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Dimensional Metrology
Published in Richard Leach, Stuart T. Smith, Basics of Precision Engineering, 2017
Massimiliano Ferrucci, Han Haitjema, Richard Leach
In profile characterisation, there are three types of parameters which depend on how the surface has been filtered. The primary profile is defined as the total profile after application of the short wavelength (low-pass) filter and an example primary profile parameter is Pa. The roughness profile is defined as the profile derived from the primary profile by suppressing the long-wave component using a long-wavelength (high-pass) filter, and an example roughness parameter is Ra. Roughness is usually the process marks produced by the action of the cutting tool or machining process, but may include other factors such as the structure of the material. The waviness profile is derived by the application of a band-pass filter to select the surface structure at longer wavelengths than the roughness and an example waviness parameter is Wa. Waviness is usually produced by instabilities in the machining process, such as an imbalance in a grinding wheel, or by deliberate actions in the machining process (waviness is an important consideration in the optics industry). Figure 5.34 shows examples of the same measured profile after the various filtering operations.
Three-Dimensional Shapes
Published in F. Brent Neal, John C. Russ, Measuring Shape, 2017
Waviness represents departures from the specified smooth or flat surfaces and straight or curved edges, typically at spatial scales that are much smaller than the dimensions involved in the form. Waviness is assumed to arise from vibrations or deflections in the machine (or in the workpiece) that occur over time or through indirect connections, allowing relative motion between the workpiece and the tool that may be significant in extent but is relatively low in frequency. Principal components analysis of the waviness profile of tool marks is reported to be useful for quantitative comparisons in forensic applications (Gambino et al., 2011).
Surface Finish, Integrity, and Flatness
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
The finish of machined surfaces is most commonly measured with a stylus-type profile meter or profilometer, an instrument similar to a phonograph that amplifies the vertical motion of a stylus as it is drawn across the surface [3–5]. The output of the profilometer is a two-dimensional profile of the traced surface segment, amplified in the directions both normal and along the surface to accentuate surface contours and irregularities (Figure 10.1). On a gross scale, the surface profile of a nominally smooth surface gives an indication of the surface’s shape, waviness, and roughness (Figure 10.2). The shape of the surface is the macroscopic surface contour. Shape errors may result from errors in the machine tool guideways or machined part, distortions due to clamping forces or subsequent heat treatment, and from tool wear. For nominally flat surfaces, the shape is referred to as the slope or lay of the surface. Waviness refers to variations in the surface with relatively long wavelengths or, equivalently, lower frequencies. Waviness may result from clamping errors, errors in the tool or cutter geometry, or vibrations of the system. As discussed in Section 10.4, spindle tilt in face-milling operations also produces a waviness or shape error. Roughness is the term for surface profile variations with wavelengths shorter than those characteristic of waviness. As discussed in the previous section, roughness has a geometric component dependent on the feed rate, tool nose radius, tool lead angle, and cutting speed, as well as a natural component resulting from tool wear, inhomogeneities in the work material, higher frequency vibrations of the machining system, and damage to the surface caused by chip contact. In measurement practice, roughness, waviness, and lay are generally distinguished by cutoff wavelengths.
Functional surfaces through texture management
Published in Surface Engineering, 2023
Lakshmi Gopal, Tirumalai Sudarshan
Manmade surface textures can be perceived as nominal or actual. The nominal surface refers to the intended contour of the surface, while the actual surface is determined by the manufacturing processes used to create it [5]. Surface texture is typically categorised into roughness, waviness, lay, and flaws Figure 2. Roughness is determined by the characteristics of the materials and processes used to form the surface and manifests as small, finely-spaced deviations from the nominal surface. Waviness, on the other hand, consists of much larger deviations caused by factors such as work deflexion, vibration, and heat treatment. Roughness is typically superimposed on waviness. The lay of the surface texture refers to the predominant direction or pattern of the surface, while flaws are irregularities that occur occasionally on the surface, such as cracks, scratches, and inclusions. Although flaws are related to surface texture, they also affect surface integrity.