Research On The Key Technologies Of Cold Roll-forming Of The Cars' Anti-collision Beam

The cold roll-forming process is a kind of the large three dimensional elastoplasticity distortion,the steel sheet own the characteristic of geometric nonlinearity, material nonlinearity,contact boundary nonlinearity in the cold roll-forming process. Moreover, a lot of factors affect it's forming process, so the simulation of cold roll-forming is very difficult and the commanding of the forming law is also difficult. At present, the domestic and foreign scholars had not proposed a very perfect and precise analysis method regarding this process, in the production the technological design and the roller design still mainly depend on the experience knowledge. Under this background,the paper takes the cars' anti-collision beam for example, using the large finite element software MARC carries on the three dimensional elastoplasticity finite element simulation of cold roll-forming and on-line three-rollers bending process. This paper primary coverage and the conclusion are as follows:1. Establishment of finite element modelAccording to the characteristics of cold roll-forming and the structural characteristics of work piece, the paper established the simplified model of the finite element simulation, imposed the effective boundary conditions and geometric constraints on the deformed metal sheet to simulate forming process using the three-dimensional solid elements; The fading approach of the top roller move downward was adopted to fade the metal sheet into slot, through analysis of the fading process, this fading process model was proved to be available.2. FEM simulation of the cold roll-forming processThis part focused on analyzing stress and strain distribution, the history-curves of stress and strain of the special nodes, the stress and strain distribution of forming transition zone and the impact of technical factors on the work piece stress and stain, and then drew the following conclusions:(1) The distribution of equivalent stress and strain in the horizontal direction is similar, but the distribution of equivalent stress is more complex than the equivalent strain,equivalent stress and strain mainly concentrated in the corners and the surrounding region of the corners, equivalent strain reached the largest in the corner, and equivalent stress in the region near the corner.(2) In the deformation process, the equivalent stress of the corner region will occur a change of increasing and reducing when the metal sheet through each group of rollers, from this point of view, the cold roll forming process can be regard as a many times'loaded and unloaded process; By analysis of the strain, we can see that, the change of equivalent strain in the forming process likes a step, the deformation of plate is a joint effect's result of horizontal deformation and vertical deformation, but the horizontal deformation plays a major role, and therefore in the designing process of rollers, the distribution system of the plate horizontal deformation is mainly to be considered, thus ensuring the quality of products; Metal sheet,in the bending deformation process, at the beginning occurs elastic deformation, and then the elastoplasticity deformation, and finally the plastic deformation.(3) The metal sheet between the two rollers exists deformation transition zone, in this zone the value of equivalent stress and strain is also big, and the distribution of stress in the transition zone along the width direction is regional, in the corner part, the stress is largest, and in the web smallest, but the closer rollers, the more complex distribution; The equivalent stress in the length direction is gradually increased along the direction of metal sheet movement, the distribution of equivalent strain is in accord with the distribution of stress; The metal sheet before into the rollers occurred horizontal bending deformation, at the same time, edge occurred the vertical tensile deformation, metal sheet web occurred the vertical bending deformation and cross-section shape also occurred the horizontal reverse deformation, as a result formed a complex 3-dimensional space, but when the metal sheet through the roll-axis plane, the original longitudinal reverse side would be leveled and the longitudinal bending deformation would be greatly reduced, it can be seen, Roll cold forming is horizontal bending, horizontal torsion, longitudinal bending, longitudinal tensile and a coupling process of elastic, elastic-plastic, plastic deformation.3. Online three-rollers bending deformation FEM simulation This part analyzed the evolutions of stress and strain field and the impact of the spring back on the stress and strain of profile in the three-rollers bending deformation, reached the following conclusions:(1) In the three dimensional stress of the metal plate wing, the bending stress is much larger than the other two direction stress, the absolute value of bending stress from the neutral layer to both sides is gradually growing, in the neutral layer, the bending stress value is smallest, the distribution of bending strain is similar with the distribution of bending stress on the metal plate; The stress and strain on the web and wing were significant different in the numerical, the value of stress and strain on the web is far less than the value of the stress and strain on the wing, while the stiffness of the web is much larger than the stiffness of the plate wing, so the web is the main part on which the bending force is imposed to produce deformation in the bending forming.(2) Through the analysis of bending process, we can see that the deformation of profiles changes from elastic deformation to elastic-plastic deformation and plastic deformation occurred in the final with the rollers rotating, when the profile passed the second rollers'group,it has occurred a certain curvature plastic bending deformation, so the profiles'final round forming is completed on the combined action of the three groups rollers.(3) Through spring back simulation results drawing the fallow conclusion: After the spring back, due to the release of elastic potential energy, resulting in elastic strain and stress declined largely, but after spring back, there are still some residual stress on the profiles; From stress-curve on the edge we can see that the direction of the stress on both sides of the stress neutral layer is contrary before spring back, but the rebound towards the direction of reducing to occur, this is also one of the reasons for greater resilience of three-rollers bending.4. Experimental research on the forming technics of rubbing beamAccording to the simulation results, the rubbing beam forming process was studied, the forming system was ascertained, the roll flower plan was designed, parameters of forming units were choose reasonably,and then the debugging of process equipment was carried out, test problems and proposed solutions were analyzed, and mass production of the car's anti-collision beam in the actual production was achieved.