Correction of solid aluminium extrusion dies. Examples

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Once manufactured, every aluminium extrusion die is sent to the press for testing or production [1]:

If the produced shape is successful in the first trial, production continues with proper checks and measures.
If the extrusion does not succeed, the die needs to be corrected based on the report of the test run along with the front piece of the extrusion.

Die corrections or maintenance could be required due to many reasons, such as [1]:

improper metal flow
dimensional variation
surface finish
interference with runout table.

However, die correction procedures require considerable practical experience. There are many ways to correct the same problem based on the skill and experience of the die corrector. It is important that the die corrector be present at the press to see the test run. The presence of the die corrector at the press will provide the information about the press, billet and die variables. This information will help the die corrector to rectify the die quickly or to relay some information to the die manufacturer if any major changes need be made [1].

Die corrector

The key figure in every aluminum extrusion press is an experienced die adjuster. When he plans to correct the next die, he scrolls in his head at least the following parameters of the extrusion press with which he works [1-6]:

die temperature
container temperature
billet temperature
extrusion speed
alignment of the press
technical condition of the die
the degree of wear of the auxiliary diex tool (backers, bolsters).

A good die corrector always has more than one way to solve a particular die problem. Therefore, some believe that die correction is closer to art and intuition than to science and technology.

However, over the years, some typical, and quite technical, methods for adjusting dies have developed in the aluminium profile industry, such as in the source [2].

Correction of a solid die

Correction of a solid die requires [1], either/or:

modification in the pocket
the feeder plate
modification of the bearing length from the front or exit side of the die.

The method of correction can be by using [1]:

a milling machine
a flexible grinder
an carbide-tipped method.

Methods of Correction

The most common methods of correcting an extrusion:

Choking and relieving bearings.
Correction by flow.

Correction of the die bearings

What is extrusion die bearing?

Each extrusion die contains bearing of various length. Bearings are land that act as frictional control on metal flow. The bearing is an outline of extrusion product (bar, rod, tube or profile) cut through the die to the highest precision possible [3].

Figure 1 – In the direct extrusion process,
the frictional resistance at the billet/container
interface slows down the metal flow near the billet surface.
The center of the billet thus moves faster
than the periphery of the billet.
To balance the flow, bearing length must be
inversely proportional to its distance
from the center of the billet [1]

Figure 2 – Choke and relief in die bearing:
(a) Choke at front of bearing.
(b) Increased relief angle at the back or exit side of the bearing

Speeding up of the metal flow

The method of speeding up the flow of metal in a certain section of the profile in the corresponding place of the bearings of the die made the relief at the exit from the bearings.
To do this, with a file or a drill, the edge of the bearing plane is cut off at a certain angle on both sides of the channel.
For new dies, all initial bearings are usually horizontal and parallel.

Figure 3 shows how the die corrector balanced the flow of metal by performing a releasing angle on the bearings.

Figure 3 – The die corrector speeded up the flow of aluminum by relief filing the die bearings [2]

Slowing down of the metal flow

To slow down the flow of metal in a certain section of the profile in the corresponding place of the die bearing belt, the corner of the bearinglt is cut off, but not at the exit, but at the entrance (Figure 4). This angle is called the choked angle.

Figure 4 – The die corrector slowed up the flow of aluminum by choke filing the die bearings [2]

Correcting a “U” channel

As you see in Figure 5, the “U” channel extrusion is extruding with the side legs moving extremely fast in relation to the top.
To correct this uneven balance of flow, we must speed up the bearing where the flow is slow by relief filing the bearing as shown on Figure 6.

Figure 5 [2]

Figure 6 [2]

Correction of "filling up" shelves

In cases where angularity is off on legs, whether they are in or out, the die corrector will file choke and relief in the directions in which he wants the leg to move (Figure 7). Depending on whether the leg is falling in or out, the die corrector will perform both the choke and the relief on the bearing with a file or a drill to make the leg move in the right direction.

Figure 7 – In cases where angularity is off on legs,
whether they are in or out,
the die corrector will file chock and relief
in the directions in which he wants the leg to move [2]

Figure 8 shows how the correcor performed the relief angle on the inner bearing and the choke angle on the outer bearing. After such operations, the leg will move inside the channel.

Figure 8 – Correction of the bearing of the channel
when needed to move the right leg in [2]

Figure 9 shows how the relief angle on the inner bearing and the choke angle on the outer bearing are performed on the right shelf. After such operations, the leg will move inside the channel.

Figure 9 – Correction of the bearing of the channel
when needed to move the right leg out [2]

Correction by flow

Per Figure 10a and 10b, the die corrector will work the die strictlv by flow. The bearings will be at 90° with the face of the die at all times.

Speeding up the flow is achieved by:

grinding the face of the die around the areas he wants to speed up, or
cutting excess bearing from the back of the die.

Figure 10 – Speeding up the flow by shortening bearing surface [2]

Sources:
1. Aluminum Extrusion Technology /P.R. Saha – 2000
2. Luis Bello, Die Corrections for Changing Flow Characteristics, Aluminum Extrusion Technology Seminar, Chicago, 1977
3. Die Defects and Die Corrections in Metal Extrusion /S.Z. Qamar, T. Pervez and Jo.Ch. Chekotu – Metals 2018, 8, 380
4. Test a new aluminium extrusion die – MEM07044A – Manufacturing Scills Australia – 2013
5. Process Factors to Consider before Modifying the Die /H. Glicken //Aluminum Extrusion Technology Seminar, Chicago, 1977
6. Undertake corrections and basic maintenance to aluminium extrusion dies and die support systems, MEM07042A, Manufacturing Skills Australia, 2013