In-plane tension and compression experiments on an austenitic stainless steel sheet SUS304 0.3 mm in thickness for electronic parts were conducted using a specially designed testing apparatus. The apparatus is equipped with comb-type dies so that stress–strain curves of a sheet specimen subjected to tension followed by compression, and vice versa, can be measured without buckling of the specimen, as well as those for monotonic tension and compression. A difference was observed in the flow stresses between tension and compression for the test material both in the rolling and transverse directions. Moreover, stress reversal tests, such as tension followed by compression and compression followed by tension, were carried out in order to measure the Bauschinger effect. In the second part of the experiment, bending moment–curvature diagrams were measured both in the rolling and transverse bending. The bending moment–curvature diagrams were compared with those calculated using the stress–strain curves obtained from the tension–compression tests, and were in good agreement with those calculated with the tension–compression asymmetry and the Bauschinger effect correctly reproduced.
In this paper, reliability based design optimization method for the determination of tension leveling process combining Finite Element (FE) simulation and numerical stochastic optimization method has been proposed. For the tension leveling calculation, steady state analysis based on the incremental deformation theory of plasticity is adopted. In the simulation, Chaboche-Rousselier hardening rule is used for accurate cyclic stress-strain calculation. Since only steady state of a metallic strip is calculated and contact analysis can be avoided the computing cost of the FE simulation is very small compare to other non-steady FE simulations. The optimization problem is formulated to minimize the probability of failure. In this problem, it is assumed that a failure product appears due to the tolerances of design variables such as tension load, roll-intermesh and so on, and uncontrollable variables like geometric parameters and mechanical properties. Tolerances of such parameters are assumed to appear in stochastic manner. For probability of failure estimation, Monte Carlo simulation, which virtually demonstrates a mass production by iteratively generating the design and uncontrollable variables randomly, is employed. Additionally, the response surface with Moving Least Square Method is used to reduce the computing time. The proposed optimization has been applied on the four-work-roll tension leveling process design problem. The obtained result is more reliable than the optimum obtained by the ordinary deterministic optimization method. Additionally, it is found that the tolerances of the initial yield stress and Young's modulus have a great influence on the residual curvature.
Numerical simulation of roller leveling of thick plate was conducted using a dynamic explicit finite element code DYNA3D. The straightening process of a thick plate whose tip portion was initially bent was first calculated to check the applicability of the numerical simulation. The number of rolls was reduced from that used in practice. The effective intermesh setting of the rolls was found. The influence of the feeding speed of the plate was also checked to examine the effect of speed-scaling technique for the improvement of computational efficiency when the dynamic explicit finite element code was used. The shape defect of undulation at the tip portion of the plate was numerically predicted when the flat plate passed through the leveler. The amplitude in undulation was found smaller for the thicker plate by comparing the calculated surface profile with the circular arc of steady-state deformed shape. The thicker plate caused a local thinning phenomenon due to the severe bending deformation. The shape defect of undulation at the end potion of the plate after leveling process was also numerically predicted. The end portion of the plate showed a sigmoidal or V-bent pattern in accordance with the intermesh setting. The length of defect part was shortened by decreasing the diameter and pitch of the final two rolls.
At Present, the flattening process has been operated by experience and intuition of the expert. On the other hand, the quantification of the flattening condition has been required, and it is urgent to clarify the mechanism of the flattening process. This study carries out the roller leveler flattening for the plate, and it aims at the quantification of the flattening condition, while the mechanism of the flattening process is clarified by surface strain measurement under straightening and contact point observation with the roll, after shape evaluation. As a result, the quality of 3-points bending condition in the top and bottom roll greatly influenced the plate shape by the surface strain comparison of maximum value and roll contact location under flattening, and it became clear that the possible range for flattening had been decided. And, the prospect that the intermesh of the top and bottom roll uniquely sets became possible was obtained as the flattening condition.
Most of metal products are manufactured through leveling process. In late years, with improvement of product quality and precision, materials with high quality are demanded. However, automation of leveling process does not advance. For automation of leveling process, elucidation of deformation mechanism of plate in leveling process is important. In this paper, the leveling effect of stable zone, the leveling effect of unstable zone and the change in mechanical qualities of material after leveling were examined. As a result, the following things were found. 1) Curls and waves except the top and end of plates are leveled enough, when large bending deformation of more than plastic deformation ratio 70% are given to the plates more than twice. 2) The curl at the top of plates gets in an irrelevant condition by leveling, but it can be leveled in a proper condition. In addition, leveling effects are different depending on the directions of the curls at the top of plates. 3) Large bending transformation is necessary to get a leveling effect enough. But changes in mechanical qualities of materials occur. In consideration of this abhorrent relation, it is necessary to devise the way how plates are leveled.
An on-line model predicting the residual stress in roller leveling process is developed. In order to simplify the formulation, the plain strain (dεz=0) condition is assumed and the stress in thickness direction is ignored (σy=dσy=0). The camber and gutter deformation of the real sized plate are measured and compared with the prediction values of the model to validate the accuracy of the model. The variations of residual stress are studied according to the entry and the delivery intermeshes, respectively. The camber deformation decreases linearly as increasing the entry intermesh. But the gutter deformation does not vary directly as the intermesh. Therefore, the optimum intermesh values should be found to minimize both the camber and the gutter deformation.
