Case Analysis of Defects in Car Door Panel

There are normally four Interior door pannels in a car, including Front, Rear, Left and Right parts which are usullay made from PP material. As known, the quality is demanding for these A class plastic parts. No visible defect is allowed. However, ejector mark is a  commonly seen defect that is difficult to overcome with most injection molder. Below is a study case to show that how HSMold solves the headache.

name Car door panel Injection pressure 40MPA    
material PP Adhesive method Side gate Holding pressure 18MPA
colour gray weight 1400G    

The picture below shows the ejector mark defect of car door panel. There is a around ejector rod on the back of the white mark. This defect greatly affects the aesthetics of the car door panel,which is  an unacceptable


1) Possible cause analysis and improvement measures

Possible cause: The main reason for the ejector mark is that the ejector pressure applied is too high, causing a gloss mark in the area of the plastic part where there is an ejector pin.

I mprovement measures:

Through the optimization of the mold structure and molding process, the force applied by the ejector pin is effectively reduced, and the possibility of the ejector mark is reduced.The solutions adopted in this case are considered from the following two aspects:

  1. Mold structure: When the draft angle of the mold is small or the polishing effect of the rib position is not good, the demoldingresistance of the plastic part will be increased.The force exerted by ejector rod is increased, resulting in whitening or bulging.The improvement measure is to improve the polishing of the ribs or to increase the draft angle of the part.
  1. Molding process: When the holding pressure is too highor the holding time is too long, the parts will be overfilled.At this time, the plastic “wraps” the core tightly, the ejection force applied to demold the plastic part is also very large, resulting in the whitening mark. Reduce the holding pressure or holding time is the solution
  • After improvement


3) Important Notes

Some injection molded parts are not allowed to have ejector mark for either cosmetic requirement or mechanical property. For transparent parts, if there is ejector mark, it will affect the appearance.Or if the wall thickness is too thin, etc., there is no room to place ejector pins. The issue   can be solved by using a hidden ejector.  For more information on the ejector mark, please also click “ Best way to solve ejector mark”!

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