Waviness

Waviness is the measurement of the more widely spaced component of surface texture. It is a broader view of roughness because it is more strictly defined as "the irregularities whose spacing is greater than the roughness sampling length". It can occur from machine or work deflections, chatter, residual stress, vibrations, or heat treatment. Waviness should also be distinguished from flatness, both by its shorter spacing and its characteristic of being typically periodic in nature.

There are several parameters for expressing waviness height, the most common being Wa & Wt, for average waviness and total waviness, respectively. In the lateral direction along the surface, the waviness spacing, Wsm, is another parameter that describes the mean spacing between periodic waviness peaks. There are numerous measurement settings which influence these resultant parameter values, which are mentioned below. One of the most important is the waviness evaluation length, which is the length in which the waviness parameters are determined. Within this length the waviness profile is determined. This is a surface texture profile that has the shorter roughness characteristics filtered out, or removed; it also does not include any profile changes due to changes in workpiece geometry that are either unintentional (flatness) or intentional (form).

Waviness is included in the ISO standards ISO 4287 and ISO 16610-21 as well as the U.S. standard ASME B46.1, and it is part of the surface texture symbol used in engineering drawings.

The measurement of the waviness can be done with a variety of instruments, including both surface finish profilometers and roundness instruments. The nature of these instruments is continually progressing and now includes both stylus-based contact instruments as well as optical & laser-based non-contact instruments. In earlier instruments, the measurement output was inherently linked to the instrument itself, whereas there is now emerging some divergence between the instrument that collects the surface profile data and the analytical software that is able to evaluate this data.

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