Based on part geometry, gate location(s) will determine how the polymer fills the cavity.  If the cavity doesn't fill in a balanced/uniform fashion, the internal stresses will be anisotropic- meaning non-uniform properties.  So it is important to place a gate in a location such that the polymer flowfront fills the cavity at a uniform rate and reaches the end of the cavity at all locations simultaneously. 

With simple part geometry, identifying an ideal gate location may be possible by using experience and examining the part.  With more complex geometry and gating limitations (cooling line interference, ejector pin interference, slides, etc.), it is nearly impossible to determine the appropriate gate location(s) without using FEA.  Not only can FEA produce actual deflection results(warpage), but it can also provide data that is a precursor to warpage-such as volumetric shrinkage and frozen-in stress which is typically due to forcing material in a cavity while it is trying to freeze off.

 

Gate location(s) will determine polymer orientation.  Based on that location, it will ultimately determine polymer shrinkage.  As the cooling lines relate to the gate location, different regions of the part will cool at different rates(regions near the gate start cooling before regions furthest from the gate). 

 

Why is this important?  Because there are 3 major components that contribute to warpage and they are:

Shrinkage and orientation are both directly correlated to injection location(s) on a part as it relates to processing conditions.  Warpage due to cooling effects is obviously a result of the cooling circuit layout and its efficiency. 

Because gate location directly correlates to and effects the contributors of warpage, gate location is therefore extremely important in the tool creation process.