An experimental study was carried out to investigate the possibilities to use rolls made from Si3N4-TiN ceramic composite in hot rolling of steel. The results show that the wear of the ceramic material was lower than the wear of a reference cast iron. The results suggest that the Si3N4-TiN material is beneficial to use in a hot rolling process, on condition that the temperature of the work piece material is held sufficiently high. © 2008 Elsevier B.V. All rights reserved.
A set of cold-rolling experiments with ceramic rolls was carried out using facilities for the production of profiled steel wire. Based on the experiments, the strength of sintered silicon nitride was found sufficient for allowing cold-rolling of austenitic stainless steel wire. The wear rate of the silicon nitride rolls in the tests was low. Metal was transferred from the wire to the rolling tracks of the ceramic rolls. The surface texture of the rolls was reproduced on the rolled product. © 2006 Elsevier B.V. All rights reserved.
A method for the evaluation of friction models is described. A wedge is rolled to uniform thickness, a range of reductions being investigated thereby in one experiment. Finite-element simulations are performed in order to estimate the friction parameters that can be used in the simulation of hot rolling. The influence of the material parameters and the friction parameters on the calculated results are investigated and the latter are compared with experimental results. It is shown that it is possible to separate the influence of the material parameters and the friction parameters, thus enabling the friction parameters to be evaluated from a minimum number of nexperiments. © 1994.
In order to characterise the mechanical response of materials in manufacturing processes, such as wire and bar rolling involving very high strain rates, temperatures and level of straining, an experimental device is presented. The device is suitable for testing at strain rates up to approximately 4000 s-1, temperatures up to 1200 °C (≈1500 K) and strains around 0.5. It is based on the classical Split Hopkinson pressure bar and is complemented with an inductive heating source for achieving requested temperatures. By keeping the specimen separated from the Hopkinson bars just until an instant before impact (50 ms) considerable cooling and temperature gradients in the specimen are avoided. Three steel grades, two stainless steels and a high-speed steel, were tested. Four different material models whose parameters were fitted to the obtained experimental data were used for mechanical characterisation: two empirically based and two physically based. Overall, one of the physically based models showed the best agreement between experimental results and the predicted flow stresses.
Electron Beam Melting (EBM) has been recognized as a revolutionary technique to produce mass-customized parts to near-net-shape from various metallic materials. The technique produces parts with unique geometries from a powder stock material and uses an electron beam to melt the powder layer-by-layer to fully solid structures. In this study we have investigated the use of two different Ti-6Al-4V powders of different size fractions in the EBM process; a larger 45-100 μm powder, and a smaller 25-45 μm powder. We have also investigated the effects of two build layer thicknesses, 70 μm and 50 μm, respectively. We hypothesize that the smaller powder has the potential to improve surface resolution of parts produced in the EBM process. The EBM as-built parts were investigated regarding surface and bulk chemistry, surface oxide thickness, macro- and microstructure, surface appearance and mechanical properties. We conclude from the results that both powders and both build layer thicknesses are feasible to use in the EBM process. The investigated material properties were not significantly affected by powder size or layer thickness within the studied range of process parameters. However, the surface appearance was found to be different for the samples made with the different powder sizes.
The computational efficiency of the explicit finite element code DYNA2D and the implicit code NIKE2D are compared in the case of simulation of rolling. It is found that the explicit code is preferable. The advantages of the explicit formulation will be even more pronounced in three-dimensional simulations. © 1990.
Multi-layer perceptron (MLP) neural networks were trained using measured process data from Rautaruukki Hämeenlinna and Raahe Works. The MLPs had process parameters as inputs and the difference between the average and the actual yield strength (ΔRp02) as output. The data set consisted of various steel grades, the average Rp02 values being calculated separately for each grade. By studying the response of the MLP to changes in input variables it was possible to draw conclusions of the causes of variation in measured yield strength. It was observed that the process parameters contain sufficient information to predict the variation and that the variables responsible for the variation differ from grade to grade. A sensitivity analysis on the variations of input variables showed that the response of MLP on the variation of one variable may depend greatly on the values of the other variables. © 1998 Elsevier Science S.A. All rights reserved.
The so-called CROWN programs have been developed as a result of the co-operation in the Scandinavian Steel Industry. They consist of separate physical models for calculation of plate or strip temperature and roll thermal expansion, wear and elastic deformation. Flatness and residual stresses in the material are deduced from the relative change in profile during rolling with the aid of a shape vector method which considers the transverse metal flow in the roll gap. The CROWNON model is an on-line model which can be used for process control in rolling mills. A new optimized pass schedule generation system has been developed for the plate mill in Rautaruukki. The pass schedule is calculated in the forward direction for the sizing pass, broadside passes and the longitudinal passes. The drafts for the broadside and the first longitudinal passes are limited by maximum force, torque and strain. For the last longitudinal passes, the shape vector method is applied and the draft is restricted by the maximum steepness and flatness criteria. The change in the relative elongation differences between the centre and the edge of the plate together with experimentally determined values for the transverse metal flow (e.g. ξ-values) are used in the schedule calculation. To predict correct rolling loads during the scheduling, an adaptive temperature-dependant force-draft model is used based on statistical analysis of the rolling process. The system has decreased the number of passes, improved the yield and has provided the possibility of rolling thin, wide plates, e.g. 4.7 × 3250 mm with good flatness and minimum crown. The barrel length of Rautaruukki's plate mill is 3,6 m and the maximum rolling speed is 5 m/s. During the last years two dimensional and three dimensional Finite Element simulations of hot rolling of flat products have been made. The calculated rolling forces show very good agreement with experiments made in Rautaruukki's plate mill. © 1992.
In this work, finite-element simulations have been made to model camber and lateral movement (strip walk) during hot rolling. Experiments have been performed in a pilot plant rolling mill to verify the results. The FE model used to determine strip camber and strip walk was developed using the explicit code Dyna3d. The roll in the FE model was modelled partly stiff, to avoid generating an excessively large model. Roll deflection and roll flattening was calculated with MEFOS's profile and flatness program Crown426. The results show fairly good agreement between the FE simulations and the experiments. © 1998 Elsevier Science S.A. All rights reserved.
The aim with this work has been to improve the temperature calculation used to pre-set the roll gap in a finishing train. The calculation is used for estimation of the rolling force. Currently an empirical model together with the measured surface temperature is used to calculate the threading temperature. In this study a predictor, based on thermal simulations of the process and neural networks, has been developed. The influence of slab dimensions, initial temperature, edging, reduction and number of passes has been studied and also delays have been considered. A part of the model has been tested on measured surface temperature and estimated mean temperatures at SSAB Tunnplat AB, Borlange, Sweden. © 1998 Elsevier Science S.A. All rights reserved.
A major problem in sheet bending is to compensate for springback. Analytical descriptions are not sufficiently general to accommodate influences from the material and the geometry due to the simplifications that have to be made. Practical experiments are still needed to be able to compensate for springback. The aim of this work has been to test the finite-element method on its abilities to predict springback for free bending in a V-die. The work shows that the finite-element method can be used to predict springback off-line. The true stress-true strain curve from a tensile test is used as the material description. Springback has been studied for eight different materials of varying thickness. The process has been simulated with the code Nike2d and the results from the simulations compared with those from experiments, good correlation between the simulations and the experiments being achieved. © 1997 Elsevier Science S.A.