On the manufacturing of compliant foil bearings

Karim Shalash,Jürg Schiffmann

doi:10.1016/j.jmapro.2016.12.021

Karim Shalash, Jürg Schiffmann

Open Access

https://doi.org/10.1016/j.jmapro.2016.12.021

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Abstract

The fabrication of foil bearings is challenging due to the dependence on sheet metal forming to produce the compliant structure. This paper is an attempt to shed light into the foil bearing manufacturing know-how. Design of experiments techniques are used to quantify the effects of the different manufacturing parameters, as well as defining an optimum manufacturing procedure. The effect of manufacturing noise on the static performance of foil bearings is quantified using a Monte Carlo simulation of a bump foil stiffness model. A non-intrusive optical measurement technique which has been developed to measure the formed bump foils is also presented. An uncertainty quantification was performed for the produced foils, showing large uncertainty in the bump dimensions, which significantly affect both nominal bearing clearance and compliance. Finite element simulations are used to model the bump foil forming process that would present potential problems during fabrication, suggesting sharp bends in the bump foil as the main driver for manufacturing deviations. Based on this outcome an improved design for the compliant bump foil with reduced curvature is proposed, manufactured and measured. The novel design allows to reduce springback error by 69% compared to classical bump foils and thus offers an equivalent yet more robust foil bearing design.

Highlights

Foil bearings are compliant self-acting gas lubricated bearings, which are known for their extended lifetime, high load capacity, extreme temperature operation, and their ability to cope with a large variety of process fluids [1, 2]
It was shown that the available know-how is not sufficient for the accurate manufacturing of foil bearings
The bump foil compliance was shown to be sensitive to the bump angle and radius, even for small errors of bump geometry (5% error in compliance for each 1% error in bump radius)

Summary

INTRODUCTION

Foil bearings are compliant self-acting gas lubricated bearings, which are known for their extended lifetime, high load capacity, extreme temperature operation, and their ability to cope with a large variety of process fluids [1, 2]. The objectives are to (1) assess known manufacturing procedures, (2) investigate the effect of process variables on springback, (3) identify the springback distribution on classical bump foils and (4) propose a new, more robust corrugated foil design. The statistical evaluation of the measured bump radii and angles further allows to identify error distributions The effect of this manufacturing noise on the performance of foil bearings is presented using a Monte Carlo simulation with the foil bearing stiffness model developed by Iordanoff [19]. Similar but less accurate techniques could be found in [51,52,53]

OPTIMIZATION OF THE MANUFACTURING PROCESS

MANUFACTURING UNCERTAINTY ASSESSMENT

FINITE ELEMENT SIMULATION OF BUMP FOIL FORMING PROCESS

IMPROVED DIE DESIGN

Findings

CONCLUSIONS