Papers in JOURNAL OF THE JAPAN SOCIETY
FOR TECHNOLOGY OF PLASTICITY

(Vol.41 No.472 May 2000)

Automated Design System of Rolls for Reshaping
of Circular Pipes into Channel-Type Pipes

Manabu KIUCHI, Hassan MOSLEMI NAEINI and Ken SHINTANI

(Received on June 15, 1999)

The reshaping of circular pipes into pipes with various cross-sections is an effective and useful manufacturing process for adding value and improving productivity in the pipe/tube industry. Although the reshaping technology has rather long history, the design of roll profiles and pass schedules is still relying on experience-based knowledge. This is due to the complicated deformation behavior of pipes during reshaping. Thus, systematic approaches to the reshaping technology and theoretical studies on the design of rolls and pass Schedules are strongly required. In this research, a numerical simulation method called the finite difference method (FDM) was extensively developed in order to analyze two-dimensional elasto plastic deformations of pipes' cross-sections during various reshaping processes. In this work, the numerical analyses of forward and backward deformations of pipes are performed using the modified FDM. These analyses enable the determination of roll profiles, which can be used for reshaping circular pipes into the desired products. The developed roll design method is applied to the fabrication of channel-type pipes. As a result, the ideal roll profiles were obtained.
Key words : cold roll forming, reshaping process, forward deformation analysis, backward deformation analysis, roll design, process design

Net Shape Processing for a Watch Crown
by Cold Multistage Forging and Form Rolling

Isao KUBOKI，Toshio KUSANO and Kazunari YOSHIDA

(Received on June 23, 1999)

By means of cold multistage forging followed by form-rolling processing in a ferritic stainless steel wire, a wristwatch crown, which is small and complicated with a groove, can be formed into its final shape in a fairly short time which is about 1/40 of the time required in conventional cutting processes. The position accuracy of the groove is improved by form-rolling performed while the bottom edge of the crown head is brought into contact with dies. Since annealing before form-rolling decreases the exfoliation of the groove that is caused by form-rolling, the surface roughness of the groove is improved. The Mannesmann defect is generated by form-rolling, however the load necessary to bend the stem of a form-rolled crown is greater than that of a cut crown.
Key words : cold forging, form rolling, stainless steel, crown, process design, surface roughness

Development of a New Yube-Drawing Process for
Achieving Ultrasmooth Inner Surface

Yoichi IMAMURA, Munekatsu FURUGEN, Yoshinobu ANDO and Hajimu CHOBA

(Received on June 30, 1999)

Clean tubes, which are stainless steel tubes used in semiconductor manufacturing apparatus, require ultrasmooth inner surface of the material, it is well known that is necessary for the material to be subject to high contact pressure and large plastic strain. A new drawing process are characterized by using a plug with a protruding ring on the finishing zone. The protruding ring induces large plastic strain at the inner surface layer. The amount of plastic strain induces by the protruding ring plug is 4-5 times greater than that induced a conventional plug. The new process can achieve a finished inner surface of roughness, Rmax, of 0.4-0.6μm without electrical polishing. The new process, ultrasmooth drawing process, is successfully applied to a manufacture of clean tubes. The clean tubes manufactured by the new process have excellent performance equivalent to tubes manufactured by electrical polishing.
Key words : Clean tubes, surface roughness, drawing, smoothing, protruding ring plug

Die Design in Multistage Redrawing of Cups of Arbitrary Convex Shape

Kunio ISOBE

(Received on July 23, 1999)

The slip line field method is employed to design the shapes and angles of dies for redrawing. The arbitrary convex shape of a product is approximated with a spline function and the start points of slip lines are searched for numerically. An equiangular net of slip lines is constructed on the flange by a geometrical method. The outer fringe of the die, which coincides with a minimum stress trajectory, is derived from the condition that the material points on the outer fringe reach the inner fringe simultaneously. Because the die angles are varied along the fringes to compensate for the nonuniform material speeds at the outer fringe, points at a certain height on the predrawn wall reach and pass through the inner fringe simultaneously during redrawing. This method is repeated from the final redrawing to the first deep drawing. The computing time is only a few seconds using a personal computer. Therefore, the method is useful for the process planning and die design for the redrawing of cups of arbitrary convex shape.
Key words : deep drawing, redrawing, multistage redrawing, sheet metal forming, die design, slip line field

