A comprehensive guide to surface treatment processes for parts
Designers determine the requirements of the final part. Basic parameters include geometry, size and material. However, as the industry develops, parts must have more and more quality parameters that are not so easy to select or analyze. This can include hardness, grain, tolerance and surface treatment. A good designer must be able to choose from the best combination of part parameters to make it work perfectly and cost as little as possible. This article aims to wisely choose the right surface treatment process for the part.
1.Surface Texture Parameters
There are many possible ways to get the desired surface texture. The texture itself is described in a number of important ways. First of all, the machined surface (uncoated) can be determined by its layout, waviness and roughness. The coated surface texture can be mirror-like, matte or have a customized texture. In addition, when it comes to functional coatings, the hardness and corrosion resistance of the surface 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 layers of paint are much thinner. Therefore, powder coating can better serve delicate parts, and due to the details of the process (plastic powder is sintered onto the surface of the part), you can’t really have a lot of different textures, so you can only get a matte or smooth surface with it. The advantages of powder coating are elsewhere.
③Anodizing and Plating
These are processes of covering the surface of one metal with another metal. You should choose them if you want to keep the feel of the part as metal, but if you want to significantly improve the texture quality of the surface, you should choose them. Such methods can give you a good metallic texture in any color you want. But the textures are limited to metals. You can’t expect to have all the options of paint or even powder coating. Anodizing or plating is a layer below the paint layer, so the dimensions of the part remain the same.
4.Conclusion
There are many parameters for surface treatment. Some are simply aesthetic and determine the appearance of the part, while others also determine its functionality (surface roughness). In the end, I think the best way to get the desired texture without spending a lot of money on machining is to machine the part to a medium quality and then cover it with paint. This way you don’t spend too much money on the treatment, and the paint provides the most variety of textures.
We really hope that this article was helpful to you, and if you want more advice on surface treatment, contact Xavier to provide effective and professional surface treatment advice for your parts.