A Topographic Study of Functional Surfaces

Abstract: Surface topography through the years has taken on increased importance, because of the rise in quality demands. The surface often has to meet additional functional demands when products become more complex in accordance with customer preferences. This poses great demands on the manufacturing process to produce the characteristics needed for optimal function. This makes the field of surface topography not only interesting but necessary, since erroneous specifications can be very costly and result in a nonfunctional surface.

This thesis is a contribution to the area of surface topography. The results are presented in eight separate but related papers concerning how to measure and characterize the topography on functional surfaces enabling control of the manufacturing in order to ensure that the desired surface properties are obtained. The results presented are relevant for many engineering surfaces even though mainly one of them has been used in this work: the surface of the cylinder liner in motor vehicle engines.

When manufacturing such a surface, knowledge about the interdependence between functional demands, characterization, and manufacturing of the surface is essential. A PC-based knowledge system, Interactive Surface Modeling (ISM), has been developed, making a structured storage of the surface-related information possible. The concept used in ISM is to divide the functional surfaces into separate functional requirements and connect these with proper design parameters, process variables, and measuring strategies. The system also comprises databases with standards and reference literature making it a useful support in the manufacturing of surfaces.

A great amount of effort has been made in order to use 3D surface roughness measuring and evaluation, since it opens up a whole range of possibilities to understand the surface from its functional aspect. Advantages of 3D measurements and peculiarities involved in this technique are discussed together with methods for optimizing the measuring strategy. Two different types of instruments for these measurements have been evaluated: stylus and focus detection. An Atomic Force Microscope (AFM) has been used here as a reference instrument to give a quantitative judgment of the deviation between the two instruments.

The wear process in the cylinder liner has been studied by measuring unworn and worn surfaces using effective relocation and replication techniques. The AFM was used and was found to be a necessary complement to ordinary stylus instruments for a proper characterization of the wear process. The new 3D topography information accessible by the AFM made it possible to verify that the plasticity index could be used for the prediction of wear, requiring only the measuring of slopes in the surface. The cylinder liner surface also was found to have a fractal behavior over more than three orders of magnitude in sampling distance.