Three-dimensional finite element analysis of a roller straightening of an equal leg angle was performed in the present paper in order to validate the usefulness of the employment of FEM to the determination of the intermeshes of rolls in actual roller straightening process. SS400 was employed for the material of equal leg angle. For the plastic constitutive equation of the material, Armstrong–Frederick type combined hardening law was used. Initial shape of the equal leg angle had a uniform curvature lengthwise. A dynamic explicit procedure was used to realize the feeding of the equal leg angle into the intermeshed rolls by rotating the bottom rolls and to accomplish the calculation under the condition of frequent contact-separation between equal leg angle–roll interface. A static implicit procedure was subsequently used to obtain the final shape of equal leg angle by using the last state of equal leg angle by dynamic explicit process. Elastic spring elements were introduced in order to support upper rolls to realize the elastic deflection of the roller straightener apparatus. The spring constant was determined so that straightness of equal leg angle after straightening can be less than 0.1% of its length. The distribution of bending stress, bending plastic strain during and after straightening were observed and discussed. Finally, the effect of intermesh of final roll on the straightness of equal leg angle was calculated.
Straightening has been widely used to the industry for bars and wires to remove or change curvature, such as a cast or helix (curved and twisted) of coiled bars, produced by the wire rod rolling or wire drawing process. Roller leveler straightening is one of the most popular methods on straightening wires or coiled bars. Recently, required straightness for parts of such as automobile and precision apparatus has been getting higher. But higher straightness was not able to achieved by roller leveler, and it was considered whether there was a limit in the straightening technology. The purpose of this study is to investigate roller leveler mechanism by numerical and experimental analysis. The limit value of straightness was found only when coiled bar was straightened. The limit value of straightness was caused by the 3-dimensional shape of coiled bars (curved and twisted) and the tilting of bars during straightening. The numerical results by FE analysis on straightness and tilting of bar are good agreement with the experimental ones. Therefore, the numerical analysis is promising tool for estimating the limit value of straightness and bar tilting. From the numerical and the experimental analysis, initial shape of curved and twisted coiled bar is main factor causing bar tilting.
Exacting requirements, such as high dimensional accuracy, straightness, fatigue characteristics and high strength, must be satisfied for fine wire used as saw wire, discharge machine wire and bonding wire. In this study, the changes in the straightness and the residual stress of a drawn wire after tension straightening and roller leveler straightening were examined experimentally and by a finite element method (FEM). It was clarified that tension straightening is effective not only for improving straightness but also for decreasing the residual stress of a wire. Improved straightness is observed when the applied tensile stress is 70–80% of the wire strength. By tension annealing treatment, extremely high straightness, which cannot be obtained by cold tension straightening, was obtained. Meanwhile, the straightening of less fine wire using a roller leveler has various merits, such as a simple mechanism and a low machine cost. FEM analysis of roller leveler straightening is effective for predicting the straightness and residual stress. Using a roller leveler with a horizontal roller arrangement, the straightness of a drawn wire improves only slightly. In contrast, using a roller leveler with an inclined roller arrangement, the straightness of a drawn wire improves greatly and an almost perfectly straight wire can be obtained.
Higher straightness of superfine wires of 0.1 mm or less in diameter is in demand for recent development of electronic devices. A rotational blade straightener is effective for straightening superfine wires. It is particularly effective for straightening coiled wires because the straightener can bend wires along the longitudinal and circumferential directions. We found that a higher rotational speed of blades, lower feeding velocity, and gradual decrease in curvature ratio during straightening were very effective in producing excellent straightness in rotational blade straightening. Tension annealing is also one of the popular methods to straighten superfine wires. The tension annealing has a higher level of straightening effect without surface damage. The phosphor bronze and the tungsten superfine wires are used in this study. We observe that the initial radius of curvature, roundness and work hardening exponent are very important factors to make excellent straightness in tension annealing.
Straightening process of steel tubes is the final process in tube making processes and it has a very important role for straightening in the longitudinal direction and improving roundness and thickness distribution of the cross section. To satisfy the demand for the higher tolerance of steel tubes, optimization of the working conditions in this process has been a serious problem. However, there are few studies on the straightening process of tubes because of the complexity of 3-D deformation behavior. In this research, effects of roll inclination and crushing on the roundness of a tube are examined by FE analysis of rounding of the cross section with a single straightening machine. When the crushing is large, spiral redundant plastic deformation occurs in the tube and the roundness of tube becomes bad. When the crushing is very small, elastic strain which occupies almost of the deformation is recovered. Since the roundness is improved by bending and unbending the cross section repeatedly, it is clarified that the number of cycles of the spiral deformation is an effective parameter. Therefore, we define the contacting ratio between the rolls and the tube and improvement of the roundness can be estimated by this ratio. When the contacting ratio is larger than 80%, the roundness becomes good.