When designing a mold for a multi-cavity part, ensure the flow of the material is balanced.
With unbalanced runners, hesitation can occur in the gates of the parts closest to the sprue. Hesitation causes underpacking and short shots.
In the following animation, the material reaches the first gate before the runner system has filled. The higher pressure at the gate will cause the polymer to flow more readily through the runners. Polymer flow will slow at the first gate and then freezes, as indicated by the red arrow.
To avoid hesitation at the gates, the runners should be balanced so that the flow reaches the gates simultaneously. You can use the Fill time result to ensure that the flow paths are balanced. Hesitation at the gates might lead to underpacking or a short shot.