Maintaining injection molding surface finish standards is essential for producing high-quality products. In this blog post, I will take a look at the different surface finish standards that are available and the benefits of using them. I will also provide tips on how to choose the right surface finish for your injection molding project, as well as discuss some of the common problems that occur when using incorrect surface finishes. So if you’re looking to produce high-quality products, read on to learn about the different surface finish standards and how to choose the right one for your needs. So, let’s dive in.

Injection Molding Surface Finish Standards for Quality Molded parts

Why It is Important to Maintain Injection Molding Surface Finish Standards?

It is important to maintain injection molding surface finish standards to ensure that the final product has a smooth and uniform surface. This helps to improve the quality of the end product and reduce defects or inconsistencies. But the question is, Why is it important? Let’s put blink on it.

  • The surface of an injection molded part can be critical for its performance and durability. Having a smooth, uniform surface allows for better adhesion and bond strength between the material and the part. This increases the overall durability of the part and reduces the chances of breakdown or failure.
  • The poor surface finish can cause premature wear or degradation of components over time. 
  • Maintaining injection molding surface finish standards helps reduce manufacturing costs as each part made using high-quality materials will be more durable and cost-effective to produce.
  • Injection molding surface finish standards define the level of smoothness, luster, and other visual qualities of the surface of a part or piece of molded material. They help to ensure that the injected material is properly processed and prepared, resulting in a quality product that meets client expectations. 

4 Useful Tools to Maintain Injection Molding Surface Finish Standards

Mold Cleaner:

The mold cleaner is a chemical that helps maintain injection molding surface finish standards by removing impurities and residue from the surface of the plastic.

  • Injection molding involves heating material and forcing it into a cavity, which creates a part. As the material flows through the machine, impurities, and residues are left behind on the mold surface. Mold cleaner breaks down these compounds so they can be removed from the surface, leaving a smooth finish that is free of defects.
  • This prevents defects like scratches and cracks from occurring in the finished parts and ensures high-quality manufacturing.

Mold Temperature Control Unit:

Mold temperature control units use several different methods to maintain injection molding surface finish standards. These methods include regulation of the temperature of the mold, airflow, and the cooling system.

  • By controlling the temperature of the mold, this unit helps ensure that the plastic injected into the mold has the desired hardness and consistency.
  • Airflow is also controlled to ensure that an there is adequate oxygen supply to the plastic as it is being melted. 
  • This helps maintain a high-temperature gradient between the inside and outside of the mold, which helps to prevent defects in the finished part.

Solvent Cleaners:

  • They are useful in removing contaminants and impurities from the surface of the plastic. These contaminants can include minerals, oils, and other materials that can affect the appearance and performance of the resulting part.
  • The cleaners can also help to remove build-up and debris that can hinder the flow of plastic during injection molding processes.
  • The cleaners can help to prevent potential surface defects such as scratches or cracks from forming.

Solvent cleaners are an important tool for maintaining injection molding surface finish standards.

Abrasive Blasting Equipment:

  • The Abrasive blasting equipment helps to remove material defects from the part surface. 
  • The process of Abrasive blasting involves using a high-powered abrasive material to remove unwanted parts from the injection molding process.
  • This method is often used in cases where it is difficult or impossible to make surface improvements through other methods.
  • In many cases, this process can be used for both small and large parts with different tolerances and requirements.

Injection Molding SPI Surface Finishes You Can Follow

Diamond Finish (Grade A):

Diamond-like finish (DLC) is a surface-injection molding (SMI) process that produces a high-quality, durable, and scratch-resistant finish. It is created through the injection of a diamondized resin into the mold cavity. This process creates a surface that has an extremely smooth and glossy appearance with a high degree of durability and resistance to wear and tear.

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

Semi-Gloss Finish (Grade B):

This type of finish is often used on injection molded parts, as it provides an easy-to-clean, durable surface for the part. A semi-gloss finish is produced by applying a clear coating to the part during the injection molding process. The coating typically consists of a combination of lacquer and pigment (dyes). The lacquer component provides durability and adhesion while the pigments provide gloss and color. The result is a smooth, high-quality surface with good optical properties.

FinishSPI StandardFinishing Method
Fine Semi-Glossy FinishB-1600 Grit Sandpaper
Medium Semi-Glossy FinishB-2400 Grit Sandpaper
Normal Semi-Glossy FinishB-3320 Grit Sandpaper

Matte Finish (Grade C):

A Matte finish (Grade C) is a surface injection molding finish that consists of a combination of two types of polymers combined during the injection process. Polyethylene terephthalate (PET) and polyethylene glycol (PEG) form the base polymer while titanium dioxide and iron oxide are added to provide additional opacity. The resulting mixture has excellent scratch and slip resistance, good toughness, and low coefficients of friction. It also exhibits high hardness, which makes it suitable for use in applications where durability is necessary, such as in automotive parts or appliances.

