Analysis and Solutions for Poor Demolding in Injection Molding

Router Injection Molding Products poor demolding, also known as die adhesion, occurs when sprues or molded parts stick to the mold, often due to inadequate contact between the injection port and the nozzle arc, incomplete removal of gate material, or abnormal filler conditions. The main runner diameter must be sufficiently large to ensure that the gate material does not fully solidify during demolding. Poor demolding is a significant issue in plastic injection molding, often resulting from various aspects of the injection molding equipment or improper processes. Although design flaws like insufficient draft angles or reverse draft angles can contribute, molded parts can still experience poor demolding under certain circumstances. Forced ejection can lead to warping, whitening, or cracking of the part, particularly if it sticks to the static mold side.

Causes and Solutions for Die Adhesion

1. Mold Failure

– Surface Roughness: Rough surfaces with gouges, marks, or depressions can cause parts to adhere. Improving the mold cavity’s surface finish, ideally through chrome plating and polishing in the direction of material flow, can mitigate this issue.
– Wear and Gaps: Worn or scratched molds, or excessive gaps at inserts, can create flash and hinder demolding. Repairing damaged areas and reducing gaps can help.
– Insufficient Rigidity: If the mold deforms under injection pressure, it may not open properly. Ensuring adequate rigidity and strength in the mold design is crucial. During testing, monitor for deformation and adjust injection pressure accordingly.
– Inadequate Draft Angles: A lack of sufficient demolding slopes can make it difficult to eject parts, leading to warping or cracking. Ensure proper draft angles and parallelism between moving and fixed templates.
– Poor Runner Design: Long or small runners, insufficient connections between runners, and improperly matched diameters can cause sticking. Optimize runner design to improve flow and reduce sticking risks.
– Ejection Mechanism Issues: An improperly designed or malfunctioning ejection mechanism can prevent parts from demolding. Ensure adequate ejection stroke and balance, and address any sticking between sliding components.
– Poor Exhaust Conditions: Insufficient mold exhaust can lead to air trapping and sticking. Improve exhaust conditions and add air inlets where necessary.
– Temperature Control Issues: Improper mold temperature management can hinder demolding. Adjust temperatures based on parting surface or cavity surface conditions to facilitate easier ejection.
– Runner Issues: Ensure runners are properly designed and maintained to avoid sticking.

2. Improper Process Control

– Excessive injection pressure, high screw speeds, and prolonged holding times can lead to overfilling and shrinkage issues. Adjust injection parameters to facilitate easier demolding.

3. Raw Material Quality

– Contaminants or improper grading of raw materials can affect adhesion. Ensure raw materials are clean and consistent in size.

4. Release Agent Misuse

– Release agents help reduce adhesion but must be selected and applied correctly based on material and processing conditions. Use appropriate types and amounts to achieve optimal results.

5. Overfilling

– Excessive injection pressure can lead to difficulties in demolding. Reducing injection pressure, time, and temperatures can alleviate these issues.

6. Static Mold Adhesion

– Parts may stick to the static mold due to jamming or excessive resistance. Ensure proper alignment and finish of the molds, and consider using pull rods or temperature differences to aid in ejection.

7. Mold Surface Issues

– Scratched or porous mold surfaces can contribute to sticking. Regular maintenance and polishing are necessary to keep the mold surfaces smooth.

By addressing these factors, ‎‎HDPE Plastic Injection Molding Manufacturer can significantly reduce instances of poor demolding (die adhesion), improving the efficiency and quality of the injection molding process.