Plastic fuel systems manufacturing, based on extrusion blow-molding process, requires 5 major steps:

• Extrusion: Plastic raw material (in pellets) is being heated and melted using an extrusion screw. As it is being pushed through an extrusion head, it forms a large plastic tube called parison.
• Blow-molding: The parison goes down between the two shells of a mold. Mold is being closed and gas injected into the mold. The plastic material, due to the pressure, is projected on the surface of the mold to take its complex form. At the end of the process, the mold opens and tank shell comes out. Excess material is being cut and regrind to be reused in the extrusion process.
• Cooling: Tank shell has to cool down before assembly of the components. Post-cooling devices can be used for this step to accelerate this part of the process.
• Finishing: Tank shell goes through a machining center to cut necessary openings and weld required components (such as valves, clips and sometimes filler pipe) onto the tank. Special finishing centers have been developed to optimize and robotize this part of the process.
• Assembly: Finished tank are being equipped with complementary components such as fuel delivery module, fuel lines or straps. Those complete Fuel Systems are then being delivered to vehicle assembly line, sometimes in sequence, to be mounted on the car.  

Plastic material commonly used for automotive plastic fuel tank is a special grade of HDPE (High Density PolyEthylene). Particularly suitable for the extrusion blow molding process, it confers to the tank a real advantage in terms of performance: ability to manufacture complex shapes to embark a maximum of useable fuel in tight space, excellent behavior during crash, light weight and optimized cost for the function.

Fluorination

The fluorination process consists in treating monolayer HDPE parts using a mix of fluorine and nitrogen to lower the permeability of these parts to hydrocarbon. Without fluorination, H and C molecules are spaced out. With fluorination, H molecules are replaced by F molecules; F and C molecules are tightened.