In the field of plastic injection molding, molds are the core “tools,” and their structural design and processing quality directly affect the quality and production efficiency of plastic parts. However, during actual production, molds inevitably encounter minor issues. So, what are the common mold faults, and how can they be effectively resolved? Below is a detailed analysis.
Guide Column Damage: The Crisis of the Precision Guide “Guardian”
The guide column plays a crucial guiding role in injection molds, ensuring that the molding surfaces of the core and cavity do not touch each other under any conditions. It’s important to note that the guide column is not a load-bearing or positioning component. When the following situations occur, a significant lateral offset force will be generated between the moving and fixed molds during injection:
- Uneven wall thickness of plastic parts: When the wall thickness of plastic parts varies, the material flow through the thicker section is large, generating substantial pressure there.
- Asymmetric side of plastic parts: For example, in molds with stepped parting lines, the opposite pressures on the relative sides are unequal.
Under these circumstances, the guide column will be subjected to a lateral offset force during injection. When the mold opens, the guide column surface may be pulled and damaged. In severe cases, it may bend, break, or even prevent the mold from opening.
To address this issue, high-strength positioning keys can be added to each side of the mold parting line. Cylindrical keys are an ideal choice. Meanwhile, the perpendicularity between the guide column hole and the parting line is critical and must be strictly controlled. Additionally, the heat treatment hardness of the guide column and guide sleeve must meet the design requirements to ensure their strength and stability.
Ejector Rod Bending, Breaking, or Leaking: The “Small Trouble” of the Ejection Mechanism
The ejector rod is responsible for ejecting the molded plastic parts from the injection mold. If the clearance between the ejector rod and the hole is improperly handled, it can lead to various problems.
- Excessive clearance: This can cause leakage, affecting product quality and the production environment.
- Insufficient clearance: Due to the increase in mold temperature during injection, the ejector rod will expand and may get stuck.
To solve this problem, the ejector rod needs to be reground. A fitting section of 10 – 15mm should be maintained at the front end of the ejector pin, and the middle section should be ground smaller by 0.2mm. After assembly, the fitting clearance of all ejector rods must be strictly checked, generally kept within the range of 0.05 – 0.08mm to ensure that the entire ejector mechanism can move freely back and forth.
Poor Cooling or Water Leakage: The “Invisible Killer” Affecting Quality
The cooling effect of injection molds has a direct impact on product quality and production efficiency. If the cooling is inadequate, the product shrinkage rate will increase, and deformation may occur due to uneven surface shrinkage.
The design of the cooling system should be closely integrated with the product shape. Although the mold structure may be complex or the processing difficult, the cooling system cannot be omitted. Especially for large and medium-sized molds, the cooling problem must be fully considered. The layout, diameter, and flow rate of the cooling water channels should be reasonably planned to ensure uniform mold temperature and improve product quality and production efficiency.
Difficult Gate Ejection: The “Stumbling Block” in Product Demolding
During the processing of plastic injection molds, the gate often sticks to the gate bushing and is difficult to peel off. When the mold opens, the product may break. This fault is mainly caused by the following reasons:
- Poor gate smoothness: Tool marks exist in the gate hole’s circumferential direction, affecting the gate material’s smooth ejection.
- Excessively soft material: After a period of use, the small end of the conical hole deforms or is damaged, and the spherical curvature of the nozzle is too small. This causes the gate material to form a rivet-like head here, making it difficult to eject.
The processing of the gate in the gate bushing is challenging. Standard parts should be used as much as possible. Meanwhile, the performance of the gate pull rod or ejection mechanism must be improved to ensure that the gate material can be ejected smoothly and prevent product breakage.
Troubleshooting common faults in plastic injection molds requires a deep understanding of the mold structure and working principles, as well as rich practical experience. By promptly identifying and solving these common faults, the service life of molds can be effectively increased, production efficiency improved, and the quality of plastic parts stabilized. It is hoped that the above content can provide some assistance to those engaged in the plastic injection molding industry.
