Ejector Pin Push Marks

The role of the ejector pin is push the part from the mold after cooling. However, localized deformation can occur on the part as a result of the forces placed on the part by the ejector pins. This deformation can take the form of stress whitening on the part surface. Ejector pin push marks can be caused by several factors. The cause and solutions for ejector pin push marks.

Causes:

1. An insufficient number of ejector pins for ejecting a

part can cause high ejection forces, forming concentrated areas of stress on the part

2. Placement of ejector pins is critical to preventing pin

push marks

3. Uneven ejector pin lengths can force a part to eject

unevenly, forcing ejector pins to distort and deform the part

4. Ejecting a object that has not cooled sufficiently can

cause an ejector pin to distort or even puncture and push through the part

5. If ejection takes place after the part has shrunk onto the core, the amount of force needed to eject the part is high, giving way to formation of pin push marks

6. A vacuum can be formed beneath the core, causing the workpiece to resist being ejected

Solutions:

1. Adding more ejector pins to the mold can alleviate this and facilitate part ejection. Another method to reduce the possibility of pin push marks is to add added draft angles to eject the part easier and to polish any imperfections on the part surface resisting part ejection

2. Placement of ejector pins should be distributed so that ejector forces are spread evenly over the ejector plate

3. Ejector pins should all be machined to the same length

4. Improved cooling of the part either by increasing cool time or

decreasing mold temperature will allow the part to cure enough to resist

5. To reduce ejection forces, it is recommended that the object be

ejected before the part shrinks fully onto the core

6. Vents have been used to try to force this vacuum out, but this

method has had limited success. An air poppet assist located in the core to reduce ejector forces has been used with a lot of success