The Mechanics and Tribology of Vibratory Surface Finishing

Vibratory finishing is a widely used industrial process to modify the surface properties and microtopography of metal, ceramic and plastic parts. Its applications are diverse, ranging from the polishing of coins, gears, and golf balls to smoothing the sharp edges of cast or stamped automotive parts, and from hardening and texturing the surfaces of electrical connectors to cleaning surfaces by removing rust and other contaminants. Current industrial practice relies on experience and experimentation to optimize the process for new parts and materials.

In a typical configuration, a vibrating container fluidizes a bed of granular media creating a circulating bulk flow. A workpiece entrained in this flow is subject to the impacts of the vibrating media. The impact velocity of the vibrating media will control the impact force and hence the degree of plastic deformation and erosion of the workpiece surface.

Our research is aimed at developing models to assist in the prediction of wear, hardening and residual stress as a function of the granular media and the motion of the vibratory finisher. The presentation will review our efforts to develop an understanding of the mechanics of vibratory finishing and its relation to erosive wear, hardening and residual stress. This includes the identification of media-workpiece impact characteristics under various conditions, and measurements of local impact velocities which provide a general means of quantifying the rate and extent of surface work regardless of workpiece-media compliance. These data have then been correlated with erosion rates and the rate and extent of plastic deformation occurring in Almen strips. Numerical models have been used to simulate edge chipping of brittle materials, and the motion of granular media as they flow past a workpiece and collide with its surface at the vibration frequency of the finisher.

Margaret Stack is Professor and Leader of the Graduate School in the Department of Mechanical Engineering at the University of Strathclyde. Her research interests include the interactions of solid particle erosion and wear of materials in corrosive environments, with specific emphasis on the development of mapping techniques for understanding the mechanisms of material loss. 

Tribo-Corrosion maps:  from marine renewable to bio-medical environments

Advances in the understanding of tribo-corrosion mechanisms in recent years have resulted in development of maps which chart the transition boundaries.    Subsequently, such concepts have evolved further and, through models and experimentation, have been applied to a wide range of environments.  From an initial “sketch” of the boundaries, there is now a body of mapping data available for various materials including pure metals, steels, thin films and composites and in a range of environments.  This talk charts the historical development of the tribo-corrosion map, from the initial features of the erosion-corrosion map, for solid particle impact in aqueous and dry conditions, to the more recent maps developed for micro-abrasion-corrosion for dental, hip joint and marine conditions.  The results from models in 2-D and 3-D spaces are appraised in the context of how such maps can be applied to complex shapes and processes.  Future trajectories in the subject are explored in the context of emerging technologies in the bio-medical and renewable energy research areas.             

Prof Dr Ing Eckart Uhlmann, TU Berlin

Eckart Uhlmann is Director of the Fraunhofer Institute for Production Systems and Design Technology and Chair of Machine Tools and Manufacturing Technology at TU Berlin.  He has published over 500 papers in journals and conference proceedings and has a particular interest in the development of manufacturing processing involving abrasion.

Manufacturing with Abrasives - Current Research Topics

Abrasives are widely used in manufacturing processes and a large variety of abrasives is available, both natural and synthetically produced. Predominately abrasives are applied in cutting with undefined edges and cleaning processes. In particular these processes include all forms of grinding, finishing, honing, lapping, blasting and abrasive water jet cutting. While similar abrasives might be used throughout all aforementioned processes, the fundamental working principles differ largely. This explains the wide variety of applications but also the complexity of research and development in this field. Good examples of this are current research topics such as abrasive water jet turning and speed stroke grinding of high performance ceramics. With abrasive water jet turning, high performance materials such as hypereutectic aluminum silicon alloys and titanium aluminides are machined and empirical models to predict material removal rates are currently being developed. The example of speed stroke grinding of high performance ceramics shows, how a brittle cutting mode can be employed to lower energy input into the work piece without introducing subsurface damage.

Professor John Nicholls, Cranfield University

John Nicholls is Professor of Coating Technology  and head of the Surface Engineering and Nanotechnology Institute, Cranfield University. He has extensive experience in high temperature surface engineering, oxidation, hot corrosion and high temperature tribology.  His most recent work has been on the erosive wear and foreign object damage of thermal barrier coating systems.

Volcanic ash: its role as an erodent in the aero gas turbine 

J R Nicholls1 and R G Wellman2
1 Cranfield University, UK, 2 Rolls Royce Plc, UK
Following the eruption of the Eyjafjallajökull volcano in Iceland considerable disruption to the European air space occurred with many flights cancelled as the airline companies assessed the risk of flying through such dust ladened air space. This study examines the erosive role of volcanic ash as it is ingested in and passes through an aero-gas turbine engine. The study was initiated as part of a European collaborative programme to assess the impact of volcanic ash on aero-engine performance.

This presentation, first, considers the erosion of compressor components. Modelling work at Turbomeca was used to calculate particle flow patterns allowing prediction of leading edge compressor blade wear.

At Cranfield a comparative study of volcanic ash and silica was undertaken and will be presented. For volcanic ash, peak erosion rates occur at 30 degree impact, a ductile erosion mechanism, with only a small dependence on particle size. By way of comparison fine silica sand is more erosive than volcanic ash, while for coarse silica the relative performance depends on impact angle; less erosive at 30 degree impact but more erosive at 90 degree impact.

As volcanic ash passes through the combustor of the gas turbine it may melt and fuse. If it impacts the thermal barrier coating in the solid form, the erosion performance is similar to that of silica sand as has been previously published by the authors. However, if it melts it effuses into the thermal barrier coating structure and therefore stiffens the TBC and modifies its erosive response; increasing the erosion rate by factor of x4. This new damage mechanism for TBCs will be discussed.

For further information, please contact:

Joanne Griffiths

Event Manager

IfM ECS

Institute for Manufacturing

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Cambridge CB3 0FS

Tel: +44 1223 748260

Email: jg393@cam.ac.uk