Problems with GAS_2

[biricio]

Hi, I've got a problem with a gas analysis.
The model of the image is moulded with gas. I want to simulate the behavior of the gas.
In MPI the gas doesn't follow the contour of the model.
How can I do?

thanks

[biricio]

This is the settings in Moldflow

[biricio]

...and the Gas time (3D) result.

I don't know why the gas doesn't follow the perimeter of the model (thick thickness).
Bye

[niemoeg]

It looks like the gas penetration is following the hottest flow front which will be directly back to the gate; the best location to gate the part would be near the gas injection location it will reduce the gas jumping out of the channel but it still may try to follow the hottest flow front which could be down the middle of the part. Check temperatures to see the hottest area gas will try to penetrate that area first.


George

[niemoeg]

Add two gates on the end of the part in the corners to help the gas start along the edge

George

[biricio]

If I understand good, I must to move the gate near the gas injection gate (like the attach image).
Is it correct?
In your opinion, the settings are OK?

thanks

[biricio]

you wrote: "Add two gates on the end of the part in the corners to help the gas start along the edge"

Shall I add a plastic injection gates or gas gates?
thanks

[niemoeg]

I would try moving the injection molding gate to the corners the hot flow front will help start the gas along the edge in your thick wall section but it may also jump out of the thick wall if it finds areas with a higher temperature

George

You could also fill to about 97 to 98% and use a gas delay to help the gas stay in the channel only issues with that is the weld line could be a issue if the temperature drops

[niemoeg]

I think this is what you want to do

George

[biricio]

Thanks niemoeg for the help.

I had done an analysis with 3 gates but the results and that you see in attach image.
Now, I try with 2 gates and change the volume filled at 97/98%

[biricio]

Hi, I've done a new analysis with 2 injection gate on the corner.
But the situation is the same of the other analysis.
I don't know where I do wrong.

[GalSherbelis7635]

Hi Biricio,


The gas flows in the "path of least resistance". Resistance to flow is proportional to the channel thickness, width, length and viscosity. Creating thick channels in the frame does not mean this is the path of least resistance and this is exactly what the software is showing you. The gas finds lower resistance in breaking through the center surface (shorter length to the polymer flow front) than going around the frame.

It is hard to tell what to do without looking at the polymer fill pattern. It is usually easier to control the gas flow after the cavity had been filled with polymer. To do that you have to create an overflow well as far away from the gas injection point/s as possible and open it after the cavity had been filled. I am not sure if you can use this technique for this part.

It is a bit tricky to get the gas to flow around the frame because it will find one path that offers lower resistance ( ie half frame). You have to create two distinct flow channels (change the geometry).

Regards

Gal

[biricio]

Hi, I attach an image of the filling.

We want only one gate, almost central.
How do I proceed?
1- builds overflow beams
2- modify the analysis settings. but what?
thanks

[biricio]

I ask a BIG favor.
When you have time, you can look at the file and tell me how to set it.
The file is not big (as dimension).
thank you very much.

http://rapidshare.com/files/375957567/p132030235_08_ste__study__copy_.rar.html

[sernas]

Hello,

I hope by now you have made some progress in your gas assist, but if not, might I offer my 2 cents worth of opinion:

Initially, when first reviewing the part, I must ask "why gas it at all - why not add ribs since it seems you have 4 side/slide actions to begin with and could probably add an equivalent number of ribs for the strength requirements.

That said, if you still must gas, the only advice I can offer is:
I would start with full shot and over flows, the displaced volume of the desired channels most likely will not fill the remaining 25% or so of a short shot as you have set up in one of the images. You should be able to calculate a best case volume of the desired gas channels and fill accordingly, but a center of mass polymer gate will probably prevent any effective short shot use.
Then try to modify the geometry to include a molded in manifold for a single gas input location to create a channel to all 3 ribs.

Let us know what worked.

Good Luck - SPS

[biricio]

Thank you for your reply.
Maybe I explained it well. But the piece has already done. Already exists.
I want to simulate in Moldflow filling og the gas.
But unfortunately I can not.

I attached the MPI file two posts ago.
If you can look. You would do me a big favor.
Thank you.
Stef

[sernas]

Hello,

If I understand you correctly, the part is in production but you want to gas-assist the part, perhaps to address warpage issues?

I reviewed the SDY file and the aspect ratio could be decreased and layer number increased. But I believe that the gas pin is in a bad place. All gas pins I have seen go into thick areas. The current placement is in a thin area between the ribs to be gassed. So I would:
- move the gas pin to the outside so you can more accurately place it in the middle of a rib (any rib) and see if you can gas just that rib alone. I would try the center rib and place the gas pin so the notch on the other end of the part is about equidistant from the gas pin location.
- Approximately at the notch, 180 degrees opposite the gas pin, on the same center rib, attach an overflow well and valve of beam elements approx equal to the volume you expect to gas out. .
- change the short shot to fill completely
- change the fill time to whatever the production part is and adjust other settings accordingly.
- once a single rib is gassed, then copy the configuration to do all 3 ribs individually.
- My guess is the geometry will then have to be modified to join the ribs together to give the gas a path to follow from 1 central gas injection point.

Good Luck
Stephen.

[biricio]

Yes, the part is already in production and it mades with GAS. I just want simulate the real moulding process with MPI.
I'll give you a few questions:
1-How can I 'increase the layers'?
2-How do I 'change the short shot to fill completely'?

I can not move the point because the gas injection and now in that position.
I attach the latest results.
How can I improve?
I would like the GAS did all the perimeter.
Thank you.

[yannick.moret]

Hello,

Number of layers is in the meshing option, on tetra tab. Go for a fine mesh.

If you want to reproduce molding conditions, model also your runner system,and ensure you reported properly the molding conditions from the injection molding machine to the process settings. Do not hesitate to add the injection molding machine characteristics, like the screw diameter.
I can see on your pdf that you are using the automatic option for the fill time, and all the default settings.

If you want simulation to match experimental data, you need to have the model, the material, and the process settings to match also between experiment and simulation.

Regards

Yannick