Effect of Forming Conditions on Springback in Rotary Bending of Sheet Metals
-An Investigation of Rotary Bending of Sheet Metals I -

(Received on December 27, 1993)

Ken UENO, Makoto MURATA and Hideo SUZUKI

Rotary bending of various metal sheets was carried out and the effects of applied radial pressure, sheet thickness and bend radius on springback and roundness are investigated. The roundness of specimen formed by rotary bending is markedly improved compared with press bending. Springback decreases with an increase in radial pressure. However, in the case of high pressure over a certain level, it increases because of thinning of a sheet. Also, the springback decreases as the sheet thickness increases and the bend radius decreases.

Keywords: bending, forming property, rotary bending, accuracy, roundness, springback



Strip Rolling Analysis by Rigid-Plastic Finite Element Methods considering both Roll Flattening and Strip Deformation

(Received on March 9, 1994)

Kenjiroh NARITA, Ken-ichi YASUDA and Shigeru SHIDA

In recent years, rigid -plastic finite element methods have been used to investigate the thickness distribution of sheets during rolling. Although such studies often use a surface deformation model based on a modified semi -infinite body in place of the roll surface for caIcuIating the deformation of the rolI surface in the direction of sheet width, the difference of the deformation between the modified semi-infinite body surface and the roll surface has not been studied sufficiently. In other cases, rigid-pIastic finite element mothods and elastic finite element methods are used to calculate the deformation of the roll surface and the thickness distribution during rolling. Iii these analyses the contact boundary conditions dependent on a flow line on a sheet are considered but there is not enough information aboout how movement of contact boundary are affected by the roll surface deformation. We, therefore, studied the difference between the be betweeeii the behavings of modified semi-infinite body surfaces and the roll surfaces and found that the difference of the deformation idcreases with increasing rolling load. To take intn account the ways that the contact boundary movements are affected by the roll surface deformition in the finite element analysis, we propose a new method in which movable r(ill surface nodes are used. Computational results show that the contact length increases with iiicreitsing rollitig-load and it is possible to predict the change in the contact length in the finite element analysis by use of the new method.

Keywords:rnlling, stril) rolljiig, thenretical analysis, FEM, rigid-plastic analysis



Three-Dimensional Elastic-Plastic FEM Analysis of Square-Crosssection Bar Torsion
A Study on Combined Forming with Torsion and Bending I

(Received on June 29, 1994)

Naozumi HATADA, Ken UENO, Masanobu UEDA, Keiichi NAKAMURA and Takeshi KAWANA

This paper deals with FEM analysis of the torsion of solid bars. Using FEM program MARC, three-dimensional elastic-plastic torsion problems were analyzed. The longitudinal strain during twisting of solid bars are calculated. Torsion moment and spring back angle show a good agreement with the results obtained by the sand heap analogy. Axial lengths of square and circular-crosssection bars increase in the elastic region and tend to decrease in the plastic region. The decreasing ratio of axial length of the square-crosssection bar was larger than that of the circular-crosssection bar. The decreasing ratio of axial length becomes smaller with the increase of strain-hardening ratio. The tendency of the results are coincide with the former experimental studies.

Keywords:finite element method, torsion, numerical analysis, longitudinal strain,square-crossection bar, circular-crosssection bar



Mechanical Properties of Uniaxially and Biaxially Rolled Polymer Sheets

(Received on june 29, 1994)

Yasuhiro HIGASHIDA, Toshio KIKUMA and Kazuo WATANABE

The effects of uniaxial and biaxial rolling elongations ( k i and k2 : elongation ratios in the first and second rollings, respectively) on the tensile strength, elastic modulus, molecular orientation and degree of crystallinity are investigated experimentally in order to obtain thick sheets of polypropylene and polyethylene which have large tensile strength, high elastic modulus and small anisotropy in these properties. The biaxially rolled sheets become isotropic in tensile strength when k 2 is nearly 1.5 for any values of k i . The tensile strength of the rolled polypropylene sheet, initially elongated up to k i =5.0 in L-direction and then ?, 2--l.5 in C-direction, reached almost IOOMPA in all directions in the plane, which is three times as large as the strength of non-rolled sheet. The sheets are reheated between the first (C-direction) and the second (L-direction) rollings and thickened by thermal shrinkage in both C-and L-directions, and if the shrinkage is taken into account , the substantial elongation ratios in L- and C-directions are almost the same when k i =5.0 and k 2 = 1.5. The tensile strength characteristics of uniaxially and biaxially rolled sheets correspond with the tendency of molecular orientation.

