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What is surface (area) roughness?

What is Surface Roughness?

If you look at machined parts, you will notice that their surfaces embody a complex shape made of a series of peaks and troughs of varying heights, depths, and spacing. Surface roughness is defined as the shorter frequency of real surfaces relative to the troughs.

A product’s exterior cover, a vehicle’s dashboard, a machined panel, the differences in appearance, specifically whether something is shiny or rough and matte, are due to the difference in surface roughness.

Surface roughness not only affects the object’s appearance, but it also produces texture or tactile differences. Appearance and texture can influence a product’s added values such as class and customer satisfaction.

If a part makes contact with something, its surface roughness affects the amount of wear or the ability to form a seal. If the part is to be painted, the roughness also affects the wetting and thickness of the paint. It has therefore been required in recent years to numerically control the subtle asperity of a surface.

ISO 25178 Surface Texture

ISO 25178 Surface Texture (Areal Roughness Measurement) is a collection of international standards relating to the analysis of surface roughness.

While JIS B 0671-1 and ISO 13565-1 (Surface Texture: Profile Method) are based on analyses using the stylus method, ISO 25178 Surface Texture (Areal Roughness Measurement) standards support two evaluation methods: contact type (stylus method) and non-contact type (optical probe).

The dual-method approach resolves the existing problems in the profile method: variations in measurement results depending on the measurement site and variations that are attributable to scanning direction.

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