The major contribution for the lifters scoring was the load of the molded part itself. The ejector pins were not sufficient enough to eject the part out in a balanced way. This was in turn creating excess load on the lifters leading to twisting or imbalance within the whole of the ejector assembly especially when the part fills completely. This time we added nearly 50 ejector pins apart from the existing pins.
There is nothing wrong with using the same material for the lifter and the lifter pocket. The issues to check for are
- Is there a difference between the angle of the back wall of the lifter and the lifter rod (usually if the back wall is greater by at least 3 deg you should be good there).
- Are all the other lifter walls drafted sufficiently?
- Are the lifter carriages sliding freely? No binding etc.
- Is the ejector plate flexing?
- Use the ejector plate guided sufficiently to ensure it is not cocking?
Some steps should be followed: relieve the lifters keeping the fitting area to the minimum required to allow proper sealing of the molded part; adding lubricating grooves almost to the top keeping a safe area so you don’t drag grease to the part between cycles; coating the existing P20 lifters (nitration can work as well); replacing the lifters with a new H13 Hardened (around 54 HRc) set; replace the brass guides with hard bronze guides; how long is the mold? Check out the ejection plate guiding pins and make sure they aren’t trapped at the end between plates in order to allow expansion; how many K.O. rods are you using to eject? if the injection mold is long you should connect the ejection system of your injection molding machine to the mold with more than one K.O. rod, in order to balance the force applied and keep the ejection plates always straight (to avoid bending), maybe if you show us some pictures of the mold and a cross section of the assembly drawing of the area we could probably help you even better.
