Casting And Machining the Porsche Cayenne Block
With a specialized vehicle like the Porsche Cayenne there’s a need for specialization in aspects of its production. Like the use of a specialist casting supplier to not only produce the aluminum-silicon alloy block, but to completely machine it as well. seat.
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There’s something different about the Porsche Cayenne. No, not the fact that it is an SUV and a Porsche. Though there is that. Rather, one would assume that the single most important contributor to its “Porscheness,” its 4.5-liter V8 engine, would be wholly manufactured by the Stuttgart-based firm. It isn’t. The aluminum block for the V8 is being supplied to Porsche fully machined by the firm that casts the block, KS Aluminum-Technologie AG (KS ATAG), part of the Rheinmetall Group, in that firm’s Neckarsulm, Germany, facility.
KS ATAG is certainly no stranger to casting blocks. In fact, it provides them to a variety of European manufacturers, everything from blocks for the Mercedes A Class to the VW W12. It particularly specializes in premium products: for example, the V12 for the BMW 760i and the Rolls Royce is being produced by KS ATAG. According to Dr. Gerd Kleinert, CEO of Kolbenschmidt Pierburg AG, of which KS ATAG is a part, the firm casts some 500,000 aluminum engine blocks per year.
Prior to working on the Cayenne S (340 hp @ 6,000 rpm) and Turbo (450 hp @ 6,000 rpm) blocks with the people at Dr. Ing. H.c. F. Porsche AG, KS ATAG had, like other block casters, performed simply a cubing operation on the blocks: the initial Op. 10, squaring the block. But according to Horst Binning, executive chairman of the board of KS ATAG, they’re removing 17 kg from each of the Cayenne blocks via the machining operations. The as-cast top and bottom sections of the block (i.e., the V8 features what’s known as a “closed-deck” design, which means that the crankcase is cast separately from the cylinder heads) start out weighing a combined 72 kg and finish at about 55 kg. (FYI: A comparable gray cast iron engine would weigh 40 to 50% more—which might have an effect on the Turbo reaching its top end of ~165 mph [not that anyone would off the autobahn, of course].) The machining is being done on a 30-station line that was developed in cooperation with Grob-Werke (Mindelheim, Germany). Operations performed include milling, deburring, boring, honing, threading, washing, assembling the two pieces, leak testing, and dimensionally inspecting (this last on a Zeiss VAST coordinate measuring machine). The maximum line capacity is 30,000 units per year (the cycle time is 500 seconds). They’re producing 25,000 annually for the Cayenne. The finished blocks are sent directly to Porsche’s plant in Zuffenhausen for final assembly.
Binning stresses that their concentration with regard to the total machining of blocks is for low-volume production. If there were to be a demand for more blocks, say from another customer that’s looking for the dimensional control that results from having a single-source responsibility for performing the casting and the machining, then they would undoubtedly secure additional equipment to perform the tasks.
The casting is performed with a low-pressure casting setup. In low-pressure casting the steel mold is above the molten aluminum. The alloy is introduced from the bottom of the mold with a small amount of pressure, which means that there is comparatively low turbulence in the mold. The fill time is approximately 50 seconds. The cooling occurs from the top of the mold to the bottom. Because the cooling process is critical to the quality of the cast part, there are multiple sensors in the mold so that the temperature can be adjusted if the measures indicate that it is necessary.
One interesting aspect of the Cayenne blocks is that the material that is used harkens back to 1973, when Porsche and KS ATAG’s predecessor company were working on an aluminum alloy with a high silicon content. The objective was to create an aluminum block that wouldn’t require the cylinder liners or coatings that are typical of most aluminum blocks (e.g., to resist the wear from the pistons). The material used for the Cayenne blocks is alusil, which has a hypereutectic silicon content of 16 to 18%. During a specially developed multi-stage honing process, the silicon is uncovered in the bores in small-particle sizes. These particles provide the wear resistance required.
COMPLETE ENGINE SPECIALIST?
Although there are things that Kobenschmidt Pierburg doesn’t produce for an engine, like crankshafts and fuel injectors, it has a sufficient range of capability, know-how, and experience in other engine-related products such that it isn’t hard to imagine that the company could become a complete low-volume specialist engine manufacturer. For example, looking at some of the new products from its divisions there are:
- PIERBURG: Electric secondary air valves; secondary air pumps; EGR modules; intake manifolds; electric coolant pumps; variable-flow oil pumps
- KS Kolbenschmidt: Pistons for both gasoline and diesel engines
- KS Plain Bearings: Engine bearings
- KS Aluminum-Technologie: Engine blocks
Consider the company’s content on the 438-hp BMW V12. The company provides a magnesium intake manifold, engine block, solenoid valves, oil pump, secondary air system, and EGR valve. (The intake manifold is an especially interesting bit of work that is unique among BMW intake manifolds because it is not covered in plastic, but simply powder coated. The manifold measures 625 x 615 x 135 mm, has an enclosed air volume of 11.3 liters, and weighs 7 kg.)
If there’s one thing (and it may be the only thing) that the aluminum and steel industries agree upon, it’s this: We’re leaving the steel era and entering an age of automotive material options, where there are combinations of different materials, not just one dominant material.
According to Sandor Piszar, Chevrolet truck marketing director, “We engineer and build our trucks with customers’ expectations in mind.”
If aluminum-intensive cars are ever to become more than an occasional curiosity, automakers may have to give up their weld shops.