Filling hesitation (jump in filling time)

[maxmarautodesk]

Dear community,

I have reused a study that I created, meshed, and set up entirely in ASMI 2014 in ASMI 2015. I have not changed anything in the study. It was a simple duplication step. I have then carried out the analysis again.

When the analysis was finished, I have recoginized that the polymer flow shows a weird hesitation at the very beginning of the injection. This was not the case in the old 2014 version.

In fact, the simulations results seem to be very similar. Below you find a selection of results (analysis log) from ASMI 2014 and 2015 respectively:

FILL
Current time from start of cycle = 0.3387 s // 1.6297 s

Total mass = 0.4411 g // 0.4409 g
Frozen volume = 0.0721 % // 0.0692 %
Injection pressure = 85.6628 MPa // 85.5401 MPa

Maximum Clamp force - during filling = 0.6687 tonne // 0.6517 tonne
Time at velocity/pressure switch-over = 0.3364 s // 1.6274 s
Injection pressure at velocity/pressure switch-over= 93.4589 MPa // 92.9957 MPa

Volume filled at velocity/pressure switch-over = 99.0140 % // 99.0145 %

PACK
Current time from start of cycle = 50.3364 s // 51.6274 s

Total mass = 0.4596 g // 0.4606 g

Frozen volume = 100.0000 % // 100.0000 %

Injection pressure = 0.0000 MPa // 0.0000 MPa

Volumetric shrinkage - maximum = 8.9326 % // 8.7863 %
Volumetric shrinkage - minimum = 0.7592 % // 0.6583 %
Volumetric shrinkage - average = 3.3447 % // 3.0865 %

Volumetric shrinkage - root-mean-square deviation = 1.8487 % // 1.9424 %

As you can see, most results are similiar besides the injection time. I believe the small differences in the other results come from improved calculation methods in the 2015 version and limited numerical precision.
However, the difference in injection time is striking and comes from the fact that the polymer flow does not really enter the cavity at the injection location but hesitates there. Furthermore, the analysis log in the 2015 version looks very strange, as it starts with two big jumps in injection time:

Filling Phase: Status: V = Velocity control
============= V/P = Velocity/pressure switch-over
P = Pressure control
|----------------------------------------------------------------------|
| Time | Fill Vol| Inj Press | Clamp F | Flow Rate| Frozen | Status|
| (s) | (%) | (MPa) | (tonne) | (cm^3/s) | Vol (%)| |
|----------------------------------------------------------------------|
| 0.315 | 0.115 | 6.718e-06 | 2.08e-09 | 0.001 | 0.00 | V |
| 1.446 | 0.357 | 2.894e-03 | 8.99e-07 | 0.022 | 0.00 | V |
| 1.457 | 0.629 | 7.245e-01 | 2.28e-04 | 1.226 | 0.00 | V |
| 1.458 | 0.888 | 8.293e-01 | 2.63e-04 | 1.952 | 0.00 | V |
| 1.458 | 1.171 | 1.039e+00 | 3.31e-04 | 1.362 | 0.00 | V |
| 1.458 | 1.492 | 1.342e+00 | 4.32e-04 | 1.204 | 0.00 | V |
| 1.459 | 1.826 | 1.677e+00 | 5.47e-04 | 1.165 | 0.00 | V |

....

I thought it might be just some mistake in the displayed time. If you take the filling time and subtract the first time of 1.446 s though, the difference will not match at all the filling time of ASMI 2014.

Consequently, my question is: What is happening there? Has anybody seen the same problem? Any suggestions for solutions?

Background information about the study I am working on:

OS: Windows 7

CPU: XEON E5-2687W v2 3.4 GHz

RAM: 64 GB

Moldflow: Synergy/Insight 2015
Study type: Thermoplastics Injection Molding

Analysis type: Fill+Pack+Warp

Number of tetras: 2,800,000

I am looking forward to your answers,

Max

[ben_mendenhall]

Max,

I see the same problem using SVG. It's like the pressure is just gone from the 1st gate when you trigger the 2nd gate.

My peers tell me that when this happens in the tool, it creats a pressure line mark. When this happens, they install "Flow Controllers" in the manifold (see attached picture) to sort of ease the pressure release rather than dump it all at once. This takes away the pressure line mark.

A tool shop we use describes it like this :

Sequentially controlled valve gated systems offer a proven method to achieve superior part quality by selectable placement of weld lines, especially in large part molding applications. The SoftGate® system is an enhanced feature that precisely controls the opening phase of the hydraulic actuated valve pin. This allows for the “gentle” flow of plastic into the cavity eliminating blemishes that can occur with uncontrolled plastic flow.

Source - http://www.incoe.com/hotrunners/incoeproducts2.aspx?prid=15

As far as I know, there is no way to simmulate this in moldflow.