Differential shrinkage

[Anonymous]

Hello

I need to tweak a model by making it longer because of the shrinkage that Moldflow is suggesting. Is the differential shrinkage the values to look at?

Should I trust these values?

Thanks

MS

[Wago0850 · Accepted solution]

Hello

ISO 294-4 defines terms and measuring methods for processing shrinkage. Shrinkage is defined as the difference between the dimensions of the tool

and those of the molded part at room temperature. It results from the volume contraction of the molding compound in the injection mold as a result of cooling, change in the aggregate state

and crystallization. Shrinkage is measured according to ISO 294-4 after storage for 16-24 h in a normal climate (23 °C, 50 % r. h.). Shrinkage is also measured by

influences the geometry (free or restricted shrinkage) and the wall thickness of the part. In addition, the position

and size of the gate, the processing parameters and the

the storage time and temperature play a decisive role. The interaction of these different factors makes it difficult to predict shrinkage accurately.

( Extract from: Ultramid (PA) main brochure of BASF )

The table shows that even unreinforced polyamides do not shrink uniformly parallel and perpendicular to molecular orientation!

Since shrinkage is dependent on too many processing parameters, I would approach the required level, the tolerance, step by step, at least 2 steps! See also BASF publication 

hope the information will help you