Virtual Rollforming Machine (VRM) is the third step of the three steps quality management concept. The numeric simulation of the roll forming process by FEA (Finite-Element-Analysis) enables the designer to get very precise information about stress and strain within the profile while running through the rollforming machine and after leaving the final stand of the machine. Furthermore is calculates the profile shape that is formed by the designed rolls. To enable the designer to benefit from the FEA result without being an FEA expert, the software PROFIL has a built-in interface to the leading FEA system ABAQUS/Explicit from SIMULIA Dassault Systèmes.
Proceeding the simulation: After designing the rolls the input files with the simulation model for the FEA system are created by key-stroke. The thin shell model is used, that is optimal for sheet bending. The shell width can be selected dependent on the desired accuracy, either general or user defined. General means: for each type of profile element (line and arc) a constant shell width can be pre-set. User defined means: for each profile element can be selected in how many shell segments it should be divided. This enables the user to define a higher accuracy for the parts of the profile with most interest. The material properties are defined by the stress-strain-diagram. Furthermore the step interval for the mass scaling can be pre-set, this is useful to accelerate the computing procedure. A recommended step interval is calculated dependent on minimal shell width and material properties. Afterwards the FEA simulation is started. The simulation process should run on a separate computer, since it takes between some hours and some days, dependent on how complicated the profile is and how many rollforming stands are used. This process should not block the CAD working station of the designer. The FEA system calculates explicit and is able to consider oil-canning effects that occur very often when thin sheet is formed. An implicit calculation needs special measures to avoid break off when the function becomes irregular.
Checking the result: As a result of the simulation the designer first gets the shape of the profile after leaving the final stand. This drawing can be compared with the designed shape. If the allowances are not kept, the designer can browse through the different time intervals within the machine to track the error. Colors inform about positions of high stress and remaining strain. This enables the designer to locate the reason for unwanted deformations and gives him the information which rolls need to be modified.
Compared with step 1 (stress of band edge) and step 2 (PSA - Profile Stress Analysis) the FEA simulation has the advantage that it calculates most precisely not only stress and strain. FEA is also able to predict the profile shape that is formed by the designed rolls and shows unwanted deformations. Since more computing time is required, it makes sense to use the FEA simulation at the end of the design process.