Keywords:rolling, polymer, polypropylene, polyethylene, uniaxial rolling, biaxial rolling, tensile strength, elastic modulus, molecular orientation, crystallinity.



Equilibrium of Force at Onset of Necking

(Received on june 13, 1994)

Hitoshi MORITOKI and Eiki OKUYAMA

An equuibrium condition is investigated in a diffuse and localized neckings. 'ne localized necking is a phenomenon wherein velocity gradient or strain rate becomes discontinuous on a necking plane. Equilibrium of forces must be maintained across the necking plane. Since the necking plane is in the interior of a deformed material, its area and normal direction change with the deformation. Consequently, the rates of these changes must be taken into consideration in the equilibrium condition. So far, the analyses for the localized necking were established without considering these effects. This paper presents the basic concept of equilibrium of force, and the equilibrium conditions used in the previous analyses are reconsidered. Tlrough the necking analyses based on the proposed method, it has been clarified that the assumptions employed in the theories by HUI and by S16ren and Rice are similar, and the necking deformations predicted by these theories become identical each other. T'he diffuse necking proposed by Swift is represented by the criterion that in-plane loads become simultaneously stationary under plane stress condition. However, the loads obtained based on this criterion, in general, do not provide the stationary value. In this case, the cause for the unreasonable results is discussed, and an altemative criterion is proposed which afford to introduce an rigid solution as well as plastic solutions. All the criteria in both the diffuse and localized necking are contained in the general criteria brought by the permissible condition for the existence of multi-solutions.

Keywords:Localized Necking, Diffuse Necking, Plastic Instability, Formability, Equilibrium



Plane of Localized Necking as Characteristic Plane

(Received on July 8, 1994)

Hitoshi MORITOKI and Eiki OKUYAMA

Localized necking is a phenomenon wherein multiple solutions in stress and strain rates can exist on necking plane. In this case, the necking plane acts as a discontinuous plane. On the other hand, the characteristic plane is a plane over which in nunierical integration solutions cannot be extended without additional information, because sonte derivatives on it caiiriot be determined froni the governing equations alone. The indetemiinacy of such derivatives is niathematically related to the possibility of the existence of multiple solutions. The slip ]me in plane strain ajid the velocity discontinuity iii plane stress were proposed in the theory of plasticity. Tlese lines have been considered as characteristic lilies, but it has not yet been exanihied whether or nof these Iiiies are contained iii the original characteristic planes. We propose that characteristic planes provide the properti6s needed for planes of localized iieckiiig, and they have only three niodes under plane strain rate. Thereforc, the discontinuous Iiiie of velocity in plane stress cannot be considere4d to be a part of a characteristic plane.

Keywords:Characteristic Plane, Characteristics, Localized Necking, Plastic Instability, Necking Plane, Velocity Discontinuity



Welding Defect Occurring in Filling Stage in Injection Moulding of Ceramics

(Received on August 15, 1994)

Kazunori KATO, Ren Haw CHEN, Norihiko SUZUKI and Naoto OTAKE

In injecfion moulding of ceramics, fountain flow does not occur at a flow front, so front material is severely cooled and welding defects may be generated in some cases of joining flows. In this paper injecfion moulding into the die cavity with an insert is dealt with and the mechanism of the generation of welding defects downstream of an insert is discussed. 'Me following results are obtained. (i) There are two types of welding - joining of inifial flow fronts and that of new fronts- generated downstream of an insert. Severe welding defect-9 are somefimes found in ttie former. (ii) Size of welding defects increases rapidly-when the cooling time A t of flow fronts becomes longer than some critical value, where L t is the time interval between the generation and the joining of new fronts. Material temperature T N, and holding pressure p H greatly influence the welding defects, whereas die temperature T i) does not. (iii) 'ne experimentally observed size of welding defects has negative correlafion with the maximum front temperature T mAx after front joining, which is determined through@numerical calculafion.

