Die Block Caused by Relief Design
The working belt without support is easy to deform and crack when the relief is too large.  Profile in the export stage of the material head out of the working belt due to the flow speed, wall thickness, resistance and other reasons, not necessarily radial outflow, most will sway bending shaking.  

The relief is too small or not smooth, so that the material head is blocked or bonded after friction.  Make the material head no longer forward but extrusion still make relief space filled with aluminum and the working belt gap is also filled with aluminum after blocking.  

The size of the relief depends on the mold, the small mold 500 tons of machine is generally not less than 0.5mm, 10000 tons of large machine will not exceed 3mm.  Most are between 0.5-1.0mm.  

Relief processing if the use of step type, that is, outside than inside big 2 or 3 level blocking die situation will improve, relief surface must be polished smooth.