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Rolling Process Modeling - Numerical




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Measurement of flow stress with torsion test

Flow stress of Steel DIN 19Mn6 was measured at 850C, 900C, 950C and 1000C, strain of 0.05 to 0.75, and strain rate of 0.05 to 5/s. Measured data was used to formulate a mathematical model for the flow stress, considering the temperature rise during the torsion test predicted by FEM simulation.



FEM simulation of the steel torsion test to determine the temperature profile during the test

FEM simulation of the torsion test was used to measure the flow stress. This is to study the actual temperature profile in every stage of the torsion test. Due to the heat generation, the actual temperature is higher than the initial temperature. This may cause the difference of the temperature pattern between the torsion sample and the sample for the hot rolling and, thus cause the error of the FEM simulation of the rolling process. In prior FEM modeling this negative factor was removed.



Measurement of E-modulus

The E-Modulus for steel was heavily temperature-dependent, so the E-Modulus for steel 19Mn6 used for the FEM investigation for the angle steel rolling was measured at various temperatures, from 200C to 1200C. A formula modeled with the measured data in the temperature range 850C to 1000C was used for the FEM calculation for the angle steel rolling.



FEM Modeling for the hot flat rolling with thermomechanical model

This wass a pre-simulation for the angle steel simulation. Due to the high technical challenge of the thermo-mechanical modeling of the angle steel rolling, a hot rolling model for the flat rolling was established at first. Rolling parameters for the FEM model corresponded to the hot flat rolling tests. Calculated data were compared with the testing results, so the model was verified and improved.



FEM Analysis for the 6 passes of angle steel rolling with thermomechanical model

The input file consisted of the data for mesh generation, material data and boundary conditions, rolling parameters, parameters relating to the output (out-file, post file and restart file), special control parameters for FEM calculations (such as convergence errors for temperature and stress or displacement, time step for each increment), etc. The rolls and stock were taken into account separately as rigid and elastic-plastic. At first, the initial cross section of a groove was estimated. The inputs were the flow stress formula, temperature dependences of E-modulus, specific heat, thermal conductivity, coefficient of thermal expansion and mass density, etc. The directly calculated outputs were rolling force, rolling torque, elastic and plastic strain, elastic and plastic strain rate, plastic work, shape of deformation zone, stress and temperature distribution, as well as the stock geometry during and after rolling. The definitions for partial upsetting, partial spread and partial elongation were provided as input into the MARC main program through a user subroutine, so those forming technical parameters were also calculated. Both integrated and local metal flow, as well as the force and power, showed an excellent agreement of the measured and calculated results.



FEM modeling for hot rolling of the H-beam with thermomechanical model

H-beam rolling, starting with the cast profile, was analyzed for the example of rolling of IPE140. The pass sequence consisted of three universal and two edging passes in a continuous mill. The rolling processes of three universal passes in a continuous mill were simulated. Rolling parameters for the simulation corresponded to those of a practical rolling test: initial temperature was 1000 1015C, and rolling speed was 4 6 m/s, etc. The model was improved by comparison of the measured and predicted parameters.



FEM modeling for the cast-rolling with liquid core

A study of the cast-rolling process of a thin slab with a liquid core. At first, the cooling process of the cross-section from liquid state of 1394C to a state with a thickness of solid shell of 10mm, 15mm, 20mm, 25mm, respectively, was studied by means of two-dimensional finite element simulation in which the liquid-solid interface was determined. Then the three-dimensional simulation of workpieces with corresponding thicknesses of the solid shell was carried out, in which the workpieces were simplified to hollow bodies. Meshing of the cross section with each wall thickness was optimized. A comparison of the analytical results with those of experiments described in the literature followed for each calculation.



Establishment of a simplified FEM model that takes only 5% of computing times

After studies of the relative movement of the stock and the rolls, a special upsetting model for shape rolling simulation was developed through a functional combination of the slab method and the FEM, with direct modeling of the speed and the deformation pattern in the length direction. The simulation of an angle rolling pass was performed in only 5% of computing time of the regular model, with sufficient accuracy. (Due to the great interest in this simplified model from industry, German colleagues spent another year to further study it, after the initial development). The study was financed by DFG. There was a great potential for this simplified model to be integrated into a roll pass design program or a Level 2 model, to describe the microstructure parameters over the stock cross section.



FEM analysis for RD-OV and OV-RD passes for force, temperature, grain size and recrystallization, etc.

Data for the simulation was provided from Morgans lab mill data. A microstructure model was developed and provided to the FEM. The percentage of completion of the recrystallization and recrystallized grain size, etc. were predicted and graphically plotted, besides regular parameters such as force and temperature.


    Project Categories (Notes)

     1.  Level 2 Development
     2.  Level 2 Support
     3.  Mechanical properties improvement
     4.  Mill Application Development
     5.  Productivity Improvement
     6.  Rolling and Roll Pass Development
     7.  Rolling Process Modeling - Numerical
     8.  Rolling Process Modeling - Empirical
     9.  Shape and yield improvement
    10. Web and Web Resource

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