Shear rate in sequential gate analysis

[teopado89]

Good morning everyone, 

i have this problem with a 3d model (see attachment pdf please)

i'm using a sequential gate. The second gate opens after 2.3 seconds.

If i see maximum share, ti exceeds datasheet value.

How can i reduce it?

Guide says:

To reduce internal shear strain:

• Slow down the flow rate.   -------> i tried to modify speed profile but nothing change
• Use programmed injection speeds.-------->????
• Increase wall thickness. -------> i can't
• Avoid differential orientation and differential shrinkage.------> the part in this area has the same thickness

Thanks

[teopado89]

Another thing please:

i cannot explain this temperature distribution.

Thickness is the same in all the surface (1.8mm)

 I'm showing the second gate (opening after 2.6 seconds).

[teopado89]

Good morning, i've tried this solution:

in the process settings i tried to modify the injection profile and the best result (which DOESN'T correct completely the problem of share rate maximum under data sheet value)

is this:

I tried to reduce flow rate (as guide says) so flow rate drop i'm imposing will be compensated by the flow rate peak when the second gate is opened.

I tried many profiles and results get better when my profile drop (localized near second gate opening % on shot volume) becomes higher, so when flow is lower.

But if i try to reduce more flow rate, results become worse and i have this error in filling's log:

| 2.349 | 86.619 | 6.107e+01 | 1.51e+01 | 2.062 | 12.54 | V |
Open valve gate group: Valve gate controller defaults
** WARNING 302104 ** Flow solution for this time step diverged.
| 3.131 | 87.955 | 1.142e+02 | 3.23e+01 | 2.013 | 15.96 | V |
** WARNING 302104 ** Flow solution for this time step diverged.
| 3.132 | 87.991 | 8.359e+01 | 3.28e+01 | 122.898 | 15.81 | V |

Guide says:

Solver message 302104

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Message text

** WARNING 302104 ** Flow solution for this time step diverged.

Explanation

Flow solution for this time step diverged. However the overall flow solution precision may not be affected.

Resolution

Shorten the time step or increase the number of iterations.

I didn't understand what to do to solve...

Any help please?

Thanks

[madhukeshwart]

Try the folllwing it may help you

==========================

1. Check the mesh quality, try to remesh with higher mesh density & Re-run. Then compare results.

2. Double the filling phase solver parameters and re-run. Then compare the results.

3. Try to model gate/hot runner tip with 3d model & 3d mesh. Then compare the results.

Hope 3rd option, with surely help.

If any thing else helps. Share the solution

[teopado89]

1 mesh was already good. I respected all the parameters (i'll refine it if 3rd solution won't help)
2 i halved maximum %volume to fill per time step and i don't get the 302104 error.
3 when out costumer will send us the defined runner system i'll analyze with 3d mesh.

By the way i tried to reduce more the flow rate in the process settings and now reducing it 'till 2% (in the previous picture it was almost 15%) shear rate increases a bit both the value and the affected area, and this result surprises me.

[tim.vanast]

Reducing the flow rate too fast can also cause shear as the material is trying to change speed too fast.  I've seen this switching to pack when the pack is set low.  You can see a negative flow rate, which means the pressure is acutally pushing the material backward due to the sudden large change in pressure.  Thus large shear. 

That being said, in reality I don't think this actually happens due to the machine response time.  So you may with to ignore the instantanious high shear.

Tim

[teopado89]

Thank you too Tim for your advice.
I don't have a negative flow rate in filling logs, but maybe as you said i have a too high slow down. If it is the reason, shouldn't i have the shear rate problem also before the opening of the second gate? Because before it i don't see the problem on my result.
As soon as possible i'll check with 3d runners.

[ethan.lcq]

Hello,

We are a moldmaker and one of our project has the same problem of high shear rate. 

Have you solved this problem and be about to reduce shear rate to material limits?we're also looking for answers.

we have a mold with 3 value gates, the mold will be running on 1,500T Demag machine.

Have you try to change below parameters and does it work for your simulation?

Screw Speed

Plasticizing Capacity/ps

Injection Rate

B.R

Ethan

ethan.lcq@yahoo.com

From drawing, to mold, to finished parts.

//Injection Moldmaker in China//

[mppkumar]

Hi @ethan.lcq

No worries, if the shear rate is momentarily when the second valve gate gets opened... you can ignore this

now a days, Syncflow hot runner is available with Synventive, which will ensure profiled opening of valve gates and this can be simulated in Moldflow using DD mesh

[ethan.lcq]

Hello M P Pradeep Kumar,

Thank you.

We solved the problem after set the below parametres of molding machine into simulation:

Screw Speed

Plasticizing Capacity/ps

Injection Rate

it works and shear rate is now within material tolerance.

B.R

Ethan

ethan.lcq@yahoo.com

From drawing, to mold, to finished parts.

//Injection Moldmaker in China//

[mppkumar]

Hi @ethan.lcq

Great to know you have solved your issue