ID shrinkage observed on Brass Metal Insert (C3604) after plastic injection over Moulding

My production team is facing the ID shrinkage on brass metal insert after plastic injection overmoulding. Before the Moulding process I performed measurement on the brass inserts and it found within specification, but after the Moulding found that there is a decrease of 40 to 50 micron in ID after the over mould. Appreciate if anyone could give some useful suggestion we can contribute towards our RCA.

Our internal RCA strikes out the below possibilities after testing.

Tool
Moulding Machine
Raw Material
Process temperature.

The only thing which we yet to try out is the plastic resin material (using PEEK CF30 & CF40)

Thanks in Advance.

Hello,

It could be that your metal insert is not thick enough and cannot withstand the plastic pressure causing it to collapse. Try to see of you can decrease the speeds and pressures and the situation improves. Also run a short shot and see if the dimension has changed. If it had not, then you know it is the pack and hold pressures causing the issue. In this case, you will need to get thicker inserts.

Suhas

Thank you for replying. But May I know what is the contribution of 'speed' to the ID shrinkage. I am quiet new to this process, so what I can think of is it will probably contribute towards giving a short shot or not. can you please help to clarify how it will affect on the ID shrinkage?
Thank you.

All we are trying to do is to reduce speed and pressure to check if it is influencing the diameter reduction. So so reducing speed and pressure may help.
Just thought of this: This can also be a result of post mold shrinkage. So check the dimension as soon as it comes out of the mold. Also, I am assuming the insert it loaded on a pin or something.
-Suhas

Thank you for the reply Suhas. I will try to adjust the pressure and speed.

When the mold was designed did you calculate the brass shrinkage due to heat (considering that PEEK has a melt index approx. 360C). If it is a cylinder the ID will actually get smaller as it heats up. Sounds like it is not returning to original ID.

I have 4 tools A, B,C,D .All given pressures in unit "Bar"

Tool Injection Pressure Holding Pressure
A 2350 2200
B 2100 2200
C 2050 2200
D 2100 2200

Are these parameters are correct or wrong to follow. I read from an article which mentioned that the holding pressure shall be lesser than the injection pressure. Is it a must to have or different Moulding system has different parameter adjustments. can help to advise?

Hi Oldbob,

Yes, it is an insert with somewhat cylindrical type tail with a closed end. Which eventually cutoff after wards. But now the problem is after heats up it shrink and never returns back to original ID.

Hi Curious,
Without observing the entire process, I could not hazard a guess as to how accurate those holding pressures are. Generally speaking you should have done a cycle optimization when you started running this initially. There are a lot of you tube videos on processing. Current logic is that you fill to about 90-95% on primary and finish filling and pack for dimensional stability on hold, but you should do the math with some Rheology curves to get the best process (Cycle Optimization). Otherwise if your ID finish requirements are not to bad, you could just drill the finished product to size in a secondary op.