Injection Molding Surface Finish Standards: Get Quality Product

Injection Molding Surface Finish Standards Get Quality Product

Injection Molding Surface Finish Standards play a critical role in producing high-quality plastic parts. Surface finish determines the final appearance and performance of the molded product, making it essential to understand the standards and specifications required for a particular application. Whether it’s enhancing the aesthetic appeal of a product, improving its grip, or reducing friction, the right surface finish can make all the difference. In this article, I will explore the different types of surface finishes used in injection molding, their specifications, and how to choose the right surface finish to ensure that you get a quality product. So, let’s dive into the world of injection molding surface finish standards and discover how they can help you achieve your desired product outcome.

What Is Injection Molding Surface Finish?

Injection molding surface finish refers to the final appearance and texture of a plastic part that is produced through the injection molding process. The surface finish of an injection molded part is critical because it can affect its functionality, aesthetics, and durability.

There are several factors that can affect the surface finish of an injection molded part, including the type of plastic material used, the temperature and pressure of the injection molding process, and the design of the mold. Different surface finishes can be achieved by altering these factors, and they can range from a high gloss, mirror-like finish to a matte or textured surface.

Why Do You Need to Use Surface Finishes in Molding Surfaces?

Surface finishes are used in molding surfaces for several important reasons:

1. Aesthetic Appeal:

The surface finish of a molded part can greatly affect its appearance and overall aesthetic appeal. By using surface finishes, manufacturers can create parts that are highly polished, textured, or have a specific color or finish that enhances their appearance.

2. Functional Requirements:

Surface finishes can also be used to meet specific functional requirements of the part. Suppose, a highly polished surface can improve the part’s wear resistance and reduce friction, while a textured surface can improve grip or help hide scratches and other imperfections. 

3. Mold Release:

A surface finish can help the molded part release easily from the mold surface, reducing the risk of damage or defects. Surface finishes can also help prevent the buildup of residue or debris on the mold surface, which can impact the quality of subsequent parts.

4. Consistency and Quality Control:

By using consistent surface finishes, manufacturers can ensure that each part is produced to the same level of quality, with the same surface characteristics and appearance.

The use of surface finishes in molding surfaces is critical to achieving high-quality, functional, and aesthetically pleasing molded parts. By carefully selecting the appropriate surface finish and applying it consistently, manufacturers can improve the performance, durability, and overall value of their molded parts.

Specifications of Tools Used in Injection Molding Surface

Injection molding surface finishes are created using various types of tools, each of which has its own specifications. The two main types of tools used in injection molding surface finishes are the Society of the Plastics Industry (SPI) tool and the Verein Deutscher Ingenieure (VDI) tool.

The SPI tool is widely used in North America and Asia and has four grades of surface finishes. The VDI tool is used in Europe and has 27 grades of surface finishes.

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What You Should Consider When Choosing Injection Molding Surface Finish Tools?

The tools used in the injection molding surfaces typically include the mold and any auxiliary equipment required to control the temperature, pressure, and flow of the plastic material during the molding process. The specifications of these tools will depend on the specific requirements of the molding project, including the size and complexity of the part, the type of plastic material being used, and the desired surface finish. Some of the key specifications of injection molding tools include:

1. Mold Material

The mold is typically made of steel or aluminum, and the specific material used will depend on the requirements of the project. Steel molds are more durable and can withstand higher temperatures and pressures, making them suitable for high-volume production runs. Aluminum molds are less expensive and easier to machine, making them a good choice for smaller production runs or prototypes.

2. Mold Cavities

The mold cavity is part of the mold that shapes the plastic material into the desired part. The number of cavities will depend on the desired production volume and the size of the part. A mold with multiple cavities can produce multiple parts simultaneously, increasing production efficiency.

3. Temperature Control

Temperature control is critical to ensuring that the plastic material flows evenly and solidifies correctly. The mold may be equipped with heating or cooling elements to control the temperature of the mold surface and the plastic material.

4. Pressure Control

Pressure control is used to ensure that the plastic material fills the mold completely and evenly. The injection molding machine may be equipped with hydraulic or pneumatic pressure control systems to ensure consistent pressure throughout the molding process.

5. Injection Speed Control

Injection speed control is used to ensure that the plastic material flows into the mold cavity at the desired rate. The injection molding machine may be equipped with a variable speed control system to adjust the injection speed as needed.

