Johan Wall

Dynamic characteristics of a combined bellows and liner flexible joint

Abstract A bellows combined with an inside liner and an outside braid is commonly used as a flexible joint in automobile exhaust systems to reduce transmission of engine movements to the exhaust system. It greatly influences the dynamics of the complete system. Understanding of its dynamic characteristics and a modelling method that facilitates systems simulation are therefore desired. This has been obtained in earlier works for the bellows itself. In this work an approach to the modelling of the combined bellows and liner joint is suggested and experimentally verified. Simulations and measurements show that the liner adds significant non-linearity and makes the characteristics of the joint complex. Results are presented for the axial and the bending load cases. In torsion, influence of the liner is negligible. Peak responses are significantly reduced when the excitation level approximately corresponds to the friction limit of the liner. The complexity of the combined bellows and liner joint is important to know of and consider in exhaust system design and proves the necessity of including a model of the liner in the theoretical joint model when this type of liner is present in the real joint to be simulated.

Influence of a bellows-type flexible joint on exhaust system dynamics

Abstract Most modern cars have a bellows-type flexible joint between the manifold and the catalytic converter to allow for thermal expansion and to decouple large engine movements and vibrations from the rest of the exhaust system. To obtain better understanding of the influence of this joint, the dynamic response of a typical exhaust system is studied when excited via different joint configurations. Measurements show the great order of reduction in vibration transmission to the exhaust system that a bellows joint, with and without an inside liner, gives in comparison with a stiff joint. For the combined bellows and liner joint, vibration transmission is, however, higher than for the bellows alone. Together with some other aspects this makes the choice of including a liner in the exhaust system application complex. For a system in general the possibility of tuning the friction limit of the liner, to minimize overall vibrations through friction-based damping, depends on how close to ideal the excitation source is and its location. Anyhow, the combined bellows and liner joint makes the exhaust system behaviour significantly non-linear, whereas the system behaviour proves to be essentially linear when the bellows has no liner, which imply that the liner needs to be included in theoretical models when present in the real system.

Data-driven modelling in the era of Industry 4.0: A case study of friction modelling in sheet metal forming simulations

With growing demands on quality of produced parts, concepts like zero-defect manufacturing are gaining increasing importance. As one of the means to achieve this, industries strive to attain the ab ...

Framework for simulation-driven design of stamping dies considering elastic die and press deformations

Sheet metal forming (SMF) simulations are used extensively throughout the development phase of industrial stamping dies. In these SMF simulations, the die and press are normally considered as rigid. Previous research has however shown that elastic deformation in these parts has a significant negative impact on process performance. This paper demonstrates methods for counteracting these negative effects, with a high potential for improved production support and a reduced lead time through a shorter try-out process. A structural finite element model (FE-model) of a simplified die is studied. To account for elastic deformation, the blankholder surfaces are first virtually reworked by adjusting the nodal positions on the die surfaces attaining a pressure distribution in accordance to the design phase SMF simulations with rigid surfaces. The elastic FE-model with reworked surfaces then represents a stamping die in running production. The die is now assumed to be exposed to changed process conditions giving an undesired blankholder pressure distribution. The changed process conditions could for example be due to a change of press line. An optimization routine is applied to compensate the negative effects of the new process conditions. The optimization routine uses the contact forces acting on the shims of the spacer blocks and cushion pins as optimization variables. A flexible simulation environment using MATLAB and ABAQUS is used. ABAQUS is executed from MATLAB and the results are automatically read back into MATLAB. The suggested optimization procedure reaches a pressure distribution very similar to the initial distribution assumed to be the optimum, and thereby verifying the method. Further research is needed for a method to transform the calculated forces in the optimization routine back to shims thicknesses. Furthermore, the optimization time is relatively long and needs to be reduced in the future for the method to reach its full potential.Sheet metal forming (SMF) simulations are used extensively throughout the development phase of industrial stamping dies. In these SMF simulations, the die and press are normally considered as rigid. Previous research has however shown that elastic deformation in these parts has a significant negative impact on process performance. This paper demonstrates methods for counteracting these negative effects, with a high potential for improved production support and a reduced lead time through a shorter try-out process. A structural finite element model (FE-model) of a simplified die is studied. To account for elastic deformation, the blankholder surfaces are first virtually reworked by adjusting the nodal positions on the die surfaces attaining a pressure distribution in accordance to the design phase SMF simulations with rigid surfaces. The elastic FE-model with reworked surfaces then represents a stamping die in running production. The die is now assumed to be exposed to changed process conditions giving an ...