# :( Extrusion flow in a cavity

I am trying to use a plastic screw extruder that I have and I would like to have it fill a cavity that I machine with an inlet and outlet hole. A simple mans injection mold/casting machine

The cavity is a ‘pillow’ shape and I need to make sure that the pillow cavity is 100 % full when the plastic exits the outlet (no air pockets). Possibly at different inlet flow rates and temperature of the cavity surface if I have to.

The cavity inlet is on one pillow corner and the outlet is on the diagonally opposite corner.

I believe that I can obtain a filling flow velocity of up to 0.14 m/s at the inlet and also have a zero pressure outlet.

I am unsure about how to define my material kinematic viscosity. This is some information I know about my ‘polypropylene’ like plastic:

Here is what the pillow looks like:

Here is a link to the project so far.

I am also unsure about how to define my boundary layers (turbulence model and parameters etc) for this material and whether I have enough material specs to make this work.

I assume I wanted a transient incompressible simulation so I have started one in the project but right now I am stalled.

I have not find any successful projects/tutorials concerning plastic flow through a cavity.

I may have to vent the other two pillow corners with holes smaller than the outlet and if I see plastic coming out the outlet before I see plastic come out both the corner vents, then I plug the outlet until plastic comes out both corner vents at which point the pillow should be full and it could be removed to cool, but it would be nice to try to simulate this

Any help would be appreciated…

Thanks,
Dale

Hi Dale - interesting project!

First thing that came into my mind is this here: Non-Newtonian Models @ SimScale. I would assume that some of the materials used can be seen as laminar thus no k-epsilon or k-omega approach is needed but that’s just my intuition and I would probably have to look for some papers to see what the state-of-the-art is, especially for such a case

Hope that makes sense so far. Let’s see what @LWhitson2, @Retsam and @anirudh2821998 want to add here.

Cheers!

Jousef

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Thanks,

And I thought this might be easy, hahaha

I agree that is likely laminar and I can slow the fill down if I have to, no rush to make many parts per hour.

Hi Sir

Woah!! such a cool thing you are trying to simulate. I see some problem with the placement of inlet and outlet holes. From what I have learned about the casting process, I would advice you to keep the outlet on the top and reserve one hole(in the present geometry) to serve as the inlet. In the present configuration the plastic would try to move out from the outlet face even before filling this cavity to its top.

Also, the perpendicular configuration of the inlet and outlet faces will make it easy for you to run a multiphase simulation where your liquid plastic is filling the cavity and air is moving out of the cavity from the top. But, the problem is that there are not enough materials to choose in multiphase simulations. So, only @jousefm sir can explain on how to add new materials for multiphase simulations.

Also, there are many research papers available which are using VOF approach for such problems and I am attaching some of them here- oops we cannot upload doc file .

Thanks
Ani

Intuitively with a plastic state that is still very viscous, I would not expect that there is any need to worry about a Top or Bottom relationship. I do not think gravity plays much of a role here. And I was thinking that even multiphase aspect would be less important. I was thinking if I did not use multiphase we would just do transient sim and watch the cavity fill but there is likely not any basis to my intuition here.

Also, if this gets too hard I am pretty sure that my sequential hole plugging concept (3 corner outs, plug first to see material, then plug second, then end fill when 3rd starts oozing) will work and I will just forget this sim project I just thought it would be cool to try. For the use of the pillow, it would be best not to have any runners which would have to be trimmed manually at the outlet location you suggest.

At best I would expect that maybe a sim might show me the order in which I would have to plug those corner outlets

I see it as manufacturing problem, simulation was intended to comfort your choice… I would avoid extrusion in such a tiny object production. I guess you need Face1 and Face66, Probably a pressing method would be the easiest one. In that case you would need Face1 and Face66 as outlets.

I have not much choice on size of this object.

I usually am pretty adept at visualizing flows in my mind, I just wanted to see if SimScale could one up me here without too much effort

I just realized how much small geometry we are dealing with.

I thought the geometry would be few 100cm’s but just saw that it is just 5cm long. Now I completely agree with the above point.

Then you both will think I am really crazy, because I expect to re-heat the pillow and press it into a sheet of plastic ~0.002" thick x ~5" x ~8"

@DaleKramer there is a lot to take in here, but my first thought is that this will definitely be a multiphase flow and possibly non-Newtonian. The multiphase part I have done previously in OpenFOAM, but I wouldn’t say I am super adept at it. I have absolutely no intuition about the non-Newtonian part though; never done anything with it in my life.

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@jousefm

HEY, for the first time in almost ever, I see a checkbox on each reply post in this topic that would let me select the post as an answer, wow

Maybe this could help figure out this nasty, missing checkbox, issue…

At this time I do not see any checkboxes on my regular forum topics…

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@jousefm sir, is there any way to add new materials(and their properties) for multiphase simulations?

I just realized that the checkbox comes when you post something in the project support section(or any public group). It will not come in private groups.

From what I understand, they should be there for ALL topics that YOU create.

Do you have them there for topics you create in all Categories in this forum?

I have never seen them on any of my topics before today (and only today on this Project Support category), since I have been told they should be there for all topics I create.

Ideally, the checkbox should be there in every post created by a person in either a closed group or an open group.

This is the post created by me in an open grp

and this was crerated in a closed grp.

I was was considering that I covered our private group as it does show up in my Categories list at the Forum link

Ani, you can change for Phase 0 & 1 the viscosity, density as well as the model of the viscosity respectively. Is that what you intended to do?

Best,

Jousef

No sir, In the below img, there are limited number of materials to pick from in the multiphase simulation case. Can we somehow add/define a new material(for instance, can I add blood as my material)

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I think you can pick any and then change the name and values after it is added, is that what you mean?

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