Managing Thermal Growth for Large Class “A” Polymer Body Panel Closure Systems 2002-01-0276
The history behind Polymer Class “A” Body Panels for automotive applications is very interesting. The driving factors behind these applications have not changed significantly over the past sixty years. Foremost among these factors is the need for corrosion and dent resistance. Beginning with Saturn in 1990, interest in polymer body panels grew and continues to grow up to the present day, with every new global application.
Today, consumers and economic factors drive the industry trend towards plastic body panels. These include increased customization and fuel economy on the consumer side. Economic factors such as lower unit build quantities, reduced vehicle mass, investment cost, and tooling lead times influence material choice for industry.
The highest possible performance, and fuel economy, at the lowest price have always been a goal. The following quote from Henry Ford states this goal very well,
“…We build most of our vehicles as though dead-weight fat increased speed… I cannot imagine where the delusion that weight means strength came from.”
“Saving even a few pounds of a vehicle's weight… could mean that they would also go faster and consume less fuel. Reducing weight involves reducing materials, which, in turn, means reducing cost as well.” Henry Ford, 19231
The technical challenge associated with a Body Panel Closure system is best determined by understanding the requirements of the system:
Create comfortable interior environment
Maintain Body Gap and Flush
Provide proper stiffness for Ride and Handling
Provide proper interface with all adjacent Sub-systems (handles, license plate, window, wiper system, struts, wire harnesses and interior trim.
Keep out road noise
Comply with all applicable FMVSS/CMVSS
Comply to all additional requirements set by each OEM
The technical challenges associated with developing a hybrid closure system, including the use of dissimilar materials for the inner and outer panels, must be thoroughly examined to assure successful execution. At the same time, maintaining system requirements becomes key in minimizing program risk to the OEM. An automotive case study in balancing science and finance.
This paper will discuss preliminary findings in thermal growth management for a hybrid liftgate system using the 2002 Ford Explorer liftgate as a surrogate closure system. In particular, Body Gap and Flush requirements are investigated in this paper. The system was constructed using a polycarbonate/acrylonitrile-butadiene-styrene (CYCOLOY® MC 8800 resin) outer panel, along with a propriety lightweight metallic inner panel. The inner panel will not be discussed because of the propriety nature of the development program.