Rui Bin Mei

Heat Transfer Coefficient Prediction by FEM in the Hot Strip Rolling

It is necessary to know the heat transfer intensity for predicting temperature distribution in the hot strip rolling process. The HTC (heat transfer coefficient) was usually obtained by the experiments and mathematical model. In this paper the HTC prediction was discussed based on the measured or target temperature by the proposed finite element method (FEM). The temperature evolution and HTC in the hot strip rolling process according to a certain plant were analyzed by the iteration calculation. The result shows that the HTC between strip and work roll was much more than the value in the air cooling and water cooling process. Furthermore, the HTC value is lower in the air cooling process compared with that of water cooling. The maximum and minimum value of HTC were about 1.5×105 (W/m2.K) and 80(W/m2.K) respectively. The temperature in the rough rolling according to the predicted HTC has been solved and the calculated results have a good agreement to the meausred value. Therefore, the research could be used to control the temperature distribution accurately and optimize the parameters.

Numerical Analysis of Deformation of AZ31 Magnesium Alloy in Backward Extrusion with Counter Pressure

A numerical simulation on the deformation behavior of AZ31 magnesium alloy during backward extrusion with counter pressure was investigated by FE software DEFORM. The results show that the steady load increases nonlinearly with the increment of counter pressure. The equivalent strain gradient decreases significantly results from the counter pressure and the unevenness in the top of wall disappeared approximately when the counter pressure is 10~15MPa. Furthermore, there are obviously shear band along the inner fillet to outer fillet of workpiece. Higher hydrostatic pressure generated with counter pressure compared that of no counter pressure leads to improve the plastic deformation limit. The damage factor is reduced significantly in the backward extrusion with counter pressure, which is beneficial to the improvement of crack.

Influence of Temperature Difference on Front End Bending in Hot Slab Rolling

Front end bending often occurs in the heavy plate mills and roughing stands, which reduce productivity efficiency and the quality of the plates considerably. The effect of temperature difference between top and bottom surfaces of slab and reduction ratio on front end bending was investigated by 3D FEM and the mathematical model was induced. The hexahedral mesh was generated by HyperMesh and embed into the DEFORM system. The results show that the temperature difference leads to the asymmetric distribution of equivalent stress, strain and strain rate in the deformation zone. With the increment of temperature difference and reduction ratio the slab head bends more significant. Additionally, the slab front end perhaps bends to higher temperature side in double phase rolling because of resistance of deformation with different phase. Reducing temperature difference, reducing reduction ratio and avoiding double phase rolling is benificial to reduce front end bending in hot slab rolling.

Numerical Simulation for Microstructure Evolution in In718 Alloy During Cylindrical Cup Backward Extrusion

A coupled numerical simulation between thermal-mechanical and microstructure evolution was realized through embedding the developed user subroutines into the FEM software DEFORM-3D system. Then the dynamic recrystallization fraction and average grain size of In718 alloy in cylindrical cup backward extrusion with different parameters was solved and analyzed. The complete dynamic recrystallization occurs in the middle of cylinder wall and the grain size is the finest. However, the grain size of top of cylinder wall changes less because of the less plastic deformation. Furthermore, higher speed of punch is useful to the DRX but it is not enough time to occur dynamic recrystallization completely with much higher speed of punch. In spite of more recrystallization occurring in the bottom, the grains grow in the cylinder wall so that much higher temperature goes against improving finer and uniform of grain size. Therefore, it is better for obtaining finer and uniform grain size with 1000(°C)-1050(°C) and 5(mm/s) in In718 alloy cylindrical cup backward extrusion according to the research.

Numerical Simulation of Microstructure Evolution of TC6 Alloy Blade during Finish Forging

In order to predict the evolution of microstructure and grain size in TC6 alloy blade finish forging process and optimize the parameters, a series of constitutive equations for dynamic recrystallization and grain growth were developed and implemented into a 3D FE simulator. The grain size has been illustrated for the upsetting of TC6 alloy and the calculated grain size is in a good agreement with the experimental results, which shows that the microstructure prediction tool was validated and reliable. Then the distribution of stress, strain, temperature and microstructure, grain size and deformation has been predicted in TC6 alloy blade forging successfully using the 3D FEM at 930°C deformation temperature, 250°C die temperature and 50mm/s deformation velocity. The results show that the temperature of blade edge is higher than that of center because heat transfer, friction work and deformation work. The equivalent stress and strain have the same distribution as temperature after forging and the refined grain is obtained because of dynamic rescrystallization occurred with larger deformation. The uniform distribution of grain size are obtained in the blade and the shape after finish forging under the condition of technology parameters meet the user’s requirement comparing the calculated deformation with experimental results.

