Forming Simulation and Stiffness Prediction of a Rear Axle Pinion Bearing Collapsible Spacer

This paper presents a method to predict the nonlinear spring rate of an axle pinion bearing collapsible spacer (see Fig 6 & Fig 7) with special consideration for manufacturing residual stress and strains. Typical manufacturing forming operations of the pinion bearing spacer can produce 5 to 30% residual plastic strain, resulting in significant change to its mechanical performance. Thus it is very important for the design engineer to include the effects of residual stress and strain in the collapsible spacer design process.

To accurately predict the residual stress and strain in a spacer, and hence accurately calculate its spring rate non-linear finite element [1] analysis is performed to simulate the entire manufacturing process. The non-linear CAE analysis has 3 simulation steps: (1) die forming; (2) collapsible spacer system assembly and; (3) spring rate prediction with residual stress-strain information. Since the choice of material constitutive laws and hardening properties may significantly affect the accuracy of the finite element simulation, four different material models [2] are evaluated and compared with experimental result. The four different material models evaluated in CAE modeling are: (1) elasto-perfect plastic material model with isotropic hardening (2) elasto-perfect plastic material model with kinematic hardening (3) true stress-strain material model with isotropic hardening (4) true stress-strain material model with kinematic hardening. Through comparing CAE and test results, it is found that material model “3” is the best material model for this type of application. Using material model “3” and CAE analysis, several different design alternatives for a drive-shaft spacer design are evaluated and an optimized design is obtained.

This paper also discusses the accuracy of calculated results compared with experimental test. Accuracy of the analysis was within 8% of the experimental test.