CHARACTERIZING SURFACE QUALITY THROUGH 3D PARAMETERS: WHY 2D AVERAGE ROUGHNESS ALONE IS NO GOOD

摘要

Typically, the design of machine parts is based on the dimensional and form tolerances and fragmentally on the surface roughness parameters (predominantly roughness average Ra). Despite the range of available 3D surface quality parameters, and the modern equipment to accurately measure them, design and quality professionals continue to specify surface finish based solely on the value of Ra. There are many reasons that contribute to this tendency: average roughness remains so easy to calculate, it is well understood, and vast amount of published literature explains it, and historical part data is based upon it. The same outlook trails in undergraduate education and their textbooks. It has been seen that Ra, typically, proves too general to describe surface's true functional nature. Additionally, the push for complex geometry, coupled with tight tolerances, has reinforced the need to maintain increased process control along with improved surface finish. In turn, the surface finish over the entire area, not just the 2D parameters, tends to dictate the performance and reliability of the component. This article explores how these multitudes of 2D and 3D surface quality parameters are to be understood in the design and development of high performance surfaces, and the strong need for them to be incorporated into undergraduate engineering curriculum, and be taught as an improved toolkit to the aspiring engineers, process engineers and quality control professionals.