Abstract

In today’s serial production processes, automation and cycle time reduction is critical. Many industries require short cycle times and a high degree of automation driven by high volumes and extreme cost pressure. Therefore, assembly of sealing systems is often done automatically with short cycle times. The speed of the automatic assembly process is limited by the strength of the seal material. In general, forces and stresses acting on the seal during assembly increase with speed due to inertia. In case of elastomer seals, stresses also increase due to the viscoelasticity of the material. The higher the rate of deformation, the higher the stresses inside the material. Considering typical cycle times and material properties, the effect of viscoelasticity is more significant compared to the effect of inertia when considering elastomer seals. Furthermore, the maximum occurring stresses depend on the type of assembly machine and the design of the handling grippers. If the assembly speed is too high or the design of the grippers is not appropriate, the seals can often break or show other permanent damage. Furthermore, it can lead to poor performance of the sealing system after installation. The present contribution considers the effect of viscoelasticity on the speed limit during assembly and the effect of the design of the grippers on the maximum occurring stress. On the one hand an O-ring is analyzed and on the other hand a seal with a more complex cross section is simulated. In addition, two different types of elastomers are modeled: an HTV silicone elastomers and an HNBR elastomer. The investigations are be carried out by finite element analyses which are capturing the viscoelastic material properties. The viscoelastic material properties are derived from different material tests, which will be described in the contribution. Furthermore, the corresponding viscoelastic material model will be described in detail. The contribution will also include an overview about the state of the art of assembly simulations of seals and about the state of the art of viscoelastic material models. There are no numerical investigations documented in literature, where fast assembly processes of seals were simulated and the rate-dependent material behavior was taken into account. Finally, the simulation results will be compared to fast assembly tests of sealing systems in order to verify the simulation procedure. It will be demonstrated how simulation allows an improvement of the handling process during assembly and how it can insure successful operation of both the assembly process and the resulting seal performance after assembly.