Papers by Author: Hei Jie Li

Abstract: Roll forming is a 3D deformation complex process. Stiffness of stands and strength of shafts are the preconditions for the production of precision products. However, the existing roll forming equipment cannot meet the requirements of the production for high strength steel or ultra high strength steel. In order to solve the forming problem of high strength steel or ultra high strength steel, it needs to redesign a set of roll forming equipment. The redesign of roll forming equipment not only makes the production cycle too long, but also results in a high cost. So it is not suitable for the production of forming products. In this paper, based on the existing roll forming equipment a new method of roll forming operation is proposed to optimize the production of U shaped products. The influences of the new method on the roll forming products such as mechanical properties, microstructures and surface qualities, have also been discussed, Based on the new warm roll forming operation, numerical simulation has also been carried out. The simulation result of geometry is in good agreement with experimental result.

Abstract: In the paper, a crystal plasticity finite element method (CPFEM) model was developed based on ABAQUS to analyse the surface roughness transfer during metal manufacturing. The simulation result shows a good agreement with the experimental result in the flattening of surface asperity, and the surface roughness decreases significantly with an increase of reduction with considering friction effect. Lubrication can delay surface asperity flattening. The effect of surface roughness on produced metal defect (crack) was also studied, and the surface roughness affects the crack initiation significantly in cold strip rolling. In addition, the surface roughness variation along the metal plate width contributes to stress distribution and then inhibition of crack nucleation.

Abstract: In recent years, the number of automobiles has been steadily increasing, which has significantly impacted on the society and human life, and led to many social problems such as fuel crisis, environment pollution. Therefore, lightweight designing becomes a focused issue. Lightweight materials application, optimized structure design and advanced manufacturing process are the main ways to achieve the lightweight. However, low plasticity and ductility of high strength steel constrain the application of high strength steel. In this paper, the basic principle of roll forming for automotive parts is investigated, and it is innovatively applied in the hot roll forming process of the ultra high strength steel.

Abstract: The friction is a key factor that influences the surface quality in metal forming. To figure out the relationship between the friction and the surface roughening, a finite element model is employed in the commercial finite element software ABAQUS to simulate the surface roughness of top side of Al plate during uniaxial planar compression. With the change of friction conditions, the surface roughening varies. The average surface roughness (Ra) shows a relationship with the friction coefficient. During the surface roughening process, the grain slip takes place in the “soft orientation”, and the “hard orientations” become the barrier of the slip.

Abstract: With the technology advancement, crystal plasticity finite element modeling becomes more and more popular in the simulation of metal forming process. In order to obtain a better understanding of the difference between the Taylor model and finite element model during the simulation of metal forming process, an implicit time-integration procedure with the two polycrystal models is applied in the commercial finite element code ABAQUS to simulate the plane strain compression separately. FCC metal is used in this study. The simulation shows that the two polycrystal models both can predict the compression process approximately. The two modelling results of surface roughness show an agreement with that of the experimental results. However, the side profile calculated by the Taylor polycrystal model is much steeper and straighter than that of finite element polycrystal model. The experimental surface roughness curve shows a high frequency fluctuation. It is much steeper than those of the two models. The simulation results also show that the von Mises stress from the Taylor model is much higher than that of the finite element model.

Abstract: Taylor-type and finite element polycrstal models have been embedded into the commercial finite element code ABAQUS to carry out the crystal plasticity finite element modelling of BCC deformation texture based on rate dependent crystal constitutive equations. Initial orientations measured by EBSD were directly used in crystal plasticity finite element model to simulate the development of rolling texture of IF steel under various reductions. The calculated results are in good agreement with the experimental values. The predicted and measured textures tend to sharper with an increase of reduction, and the texture obtained from the Taylor-type model is much stronger than that by finite element model. The rolling textures calculated with 48 {110}<110>, {112}<111> and {123}<111> slip systems are close to the EBSD results.

Abstract: In twin-roll strip casting process, the temperature variation of casting roll can result in roll thermal stress and fatigue. It not only affects the thermal deformation of casting roll and the generation of the roll surface cracks significantly, but also influences the surface quality, shape and profile of the produced strip, and the service life of the casting roll. In this paper, a 3D coupling thermal-flow finite element modelling has been conducted. For twin-roll casting of stainless steel, the influences of the casting speed and liquid level in molten pool on the temperature field of casting roll have been simulated and discussed. The developed model is very helpful in optimising the processing parameters and the design of casting roll during twin-roll thin strip casting.

Abstract: The consumption of work rolls in cold strip mills is significant. One of the key issues for work rolls is the surface roughness which affects the rolling stability and surface finish of the strip. The produced strip has lower surface finish if the roll surface roughness is large. However, if the roll surface roughness is small, it is not helpful for establishing the rolling process, which will reduce the productivity. In this case, a laser treatment is employed to increase the value of roll surface roughness. In order to reduce the times of roll grinding, the cold strip mill and roll manufacturers have developed new types of rolls such as the rolls containing Ti to increase the roll wear resistance in cold strip rolling. Results show that the new 4CrTi roll has a significant advantage of preventing decrease of the roll surface roughness. The size and generation of particles during roll wear process and the effect of Ti on roll wear have been discussed.