An application of optical surface assessment to engine preparation techniques

Although the advantages of optical techniques have long been appreciated, the inherent limitations of such methods have meant that stylus techniques remain the accepted "standard" for surface assessment. The study of many engineering processes, such as engine preparation techniques, have been based on stylus methods. Much of this research may be extended to optical techniques for surface assessment if a detailed comparison of results obtained from the two techniques is carried out with respect to the process under investigation. A study of this kind will help to develop optical assessment techniques which, although will initially be limited to specific processes, may prove useful in the production environment. This paper presents a study of established two dimensional models which have been applied to the characterization of the preparation of engine cylinder liners and bores. These models are extended to three dimensions and quantified using a three dimensional stylus measuring system consisting of a computer controlled Talysurf 5 stylus instrument and a precision linear translation stage. Relocation techniques are then employed and the surface finish is assessed using a computer controlled laser measuring system. With reference to the original models it is shown that engine preparation techniques may be monitored using an optical assessment of this kind. Thus an alternative method of assessing the evolution of engine preparation is proposed for optically based techniques. It is hoped that studies of this nature will eventually lead to the development of an on line optical surface assessment system for engine preparation techniques with all its associated advantages. Introduction The specification of the preparation process of cylinder liners and bores is of fundamental importance to the engine manufacturer. Monitoring the evolution of the surface texture of cylinder liners and bores during preparation processes is usually limited to stylus methods of assessment which involve removing the component from the production line for detailed examination. Although surface texture is of great importance to the engine manufacturer, its inspection, at least by traditional stylus techniques, severely restricts the flow of work in the production environment. Optical methods of surface assessment offer the basis for an on -line, system for the inspection of cylinder liners and bores. Information obtained from such systems, however, is intrinsically different from that obtained by stylus methods. Thus characterization techniques developed for engine preparation based on stylus methods can only be used as a basis to form analogous techniques for optical assessment. A method for investigating the optical assessment of cylinder liners and bores may be established as follows. Investigations have shown that the surface changes which occur as honed engine liners are plateau honed follow a simple truncation wear model. The evolution of parameters such as Rq, skewness and kurtosis, which are used to describe the scale and shape of surface profiles obtained from stylus instruments, may be derived from such models. Wear models of this kind may easily be èxtended to three dimensions to give a more realistic interpretation of the wear mechanism. This approach is also more analogous with optical assessment which directly provides a information pertaining to a three dimensional area. Simulation techniques may then be used to assess the effects of light scatter as surface parameters such as Rq, skewness and kurtosis are changed. As the evolution of these parameters may be predicted from the truncation wear model it is then possible to relate these values to surface scatter and so evaluate truncation wear from an optical assessment. In this way it is hoped to study the optical assessment of the evolution of the honing process and so provide an on -line technique for its evaluation. 112 / SPIE Vol. 802 InProcess Optical Metrology for Precision Machining (1987) y, . s, . . (