FEM analysis of the forming process of automotive suspension springs

This paper deals with the FEM analysis of the forming process of automotive suspension coil springs. Nowadays in automotive industry great efforts are spent in achieving weight reduction of cars components. The coil springs are not exempt. For this component weight reduction can be obtained by reducing the spring wire diameter. However, to assure that springs maintain the required mechanical properties, it is necessary to adopt material with high strength [1]. Concerning the manufacturing process of coil springs, the trend is to produce springs by cold forming of strain hardened wires. In this case the wires are subjected to heat treatments of hardening and tempering before the coiling process. This leads to an improvement of productivity since it is not required an heat treatment after forming. However forming a high strength material already hardened and tempered is critical. The material has a very low ductility that can lead to coil's failure during forming process. The process is sensitive both to the process conditions (such as friction), and to the set up of the spring making machine. Aim of this work is the numerical investigation of the coiling process. Different friction conditions and different configurations of the coiling machine are considered. The main target is the determination of a satisfactory lubricant condition and a configuration of the coiling machine which allows the correct production of the spring without any breakage of the wire.