During a recent consultation, I was asked this question...
Engineer
Could you explain how to pack-out a thin-walled part which requires a large amount of pressure to fill?
My Response
In such a case, the pressure to fill the part is typically very high... therefor, the pressure at transfer is also high. In such a case, you may have to complete the part filling at a pressure approximately the same as the pressure at transfer.
In some cases, this pressure is actually higher than the pressure at transfer... depending on the amount of pressure that is necessary to fill the remainder of the mold cavity. The benefit to this is you are using just enough pressure to fill the mold cavity, which will help reduce the amount of flash which is produced.
Additional Thoughts
Some processors have a tendency to fill the mold completely during first stage because they are not used to using a high second stage packing pressure.
-Andy
Hello.
I used for producing thin wall parts DIII process. It's very stable. With second injection speed, used for packing, you can adjust pressure at transfer to hold pressure.
Milan
Good point Milan,
Thin wall molding is a good application for a DIII process... assuming you have a pressure transducer at the gate.
-Andy
Andy,
I had just pressure sensor at EOF. But I adjusted V/P by position of screew regards on presure at EOF. With electric Demag it works very well, standard deviation for cushion 0,07 mm.
Milan
Excellent Comment Milan,
Although most methods focus on cavity pressure at the end of gate, the end of fill is becoming popular lately due to the vast improvements on newer molding machines. Theoretically, it is a better way to run a process... but it requires very responsive equipment.
-Andy