Keywords:injection moulding, ceramics, welding defect, joining flow, fountain flow



Evaluation of Testing Methods for Strength of Bonding Interface in Clad Steel

(Received on September 27, 1994)

Akio SEGAWA, Takaaki HOSOTANI, Osamu AOKI and Takao KAWANAMI

The strength of the bonding interface is a major consideration when using clad material, and therefore both the shear strength test and ram tensile strength test are standardized in J I S as the means of evaluating the strength of the bonding interface of a clad material. However, the correlation between the two strengths measured by those tests has not been clarified. In the present paper, we first describe studies on the metallurgical structure of the bonding interface using titanium clad steel manufactured by the hot rolled method, explosively welded method, or explosively welded and rolled method, together with stainless clad steel manufactured by the hot rolled method, and then evaluate several factors affecting the strength of the bonding interface by performing two kinds of experimental strength tests. The correlation between the shear strength and the ram tensile strength was further studied and problems occurring during the strength tests of the bonding interface for the clad material are also discussed on it. It was confirmed from these test results that there is different correlation between the two measured values of shear strength and ram tensile strength in either case of the said clad manufacturing methods, and the ram tensile strength was higher than the shear strength in case of the clad material having a strong bonding interface (explosively welded titanium clad steel, hot rolled stainless clad steel), but the shear strength was higher in the other materials.

Keywords:material testing, clad material, titanium clad steel, stainless clad steel, shear@strength test, ram tensile strength test, strength of bonding interface



Development of an Extremely Precise Model for Gauge Set-up in Cold Strip Mills
-An Experimental Study of High-Speed and Stable Cold Rolling I

(Received on November 10, 1994)

Toshiyuki SHIRAISHI, Hiroyasu YAMAMOTO, jyun HASHIMOTO and Teruhide NIITOME

To improve the accuracy of gauge in cold strip mills, an extremely Precise gauge setup model is developed.This model consists of four equations. 1)To describe rolling load, we use Hill's equation. 2)For forward slip ratio,we use the equation by Bland and Ford, considering sliding nummer. 3)For friction coefficient, we use an experimental equation, considering cold rolling factors. 4)For deformation resistance, we use an empirical equation, considering hot and cold rolling factors. lt is confirmed that accuracy of friction coefficient and deformation resi- stance is improved by an experiment using a cold tandem mill from YAWATA Works.

Keywords:sheet rolling, experimental analysis,cold rolling,forward slip ratio,load,torque, friction coefficient,setup



An Expert System for Roll Pass Design in Shape Rolling of H-Beams

(Received on December 12, 1994)

Ken-ichiro MORI, Masaki KOBAYASHI and Kozo OSAKADA

An expert system for designing grooved rolls and pass schedules in shape rolling of H-beams from a bloom or beam blank is presented. In this expert system, roll pass sequences in shape rolling are generated by searching into a database for the geometries of intermediate workpieces and roll grooves and by tracing roll pass sequences backward from the geometry of a final beam. A considerable amount of data stored into the database are efficiently acquired from rigid-plastic finite element simulations of shape rolling with generalized plane- strain modelling and a mesh generator. The generated roll pass sequences are verified by not only the finite element simulation but also a model experiment using plasticine workpieces and plaster rolls. The model experiment system consists of a rolling mill andanNC machine for cutting the roll grooves, and the geometrical data of the roll grooves inferred by the expert system are directly input to the NC machine. When the verified fill in the roll groove is evaluated to be insufficient, the shapes of the roll grooves are modified by changing weighting factors for the geometrical parameters of the workpiece in the search into the database.

Keywords:rolling, shape rolling, expert system, roll pass design, H-beam, FEM, database, model experiment.



Production of Aluminum Strip by Means of Melt Direct Rolling

(Received on December 22, 1994)

Yoshihiro SAITO, Toshiya IKEDA and Noblihiro Tsuji

Strips of commercial-purity aluminum 0.8-2.Omm thick have been direct-rolled from the molten state using a rolling mill with a closed pass 40mm wide. Surface defects appear when the rolling speed exceeds a critical value. The critical value of the rolling speed decreases with increasing pouring temperature and roll gap. The roll force and strip thickness increase with decreasing rolling speed, because thickness of the solidified shell, i.e., the substantial initial thickness, increases. In the direct-rolled strips, a large amount of rolling reduction exceeding 50% is applied on the material, and consequently the solidified structux-e is completely destroyed. The direct-rolled strips show greater value of tensile strength and elongation than the hot-rolled strip.

