A quality control system is a necessity for companies that use injection molding. When items don’t work, aren’t the right color, or don’t fit correctly, it can damage a company’s reputation.
It starts at the design phase and includes discussions about surface finishes affecting aesthetics and performance. The best way to ensure your injection molded product works is to partner with a manufacturer prioritizing precision, consistency, and durability.
Part Lines
The injection molding process is highly controlled and can ensure consistent results. Nevertheless, even with this high level of quality control, mistakes can sometimes occur. These errors may lead to products not being made according to specifications and can upset customers.
A standard error in injection molding is the creation of part lines. These unsightly seams can form when different product parts come together. While good design can hide these lines, poor production quality makes them appear more prominent and cheap.
Machinists must select the best location for the parting line during mold design to avoid this issue. The part’s geometry usually determines this and how it needs to be drafted for release. Simple techniques will have a parting line that exists on a flat plane, while more complex and curved designs will require a parting line to follow the contour of the product.
Insufficient Plastic
If your injection molded products don’t fit, are the wrong color, or have flaws in the design, you’ll upset customers and may even lose business. That’s why rigorous quality control is essential.
Discolored lines appear on the surface of finished molded parts and are most commonly caused by the plastic resin cooling at different rates as it flows through the mold. They can also result from uneven wall thickness or varying injection speed.
Flash is a thin flap of extra molding material that appears at the edges of the part, often in ejector pin locations or parting lines. It is usually a minor defect and can be easily trimmed off from the final product, but it could indicate insufficient pressure in the mold cavity. The best way to prevent flash is to increase injection pressure and nozzle temperature. Ventilation can also help if the injection mold is designed correctly.
Flashing
Flash is excess plastic that escapes the mold during the injection molding process. It can get out through ejector pin locations, the parting lines, or anywhere else that doesn’t properly seal. It can also occur because of improper clamping pressure or sprue bushing dimensions that are not appropriately adjusted for the application.
Sink marks are visual depressions or indentations that appear on the surface of a finished molded product. Varying cooling rates can cause them, mismatched wall thicknesses between sections, or several other factors that require quality control to identify and correct.
Professional mold manufacturers ensure the highest quality injection molded parts. It also ensures that a product is designed with optimal manufacturing efficiencies and optimized for the specific equipment used in production. This helps achieve the lowest unit costs without compromising quality or functionality. This is accomplished by analyzing the design and integrating it with a comprehensive injection molding process to deliver the quality and consistency your customers demand.
Part Ejection
Injection molding produces complex plastic components with high tensile strength. With proper design, these parts can meet or exceed the performance and durability of metal products. However, even the best injection-molded pieces can have issues that don’t necessarily stem from the manufacturing process.
For example, if the parts aren’t the right size or shape, they can cause problems for customers when they try to use them. Finding these issues through quality control early can help companies avoid situations that could significantly impact their business.
Quality control begins with comprehensive injection mold trials before production to prevent these issues. This testing ensures dimensional accuracy, uniform cooling channels, balanced filling, and accurate part ejection. Additionally, carefully polishing all the mold surfaces that come into contact with a molded part minimizes the risk of defects such as marks. Ejector pins – the “bouncers” of the injection molding world – can also leave scars, but experienced injection molders know how to position them to minimize this effect.