Analysis of Multi-Pass Angle Rolling and Experiments with Plasticine and Hot Carbon Steel
-Development of Computational Simulation System for Shape Rolling Processes 2

(Received on March 2, 1994)

jun YANAGIMOTO, Manabu KLUCHI and Kazuyoshi SHIBATA

A computer simulation program for rolling processes, developed based on Lagrange multiplier rigid-plastic FEM for analyzing various three steady- state deformations of workpieces at roll gaps in various rolling processes, is applied to analysis of multi-pass angle rolling. In this paper, the program, named "CORMILL (Computational Rolling mill) System," is used for a series of simulations of angle rolling through six passes, and the numerical cross-sectional profiles and rolling forces are compared with those of experimental measurements obtained using plasticine and hot carbon steel. Both numerical and experimental results for hot carbon steel show fairly good agreement. As a result of the investigation, it is concluded that CORMILL System is capable of predicting cross-sectional profiles of rolled products and rolling forces and is, therefore, useful for the design of pass schedules for angle shape rolling.

Keywords:numerical analysis, rigid-plastic FEM, angle rolling, plasticine, hot carbon steel



Deformation and Working Limit of Square Tubes in Draw Bending Process

(Received on May 16, 1994)

Shun SAKAKI, Takuma TOIN and Toshikazu HARASHIMA

Square tubes of aluminum alloy have many advantages in use as lightweight structural members. A secondary forming process such as bending is required when square tubes are used for structural members of automobiles or modern buildings with a curved shape. However, buckling deformation tends to occur easily on the compression side of the tube in the bending process, because the thickness of the blank is small. The deformation of the tube and working limit in the bending process have been investigated through experimental research. The draw bending process has been carried out. It has been shown that applying a straight rigid mandrel to this working process is very effective in preventing undesirable deformation including buckling, and in raising the working limit. Annealed square tubes of aluminum alloys A6063S-0 and A606 1S-0 with a height HO=40mm and a thickness t,=3.Omm can be bent without defects using a mandrel, when the degree of working represented by the ratio of the radius of curvature to the height of the bent tube R, IHO is 2. 1.

Keywords:bending, draw bending, square tube, mandrel, forming property, working Iiinit.



Discontinuous Plane and Equilibrium in Analyses of Localized Necking

(Received on june 2, 1994)

Hitoshi MORITOKI and Eiki OKUYAMA

The criteria of localized necking are proposed by Hill, and Stijren and Rice. They are widely accepted for their ability in predicting sheet formability. Though Hill's analysis cannot be applied to the sheet formability under biaxial stretching, the one by St6reii and Rice leaves stronc- impression that it can be applied to biaxial stretching. However, the detail examination discovers that both analyses are substantially identical for assumptions in equilibrium and deformation rate. Therefore, the analysis by Stbren and Rice remains still within the territory of Hill's analysis, and it also cannot be applied to biaxial stretching fundamentally. Localized necking is a phenomenon where velocity gradient or strain rate becomes discontinuous on a necking plane, while the eqtjilibriuni of force must be maintained on both sides of the plane. However, the analyses published so far were insufficient with respect to the equilibrium and the mode of necking planc. Rigorous treatment for thein is demonstrated.

Keywords:Plastic Instability, Localized Necking, Mode of Necking Plane, Formability, Equilibrium, Multi-solutions



Effects of Die Shapes on Welding Strength of Extruded Pipes by Port-Hole Die
-Improvement in Quality of Hollow Extrusions I -

(Received on june 29, 1994)

Norio TAKATSUJI, Mitsugu TOKIZAWA, Satoshi MURAKAMI Kazuo MUROTANI, Kenji MATSUKI and Kazuhiro YUASA

The relation between the behaviour of metal flow and the extrusion pressure in the pipe extrusion process by a port-hole die is investigated from the model extrusion test by using a plasticine billet. The extrusion pressure curve is classified into three categories; the filling process in port-holes, the filling and welding process in a welding chamber, and the stationary process of extrusion. The effect of the shape of die cap and the number of port-hole on the welding strength of extruded pipe is investigated experimentally. The welding strength of extruded pipe obtained from expanding test is influenced severely by the filling and welding pressure in the welding chamber, and the area of high energy welding zone and the length of sliding friction observed from macro-structure on the welding plane. The welding strength of extruded pipe is improved by the port-hole die with a high welding chamber, a small die semi-angle and many port-holes.

Keywords: extrusion, die design, port-hole die, extrusion pressure, welding strength, aluminum pipe,@die semi-angle, welding chamber, number of port-hole



Analysis and Measurement of Oil Film Thickness Considering Surface Roughness
-An Investigation into Friction and Lubrication in Cold Rolling V -

(Received on June 30, 1994)

Akira AzusHIMA

Analysis and measurement of oil film thickness In rolling are made In order to clarify the effect of surface roughness of roll and sheet on oll film thickness. The oll film thickness In the Inlet zone of contact region Is calculated analytically based on Reynolds equation consldering the surface roughnesses of roll and sheet, and the effect of temperature and pressure on vlscoslty of lubricant. Then, the oll film thickness In rolling Is experimentally measured by a method whlch Is to measure the oil film thickness from the relatlon between the volume of lubricant trapped on the sheet surface before rolling and the area of lubricant spread on the sheet surface after rolling. The results obtained from calculation and experiment are as follows: (1) The Inlet oil fllm thickness Is affected by the surface roughnesses of roll and sheet In the range of the ratio of Inlet oil film thickness to combined surface roughness a of 0.5 to 3. (2) If the calculated Inlet oll film thickness Is smaller than a half of combined surface roughness a , lt can not be used quantitatively.

