Kolbenschmidt Pierburg Group

ALUSIL® cylinder blocks for the new V6 and V8 SI engines 1. Audi setting standards in lightweight design 2. Reasons in favor of ALUSIL® from the viewpoint of Audi: With its vehicle model series, Audi is setting new standards in lightweight design. So it is only logical for the carmaker again There are many technical reasons which induced the car- to count on in developing the cylinder blocks for maker Audi to adhere to the proven ALUSIL® concept: its new spark-ignition V-engines (Fig. 1). On account of the reduced wall thickness (cylinder land width of only 5.5 mm ALUSIL® makes a minimum weight at a high degree of in- (Fig. 2) between cylinder bores), Audi relies on the hypereu- tegration of engine functions like lubricant, coolant and tectic aluminium-silicon AlSi17Cu4Mg registered for KS engine venting circuits. ATAG under the brand name of ALUSIL®. This concept allows the pistons to move directly along the honed cylinder bore ALUSIL® enables minimum overall cylinder block lengths surfaces of the aluminium casting – an ideal condition for to be implemented because the engines can be operated high-performing engines. 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

V6 cylinder block V8 cylinder block (fuel stratified injection [FSI])

V8 cylinder block cylinder block of the (multi-point injection) existing Audi

Fig. 1: ALUSIL® cylinder block of the new Audi V6 and V8 SI engine generation.

2 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 cylin- der head gasket, by the cutting pressure applied for ma- chining and the cylinder distortion in engine operation.

ALUSIL® boasts excellent tribological characteristics. As the pistons and piston rings slide along the exposed sili- 5.5 mm con 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 per- formance.

ALUSIL® does not imply any recycling problems because Fig. 2: Cylinder head flange surface with a land width of only the cylinder block does not contain extraneous materials 5.5 mm – 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 cyl- inder 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 addi- tional 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 hon- Fig. 3: Material structure of the alloy AlSi17Cu4Mg / ALUSIL® ing process which was a must before. Laying bare the with primarily precipitated silicon crystals (dark areas in the picture) silicon grains by mechanical means allows perfect on- line production.

The above described assets of the ALUSIL® alloy are certain- ly 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®.

Fig. 4: Mechanically exposed ALUSIL® cylinder bore surface

3 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). Sleeve yoke with In this way, structurally rigid closed-deck cylinder blocks movable die half can be produced, a prerequisite for high specific engine Hydraulic cylinder outputs. sleeve lifters

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 imple- mented today computer-assisted. Especially a purpose- Cylinder designed cylinder sleeve cooling system is an indispens- sleevers able prerequisite for uniform precipitation of the silicon Open die Casting crystals in the cylinder area (criteria: distribution, grain size range (Fig. 8) and number of crystals per cm²), low Stationary die half Hydraulic lateral shifters porosity and minimizing casting flaws like blowholes, pores, cold fusion, etc. This process control ensures con- Riser stant quality of the castings.

LPDC permits unrestricted heat treatment of the casting. Holding furnace It is already possible to achieve a certain increase in hard- with melt ness 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, Lifting table, but primarily also to stabilize the volume, i.e. avoid an stroke about 2 m irreversible expansion in length and volume (distortion) referred to as “growth” when the casting is exposed to the operating temperature of the engine.

Fig. 5: Low-pressure die casting, illustrated principle of a cast- For still higher thermal stresses in engine operation, a modi- ing cell with opened die (movable die half in lifted position) fied T5 heat treatment method is available by which the components of casting temperature are chilled locally, for example in the cylinder deck or bearing bulkhead areas by means of water showers, and their hardness and strength are raised through precipitation hardening. The heat treat- ment is additionally utilized for stabilizing the alloy.

For absolute high-performance engines, Audi will in the fu- ture apply full heat treatment (T6) comprising homogenizing, chilling and artificial aging. This method contributes toa further distinct improvement in terms of static and dynamic strength. As “mere” T6 heat treatment without specific ar- tificial aging only leads to a low degree of volume stabili- zation and involves the risk of distortion at operating tem- perature of the engine, the artificial aging time is frequently even extended. This extension of the aging time improves the expansion characteristics.

