Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(Vol.38 No.440 September 1997)

Prediction of Wrinkling and Strain of Rectangular Aluminum Tubes in Draw Bending

Masatoshi YOSHIDA and Akibumi FUJIWARA

(Received on September 17, 1996)

Extruded rectangular aluminum tubes are used as automobile parts such as for bumper reinforcement and are expected to be used for frame body structures. Curved versions of these tubes are produced from straight ones by bend forming. In the bending process, wrinkling of the compressive flange and rupture of the tensile flange sometimes occur. A theoretical analysis model for estimating wrinkle pitch and depth in the compressive flange and strain in the tensile flange was developed. Some numerical calculations and experiments were performed. The main results are as follows :
1. The calculated wrinkle depth and pitch in the compressive flange and strain in the tensile flange agree well with those determined by experiment.
2. The nondimensional wrinkle depth can be estimated from the nondimensional bending radius, aspect ratio, proof stress, work hardening constant and work hardening exponent.
3. The wrinkle depth decreases with increasing work hardening exponent and decreasing proof stress.
Key words : bending, draw bending, rectangular tube, wrinkle, plastic buckling, aluminum

Analysis of Roll Straightening and Cooling of Thick Plates

Shogo TOMITA, Masahisa FUJIKAKE, Yoneaki FUJITA and Yuuji MATSUOKA

(Received on October 2 1996)

A method of numerically analyzing strains and residual stresses occuring in roller leveling and cooling of thick plates was developed. A roller leveler model including analysis of deformation of leveler rolls and a thermo-elasto-plastic model based on FEM for the cooling process were formulated and combined. Using these models, a series of analyses were carried out and the following conclusions were reached; (1) The residual stresses in plates can be reduced by hot leveling, but nonuniform cooling of plates induces further residual stresses in plates. (2) The stiffness of the frame of the cold leveller should be high enough to reduce residual stresses in plates.
Key words : Shape correction, Leveling, Roller leveler, Plate rolling, Thermo mechanical control process, Numerical analysis, Thermal-elasto-plastic FEM, Residual stress

Development of Flexible Spin-Forming Method

Susumu SHIMA, Hidetoshi KOTERA and Hirotaka MURAKAMI

(Received on October 18 1996)

An attempt is made to develop a flexible spin-forming system, where spin-forming is performed without using a mandrel. It is shown that forming is possible if a pair of rollers that grip the workpiece move so that the moving direction is parallel to the common tangent at the contact between the rollers and the workpiece. A simple cone-shaped product is thus formed. The thickness variation along the radius of the workpiece is similar to that in conventional spin-forming, but is influenced by the feed rate of the rollers. The lowest feed rate in the experiment provides the smallest thickness and a cone half angle that is nearest to the desired one, and they both increase with increasing feed rate. When the feed rate is small enough, over-shearing occurs. By performing proper control of the movement of the rollers, it would thus be possible to develop a metal forming robot that performs spinning without mandrels.
Key words : spin-forming, spinning, flexibility, forming robot

Improvement of High-Strength Steel Sheet Mechanical Properties by Rolling with Small-diameter Rolls

Toshirou FUJIWARA Tetsu MATOBA, Yasuhiro ITAZURI Matsuo ATAKA and Itaru AOKI

(Received on October 31, 1996)

A high cold rolling reduction ratio is required for improving the mechanical properties, especially the r-value, of high-strength automotive steel sheets. For the high reduction ratio of cold rolling, the first stand of an existing 4-high tandem cold rolling mill was replaced with an asymmetric cluster mill having a small-diameter upper work roll, two intermediate rolls and three transversely divided backup rolls. By reduction of the upper work roll diameter, the rolling load of high-strength steel sheets is reduced by 20%. Also, a crown control mechanism comprising an intermediate rolls bender and a crown bender of backup rolls prevents deviation of the strip shape and enlarges the reduction range. This study was carried out under various conditions to determine whether rolling with a small-diameter asymmetric upper roll would affect the r-value. The r-value and the texture which affects the r-value did not significantly differ between asymmetric and equal-diameter roll rolling. The small-diameter upper work roll wears faster than the large-diameter lower one. However, this can be dealt with by using semi-high speed steel as the roll material. With the high cold rolling reduction mill, it has become possible to produce on a stable basis high r-value, 340-440 MPa-class, automotive deep-drawing cold-rolled steel sheets nearly 1.5 m wide.
Key words : rolling, strip rolling, high-strength steel, asymmetric rolling, material property, r-value

A Forward-Backward Extrusion Method with Axially Driven Tapered Container

Xin WANG, Kozo OSAKADA and Shinji HANAMI

(Received on November 6, 1996)

