Requirements for a die corrector

A complete list of qualification requirements for a aluminium extrusion die corrector.
Can be used when hiring new matrix spotters and to improve the skills of existing spotters.
Moreover, provides an overview of the tools, fixtures and equipment, which are used when correcting extrusion dies.

Adjustment of extrusion dies It is destiny, and the privilege of a limited number of professionals. At each manufacturing aluminum extrusions the figure of the die corrector it is a very important and difficult nonessential.

Available technical information on updating dies is very limited. Below are the qualification requirements for extrusion die spotters based on fairly recent materials from sources [1-3].

1 What is die correction

Aluminum Extruders are well known, that a good state of extrusion dies is a critical factor for the good quality of extruded aluminum products - profiles, pipe, rods and bars, as well as for performance of the extrusion press.

Figure 1 – Scheme of the extrusion press [1]

A die correction shop at the factory for pressing aluminum - a manufacturing site or manufacturing workshop, where dies run technical inspection, maintenance and repair. Usually, two types of die adjustments are distinguished [1]:

Adjustment of the new die before running it in production. It is made after the test extrusion of this die. Its main goal is small changes in the design of the die to improve the accuracy of the geometric dimensions of the pressed profile.. Moreover, At this stage nitriding dies to increase their surface hardness.
Correction of dies after, as it fulfills the next production cycle on the press. In this case, the reasons for adjusting the die may be necessary to change the flow of aluminum, damage and wear, destruction, deflections and loss of hardness.

2 Requirements for a die corrector

2.1 A die corrector

Worker of dies correction shop, that perform operations on the adjustment of the dies, They are called die correctors. They control dies resources and are usually responsible for the preparation of die sets, perform a test extrusion of new or corrected dies, die repair, as well as technical die service and related auxiliary support tools, such as bolsters and backers.

Die correctors must have a high level of technical skills and knowledge. When making a decision to correct the die, it is necessary to take into account the following [1]:

To eliminate one and the same profile of the defect can be carried out several options for the die correction.
Some corrections may be costly and time-consuming.
Improperly selected correction can reduce the service life of the die.
Sometimes it may take several corrections to eliminate the only problem.

Therefore, the correct selection and implementation of optimal corrective operations on the matrices are very important. To make the right decisions dies correctors must have many practical skills and abilities, as well as the necessary technical knowledge.

2.2 Skills and abilities

Required skills and abilities include [2]:

Reducing the length of the bearings by milling, grinding, hand and machine polishing to accelerate or increase the metal flow velocity
Methods to slow flow
Machining die bearings to reduce their surface roughness
Extensions running web using a punching
Grinding mirror of the die
mandrels processing to facilitate the flow of metal
Accurate measurement
Adusting bolster and support other components of the die
Simple changes in the design of dies (location, orientation, holes, etc.. e.) to increase productivity and increase the amount of good products
Storing information on the adjustments in the matrix passport and provide feedback to the developers of matrices.

Figure 2 – Typical tools for measuring matrices [1]

2.3 Technical knowledge of a die corrector

Required technical knowledge, should possess a die corrector , include [2-3]:

1) Dies:

construction:
solid dies
–hollow dies
– die support components
– chemical composition and characteristics of various steels for the manufacture of dies
die manufacturing process
die nitriding process and its purpose
aluminum profiles design process and the behavior with typical profiles in extrusion sections
bearings:
- form and purpose
- deviations of the plane of the bearing
- braking of the bearing
– release of the bearing

2) Die support components and typical errors:

bolsters:
– correspondence of dies to bolsters
– typical mistakes in aluminum extrusion, due to wrong selection or installation bolster
backers:
– decrease in hardness
– bowl-shaped
feeders:
– influence on the formation of surface defects
- the dimensions do not correspond to the bearings

