Journal of Materials Processing Technology 211 (2011) 467–474 Contents lists available at ScienceDirect Journal of Materials Processing Technology journal homepage: www.elsevier.com/locate/jmatprotec Flexible forming tool concept for producing crankshafts L.M. Alves, P.A.F. Martins ∗ IDMEC, Instituto Superior Técnico, Univ. Tecn. Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal article info Article history: Received 12 August 2010 Received in revised form 6 October 2010 Accepted 27 October 2010 Keywords: Crankshafts Flexible forming tool Finite element method Experimentation abstract Forging, casting and machining compete on quality and price for the production of crankshafts. Forging and casting are commonly utilized for mass production because the capital investment in equipment and tooling are very high. Machining is employed only in case of small production batches of high quality crankshafts made from materials that are normally difficult to forge or cast because it is time and energy intensive, generates a lot of waste and is generally more costly than forging and casting. As a result of this, conventional manufacturing routes for crankshafts are not suitable for flexible small to medium-batch production and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles and very short development and production lead times. This paper is concerned with these issues and is focused on the development of an innovative forming tool concept for producing small to medium-batches of cost competitive crankshafts. The proposed tool concept combines knowledge on buckling of solid rods under compression with flexible construction solutions based on modular dies to allow crankshaft production to change output rapidly. Single cylinder to multi cylinder crankshafts including multiple main bearing journals, crankpins and crank webs can be easily produced by fastening or removing appropriate die modules in the overall tool set. The presentation is illustrated with test cases obtained from finite element modelling and experi- mentation with a laboratory prototype tool conceived to operate exclusively with lightweight materials exhibiting high ductility in cold forming. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Crankshafts are employed to convert circular into reciprocating motion or reciprocating into circular motion. Its application draws from ancient water powered saws, which combined crankshafts with connecting rods for cutting rectangular blocks of stone to mod- ern internal combustion engines where crankshafts are necessary to translate the reciprocating motion of pistons into rotation. Forging, casting and machining are competitive manufacturing processes in crankshaft production industry. Forged crankshafts are shaped in a sequence of stages. Starting with a solid rod, the cross- sectional area of the rod is first altered in shape by roll forging, subsequently formed into the final shape by close die forging oper- ations and then trimmed. The intermediate stages in forging are necessary for distributing the material and filling the die cavities properly (Thomas, 1986) but trimming can be eliminated by the application of precision forging technology. The work of Behrens et al. (2007) presents a comprehensive investigation on the subject and shows the potential of precision forging technology to reduce material waste and energy consumption and to improve the overall physical and mechanical properties of crankshafts. ∗ Corresponding author. Tel.: +351 21 8417561; fax: +351 21 8419058. E-mail address: pmartins@ist.utl.pt (P.A.F. Martins). Casted crankshafts are less expensive than forged because they can be made close to the required shape and size in a single oper- ation. They are favoured for low cost production of engines that operate under moderate loads whereas forged crankshafts are cho- sen in case of engines working under heavy load conditions. This is because forged crankshafts generally offer higher toughness, resis- tance to impact and fatigue and better strength to weight ratio than casted crankshafts (Montazersadgh, 2007). Machining starts with a solid piece of material, usually in the shape of a cylinder, from which the desired crankshaft is achieved by removing away unwanted material. The process is mainly used for small batch production of high quality and high priced crankshafts made from materials that are normally difficult to forge or cast. A comprehensive comparison of the above mentioned manu- facturing processes with respect to fabrication aspects, mechanical properties and final costs is available in Zoroufi and Fatemi (2005). The study allows concluding that conventional manufacturing routes are not suitable for flexible small to medium-batch pro- duction (that is, low to medium volume of custom and specific products) and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles and very short development and production lead times. In fact, the present need for flexible manufacturing processes requires the develop- ment of innovative technological solutions that are capable of 0924-0136/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2010.10.024