Profile Characterization of Surface Roughness in Shot Peening: There are more parameters besides Ra

Author:  Stefanie Stöckel, Sophie Gröger
Source:  The Shot Peener magazine, Vol 40, Issue 4, Fall 2026
Doc ID:  2026058
Year of Publication:  2026
Abstract:  
INTRODUCTION TO ROUGHNESS Roughness is a term frequently encountered in the context of surface evaluation, yet it represents merely a component of surface texture. The overall surface structure of a part in terms of geometrical irregularities is defined as surface topography. [1] Surface texture is a subsequent term and refers to the surface without the nominal form, respectively the underlying shape. [2] It is important to note that all terms refer solely to geometry and do not include other surface properties. The model for the evaluation of real surfaces, with all their deviations, is the superimposition of waves of different wavelengths and frequencies. The differentiation of these is achieved by filtering. The procedure and the definitions for the calculation of the profiles are given in ISO 21920-2 and illustrated in Figure 1. [2] The initial step is the removal of noise, which is the very small-scale lateral component. Secondly, the form (very large-scale lateral components) is removed. The resulting profile is the primary profile, which can be evaluated with P-parameters, for example Pa. This profile is then separated into waviness and roughness. Roughness incorporates only the smaller waves, with high frequency. In essence, roughness represents only a specific component of the entire surface profile. It is not a static property either, because the wavelengths included can change depending on the surface. Roughness for a rough cast surface is different from that of a smooth, polished surface.