How carefully and delicately a CNC machining process is being carried out, finally, it might have some unwanted marks on the surface of the part. Such as some minor tool scratches might appear, not intentionally, on the surface of the workpiece. In this case, a correctly selected surface finish method will be beneficial to clear out the surface.
Polish surface finish is a great method to get your wanted surface attributes and functioning capability to achieve aesthetics, higher corrosion resistance, and wear resistance. Many metal surfaces are generally inclined to corrode and deteriorate over time. But polishing not only magnifies the exterior of a part, but it also improves its workability and life span.
Metal surfaces mostly get damaged by reacting with oxygen from the air. Other than oxidation, high temperature and wear play their part too. But if metal surfaces are polished adequately then they can be averted from being oxidized, tainted, and corroded.
This article is solely dedicated to enable you to apply the polish surface finish in the most productive way. In the end, you will learn the different polishing processes best for customized CNC machined parts. The pros and cons and the application requirements of each process will be discussed. Then, you will be introduced with some important tips to get a fine surface finish. Let’s straight dive into it.
Working of Polish Surface Finish
Normally, a smooth and shiny surface is achieved through polishing. It requires rubbing the part using an abrasive material to finish a metal surface. It objects to eradicate undesired scratches from finished machined parts while ameliorating their beauty and glisten. Which results in a cleaned surface with a significant specular reflection.
Applying a polished surface finish to some materials helps to reduce diffuse reflection to minimal values. As a result of buffing a polished surface, we get a mirror-bright finish.
There are numerous materials and customized metal parts that can be polished. Although, every polishing technique cannot be applied to every metal material. For example, for hard metals, automatic polishing is more reasonable while soft materials require manual polishing plus buffing. There are specified processes for a particular type of material.
Generally, there are main four steps involved in the polishing process for custom manufactured parts.
- Rough the Part Surface
As discussed in the intro, machining parts can have some scratches and defects because of the involvement of processes that inherent these small shortcomings like welding. That’s why before polishing, these parts need some roughing to wipe out these shortcomings.
Not every part requires roughing. It is used where necessary. To attain better roughing, a pneumatic roto orbital sander can also be used. Note the abrasive specifications for small and large area surfaces. For a small area, an abrasive disk with 32mm in diameter having grains between 1500-3000 is suitable. But for large surface areas, an abrasive disk with 150mm in diameter and 1200 or 1500 grains are good.
- Apply Polishing
After roughing the surface, a nice and accurate rubbing with an abrasive material finds it perfect to fine-tune the prototypes and custom parts. Wool berets and polishing sponges can be used to properly spread the abrasive paste. After that, just clean the surface with a microfiber to optimize results further.
- Brighten the Surface
Sometimes polishing the surface after roughing leaves some tiny scratches. So here, brightening plays its role to achieve an even better look. The brightening process also assists to introduce uniformity to the finish.
- Protect the Finishing
Metal finishing processes are provided a protective layer that preserves the surface of metal against rust, corrosion, and wear. But taking care of this layer is also important. Therefore, after finishing the brightening process, a coat of protective wax is applied to keep the finishing fresh.
Types of Polish Surface Finish
There are many types of polish surface finish used in manufacturing. Every application type possesses its pros and cons. But the right polishing method is the one that meets your end requirements. Many factors influence the method to be applied. These factors may include part’s usage, its cost, environmental effect, etc. They are discussed in detail as follows
Mechanical Polishing
Mechanical polishing involves mechanical smoothing of the surface. It uses abrasives to remove contaminants and scratches for improving the surface conditions of a part for decorative or functional purposes. Materials used to perform mechanical polishing finish are sandpaper, flat wheels, abrasive stick, etc.
If a surface demands extra cleaning then some auxiliary abrasive tools can be used. These incorporate ultra-precision polishing and turntables. To bring off nicety in polishing, these special auxiliary tools are pressed against the part’s surface at high speeds in a polishing fluid that contains abrasives. This finishing process offers an excellent and optimal surface roughness of about 0.008μm. That is the best amongst all the polishing methods.
Pros of Mechanical Polishing
- It provides an excellent surface finish.
- This method offers higher surface brightness.
- It helps to optimize the part’s beauty.
- It brings sharp aesthetic appeal.
Cons of Mechanical Polishing
- It is not capable to polishing complex-shaped parts.
- Even after subjecting to mechanical polishing, the surface may be vulnerable to
corrosion.
- Its gloss is not long-lasting.
Chemical Polishing
Chemical polishing offers a quick method for obtaining passable results. Although, it is not preferred all the time to obtain a perfect surface. But it is the best method for obtaining a deformation-free surface, in the case of some soft metals. The chemical polishing finish can be applied alone or after applying mechanical polishing.
Generally, the whole part or required surface is immersed in or wiped with the solution. After a suitable time when the desired polish is obtained then it is etched or washed and dried, as appropriate.
Pros of Chemical Polishing
- The big advantage is that it can polish any complex-shaped parts.
- It can polish parts made of very soft metals.
- It can process several parts simultaneously depending on the quantity of the solution.
- It is economical method in terms of equipment.
- It offers higher efficiencies and good corrosion resistance.
Cons of Chemical Polishing
- Dealing with dangerous solutions can be difficult and unsafe.
- It may emit hazardous gasses.
- It may result in inhomogeneous surface brightness.
Electrolytic Polishing
This type of surface finish is mostly regarded as electrochemical polishing and sometimes, it is also referred to as anodic polishing. These all are synonyms of a process that is similar to chemical polishing. As in chemical surface finish, we also have to dissolve the parts into a chemical solution to get a quality surface finish.
The name anodic polishing is derived from the reason that in electrolytic polishing the effect of the anode is prominent for the chemical reaction. When a customized metal part is dipped into the chemical, it removes unwanted extra pieces of material from it. It removes any micro peaks from the surface which in turn improves the surface roughness and optimizes the surface finish.
Electrolytic polishing is much better than chemical polishing in many ways.
Pros of Electrolytic Polishing
- It is comparatively cheaper.
- Its luster remains for a longer period.
- It offers a wide range of mats.
- It introduces high corrosion resistance.
- It is environmentally friendly.
Cons of Electrolytic Polishing
- Its pre-polishing processes are complicated.
- It requires high capital for equipment.
Conclusion
If your CNC customized parts required to ameliorate their beauty and glisten, then they can be applied with polish surface finish. This method is suitable for decorative purposes and enhances the functional properties of the part as well. We covered polish surface finish in detail, its important types and their advantages and disadvantages are particularly discussed.
