Faurecia says the switch to extruded TPV seals reduced capital expenses by 15%, lowered seal mass by 48%, and produced double-digit cost savings. The success didn’t go unnoticed, with the application recognized in the Chassis/Hardware Category of the 2007 SPE Automotive Division Innovation Awards.
Leaving no subassembly unturned
In a drive to cut vehicle weights, OEMs and their suppliers are taking a holistic view of cars, examining every subassembly and component. Faurecia targeted the door core module, which is a carrier plate on which sub-assemblies like window-lifting systems, electronics, door locks, and audio speakers are mounted and integrated. Because of its contents, the door core seal must offer a water-tight barrier to the elements on the other side of the door, as well as boost the acoustical performance of the door, preventing wind noise, rattles, and squeaks.
Door core seals are traditionally manufactured using an external molder applying thermoset EPDM rubber, which is manually assembled onto the module, or they can use PUR foam seal applied by the system supplier. ExxonMobil Chemical says PUR foam seal has limited profile geometry options, while also occupying floor-space and assembly time while the PUR cures before any further processing.
For more than a decade, ExxonMobil Chemical and Reis Extrusion have been jointly developing a robotic extrusion process utilizing Santoprene TPVs, with the first commercial applications coming in static weatherseals robotically extruded onto vehicle windows and seals on large PP underbody panels.
The companies say the robotic extrusion’s benefits include a reduction in labor costs since adhesives or mechanical attachment mechanisms are eliminated; faster cycle times since no curing is needed; greater design freedom with thin-wall geometry and profile extrusion in X-Y-Z directions; fully automated production set-up with the possibility for integrated injection molding and robotic handling; and the ability to bond to a variety of substrates.
The Faurecia Interior Systems subassembly includes an injection molded door core, made with glass-filled PP from ExxonMobil Chemical. Next, the TPV— Santoprene TPV 121-50E500—which is specifically designed for robotic extrusion, is applied, reportedly allowing the seal profiles to maintain their shape without any further support. The companies conducted relaxation and adhesion tests on the PP substrate to ensure the seal bond was strong, and design studies were undertaken to fine tune the profile geometry. Final testing to prove the effectiveness of the seals was conducted by Faurecia and Chrysler.
Prior to extrusion, Santoprene TPV E500 is melted in a conventional thermoplastic extruder and pumped into a heated, pressure-resistant, flexible hose. This hose is connected to a special extrusion die mounted on an industrial robot. With the door module fixed on a table, the TPV seal is extruded onto the module in the required position via the six-axis robot.
ExxonMobil chemical calls the TPV seal’s bond with the glass-filled PP substrate a cohesive one, adding that due to the TPV’s shear-sensitive nature, the profile remains in the desired shape without curing or calibration. Ready to go, the parts can be handled and transported almost as soon as the robot has moved away, saving tack/cure time by 90%.
Faurecia has taken workflow a step further so that the robotic extrusion process is set up where the left-hand and the right-hand door modules are injection molded, component sub-assemblies are installed, and both sides’ seals are applied by one robotic extrusion system in one location.
The companies say that this is the first time a TPV has has been extruded onto a door-module carrier, with the 360° coverage acting as a water barrier between the wet and dry sides, an acoustic barrier, and a seal against dirt and dust.