3) Extrusion process:

behavior of various profile shapes during extrusion
profiles defects, associated with the deviation of "tongues"; appropriate die adjustment
differences in profile lengths in the die and possible causes:
– uneven cooling of ingots during homogenization
– misalignment of press components
– wear of bearings or their uneven polishing
press control:
– incorrect setting of heating parameters
– wrong choice of bolster for the die
– incorrect control of the process of extrusion an aluminum billet through a die
aluminum flow principles:
– differences in the flow rate of aluminum through various parts of the die
is the flow rate of aluminum over the cross section of the container
– dependence of the flow of aluminum on the length of bearing
– the rate of aluminum flow through the die and its temperature determine the degree of filling of the die with metal
heat:
- blanks
– matrices
– profile during extrusion
surface defects aluminum profiles and their reasons:
– matrix traces (risks) are caused by roughness or damage to the working bands, wear of the working bands or delamination of the nitrided layer (die lines)
–pick-ups
– streaking
- bubbles
– inclusions in the metal of aluminum blanks
influence of improper heating:
– warping of thin-walled profiles as a result of overheating
– matrix blocking
risk, associated with welding extrusion dies
matrix efficiency questions:
constant monitoring of the technical state matrices by regular checkup matrices and matrix entries in passports
balance amount adjustment to matrix volume profiles produced, the pressing speed and the number of marriage
If you need a new matrix or major alteration of the matrix array manufacturer.

3 Identification of the causes of defects in aluminum profiles

The matrix corrector (senior corrector) must have the skills and knowledge, required to participate in the following activities:

systematic inspection of aluminum profiles in order to identify defects and inconsistencies, caused by both solid or hollow matrices, and other defects, not related to matrices;
determination of the most effective corrective action to eliminate the identified defect
if necessary, development of recommendations for extrusion press operators, matrix designers and matrix manufacturers.

3.1 Detection of an aluminum profile defect

Check profile for shape distortion, transverse and longitudinal
Check the conformity of the profile dimensions to the drawings
Checking the profile for surface defects
Determine the location of the defect: at the beginning or at the end of the pressing cycle
Make a preliminary assessment of, whether the cause of the identified defects is the matrix (matrix set) or they have other causes

3.2 Defects, that are not associated with a die or die kit

Check the heating of the matrix and workpiece, as well as temperature records. Make sure, that the heating and temperature are in accordance with the requirements
Make sure, that the profile was pressed at the correct speed and other parameters, set for this profile
Set workpiece quality characteristics: primary or secondary metal, foundry quality
Obtain confirmation from the service of the chief mechanic and chief power engineer, that there are no problems on the extrusion press line: mechanical, electrical, structural or electronic control

3.3 Defects, that are associated with a die or with die kit

Perform a technical inspection of the matrix and matrix kit
Inspect die for excessive wear, deflection, damage or other defects
Inspect work belts for shortening, surface defects, loss of the specified angle and gaps
Define, whether the matrix needs to be corrected, scrap or return to manufacturer
Inspect the die kit components for defects and misalignment when installing the die in the die holder

3.4 Development of recommendations

Prepare recommendations for adjusting the matrix, if necessary
Prepare recommendations for possible changes in pressing technology or temperature settings, if necessary

4 Possible causes of defects in aluminum profiles

4.1 Excessive die deflections:

Damaged Matrix
Insufficient or incorrect support of the matrix by the matrix kit due to:
– low quality components
– component wear
– incorrect selection of matrix kit components

4.2 Die or support die kit design:

Dimensional tolerances and gaps too tight, which the corrector is not able to put into practice
Excessive dimensional tolerances and gaps, which leads to displacement of components during extrusion and blockage of metal flow

4.3 Die blocking:

Die damage
Over polishing or improper polishing of the die
Matrix tongue bend
Bearing gaps too small
Billet overheating

4.4 Support die kit problems:

Excessive mandrel deflections
Excessive die deflection
Die displacement during extrusion

4.5 Billet:

Chemical composition and structure
Billet heating process
Changes in the chemical composition and structure of the billet during heating

4.6 Extrusion technology

Incorrect temperature parameters when heating the billet
Insufficient control of the initial upsetting of the billet through the die (too fast or too high pressure)
Wrong pressing parameters:
– too high/low speed of metal flow through the die
– insufficient and incorrect profile support at the exit from the die
– weak or uneven hardening

4.7 Fabrication and adjustment of the die:

Shape distortion:
– during extrusion
– at the exit of the die
– during hardening
Uneven thread flow for multipoint die
Profile collapse
Surface defects, including:
– pickups
– cracking
– streaking
– die marks.

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