ALUSIL ® -Cylinder Blocks Porsche V6/V8 - KSPG AG

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4 5.5 mm Fig. 2: Cylinder head flange surface with a land width of only 5.5 mm Fig. 3: Material structure of the alloy AlSi17Cu4Mg / ALUSIL ® with primarily precipitated silicon crystals (dark areas in the picture) Fig. 4: Mechanically exposed ALUSIL ® cylinder bore surface ALUSIL ® makes a minimum weight at a high degree of integration of engine functions like lubricant, coolant and engine venting circuits. ALUSIL ® enables minimum overall cylinder block lengths to be implemented because the engines can be operated without inserted cylinder liners. To achieve the shortest possible engine length at a specified swept volume and stroke, the cylinder bore diameter should be kept as large as possible, at minimum land width. In such cases, the land width of the jointly cast cylinders is determined in practice by the safe and reliable performance of the cylinder head gasket, by the cutting pressure applied for machining and the cylinder distortion in engine operation. ALUSIL ® boasts excellent tribological characteristics. As the pistons and piston rings slide along the exposed silicon crystals, their susceptibility to seizing is minimized (Fig. 3). ALUSIL ® displays optimum thermal conductivity; Audi is thus in a position to achieve a high specific engine performance. ALUSIL ® does not imply any recycling problems because the cylinder block does not contain extraneous materials – such as cast-in cylinder liners made of grey cast iron. ALUSIL ® allows cylinder blocks to be cast monolithically without cylinder liners or subsequent coating of the cylinder bores. This makes it possible to achieve: components of optimum structural rigidity through the benefit of a by 12 % higher Young’s modulus of the ALUSIL ® alloy compared to a hypoeutectic standard alloy as well as, process reliability in machining without having to interrupt the process flow for costly additional working steps specifically for the cylinder bore surfaces. A decisive milestone in this area was the mechanical exposure of the silicon crystals by means of a third honing step (Fig. 4) as a substitute for the chemical laying bare (etching) after the two-step honing process which was a must before. Laying bare the silicon grains by mechanical means allows perfect on-line production.
The above described assets of the ALUSIL ® alloy are certainly significant arguments in favor of the use of this material. But also the low-pressure die casting method (Fig. 5) which has since then proven to be the best by far is an important prerequisite for process reliability in making mass-produced cylinder block castings of ALUSIL ® . 3. Reasons in favor of low-pressure die casting from the viewpoint of Audi: Low-pressure die casting, LPDC (Figs. 5 – 6) allows to use sand cores where necessary, e.g. for water jackets (Fig. 7). In this way, structurally rigid closed-deck cylinder blocks can be produced, a prerequisite for high specific engine outputs. LPDC allows controlled, low-turbulence die filling, and what is even more important, controlled cooling of the die to ensure component-specific, virtually ideal directional solidification. The compilation of all casting-relevant data and the resulting control of the casting process are implemented today computer-assisted. Especially a purposedesigned cylinder sleeve cooling system is an indispensable prerequisite for uniform precipitation of the silicon crystals in the cylinder area (criteria: distribution, grain size range (Fig. 8) and number of crystals per cm²), low porosity and minimizing casting defects like shrinkage holes, pores, cold fusion, etc. This process control ensures constant quality of the castings. LPDC permits unrestricted heat treatment of the casting. It is already possible to achieve a certain increase in hardness and strength by applying controlled cooling of the cylinder blocks from the casting temperature by means of customary T5 heat treatment. The subsequent artificial aging not only serves to enhance hardness and strength, but primarily also to stabilize the volume, i.e. avoid an irreversible expansion in length and volume (distortion) referred to as “growth” when the casting is exposed to the operating temperature of the engine. To cope with even higher engine stresses, a modified T5 heat treatment solution is available where the hardness and strength of the components are enhanced through the casting heat, e.g. locally in the cylinder deck or bearing bulkhead area by means of chilling with water which leads to precipitation hardening. Sleeve yoke with movable die half Open die Stationary die half Crucible with melt (holding furnace) Cylinder sleeves Casting Lifting table, stroke about 2 m Hydraulic cylinder sleeve lifters Hydraulic lateral slides Feed tube Fig. 5: Low-pressure die casting, illustrated principle of a casting cell with opened die (movable die half in lifted position) Fig. 6: Design of a low-pressure die for aluminium cylinder block 5
Page 1: ALUSIL ® Cylinder Blocks for the A
Page 6 and 7: For absolute high-performance engin
Page 8 and 9: Whereas in the standard FSI engines
Page 10 and 11: nearly 100 %, depending on the heat
Page 12: KS Aluminium-Technologie GmbH · Ha

ALUSIL ® -Cylinder Blocks Porsche V6/V8 - KSPG AG

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