Most injection-molded products go through an added step of surface texturing before they are ready for the market. The uses of a mold texture extend far beyond enhancing the look and feel of a product.
They also influence the longevity and functionalities of the product, like impact-resistance, surface adhesion, and friction. So, the choice of mold texture can make or break your product in the market.
As there are so many types of mold textures, selecting the ideal finish can be challenging.
In this guide, we delve into the benefits of surface textures, the different types of finishes available, and things to consider before selecting the right mold texture for your product.
What is Meant by Surface Texture?
Texturing in injection molding refers to the creation of a pattern on the surface of the molded product. Every part created will have some texture imprinted on the surface by the tools used in the injection molding process. It is a result of many factors, such as roughness, waviness, lay, and flaw.
In this regard, the topography of the 3D product will be modified with geometrical characteristics. Surface textures alter the visual appeal as well as the usability of the product.
How Does Surface Texturing Work for Plastic Injection Molding?
In injection molding, the required surface texture for the product is applied to the metal mold itself. The effect will be transferred to the plastic part during the molding process. Therefore, secondary finishing is not available for thermoplastics, unlike metal products.
Advantages of Mold Surface Textures
Improves the External Appearance
Mold surface textures help manufacturers reduce imperfections on the product’s surface created during the molding process.
They are great for covering dents, flow creases, parting lines, shadow markings, and sink marks. They enhance the aesthetics of the product and make it look more attractive to the user.
Makes the Product User-Friendly
A textured finish on the product increases the grip and slip resistance, allowing the user to handle the product with ease. It will contribute to the safety and usability of the product. These characteristics are vital for the optimum functionality of the product.
Enhances Durability and Strength
Mold surface textures increase the friction and abrasion resistance of the product. It will improve the fatigue strength of the part, making it more resilient to impact.
Also, a degree of roughness on the surface will prevent the product from being damaged during shipping and also reduce the appearance of fingerprints.
Different Types of Mold Surface Textures
Let’s take a look at the various mold textures categorized based on the method.
Mold Surface Textures Made by Polishing
Polishing is a high-grade surface finish that gives a smooth and reflective surface to the product, making it appear bright and attractive.
It is ideal for parts for which aesthetics play a huge role and for products that can be cleaned easily. A variety of methods, like rotary tools, wool wheels, and whetstone strips, are used for sanding and polishing the surface.
Some polishing techniques used in the injection molding process include chemical mold polishing, magnetic mold polishing, fluid mold polishing, and electrolyte mold polishing.
It’s noteworthy that the final result also depends on the plastic material.
Mold Surface Textures Made with Sandpaper
Finishes done with sandpaper fall under category B and give a semi-gloss appearance to the product. The texture is more prominent compared to polishing as the back-and-forth movement of the technique leaves linear scratch marks.
Sandpaper texturing is ideal for concealing machining marks well and is a cost-effective choice than polishing.
Although with marks, it offers a very smooth and attractive finish. Grit sizes used for sanding purposes range from 320 to 600.
Mold Surface Textures Made with Grit Stone
Textures made with grit stone are a category C finish, and they help manufacturers achieve a matte finish. The grit size used for this technique ranges from 600 to 320, and the process is more aggressive than sanding. Therefore, the surface is rougher and less flat.
SPI matte finishes are for hiding molding marks, and the surface usually has a muted or subdued look. The lack of a glossy appearance is also useful for hiding fingerprints. For this reason, it is ideal for consumer products handled regularly.
Mold Surface Textures Made by Blasting
Abrasive blasting made using sand or glass beads is similar to a category D finish and results in a rough, dull, and even surface.
The process involves shooting fine-sized glass beads from a machine to the material’s surface at high pressure. It polishes and roughens the surface.
The nature of the blastic and spraying process delivers a non-directional finish. It masks imperfections to a great extent. It also increases the durability and hardness of the product. Bead blasting is also a technique ideal for delicate parts.
Mold Surface Textures Made with EDM
Electronic Discharge Machining (EDM) is a heat-based process. It converts electrical energy to thermal energy with the use of a graphite or copper electrode. The process melts and removes particles from the surface, giving a polished finish.
EDM process also helps in achieving the required cuts and holes, especially complex features that are difficult to do with traditional methods. With no directionality, it delivers a flawless finish despite the material’s toughness.
The EDM technique can differ based on the expected result and the material of the product. Also, it is only ideal for materials that conduct electricity.
Mold Surface Textures Made with Satin
The satin finish is suitable for masking weld lines and other imperfections on hard materials. It is a quick approach for flat surfaces and a more long-lasting option than a bead-blasting finish.
The satin finish process uses abrasive belts or brushes to achieve the required texture and results in a muted appeal.
SPI Surface Finish Standard
SPI (Society for Plastic Industry) has a set of standardized finishes for injection molded plastic units. SPI finishes set by the Society for Plastic Industry is a global standard for injection-molded plastic units.