Keywords:direct rolling, non-ferrous metal (Al), strip casting, near net shape process,@mechanical property, microstructure, surface defect



Effect of Annealing on Reducing Cavities in Superplastic Tension Test of 5083 Aluminum Alloy

(Received on January 9, 1995)

Hajime IWASAKI, Yoshikatsu YAMAMOTO, Takasuke MORI, Tsutomu TAGATA, Mamoru MATSUO and Kenji HIGASHI

The effect of prc- and post-anncaling at superplastic tension test on the cavity volume fraction of deformed specimens has been investigated in a 5083 aluminum alloy. Tensile specimens werc deformed to selected strains at a constant strain rate of IxJO-3s- I and temperature of 783 K. Pre-annealing was performed at 783K for lh and post-annealing was performed at temperatures ranging from 733 to 833 K for 1 to 4 h. Cavity volume fraction of deformed specimens was measured to examine the effect of annealing on cavitation reduction. Cavity volume fraction of a pre-annealed specimen was 0.43% at a strain of 0.69, which was only 0.05% Icss than that of an unannealed specimen. Post-annealing at 783 K for 1 h of the pre-annealcd specimen after applying a strain of 0.69 gave rise to a further 1% reduction of cavity volume fraction. The cavity volume fraction of 0.43% was markedly reduced to 0.02% by post-annealing at 783K for 4 h; furthermore, it was reduced to 0.06% by post- annealing at 833 K for 1 h. It is likely that the improvements of cavitation by post-annealing were due to shrinkage of cavities by lattice diffusion.

Keywords:tension test, superplasticity, density, anncaling, cavitation



Proposal of T and N Parameters for Checking Magnitude of Increments in an Elastic-Plastic Model

(Received on January 30, 1995)

Toshio TATENAMI

Stress value calculated by elastic-plastic incremental theory may bc largely overestimated because of the nonlinear characteristics of the material. Thus, the T parameter is proposed for the purpose of reducing the error. Furthcrmorc, the N paramcter is proposed for the purpose of suppressing the phenomenon that stress points may vibrate in stress fields under deformation. Tand N parameters are applied to the calculation of deep drawing processes. The effect of the T parameter is examined on the error of stress value at the end stroke of the process and it is shown that N<1.5 suppresses the vibration phenomenon.

Keywords:sheet metal forming, numerical method, elastic-plastic material, incremental theory, error accumulation, stress evaluation.



Development of a General Purpose Physical Forming Simulation System

(Received on February 3, 1995)

Kenji NAKANISIll and Yuji MURE

Forming simulation has been developed and applied to die and process design to achieve successful and optimal metal-forming Processes. Quantitative information on boundary conditions and deformation characteristics of a workpiece is required in computer simulation; however, information on these is insufficient. Structural changes of the workpiece cannot be evaluated by computer simulation. Thus, a physical forming simulation system, in which incremental forming experiments could be carried out under actual forming conditions and strain analyses could proceed semi-automatically by visioplasticity method under plane strain condition or axisymmetric strain condition, was developed. The die forging process of an ornamental head bolt was examined and analyzed using the physical forming simulation system. It was confirmed that useful quantitative and graphic information concerning metal flow, strain rate and strain could be obtained by the physical forming simulation system.

Keywords: forging, experimental analysis, finite difference method, incremental forming analysis.



Calculation Method of Roller Leveling Conditions for Steel Plates

(Received on December 22, 1994)

Tetsu MATOBA, Matsuo ATAKA and Takeshi JIMMA

The strain induced on a steel plate and the leveling load during roller leveling are measured. The relationship between plate curvature and roll position is approximately equal to the calculated result obtained under the assumption that the plate is deformed elastically. If the distar)ce between each leveler roll is assumed to be i and the amount of intermesh of the center roll relative to the adjacent rolls is 5 then the plate curvature at the center roll K is 6,5 / -c 1. Since the curvature can be expressed by such a simple equation, nuff)erical mc)dels to calculate leveling load, roll deflection, and curvature are investigated using the above experimental results, taking the mill modulus of the leveler into consideration. It is four)d that the model describing the displacement of the rolls from the initial set positions in proportion to the individual roll loads can explain actual phenomena well.

