Metal Surface Finishes: Understanding the Basics of Applying Finishes

Metal Surface Finishe-Metal Surface Finishes: Understanding the Basics of Applying Finishes

Metal Surface Finishes are vital in making parts. They are key to greatly improving product quality and performance. No matter how good a metal stamping or CNC machining service is, proper metal finishing can make a part better. It can improve function and appearance.

Just as there is diversity in metals, there is a wide variety of types of metal finishes available for machinists and welding fabricators. However, failing to pick the right metal finish for a project can cause problems. These include wasted material and higher production costs.

Also, ignoring the need to pick the right finish can make production cycles longer. It can also hinder the path to becoming an industry leader. That’s why it’s critical to understand how to provide the ideal finish for your product. This decision’s impact goes far beyond looks. It’s about cost, quality, and your project’s appeal.

To handle these complexities, we’ll dive into surface finish basics below. We’ll also explore the many options to get the best results.

Table of Contents

Surface Finishing Basics

Surface treatment involves “surface topography”, “surface texture” or “surface roughness”. Surface roughness” are terms that reveal themselves. Surface finishing changes the look of metal. It does this by adding, removing, or rearranging its surface. In metal finishing, a machinist treats a metal surface through a chemical reaction to give it a more pleasing appearance.

Surface Topography:This term describes the three-dimensional features and structure of a metal surface. Evaluation of surface topography can help to understand how a material interacts with the environment or other materials.

Surface Texture: This refers to the fine structure of a metal surface. It can occur naturally or form through machining, like grinding or etching. Texture affects the optical properties and coefficient of friction of a material.

Surface Roughness: This is the degree of unevenness of a surface and is often used as a measure of the microscopic unevenness of a surface. Smoother surfaces are stronger and resist corrosion. Rougher surfaces are better for bonding or coating.

The choice of metal surface finish is as important as the processing. Different products need different finishes. For example, medical and optical tools require the highest quality finishes for performance and safety. However, some industries or applications may have less strict requirements for surface finishes. They are less sensitive to surface details.

Why Is Surface Finishing Important?

Machinists use surface finishes for more than just making them look pretty. They also protect metal parts better. Metal surface finishes typically contain the following benefits:

Improved Product Aesthetics

For many customers, the appearance of a product is just as important as its performance. With a metal finishing process, metal parts can be made to look better than ever before.

Improved Corrosion Resistance of Metals

One of the worst things that can happen to metal surfaces and parts is rust. With metal finishing you can better protect the metal and make it last longer.

Make the Production Process Easier

A good surface finish can make the production process easier. For example, paint adheres better to surfaces that have been brushed and sandpapered, making the manufacturer’s job easier.

In addition to this, the following advantages can be gained by surface treating metal parts:

  • Surface-treated metal conducts electricity better.
  • It reduces the sensitivity of the metal surface to chemicals, thus preventing them from attacking the metal parts.
  • It makes things stronger and less prone to wear and tear.
  • A good surface finish helps reduce the effects of friction.

Types of Metal Finishes

There are many different metal finishing processes you can use for your next job. You should choose the right type of finish for the job. Here are some of the types of metal finishes you should know about:


Anodizing is an electrolytic process. It improves the wear and rust resistance of metals by increasing the natural oxide layer on their surface. In addition, anodized metal surfaces are better suited for bonding alkalis and glues. Anodizing can change a metal’s surface texture to make it tougher. But, it mainly works for aluminum and titanium. Also, its color may fade after long exposure to UV light.

Powder Coating

Powder coating uses electricity to evenly deposit dry powder on metal. The powder is then heat-cured in an oven to form a tough layer. Powder coating is particularly suitable for automotive parts and outdoor furniture that require high durability and an attractive appearance. However, this method is costly. It also needs strict temperature control during curing.


Pickling is the removal of impurities and defects from a metal surface by means of a strong acid solution in preparation for subsequent painting or other treatments. Pickling effectively cleans the metal surface and makes it smoother. Pickling is great at removing oxidation. But, it can make the metal corrode. This requires further treatments to neutralize the acid.