Fig. 6: Design of a low-pressure die for aluminium cylinder block

4 4. Audi’s new V-engine generation: 5. The Audi V6 and V8 engine concept:

The new V-engine generation of Audi – both petrol and die- The new V6 in the large displacement version of 3.2 l and the sel engines – is setting standards with respect to compact- new V8 with a swept volume of 4.2 l originate from the new ness and overall length. Customers’ requests for more pow- Audi V-engine family with a stroke of 92.8 mm (Fig. 9), a V erful engines even in smaller vehicle model series implied angle of the cylinder banks of 90° and a central division of the need for shorter overall engine lengths and for reducing the cylinder block (bedplate concept). The distance between the vehicle front-part weight. As a result a new V-engine gen- cylinders is 90 mm, the cylinder bank offset being 18.5 mm. eration has been created. For the V6 of 3.2 l as well as the V8 of 4.2 l swept volume, the cylinder bore is 84.5 mm. For the smaller V6 engine of 2.4 l Audi is the market leader in lightweight design, specifically swept volume, it is 81 mm. The cylinders are cast jointly at in the premium segment. The lightweight strategy is impres- a land width of 5.5 mm and of 9 mm, respectively for the V6 sively implemented in the car body through the Audi space with the smaller swept volume. frame aluminium technology. It was a logical consequence therefore to rely on a weight-optimizing all-aluminium solu- The V6 of the large swept volume version operates with fuel tion for the petrol V engines – i.e. ALUSIL® cylinder blocks. stratified injection (FSI), and in the small version, with multi- Thanks to its high competence as the European market lead- point injection (MPI). The different cylinder bore diameters er KS ATAG was able to convince the market with ALUSIL® for do not require an adjustment on the water-jacket side. The cylinder blocks of passenger-car SI engines in the respective V8 SI engines are available in three versions. To the existing market segment. Attractive contracts from Audi are contrib- two engine versions with MPI, a new version with FSI was uting to the further strengthening of KS ATAG’s location in added which also distinguishes itself by its cylinder block Neckarsulm and its market leadership. design.

Fig. 7: View of a water-jacket core box in the core shooter: water-jacket sand cores for Audi V6 cylinder block (left) and V8 cylinder block (right)

5 6. Description of the cylinder block top: front, above the V space but connected with it. Water supply to the jackets of the two cylinder banks is accomplished by As mentioned above, the Audi cylinder blocks (Fig. 10) are means of a manifold, flange-mounted in the V space. made of the hypereutectic alloy AlSi17Cu4Mg. The low-pres- sure die casting method is applied, with controlled cooling The oil circuit ducts are partly pre-cast, partly drilled. The from the casting temperature. Cooling takes place at ambi- two deep-hole bores centrally arranged in the V, for the main ent air or its partly assisted by an air blower. This is followed oil and injection nozzle channels for piston cooling, which by artificial aging for volume stabilizing (T5 heat treatment), virtually cover the whole block length, are pre-cast for the V8 a process which only implies a slight decrease in hardness. in the same way as the non-pressurized oil drain backs and The associated bedplates – not included in the scope of sup- cylinder block vent ducts. They are arranged externally on ply of KS ATAG – are high-pressure die castings made from the side walls, in parallel with the cylinders. These channels the hypoeutectic alloy AlSi9Cu3 with cast-in bearing bulk- are connected with the bedplate through bores in order to heads of spheroidal cast iron in the case of the V6. In the exclude the risk of casting fins being left. new V8, high-pressure die castings from alloy AlSi12Cu1(Fe) are employed for the bearing brackets. The cylinder block of It goes without saying that after removing the sand cores the the V8 FSI engine was submitted to further structural optimi- cylinder blocks have to be submitted to first-cut machining zation for the purpose of boosting performance output; this (Fig. 11). is recognizable from the outside on the basis of the cross members in the V space between the cylinder banks. Further Adjustment in the crankcase area is achieved by alignment modifications relate to the oil filter flange area. in the first clamping step, starting from cast locating points at the interface to the bedplate. To this effect, the three lo- The water jackets of the cylinder banks produced by using cating points on the gearbox side are machined and two in- sand cores as well as the water supply channels are inte- dex bores (fitting bores) are set. grated on the left and right sides in the cylinder blocks. In the case of the V6, in addition the part of the water pump housing on the discharge-nozzle side is arranged at the

25.0

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5.0 Number of grains in the area measured in the area grains Number of

100.2 micron 0 10 20 30 40 50 60 70 80 Grain size [µm] Area measured

Fig. 8: Representative grain distribution of the primarily precipitated silicon crystals

