Choosing the right surface
As a product developer, engineer, or designer, you know how much time it takes to choose the right surface texture. You determine how your product should look, feel, and function. The mechanical properties and functions of a plastic or metal component play an important role here. For example, surface finish affects friction, corrosion, heat transfer, wear and tear, and other factors. However, surfaces are often used to imitate other materials, to hide the manufacturing process or to provide a clean basis for post-processing. In this way, dividing lines of injection-molded plastic housings can be hidden, plastics can be transformed into imitation wood, or the component can be optimally prepared for post-processing. Therefore, choice of surface finish is essential.
The technical description of a surface and the technical terms used have an impact on the efficiency of communication between the manufacturer or production and the customer. It’s therefore important that both sides master and understand the technical vocabulary. Some essential components of the surface texture are described below.
The direction and undulation of the surface
The general direction of a surface pattern describes a large-area or uniform overall pattern that is produced by the different manufacturing processes and processing steps, for example by forging, sawing, milling or grinding.
Roughness (Ra)
The desired roughness and its description cause most misunderstandings between customer and manufacturer. In colloquial language, country-specific designations such as Ra, Rt or Rz are mostly used. Physically, there is no such thing as a perfectly smooth surface. From a manufacturing perspective, roughness is therefore referred to as a solid’s the three-dimensional topography.
Different levels of roughness can occur on a component using cutting tools or surface effects. There are different calculation methods for the quantitative characterization of the roughness. These consider various peculiarities of the respective surface. Surface roughness can be affected by polishing, roller burnishing, grinding, lapping, honing, pickling, sandblasting, etching or corrosion.
Interpretation of the surface finish in relation to the manufacturing costs
When choosing surface texture, a balance must be struck between quality and quantity. The value should therefore be set in such a way that the optical quality requirements do not impair the component’s functionality. The following questions are important here:
What is the area of application of the component? How should the component look optically? Does the interface affect functionality? Who sets the requirements for the surface? Did I specify my interface?
A rule of thumb:
“The finer the surface and the more complex the manufacturing process, the higher the manufacturing costs.”
International comparison table (without guarantee)
Some country-specific roughness depths of surfaces are listed below. The values assigned to one another are not mathematically related to one another.
The table serves as a guide.