It was not that many years ago that glass-fiber reinforced polyamide began to push steel and other metals out of underhood automotive applications such as air intake manifolds. The inter-materials' competition continues, as shown by Volkswagen's experience that it can replace nylon with polypropylene in these manifolds.
VW and its partners on the air intake manifold project, which was first discussed in 2009 at a conference in Germany (see our initial report here) and now has placed PP manifolds on a wide variety of VW car models, reckon this is the first time that an automotive OEM has switched from a glass-fiber reinforced polyamide to PP for this application. The molder of the parts is Mahle Filter Systems UK, using glass-fiber reinforced (GFR) PP compound XMOD GB306SAF from polyolefins supplier Borealis (Vienna, Austria).
"Plastic air intake manifolds are used in the majority of vehicles produced worldwide today because of the optimized air flow, design freedom and general reductions in weight and cost they offer over their metal counterparts," said Dennis Nicholls, project manager Mahle UK. "However, rising under-the-hood temperatures, demands for improved function integration capability, noise reduction and ever-lighter components, plus the need to reduce our own and our customers' overall system costs, means we have had to look beyond polyamides to meet these challenges."
VW committed to the change in materials under the premise it would realize lower system costs without significant change in tool and part design, better acoustic behavior and use of an environment-friendly material. To eliminate Mahle's need for equipment investment, same-speed production with existing injection molding processes and post-molding secondary processing, such as direct screwing, was also considered key. Harold Hammer, VP mobility at Borealis says the grade of PP used on the air intake manifold can be molded on tooling designed for polyamide, with minor changes to the entire process.
The material processed, XMOD GB306SAF, has a 35% GFR loading, with parts made from it able to function in an operating temperature range between -40°C and +120°C. Lighter weight and less dense than the polyamide it replaced, it enables weight reductions for these manifolds of up to 15%, while also offering improved sound damping that surpasses current acoustic behavior for the parts.
The material also costs less per kilogram, helping contribute to a lower overall production costs. Lower processing temperatures and the lack of pre-drying further reduce overall energy consumption and eliminate some manufacturing steps.