Shear rate 3D result

[HugoHerrera7042]

Hi,

I have a pretty standard part, that I am trying to validate what nozzle diameter to use to mold it.

THe shear rate is my main concern, since it is a class A part.

However, the problem comes, when I look at the result from a different type of meshes.

Since it is an easy part to mesh, I try comparing midplane/fusion/3D shear rate predictions, and I got similar results for midplane and fusion (at the limits for an acrylic), but for the 3D mesh I got excessive shear rate, around 5x the ones from midplane and fusion. I kept all of the inputs exactly similar for the 3 analyses, but the shear rate output is significantly higher on the 3D type.

Has anyone experienced this? Which result would be the most accurate??

this is a pic of how the 3D prediction (cut section at the nozzle) looks like:

h.

[Anonymous]

Hugo,

I believe the difference is in how the beam elements calculate and display the shear rate with the two technologies. With the midplane and the fusion it is an averaged shear rate through the cross-section of the gate. This would at least be true for the shear rate, bulk result. However, with shear rate (3D) it calculates and displays the entire cross-section result at the time specified. Since the shear rate is highest just inside the frozen layer that is why you are seeing a thin layer of red. See attached image complements of Jay Shoemaker. The red line in the picture represents the shear rate through the cross section. Notice how it peaks just inside the frozen layer.

For sizing gates, I typically use the shear rate calculations that are found in most injection molding handbooks. I also try and keep the land as short as possible. I believe these calculations and guidelines fall more in line with the shear rate, bulk result. I also believe that the shear rate, bulk result is what you would want to compare to the listed maximum shear rate in the material file.

As far as which is most accurate, that would depend on your mesh quality. The gate is the one area where you do not have to follow the L/D rule for beam elements. You should have at least three elements in the gate. When the beam element calculates the pressures and shear rates it actually uses the average diameter of the beam element (start diameter + end diameter/2). So the shear rates may be a bit lower than the calculations I specified earlier. If you are using a 3D mesh to model the gate and runner than you need to make sure you have enough of a mesh density and the quality is very high.

Hope that helps,

Erik

[GalSherbelis7635]

Hello,

It is possible to look at the actual shear rate results in midplane and fusion.

Go – Advanced Options -> Solver Parameters -> Intermediate output  -> Profiled results  . Pick the option you need and the time you want the result written.

When the analysis finish you will have a new result called "shear rate" (and a few more). Create a new  result plot and pick XY then pick the elements you want to study. Open the "plots properties" and change the "independent variable" to "normalized thickness" . Then set the time to the time of interest.

If this is relevant please inform us how the analysis compare.

Regards

Gal

[StephaneCorduan1456]

The shear rate in 2D (miplane or fusion) is comparable to the 3D.

If not, we may have a problem on your model as suggested by Eric.

[kulandaivel_palanisamy]

Dear all,

Attached is the same pin point gate dia of 1.8mm for both Dual domain and 3D mesh.

Shear rate of 3D is higher than the Dual domain. As i am mostly using 3D analysis, how do we correctly inform the right gate diameter after shear rate optimization to customer in this case?

Please share your views.

Regards

JK