Warpage in Thin Wall PP Lids

No way anybody here can help with nothing more to go on than that.

Send a drawing of the mold, showing gate locations, and runner system, number of cavities, cooling channels, and include all processing parameters. (temp. pressure, speed, hold time, material, drying time/temp......................the list goes on and on.

Your tooling manufacturer and material supplier may be able to help, if you have noone on staff who can dial the process in.

Or, hire somebody to fix it.

You will never get a flat, unrestrained lid. Warpage goes with the material.

Thanks for the info.

However, I have seen flat lids. Any guess on material blending ?

I would try annealing or stress relieving between flat metal plates. This might give you some clues.

That might work, but lots of expense to do.

Seems like poor gate location/size/quantity, and inconsistent cooling/part shrinkage in the mold may be the problem.

Hard to tell.

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Fine tune all steps of process, use good raw material and get somebody who understands the process.

Thanks for the info.

Agreed. Proper mold cooling/heating is very often overlooked as a critical process parameter.

Initially the problem area is to be ascertained ie. on which side of the lid the warpage exists. Then the die can machined with a surface which has a contour opposite to the direction of the warpage such that after the mould operation the done it gets straightened.

Another method is to adopt is differential cooling , ie. to cool the area faster in which the warpage exists, than the area in which it is OK.two seperate water jackets can be used with different flow rates.

by providing I sectioned ribs diametrically at 2 locations, , problem may be solved,

If not required , then remove those sections.