Bedplate machining for Porsche

Neckarsulm, (PresseBox) - Back in 2002, KS Aluminium-Technologie AG (ATAG) started supplying Porsche with net- or finish-machined V8 engine blocks. These blocks being built into the off-road Cayenne S, Cayenne Turbo and more recently the Cayenne GTS, are low-pressure cast, pre-worked and finally shipped out to Porsche net machined as a single unit including the bedplate. The positive experience acquired with the 4.5-liter V8 gasoline engine has prompted Dr. Ing. h.c. F. Porsche AG to continue this cooperation on a new 4.8-liter engine recently launched onto the market. A new feature of this contract is that the bedplates are also being cast and pre-worked by ATAG. Hence, and despite the short development period, right in time for SOP (Start of Production) quality is squarely within the aspired target corridor and proving superior to the previously outsourced parts.

Originally at the start of the second generation of engine block shipments (September 2006), the bedplate had also been an outsourced part. But due to the critical quality and delivery situation for this part, ATAG was then awarded the follow-up contract to likewise manufacture the bedplate. Within a very short period, product and process development was underway and after only five months the product was shown to be ready for series production.

"With the manufacture of the bedplate, the entire value-adding chain-from casting, pre-working to net machining of the complete engine block including certain add-on parts such as bolts, pins and gaskets-is now in our hands," says Horst Binnig, CEO of KS Aluminium-Technologie AG.

On account of the challenging performance benchmarks, the production technique for the part is not the normal die-cast method but instead low-pressure permanent-mold casting. The material cast is an AlSi7Mg0.3 alloy; its downstream heat treatment consists of solution annealing, quenching, and elevated temperature age hardening.

Significant weight savings

Since the commencement of series production, this generation of V8 gasoline engines has been repeatedly refined for use in the Porsche Cayenne, with the prime goal of-alongside an increase in specific and absolute engine performance specifications-a marked reduction in fuel consumption under customer-relevant operating conditions. Another aim was to arrive at additional weight savings without impairing the ruggedness and longevity of this gasoline engine.

Within this development effort, Porsche and ATAG engineers have together succeeded in significantly reducing the weight of the new engine block through both casting techniques for the engine block itself and by virtue of engineering changes to the engine.

The crankshafts on the first-generation models had turned on gray cast iron inserts; on the second generation engines, these inserts are dispensed with and instead, the crankshafts themselves are mounted in the casting, a technique calling for the ultimate in terms of casting process and quality.

The engine block of the new Porsche V8 is, just as its predecessor, a two-part extremely rigid construction comprising a top section and the bedplate. The former is of closed-deck design and low-pressure gravity cast from the proven Alusil alloy. The housing is stabilized, i.e., T5 heat treatment is applied.

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