Study on hot deformation behavior of 7085 aluminum alloy during backward extrusion process

Compression test was carried out and the true stress-strain curves were obtained from the hot compression of 7085 alloy. A numerical simulation on the deformation behavior of 7085 aluminum alloy during the backward extrusion was also performed by finite element method. The results show that dynamic recrystallization occurs in the hot compression of 7085 alloy and the peak stress reaches higher values as the strain rate increases and deformation temperature decreases. The backward extrusion processes include contact deformation, initial deformation, and steady deformation. Severe plastic deformation of shear and compression occurs when the metal flowed into the channel between fillet of punch and wall of die so that the grain size can be refined by backward extrusion. The deformation in the region of top of wall is too small to meet the mechanical properties of requirements and the metal usually needs to be trimmed. The experiments with the same parameters as simulation had been carried out and the experimental cup after extrusion has better quality.

Research on Compressive Behavior and Deformation Heating of 7075-T6 Aluminum Alloy during Hot Compression

The flow stress behavior of the 7075-T6 aluminum alloy was studied through single-pass compression experiment by using MMS-300 simulator within temperature range of 300-450°C and strain rate range of 0.01-40s-1. Then a simulation of compression was carried out and the influence of deformation velocity on load and deformation heating was investigated according to the relationship between stress and strain. The results show that dynamic recrystallization occurs in hot compression of 7075-T6 alloy and the stress-strain curves are presented as wave. Furthermore, the flow stress curves have the same wave period and the fluctuation range increases with an increase of strain rate and a decrease of strain. Increasing of deformation velocity results in higher critical strain but the value decreases when the deformation velocity is much higher. The temperature rise increases with the increase of deformation velocity and decrease of deformation temperature. The maximum of temperature rise is more than about 30°C, so that the deformation heating is significant.

Fast Prediction of Temperature by FEM in Hot Strip Rolling

Finite element method (FEM) has been one of the most important numerical simulation tools with the development of computer technology. However, it is only used to simulate and analyze different process offline in many fields because of the longer computational time. The influencing factors of prediction of temperature in the strip rolling by FEM including equations, mesh and storage of matrix was investigated in the paper. The lumped heat capacity matrix was introduced to resolve the oscillation problem and improve precision. Furthermore, the refined elements layer upon layer was discussed to improve solution efficiency and precision. In addition, in order to improve the solution efficiency one dimensional compressed storage method was employed to carry out in the solution of equations. The FEM program code for the solution of temperature was embed in the online rolling control system program successfully. The predictive results are in good agreement with the measured value. The computational time and precision are satisfied in the strip rolling process.

Rigid Plastic FEM Model of Fast Solution to Strip Rolling

Rigid plastic finite element method (RPFEM) is one of the most efficient numerical methods during the rolling process. Realizing FEM online application has been main target for many researchers. The influence of compile method, elements number, compressible parameter, friction factor and convergent criteria were investigated and RPFEM model of fast solution to strip rolling was proposed in this work. Compile method and compressible parameter have less influence on calculated rolling force. However, the iteration steps are reduced and computational efficiency is improved greatly with compile method of release and compressible parameter 0.01. The change of calculated rolling force becomes less but iteration steps become more and more with the increment of elements number. Both accuracy and efficiency is satisfying with the change of elements number from 50 to 200. In addition, the typical rolling schedule from a certain plant has been solved with the developed program FFEM-2D by FORTRAN. The predicted rolling force has a good agreement with the measured value. The iteration steps change from 12 to 36 and computational time is less than 200(ms) with the model in one pass rolling. Therefore, the accuracy is satisfying and computational time fully meets the basic requirements of FEM online application. Keywords: Rolling; RPFEM; Fast solution; Computational time

Evaluation of Thermal Comfort in an Air Conditioning Room Using a CFD Model

In order to obtain the thermal comfort work environment, the distribution of temperature and airflow velocity in typical computer room of school building is discussed with different supply air angles and velocities of incidence by CFD model. The calculated temperature after cooling in the room has a good agreement with the measured value. Furthermore, the distribution of temperature and airflow is uniform and the environment is comfort for working with supply air angles and velocity of incidence 45° and 60° and supply air velocity of incidence 1m/s comparing with that of other parameters. Additionally, the change of temperature becomes slow down with the increment of time and the air-conditioning has less influence on the change of temperature after about 900s with supply air angle and velocity of incidence 45°and 1m/s, respectively. The research is of great significance both in theory and practice to design air conditioning systems and evaluate the thermal comfort conditions.