ASME B46.1:2019 pdf download

ASME B46.1:2019 pdf download.Surface Texture (Surface Roughness, Waviness, and Lay)
1 GENERAL
Incases ofdisagreementregardingtheinterpretationof surface texture measurements, it is recommended that measurements with skidless stylus–based instruments with Gaussian filteringbe used as the basis for interpreta- tion. The followingkeymeasurementparameters mustbe established for proper surface texture specification and measurement.
2 FILTERING
The spatial wavelengths to be included in a surface texture measurement are generally limited by digital band-pass filtering. For measurement of roughness, short-wavelength cutoff, λs, specifies the short spatial wavelength limit and is defined as the wavelength where the Gaussian filter will attenuate the true profile by50%. Spatial wavelengths less thanλsareseverelyatte- nuated and minimally contribute to the roughness measurement. The roughness long-wavelength cutoff, λc, specifies the long spatial wavelength limit and is defined as the wave- length where the Gaussian filter will attenuate the true profile by 50%. Spatial wavelengths greater than λc are severely attenuated and minimally contribute to the roughness measurement.The ratio of λc to λs (λc:λs) is the bandwidth of the measurement. Some instruments allow the selection of λcand λsindividuallyand/orthe selection ofa bandwidth, typically 100:1 or 300:1. The spatial wavelengths comprising the texture between λs and λc are minimally attenuated by the Gaussian filter. The cutoffs, λcand λs, should be chosen by the designer in light of the intended function of the surface. When choosing λc and λs, one must be cognizant that the surface features not measured within the roughness cutoff bandwidth may be quite large and may affect the intended function of the surface. Thus in some cases it may be necessary to specify both surface rough- ness and waviness. When surface waviness control is important, digital band-pass filtering is applied similarly as it is for rough- ness filtering. For waviness, the waviness short-wave- length cutoff, λsw, and waviness long-wavelength cutoff, λcw, are applied to obtain the waviness profile. An important consideration is the correspondence of the roughness long-wavelength cutoff and the waviness short-wavelength cutoff. When these respective cutoffvalues are not equal, the discrimination ofthe roughness and waviness features of a given surface can become confounded. On all surface texture specifications as ofJanuary1997, λcand λsmustbe stated. When λcand λsare notspecified, guidelines are given in paras. 3-3.20.1 and 3-3.20.2 forthe metrologist to establish λc and λs. These guidelines are intended to include the dominant features of the surface in the measurement whether these surface features are relevant to the function ofthe surface or not.
3 STYLUS TIP RADIUS
The stylus tip radius may be chosen by the designer or metrologist based on the value ofλs (i.e., the short-wave- length cutoff). Forλsequal to 2.5 μm, the tip radius should typicallybe2 μmorless.Forλsequalto8μm,thetipradius should typicallybe 5 μm or less. For λsequal to 25 μm, the tip radius should typically be 10 μm or less.
4 STYLUS FORCE
The maximum static measuring force is determined by the radius of the stylus and is chosen to assure minimal damage to the surface and that constant contact is main- tained with the surface. Specific recommendations for stylus force may be found in para. 3-3.5.2.
5 MEASUREMENT PARAMETERS
Many surface finish height parameters are in use throughout the world. From the simplest specification of a single roughness parameter to multiple roughness and waviness parameter specifications of a given surface, product designers have many options for speci- fying surface texture to control surface function. Between these extremes, designers should consider the need to control roughness height (e.g., Ra or Rz), roughness height consistency (e.g., Rmax), and waviness height (e.g., Wt). Waviness is a secondary longer wavelength feature that is only ofconcern for particular surface func- tions and finishing processes. A complete description of the various texture parameters maybe found in Section 1.