Design and Analysis of Automotive Steering Sheet Metal Yoke for High Strength and Rigidity Requirement

The increasing demand for light weighting products due to introduction of various standards and norms for controlling CO₂ emissions and to meet the customer requirement of low cost with higher strength and rigidity of product in automotive industry, sheet metal manufacturing technique is adopted for automotive steering yoke for light commercial vehicle. Currently forged yokes are used for higher strength requirement, while sheet metal yokes are being used for small tonnage vehicle. The attempt has been made to improve overall strength and rigidity of the yoke produced by sheet metal operation using SAPH 440 steel with 6.5mm thickness for light commercial vehicle segments. The major challenge identified for this development was developing such a high strength and thickness material with consistency of dimension during forming process and meeting the torsional strength requirement of 500 Nm. In this development with the help of plastic data, the forming analysis of yoke model has been carried out to analyze the feasibility of the design at desired thickness of yoke considering the dynamic bending force, spring back effect and residual stresses generated after bending. Further the simulation of the same model has been carried out for confirmation of torsional strength of 500 Nm in the yoke as per the requirement and rigidity was evaluated with T vs. θ graph. The failure mechanism in the torsion simulation was correlated and confirmed by the physical bench test with similar available yokes. Design verification was successfully done to achieve proper articulation angle of 55^o, Spring back was found to be about 0.19^o and Maximum twisting angle detected was about 0.16°.