How to Solve These Four Common Problems Encountered in Injection Molding?


When it comes to the injection molding process, there are a number of common problems and challenges that are often encountered. These issues can lead to reduced product quality, poor appearance, dimensional inaccuracies, or non-compliant performance.

Understanding these common problems and their root causes is critical for injection molding manufacturers and engineers, as they can help them identify and resolve potential production roadblocks. In this article, we'll cover some four common injection molding problems, including air bubbles, sticky molds, insufficient filling, and slow productivity. We will look at the possible causes of these problems and offer some solutions and suggestions for solving them. By fully understanding these common problems, we can better optimize the injection molding process and improve product quality and productivity.

1. Solutions to Bubble Formation in the Injection Molding Process

Based on the causes of bubble formation, there are several strategies to address this issue:

1)For thick-walled injection molded products, the outer surface cools faster than the center, resulting in shrinkage and expansion of the plastic resin towards the surface during the cooling process. This leads to insufficient filling, also known as vacuum bubbles. To solve this problem, the following measures can be taken:

Determine appropriate gate and runner sizes based on the wall thickness. Generally, the gate height should be 50% to 60% of the plastic product's wall thickness.

Leave a certain amount of supplementary injection material until gate sealing.

Adjust the injection time slightly longer than the gate sealing time.

Reduce the injection speed and increase the injection pressure.

Use materials with higher melt viscosity.

2)Bubbles caused by the generation of volatile gases can be addressed through the following methods:

Conduct thorough pre-drying of the resin.

Lower the resin temperature to avoid the production of decomposition gases.

3)Bubbles resulting from poor flowability can be resolved by increasing the temperature of the resin and mold, as well as increasing the injection speed.

2. Analysis of the Causes of Main Runner Sticking during Injection Molding

Causes and Remedies for Main Runner Sticking during Injection Molding:

A. Insufficient cooling time, resulting in the main runner not being fully solidified.

B. Insufficient slope of the main runner, requiring an increase in the mold release angle.

C. Improper fit between the main runner liner and the nozzle, leading to leakage.

D. Rough surface of the main runner or lack of cooling channels.

E. Low temperature of the nozzle, requiring an increase in temperature.

3. Analysis of the Causes of Slow Production during Injection Molding

The causes and solutions for slow production during injection molding are as follows:

A. High plastic and mold temperatures leading to extended cooling time.

B. Prolonged melt time. To address this, reduce back pressure, minimize the use of recycled materials to prevent air entrapment, and ensure sufficient cooling in the feeding section.

C. Slow machine movements. Adjust the hydraulic and electrical systems to increase speed appropriately.

D. Injection Mold design should facilitate easy demolding and strive for fully automated operations.

E. Excessive wall thickness resulting in prolonged cooling time.

F. Nozzle drooling, hindering normal production. Consider using self-locking nozzles or reducing the nozzle temperature. Insufficient heating of the barrel. Switch to a machine with a higher plasticizing capacity or enhance preheating of the material.

4. Analysis of the Causes of Insufficient Filling in Injection Molding Products

The main reasons for insufficient filling in injection molding products are insufficient material supply and inappropriate injection pressure and speed (including excessive pressure loss due to resistance).

Several factors may contribute to this issue:

1) Injection Molding Machine Factors:

Inconsistent plasticizing capacity or heating rate of the machine. It is recommended to use a machine with a higher plasticizing capacity and heating power.

Wear of the screw, barrel, or nozzle, leading to material backflow and inadequate actual shot volume.

Malfunction of heating system components such as thermocouples or heating bands, causing the actual temperature of the barrel to be too low.

Wear of sealing elements in the injection cylinder, resulting in oil leakage or backflow and failure to achieve the desired injection pressure.

Insufficient nozzle size or improper adjustment of the nozzle centering, causing excessive resistance and pressure loss.

2) Injection Molding Mold Factors:

A. Low mold temperature, either locally or overall, causing difficulties in material feeding. It is necessary to appropriately increase the mold temperature.

B. Imbalanced distribution of the mold cavity, excessively thin wall thickness of the plastic part, leading to significant pressure loss and insufficient filling. Consider increasing the overall or localized wall thickness of the plastic part or introducing auxiliary flow or gates near areas with inadequate filling.

C. Small size of the runner causing pressure loss; excessive size resulting in weak injection; excessive roughness leading to unsatisfactory filling. Proper sizing of the runner, transition between the main and sub-runners, and appropriate use of curved transitions in the gate design should be considered.

D. Poor mold venting. Material entering the cavity is hindered by trapped gas pressure, resulting in incomplete filling. Utilize the gaps in the screw for venting or reduce the clamping force to allow venting through parting surfaces. If necessary, create venting channels or vents.