July 14, 2022

Lifter jam in Injection Mold

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The Question:
We have manufactured a new Mold for an automotive part in our tool room. This mold consists of 2 cavity (LH+RH) with 7+7 lifters and 1+1 side core. The mold is quite a big one say nearly 2 ton. Now we are having the problem of Lifters getting jammed (scoring) and damaging the core insert as well. This scoring is really heavy. We could not produce a single good part till now. Because till the time there is half shot the mold works well. But when we fill the part completely then the scoring starts and the next shot cannot be done since the lifter has got this scoring and the machine cannot push the ejection forward any more due to lifter jam. The part material is PP. The lifters go in and out of the pocket smooth manually in mold dismantled condition.

I am using both Core and Lifter made out of P20 with the same hardness and then there are brass holders in the Core plate to support the lifters. The lifters are supported by T holders at the bottom to slide in ejector plate and locked by allen screws. I really need some elaboration on this and a precise suggestion on what should be done to resolve the issue?

The Answer:
The fact that you are using P20 for your lifters and pockets leave few options for a good resolution. There are 3 basic reasons for your problem.

  1. Insufficient lubrication
  2. Thermal expansion during start up
  3. Bending/Twisting of your Lifters during ejection cycle.

Since I don’t know the size of your lifters I can only think that they are not strong enough to withstand the forces being put on them and as previously mentioned, you must have a hardness delta between 2 moving parts to avoid gauling—-a hardcoat finish on your lifter might help—but only for a limited time—so I would suggest going to a new set of H13 Lifters that are heat treated to a greater hardness than your P20 blocks.

Another option that may resolve the problem is to enlarge the lifter pockets so that Bronze plates can be installed and have a favorable effect regarding gauling.

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