What Does Pressure Holding in an Injection Molding Machine Mean?

Introduction to Pressure Holding in Injection Molding

Pressure holding in an injection molding machine is a crucial phase that follows the injection of molten material into the mold. This phase is critical for achieving precise and accurate final part dimensions. During pressure holding, the machine continues to maintain a certain amount of pressure on the mold, ensuring that the material fills the mold completely and compensates for shrinkage as the material cools. This process is instrumental in obtaining high-quality, dimensionally correct products.

The Function of Pressure Holding

Ensuring Complete Filling of the Mold

When molten material is injected into the mold, there may be areas that do not fill completely. Pressure holding helps to compensate for these gaps. By maintaining pressure, the material is pushed into all corners of the mold, ensuring that the final product is uniform and free from voids or defects.

Compensating for Resin Shrinkage

As the material cools, it naturally shrinks. Pressure holding helps to compensate for this shrinkage, ensuring that the final part maintains its intended dimensions. Without proper pressure holding, the part may shrink unevenly, leading to inaccurate dimensions and potential scrap material.

Improving Mold Replication Quality

Pressure holding also plays a role in achieving better mold replication. By maintaining the necessary pressure, the material is pushed into the mold's fine details, ensuring that the final product accurately represents the mold's design. This is particularly important for parts with intricate designs or high precision requirements.

The Process of Pressure Holding

The Injection Phase

During the injection phase, molten plastic is forced into the mold under high pressure. This phase is critical for filling the mold. The pressure is then adjusted to ensure completion of the filling process.

The Holding Phase

Following the injection phase, the holding phase begins. During this phase, the machine maintains a certain level of pressure to prevent the material from retracting back into the injection channel. This pressure is maintained for a specific duration to ensure complete filling and compensate for any shrinkage.

Setting the Holding Pressure

The holding pressure is carefully set to balance between filling the mold and preventing reflux. Reflux occurs when the material starts to flow back into the injection channel due to insufficient pressure. The holding pressure must be high enough to keep the material in the mold, but not so high that it causes the material to deform or crack.

Benefits of Proper Pressure Holding

Reducing Scrap Rates

By ensuring complete filling and consistent dimensions, pressure holding helps to reduce the number of scrap parts. This not only saves material costs but also reduces the time and labor required for reworking or discarding defective parts.

Improving Production Efficiency

Effective pressure holding can streamline the production process, allowing for faster cycle times and reduced downtime. A well-designed pressure holding routine can simplify operations and improve overall throughput.

Ensuring Consistent Quality

Consistent pressure holding across multiple molds and parts ensures that the final products meet the same quality standards. This is particularly important in industries where part uniformity is critical, such as automotive or medical device manufacturing.

Conclusion

Pressure holding in an injection molding machine is a critical process that ensures the accuracy and quality of the final product. By maintaining the necessary pressure during the holding phase, the machine can compensate for resin shrinkage and achieve complete filling, leading to parts that are dimensionally correct and free from defects. Understanding and optimizing pressure holding can significantly improve the efficiency and quality of the injection molding process.