05.10.2020 •

Surface Roughness: An Introduction

What is surface roughness?

Surface roughness indicates the condition of processed surfaces. 

Surface conditions are determined by visual appearance and tactile feel and are often described using expressions such as smooth-and-shiny, matte-and-textured, mat-silver, or mirror-finish. The differences in both appearance and texture are derived from the irregularities present on the surface of the object. 

Irregularities cause roughness on a surface. Surface roughness is a numerical scale of the surface condition of the shininess (or texture) that is not dependent on visual or tactile sensation. Surface roughness plays a significant role in determining the characteristics of a surface. 

Facial irregularities on components and materials are either created intentionally or produced by various factors including the vibration of cutting tools, the bite of the edge used, or the physical properties of the material. Irregularities have diverse sizes and shapes and overlap in numerous layers; the concavities/convexities affect the quality and functionality of the object surface. In consequence, the irregularity impacts the performance of the resulting product in terms of friction, durability, operating noise, and air tightness. In the case of assembly components, the surface feature affects the characteristics of the final product, including friction, durability, operating noise, energy consumption, and air tightness. The surface features also influence the product’s quality, such as the ink/pigment application and varnish of printing paper and panel materials.

Surface Roughness: An Introduction

Why surface roughness needs to be measured

The size and configuration of features have a significant influence on the quality and functionality of processed surfaces and the performance of the final products. Consequently, it is important to measure the roughness of surfaces to meet high performance standards for resulting end products. 

Surface irregularities measured by classifying the height/depth and intervals of surface features to evaluate their concavity/ convexity. The results are then analyzed in accordance with predetermined methods, subject to a calculation based on industrial quantification (*). 

The favorable or adverse influence of surface roughness is determined by the size and shape of the irregularities and the use of the product. 

The level of roughness must be managed based on the desired quality and performance of the surface. 

The measurement and evaluation of surface roughness is an old concept with numerous established parameters indicating various criterion of roughness. The progress of processing technology and the introduction of advanced measurement instruments enables the evaluation of diverse aspects of surface roughness. 

*The industrial quantity determines the quantitative properties defined by the method of measurement (cf: roughness; hardness) instead of physical quantities, such as mass and length.

Trends in surface roughness measurement

Measuring the surface features of components and industrial products and the qualitative management of the resulting data is increasing with the evolution of nanotechnology and the higher performance demands and size-reduction of electronic devices. Conventional stylus roughness gages and other instruments designed to acquire height information through mechanical contact with the surface being measured were broadly able to measure surface height/features and the superficial condition of the surfaces. However, the increase of soft samples, like fi lms, and surface features that are smaller than the tip of the stylus probe led to the demand for non-contact measurement techniques, from linear measurement to nondestructive/ precise area measurement. To meet these demands, laser microscopes were developed as instruments capable of providing accurate, non-contact 3D measurement of the surface features of a sample within the presence of the atmosphere.