Designing complex front-end carriers for cars is invariably a difficult challenge, with the inevitable need to control weight while ensuring that current safety criteria are met or exceeded. Use of composite materials helps, but almost every front-end carrier incorporates some metal to bolster reinforcement, which adds cost and assembly time. But working with Volkswagen, BASF created a front-end carrier for the new Golf Mk. VII that uses only plastic, eliminating the use of sheet steel parts. It is believed to be one of the first in the world to do so.
Replacing the polypropylene hybrid part used for the previous Golf with an all-plastic solution required use of BASF’s Ultramid B3WG8, a highly reinforced polyamide, during development, as well as the company’s Ultrasim simulation tool.
Obviating the need for sheet steel parts reduced the weight of the front-end module “significantly,” compared to the Golf Mk. VI, said Dipl-Ing. Torsten Hensel, Optimization & Crash Analysis specialist, with BASF Engineering Plastics Europe, based at Ludwighafen, Germany. It also saves assembly time and therefore costs. Volkswagen manufactures the part in-house.
“In addition to limited space for installation, the requirements to the all-plastic part include a variety of very challenging load cases, among them static and dynamic hood latch failure, where incorrect opening and closing of the engine's hood is simulated and tested under the harshest conditions,” said Hensel. “At the same time, the stiffness and vibration behavior of the system comprising front end and radiator was optimized on the basis of CAE analyses and validated in an actual vibration test.”
The salient aspects of the front-end carrier’s design for the new Golf included the crash sensors attached to the structure. The sensors look after deployment of the airbag in the event of a head-on collision. To achieve this crucial action, the plastic part had to exhibit a certain dynamic stiffness at a defined location and satisfy VW’s crash acceleration requirements. Stated Hensel: “In a real-world test, the vibration response of the part corresponded exactly to what was designed and predicted by Ultrasim: the Ultramid front-end carrier transmits the collision signal correctly.”
He explained that the primary load cases provide the basis for a front-end design; from these, an optimized topology can be derived. “This topology gives the designer valuable information regarding the final shape of the part. Thanks to the highly accurate predictions of Ultrasim, only slight modifications were needed in moving from the prototype of the front-end carrier to its series production. This demonstrates the kind of challenging applications that can be addressed by combining a suitable material with the correct prediction and calculation tools.”
Hensel said that Ultrasim, together with its special failure models, could be integrated seamlessly into the calculation environment for the whole vehicle. However, this requires the availability of highly specific crash-relevant material data for the plastic that describe exactly the effect of temperature, moisture, and rate of load application.
“A simulation is thus preceded by acquisition of extensive material data from experiments conducted with the aid of complex testing and measuring instruments. The simulation tool is then able to predict failure behavior, strain rate dependence, and even tension-compression asymmetry as a function of fiber orientation,” added Hensel.
The upper half of the thermostat housing for VW’s new TSI 1.4-L gasoline engine also uses a version of Ultramid. Manufactured by automotive supplier Veritas, the part is made of a new, specially hydrolysis-resistant grade Ultramid A3WG6 HRX. It has been designed and developed to withstand water temperatures up to a maximum 130°C (266°F) and also high pressures. A smaller thermostat cover is molded from the stiffer Ultramid A3WG7 HRX, to meet particularly high stresses.