Surface roughness
Smooth and glossy or rough and mat – the requirements on the surface of a material vary depending on the application. By means of destructive materialographic and non-destructive metrological inspection methods, it can be ensured that components have the required surface topography.
Table of contents
- Brief explanation: surface roughness
- Quality Analysis – we inspect your material for surface roughness
- Effect of surface roughness on different materials
- How is surface roughness measured?
- Standardisation of roughness measurement: global standards for precise product specifications
- Applications
- In summary: surface roughness
Brief explanation: surface roughness
Anyone who talks about surface roughness is referring to the microstructure on the surface of a material. The term roughness stems from surface physics and refers to the unevenness in the surface topography. Surfaces generally have complex geometries that are visible under a microscope. This fine unevenness in the surface height – that is the surface roughness – affects not only the appearance, but also the haptics and therefore the functionality of the related component.
Why should we measure surface roughness?
Surface roughness is quantified by specific parameters that specify the deviations from an ideally smooth surface. Roughness parameters are crucial for the evaluation of the functionality and quality of technical surfaces, because they have a direct effect on characteristics such as friction, wear resistance and adhesion. Precise measurements and checks on the surface roughness are therefore of major importance for quality assurance in many industrial applications.
Quality Analysis
we inspect your material for surface roughness
At Quality Analysis, we understand the critical role of surface roughness for product quality and functionality. Our expertise in roughness measurement combines materialographic and metrological methods for the preparation of precise, dependable roughness profiles exactly matched to your specific task. As such, our analyses provide valuable information about surfaces, structures and the material composition of your components.
- Analysis of microstructure and surface roughness using light microscopy after sample preparation by cutting and polishing
- Scanning electron microscopy: detailed surface information with high magnification and large depth of field
- Measurement of surface hardness and indirect evaluation of surface quality by means of hardness testing
- Laser scanning and tactile metrology for the acquisition of the surface roughness
- Surface and contour measurements: reliable results for radii, chamfers, contours, roughness, ripple, angles, recesses and length tolerances
- We work in accordance with ISO 25178, DIN EN ISO 21920-1, -2, -3 and DIN EN ISO 13565-1 to ensure the high quality and conformity of our analyses.
Effect of surface roughness on different materials
A surface roughness that is inappropriate for the application can cause numerous problems such as increased wear, insufficient lubrication in moving parts and the failure of seals. In critical applications such as aerospace or medical technology, such faults can have serious consequences.
On which surfaces is it possible to measure surface roughness?
Surface roughness can be measured on numerous material surfaces, for instance on metals, plastics, ceramics and composite materials. With the latest measuring technologies, it is possible to acquire roughness parameters on surfaces with complex shapes, on large-area components and also on microstructures.
Effect of surface roughness on mechanical characteristics
Surface roughness has a crucial role in the mechanical characteristics of materials. In general, it can be stated that materials with smoother surfaces suffer less fatigue, because there are fewer places for microcracks to occur and spread. Optimised roughness, on the other hand, can improve the strength of material joints by providing better interlocking at the microscopic level and thus optimising the transmission of force between the surfaces of the joint. In turn, this situation results in increased durability and reliability of components in their application.
Surface roughness and friction behaviour
Surface roughness also has an effect on the friction behaviour between two surfaces. Here tribology, the science of friction, wear and lubrication, has a central role. In general, a finer surface finish results in a lower coefficient of friction, which in turn reduces the wear and energy loss during the movement of the parts against each other. Careful optimisation of the surface roughness can therefore not only extend the service life of components, it can also improve the efficiency of mechanical systems by minimising friction and therefore the related energy losses. Tribological analysis permits a deep understanding of these interactions and aids the development of robust surfaces.
Improvement of coating adhesion
Greater roughness on the surface of a component increases the surface energy and in this way creates better conditions for the adhesion of coatings. Slightly increased roughness provides the coating with a larger surface, which results in an improved bond and therefore the greater durability of the coating. This aspect is important particularly in sectors such as the automotive and aerospace industries where coatings have a crucial role in the protection of components against corrosion.
How is surface roughness measured?
Surface roughness is measured using highly precise methods that acquire the microscopic unevenness on material surfaces. Depending on the component to be analysed, destructive or non-destructive methods may be used to be able to depict and analyse the topology of the surface in detail.
Metallography
Metallography is a destructive inspection method used for the analysis of the metallic microstructure in a material. Here a sample of the material is taken, embedded in resin and the surface smoothed by grinding and polishing. After these steps, the sample is etched using a chemical solution to make the microstructure visible. Under a microscope, for instance a light microscope or a scanning electron microscope (SEM), the grain structure, phase boundaries and microscopic unevenness can be analysed. This analysis permits a detailed evaluation of the surface roughness and its effects on the material characteristics and the performance of the component.
Laser scanning microscopy
Laser scanning microscopy utilises the principles of light reflection to prepare high-resolution 3D images of the surface of a material. In this way, three-dimensional microstructures can be analysed down to the nanometre range and, e.g., the causes of damage due to material wear detected. This method also permits the fast acquisition of precise data without direct contact with the measurement object. As such, it is particularly suitable for delicate or soft materials that traditional measurement methods involving contact could damage.
