ISO 25178: Geometric Product Specifications (GPS) – Surface texture: areal is an International Organisation for Standardisation collection of international standards relating to the analysis of 3D areal surface texture.
Documents constituting the standard :
Other documents might be proposed in the future but the structure is now almost defined. Part 600 will replace the common part found in all other parts. When revised, parts 60x will be reduced to only contain descriptions specific to the instrument technology.
It is the first international standard taking into account the specification and measurement of 3D surface texture. In particular, the standard defines 3D surface texture parameters and the associated specification operators. It also describes the applicable measurement technologies, calibration methods, together with the physical calibration standards and calibration software that are required.
A major new feature incorporated into the standard is coverage of non-contact measurement methods, already commonly used by industry, but up until now lacking a standard to support quality audits within the framework of ISO 9000. For the first time, the standard brings 3D surface metrology methods into the official domain, following 2D profilometric methods that have been subject to standards for over 30 years. The same thing applies to measurement technologies that are not restricted to contact measurement (with a diamond point stylus), but can also be optical, such as chromatic confocal gauges and interferometric microscopes.
The ISO 25178 standard is considered by TC213 as first and foremost providing a redefinition of the foundations of surface texture, based upon the principle that nature is intrinsically 3D. It is anticipated that future work will extend these new concepts into the domain of 2D profilometric surface texture analysis, requiring a total revision of all current surface texture standards (ISO 4287, ISO 4288, ISO 1302, ISO 11562, ISO 12085, ISO 13565, etc.)
A new vocabulary is imposed:
The new available filters are described in the series of technical specifications included in ISO 16610. These filters include: the Gaussian filter, the spline filter, robust filters, morphological filters, wavelet filters, cascading filters, etc.
3D areal surface texture parameters are written with the capital letter S (or V) followed by a suffix of one or two small letters. They are calculated on the entire surface and no more by averaging estimations calculated on a number of base lengths, as is the case for 2D parameters. In contrast with 2D naming conventions, the name of a 3D parameter does not reflect the filtering context. For example, Sa always appears regardless of the surface, whereas in 2D there is Pa, Ra or Wa depending on whether the profile is a primary, roughness or waviness profile.
These parameters involve only the statistical distribution of height values along the z axis.
|Sq||Root mean square height of the surface|
|Ssk||Skewness of height distribution|
|Sku||Kurtosis of height distribution|
|Sp||Maximum height of peaks|
|Sv||Maximum height of valleys|
|Sz||Maximum height of the surface|
|Sa||Arithmetical mean height of the surface|
These parameters involve the spatial periodicity of the data, specifically its direction.
|Sal||Fastest decay auto-correlation rate|
|Str||Texture aspect ratio of the surface|
|Std||Texture direction of the surface|
These parameters relate to the spatial shape of the data.
|Sdq||Root mean square gradient of the surface|
|Sdr||Developed area ratio|
These parameters are calculated from the material ratio curve (Abbott-Firestone curve).
|Smr||Surface bearing area ratio|
|Sdc||Height of surface bearing area ratio|
|Sxp||Peak extreme height|
|Vm||Material volume at a given height|
|Vv||Void volume at a given height|
|Vmp||Material volume of peaks|
|Vmc||Material volume of the core|
|Vvc||Void volume of the core|
|Vvv||Void volume of the valleys|
|Spd||Density of peaks|
|Spc||Arithmetic mean peak curvature|
|S10z||10 point height|
|S5p||5 point peak height|
|S5v||5 point valley height|
|Sda||Closed dales area|
|Sha||Closed hills area|
|Sdv||Closed dales volume|
|Shv||Closed hills volume|
A consortium of several companies started to work in 2008 on a free implementation of 3D surface texture parameters. The consortium, called OpenGPS  later focused its efforts on an XML file format (X3P) that was published under the ISO standard ISO 25178-72. Several commercial packages provide part or all of the parameters defined in ISO 25178, such as MountainsMap from Digital Surf, SPIP from Image Metrology as well as the open source Gwyddion.
Part 6 of the standard divides the usable technologies for 3D surface texture measurement into three families:
and defines each of these technologies.
Next, the standard explores a number of these technologies in detail and dedicates two documents to each of them:
Parts 601 and 701 describe the contact profilometer, using a diamond point to measure the surface with the assistance of a lateral scanning device.
Part 602 describes this type of non-contact profilometer, incorporating a single point white light chromatic confocal sensor. The operating principle is based upon the chromatic dispersion of the white light source along the optical axis, via a confocal device, and the detection of the wavelength that is focused on the surface by a spectrometer.
Part 604 describes a class of optical surface measurement methods wherein the localization of interference fringes during a scan of optical path length provides a means to determine surface characteristics such as topography, transparent film structure, and optical properties. The technique encompasses instruments that use spectrally broadband, visible sources (white light) to achieve interference fringe localization). CSI uses either fringe localization alone or in combination with interference fringe phase.
Part 606 describes this type of non-contact areal based method. The operating principle is based on a microscope optics with limited depth of field and a CCD camera. By scanning in vertical direction several images with different focus are gathered. This data is then used to calculate a surface data set for roughness measurement.