Keywords:cold rolling, oil film thickness, surface roughness, friction, lubrication,



Estimation of Stress in Deep-Drawing by Stress Whitening of Plastics

(Received on June 30, 1994)

Tadae MORISIIITA and Kiyoshi NISHIMOTO

Scribed-circle or scribed-lattice tests, and more recently, the finite element methods have beeen used in order to analyse the deformation bebavior during deep-drawing of irregu- lar-shaped containers. However, conventional experimental methods are incapable of measur- ing directly the stress in the blank, which is important for the full understanding of the deformation process. The purpose of the experimental method proposed in the present paper is the direct measurement of the stress induced in the formed blank, by utili2ing the stress whitening of polypropylene as the formed material. The degree of the whitening is displayed as a pseudo-coloring image through computer processing. As a result of deep- drawing experiments of polypropylene, the pseudo-coloring display has coincided with the stress that has been obtained by the computation from the measured deformation.

Keywords:stress whitening, tensile stress, deep-drawing, plastics, yield stress



Influence of Surface Topography of Punch on Blanking Forces and Tool Life

(Received on August 2, 1994)

Isamu AOKI and Toshinori TAKAHASHl

In this study, an attempt has been made to determine the influence of surface topography of a punch flank such as roughness and rrdcrotopology on blanking forces and tool life through experiment. The surface topography is varied by various process -ing methods such as lapping, grinding and shot peening. Blanking tests using 3 mm- thick aluminum sheets showed that the blank-pushing force and stripping force were remarkably reduced by using a roughly finished ground or peened punch. In the tests of continuous blanking using 0.3 mm-thick stainless steel sheets, it was found that the peened punch edge could be prevented from chipping when a ground tool was used. This seems to be due to the lubricant accumulated in the micro-pool formed by the surface@finishing processes.

Keywords:shearing, blanking, surface topography, shot peening, micro-pool, tool life



Approximate Analysis of Draw Bead Force by Energy Method

(Received on October 6,1994)

Yoshinori NAGAI and Yasutomo NAGAI

Draw bead force can be obtained analytically by using simple models. In this analytical method, the bead shape of sheet metal is approximated to the displacement function composed of circular arcs and straight lines. Then, draw bead force is determined on condition that the plastic work by using of the function becomes minimum. The conclusions are as follows. Draw bead force increases in proportion to the effective curvature "K" which is proposed in this analysis. K is the sum of absolute value of incremental curvature which occurs from entrance to the exit of the bead. Draw bead force is determined by K and the axial force at entrance of the bead which is calculated by blank holding force and friction coefficient. It is confirmed that calculating bead force with variations of bead shape, bead height and holding force agree comparatively with experimental ones. The method of this analysis can be combined with FEM simulation program of drawing of panel in order to reduce the.computing time./FONT>

Keywords:draw bead force, energy method, approximate analysis, effective curvature, round bead, rectangular bead



Composite Strips of Metal Powder and Solid by Rolling

(Received on October 24, 1994)

Sam MASAKI, junchu Li and Katsushi KUBO

A method of producing composite strips of metal powder and solid is proposed by cold rolling and sinter bonding. Copper or stainless steel powder is rolled together with a solid steel strip that has numerous punching holes. The punched strip is sandwiched between layers of the compacted powder and then is sintered. A composite strip with the compacted po%vder layer on one side of the punched strip is also fabricated. Effects of the roll gap on (1) the rolling load, (2) the relative density at powder layers and (3) the thickness of composite strip after sintering are presented. The thickness of sintered powder layer can be made very thick in comparison with the thickness of sintered powder strip made from conventional powder rolling. The bond strength between the powder layer and the punched strip is mainly dependent upon bridges of the sintered powder through the punching holes. Re-rolling of the composite strip gives higher strength, higher density and better surface roughness.

Keywords:powder forming, powder rolling, sintered powder materials, compos- ite materials, plastic forming, powder compaction



Elastic-Plastic Behavior of Sheet Metal Subjected to In-plane Reverse Loading

(Received on December 5, 1994)

Toshihiko KUWABARA, Yoshiyuki MORITA Yohsuke MIYASHITA and Susumu TAKAHASHI

A novel experimental method for measuring in-plane compressive stress-strain curves of sheet metal is proposed with using comb-shaped dies. Furthermore, using this method, uniaxial tensile test of in-plane pre- compressed specimens (CT-test), in-plane compression test of uniaxially pre-stretched specimens (TC-test), and uniaxial re-tensile test of TC-tested specimens (TCT-test) are conducted for aluminum alloy A5182-0 and AK- steel sheet (SPCE). Results obtained in this study are as follows. 1) For virgin material of A5182-0, in-plane compressive true stress lcl is almost the same as the uniaxial tensile true stress cr, , while for AK-steel, lal becomes larger than a, . 2) For TC-, CT-, TCT-tests, the plastic flow stress observed during reverse loading exhibits a definite decrease compared with that of the virgin specimen. 3) It is found for A5182-0 that the c-and ti-values of uniaxial stress-strain curves obtained from CT-and TCT-tests can be formulated as a single function of the sum of the plastic strains imposed on the specimen prior to the tensile test. 4) AK-steel exhibits either non- work hardening region or work softening region in the stress-strain curves during reverse loading. Further investigation is necessary to formulate complicated work-hardening behavior of AK-steel.

Keywords: material testing, sheet metal, in-plane compression test, reverse loading, A5182-0, AK-steel