Study On Reverse Modeling For CAR Roof Multi-Point Forming And Its Numerical Simulation

The technology of car body outer panels Multi-Point Forming (MPF) process is a flexible manufacturing method. MPF press with blank holder device can realize the car roof MPF process. MPF applies numerical control technology to control the displacement and velocity of elements, so it can form alterable envelope, and achieves flexible forming.By the existing theory of reverse engineering and surface reconstruction, a set of discrete data sampled from a car roof is given in advance during the car roof MPF process. A CAD model of the roof based on these data must be faithfully reconstructed in order to calculate the height of all elements, and that is one of the most crucial steps for the MPF CAM in practice.This paper will fit the model of a car roof in a parametric bicubic spline surface. However, someplace with flatter shape (differentiated by a given tolerance) will be fitted in hyperbolic paraboloid so that the height of elements can be immediately calculated and programmed.In this paper, to carry on the car roof MPF numerical simulation, we apply the algebraic relation between the displacement (or velocity) and time to control the movement of elements. We use Belytschko-Wong-Chiang (BWC) shell element as the car roof MPF shell element model, BWC shell element involves dimensional geometry shape. Its simulation precision is better.With the passat 1.8T roof as an example, this paper discusses impressed marks during its MPF process by dynamic explicit finite element algorithm, which establishes the base for forming quality, ascertaining reasonable technique parameters.