The heating up of the melt due to shear is called dissipation or shear heating.
In the transition area between the frozen boundary layer and the still flowable melt occurs the highest shear in the melt.
The shear depends on the flow rate of the melt and the cross section of the cavity.
The more shear occurs in the plastic the more the melt is heating up.
Too high shear leads to degradation of molecular chains.