process designs are semiautomatically carried out using the process information stored in the database. FEM is also employed to obtain a proper "ideal curve" which is required for appropriate fracture evaluation. We use three objective functions, i.e., cup height and LDR improvements, and cup wall thickness uniformity. By introducing control algorithms for all objective functions, a fuzzy adaptive control variable BHF circular-cup deep-drawing system is developed based on the concept. Through the implementation of the system using an aluminum alloy sheet, it is confirmed that the process design and control is efficiently carried out without requiring experts and a trial and error based method. The experimental results show that all the processes are more successfully carried out with this system than with the former system, and a newly developed system is available.
Key words : sheet metal forming, intelligent forming, circular-cup deep-drawing, database, finite element method, fuzzy inference, adaptive control system
Non Linearity of Plastic Deformation Problems and Its Reducing Methods
Toru SHIMIZU
(Received on December 11, 2001)
For solving rigid plastic deformation problems, on upper bound method, UBET (Upper Bound Element Technique) and rigid plastic FEM are used. However, these problems exhibit strong non linearity arising from the definition of strain rate, making it difficult to solve these problems numerically. In particular in the case of UBET, minimizing the energy dissipation rate that is expressed using many parameters is almost impossible. Therefore, two methods of reducing the non linearity of plastic deformation problems are introduced, and applied to the problems. One is approximation of the energy dissipation rate using the power function, and the other is to approximation of the energy dissipation rate using a hyperbolic function. These two methods are effective for resolving the issue of non linearity, and the problems can be solved using the Newton-Raphson method or other efficient numerical methods. Using these methods, iterative calculations are performed efficiently and stably. Also, these methods can be applied to other non linear problems similar to plastic deformation problems, for example, planning problems and crystal plasticity.
Key words : rigid plastic, non linear problem, numerical analysis, power function, hyperbolic function
Tensile Properties of an AZ31 Magnesium Alloy Sheet after Warm Forming
Hirohiko TAKUDA and Daisuke INOUE
(Received on February 12, 2002)
The influence of warm forming on the mechanical properties of the AZ31 magnesium alloy sheet is investigated in this study. Specimens are elongated in advance at 150, 200 and 250 Cels. degrees, and tension tests are carried out at room temperature on the specimens. It is clarified from microstructural observations that recrystallization occurs in the specimens deformed at 250 Cels. degrees. The properties, such as proof stress, tensile strength and fracture elongation, of the specimens deformed at 250 Cels. degrees are unchanged and are almost the same as those before warm forming. With decreasing temperature and with increasing elongation during warm forming, the proof stress and the tensile strength increase while the fracture elongation decreases. However, the decrease in ductility is comparatively small even for the specimens deformed at 150 Cels. degrees. Tension tests are carried out also at elevated temperatures for various strain rates, and the tensile properties of the sheet during warm forming are evaluated.
Key words : material testing, tension test, non-ferrous metal (Mg-3Al-1Zn), material property, warm forming
Material Properties of Steel Sheets during Continuous Tension-Unloading-Compression Process
-- Numerical Prediction of Springback Behavior of Stamped Metal Sheets I --
Noritoshi IWATA, Hideo TSUTAMORI, Naomori SUZUKI,
Hiroshi ISHIKURA, Masao MATSUI and Manabu GOTOH
(Received on February 19, 2002)
For precise prediction of springback behavior of stamped sheet metals, it is important to express exactly the material properties in the unloading process. In this study, an accurate method of measuring the continuous stress-strain curve in the sequential process of tension-unloading-compression is proposed and the characteristic of various types of steel sheets is measured using the method. The measured curves show a nonlinear property even at the beginning of unloading, and thus it is difficult to distinguish the elastic region from the plastic one. In addition, the absolute value of flow stress during unloading is smaller than that predicted using by the isotropic hardening model, although the latter is conventionally used in sheet metal forming simulation. Furthermore, the instantaneous tangential modulus (pseudo-elastic modulus) decreases by 10 to 20% for a prestrain of less than 0.02, and becomes stationary over a 0.02 prestrain. From these evidences, it is suggested that the magnitude of springback is greater for the precisely measured curve than for the one estimated based on the isotropic hardening law.
Key words : material testing, tension-unloading-compression test, sheet metal forming, springback behavior, strain-dependent elastic modulus, Bauschinger effect
Mechanical Properties and Bending of Semicured Epoxy Resin
Toshio YOKOYAMA and Hidetoshi SATO
(Received on March 11, 2002)
Tensile strength, modulus of longitudinal elasticity, and breaking strain of semicured epoxy resins, which were cured for various curing times at room temperature and 60 Cels. degrees, were measured. Tensile strength was adapted as a measure of the degree of cureDSemicured epoxy plates were bent to 90 degrees at 70 Cels. degrees, and subsequently, a heat treatment under shape restraint was applied for 32 hours at 60 Cels. degrees. The change in angle of the bent specimens was measured over the temperature range of 20 to 100 Cels. degrees. Results of the experiment indicated that the ability to hold the bent shape increased as the degree of cure was decreased. For example, the specimen cured at 40 Cels. degrees for 2 hours showed an ability to hold over 90% of the initial bent angle after the heat recovery test at 100. The holding ability was related to the tensile strength of semicured epoxy. It was also shown that the working strain (range in the present experiment:4.5 to 13%), working speed (range:10 to 1000mm/min), and working temperature (range:30 to 70 Cels. degrees) in bending did not influence the holding ability. The intended bending angle of the specimen was obtained by bending at a desired angle with taking account of the thermal shape recovery.
Key words : material testing, bending, polymer formation, solid-state formation, thermal recovery, epoxy resin
Simplified Three-Dimensional Finite Element Simulation of Roll Forming of
Wheel Rims and Determination of Wall Thickness Distribution of Rings
Ken-ichiro MORI, Naoto HIRAMATSU and Osamu EBIHARA
(Received on March 18, 2002)
A simplified three-dimensional method for simulating plastic deformation in roll forming of wheel rims with grooved rolls is developed on the basis of the rigid-plastic finite element method using generalized plane-strain modeling. In this method, the roll forming process is approximated as a forging process with dies having the same cross-sectional shapes as the grooved rolls, and the elongation in the hoop direction is kept uniform in the cross-section. The effects of the shear deformation in the hoop direction and the constraint of the elongation in the hoop direction due to the material outside the roll gap are taken into consideration. The calculated shapes of formed rims are in good agreement with the experimental ones. In addition, the wall thickness distribution of a ring before the forming is determined from iterative calculation so as to achieve an optimal distribution of the formed rim. The developed method is available for practical forming operations as a tool in the process design, because the computing time is quite short.
Key words : roll forming, rigid-plastic FEM, wheel rim, simplified three-dimensional method, wall thickness distribution, generalized plane-strain modeling