Keywords:finishirg- shape correction, roller leveler, plate, numerical analysis.



Unification of Evaluation Methods for Measuring Bow of Tin-Gauge Steel Sheet

(Received on February 7, 1995)

Tetsu MATOBA, Matsuo ATAKA, Itaru AOKI and Takeshi JIMMA

Three types of measured bow are usually used for evaluating the,flatness of manufactured tin-gauge steel sheets. An attempt is made to represent the three types of bow of the sheets by their curvature which is measured under an unrestricted condition. The results are as follows. (1). A 1 meter square sheet is hung by the central point of the top side, and the resultant bow of the sheet is evaluated b measuring the deflection of the top side. This y deflection includes the effects of 33% of transverse bow. (2) The relationship between the end up-bow of a narrow strip specimen and the curvature is investigated. The end up-bow is proportional to the square of the sheet thickness and curvature. (3) A strip specimen is hung along a vertical wall, and the distance between the specimen bottom end and the wall is measured to obtain the hanging bow value. The hanging bow value is proportional to the curvature and to the four-thirds power of the thickness.

Keywords:inishirg- shape correction, straightening, slab method, profile measurement.



Numerical AnalYsis of Shearing of Sheet Metal by Particle Flow Model

(Received on February 8, 1995)

Teruie TAKEMASU, Tatsuo OZAKI and Susumu YAMASAKI

Conventional single-side straight cutting of aluminum sheets is analysed by the particle flow model based on a rigid-plastic finite-element method. The simulation can be performed from the beginning to the end of the shearing process without remeshing. A slide element model is employed to overcome the singularity problem at the tool cutting corner. The numerical results are compared with the experimental ones with regard to the material flow, shearing load and so on. The predicted results of tool strokes of fracture initiation based on the equivalent plastic strain distribution show good agreement with experimental results.

Keywords:shearing, rigid-plastic FEM, particle flow model, slide element,singular point, fracture initiation, equivalent plastic strain



Hot Extrusion of Thermoplastics in Solid State under Constraint of Strain Recovery

(Received on February 20, 1995)

Yukio SANOMURA

Improvement of mechanical properties in thermoplastics is experimentally investigated by solid-state extrusion I at eleN,ated temperature. Hot extruded rods of polyacetal (POM) and high density polyethylene (HDPE) is cooled rapidly under constraint of strain recovery. Rods 6 to 12mm in diameter can be extruded at elevated temperatures below the melting point and have high molecular orientation. The tensile strength in the extrusion direction is improved to about 1.5 times that of solid-state extruded rods cooled under free strain recovery, and the maximum values can go up to approximately 6 to 7 times those of untreated thermoplastics (original materws). Tensile strength is improved with increasing extrution ratio; however, it is hardly influenced by extrusion temperature and extrusion rate. Extrusion pressure increases with increasing constraint of strain recovery, extrusion rate and extrusion ratio, but decreases with increasing extrusion temperature.

Keywords:extrusion, polymer forming, solid state, thermoplastics, constraint of strain recovery, elevated temperature,@improvement of mechanical properties



Fabricating Method of Ceramic Parts by Sinter joining

(Received on March 9, 1995)

Sam MASAKI, Kunio OKIMOTO and Masanari KONISHI

Sinter joining is utilized to fabricate a ceramic part with a complex shape. Two simple compacts of disk or ring shape are individually produced with different relative densities by powder forging. The two compacts are as- sembled into a unit and then sintered. Joining is achieved due to the differ- ence in shrinkage of each compact. The ceramic powder used is alumina(A'203) of high purity and 0.4 Rm in mean particle diameter. The relative density of the inner disk compact is fixed at 0.60 and that of the outer ring compact is changed from 0.52 to 0.60. The joining strength is ev aluated from Weibull statistics because there is a large variability in the shearing strength obtained from the shearing tests of the joining parts. The joining strength increases with decreasing relative density of the ring compact. The joining strength reaches approximately 70% compared with that of sintered ceramic materials with the same relative density of compacts, when mean joining strength is a@sumed to have 50% failure probability.

Keywords: sinter joining, alumina (A'203) , @'relative density, joining strength,weibull statistics