Today's KNOWLEDGE Share
How could that be, since the packing pressure is not going to really change fiber orientation ?
The mechanism is a bit more subtle.
GF induced warpage is linked to the mismatch of "shrinkage" of the glass fiber vs. the shrinkage of the matrix. Such mismatch creates a much bigger shrinkage perpendicular to the fibers because in the parallel direction, the fibers can better "resist" the pull from the matrix.
So why would a higher packing pressure reduce warpage ?
Think about it. If you could increase the packing to the point where the matrix would hit nearly zero volumetric shrinkage (check the PvT curves, it is possible although usually unreasonable) then the matrix would not want to shrink anymore, and the conflict with the glass fibers (which also don't want to shrink much) is gone !
So...no warpage !
So, remember, the more you pack a GF filled part, the less it will warp (at least from the anisotropy effect, differential shrinkage is another story).
Of course there are limits to how much you can increase the packing without running into other issues...
Source:Vito leo
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