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Products and solutions, 2000-03-20, 01:00 AM

Automotive division: Forged or cast crankshafts?

A direct comparison.

When it comes to realising highly efficient engine concepts, forged steel crankshafts are the number-one choice: the high strength and elasticity of the material and the fibre orientation brought about by the forging process allow a reduction in bearing diameters and widths. This means that forged crankshafts can be made lighter and shorter than cast components, forming the basis for more compact engine designs and weight savings of up to 20 per cent of the entire unit.

Together with its Brazilian sister company Krupp Metalúrgica Campo Limpo Ltda., Krupp Gerlach GmbH is the market leader for forged crankshafts, turning out some 4.6 million per year. Krupp Gerlach recently completed a project which demonstrated the advantages of the forged crankshaft over its cast counterpart in a 1.8 litre four-cylinder in-line SI engine. This engine belongs to a market segment which to date has been dominated by cast crankshafts, owing primarily to the constraints of existing engine designs and production concepts.

The aim of the project was to find the maximum possible reduction in weight and design length which could be achieved by using a forged crankshaft. The manufacturer's specifications had to be met, e.g. with regard to block height, mass balancing and of course the performance data of the production engine. Gerlach's partners on this project were the European engine manufacturer providing the specifications and FEV Motorentechnik GmbH & Co. KG, which had the task of optimising the engine design and engineering the crankshaft. The bearing design was provided by Glyco-Metall-Werke, a subsidiary of Federal Mogul.

The result: by modifying the engine design appropriately, the use of a forged crankshaft allows an eight per cent saving on weight and a nine per cent reduction in length. In concrete terms, the weight of the crankshaft was cut from 14.26 (cast) to 13.08 kilos (forged), with a corresponding drop in length from 521.5 to 476.2 millimetres. Further advantages for the engine as a whole include additional scope for downweighting through the compact design, lower consumption thanks to reduced frictional losses in power transmission, and smoother running as forged crankshafts generate less torsional vibration.

The study also showed that forged crankshafts provide advantages for the overall engine system in the 1.8 litre segment which can compensate for the higher unit costs compared with cast shafts. These advantages can be utilised if the potential of the forged crankshaft is taken into consideration in the project definition phase when designing the engine.

With around 36,000 employees, the Automotive division of Thyssen Krupp AG achieves sales of approx. ten billion DM. The division comprises a total of 66 individual companies worldwide, focused in particular in Europe and in North and South America. In its business sectors Body, Chassis, Powertrain and Systems/Suspensions the division produces parts, components, assemblies and modules/systems for body, chassis, powertrain and steering applications in cars and trucks.

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