In cold-combined forward-backward extrusion, a method employing an axially driven tapered container is proposed to obtain a product with arbitrary extrusion lengths under the least possible forming pressure. In this method, the container, which is tapered on one side, is moved in the axial direction using an actuator while the billet material is extruded bidirectionally by the punch. The material flow in the direction of container movement is enhanced and the flow in the opposite direction is restricted, not only by the effect of the friction over the container-billet interface but also by the effect of the axial tension caused by the tapered part of the container. Thus, the material flow in both directions can be controlled by changing the container speed, the angle of the taper and the initial position of the tapered container. The effectiveness of the proposed method is examined through experiments using a model material (plasticine) and through FEM simulation. The results show that the bidirectional material flow can be controlled to a great extent, and the sharp increase of extrusion pressure due to one directional flow at the end of forming can be avoided.
Key words : extrusion, material flow control, tapered container movement, FEM

Development of Flexible L-Bending Process System with Intelligent Tools

Ming YANG, Yosuke KITAGAWA and Ken-ichi MANABE

(Received on November 6, 1996)

A new intelligent tool system for flexible L-bending of sheet metals is proposed and developed to cope with various bending radii. The autonomous system consists of a processor and sensors and actuators incorporated in the tools. It can basically change the profile of the tool and the pressure distribution acting on the workpiece during the bending process. An important feature is that the system is capable of bending workpieces by various bending radii without tool change under any forming conditions for different materials. The control process path for obtaining the desired bend radius is determined off-line by numerical simulation elastic-plastic model. The paths are stacked into a simulation database and used for real-time control of the bending radius of the workpiece. The experimental results on the bending radius sheet correspond to not only various bending radii but also different materials, SPC and aluminum alloy. These results support the validity of the proposed intelligent tool system.
Key words : bending, intelligent machine, control system, database, bending radius, numerical simulation

Development and Features of Super Micro Mill

Kouichi KURODA, Kazuyuki NAKASUJI Yoichi IMAMURA and Chihiro HAYASHI

(Received on November 6, 1996)

A new cold wire rolling method which can replace the drawing process is proposed. A highly efficient cold rolling mill for wire has been developed after basic experimentation with a model mill to investigate rolling characteristics in 4-roll groove rolling. This rolling process is characterized by continuous rolling in 4-roll stands, and by use of the round to round pass sequence, so that there is no requirement for a guide between the roll stands. By use of this newly developed super micro mill, wire with a minimum diameter of I . 2 mm can be produced. The diameter variation in a section of rolled wire is within +-20 micro meters, so precision rolling can be carried out. This rolling can suppress generation of surface defects such as scratches due to contact with the guide, and wire with excellent surface characteristics can be rolled. Moreover, the body of the mill can be made extremely compact.
Key words : cold rolling, wire rolling, micro mill, 4-roll groove rolling, precision rolling, spreading, shrinking, ovality, surface defects

Forward Slip in Rotary Bar Rolling Using the Rotary Reduction Mill

Kazuyuki NAKASUJI Kouichi KURODA and Chihiro HAYASHI

(Received on November 6, 1996)

The rotary reduction mill has been developed as a mill which can reduce solid metallic materials efficiently in a one-pass operation, and is a rotary mill for bar rolling. The three rolls are arranged around the pass line and the roll axis are inclined or inclinable with respect to the pass line by a cross angle and a feed angle. Forward slip, in axial and circumferential directions of rolled material, varies largely in the contact area due to the rolling conditions and roll profile. In this paper, rotary heavy reduction rolling experiments were carried out using a S45C bar, as rolled material, in the rotary reduction mill, and forward slip in rotary rolling has been formulated by clarifying the friction direction in the contact area of material and roll within rolling bite zone. Using this formulation, forward slip of material in the roll bite zone and the friction direction at the contact area of the roll can be predicted with fair accuracy under various rotary rolling conditions.
Key words : rotary bar rolling, heavy reduction mill, three-roll rotary reduction mill, rolling speed, forward slip, feed angle, cross angle, face angle of rolling, elongation ratio

Note in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY


Deformation of Corner Region and Forming Limit in a Square Cup Drawing

Takaji MIZUNO and Daixin ER

(Received on February 13, 1997)

Rectangular (36mm X 72 mm) cups with different corner radii (1, 3 and 9 mm) are deep-drawn from a rectangular blank sheet of copper 0.2mm thick. Deep cups with small corner radii, which produce large values for local drawing ratio, are successfully formed. This can be explained in terms of a radial compressive stress that prevails in the middle of the corner flange. With reference to this "back pressure actions" produced by a fast inflow of the straight side flange, the effects of corner cut, punch corner geometry, punch friction and work hardenability on the forming limit are discussed.
Key words : sheet metal forming, deep drawing, rectangular cup, strain, forming limit