Flow marks-plastic injection molding defect

(1) What are  flow marks (appearance)?
Flow mark refers to the wavy lines or patterns appearing on the surface of the molded product. This usually happens when the injection speed is slow, or when the surface layer solidifies faster than resin filling

flow marks injection molding defect
Fig. 1: Flow mark on the surface of a test handle
injection molding defects flow marks
Fig. 1: Flow mark on the surface of a test handle

(2) Causes of Flow Marks

(2-1) Injection speed is too slow
When the injection speed is too slow, it is not possible to form a jet flow, thus causing the surface layer to be uneven and resulting in flow marks. There is also a secondary reason that if the product is too thick while the gate is small, the actual filling speed will be slowed down, which tends to cause flow marks.

Flow marks caused by chaotic jet flows

(2-2) Mold temperature is too low
When the mold temperature is low, the surface layer will be solidified more quickly, making it more difficult to form a jet flow, thus resulting in flow marks.

(3) Solutions for Flow Marks

(3-1) Raise the injection speed
It is the most effective method to basically eliminate the flow marks by increasing the injection speed .However, it should also be noted that if the molded product is thick and the gate is small, the actual filling speed will be slowed down.

(3-2) Slow down surface solidification
Specifically, it is to increase the mold temperature. In this way, it is, to a certain extent, easier to form a jet flow, thus effectively preventing the occurrence of flow marks.

* Other problems may occur after implementing these measures. Therefore, please note that the settings should not be over-changed.