ACKNOWLEDGEMENTS: (1) Photo above: Mark Riley, BV Products
(2) Profilomic data provided by Jack Clark, Surface Anakyrics LLC and SME Deburr/Finish Technicl group
Developing “Isotropic” surfaces can be an important surface attribute to develop when seeking to improve performance, functionality and longevity of components used in critical applications. Many components can have service life extended, wear resistance improved and premature fatigue or fracture prevented if surface characteristics are modified with high-energy and high-intensity mechanical surface finish methods. These kinds of surface finishing methods improve overall part quality by affecting the part surface in a number of different ways simultaneously.
(1) Isotropic Surface Development. In contrast to machined or ground surfaces Isotropic surfaces are non-directional or random in character. They do not exhibit a surface pattern of parallel lines, grooves or notches common to all machining methods (SEE the bottom set of diagrams in the photo above). This is a desirable surface characteristic functionally as the overall amount of surface available for bearing loads can be increased dramatically and machining notches which provide potential failure related crack propagation points are attenuated substantially. Close in importance to isotropicity is the development of (2) negatively or neutrally skewed surfaces that are plateaued or planarized
Above. Isotropic and Non-Isotopic Surfaces contrasted. Isotropic surfaces have many advantages over conventional machined surfaces including improved wear resistance and improved resistance to premature fatigue failure
(2) Negatively or neutrally skewed surfaces that are plateaued or planarized (see top set of diagrams in the photo). All conventional machining or fabricating methods (including: machining, turning, grinding, EDM, casting, forging etc.) develop positively skewed surfaces in which the predominant surface characteristic are the peaks and asperities of he surface profile. This can be disadvantageous as it can cause part life and performance deficits in many applications where parts are subject to wear and/or repeated stress or strain. Related to these is a further surface conditioning attribute of high-intensity mass finishing:
(3) Compressive stress generation, like shot peening these kinds of finishing processes induce compressive stress and cold-hardening effects to the part while producing the sophisticated surface finish effects mentioned in (1) and (2). As all features and areas of the part are processed identically and simultaneously, stress equilibrium within the part can be developed that would be difficult to replicate with other surface conditioning methods.
Above: Isotropic Micro-Finishing Part Photography by Mark Riley, BV Products