If a part short shots, the plastic does not fill the cavity. The flow freezes off before all the flow paths are filled.
Causes for a short shot are:
When a short shot occurs, there are many different ways you can try to ensure that the part fills. Before you try one of the methods listed here, check all the other results, so that you know the exact cause of the short shot.
You can then use one of these methods to improve the likelihood that the part fills:
This action can cause problems in other areas of the part.
This action can cause weld lines in unacceptable locations.
This action decreases the viscosity of the melt, making it easier to flow through the part.
This action can cause greater shear heating, which can decrease the viscosity of the melt, making it easier to flow through the part.
Complex and thin geometry in a part can cause a short shot. You can thicken thin sections, or reduce the complexity of a flow path.
A material with a higher melt flow rate requires less injection pressure to fill the part.