Digital Surf is a French software company formed in 1989 mainly known for its Mountains software, that is offered as embedded or optional OEM surface analysis software by the majority of profilometer and microscope manufacturers.Focus variation
Focus variation is a method to calculate a sharp image and to measure the depth with an optics with limited depth of field.Geometric dimensioning and tolerancing
Geometric dimensioning and tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describe nominal geometry and its allowable variation. It tells the manufacturing staff and machines what degree of accuracy and precision is needed on each controlled feature of the part. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features.
Dimensioning specifications define the nominal, as-modeled or as-intended geometry. One example is a basic dimension.
Tolerancing specifications define the allowable variation for the form and possibly the size of individual features, and the allowable variation in orientation and location between features. Two examples are linear dimensions and feature control frames using a datum reference (both shown above).There are several standards available worldwide that describe the symbols and define the rules used in GD&T. One such standard is American Society of Mechanical Engineers (ASME) Y14.5-2009. This article is based on that standard, but other standards, such as those from the International Organization for Standardization (ISO), may vary slightly. The Y14.5 standard has the advantage of providing a fairly complete set of standards for GD&T in one document. The ISO standards, in comparison, typically only address a single topic at a time. There are separate standards that provide the details for each of the major symbols and topics below (e.g. position, flatness, profile, etc.).ISO 16610
ISO 16610: Geometrical product specifications (GPS) – Filtration is a standard series on filters for surface texture, and provides guidance on the use of these filters in various applications.
Filters are used in surface texture in order reduce the bandwidth of analysis in order to obtain functional correlation with physical phenomena such as friction, wear, adhesion, etc. For example, filters are used to separate roughness and waviness from the primary profile, or to create a multiscale decomposition in order to identify the scale at which a phenomenon occurs.
Historically, the first roughness measuring instruments - stylus profilometer - used to have electronic filters made of capacitors and resistors that filtered out low frequencies in order to retain frequencies that represent roughness. Later, digital filters replaced analog filters and international standards such as ISO 11562 for the Gaussian filter were published.List of International Organization for Standardization standards, 24000-25999
This is a list of published International Organization for Standardization (ISO) standards and other deliverables. For a complete and up-to-date list of all the ISO standards, see the ISO catalogue.The standards are protected by copyright and most of them must be purchased. However, about 300 of the standards produced by ISO and IEC's Joint Technical Committee 1 (JTC1) have been made freely and publicly available.Micro pitting
Micro pitting is a fatigue failure of the surface of a material commonly seen in rolling bearings and gears.
It is also known as grey staining, micro spalling or frosting.MountainsMap
Mountains is an image analysis and surface metrology software platform published by the company Digital Surf. Its core is micro-topography, the science of studying surface texture and form in 3D at the microscopic scale. The software is dedicated to profilometers, 3D light microscopes ("MountainsMap"), scanning electron microscopes ("MountainsSEM") and scanning probe microscopes ("MountainsSPIP").Surface metrology
Surface metrology is the measurement of small-scale features on surfaces, and is a branch of metrology. Surface primary form, surface fractality and surface roughness are the parameters most commonly associated with the field. It is important to many disciplines and is mostly known for the machining of precision parts and assemblies which contain mating surfaces or which must operate with high internal pressures.
Surface finish may be measured in two ways: contact and non-contact methods. Contact methods involve dragging a measurement stylus across the surface; these instruments are called profilometers. Non-contact methods include: interferometry, digital holography, confocal microscopy, focus variation, structured light, electrical capacitance, electron microscopy, and photogrammetry.Surface roughness
Surface roughness often shortened to roughness, is a component of surface texture. It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. In surface metrology, roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface. However, in practice it is often necessary to know both the amplitude and frequency to ensure that a surface is fit for a purpose.
Roughness plays an important role in determining how a real object will interact with its environment. In tribology, rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of the performance of a mechanical component, since irregularities on the surface may form nucleation sites for cracks or corrosion. On the other hand, roughness may promote adhesion. Generally speaking, rather than scale specific descriptors, cross-scale descriptors such as surface fractality provide more meaningful predictions of mechanical interactions at surfaces including contact stiffness and static friction.Although a high roughness value is often undesirable, it can be difficult and expensive to control in manufacturing. For example, it is difficult and expensive to control surface roughness of fused deposition modelling (FDM) manufactured parts.
Decreasing the roughness of a surface usually increases its manufacturing cost. This often results in a trade-off between the manufacturing cost of a component and its performance in application.
Roughness can be measured by manual comparison against a "surface roughness comparator" (a sample of known surface roughness), but more generally a surface profile measurement is made with a profilometer. These can be of the contact variety (typically a diamond stylus) or optical (e.g.: a white light interferometer or laser scanning confocal microscope).
However, controlled roughness can often be desirable. For example, a gloss surface can be too shiny to the eye and too slippery to the finger (a touchpad is a good example) so a controlled roughness is required. This is a case where both amplitude and frequency are very important.
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