Numerical and experimental analysis of vibration damping performance of polyurethane adhesive in machine operations

Abstract Machining operations inherently cause structural vibrations of the work piece and machine involved, especially during roughening operations. This clearly adversely affects the surface roughness, tolerances and tooling lifetime. These effects are even more prominent in case the stiffness of the work piece to be machined is low and machining vibration excitation frequency range strongly overlaps the range of structural resonance frequencies of the work piece. This is typically the case for lightweight (sheet) metal structures. Additional fixation is costly, time-consuming and moreover it may induce structural loading and deformation which, after finishing, causes an out-of-tolerance work piece. This work presents an alternative approach which applies Polyurethane foam adhesive bonding as a temporary measure to reduce structural vibrations during milling operations of a large welded sheet metal construction. The first part of this work analyses the actual structural vibrations that occur during milling operations. Experimental and numerical modal analysis is carried out in order to determine the excitation and resonant vibration behaviour of the sheet metal structure. A dedicated Finite Element Model (FE – model) is set up which enables the necessary insights in where and how critical vibration levels may be reduced and how the work piece supports can be optimized. The second part of the work discusses the development and application of suitable vibration dampening supports applying Polyurethane foam adhesive. For this purpose, experiments are carried out to determine the vibration dampening performance of different foam layer thicknesses. These involve hammer excitation of dedicated small-scale adhesively bonded samples. FE modelling is applied to optimize the mounting of bonded Polyurethane dampers and to predict the effect on structural vibrations during milling operations. This part extensively outlines the specific experiments involved and the strategy for modelling the viscoelastic foam dampeners in the structural numerical model in a robust but effective way. The third part describes the validation measurement campaign and extensively compares structural vibration levels before and after providing the foam dampening measures. It concludes by showing that critical vibration levels may be reduced by over 58% with the method applied.