Lifetime evaluation of two different hot work tool steels in aluminium extrusion

by C. Sommitsch, R. Sievert, T. Wlanis and C. Redl

During aluminium extrusion, the die experience cyclic thermo-mechanical loads that can lead to materials degradation and failure. For a process optimization and a comparison of different hot work tool steels, the finite element method is an appropriate means. Local inelastic strains result from the interaction of the applied temperature and stress loading and can be computed by suitable inelastic constitutive equations. Stress amplitudes and dwell times during extrusion result in creep-fatigue damage. A lifetime consumption model sums increments of a damage variable over time and defines materials failure as the accumulation of the resulting damage variable to a critical value. The procedure for the identification of the material parameters for both the constitutive and the damage model is described in detail, including the material parameters for the description of time-effects, and applied to the hot work tool steel Böhler W300 ISOBLOC (EN 1.2343). The lifetime consumption for two different hot work tool steels is compared on the basis of an example in aluminium extrusion.

Computational Materials Science

doi:10.1016/j.commatsci.2007.07.054

Keywords: Extrusion; Creep; Fatigue; Viscoplasticity; Aging; Failure

Different aluminum alloys extrusion

Extruded structural sections are produced by hot extrusion in which a heated cylindrical billet is pushed under high pressure through a steel die to produce the desired structural shape. The extrusion is then fed onto a run-out table where it is straightened by stretching and cut to length. During extrusion, metal flow occurs most rapidly at the center of the ingot resulting in oxides and surface defects being left in the last 10–15% of the extrusion which is discarded.

In general, the stronger the alloy, the more difficult it is to extrude. One of the advantages of the 6XXX (Al-Si-Mg) alloys is that they exhibit good extrudability. On the other hand, the 2XXX (Al-Cu) and 7XXX (Al-Zn) alloys are referred to as “hard” alloys because they are more difficult to extrude.

Alloy Relative extrusion pressure
1100 1.0
3003 1.2
6061 1.6
2014 1.8
7075 2.3

A profile’s shape factor (the ratio of the perimeter of the profile to its area) is an approximate indicator of its extrudability, i.e. the higher the ratio, the more difficult it is to extrude. The extrusion process itself and heat treatable aluminium alloys make it possible to manufacture complex, thin-walled cross-sections with a strength equal to that of ordinary structural steel. The torsional stiffness can be improved by exploiting the advantages of hollow sections.

Unsymmetric shapes, shapes with sharp corners, profiles with large thickness variations across their cross section, and those that contain fine details are all more difficult to extrude. Generous fillets and rounded corners help to reduce extrusion difficulties.


Data from ASM metals handbook vol. 14

Aluminum Extrusion for IPOD

Ilya Yakubov, a third-year Industrial Design student from Dawson College in Canada, won top prize in the 2007 International Aluminium Extrusion Design Competition.

Yakubov competed internationally against students from technical and university programs, walking away with first place and a $3,000 (US) prize for his design proposal of an extruded aluminium MP3 holder.Yakubov’s design accommodates popular MP3 players, as well as some cell phones. Yakubov attributesthe efficiency of the extrusion process to being able to produce a product with fewer parts at a reduced cost.
Noting that any MP3 player accessory would have a significant market, one of the judges noted that the design was adaptable yet had a clean, structural look.