Simulate runner pressure drop

[teopado89]

Hi everyone, 

i need to know which is the pressure drop of the hot runner system adaptation because i have to change the injection machine.

So starting from a very simple part with its hot runner system (hot gate + annular runner) like this:

i added other runners (not annular) and the hot sprue.

To see the pressure drop of the "new" system (the "not annular runners and hot sprue") is it correct to do this?

put the part on layer 1

put the old runner system on layer 2

put the new runner system on layer 3

run a fill analysis

see pressure V/P result switchover

HIDE layer 1 and 2

i obtain this:

Is it correct to say that the pressure drop in the new runner system is 89.87-50.49= 39.38 MPa?

Or is it a waste of time because it depends on too many parameters (material, injection time...) ? 

Do you have other ideas to find it?

Thanks

[madhukeshwart]

you are right 

[harald_goetz]

Maybe use the same scale to compare both sides. It might be even clearer than.

[teopado89]

Excuse me Harald, i didn't understand what you mean.

[harald_goetz]

I mean you can already see the difference, but consider to have the exact same picture (so both runner systems without parts / plates at the end).

The set the scale the same, so maybe from 30 to 90 MPa, so everybody can judge with one view, that the pressure drop is higher, or lower, or...

There is an Excel tool provided by Jay Shoemaker and Tim Vanast, that helps to set the scale for different studies.

You may need to search Autodesk University once to make your life easier.

Harald

http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2012/autodesk-simulation-moldflow-p...

(Under additional class materials)

http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2013/moldflow-insight/sm3881-p

[teopado89]

Thanks guys.

I have another question, if i can.

I have to model this hot runner system in my simulation.

In the left picture a section of the runner system, and in the right picture how i'm thinking to model it.

Obviously i should model each different diameter part (in the left picture) with a dedicated beam, but these beam elements maybe couldn't respect the ratio of 2-2.5*diameter length.

So my idea is to model like the red lines in the right picture.

Do you think it is correct? Honestly i don't like to make a gate of 18mm, usually i make an annular runner (maybe a bit longer) and then a gate of 10mm length.

How would you model this runner system?

Thanks in advance.

Matteo

[madhukeshwart]

 Matteo,

1. Maintaining Aspect in cooling channels is quite possible

2. In feed system some times impossible, due to need of proper density of beams to capture better flow results. It is  Ok with warnings. 

3. Model the feed system with 3D model and use Tetra mesh for feed system is best recommended.

Refer following link with similar discussions 

http://forums.autodesk.com/t5/simulation-moldflow-insight/beam-l-d-ratio/td-p/3172746

[teopado89]

ok and can i mix the first part of the runner system (the one i show in the picture) using a 3d mesh, with the rest of the circuit in beam elements?

is it wrong my approximation in my previous message?

[kameshg]

HI,

i would like to add some comments on to this discussion.

1.Since you wanted to capture the pressure drop in your feed system , and you have modelled it as 1D elements, i feel you should model one half and use occurence number to simulate the required no of cavities.  beam elements capture flow only in one direction and when your flow splits in to two the shear heating effects and the imbalance with it is not considered.

2. When you want to model your feed system as 3Dm keep in mind that the juncture loss coefficients will not be used in the 3D feed system, you need extensional viscosity coefficients to account for the juncture loss, Also your material and the part geometry plays an important role here.

If you think your material is pressure dependence on its viscosity, make sure you have the juncture loss coefficients to be used in the cross wlf equation.

regards,

kamesh

[teopado89]

Hi kameshg, 

thanks for your answer.

Yes i usually use the occurrence number to consider multiple cavities, and beam elements. My question was related to the element type and length in the runner system to find the better way to model the runner.

regards, 

Matteo

[kameshg]

Hi Matteo,

With reference to your  question to mix the 3D elements and beam elements, i reminded you about the coefficients required, based on the element type you choose, If you dont have these values in your material data , then the pressure drop calculation across your runner may not be accurate. Also i would like to add that, if you were to mdel the hot runner as beam elements, then it is advised to capture any taper in the hot  runner with a min of 3 beam elements elements along the length.

regards,

kamesh

[teopado89]

Ok thanks kameshg.

i'll follow your suggestions.

regards.

[mppkumar]

Hi

To calculate more reliable pressure drop in feed systems, ensure the selected material's UDB have Juncture loss coefficients

need to model any transitions in runner sizes with three elements

Thanks

M P Pradeep Kumar

[mike.yakonich]

@ kameshg

i am modeling my runner in 3D.

how do you make sure extensional vicosity modeling is being taken care of? isnt it coming from material datebase? I dont see how i can change it or even should i change it at all?

i appreciate your input.

thanks.

[kameshg]

Hi Mike,

the extensional viscosity details need to be requested from Moldflow, i am not sure if its avaialable by default in the material database.

regards,

kamesh

[Methusalix]

Hi,

in the case that your UDB does not contain c1 & c2, you can estimate junc. loss data from the following table

regards,

Roman

[mike.yakonich]

has anyone got the  chance to simulate the runner system in 3D ?

I had done so but it seems most of the pressure loss occures a the very begining of the injection.

just wanted to make sure i am on the right track.