SPI Injection Mold Surface Finishes

Table of Contents

SPI Injection Mold Surface Finishes

SPI injection mold surface finishes is a widely recognized classification system used in the plastics industry to define the surface finishes for injection molded parts. SPI stands for the Society of the Plastics Industry, an organization that has developed these standards to ensure consistency, quality, and performance across the industry.

The surface finishes play a crucial role in determining the final appearance and functionality of a molded part. The SPI has categorized the surface finishes into four main groups: Category A – High-Gloss Finishes, Category B – Semi-Gloss Finishes, Category C – Matte Finishes and Category D – Textured Finishes. Each category represents a specific range of finishes, from high-gloss to textured surfaces, catering to different product requirements.

SPI surface finish chart

SPI FinishManufacturing MethodSurface Roughness RaTypical Application
A1Grade #3 Diamond0.012-0.025Mirror Polish
A2Grade #6 Diamond0.025-0.05High Gloss Polish
A3Grade #15 Diamond0.05-0.1Normal Gloss Polish
B1600 Grit Paper0.05-0.1Fine Semi Glossy Finish
B2400 Grit Paper0.1-0.15Medium Semi Glossy Finish
B3320 Grit Paper0.28-0.32Normal Semi Glossy Finish
C1600 Grit Stone0.35-0.4Fine Matte Finish
C2400 Grit Stone0.45-0.55Medium Matte Finish
C3320 Grit Stone0.63-0.70Normal Matt Finish
D1 #11 Glass Bead0.8-1.0Satin Textured Finish
D2#240 Aluminum Oxide Blast1.0-2.8Dry Textured Finish
D3#24 Aluminum Oxide Blast3.2-18Rough Texture Surface

SPI injection mold surface finish standard specifies an machined surface finish with a typical surface roughness of Ra 3.2 as visible machining marks.

What is the right material for each SPI surface finish?

The outcome of SPI mold finishes can vary based on the material utilized in the injection molding process for components. The following tables provide guidance on choosing the appropriate mold finish and materials tailored to your specific application requirements.

SPI A1AverageAverageXAverageAverageExcellentXX
SPI A2AverageGoodAverageAverageAverageExcellentAverageX
SPI A3GoodExcellentAverageGoodGoodExcellentAverageX
SPI B1GoodGoodGoodExcellentGoodGoodGoodX
SPI B2GoodGoodGoodExcellentExcellentGoodGoodAverage
SPI B3ExcellentAverageExcellentExcellentExcellentGoodExcellentAverage
SPI C1ExcellentAverageExcellentExcellentExcellentGoodExcellentGood
SPI C2ExcellentXExcellentExcellentExcellentGoodExcellentGood
SPI C3ExcellentXExcellentExcellentExcellentGoodExcellentGood
SPI D1ExcellentExcellentExcellentExcellentExcellentAverageExcellentExcellent
SPI D2ExcellentXExcellentExcellentExcellentAverageExcellentExcellent
SPI D3GoodXExcellentGoodGoodAverageExcellentGood

How to choose the best SPI surface finishes for your injection molded part?

Choosing the best SPI surface finish for your injection molded part involves considering various factors related to the material, product requirements, and manufacturing process. Here’s a step-by-step guide to help you select the ideal SPI surface finish for your injection molded part:

1. Define your product requirements:

Consider the desired appearance, functionality, and performance of your final product. Ask yourself the following questions:

What aesthetic qualities are important for your product (e.g., high-gloss, semi-gloss, matte or textured appearance)?
How will the surface finish impact the product’s performance, such as wear resistance, grip, or light transmission?
Are there any industry-specific standards or regulations that dictate the surface finish for your product?

2. Understand the material properties:

Research the material you plan to use for your injection molded part. Consider its mechanical, thermal, and chemical properties, as well as how it responds to different surface finishes. Some materials may be more suitable for high-gloss finishes, while others may work better with textured finishes.

3. Consult with your mold manufacturer or design engineer:

Discuss your product requirements and material properties with an expert in the field. They can provide valuable insights and recommendations on the most suitable SPI surface finish based on their experience and expertise.

4. Evaluate manufacturing constraints:

Consider any limitations or constraints in your manufacturing process that could influence your choice of surface finish. For example, certain finishes may require additional processing steps, increasing the overall production cost.

5. Assess cost implications:

Analyze the cost implications of your chosen surface finish. More complex finishes, such as high-gloss or textured surfaces, may require additional processing steps and increase the overall production cost. Determine if the added expense is justified by the benefits provided by the chosen finish.

6. Review and finalize:

After considering all the factors mentioned above, review your selection and make any necessary adjustments. Ensure that your chosen SPI surface finish meets your product requirements, material properties, manufacturing constraints, and cost considerations.

By following these steps and consulting with experts in the field, you can confidently choose the best SPI surface finish for your injection molded part, ensuring a high-quality final product that meets your desired aesthetic and functional needs.