They consist of 12 standardized finishes categorized into four main groups.
The result of these finishes primarily depends on the materials used, and it is paramount to select the right finish for your requirement. Let’s take a look at the main categories of SPI mold finishes.
Shiny Finish
Grade A category includes high-gloss and glossy finishes usually achieved from the method of diamond buffing. They deliver a high-quality, smooth, and attractive result. Shiny finishes are the most expensive because they require time and precision for a flawless result.
We use a rotary tool and fine-grain diamond buffing paste for the purpose. As the tool moves in random directions, the texture is unclear and leads to a reflective surface.
There’s A-1 (super high-gloss), A-2 (high gloss), and A-3 (glossy), and you can achieve the required finish using different grades of diamond buff. Shiny finishes are ideal for creating visually attractive parts.
Semi-Gloss Finish
Grade B category includes semi-reflective finishes that are ideal for hiding minor imperfections on the surface of the product. The grit size of the sandpaper will determine the degree of gloss.
As the sandpaper is brushed on the surface in a linear motion, semi-gloss finish surfaces have some linear patterned texture on them.
Semi-gloss finishes are relatively cheaper than high gloss finishes.There’s B-1 (fine semi-gloss), B-2 (medium semi-gloss), and B-3 (normal semi-gloss). As there’s some sheen, the texture is still attractive but not very eye-catching.
Matte Finish
Grade C category includes muted finishes and is one of the most preferred choices for many consumer and commercial products. You can achieve the matte surface texture by polishing the steel molds with grit sanding stones.
The degree of roughness depends on the grit size used, and a higher size results in a rougher surface. There’s C-1 (fine matte), C-2 (medium matte), and C-3 (normal matte) in this category.
Matte finishes don’t reflect light well and hide imperfections well. It also doesn’t scratch easily, making it one of the low maintenance options. It is an economical choice for making your plastic component look better.
Textured Finish
Grade D category includes textured finishes that make the surface appear dull and rougher than previous options. However, this type of finish can make the product durable, scratch-resistant, and easy to use due to the non-slip surface.
Textured finishes require abrasive pressure blasting techniques. The surface smoothened by stone powder is blasted with glass beads or aluminum oxide.
Textured finishes often have non-directional patterns and are available in D-1 (satin textured finish), D-2 (dull textured finish), and D-3 (rough textured finish) grades. They are also excellent at hiding deformations visible on the surface.
Factors to Consider While Deciding Mold Surface Textures
Aesthetics and Functionality
The surface finish grade you choose highly depends on the expected visual appeal of the product. For example, if the aesthetics of the product play a big role, manufacturers go for high gloss or semi-gloss finishes. These surfaces are also easy to clean as they are very smooth.
On the other hand, if you want to improve the friction of the product and its durability, a more abrasive surface with a textured finish is ideal.
It’s vital to consider both the appearance and functionality of the product and select the finish grade that will optimize each.
Material Choice
The result of the surface finish will also depend on the material. That is to say, not all thermoplastics guarantee the same quality of finish due to their varying degree of hardness, melting points, and other characteristics.
For example, acrylic is considered excellent for products with high gloss finish, while HDPE is one that’s not recommended as they are opaque in color and soft in nature. Similarly, ABS is an excellent choice for matte or textured surfaces because the hardness can resist impact well.
We highly recommend you consult with your manufacturer before making a decision.
Temperature & Injection Speed
A low injection speed will often result in flow lines, weld lines, and other surface imperfections, and in such a case, a high gloss finish is difficult to achieve. A quick fill will reduce the appearance of weld lines and produce a better-looking product because the plastic cures evenly.
Also, the mold temperature will dictate the cooling time and the level of stress within the product. A higher mold temperature and a high injection speed will result in a glossier and smoother finish.
A low mold temperature and low speed may sometimes be necessary to achieve other product requirements. But they result in a rougher surface.
Kemal Your Plastic Prototype Manufacturing Service Provider
If you are looking for a reliable manufacturing company offering high-quality injection molding and post-processing solutions, look no further. Kemal is one of the top manufacturers in China, with over a decade of expertise in injection molding.
Our specialty is not just about offering high-quality services. We also help our clients select the right material, technology, and mold texture for their requirements. Our team has in-depth knowledge of plastic prototyping and high-volume manufacturing solutions.
We are aware of the many challenges businesses face when customizing plastic parts and can help you successfully navigate these issues. With Kemal, an amazing customer experience is a promise!
FAQs
Conclusion
We hope our guide on mold textures helped you understand the different types of finishes available for plastic injection-molded products. It’s vital to consider the pros and cons of each finish and the material used for your part before selecting the mold texture.
Designing a textured mold is a complex process, and we highly recommend you consult an expert manufacturing company to ensure you have a flawless mold for a foolproof output.
