Reduce volumetric shrinkage

[praphotSYZN3]

Hi Everyone

This picture show size of volumetric shrinkage results

I would like to know how to reduce this value, but do not modify part thickness. 

I would like volumetric shrinkage value good for typical part.

please share knowledge to me.

Thank you

[bernor_mf · Accepted solution]

Hi
well, seems as gate and runner freeze off to soon to be able to pack the part.
Check when gate freeze off compared with part, to get time for packing phase.
Could you pack at higher pressure, when gate still is open?
Could gate dimension be increased?

An option is to put a direct hot gate on part, like a valve gate, to be able to pack a thick part.
Or a direct cold sprue with larger dimension, but that requires a post molding operation.

Hope this helps.

Regards,
Berndt

[praphotSYZN3 · Accepted solution]

Hi Mr. Bernor

Would like  to you check results item this Temperature and Packing.
1.Temperature at gate enough at 5.123sec for polymer flow .?
2.Pressure for packing enough at 60 Mpa and could I how to process seting .?
3.Time for packing enough at 7.81sec ,please see final item results , could I adjust temperature , pressure or time packing?

[PascalGosset]

Hi simulators,

Can you tell us what is the material injected and what is the thickness of this part?

I guess this part is thick.

So if you don't pack it enough, a void can occur in the part center or a sink mark could be visible on its surfaces.

The prediction of sink marks has been improved with Moldflow AMI2021.

But not the one of voids.

As Berndt wrote, to reduce the shrinkage, you can act on the packing pressure, packing time and on the gate size.

If possible, try other materials.

Good luck  😉

[bernor_mf · Accepted solution]

Hi @praphotSYZN3 ,

Agree on comments from Pascal.

Would like to add:
From picture I see POM noted, but not if it is filled or unfilled.
POM : a typical packing pressure range is 60-80 MPa
The gate opening size is by rule of thumb 50-60% of thickness.

1.Temperature at gate enough at 5.123sec for polymer flow .?
> No, melt has frozen at gate as 115C is well below the transition temperature of 145C
At 3.295s gate is still open.
You might need to add intermediate intervals before running analysis to get more time steps to better find freeze off time.

You could review Temperature result with transition temperature of 145C.
Create new plot Temperature, with Plot Properties:
Selection: Contour
Contour: check Single Contour
Contour value: key in 145 for transition temperature of 145C

2.Pressure for packing enough at 60 Mpa and could I how to process seting .?
> POM : a typical packing pressure range is 60-80 MPa

3.Time for packing enough at 7.81sec ,please see final item results , could I adjust temperature , pressure or time packing?
> Packing time of 7.81s is too long, as gate freeze off around 3.295s-5.123sec

If you attempt to stick with this kind of gate design, and reduce volumetric shrinkage,
you need a larger gate opening , to get longer packing time. And also test the outcome of a packing pressure of 80MPa.
Also, the gate is at a thinner area (rim?) of part, that freeze off sooner.

Regards,
Berndt

[praphotSYZN3]

Hi Mr. Bernor

I follow recommend and I analyze again.

- I increase gate diameter from 1.0mm. to 1.2mm (If gate diameter morethan is 1.2mm. ,I concern it will not cut while ejection part.) and  changed setting about pressure packing from 60Mpa to 80Mpa. 

1.This picture show parameter my setting. 
My packing profile right or wrong.? or You please recommend.

2.This picture show temperature result and temperature X,Y plot ,Could I improve packing time  how, in my process setting.?
2.1 At 5.432(S) ,gate is freeze.?
2.2 Could I temperature more for packing time more or something else.?

Thank you for your recommend but please explain more. 

-You might need to add intermediate intervals before running analysis to get more time steps to better find freeze off time. =I don't understand this message ,please share how to or send link learning for me.

[bernor_mf · Accepted solution]

@praphotSYZN3 

Hi,

To change Intermediate intervals:
Process Settings
Advanced options...
Solver parameters ; Edit...
tab Fill+Pack Analysis
section Intermediate results
Write at constant intervals ; Edit intervals...

Change to more intervals if needed in filling, packing or cooling phase.

1. Packing time set is 10s and too long as gate freeze off is at about 5.5s
After 5.5s you are packing the cold runner.

Packing phase should stop at around 6s, I think.

2. Time available to pack this part depends on when cold gate freeze off.
As you are restricted by gate size, this will restrict the possibility to pack the  part.
2.1 Right, seems as gate freeze off around 5.5s
2.2 Gate size controls time of packing.

Rule of thumb is to gate at thickest section of plastic part.

Regards,

Berndt