Influence of the Type of Multi-Roll Mill for Small Diameter Wire
Rolling on the Contact Geometry and Rolling Characteristics
in the Contact Area

Kouichi KURODA, Masayoshi AKIYAMA,
Takashi KUBOKI and Chihiro HAYASHI

(Received on July 27, 1999)

The influence of the type of multi-roll mill on the contact contour and rolling characteristics in the contact area was quantitatively clarified for small-diameter cold-wire rolling. A comparison was made among 2-roll-, 3-roll-, and 4-roll-type mills, and it was clarified that the influence of the groove geometry on the contact contour is maximum for the 2-roll-type mill, and minimum for the 4-roll-type mill. The contact area is almost rectangular and is less affected by the groove geometry in a 4-roll-type mill. As a result, it was found that the uniformity of forward slip or backward slip is largest for the 4-roll-type mill. The results of quantitative evaluation of rolling characteristics in the contact area were presented to reveal the stability of the 4-roll-type mill.
Key words : cold rolling, wire rolling, multi-roll mill, micro mill, contact contour, contact area, FEM, forward slip, backward slip, contact pressure

Multivariable Control of Wire Rod Rolling and Precision Rolling System

Yukio NOGUCHI, Harutoshi OGAI, Kunihiko OKAMURA,
Takayoshi HIZUME, Koji TANABE and Koji YOSHIMURA

(Received on August 2, 1999）

This paper deals with the multivariable control and precision rolling system for the No-Twist rod finishing block mill. The roll gaps of 1st and last stands (control inputs) greatly influence the exit height and width of the last stand (controlled variables) due to a common drive. First, we derive a linear state-space model which is applicable to the discrete-time optimal regulator theory, by adding a feedforward control. The control law is implemented by the state vector feedback and the disturbance vector feedforward. In order to evaluate the control performance, responses to entry diameter and entry temperature changes are computed and measured on a model mill and computed on production mills. On the basis of the computed and experimental results, the validity of the present control system is confirmed. With the multivariable control system, the precision rolling of a wire rod with a nominal diameter tolerance of ±0.1 mm has been put into practical operation.
Key words : extended discrete-time optimal regulator theory, multivariable control, wire rod rolling, no-twist rod finishing block mill, precision rolling system

Dynamic-Explicit Elasto‐Plastic Finite Element Analysis
of Roll Forming

Eiji NAKAMACHI and Yoshinori HAMADA

(Received on August 30, 1999)

Recently, the virtual manufacturing technology by using the finite element analysis and optimization codes has shown the great progress in automotive, electric appliance, train and aviation industries. In this study, the roll forming process to produce the automotive bumper was analyzed by using the dynamic-explicit elasto- plastic finite element method. We obtained the deformation, strain and stress of the long strip sheet formed by passing twelve roll stands. Further, the availability of our finite element code was confirmed through the comparison with the experimental measurement.
Key words : finite element method, shell element, elasto-plastic FEM, roll forming process, virtual manufacturing

Numerical Simulation on Stress Relief Processes Using
an Extended Thermo-Elastic-Plastic FEM

Masahiko YOSHINO and Tomohiro SHIRAISHI

(Received on September 10, 1999)

In this paper, an extended thermo-elastic-plastic FEM system is proposed, and its application to stress relief annealing processes of bent specimens is shown. The FEM system is constructed by introducing a new constitutive equation, that includes the generalized deformation energy as an internal variable, into the ABAQUS code. In the system, elastic-plastic analysis and thermal analysis are combined, and distrotion of the specimen and temperature distribution are determined simultaneously. A new calculation method to compensate thermal stress in the thickness direction that arises when a conventional plane strain element is applied to a heat-treatment process is also proposed. The FEM system was applied to three-point-bending and annealing processes. The results agreed qualitatively with experimental ones. Based on the simulation results, this paper discusses mechanisms of stress relief annealing.
Key words : bending, constitutive equation, annealing, elastic-plastic FEM, thermal analysis, stress relief annealing, residual stress