Multi-Objective Optimization of a Paper Machine Lead Roller Support
The intent of the study was to produce a new design for a cast iron (GJS400) lead roller support used in a paper machine which reduces its weight, while maintaining or reducing its fatigue life cycle resulting from regular production use. Since these two objectives could be construed as conflicting, a multi-disciplinary design simulation that encompassed the main life cycle stages of the component, from its design to its production and in-service use, was set up in order to produce a new design where both of these objectives were optimized.
The engineering simulation technologies involved in this study spanned three different design fields. MAGMASoft was used to evaluate the mechanical properties and residual stress caused by the forging process, ANSYS was used to calculate the torsional effect and modeFRONTIER was used to explore different geometric configurations to identify the optimum trade-off between the conflicting objectives.
The Multi-Disciplinary Design Optimization Approach
The optimization process involved:
- a preliminary study carried out on the original design to evaluate its current state
- an optimization simulation to find the best design that would decrease the component’s weight while maintaining or improving its fatigue life cycle. With respect to the original design the optimal weight was identified at 360 kg, a decrease from the original 476 kg, while its deformation from normal production use decreased from 0.21mm to 0.187mm. This simulation assumed that the material is isotropic, without defects and residual stresses due to the manufacturing process
- the next stage analyzed the manufacturing process. The optimized component geometry was evaluated for its castability and the corresponding mechanical properties and residual stresses due to the forging process were accounted for
- a further structural simulation used the spatial distribution of the mechanical properties and the residual stresses as an initial condition in order to analyze the stress change distribution with respect to the isotropic structural analysis results. Stresses were not homogeneously distributed on the component, due to different pre-stress conditions and non-homogeneous mechanical properties
The Benefits of the Multi-Disciplinary Design Optimization Approach
As verified in the initial study, the classic single objective design simulation neglects the presence of residual stress and assumes the component has isotropic properties at the end of the casting process. The benefits of the multi-objective study, that includes both the casting and structural simulation, are evident from the final results which gave a more realistic assessment of the fatigue life of the component. These results show some zones with high stress peaks which will result in a decreased fatigue life of the roller support.