Analysis and Control of Cracking and Wrinkling at the End of Seamless Steel Tube with Multi-Pass Large Deformation Diameter-Reducing

Axial cracking and circumferential wrinkling are found at the end of seamless steel tubes during multi-pass large deformations pushing diameter-reducing (PDR), which seriously affects product quality. However, the cracking and wrinkling mechanism of PDR has not been elucidated yet. In this paper, the Equation of circumferential residual stress at the end was deduced from the warping deformation and shear stress. It is revealed that the circumferential residual stress in the end warping area from the inner to outer surface is tensile, and the generation mechanism of circumferential wrinkling on the inner wall at the end was revealed through the deformation analysis of PDR. The geometric model of the tube with periodic alternating variation of wall thickness was established to reveal the generation and development of circumferential wrinkling. In addition, the four-pass PDR experiments and simulations were developed to reveal the influence of reducing pass and wall thickness deviation on the end warpage, unevenness and circumferential residual tensile stress. The pushing-pulling diameter-reducing (PPDR) method was proposed to control the wrinkling and cracking. The simulation and experimental results showed that the end warpage, unevenness and circumferential residual tensile stress are all greatly decreased, and the risk of axial cracking and circumferential wrinkling is eliminated.

Prediction of Mechanical Properties of Seamless Steel Tubes Using Artificial Neural Networks

A bottleneck of laboratory analysis in process industries including steelmaking plants is the low sampling rate. Inference models using only variables measured online have then been used to made such information available in advance. This study develops predictive models for key mechanical properties of seamless steel tubes, by strength, ultimate tensile strength and hardness. A plant in Brazil was used as the case study. The sample sizes of some steel tube families given namely, yield a particular property are discrepant and sometimes very small. To overcome this sample imbalance and lack of representativeness, committees of predictive neural network models based on bagging predictors, a type of ensemble method, were adopted. As a result, all steel families for all properties have been satisfactorily described showing the correlations between targets and model estimates close to 99%. These results were compared to multiple linear regression, support vector machine and a simpler neural network. Such information available in advance favors corrective actions before complete tube production mitigating rework costs in general.

Effect of the Friction and Reduction Angle on the Accuracy of Cold Drawing Steel Tubes STL Model Based on FEM Analysis

The object of the study was to create a computer model that resembles the process of cold drawing seamless steel tubes, and evaluate the influence of selected process parameters on selected final dimensions and tolerances of STL models of the tubes obtained from DEFORM simulation software. The STL models of tubes generated from the simulations were evaluated, and the effects of the reduction angle and the friction coefficient on the inner/outer diameter, inner/outer roundness and concentricity were subsequently found. It was proven that the inner and outer diameters are not influenced by different values of the friction coefficient at the same reduction angle. On the other hand, increasing value of the reduction angle affects decrease of the outer and inner diamaters after drawing. Furthermore, this experimental investigation vindicates that friction coefficient and reduction angle have the minimal impact on the inner/outer roundness and outer concentricity.

Using 2D/3D FEM Simulation to Determine Drawing Force in Cold Drawing of Steel Tubes with Straight Internal Rifling

The most comprehensive steel tube portfolio is used to produce all kinds of modern energy production and the corresponding auxiliary unit such as boilers and heat exchangers. Multi-rifled seamless steel tubes are distinguished by maximum pressure, heat resistance, strength and durability. Production of multi-rifled seamless steel tubes by cold draw process using multi-rifled mandrel is quite a new technology. Shape and dimension of the drawing tool depend on drawing tube reduction degree, i. e. on the original diameter of the initial tube and final diameter of the tube. The technology of drawing tubes is influenced by process parameters, dimensions of tools and cold forming process conditions. Optimization of the whole forming process naturally involve the FEM analyses and simulation. One of the most important information of the cold drawing process is the load stroke of the tools. The contribution is concerned at the usability of FEM simulation on an evaluation of cold draw forming process condition and prediction of load stroke of the forming tools. DEFORM 2D/3D FEM software is used to compare the result of the drawing force and to determine the appropriate methodology to set FEM simulation of cold forming.

Numerical Simulation of Material Plastic Deformation Using the Drawing Forming Process of Contoured Internal Surface Tubes

Production of multi-rifled seamless steel tubes employing cold draw process using multi-rifled mandrel is quite a modern technology. The important characteristic of the tube drawing process, unlike the tube with internal rifling, is the corner filling which influences the dimension accuracy of the internal shape of the tube. In this study, the influence of drawing tool dimensions and mandrel shape on to final rifling filling was investigated. Draw process has been simulated by using the three-dimensional rigid-plastic finite element method (FEM) by using DEFORM 3D software. The results of numerical simulation show that the shape of drawing tools and process conditions have a significant influence on the forming process and final shape and properties of the workpiece.

Model-Based Residual Stress Design in Multiphase Seamless Steel Tubes

Residual stresses in quenched seamless steel tubes highly depend on the cooling conditions to which the tubes have been subjected. The design aspect of how to use controlled cooling strategies in multiphase steel tubes to achieve certain residual stress and phase configurations is discussed. In an experimentally validated finite element (FE) model considering a coupled evolution of martensite and bainite, three cooling strategies are tested for a low-alloyed 0.25 wt.% C steel tube. The strategies are (i) external cooling only, (ii) internal and external cooling for low residual stresses in a mainly martensitic tube, and (iii) internal and external cooling with low cooling rate for a mainly bainitic tube. The strategies represent design cases, where low residual stresses with different phase compositions are provoked, in order to show the potential of numerical analysis for residual stress and property design. It can be concluded that, for the investigated steel class, intense external cooling leads to a characteristic residual stress profile regardless of the dimension. A combination of external and internal cooling allows a more flexible design of residual stress and phase distribution by choosing different cooling parameters (i.e., water amount and cooling times). In general, lower cooling rates lead to lower thermal misfit strains, and thus less plasticity and lower residual stresses.