Problems and solutions for plastic injection molding

Plastic products are mostly produced by injection molding machine. With the injection molding method, there are often defects occurred in plastic products, such as jetting, flow marks, short shot and many more. Therefore, it is important for us to know the defects as to ensure a high quality product.

Most commonly, defects happen when there are errors in materials used for the product, mold itself or the machine setting.

Some of the common defects and solutions are:

Defects name	Descriptions	Possible solutions
Bubble	It is referred to the phenomenon where bubble or blister occur within the plastic product.	- Increasing the back pressure - Dry the material properly - Decrease the material temperature - Reduce the injection speed
Drag marks	It is referred to the phenomenon where scratches occur when it is ejected from the mold.	- Maintenance of the mold itself
Flash	It is referred to the phenomenon where excess plastic overflow and penetrate out of the mold gap.	- Reduce the injection speed - Reduce the injection pressure - Reduce the material temperature - Increase the clamping pressure
Flow marks	It is referred to the phenomenon where wave pattern is formed around the gate.	- Increase the mold temperature - Raise the gate and runner.
Jetting	It is referred to the phenomenon where a snake line of material formed on the surface of the molded product.	- Reduce the injection speed - Increase the mold temperature
Short shot	It is referred to the phenomenon where the plastic does not reach certain portions of the mold.	- Increase the injection speed - Increase the pressure - Increase ventilation lines
Silver streaks	- It is referred to the phenomenon where circular marks appear at the molding surface.	- Proper drying of material before use - Increase back pressure
Sink mark	It is referred to the phenomenon where indentation occurs on the surface of the plastic product.	- Increase injection speed - Increase back pressure - Reduce material temperature
Warping	It is referred to the phenomenon where deformation caused by difference in the degree of shrinkage.	- Increase injection pressure - Increase barrel temperature
Weld Line	It is referred to the phenomenon where the two different flow fronts meet and formed a narrow V-shaped line.	- Increase injection speed - Increase mold temperature - Increase material temperature

The following information is provided for reference only, without guarantee of any kind. It is encouraged to verify all information with experienced plastic experts, as there are always specific conditions that cannot be anticipated.

Please feel free to contact YHK design for more plastic advices or new product development.