Volumetric Shrinkage

[sharbaf]

Hello,
Does anyone knows how to use volumetric shrinkage result to predict possibility of sink mark?I found the range of e.g from 0.4 to 7.12 in my result, but i dont know how can I use it to predict of shrinkage.
beside, what is the meaning of this range?
thanks.

[GoncaloRodrigues]

Hello Mr. Sharbaff,

Gonçalo from MOLIPOREX is writing.
I hope everything is Ok with you and your team.

Have you look to help in Moldflow concerning Volulmetric Shrinkage? I think there you have the answer you look for. At least you can understand how to predict sink marks.

High shrinkage values could indicate sink marks or voids inside the part.
For thermoplastic materials, volumetric shrinkage should be less than the observed maximum value for the material. You can find material shrinkage information in the Thermoplastic material database. Right-click the material in the Study Tasks pane and select Details.

Volumetric shrinkage can be controlled by the use of packing profiles.

I hope it help you...!!!

Engº.Gonçalo Rodrigues
MOLIPOREX
Portugal

[kameshwarang]

values should be well below 6%.if the value is more , and if the location is near thick regions or ribs and bosses, u can predict sinkmarks.u cannot measure the value of sinkmarks with volumetric shrinkage

[HaraldLoacker2976]

You can calculate out of the volumetric shrinkage (S_V) the linear shrinkage (S_L) by this equation.

S_L = (1 - (1 - S_V)^(1/3)) * 100

Example:

S_V = 6 % = 0.06

S_L = (1 - (1 - 0.06)^0.3333) * 100 = 2.04 %



I hope this helps to answer your question.

Harald

[svennelin5284]

Hi there

Is there any scientific reference for this calculation and observations?
Does anyone know if this is relevant for all types of materials and wall thicknesses?

Regards Sven

[HaraldLoacker2976]

Here is a link to a more detailed explanation.
http://mfg.eng.rpi.edu/aml/course/Shrinkage%20Rate%20Exercise.pdf

I hope I don't break any copyright law by this link.
Regards Harald

[kameshwarang]

thank you for sharing a valuable information

[madhukeshwart]

For isotropic 3D solid materials, linear shrinkage is approximately one third of the volumetric shrinkage, where volumetric shrinkage is evenly distributed in all directions.


For transversely isotropic materials in thick parts, volumetric shrinkage is approximately equal to the shrinkage in the flow direction plus two times the shrinkage in the transverse direction.

For shell-like geometries, it is expected that the shrinkage in the thickness direction should be higher than the shrinkage in the plane of the part.

Shrinkage in the thickness direction is likely to be greater than one third of the volumetric shrinkage, while in-plane shrinkage should be less than one third of the volumetric shrinkage.

Many mold features act as constraints to in-plane shrinkage. If you are using a fiber-filled material, the orientation of the fibers in the plane of the part will limit shrinkage in this direction.

Shrinkage in the thickness direction is relatively unconstrained.

[madhukeshwart]

refer moldflow help