Query regarding Volumetric Shrinkage Result

[birajlahkar]

Dear All,

Hope you all are doing great!!

1. Most of the material doesn't have the observed max. shrinkage information in observed shrinkage section in my MPI version. Is there any option to get it or calculate it from material properties?

2. I know that shrinkage value should be uniform throughout the part to prevent from sink marks & warpage as well internal voids. But, how to measure it. Generally what I do- I used to check the volumetric shrinkage value at ''starting stage of volumetric shrinkage calculation (calculation started once the cavity filled)'' & afterwards ''volumetric shrinkage value at the end of the Injection+Packing+Cooling time'' and try to come into the possession about the chnging ratio. Is it correct? (If I failed to understand you hopefully I will try to elaborate more in comment thread).

3. How does volumetric shrinkage relate to warpage (I am asking about the causal connection between volumetric results on Moldflow and Deflection results on Moldflow) ?

Your kind counsel will be greatly appreciated!!

[Anonymous]

Hi, Biraj

1. The "Observed Shrinkage" data field shows the range of the real linear shrinkages measured during shrinkage testing (used to fit shrinkage correction parameters). It is very useful to compare predicted shrinkages with this data and if the predicted shrinkage is significantly outside this range for a significant part of the molding you better take the shrinkage correction models (CRIMS and especially Residual Strain) with a big grain of salt. The Residual Strain should give you a warning in this case. This is an experimental value so it cannot be deduced from other material data. It is not very useful for Uncorrected Shrinkage anyway and usually if a shrinkage correction is fitted then the data field is populated.

2. The rule is the more uniform the Volumetric Shrinkage the lower are variations of the Linear Shrinkage and so the lower is "Warpage due to Differential Shrinkage Effect" that is usually the main cause of the warpage. Thus, the lower is the range of the Volumetric Shrinkages the smaller is usually) the warpage. No need to check the warpage history for this. The history might be useful to get some optimization of packing profile though. E.g. if volumetric shrinkage stays the same after some time, then probably there is no much sense to continue packing after this. Or e.g. if volumetric shrinkage at some time is uniform and then becomes worse due to overpacking near the gates, then it is probably a good idea to decrease the packing pressure after that time so to prevent overpacking

3. The volumetric shrinkage is distributed (via a complex proprietary algorithm between parallel, perpendicular and thickness linear shrinkages. The variations in the inplane shrinkages are responsible for the differential shrinkage effect on warpage. The differences between the parallel and the perpendicular shrinkages are responsible for the orientation effect on warpage. The differences between inplane and thickness shrinkage on curve surfaces and in corners are responsible for the corner effect while the asymmetry of shrinkage over the middle of cavity is responsible for the differential cooling effect on warpage. It is reasonably complicated complicated. If you want to repeat the calculations by yourself you can export the residual stresses and (for fiber-filled the mechanical properties) into Autodesk Simulation Mechanical, Multyphisics or into Abaqus using Autodesk Moldflow Structural Alliance package (provided free). Usually the results are very close to Warp. 

[birajlahkar]

Thank you so much for such an enlightening reply! It's really informative and I am cleared now.

Hopefully I will apply it in work.