Abstract
The present work entails on an advanced material engineering solution for lightweight design for side doors. By considering the "state of the art" of the vehicles doors prototyping and development, the idea of the a magnesium (Mg) diecasted door frame, combined with an aluminum (Al) external panel solution, has to be regarded as a new
"archetype" in terms of product and process engineering. In fact, from the adopted materials view point and from the process method as well, the solution which will be described in this work has to be regarded as highly innovative in terms of weight saving, geometric precision, recycling opportunities and money saving.
The Mg, due to its physical characteristics (density 1.74 kg dm-3) guarantees an enhancement of the vehicle performances in term of weight reduction (which allows the optimization of the fuel consumption), of the gas emission and the use of recyclable materials; i.e. all items deeply environment-friendly. Last but not least, if well dimensioned, the Mg guarantees the same performances of the steel. In the meanwhile, the diecasted process method enhances the geometric precision of the door system (due to the adoption of a cast and machined part), dramatically reduces the dies costs (only one die casting instead of many sheet metal dies), the time and the costs of the door assembly on body in white (50% reduction of the specific investments) solution. Finally, the total production costs (variable + fixed) results equal to the traditional process.
During the present work, a heavy feedback between the prototyping and virtual validation (massive use of CAE solutions) was adopted, in order to optimize the resources in term of physical product behavior and budget administration.
Step by step, several different virtual prototypes were virtually checked and validated by performing the following different tests (FEM Analysis):
Backling and denting
Longitudinal compression
Side Intrusion
Hinges cave-in
Local stiffness
For this research, it was considered a current sport car door. In order to be accepted by the technical board, the new developed door had to pass several different destructive and non-destructive tests to obtain the product technical certification, which will allow it to be adopted as the new solution for future sport vehicles.
The adopted material for the doorframe was AM50 alloy (composition: Al (4,4-5,4%), Zn (0,22% max), Mn (0,26-0,6%), Si (0,10% max), Cu (0,010% max), Fe (0,004% max), Ni (0,002% max)). This material was suggested by the numerical simulations performed during the feasibility studies (Longitudinal compression, intrusion tests) and by the Brite Magdoor project results. The AM50 material was chosen instead of AM60, because of its better characteristics in term of longitudinal compression and intrusion. The AM50 frame was superficially covered with an anodic film (thickness 10mm) to prevent it from the galvanic corrosion (induced at the steel interfaces). A powder painting process to prevent the surface film from occasional abrasions during the piece motion and the assembling has covered this surface film.
In the AM50 doorframe, up to 15 steel parts have been integrated, including:
Hinges parts
The carrier
Inner reinforcements
Anterior door pillar reinforcement
Hinges reinforcement plates
Five different frame solutions were tested in order to optimize the door performances. Briefly, the final built proto-type characteristics are:
45% door in white weight saving
Integration of 15 steel different parts in the single Mg frame (including the moving hinges)
After passing the virtual tests, the Mg door archetype was produced in a series of prototypes and tested physically, for corrosion and for life testing, static stiffness, side intrusion test, and dynamic crash test. The obtained AM50 based prototype definitive solution was experimentally tested and approved from the technical viewpoint by the customer on November 2001.