Influence of manufacturing processes and their sequence of execution on fatigue life of axle house tubes in automobiles

• Study of manufacturing processes and their execution sequence on fatigue life.
• Experimental fatigue tests and XRD measurements of residual stresses.
• Finite element analysis of key process and prediction of residual stress.
• Theoretical estimation of fatigue life under different process conditions.
• Selecting best process sequence that will maximize its fatigue life.

Axle housing tubes are used in automobiles and are subjected predominantly to bending fatigue during its service life. The fatigue life of the tubes is largely dependent on the residual stresses induced in them at the manufacturing stage. The manufacturing processes and their sequence of execution have profound influence on the nature of residual stress distribution. Induction hardening and tempering, extrusion, and turning are the manufacturing processes involved. Residual stresses induced by each of the manufacturing processes involved are studied. The influence of process sequence on residual stresses is studied by conducting experimental fatigue tests and measuring residual stresses by X-ray diffraction. Based on the studies, it is found that the manufacturing process sequence with turning as the final process step is detrimental to fatigue life, whereas the sequence with induction hardening and induction tempering as the final process step produces least tensile surface residual stress and hence improves the fatigue life.