How to change MFI

[Anonymous]

I chose a material to analysis the model. The real material that I use to produce doesn't exist in the list. But when I setup Process Settings I find that can change the value of mechanical properties. Like this Process Settings > Advanced Options > Modeling material > Edit. And I can change the value in this table. But when I change the different MFI, the results that I get are the same with every MFI. Could anyone tell me why?

[raalteh]

Hi,

The MFI is a very rough indication of viscosity, and not actually used in the simulation. The way the MFI is measured is using an extremely low shear rate (a statis weight on a plunger, producing one data point). The MFI data is included in the database because it's used in the industry to provide some very crude idea of whether the material is very viscous or not. So it is there for comparisson purposes, but the MFI data is not sufficient for analyses. 

The real injection molding is actually a process that covers a wide range of shear rates, from  very high share rates (at the mold wall and in the gate during injection) to very ow shear rates (in the packing phase), and at different temperatures (hot during injection, and cooling down from there).

We capture this data using viscosity tests in our materail testing labs in Melbourne and Ithaca, and this viscosity data is captured and represented (at different tempertures) in the so calle Cross-WLF viscosity curves (or alternatively the Second Order viscosity curves or matrix data). This data is much more representative of the real injection molding conditions and ensures accurate simulation results.

I hope this helps.

Hanno