Your Experienced Surface Finishing Services

Why RapidDone Surface Finishing Services?

RapidDone is an experienced manufacturing supplier from China including material purchasing, machining, fabrication, and surface finishes services.

RapidDone has a good outsource team, make sure that we can work with excellent certified finishing suppliers in China. Those suppliers can work on all kinds of finishing services including anodizing, painting, powder painting at high quality at a reasonable price.

Over the years, we have done thousands of projects with a full range of manufacturing process that includes CNC machined parts, sheet metal parts, injection molding plastic parts, forging parts, and more. Those come with custom surface finishes for these parts. With such a rich manufacturing experience, we build up a professional team with specialized knowledge of finishes. Therefore, we can handle any finished requirements for our customers.

Color matching is an important parameter for finishing. At RapidDone, we have a good color mixing system that we can match any standard Pantone® or RGB color precisely.

No matter for prototyping projects or volume orders, we can work for you. If you need further info about finishes, feel free to contact us. We are pleased to serve our dear customers.

Complete FAQ Guild For Surface Finishing

Surface finishing is the final step and also an important step in the whole manufacturing process. Therefore, it is suggested to know some general information for the finishes if you want to involve the on-demand manufacturing industry.

Today in this guild will cover the basic things to help you in choosing a metal finishing process. So read on to learn more.

What Is The Definition Of Surface Finish?

As we know, there are three important callouts inside the formal engineering drawings. Besides dimensions and tolerances, surface finishing is the third callout that is a must parameter in the drawing.

Surface finish is also known as surface roughness or surface texture by machinists. Roughly speaking, it tells a distinct or desired look and feels for the surfaces. The measure of the overall texture is defined by the three parameters of surface roughness, lay, and waviness. In other words, an different surface finish means different values between these three characteristics.

The below diagram shows the relationship between Waviness, Lay, and Roughness.

What Is The Difference Between Ra And Rz?

Ra is calculated by using an averaging process. It calculates the average roughness in the area between the roughness profile and its center line on the entire surface within five sampling length.

Rz, on the other hand, measures, and averages the vertical distance from the highest peak to the lowest valley within five sampling lengths.

Therefore, there are two main difference points between Ra and Rz.

First, Ra is the most commonly used Surface Finish parameter all over the world, while Rz is only used wildly in Europe.

Secondly, extreme points have a smaller influence on the final results for Ra but a significant impact on the Rz measurement result.

What Is The Typical Finishing Methods At RapidDone?

There are numerous processes for surface finishes. As a professional prototyping expert, RapidDone needs to work on different projects with different finishing requirements, so we accumulate huge experiences and know well for them. We list the most common types below.

1. Anodizing Surface Finish

Anodizing finishing is a manufacturing process that creates a compact aluminum oxide film layer on the aluminum part surfaces. This layer enhances surface hardness and provides good corrosion, wear resistance,  and good cosmetics.

There are two kinds of subtypes including type II and type III anodizing. Type II anodizing can be created into clear and any other colors you need, the layer thickness varies from 4um to 25um. Type III anodizing, on the other hand, can create a thicker layer from 50 um to 125 um, but only clear color and black color are available.

Anodizing is the most popular finishing for aluminum parts in the manufacturing industry.

2. Painting

Painting finishing involves the process of spraying a paint layer onto the surface of the parts. This type of finish can supply millions of colors to be matched to any Pantone color number. Besides, the texture can range from matte to gloss based on your cosmetic requirements.

3. Printing And Etching

This is an ideal way to provide custom printing and logo marking on your parts.

In the printing process, there are silkscreen and pad printing. Both ask for custom stencil tools that are not expensive. The silkscreen is good for flat surface printing; Pad printing, on the other hand, is available for curved surfaces.

While etching does not ask for a tool, it uses the laser way to make the most precise and permanent marks on part surfaces. Therefore, it is more popular for rapid prototyping order due to the fast turnaround.

4. Sandblasting

Sandblasting adds a uniform matte or satin surface finish on a machined part by using the sandblasting machine, this can remove the tool marks, paint, rust. Depend on different sand particles, the texture can be created into different roughness from 36 grit to 320 grit.

After sandblasting, the surface is ready for a new paint job and renovation.

5. Glass Bead blasting

Bead blasting is similar to sandblasting but less aggressive, it typically uses glass beads instead of the other media. It also can be graded into different grits by indicating the size of the bombarding pellets.

6. Sanding Polishing

Sanding often involves a process of using hand sanding to polish the surface into a variety of grits for both plastic and metal surfaces.

This can be used for both panting prep and final surface finish such as brushed and satin surfaces. Therefore, sanding services are one of the most important polishes for a part manufacturing shop.

7. Vapor Polishing

Vapor polishing is a process that polishes plastic to be clear by using a chemical vapor way. This method is ideal for polycarbonate, acrylic, polysulfone, PEI, and ABS plastic material, it works well in the internal features of components, especially for the complex geometries surface that is hard to reach.

Compared to hand polishing or machine polishing, vapor polishing is a simpler and faster process. Therefore, vapor polishing is a cost-saving way to achieve optimal transparency.

