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16/07/2024
SDI Finish vs. VDI Finish
Comparing SDI Finish vs. VDI Finish
In this article, we will compare SDI finish vs. VDI finish in injection moulding.
We will define what each type of finish is and how they differ. We will also explore the benefits associated with each, and we will examine the key factors that should be considered when deciding on an SDI finish vs. a VDI finish for your injection moulded parts.

VDI Finish
What is VDI Finish in Injection Moulding?
VDI Finish (Verein Deutscher Ingenieure) refers to the surface finish or texture of a plastic part created by the injection moulding process.
The VDI finish is a standard classification system which defines various types of surface finishes that can be achieved on injection moulded parts. These finishes are usually specified using a numerical scale, which ranges from VDI 1 to VDI 100. The lower the number, the smoother the surface finish will be.
Different surface finishes are achieved by modifying the mould surface or by subjecting the part to various post-processing techniques, such as polishing, texturing, sandblasting, applying mould release agents, or using chemical treatments.

The choice of VDI finish depends on the specific requirements of the part, including its appearance, functionality, and any specific manufacturing or design considerations. A smooth surface finish may be desired for parts where aesthetics is important, while a textured finish may be preferred for improved grip or to hide any defects or imperfections.
The most common type of VDI finish in injection moulding is VDI 3400 texture. This finish is typically characterised by a fine, grain-like texture on the surface of the moulded part. VDI 3400 is widely used in various industries, including automotive, consumer goods, and electronics, due to its versatility and aesthetic appeal.
What are the Benefits of VDI Finish in Injection Moulding?
Improved surface quality: VDI finish achieves a smoother, more aesthetically pleasing finish. It helps to eliminate the appearance of flow lines, sink marks, and other surface defects.
Consistency: VDI finish ensures consistent surface quality across multiple moulded parts. It maintains uniformity in appearance and texture, which is crucial for industries that require high-quality surface finishes, such as automotive and consumer electronics.
Increased productivity: VDI finish reduces the need for additional finishing processes, such as polishing or sanding, as it ensures a high-quality surface directly from the mould. This can significantly reduce production time and cost, resulting in improved overall productivity.
Enhanced mould release: The VDI finish provides a smoother surface, allowing for improved mould release. It prevents the sticking of the moulded part to the mould, reducing production delays and minimising the risk of damage to the mould or part during ejection.
Improved part functionality: In certain applications, a VDI finish can enhance the functionality of the moulded part. For example, it can reduce friction on moving parts or improve the seal between components, leading to improved performance and longevity.
Design flexibility: VDI finish allows for greater design flexibility, as it enables the production of parts with complex shapes, thin walls, and intricate details. There is no need for additional post-processing steps to achieve the desired surface quality.
SDI Finish
What is SDI Finish in Injection Moulding?
SDI finish (also known as Super Diamond Finish or SPI Diamond finish) is a type of surface finish that is achieved in injection moulding. It is a high-gloss finish used to enhance the appearance and quality of the moulded plastic part.
The SDI finish involves the use of specialised polishing techniques, often involving diamond abrasive compounds, to create a smooth, reflective surface on the moulded part. This finish gives a glossy, mirror-like appearance, similar to that seen on high-end consumer products.
The SDI finish is often used for applications where visual appeal and aesthetic quality are important, such as automotive interior trim, consumer electronics, and cosmetic packaging. The smooth and reflective surface reduces the visibility of any imperfections or mould marks, resulting in a more visually appealing final product.
The most common grades for an SDI finish in injection moulding typically range from A1 to A3. The finish is often specified using a numerical grade, with A1 being the highest-quality finish and A3 being the lowest.

What are the Benefits of SDI Finish in Injection Moulding?
Improved Moulding Performance: The SDI finish provides a smooth and consistent surface on the mould cavity, which helps in reducing friction and minimising the risk of defects such as flashing or burrs. This leads to improved overall moulding performance, resulting in higher yields and better part quality.
Enhanced Part Release: With its low surface energy, the SDI finish allows for easier part release from the mould without the need for additional mould release agents. This reduces the risk of parts sticking to the mould, which can result in costly production delays and damage to the parts.
Increased Mould Life: The SDI finish is highly wear-resistant and has excellent anti-corrosion properties. It helps in extending the lifespan of the injection mould by reducing the frictional forces between the mould surface and the molten plastic. This leads to reduced mould maintenance and repair costs, resulting in overall cost savings.
Better Surface Finish: The SDI finish provides a high-quality surface finish on the moulded parts, reducing the need for secondary finishing operations such as polishing or painting. This not only saves time and costs but also ensures consistency in part appearance.
Improved Mould Cleaning: The SDI finish is easy to clean and maintain due to its non-stick properties. It resists the build-up of deposits or residues from the moulding process, making mould cleaning more efficient and reducing downtime for mould maintenance.
Enhanced Mouldability of Complex Parts: The smooth surface offered by SDI finish allows for the easier flow of molten plastic through the mould cavities, especially in intricate or complex part designs. This helps in achieving better dimensional accuracy, reducing the chances of flow marks or sink marks on the moulded parts.

SDI Finish vs. VDI Finish
Key Factors to Consider When Deciding Between SDI and VDI Finishes
When deciding between a VDI finish or an SDI finish in injection moulding, there are several key factors to consider:
Cost-effectiveness: Evaluate the initial investment, recurring expenses, and the longevity of the finish. Consider the cost of maintenance and repair as well.
Product requirements: Determine the specific requirements of the product being manufactured, including surface smoothness, texture, glossiness, and aesthetic appeal.
Material compatibility: Consider the compatibility of the finish with the material being used, as well as any potential chemical interactions or degradation.
Production volumes: If the expected production quantities are high, a finish that can withstand the wear and tear of continuous production may be preferred.
Time constraints: The time required for achieving the desired surface quality should be considered. Some finishes may require more extensive processing or longer curing times.
Durability and wear resistance: Evaluate the expected durability and wear resistance of the finish under the anticipated conditions of use. If the product will be subject to harsh environments or frequent handling, a high resistant finish may be preferred.
Consistency and repeatability: The chosen finish should be capable of producing reliable and repeatable results across multiple production runs to ensure consistent product quality.
Customer preferences: In some cases, customer preferences, market demand and various industry standards/guidelines may influence the choice of finish.
Environmental impact: Evaluate environmental factors such as the toxicity of the finish, its potential for emissions or hazardous waste generation, and its recyclability/biodegradability.