A New Approach to Hybrid Front-End Systems 2002-01-1229
The front-end carrier (FEC) refers to the part of a car, which supports most of the cooling package, headlights, latch and various other components. It also ties the upper and lower longitudinal rails and plays a role in the structural stiffness of the car.
Traditional front-ends carriers are built up from steel and bolted or welded to the body-in- white (BIW). In recent years, however, there has been a trend towards mounting the complete front-end system (FES), as a module, onto a BIW with an open structure. The FEC assembly then connects the longitudinal rails. This allows reductions in cost, moves part of the assembly away from the OEM and often improves the overall quality.
The move to modular systems opened the door to the use of plastics. Use of molded plastic carriers allows integration of parts and functions, weight reductions and cost advantages. However, in most cases, a hybrid structure of metal and plastic is still required, in order to resist the high loads exerted on the carrier during crash and other load cases.
The approach to building a hybrid system started with the use of glass mat technology (GMT) carriers with the addition of metal, which was riveted to the plastic structure. Advances on GMT, such as compression-molded plastic or injection molding, improve the plastic carrier economics and the options for integration and weight reduction. The addition of metal still remained a challenge, with riveting and heat staking being the most common approaches. The advent of the overmolding concept tackled this problem and allowed better coupling of the plastic and metal, although it introduced several other challenges.
This paper outlines a new approach where the metal parts are bonded to the plastic. Through clever design of the plastic and metal parts, a continuous joint between the plastic and metal is achieved, incorporating a closed box section, not possible with the overmoulding technique. In areas where the stiffness and strength of the system are critical, this continuous joint and the closed box section deliver a very flexible approach and an efficient method of getting the most out of the hybrid system.
The system is bonded using a low energy substrate adhesive (LESA). This newly developed adhesive allows materials with low surface energies, such as polypropylene (PP), to be bonded without the use of pre-treatment.
The design and performance of such a hybrid system where long glass fiber reinforced PP (LGF PP), specially developed for this application is bonded to e-coated metal without pre-treatment, are demonstrated compared to current systems. The weight reductions and performance improvements are outlined. The potential for cost saving in parts and investment is shown, and a possible approach to production and assembly in mass production is introduced.