8. Black Oxide Surface Treatment

The black oxide is a chemical conversion coating with black color. It is used to improve corrosion resistance that can be applied to a variety of industries.

9. Brushed Surface Finish

The bushing is a dull and matte polish that is made by polishing the metal with a fine bristle brush, the Surface roughness range from 0.8um to 1.5um.

This is a distinctive look that is often chosen for decorative items, but it is not suggested to be used in corrosion resistance applications as it is slightly more susceptible to corrosion.

10. Powder Coating

Powder coating finishing is a dry finishing process. It is used as protective and decorative finishes.

This finish is strong, wear-resistant for all metal materials, and reduces the risk of scratches, abrasions, corrosion, and other wear issues.

The powder coating color can be black and any RAL code or Pantone number. It is one of the most common types of paint application processes and wildly used in vehicle parts, household parts, aluminum extrusions.

11. Nickel Plating

Nickel plating is a manufacturing process that electroplates a thin nickel layer onto a metal object.

This nickel layer provides a combination of corrosion resistance and wears resistance. Besides, it also can be used for decorative purposes.

12. Heat Treatment

Heat treatment is is a process that heat and cool metals material. It can create a hard surface on relatively soft components and improve material properties.

What Is The Relative Surface Finish Roughness For Different Manufacturing Processes?

Surface Finishes vary tremendously by the different manufacturing processes. That means, different manufacturing process brings to a different finish roughness. Thus, it is important to choose a proper process that’s capable of achieving the desired surface finish you want. At RapidDone, we have an engineering team that can help you to choose the best finish solution when you work with us on a project.

Here’s a chart table showing the maximum and minimum Ra values of various manufacturing processes and is intended to be used as a general guideline.

• Grinding, lapping, buffing surface finish: Maximum Ra is 1.6um, Minimum Ra is 0.1um.
• CNC Machining: Maximum Ra is 6.3um, Minimum Ra is 0.8um.
• Wire EDM: Maximum Ra is 4.75um, Minimum Ra is 1.6um.
• Die casting: Maximum Ra is 1.6um, Minimum Ra is 0.8um.
• Forging: Maximum Ra is 1.25um, Minimum Ra is 3.2um.
• Reaming: Maximum Ra is 3.2um, Minimum Ra is 0.8um.

How To Choose The Surface Finishes Correctly For Your CNC Machined Part?

Finishing is an important process for part manufacturing. There are many finishing types, each method brings different surface performance, as well as different cost.

To choose the correct finishes for your machined part, first, we need to select the proper process to apply the layer to get the desired surface characteristic for your product. Besides, the selected solution should be cost-saving.

At RapidDone, some of the most typical treatments are as-machined, anodizing, bead blasting, and powder coating, and more.

Among them, “as-machined” is the finishing that comes straight off the machine with no additional treatment, the standard roughness is Ra 3.2um. Therefore this is the most cost-saving treatment and was strongly suggested to be used. As for others, it takes additional cost compared with as-machined, please reach out to our support team and we will be happy to help!

How to Measure And Test Surface Finish?

In general, surface texture refers to a lot of parameters such as profile, roughness, waviness and the lay direction, and more.

It is too complicated and unnecessary to measure all these parameters. To simplify, it is suggested to measure two of the most important parameters. These two parameters are the height of the roughness peaks and their separation, which is often referred to as “Ra” and “D”.

As for the measurement for “Ra” and “D”, it is suggested to use a Profilometer measure machine.

What Kinds Of Typical Surface Finish Standards Are There?

1. VDI 3400 Surface Finish

VDI 3400 surface finish is a texture standard that is set by Verein Deutscher Ingenieure from German, this is mainly processed by the mold machining industry. It was used in Germany in the beginning but now it spreads to the whole world.

2. SPI Surface Finish

This refers to a standard that specifies the mold finish ratings of the plastic injection molded parts in the United States. These finish call outs for the mold itself and not the finished part.

The whole chart includes twelve grades in four categories, they are Shiny Finishes(SPI-A1, A2, A3), Semi-Gloss Finishes(SPI-B1, B2, B3), Matte to Dull(SPI-C1, C2, C3), Texture(SPI-D1, D2, D3).

3. ISO 1302 Surface Finish

ISO 1302 refers to a complete indication of surface texture in technical product documentation, it is wildly used by all the countries in the world except the USA.

4. ASME Y14.36M Standard

This standard specifies the surface texture for solid materials, it is one of the most common standards in the United States.

Can You Make Powder Coating Surface Finishing Over Anodized Aluminum?

Yes, you can do that.

Anodizing is a great anti-corrosion coating, no need to worry about the adhesive force problem if you follow the below.
For new anodized aluminum, it is suggested to use a light sanding and acetone wipe for the surface, then you can apply powder coating process.
For the older anodized aluminum, we suggest using a harder abrasive blasting before your powder coating process.

How Do You Convert Grit Finish To Ra Finish?

As both grit and Ra are important parameters for surface roughness, there is some kind of relationship between them. Below is a table cross-referencing grit finishes with Ra finishes values.

Get Your Project Started Today

Have you found the type of finish you want? I think you surely do. If you still have any other special requirements, talk to our engineering team, we are sure to get the solution for you. Contact our finishing expert today to get your next project started.