Surface Finishing Service

One-stop surface finishes solution for plastic and metal parts with both functional performance and aesthetic appeal.

Mold surface finishing: Compliant with SPI, VDI, and Mold-Tech standards

Secondary surface treatment: Polishing, beadblasting, coating, Brushing etc.

Injection Mold Surface Finishing Standards

Zhongde provides comprehensive mold surface finishing services, offering all standard finishing options. These finishes range from glossy and matte to textured or patterned surfaces. The texture or polish of the mold cavity is directly reflected on the molded part’s surface. For example, a mold surface that is polished to be reflective will make a reflective (or transparent) part.

Mold finishes differ from CNC machined parts or 3D printed parts, where each component is treated individually. Adding a finish or texture can change the tool’s price depending on the process required, but it does not alter the price of the individual parts.

Our standard mold finishing includes the following:

SPI Surface Finish
VDI Mold Finish
Mold-Tech Surface Finish

SPI vs VDI Surface Finishes

SPI Surface Finishing Standard

The SPI Surface Finish, or SPI Mold Finish, is a standard developed by the Society of the Plastics Industry (SPI) in the United States to classify plastic Injection mold surface textures based on their level of polish or roughness.

SPI A Finishes

SPI A-1

Diamond buffed with grade #3, 6000 grit for a highly polished finish. Also suitable for producing optically clear parts. Has an average surface roughness of 0.012-0.025µm Ra.

SPI A-2

Diamond buffed with grade #6, 3000 grit for a high polish finish. Also suitable for producing transparent parts. Has an average surface roughness of 0.025-0.050µm Ra.

SPI A-3

Diamond buffed with grade #15, 1200 grit for a high-to-medium polished finish. Also suitable for producing non-optical transparent parts. Has an average surface roughness of 0.050-0.100µm Ra.

SPI B Finishes

SPI B-1

A 600-grit sanded finish for a medium polish with a surface roughness of 0.05-0.10µm Ra.

SPI B-2

A 400-grit sanded finish for a medium polish with a surface roughness of 0.10-0.15µm Ra.

SPI B-3

A 320-grit sanded finish for a medium-to-low polish with a surface roughness of 0.28-0.32µm Ra.

SPI C Finishes

SPI C-1

A 600 stone finish for a low polish with a surface roughness of 0.35-.40µm Ra.

SPI C-2

A 400 stone finish for a low polish with a surface roughness of 0.45-.55µm Ra.

SPI C-3

A 320 stone finish for a low polish with a surface roughness of 0.63-.70µm Ra.

SPI D Finishes

SPI D-1

Dry blasted with glass bead for a satin finish with a surface roughness of 0.80-1.00µm Ra.

SPI D-2

Dry blasted with #240 oxide for a dull finish with a surface roughness of 1.00-2.80µm Ra.

SPI D-3

Dry blasted with #24 oxide for a dull finish with a surface roughness of 3.20-18.00µm Ra.

VDI Surface Finishing Standard

VDI 3400 Surface Finish (also known as VDI Surface Finish) refers to the mold texture standard developed by Verein Deutscher Ingenieure (VDI), the Society of German Engineers. It defines the surface textures produced by EDM during mold manufacturing.
Widely used as an international standard for matte mold surfaces, VDI 3400 provides textures ranging from fine to coarse, depending on the selected VDI number.

VDI (EMD) Finishes

VDI 12

A 600 stone low-polish finish with an average surface roughness of 0.40µm Ra.

VDI 15
A 400 stone low-polish finish with an average surface roughness of 0.56µm Ra.

VDI 18

A glass bead blast satin finish with an average surface roughness of 0.80µm Ra.

VDI 21

A #240 oxide dry blast dull finish with an average surface roughness of 1.12µm Ra.

VDI 24

A #240 oxide dry blast dull finish with an average surface roughness of 1.60µm Ra.

VDI 27

A #240 oxide dry blast dull finish with an average surface roughness of 2.24µm Ra.

VDI 30

A #24 oxide dry blast dull finish with an average surface roughness of 3.15µm Ra.

VDI 33

A #24 oxide dry blast dull finish with an average surface roughness of 4.50µm Ra.

VDI 36

A #24 oxide dry blast dull finish with an average surface roughness of 6.30µm Ra.

VDI 39

A #24 oxide dry blast dull finish with an average surface roughness of 9.00µm Ra.

VDI 42

A #24 oxide dry blast dull finish with an average surface roughness of 12.50µm Ra.

VDI 45

A #24 oxide dry blast dull finish with an average surface roughness of 18.00µm Ra.

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Secondary Surface Finishing

Zhongde's post-processing process can improve the appearance, durability and functionality of parts, and achieve visual or performance effects that cannot be achieved by mold texture alone. Here is a list of optional super surface finishing.

As Machined

For as machined all sharp edges are removed and parts are deburred. Tool marks are visible.

Smoothing

A finishing CNC machining operation can be applied to the part to reduce its surface roughness. Machine marks are less evident but still visible.

Material Compatibility: All plastic and metals

Bead Blasting

Bead blasting creates a uniform matte or satin finish on a machined part by removing tool marks. It is primarily used for visual purposes and is available in different grit levels, which indicate the size of the abrasive media.

Material compatibility: All metals

Powder Coating

Powder coating is a strong, wear-resistant finish that is compatible with all metal materials and can be combined with bead blasting to create parts with smooth and uniform surfaces and excellent corrosion resistance.

Material compatibility: All metals

Anodizing Color (Type II)

Ordinary decorative anodizing offers corrosion resistance and a choice of colors. It's primarily used for exterior design or lightly protective parts.

Material compatibility: Aluminum alloys

Anodizing Hardcoat (Type III)

High-hardness anodizing significantly improves wear and corrosion resistance and is suitable for functional parts or mechanical components.

Material compatibility: Aluminum alloys

Electropolishing

Electropolishing is an electrochemical process used to polish, passivate and deburr metal parts. It is useful to reduce surface roughness.

Material compatibility: All metals

Black Oxide

Black oxide is a conversion coating used to improve corrosion resistance and minimize light reflection.

Material compatibility: Stainless steel and copper alloys

Chromate Conversion Coating (Alodine/Chemfilm)

Chromate conversion coating is used to increase the corrosion resistance of metal alloys while maintaining their conductive properties.

Material compatibility: Aluminum and copper alloys

chromate conversion coating surface finishing

Brushing

Brushing is produced by polishing the metal with grit resulting in a unidirectional satin finish. Not advisable for applications where corrosion resistance is required.

Material compatibility: All metals

FAQs of Plastic & Metal Surface Finishing

View our FAQ for more questions.

How can I choose the right surface finish for my part?

Different finishes serve different purposes, some improve appearance, while others enhance wear or corrosion resistance. Our engineers can recommend the best option based on your material and application.

Can I apply multiple finishing processes to one part?

Yes. For example, bead blasting can be followed by anodizing or painting to improve both appearance and durability.

Can you match a specific texture or gloss level from a reference sample?

Absolutely. You can send us your sample or surface reference, and we’ll reproduce the finish according to SPI, VDI, or custom standards.

Does surface finishing affect the final dimensions or tolerances?

Yes, some processes (like plating or powder coating) slightly increase surface thickness. We account for this during DFM and machining to ensure final tolerance accuracy.

Can complex-shaped parts be surface-treated uniformly?

Yes, but some processes (like plating or anodizing) may require special fixturing to ensure even coverage on internal or deep areas.

Do you offer surface finishing as part of the production process?

Yes. We integrate finishing into our molding and machining workflow, so you receive fully finished parts without outsourcing.

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