Mold Texture Design for Injection Molding: Principles and Case

In modern manufacturing, mold surface texture has become an important part of product quality control. Precision surface treatment technology can not only enhance the visual effect of the product, but also significantly improve its functional characteristics.

In addition to improving aesthetics, surface texture also affects the functionality of the product. Texture can reduce glare, hide defects, and improve wear resistance. Therefore, manufacturers must determine the optimal texture solution based on the specific application scenario of the product, taking into account material properties, production costs, and performance requirements.

To help you better understand this key aspect of mold design, we have put together a practical introduction to mold textures. In the following sections, we will explain the types of surface texture processes, and the specific application scenarios of different surface textures.

What is Surface Texture?

To help you better understand this key aspect of mold design, we have put together a practical introduction to mold textures. In the following sections, we will explain why surface texture is important, the types of surface texture processes, and the specific application scenarios of different surface textures.

Important parameters of Surface Texture

Lay

Lay describes the main direction of the surface pattern, which is mainly determined by the specific processing technology. For example, milling will produce a striped texture parallel to the tool movement path. Sanding will form a scratch pattern that is consistent with the direction of the sandpaper movement.

Roughness

Surface roughness reflects the degree of unevenness of the surface. A surface roughness of Ra 0.8 μm is generally considered smooth, while a surface roughness of Ra 3.2 μm is significantly rougher and is usually used for matte treatment.

Waviness

The periodic fluctuations caused by equipment vibration or process parameter fluctuations when the machine tool moves in a large area. A typical example is that when a CNC machining center is cutting at high speed, the tiny vibration of the spindle will leave characteristic wavy marks on the workpiece surface. Its wavelength is usually in the range of 0.8-25 mm.

Why Is Mold Texture So Important?

Surface Texture of an object can make a product more user-friendly. It’s not just about appearance; it has practical advantages. For instance, it can make medical devices easier to grip and more non-slip, and it can make beautiful packaging feel smooth and comfortable to the touch. Additionally, it can also show brand characteristics through special patterns.

Main Methods for Creating Mold Textures

Let’s now take a look at the three main methods used to create mold surface textures:

1. Polishing

Use abrasive paste, sandpaper, polishing wheel and other tools to mechanically finish the mold surface to make the surface smooth to mirror level.

Features

• ● The surface can be highly smooth (such as SPI A1).
• ● Remove tiny scratches and processing marks to improve the overall quality of the mold.

Impact on Finished Products

• ● Make the surface of the injection molded part present a mirror or high-gloss effect, with clear vision and strong gloss.
• ● Suitable for transparent parts (such as lenses, lampshades) or products with high appearance requirements.
• ● High requirements for material fluidity during injection molding, and flow marks or air marks are prone to occur.

2. Sandblasting

Fine sand, glass beads and other particles are sprayed onto the mold surface through high-pressure air to form a uniform fine concave and convex texture.

Features

• ● Frosted, matte and granular surface effects can be obtained.
• ● Effectively eliminate processing marks and improve surface consistency.

Impact on Finished Products

• ● The product surface presents a soft matte texture, non-reflective, and fingerprint-resistant.
• ● It can hide small defects and improve the overall appearance of the product.

3.EDM - Electrical Discharge Machining

Using high-frequency discharge between electrodes, high temperature is released on the mold surface, causing the metal to melt and vaporize to form a micro-pit texture.

Features

• ● It can form a uniform rough texture on the surface of hard steel molds.
• ● The texture has a certain depth and metallic feel, which is suitable for industrial style appearance.

Impact on Finished Products

• ● The surface presents a rough texture with a sense of "pitting", and the visual three-dimensional sense is strong.
• ● It is beneficial to improve the anti-slip and wear resistance of the product.
• ● When the material is filled, it is easy to leave residual gas in the texture, and the demolding and exhaust design need to be optimized.

SPI Surface Finish Standard

The SPI standard (Society of the Plastics Industry) is a widely used system for classifying mold surface finishes. It categorizes mold polish levels into four main groups — A, B, C, and D, each with three grades (A1–D3). This standard ensures consistent surface quality for molded plastic parts and helps manufacturers align on finish expectations.

High-Gloss Mirror Finish (A1–A3)

Achieved through diamond polishing, this finish delivers a flawless, mirror-like surface with maximum gloss.

Semi-Gloss Finish (B1–B3)

Polished with fine sandpaper to create a smooth but less reflective surface than Grade A.

Matte Finish (C1–C3)

Created using sandpaper, this finish produces a low-gloss, slightly rough texture.

Textured Finish (D1–D3)

Applied using sand blasting, this finish results in a rough, non-reflective texture.

Application Case

Anti-slip Texture for Insulin Pen Housing

The finely textured mold surface creates a controlled micro-roughness on the outside of the pen body, improving operational safety and providing a comfortable grip. This special texture design prevents slipping during critical injections.

VR Headset Matte Surface

Sandblasted mold texture creates a uniform matte effect on the headset housing, eliminating reflections and fingerprint residue.

Car dashboard Mirror Polish

The high-polished mold surface uses diamond polishing to create a superior mirror effect for dashboard components. The precisely controlled surface topography elegantly reflects ambient light while maintaining scratch resistance.

Conclusion

The texture of the mold surface is critical to the production of injection molded parts. This article briefly introduces the details of texture processing and surface finish standards, which are necessary factors to consider when selecting mold texture.

If you choose to work with an experienced injection molding company, it will undoubtedly speed up your product to the market. LVMA's experts have systematic knowledge of SPI surface standards and surface treatment processes, and you can rely on our ability to help you determine the ideal surface texture that meets your quality goals.