A Review of Papers Presented at the Ninth International Extrusion Technology Seminar, ET’08 – Part II

by Roger A.P. Fielding, Benchmarks

In the first of this series of articles on the teaching presented at the Ninth International Extrusion Technology Seminar, ET’08, I questioned why the process of “continuous improvement” is deemed necessary to achieve benchmark performance in extrusion operations. An extrusion press designed to produce 6000 pounds (3000kg) per hour should extrude at that rate when commissioned.

In a previous article, we also reported on the factors which define the productivity of an extrusion press. These are recovery, machine efficiency, extrusion speed, and press operation (minimum dead production time). While each of these measures must be maximized before an extrusion press can produce at an annual rate in excess of 36 million pounds, all can be accounted during the Feasibility Study and Preliminary Engineering for a new press system. (1) The data presented at that time included references to a 7” 2200 ton press producing at a rate of 20 million pounds in 1989, and an 8” 2750 ton press producing at a rate of 36 million pounds in 1999. (2)

Back to basics: The ram speed and the dead cycle time dictate the ultimate productivity of an extrusion press. The ancillary equipment — : the billet furnace; die ovens, container and die slide heating systems; the section cooling system; the handling, stretching, sawing, and stacking systems—must complement the extrusion press. They must be capable of supplying billet and removing extruded sections at production rates greater than the average output of the extrusion press. The total system must be reliable, and perform to the “six-sigma” standard of reliability.

The properties of the aluminum extrusion billet limit the maximum ram speed that can be attained. However, as was reported by Ramanan and Parson, AA6xxx alloys represent more than 70 percent of the extrusion market in North America. And some of these alloys — previously registered with the Aluminum Association, but relatively new to the U.S. market (for example, AA6060, AA6005A, and AA6463A) — offer improved productivity for the customer while maintaining mechanical and other performance characteristics. (3)

The instantaneous productivity (the ram speed) of a given extrusion press is maximized when the flow stress of the aluminum billet is overcome by the unit pressure of the press. But, as is noted by Al Kennedy, “many North American extruders operate in the range 70,000 to 80,000 psi.” (4)

The “high productivity” presses referred to in reference (2) above operated at over 105,000 psi. The high unit pressure is essential if one is to achieve AA6063 mechanical properties when extruding AA6060 at high speeds and relatively low billet temperatures.

The following ET’08 papers highlight some of the key issues related to maximizing the productivity of extrusion presses:

• Against a background in which shapes are more complex, and achieving tolerances while holding correct quenching becomes increasingly difficult, Jonathan Pangborn, and his colleagues promote the use of AA6005A over AA6005 and AA6105 to maximize extrudability. In so doing they reopen the subject of performance standards for extrusions by pointing out that “At the heart of this approach is the belief that an extruder should be selling performance and functionality, not alloy chemistry.” (5)
• Dickson and Kindlihagen emphasize that die trials can be eliminated, and extrusion speed maximized while controlling the shape of the extrusions, by manufacturing dies precisely according to design. Dimensional specifications and methods of verification are defined. (6)
• In their paper “Scrap Allocation,” Johnie Adams and his colleagues address the issue of the front- and back-end scrap allowances. These allowances have to be made to eliminate the front-end (transverse weld) defect, which is an inevitable consequence of extruding consecutive billets, and the back-end (coring) defect caused by the flow of billet surface into the extrusion. Rules are provided which enable the correct weight billet to be calculated; thereby minimizing the losses, which occur as these defects are removed from the extrusions. (7)
• The paper “Recovering Recovery” by Jarat Agarwal and his colleagues, which focuses on the extrusion process and the known sources of scrap, appears to have achieved the same 15% improvement in recovery in 17 weeks as the work reported on by James Scheuing and John Funai. Employing Six Sigma methodologies, Scheuing’s and Funai’s paper: “Scrap… The Most Expensive Thing We Do”, makes for an interesting comparison with the former. (8) (9)

It is this writer’s contention that improvements in performance do not occur gradually!

1. Fielding, Roger A. P., Project Management in Extrusion and Recycling of Aluminum, Light Metal Age, Vol. 64, No. 5, October 2006, pp 10-20
2. Fielding, Roger A. P., V. I. Johannes and P. Howard Fielding, Extrusion Productivity, Light Metal Age, vol. 63, nos. 5, 6. June 2005, pp. 6-14.
3. Ramanan, Ram. and Nick Parson, New Generation of Matte Alloys from Alcan. Ninth International Extrusion Technology Seminar, ET’08
4. Kennedy, Al., Seven Steps for Selecting and Extrusion Press ibid.
5. Jonathan Pangborn, et al.,Tailor-Made Alloys: The Future of 6xxx Medium Strength Structural Applications ibid.
6. Dickson, R. F., and A. Kindlihagen, Extrusion Die Specification: How to Obtain Repeatable Peformance ibid.
7. Adams, Johnie. et al Scrap Allocation ibid.
8. Agarwal, Jajat Recovering Recovery ibid.
9. Scheuing, James H., and John A. Funai, Scrap… The Most Expensive Thing We Do ibid.

Volume 14 Issue 2

The New Spinning Log Welder: A Model of Efficiency

BENCHMARKS: A Review of Papers Presented at the Ninth International Extrusion Technology Seminar, ET'08 - Part II

Why Our Customers "Have It Made"

President's Message: Finding the Silver Lining in Tough Times

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