A comprehensive guide to surface treatment processes for parts

In modern manufacturing, surface treatment is crucial to the performance and appearance of parts. When determining part requirements, designers must not only consider basic parameters such as geometry, size and material, but also pay attention to quality parameters such as hardness, grain, tolerance and surface treatment to achieve the best performance of the part and reduce costs.

1.Surface Texture Parameters

There are many ways to achieve the desired surface texture. Texture can describe the uncoated machined surface by topography, waviness, and roughness, while the coated surface texture can be mirrored, matte, or custom textured. For functional coatings, surface hardness and corrosion resistance are also important.

2.Machined Surface Texture

Machined surfaces are surfaces without any coating and paint. Their texture depends on the machining method and the required part quality. Many parameters make up the overall result. For machined surfaces, the parameter name depends largely on the distance between two uneven elements.

①Layout

Layout is determined by which processing tool removes (or adds, in the case of 3D printing) material from the workpiece and its path. For example, milling a part leaves a visible pattern on the surface of the part. Even if the surface finish of a milled part is very smooth, you can actually see its path. You can use part layout to get better lubrication results. A cross-layout of the surface will keep the lubricant in longer. This is why honing is such a coveted technique for hole manufacturers. The inner surface of the hole is lubricated longer.

②Waviness

Waviness is much less compared to layout. Waviness is much less when layout is compared to part size, but it can still be felt if the overall quality of the part is not very high. The undulations arise from the vibrations of the machining tool when removing excess material. For unimportant parts or prototypes, both layout and waviness are considered low-grade surface textures that can be eliminated by more precise machining methods.

③Surface Roughness

Surface roughness is the parameter to check when you need a specific texture for a part without any coating. Surface roughness determines whether your part will be smooth, matte, mirrored, or notched. There are many ways to measure surface roughness. If you want better aesthetics, corrosion resistance, and overall smoothness, reduce the Ra parameter. For better part life and corrosion resistance, reduce Rz. If you want better contact strength, you must reduce Rtm (the average distance between two peaks or valleys).

It should also be noted that some machining methods may add a separate surface texture to the material. For example, sandblasting a material will leave an artificial roughness that can be used, for example, to prevent the part from slipping out of the user’s hand.

3.Surface Texture Coatings

Texturing by surface roughness is very expensive because the overall quality of the surface depends on the quality of the machining, which in turn depends on expensive equipment, cutting tools, and time. A less expensive way to get a shiny, matte, glossy, or mirror-like surface on a rough part is to apply a coating. Metal parts can be coated in many different ways.

①Spray Painting

Spray painting is the simplest way to create a reliable surface texture on a rough part. The advantage of this method is that modern coatings can not only apply color to the part, but also texture. So if you are looking for the cheapest way to make your parts look better, just ask the manufacturer to skip the delicate surface finishing process and apply a fairly heavy layer of paint to cover them and make the parts smooth. Also, the paint will prevent the material from corroding.

Paints can make your parts matte, shiny, glossy, rough, metallic, etc. They can mimic almost any texture available in the market. So if you want some custom textures, you should probably look at the options offered by paints first. However, if you choose the textures offered by paints, the size of the surface is reduced by the layers of paint, which can be quite large.

②Powder coating

Powder coating is similar to paint, but the paint layer is much thinner. Therefore, powder coating is more suitable for precision component finishing, and due to the details of the process (plastic powder is sintered to the surface of the component), you can’t get many different textures, so you can only get a matte or glossy surface. Powder coating is also advantageous in other aspects.

③Anodizing and Plating

These are surface treatments that cover the surface of one metal with another metal. You should choose them if you want to keep the metallic look of the part, but you should choose them if you want to significantly improve the texture quality of the surface. These methods can give you a nice metallic finish in any color you want.
But the texture is limited to metal. You can’t expect to have all the options of paint or even powder coating. Anodizing or plating is a layer underneath the paint layer so the dimensions of the part remain the same.

4.Conclusion

There are many parameters for surface treatment, some of which affect aesthetics and some of which determine functionality. Without spending a lot of money on machining, machining the part to a moderate quality and then covering it with paint is a good way to get the desired texture, saving costs while getting a variety of textures.

We sincerely hope that this article is helpful to you. If you need more surface treatment suggestions, please contact Xavier to provide effective and professional surface treatment solutions for your parts.