Aluminium extrusion

Extrusion die corrector: skills and abilities

  • A complete list of qualification requirements for a aluminium extrusion die corrector.
  • Can be used when hiring new extrusion die correctors and to improve the skills and abilities of existing ones.

Correcting extrusion dies is the privilege of a limited number of professionals. The personality of the die corrector it is a very important and difficult replaceablel at each aluminшum extrusion plant. Available technical information on the correction of aluminium extrusion dies is very limited. Below are the qualification requirements for extrusion die correctors based on the recent materials from sources [1-3].

1 What is die correction

All 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 – The scheme of the extrusion press [1]

A die correction shop at each aluminium extrusion plant is a manufacturing workshop, where dies run technical inspection, correction, 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 extruded profile. Moreover, at this stage dies are nitrided to increase their surface hardness.
  • Correction of dies after the 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 an die corrector

2.1 Extrusion die corrector

There are workers 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]:

  • The die corrector must choose the right option for the die correction from several possible ones.
  • 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 right 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 of an extrusion die corrector

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
  • Extending die bearing by using a punching
  • Grinding of the die face
  • Mandrels processing to facilitate the flow of metal
  • Accurate measurement
  • Adusting bolster and other support 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 die passport and provide feedback to the developers of dies.

Figure 2 – Typical tools for measuring matrices [1]

2.3 Technical knowledge of an extrusion die corrector

Each die corrector should possess the following technical knowledge [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
    – choking 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
    – 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:
    – billets
    – dies
    – profiles during extrusion
  • surface defects of aluminium profiles and their reasons:
    – die lines are caused by roughness or damage of die bearings, wear of die bearings or delamination of the nitrided layer
    pick-ups
    – streaking
    – bubbles
    – inclusions in the metal of aluminum billets
  • influence of improper heating:
    – warping of thin-walled profiles as a result of overheating
    – die
  • die blocking
  • risks, associated with welding extrusion dies
  • die efficiency questions:
  • constant monitoring of the technical state of dies

3 Identification of the causes of defects in aluminum profiles

The die 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 dies;
  • determination of the most effective corrective action to eliminate the identified defect
  • if necessary, development of recommendations for extrusion press operators, die designers and die manufacturers.

3.1 The 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 die and billets, as well as temperature records. Make sure, that the heating and temperature are in accordance with the requirements
  • Make sure, that the profile was extruded at the correct speed and other parameters, set for this profile
  • Set billet quality characteristics: primary or secondary metal, cast quality
  • Obtain confirmation from the plant services, 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 die and die kit
  • Inspect die for excessive wear, deflection, damage or other defects
  • Inspect die bearings for shortening, surface defects, loss of the specified angle and gaps
  • Define, whether the die 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 die, if necessary
  • Prepare recommendations for possible changes in extrusion technology or temperature settings, if necessary

4 Possible causes of defects in aluminium profiles

4.1 Excessive die deflections:

  • Damaged die
  • Insufficient or incorrect support of the die by the die kit due to:
    – low quality components
    – component wear
    – incorrect selection of die 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
  • Die 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 lines.

Sources:

  1. Die Defects and Die Corrections in Metall Extrusion / S. Z. Qamar, T. Pervez and J. Ch. Chekotu, Metals, 2018, 8, 380
  2. Undertake corrections and basic maintenance to aluminium extrusion dies and die support systems – MEM07042A, Manufacturing Skills Australia, 2013
  3. Identify causes of faulty aluminium extrusions – MEM07043, Manufacturing Skills Australia, 2019