6 Further machining steps in the first and second clamping honing step with “soft” hones which means hones with cut- operations are the drilling of the oil ducts, pre-drilling of the ting material embedded in a non-rigid matrix. In the process, cylinders, pre-milling of the main bearing area and cubing of the hones virtually “erase” any adhering aluminium from the the external faces. In this last step, all “important” surfaces silicon crystals (50 % is already removed in the second hon- are re-milled in order to remove casting fins, for instance in ing step when eliminating the silicon crystals destroyed on order to enable a subsequent leak test to be carried out. the surface) and, this is decisive, the aluminium matrix is thus recessed to a certain extent. Given the hardness of the For warranting absolute casting quality, every cylinder block silicon crystals, the pistons require reinforcement composed is submitted to an x-ray, hardness and ultrasonic test. The of galvanically deposited iron or a plastic layer applied to the latter serves to check the bearing bulkheads for porosity. The piston skirt by screen-printing. The piston rings also need a oil ducts and water jackets are submitted to a leak test ap- specific adjustment to the ALUSIL® bore surfaces, although plying the differential-pressure method as well as a 100 % nowadays there are not necessarily any significant differenc- visual inspection before the cylinder blocks are delivered to es with respect to the piston ring protection usually applied Audi. in the case of grey casting cylinders.

At AUDI HUNGARIA MOTOR Kft. (AHM), the cylinder blocks ALUSIL® features sufficiently high strength so that even for are integrated into the machining line on the locating points the high-strength bolt joints like those of main bearing cap and aligned on gearbox flange level by means of the fitting and cylinder head the nut thread can be cut directly into the bores provided in the gearbox flange. Next, the cylinder cast material. When “overtightening” the bolt, it will in-vari- block is machined as an individual part, with most of the ably tear off before the nut threads are shorn. The high com- machining work being done in these working steps. Subse- pressive strength of ALUSIL® has an extremely positive effect quently, the finished bedplate is “matched” with the cylinder on the bolted joints. It exceeds the tensile strength by nearly block, i.e. pinned and bolted. From this moment, the cylinder 100 %, depending on the heat treatment condition. As a re- block and the bedplate constitute one unit and move jointly sult, commercial bolt heads hardly lead to an appreciable through the assembly line. An important machining step is setting of the aluminium even if the bolt was tightened up to the mechanical exposure of the silicon crystals in a third the tensile yield point.

Fig. 9 : The new Audi V6 (left) and V8 (right) SI engines

7 7. Description of the casting die and develop- The following prerequisites, among others, had to be fulfilled ment/adjustment of the casting process to achieve this:

Audi’s intention to achieve a synergy effect between V6 and Installation of an experienced and assertive project man- V8 cylinder blocks has been fully implemented with the die agement as well as an interdisciplinary project team en- design, the concept of the machining installations and test- compassing all necessary functions. ing equipment as well as, in particular, the development/ adjustment of the casting process. Never before had KS Design engineering optimization based on the results of ATAG succeeded in supplying V8 cylinder blocks to the Audi previously completed die filling and solidification simu- plants in such a record time, quasi in fast motion from con- lations (Fig. 13). These indicated in an early stage any fill- tract award by Audi through to the production and delivery ing inadequacies or unfavourable timing of the die filling of the dies and the prompt launching of the casting process. process (e.g. local surging of the melt, Fig. 14) as well as This achievement was preceded by a series of parallel ac- isolated residual solidification zones making re-feeding tivities in the sense of consistently practiced simultaneous impossible. engineering between Audi, KS ATAG and the die manufac- turer by exploiting all possibilities in terms of virtual product Knowledge of casting problems previously occurring with development in an uninterrupted CAD, CAE, CAM sequence the V6 cylinder blocks, which are basically of the same (Fig. 12). geometric concept, and consequently provision of suit- able remedies as a preventive measure.

Exploiting the full know how available at KS ATAG and at the die manufacturer; application of the latest experi- ences concerning design and engineering of the casting dies; avoidance of time losses as a result of adjustment difficulties to the casting support; on-schedule prepara- tion of the casting cell including all peripheral installa- tions; programming of the handling robot, etc.

Activation of the full casting technique competence of KS ATAG starting with the melting operation, via melt prep- aration in the holding furnace, the filling of the die ad- justed to the component geometry, i.e. the cross-sec- tional development in the horizontal section, through to controlled die cooling. In all those cases, efforts were concentrated on local heat dissipation through the steel sleeves for the cylinders and the die bottom (bearing bulkhead area) and its correct timing.

Timely preparation and checking of the clamping fixtures for pre-machining; installation of the pre-machining sys- tem and necessary inspections of the mechanical work including availability of suitable labour and its specific qualification for the new product family.

