[Noumenon72]

At my job, we extruded plastic sheets, so we had dies which were 84 inches wide with an opening of 0.020 inches. It's quite a challenge to get the plastic to spread evenly from the barrel opening all across that width like a river delta. There are two flexible lips inside, you can supply more heat to individual die zones to make it meltier, and at the very edges you stretch the plastic out a little so that several inches of the die end up contributing to one inch of the finished sheet.

[countzeroasl]

The other option that is commonly used is using a mold with an internal manifold to heat the plastic, which is injected through heated tips or pneumatic/hydraulic valve gates. This shortens the space on the part such that the flow length of the plastic will be sufficient to fill the part, where with a single gate, it may not due to the part thickness and thermodynamic freeze.