New concept for manufacturing engine blocks by diecasting

At the end of the 1970s, engine blocks were for the first time no longer made from grey cast iron, but aluminium. This change in the raw material was triggered by the weight reductions allowed by the appreciably lower density of aluminium – despite the higher material cost. Ever since, light metals such as aluminium and increasingly also magnesium are playing an ever more important role in engine construction. Not least, more stringent environmental protection laws also favour the use of light metals. 2006 was the first year that more passenger cars left European assembly lines with engine blocks of aluminium rather than grey cast iron.

 

Advantages of aluminium diecasting

The engine block is made up of two distinct functional units – the cylinder block (upper part housing the cylinders) and the crankcase (lower part housing the crankshaft). The diecasting process has been found to be a very viable option for manufacturing aluminium engine blocks. It is distinguished by high output and flexibility in component design. The attractiveness of the diecasting process is likely to increase further still, for the potential of aluminium as an engineering material has by no means been exhausted yet, at least in the field of Otto engines. State-of-the-art diecasting machines equipped with cutting-edge real-time control systems such as those manufactured by Buhler allow highly variable selection and adjustment of the die cavity filling process. In addition, with the support of vacuum, they even permit heat treatment for increasing the strength of the components made.

 

In quest of additional improvements

Aware of the attractiveness of diecasting, the specialists at Bühler Druckguss (the Die Casting divi-sion of the Buhler Group) teamed up with their colleagues at the German die-maker Schaufler Tooling to find additional improvements. The goal was to eliminate the still perceptible drawbacks of conventional manufacture. Ultimately, this would further increase the profitability of the diecasting process for making engine blocks.

In an initial analysis, the following cost drivers were identified and dealt with:

• Long cycle times

• Large and heavy dies

• High wear on the cooling water jacket inserts

• Long downtimes due to: time consuming die maintenance (for example tedious removal of the moving die half for changing the water jacket); frequent injection of molten metal behind core slide guides; frequent die leakage; frequent rupturing of ejector pins; uncontrolled die heating and cooling.

 

Based on this analysis and Buhler’s and Schaufler Tooling’s experience, two new cost-optimised engine block concepts were developed for making inline and V-engines. This effort was supported by the experience that Buhler has accumulated in the supply of over 30 diecasting cells for making engine blocks, and that of Schaufler Tooling, which to date has supplied a number of engine block dies. Both concepts have now been patented.

 

Die-making and mechanical engineering blended

The difference between an inline engine and a V-engine lies in the configuration of the cylinders. As the name suggests, the cylinders of an inline engine are arranged in a straight row, whereas two cylinder rows are arranged in a V-shape at a certain angle in the V-engine.

The revolutionary thing about the two new Buhler concepts is that they are the first to blend cutting-edge die making with state-of-the-art mechanical engineering technology. This combination of the two disciplines produces a commercially promising solution for manufacturing engine blocks. Thus, for instance, the water jacket and the contour core slide can be pulled by a certain stroke length already after partial solidification of the metal. This reduces the heat input from the aluminium into the water jacket, which in turn appreciably increases the life cycle of the water jacket.

 

Design improvements

In addition, the project team implemented a number of die design measures. These increase the up-time of the die and therefore the capacity utilisation rate of the diecasting cell. For example, the con-tour core slides can be changed on the machine itself with great ease and within a very short time. A special locking design reduces the deflection of the outer slides by as much as 50%. This, in turn, reduces the injection of molten aluminium behind the slides while improving the dimensional accuracy of the engine blocks. A new technique for sealing the cooling bores diminishes their proneness to leakage. Furthermore, a concept which eliminates the need for ejectors in making inline engines prevents downtimes.

Machine fulfills die functions

One major problem in conventional engine block production is that very large and therefore expensive dies must be used. In the new Buhler concept, the diecasting machine fulfills certain functions of the conventional die. This eliminates the need for ejector boxes and ejector tables in the new dies. This and additional weight-reducing optimisations enable the die costs for making V-engines to be slashed by 25%, and inline engines by 10%.

The new concepts also boost productivity. An optimised temperature control design, the freshly developed 'Flextool’ die spray system from the Acheson company, and synchronised machine motions which allow simultaneous spraying of both die halves save valuable seconds. These features cut the cycle time by 10 to 20%, depending on the weight of the raw part.

Together with Schaufler Tooling, Buhler presented this novel concept to a number of renowned engine block producers as far back as early 2006 which triggered this year’s projects. At present, the prototype of a V6-engine crankcase is being tested. At the same time, a prototype die is being made for an inline engine crankcase.

 

The author is Marc Fuchs, head of product management, Buhler Die Casting at Buhler Uzwil/Switzerland. web:

www.buhlergroup.com