Fig. 10: Aluminium cylinder block concept, consisting of monolithic cylinder block top and bedplate with cast-in bearing bulkheads made of spheroidal casting

8 8. Summary, conclusion and outlook low-pressure die casting method which is firmly integrated with this concept today. There are numerous suggestions For its state-of-the-art high-performance SI engines of V de- for a further reduction of cycle times (cost curbing), but on sign, Audi stakes on the combination of ALUSIL® low-pres- the other hand, the physical laws cannot be disregarded. sure die casting and mechanical silicon grain exposure. In Dissipating more local heat per time unit can only be ac- the present situation, this combination offers optimum con- complished partly without sensibly disturbing the course of ditions for the engine functions, production and process re- the solidification fronts, e.g. in the cylinder-block skirt area liability as well as quality. Hence there are quite a number through shrink-fit cooling at the bearing bulkhead level. An- of factors speaking in favor of ALUSIL® to be rated as the other approach would be thin-wall dies to achieve a distinct best material available today for high-performance spark- reduction in the “thermal inertia” of the die. However, this ignition V engines when weighing the many convincing posi- would increase the monitoring requirements in those areas tive properties up against occasionally adduced less favour- which cannot yet be reliably controlled for the time being. able characteristics like low ductility and the somewhat All in all, improvements will only be reached in small steps, higher machining costs. What is a decisive aspect is the po- however in the right direction, including the reduction of re- tential it implies for further strength improvements through jects in fully operational condition. full hardening (T6) the entire component or local, so-called modified T5 heat treatment. Other casting methods are being taken into consideration, again and again. Whereas for in-line cylinder blocks it may For decades, KS ATAG has focused on the continuous op- be conceivable also to apply gravity die casting imply- timization of the ALUSIL® concept. The result of these ef- ing slightly lower production costs, this still appears to be forts also involves the associated progress achieved in the fairly problematic for V cylinder blocks in the present situa-

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Fig. 11: Preparation of the Audi V6 cylinder block Top: 1st clamping with machining of the locating points (1), the index bore (2) and the pressurized-oil ducts (3) Bottom: 2nd clamping with pre-drilling of the cylinders (a), pre-milling of the main bearing area (b), and cubing of the remaining external surfaces

9 tion. Process-reliable application of high-pressure die cast cept with the example of the new V6 / V8 engine generation. ALUSIL® has so far failed because of problems with silicon We also convey our thanks to the outstandingly committed pre-precipitation and hot cracking. Nonetheless there is staff of AUDI who have actively contributed to the compo- hope for further progress to be achieved. Active cylinder nent development and thus made the common success pos- sleeve cooling, a necessity for process-reliable production sible. We would also express our special thanks to Dr. Franz according to the present state of the art, is a constraint to Bäumel (V6) and Mr. Armin Bauder (V8) on behalf of all the sand core casting methods which only allow the more elabo- others who have made best efforts to keep our enthusiasm rate passive cooling due to the principle on which they are going. We also owe a debt of gratitude to Mr. Armin Bauder based. for his valuable contribution to this article.

KS Aluminium-Technologie AG would like to thank AUDI AG for the opportunity of a joint presentation of the ALUSIL® con-

Conventional product development is largely serial

abt. 18 months

die correction

process development

die manufacture

simulation

sand casting prototypes

product development

1st dataset serial 0

The challenge is: virtual development!

abt. 6 months

die correction

process development

die manufacture

simulation

product development

1st dataset serial 0

Fig. 12: Acceleration of development phases through simultaneous engineering: utilization of all available resources on the way to virtual product development

10 Critical residual solidification zone

Fig. 13: Solidification simulation with the example of the V6 cylinder block Top: Residual solidification zone (risk of blowholes) in the gearbox flange area without active cooling measures Bottom: Optimized condition; avoidance of blowholes (no residual solidification zones) through selective active cooling measures

1a 2a 3a

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Fig. 14: Die filling simulation of the gearbox flange with the example of the V8 cylinder block Top (pictures 1a -3a): turbulent filling (surging melt due to abrupt cross-sectional change) Bottom (pictures 1b -3b): stabilized filling by adjusting the geometry and optimum filling parameters

11 KS Aluminium-Technologie AG · Hafenstraße 25 · 74172 Neckarsulm · GERMANY Tel. +49 7132 33-1 · Fax +49 7132 33-4357 · www.kspg.com

Subject to alterations. Printed in Germany. A|IX|g