Case Study on Effect of Nodularity on U-Bolt Clamp Force (Torque) of Ductile Iron Spring Seat

Now a day’s ductile iron spring is becoming common in vehicles. Most OEMs prefer change over from forged spring seat to ductile cast iron spring seat particularly for lower spring seat application as there is weight benefit. The primary function of lower spring seat is to hold the axle and leaf spring together. Lower spring seat would experience pre load generated during U bolt clamping and could undergo permanent deformation when applied stress exceeds the material strength. In ductile cast iron nodularity is the prime factor which is responsible for material ductility characteristics. In this case study two spring seats A & B is compared for U bolt pre load force (Torque) where spring seat A is with nodularity requirement of 80 % min and the spring seat B is with nodularity of the order of 55%. U Bolt preload permanent deformation bench test is carried out and outcome shows that the spring seat A failed at 800 Nm torque and spring seat B failed at 600 Nm. The Method of generating preload permanent deformation was followed common for both spring seat A & B. Manufacturing of inferior Nodularity is a challenge now a days as content of magnesium, pouring times altered drastically to meet 55% of nodularity