Selecting the Right Plastic Injection Molding Surface Finish
Parts made from injection molding have the potential to have several surface finishes. The main reasons include aesthetic and functional purposes. This affects the parts’ texture, feel, and look. Designers should figure out the choice of surface finish early in the initial stages of the projects. The reasons are because the choice has a lot of influence on the tooling options. Changing the surface finish option later will delay the whole project further. At Creatingway, we noted that a rougher finish needs a higher draft angle for easy ejection from the mold. Also, the material used influences the type of finish.
Therefore, to get the right finish, you need to consider several factors. Here is a highlight of how to determine the right finish for the plastic molding injected part.
What are the Types of Injection Molding Finishes?
The plastic industry has standards for surface finishes and features. The cosmetic quality of the plastic surface determines the standard. A total of 12 grades of plastic surface finishes exist. However, the grades exist in 4 categories.
Smooth and Glossy Finish
We recommend the SPI grades A1, A2, and A3 for a smoother and glossier finish. We involve the use of hardened steel mold. Fine diamond powder buffs the steel mold to enhance the effect. Using these techniques, we can achieve a mirror-like finish on the injection mold parts. Products like plastic mirrors, visors, and optical goods benefit from these types of finishes.
A lower level than the glossy finish is the semi-glossy finish. Grades B1, B2, and B3 achieve the finish with hardened tool steel with a sheen on the surface. We polish the mold surface using emery cloth or ultra-fine grit sandpaper to get the sheen. This finish is great for concealing tooling, machining, and molding marks on plastic products.
The matte finish is one of the most used surface finishes. SPI grades this finish into C1, C2, and C3. We used mold tools polished by fine stone powder to achieve a matte finish. The finish is great for providing an aesthetic appearance to die-cast and industrial parts. Additionally, the finish masks machining marks.
The textured finish is the last surface finishing type. SPI grades the finish into D1, D2, and D3. To achieve a textured finish on a mold, we smoothen the mold surface using fine stone powder. Then, we dry blast using aluminum oxide. Alternatively, we could bead blast to get the same effect. A textured finish provides the plastic surface with good grip and masks fingerprint smudges. Additionally, the finish also hides marks and deformations that might occur.
Injection Molding Process Effect on Surface Finish
At Creatingway, we recommend constant communication between the design engineer and the injection molder. This tip will ensure you get an optimal surface finish for every product made. The chemical make-up of the material affects the surface finish option. Designers should also put other factors into consideration when picking an option. Further, a combination of certain factors improves or achieves a specific type of finish.
Choice of Material
The material used in injection molding has different chemical and physical properties. Factors such as melting temperature play a part in delivering a certain type of surface finish. For instance, you can get a glossy finish using crystalline resin that has a high melt temperature. The material has a reduced roughness level and an increased gloss effect on the part.
The mold used in injection molding, to a certain degree, affects the surface finish. Simply polishing the mold surface is not enough to achieve a high gloss level. Factors such as mold design, molding conditions, and mold material affect the quality of finish. For instance, a glossy finish needs a mold tool made from steel. Additionally, the steel tool should have a high degree of hardness.
Injection Velocity and Temperature
The speed at which we inject the molten material affects the surface finish. One can get a glossy finish with high-speed injection. A faster filling into the mold cavity also reduces the visibility of the weld lines. Additionally, the technique improves the overall appearance of the surface finish.
What’re the Reasons for Different Finishes?
During manufacturing, function aspects of the product control the final choice of surface finish. The surface finish has a role in enhancing the functionality of the product made. For instance, a textured finish improves the grip of a product. Also, when you desire more adhesion, the same finish works great. A textured finish also adds strength and enhances the safety levels of the part.
Often, a plastic product needs a specific type of surface finish to improve the feel and look of the product. A product that has a great finish usually attracts the potential customer’s attention. People tend to associate the perceived value of a good based on how the quality of finish. For instance, a matte finish can hide most imperfections associated with injection molding. This translates to an overall better-looking plastic product. Contact Creatingway today to get the most out of your plastic injection molded parts.
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