Views: 52 Author: Site Editor Publish Time: 2022-02-15 Origin: Site
The Flow Characteristics of a Die
How the Aluminium flows within a die is of great importance. The flow will not be straight
through any die because of the effects of drag / friction within the die and this will have the
effect of distorting the flow. How much distortion to the flow has a direct relationship to
the quality and shape of the extruded profile.
As this is a difficult concept to understand it will be made easier to visualise with the
sketches and diagrams in the explanation. Some basic facts have been listed on which all
Technicians will agree.
Successive billets join well.
Successive billets do not join well.
High extrusion pressures.
Low extrusion pressures.
Little “pick-up” problems
Major “pick-up” problems.
Little effect from recess.
Greater effect from recess
Details form O.K.
Details may not form well
These details are true for both Solid and Hollow profiles. It is also true that the effects will
be more pronounced as the alloy is changed from a softer alloy to a harder alloy.
As already mentioned the effects of a recess or for that matter the insides of a " port " will
have the initial effects on the flow of the aluminium. It will generally start to bend the flow
from the area of least resistance to that of greatest resistance. The amount of bending to the
flow is in direct proportion to the amount of resistance encountered. The combinations are
almost infinite, but, factors like the depth and opening dimensions for a recess or port are
all important and the conclusions are self evident for these matters. The friction generated
on the inside surfaces is also a contributing factor, but, not critical as the Aluminium does
not move to any great degree once it has come into contact with the extremities of a recess
or port opening. However, the velocity and pressure are usually sufficient to keep the
Aluminium moving over the surface of the central web and mandrel areas and the
reduction in drag / friction in these areas will pay dividends. The reduction of drag in these
areas will help prevent the nitride layer from being pulled away and slightly reduce heat