The specifications of the tools used in the injection molding surfaces will depend on the specific requirements of the project and the desired outcome. Careful consideration of these specifications is critical to achieving high-quality, consistent, and efficient production of molded parts.

Some SPI Injection Molding Surface Finishes

1. Gloss Finish/ Diamond Finish (Grade A):

This finish is characterized by a mirror-like appearance, with no visible texture. It is often used for high-end consumer products such as mobile phones, laptops, and automotive parts.

Surface FinishSPI StandardFinishing MethodSurface Roughness
Ra-um (mil)
Super High Glossy finishA-1Grade #3, 6000 Grit Diamond Buff0.012 – 0.025
( 0.5 – 1)
High Glossy FinishA-2Grade #6, 3000 Grit Diamond Buff0.025 – 0.05
(1 – 2)
Normal Glossy finishA-3Grade #15, 1200 Grit Diamond Buff0.05 – 0.1
(2 – 4)

2. Semi-Gloss Finish (Grade B):

This finish has a slightly lower gloss level than the Grade A finish and is characterized by a smooth surface with no visible texture. It is often used for consumer products such as home appliances and electronic devices.


SPI standard

Finishing Method
Fine Semi-glossy finishB-1600 Grit sandpaper paper
Medium Semi-glossy finishB-2400 Grit sandpaper paper
Normal Semi-glossy finishB-3320 Grit sandpaper paper

3. Matte Finish (Grade C):

This finish has a low gloss level and is characterized by a fine texture that diffuses light. It is often used for products that require a non-reflective surface, such as camera housings and automotive interiors.

FinishSPI standardFinishing Method
Fine Matte finishC-1600 Grit sanding stones
Medium Matte finishC-2400 Grit sanding stones
Normal Matte finishC-3320 Grit sanding stones

4. Textured Finish (Grade D):

This finish has a visible texture and is often used for products that require a non-slip surface, such as tool handles and kitchen utensils.

FinishSPI standardMedium
Satin Textured finishD-1Dry Blast Glass Bead #11
pressure blasting
Dull Textured finishD-2Dry Blast #240 Oxide
pressure blasting
Rough Textured finishD-3Dry Blast #24 Oxide
pressure blasting

Some VDI Injection Molding Surface Finishes

Other VDI Surface Finishes: VDI surface finishes range from high-gloss finishes to rough textures, depending on the requirements of the product. VDI surface finishes are often used in automotive, electrical, and consumer products.

VDI ValueDescriptionApplicationsSurface roughness (Ra)-(µm)
12600 StoneLow polish parts0.4
15400 StoneLow polish parts0.56
18Dry Blast Glass BeadSatin finish0.8
21Dry Blast # 240 OxideDull finish1.12
24Dry Blast # 240 OxideDull finish1.6
27Dry Blast # 240 OxideDull finish2.24
30Dry Blast # 24 OxideDull finish3.15
33Dry Blast # 24 OxideDull finish4.5
36Dry Blast # 24 OxideDull finish6.3
39Dry Blast # 24 OxideDull finish9
42Dry Blast # 24 OxideDull finish12.5
45Dry Blast # 24 OxideDull finish18

What Should You Consider When Choosing Injection Molding Surface Finish?

When choosing an injection molding surface finish, there are several factors to consider.

The first factor is the type of material used in the molding process. Some materials, such as ABS and polycarbonate, are easier to mold than others and can produce a smoother surface finish. Other materials, such as nylon and polypropylene, may require a textured surface to improve grip and reduce slipping.

The second factor to consider is the application of the product. Products that are used in harsh environments or require high durability may require a rougher surface finish to improve strength and grip. Products that require a high aesthetic appeal may require a glossy or matte finish to enhance their appearance.

The third factor to consider is the cost. The surface finish can significantly impact the cost of the final product, so it is important to choose a finish that is cost-effective and provides the desired functionality and aesthetic appeal.


Injection molding surface finish standards are an important aspect of the injection molding process. The surface finish can significantly impact the appearance and performance of the final product, making it important to choose the appropriate finish for the application. Working with a qualified injection molding company can help ensure that the desired surface finish is achieved and that the final product meets the required specifications. By understanding the importance of injection molding surface finish standards and choosing the appropriate finish for your product, you can achieve a high-quality product that meets your requirements and exceeds customer expectations.