The automotive crankshaft, one of the more metal intensive components in the engine, provides an attractive opportunity for the use of alternate materials and processing routes. Although performance requirements are important in the choice of a particular material or fabrication route, the final decision is usually dictated by cost.
This study evaluated the cost effectiveness of various material alternatives for the crankshaft. The technique of “Technical Cost Modeling” was utilized to estimate the manufacturing costs of the various material alternatives. Four processing routes for the manufacture of the automotive crankshaft were evaluated: steel forging, nodular casting, microalloy forging and austempered ductile iron casting.
The results indicate that although nodular cast iron is the most widely used material today, it appears that, with changing engine design, microalloyed steel can effectively compete in this application. Further, given a choice between forging or casting-and-heat-treating, engineers would rather forge a crankshaft, if performance exceeding that of nodular cast iron is necessary. This is mainly attributed to the current processing problems with austempered ductile iron (ADI), which make it a very unattractive choice for crankshafts, especially when enhanced properties can be more cost effectively achieved with microalloyed steel. The primary attractiveness of steel forgings is that they offer better specific performance in this application, which current designs do NOT exploit. Suppliers should promote forged crankshaft designs which offer components with lower weights than cast crankshafts. Any process improvements which would reduce machining requirements could have a major impact upon finished part cost in this application.