Hardness testing
Hardness testing is a further destructive method that determines the surface hardness of a material and therefore provides indirect information about the surface roughness. An indenter, such as a diamond or carbide cone, is pressed into the surface of the material using a specified force. The hardness is measured based on the size or depth of the impression. Methods such as Vickers, Brinell and Rockwell hardness testing use different indenters and methods to determine the hardness and surface quality. By means of hardness testing, it is possible to identify specific roughness features that affect the functionality and durability of the components.
Tactile metrology
Tactile metrology measures surface roughness by means of direct contact using a stylus moved over the surface. This method provides detailed profile data and is based on the ISO standard 4287, which defines terms and parameters for profile-based roughness measurements. Tactile metrology is suitable for many materials and permits the exact determination of classic roughness parameters such as Ra and Rz, which makes it a reliable tool for quality control.
Standardisation of roughness measurement: global standards for precise product specifications
For the effective communication and documentation of the results of the analysis, it is vital to state product specifications as per internationally recognised standards such as ISO 4287 and ISO 25178. By following these standards, you can ensure that specifications are consistent and comprehensible worldwide. These specifications are often given on technical drawings or in the technical documentation, where they state the requirements on the surface characteristics that a product or component must meet for its intended function.
Roughness parameters
The roughness parameters used on technical drawings are standardised. In this way, it can be ensured that it is clear what is required in the entire production process. These parameters enable engineers and manufacturers to finely match production conditions for the optimisation of the functionality and aesthetics of products and for ensuring compliance with industrial standards.
- Ra (arithmetic mean) in accordance with DIN EN ISO 4287, ASME B46.1 Ra is the mean of the absolute values of the deviations in height from the mean over a sampling length. This parameter provides a quick reference for the general smoothness of the surface and is anchored in numerous industrial standards.
- Rz (mean roughness depth) in accordance with DIN EN ISO 4287 ASME B46.1 Rz describes the mean height of the five highest peaks and lowest valleys over a sampling length. Rz provides a more detailed picture of the surface topography and is particularly helpful for the evaluation of the effect of surface defects on functionality.
- Material component of the profile Rmr in accordance with DIN EN ISO 4287 The material component of the profile Rmr(c) describes the ratio of the sum of the material lengths of the profile elements MI(c) to the total sampling length ln at a stipulated cut level c, expressed in percent. This parameter specifies the percentage portion of the material passed through at a specific depth, measured from the highest point of the profile. Alternatively, the mean line or another specified reference height (c0) can be used as the reference. The material component of the profile is crucial for the evaluation of the load-bearing capacity and the wear behaviour or a surface.
- Parameters on the P-profile in accordance with DIN EN ISO 4287 The profile depth Pt describes the vertical distance between the lowest and the highest point in the primary profile (P-profile) within a sampling length. This parameter is a measure for the total height difference in the profile and is used to characterise the roughness of a surface. The P parameters are calculated on the primary profile.
- W parameters on the waviness profile in accordance with DIN EN ISO 4287 The waviness depth Wt corresponds to the vertical distance from the lowest to the highest point in the waviness profile (W-profile).
Applications
Medical technology
By means of precise roughness measurements, in medical technology it is possible to ensure that medical instruments and implanted medical products meet strict hygiene standards and interact optimally with human tissue. Smooth surfaces are particularly important here, because they minimise the adhesion of bacteria and therefore the risk of infection. Also, they improve the compatibility and functionality of implants by aiding growth in surrounding tissue and minimising inflammation reactions.
Automotive industry
In the automotive industry, surface roughness has a direct effect on the performance and durability of vehicle components. On critical components such as engine parts, gearboxes and braking systems, optimised roughness can contribute to the minimisation of friction, which in turn increases efficiency and reduces wear. These improvements have effects not only on safety, but also on the economy of vehicles due to fuel savings and increased servicing intervals.
Aerospace
In the aerospace industry, the precision of component surfaces is of vital importance for safety and reliability. Any deviation in the surface roughness can degrade aerodynamic characteristics, which in turn can affect the fuel consumption and performance of aircraft and spacecraft. The strict control of surface characteristics also ensures compliance with the required specifications for maximum performance and safety.
Electronics manufacturing
The surface characteristics of printed circuit boards and other electronic components have a direct effect on electrical conductivity and heat dissipation. A detailed check on the surface roughness is therefore essential to prevent short-circuits, signal interference and overheating. By ensuring optimal surface roughness, manufacturers can improve the reliability and performance of electronic devices and improve the service life of products.
Machinery manufacture
In machinery manufacture, surface roughness plays a crucial role for the performance and service life of machines and components. An optimised surface roughness can contribute to the minimisation of the wear and the friction between moving parts, which in turn improves the efficiency and durability of the machines. Insufficient surface quality can lead to increased wear, uneven loading and premature failure of the components.
In summary: surface roughness
Surface roughness refers to the microscopic unevenness on material surfaces crucial for the functionality and quality of products in various sectors such as medical technology, the automotive industry, aerospace as well as in electronics manufacturing. The precise measurement and the standardisation of the roughness parameters, such as Ra, Rz and Rq, permit precise quality control and are essential for the optimisation of product characteristics such as friction, wear resistance and the adhesion of coatings.
