Views: 17 Author: Site Editor Publish Time: 2022-01-24 Origin: Site
Profile shape problems
Angle or square-ness of a profile is one of the most common defects encountered in
extruded profiles. The problems are directly related to an imbalance in the flow or feed to
part of the profile within the die itself. This may be from the bearings or flow related
factors, for example, a deep or offset recess or pocket.
A balanced flow is the first step in making a successful correction to any die; it is also the
best starting point from which to view the die. The die can be said to be in balance when the
front ends (nose-ends) resemble a saw cut, i.e. at 90 degrees.
The probable course of action will be to reduce bearing lengths where ever possible to
balance the flow to the extrusion. This is of course assuming that all bearings are producing
their optimum amount of friction, in other words that the bearings are square and flat or have
a minute amount of choke. This will be discussed later in the handbook.
Should this be the desired course of action then the die maker should be informed about the
changes if the tool is a new or replacement and has not been used for many tones of
production, which may mean that the tool has become deflected.
Corrections to flat dies that have an integral recess that is contoured to the profile may be
used to make a correction with the help of a milling machine. The usual method employed is
to increase the flow or volume of aluminum to a certain part of the profile (norm ally the
slow area) to balance the flow to the extrusion. The normal areas are the ends of legs that are
attached to the main body of the extrusion, these are usually positioned towards the outer
reaches of the feed to the die.
The normal practice is to manufacture a die that has bearing lengths that become shorter
as you approach the end of a given leg (as it gets progressively further from the centre of the
die). This is to allow for the reduced flow or lower velocity of aluminum to this point. By
increasing the velocity and volume of aluminium there will be a change to the angle of the
profiles leg. Legs that may have some detail attached to them, such as a brush path slot will
often extrude with the leg angled towards the detailed area. This is due to the extra friction
imparted from the detail and possibly insufficient bearing friction from the adjacent wall.
Multi-cavity dies may suffer from square-ness problems when the run-out lengths are
disproportionate. S mall differences in angularity will be exaggerated on the slow running
cavities by the pullers force which will be exerting a somewhat larger force to the slow
cavities. The problem of angularity can frequently disappear when a correction is made to
improve the run-out lengths.
Any profile with an unusual angularity problem (especially if the change in angle is acute)
should be examined closely to see if there is any evidence of the profile rubbing or fouling
the backing out or indeed any support tooling. Further checks may be carried out to see if the
angular problem has been generated from an outside source for example the run-out table or
graphite pegs or slats that may have been used to separate the extrusion. Look for any tell tail
signs on the extrusion that may be apparent as black graphite generated lines in the area of
Marks on the profiles surface (orange peel) may show the profile has been given a larger
than normal stretch for some reason like the profile has distorted badly during cooling. With
the maximum amount of information at hand a correction can be arrived at.