Demolding Techniques and Precautions in Plastic Injection Molding

Demolding is a key step in injection molding, which directly affects injection molding product’s quality and production efficiency. Improper demolding can lead to product deformation, surface damage and even mold wear. In this article, we will introduce some common demolding techniques and important considerations to help you optimize the process and ensure the production of high quality products.

Draft Angle

Set Right Draft Angle

When designing the mold, ensure that the vertical surfaces of the product have a slight draft angle to facilitate smooth removal from the cavity. Recommended draft angles are typically between 0.5° and 2°, depending on the material, shape, and surface texture of the product.

Stop it From Sticking

Insufficient draft angles can cause sticking during demolding, making removal difficult and potentially damaging the finished product or mold.

Release Agents

Choose Right Release Agent

Release agents reduce friction between the plastic and mold, preventing the product from sticking to the mold surface. Common types include oil-based, wax-based, and water-based agents; the selection should match the product requirements.

Avoid excessive application of release agents, as too much can affect the product’s surface quality, leaving marks or an uneven finish.

Effective Ejection Structures

Ejector Pins and Push Plates

Position and number ejector pins and push plates to distribute demolding force evenly, avoiding deformation caused by uneven force during ejection.

Air Ejectors

For complex shapes that are difficult to demold, consider adding air ejectors to the mold. These use air pressure to assist in demolding, reducing adhesion between the product and mold.

Surface Treatment & Maintenance

Mold Surface

The smoother the mold surface, the easier it is to demold. Polished mold surfaces are generally more effective in reducing friction and enabling smooth product release.

Mold Cleaning

Clean the mold surface after each production batch to remove plastic residue and release agent buildup, which can affect the next demolding cycle.

Injection and Cooling Time

Injection Pressure and Speed

Adjust injection pressure and speed to minimize the adhesion of molten plastic to the mold cavity walls, preventing products from sticking too firmly to the mold.

Cooling Time Control

Ensure adequate cooling before demolding to avoid product deformation. Insufficient cooling can lead to uneven shrinkage, impacting product appearance and dimensional accuracy.

Speed Control

Avoid applying excessive speed during demolding to prevent product damage from abrupt ejection forces. By controlling ejection speed, contact between the product and mold is gradually released, reducing demolding stress.

Demolding Issues

Ejector Pin Marks

Adjust ejector pin location, quantity, and size to avoid direct contact with fragile areas and prevent ejector pin marks on the product.

Warping or Deformation

Optimize product design and demolding structures to prevent excessive demolding stress from causing warping or deformation. Adding reinforcing ribs in the design phase can increase overall rigidity.

Conclusion

Demolding in injection molding may seem straightforward, but it involves numerous factors, including mold design, material selection, and production techniques. By carefully setting the draft angle, using release agents effectively, precisely controlling cooling and ejection speed, and performing regular mold maintenance, you can improve demolding efficiency, reduce product defects, and extend mold lifespan.

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