Polishing adds luster to a metal surface by friction or chemical means, giving it a mirror-like reflection. Polishing can be used on old and new parts to give them a new look. However, the polishing process may slightly remove some metal. It needs to be handled with care to keep the part’s dimensions accurate.

Grinding and Lapping

Grinding uses an abrasive wheel to remove rough parts of metal. Lapping achieves very high smoothness and flatness through delicate rubbing. It is often used for parts that need the highest precision. Grinding quickly removes extra material but can make heat that changes the material. Lapping needs more skill and time to ensure the needed accuracy.

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How to Measure Surface Finish

To measure the surface finish of a metal, you must first measure the roughness of the metal surface. To do this, you need to carefully observe and analyze the irregularities you find.

In most cases, there are three usual ways to solve these problems.

Using a Surface Roughness Comparator

The first method is to use a surface roughness comparator. Because it is done manually, it is not very accurate. Some common finishing methods can use roughness comparators. Such as casting, shot blasting, sandblasting, surface turning, cylindrical grinding, conventional machining, and electrical discharge machining.

Using a Surface Profile Scanner

The second method is to use a surface profile scanner. Since it uses laser readings, the measurements are more accurate. Since it is very accurate, it is the most commonly used method.

Using a Coordinate Measuring Machine

At first, machinists used CMMs to determine the height, width, and depth of parts. However new sensors on these tools allow them to measure surface roughness on their own. This makes it easy to switch between scanning parts and measuring surface roughness.

Surface Finish Roughness Charts

Surface finish charts allow you to see how different surface finishes compare. Ra is the most common method of measuring surface finish, but there are other parameters as well. On a surface, Ra shows the arithmetic mean deviation of a metal surface.

The lower the Ra value, the smoother the metal surface, and the higher the Ra, the rougher the metal surface. In the standardized methods that give ISO grades, surface roughness is usually measured in microns as a standard unit. The following is a useful chart of surface roughness as a guide.

Surface Finish Roughness Charts

How to Choose the Right Metal Finish

Choosing the correct metal surface finish is simple, just keep a few points in mind. These factors include:


Different metal finishes take different amounts of time. Some are slow and some are fast. This is why if you have a project to complete, you should consider how long it will take. It is also important to consider the processing time for each metal finishing option. That said, if you need a job done quickly, you may want to choose the finish that has the shortest processing time.


Not every metal is capable of an all-metal finish. Therefore, the first thing you need to consider is what material your workpiece is made of, and then choose a finish that matches that material. Some fabrics are soft and may be damaged by the use of strong abrasives. Nonetheless, some materials are hard and if you are too gentle with them, you won’t get the finish you want.


You may find the perfect finish for your project, but do you have the tools you need? Can you afford to buy new tools to change the finish? You don’t want to spend more money than you have to. Therefore, you should choose a finish that doesn’t cost much.

Some finished materials don’t cost much, but if you give the materials you are making an expensive finish, it may make them more expensive, which may turn away potential buyers. Therefore, it is best to choose a finish that does not cost much.

In Conclusion

Yonglihao Machinery understands the critical role of surface preparation in the manufacturing process. Whether you need CNC machining or metal stamping services, the quality of your product depends on the precision and quality of the surface finish. Choosing the right surface finish improves the look of your metal parts. It also ensures their durability and function in many uses. Also, the right finish choice can promote greener manufacturing and cut environmental impact. You may be a seasoned professional or new to metal fabrication. The team at Yonglihao Machinery is committed to giving expert guidance. They will help to ensure that your project is perfect. Contact us to learn more about how you can enhance your metal parts with the right finish.


Costs vary. Simple processes, like polishing, are usually cheaper. More involved processes, like anodizing or powder coating, tend to be pricier. This is because they require expensive equipment and materials.

Anodizing and powder coating are very durable. They offer great protection against wear and corrosion.

Consider the metal type. Also, consider the product’s use environment and your needs. These needs might be for durability or appearance.

Yes, methods like powder coating are eco-friendly. They emit fewer harmful chemicals than traditional finishes.

Common methods include dipping for anodizing. Also, spraying for powder coating, and polishing by hand or machine for a shiny surface.

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