What are the causes of injection molding defects?

What are the causes of injection molding defects?
Even a slight negligence in injection molding operations, it can easily cause the defects, such as flash, insufficient injection, shrinkage, and parting line defects. As injection molding is a complex and precise manufacturing method, there might be many possibilities of resulting defects. Although lots of sharing about improvement methods for defect could be found on the Internet, there are still the difficulties to resolve the problem as well. It is recommended that you know your injection machine first. We have sorted out the 5 major causes of common injection molding defects. They are about mechanical equipment, raw material types, molds, molding conditions and operators. It helps you understand the basic concepts of injection molding and makes the machine operate more smoothly!

The causes of injection molding product defect

Mechanical equipment

The biggest problem may be the injection machine itself. The stability and precision of injection machine is very important. If the machine is with unstable quality, it will cause a decrease in the utilization, poor injection precision, and the high defect rate of finished product. It reduces the injection production capacity and delays the shipment, which will seriously affect the performance and revenue of company. Therefore, it is very important for the injection machine to execute the maintenance, inspection and clean regularly and also the machine specification should match the need of product. Besides providing the suitable machinery and equipment, the good injection machine manufacturer can help you resolve the problem effectively to avoid injection molding defects when there is the function problem occurred on your machine or defect found on the finished product.
〈Extended reading:What are injection molding machines? What are the types?

Types of raw materials 

Raw materials are also one of the reasons that affect injection molding defects. If the purity of the plastic raw materials is not good, it will increase the defective rate of the finished product. The fluidity of raw material is also the key point during the injection operation. In addition, the storage location, humidity, and availability period of the raw materials are also important. Some raw materials need to be stored in an air-conditioned room or in a constant temperature and humidity area. It is important to follow the storage demand of raw material. If you want to avoid injection molding defects, choose the raw material manufacturer carefully is very important.


Mold design can also cause injection molding defects.  Pay attention to the mold cavity number, cold / hot runner system design, the type of gate, the gate position and size, the mold material, design details etc., as long as one mistake appeared of the above-described, there will be the defect occurred. Therefore, it is very important in the mold try stage. It is recommended to verify and evaluate the defects of the mold first to avoid unnecessary errors and meet the high quality requirements of subsequent large-scale injections.

Molding conditions

The conditions of injection molding refer to the key points of the adjustment of the injection machine. The 5 main parameter settings "pressure, speed, temperature, time and stroke", input of each product will be much different, and to set the permutation and combination, the operator needs to fully understand the sequence and relationship of the each injection molding operation. The manufacturer with rich experience can provide you with the injection machine operating skills to help the operator quickly master the know-how of the molding conditions and reduce the problem of injection molding defects.
〈Extended reading: Five Key Points to the Stability of Injection Molding


During the injection process, it is quiet important to carry out the complete SOP process, because slight operating differences will affect the final product results. If the shape of the injection part is more complicated, professional experience is needed to adjust the injection steps and details. Different operators will have insufficient experience or ignore certain injection details, resulting in defective products and injection molding defects often occur. It will delay the development time, and repeated test failures will also increase the cost of raw materials. Therefore, in order to avoid the injection defective products caused by human operation factors, the suggested improvement method is to set up a detailed SOP operation for each injection product, implement staff education and training to reduce the injection product defects.


Injection molding defects are very common, however the company does not want to increase the cost of raw materials, manpower, time etc.,due to incorrect injection. By understanding these 5 most common causes that affect injection defects, we can more effectively control and reduce the defect rate and maximize the output value! We are a professional injection molding machine manufacturer with rich manufacturing experience. Our plastic injection molding machine is stable, high-precision, easy-to-understand interface, easy to operate, and convenient to maintain. Our service concept focus on quality, communicate and credibility. We are an injection molding machine expert who provide complete after-service and warranty. Feel free to contact us if you need any other information.
〈Extended reading:What are the costs of plastic injection products?