FinishSPI StandardFinishing Method
Fine Matte FinishC-1600 Grit Sanding Stones
Medium Matte FinishC-2400 Grit Sanding Stones
Normal Matte FinishC-3320 Grit Sanding Stones

Textured Finish (Grade D):

Textured Finish (Grade D) is a surface finishing process that involves the injection of a polymer into a mold cavity and the out-pouring of the polymer as it solidifies. This process creates a surface with textures and patterns that can be used to give products a unique look. It is commonly used in injection molding and extrusion processes because it gives products enhanced durability, hardness, and strength.

FinishSPI StandardMedium
Sati 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

VDI Injection Molding  Surface Finish Standards

VDI injection molding is a type of manufacturing process that utilizes an automated machine to melt and inject plastic into a mold, forming the desired product. The resulting part has a smooth, solid surface with consistent color and texture. VDI injection molding is widely used in the manufacturing of household goods, industrial products, and consumer goods like toys and electronics. It offers several advantages over other manufacturing processes, including high quality, repeatable results, reduced waste, and low operating costs.

VDI ValueDescriptionApplicationSurface Roughness
12600 StoneLow Polish Parts0.40
15400 StoneLow Polish Parts0.56
18Dry Blast Glass BeadSatin Finish0.80
21Dry Blast #240 OxideDull Finish1.12
24Dry Blast #240 OxideDull Finish1.60
27Dry Blast #240 OxideDull Finish2.24
30Dry Blast #24 OxideDull Finish3.15
33Dry Blast #24 OxideDull Finish4.50
36Dry Blast #24 OxideDull Finish6.30
39Dry Blast #24 OxideDull Finish9.00
42Dry Blast #24 OxideDull Finish12.50
45Dry Blast #24 OxideDull Finish18.00

Which Issues You Must Consider for Choosing Injection Molding Surface Finish?

Choosing the injection molding surface finish is a critical decision because it can have a significant impact on the overall performance and durability of the part. Injection molding is a manufacturing process in which hot melted plastic is injected into a cavity formed by a tool (mold) and then allowed to cool and solidify. Depending on the type of plastic used, the resulting part can be a smooth, semi-rough, or rough surface. The surface finish of the finished part will determine how easily the material can be removed from the tool during production, as well as its durability and resistance to wear and tear. There are several factors to consider when choosing an injection molding surface finish. 

Type of Plastic:

Injection molding is typically used for thermosetting plastics, such as polyurethane foam or ABS. These plastics are specifically formulated to be heat-resistant and have a long shelf life. They also have increased rigidity and strength compared to more common thermoplastic materials like polyethylene or LDPE. On the other hand, thermoplastic plastics are more commonly used in injection molding, including HDPE (high-density polyethylene), PP (polypropylene), and PS (polystyrene). These plastics tend to be softer and more flexible, but they can still withstand high temperatures without melting or breaking down.

Plasticizer Type:

Different types of plasticizers are used in different types of thermoplastic plastics to adjust their characteristics for use in injection molding. Such as, low-molecular-weight (low-mols) compounds are often added to increase flexibility while high-molecular-weight (high-mols) compounds are often added to increase strength.

Part Size:

The size and shape of the part being molded will also affect the choice of finish. Parts that are small and lightweight, may be finished with a smoother surface to reduce resistance to removal from the tool during production. Conversely, large parts that are typically made out of more durable materials may require a rougher surface so they can withstand frequent use.

Material Properties:

Injection molding is often used to create parts with specific properties, such as glass-filled nylon or TPU (thermoplastic polyurethane). These materials are often very difficult to machine and require a finish that will protect them from corrosion and other environmental factors. Injection molding is a process that uses hot plastic to create small parts or products. The plastic is injected into the mold, which then shapes it using internal pressure and heat. This technique can be used to produce a wide variety of parts, from simple trinkets to complex biomedical devices.

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Injection Molding surface finish is one of the most important factors in the quality of a molded part. Injection Molding Surface Finish Standards ensure that all parts produced using injection molding have the same level of quality and meet specific requirements. By following these standards, you can ensure that all parts produced using injection molding have a smooth, clean, and consistent finish. This will help ensure that the part is easy to clean and maintain and that it meets your specific requirements for quality and performance. If you are looking to produce high-quality molded parts, be sure to follow the guidelines set by Injection Molding Surface Finish Standards for Quality Molded parts.