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Handbookof AluminumVolume 7Physical Metallurgy and Processesedited byGeorge E. Tot tenG. E. Totten & Associates, Inc.Seattle, Washington, U.S.AD. Scott MacKenzieHoughton International IncorporatedValley Forge, Pennsylvania, U.S.A.MARCEL DEKKER, INC. NEW YORK BASEL

Library of Congress Cataloging-in-Publication DataA catalog record for this book is available from the Library of Congress.ISBN: 0-8247-0494-0This book is printed on acid-free paper.HeadquartersMarcel Dekker, Inc.270 Madison Avenue, New York, NY 10016tel: 212-696-9000; fax: 212-685-4540Eastern Hemisphere DistributionMarcel Dekker AGHutgasse 4, Postfach 812, CH-4001 Basel, Switzerlandtel: 41-61-260-6300; fax: 41-61-260-6333World Wide Webhttp:==www.dekker.comThe publisher offers discounts on this book when ordered in bulk quantities. For moreinformation, write to Special Sales=Professional Marketing at the headquarters address above.Copyright # 2003 by Marcel Dekker, Inc. All Rights Reserved.Neither this book nor any part may be reproduced or transmitted in any form or by anymeans, electronic or mechanical, including photocopying, microlming, and recording, orby any information storage and retrieval system, without permission in writing from thepublisher.Current printing (last digit):10 9 8 7 6 5 4 3 2 1PRINTED IN THE UNITED STATES OF AMERICA

PrefaceAlthough there are a limited number of reference books on aluminum metallurgy,there is a signicant and continuing need for a text that also addresses the physicalmetallurgy of aluminum and its alloys and the processing of those alloys that will beof long-term value to metallurgical engineers and designers. In addition, a number ofvitally important technologies are often covered in a cursory manner or not at all,such as quenching, property prediction, residual stresses (sources and measurement),heat treating, superplastic forming, chemical milling, and surface engineering.We have enlisted the top researchers in the world to write in their areas of spe-cialty and discuss critically important subjects pertaining to aluminum physicalmetallurgy and thermal processing of aluminum alloys. The result is an outstandingand unique text that will be an invaluable reference in the eld of aluminum physicalmetallurgy and processing.This is the rst of two volumes on aluminum metallurgy and some of the topicsinclude: Pure aluminum and its properties. An extensive discussion of the physical metallurgy of aluminum, includingeffect of alloying elements, recrystallization and grain growth, hardening,annealing, and aging. Sources and measurement of residual stress and distortion. An overview of aluminum rolling, including hot rolling, cold rolling, foilproduction, basic rolling mechanisms, and control of thickness and shape. A detailed discussion of extrusion design. A thorough overview of aluminum welding metallurgy and practice.iii

Casting, including design, modeling, foundry practices, and a subject oftennot covered in aluminum metallurgy bookscasting in a microgravityenvironment. Molten metal processing and the use of the Stepanov continuous castingmethod. Forging design and foundry practice. Sheet forming. An overview of equipment requirements and a detailed discussion of heattreating practices. An in-depth discussion of aluminum quenching. An overview of machining metallurgy and practices, including materialproperty dependence, machining performance process parameters, anddesign. An extensive, detailed, and well-referenced overview of superplasticforming. A thorough discussion of aluminum chemical milling, including pre-maskcleaning, maskant applications, and scribing, etching, and demasking. Powder metallurgy including: applications, powder production, part pro-duction technologies, and other processes.The preparation of this book was a tremendous task and we are deeplyindebted to all our contributors. We would like to express special thanks to AliceTotten and Patricia MacKenzie for their assistance and patience throughout the pro-cess of putting this book together. We would also like to acknowledge The BoeingCorporation and Houghton International for their continued support.George E. TottenD. Scott MacKenzieiv Preface

ContentsPreface iiiContributors ixPart One ALUMINUM PHYSICAL METALLURGYAND ANALYTICAL TECHNIQUES1. Introduction to Aluminum 1Alexey Sverdlin2. Properties of Pure Aluminum 33Alexey Sverdlin3. Physical Metallurgy and the Effect of Alloying Additionsin Aluminum Alloys 81Murat Tiryakiogglu and James T. Staley4. Recrystallization and Grain Growth 211Weimin Mao5. Hardening, Annealing, and Aging 259Laurens Katgerman and D. Eskin6. Residual Stress and Distortion 305Shuvra Das and Umesh Chandrav

Part Two PROCESSING OF ALUMINUM7. Rolling of Aluminum 351Kai F. Karhausen and Antti S. Korhonen8. Extrusion 385Sigurd Stren and Per Thomas Moe9. Aluminum Welding 481Carl E. Cross, David L. Olson, and Stephen Liu10. Casting Design 533Henry W. Stoll11. Modeling of the Filling, Solidication, and Cooling ofShaped Aluminum Castings 573John T. Berry and Jeffrey R. Shenefelt12. Castings 591Rafael Colas, Eulogio Velasco, and Salvador Valtierra13. Molten Metal Processing 643Riyotatsu Otsuka14. Shaping by Pulling from the Melt 695Stanislav Prochorovich Nikanorov and Vsevolod Vladimirovich Peller15. Low-g Crystallization for High-Tech Castings 737Hans M. Tensi16. Designing for Aluminum Forging 775Howard A. Kuhn17. Forging 809Kichitaro Shinozaki and Kazuho Miyamoto18. Sheet Forming of Aluminum Alloys 837William J. Thomas, Taylan Altan, and Serhat Kaya19. Heat Treating Processes and Equipment 881Robert Howard, Neils Bogh, and D. Scott MacKenzie20. Quenching 971George E. Totten, Charles E. Bates, and Glenn M. Webster21. Machining 1063I. S. Jawahir and A. K. Balajivi Contents

22. Superplastic Forming 1105Norman Ridley23. Aluminum Chemical Milling 1159Bruce M. Grifn24. Powder Metallurgy 1251Joseph W. NewkirkAppendixes1. Water Quenching Data: 7075T73 Aluminum Bar Probes 12832. Type I Polymer Quench Data: 2024T851 Aluminum Sheet Probes 12853. Type I Polymer Quench Data: 7075T73 Aluminum Sheet Probes 12864. Type I Polymer Quenchant Data: 7075T73 Aluminum Bar Probes 1287Index 1289Contents vii

ContributorsTaylan Altan, Ph.D. Ohio State University, Columbus, Ohio, U.S.A.A. K. Balaji, Ph.D. The University of Utah, Salt Lake City, Utah, U.S.A.Charles E. Bates, Ph.D., F.A.S.M. The University of Alabama at Birmingham,Birmingham, Alabama, U.S.A.John T. Berry, Ph.D. Mississippi State University, Mississippi State, Mississippi,U.S.A.Niels Bogh, B.Sc. International Thermal Systems, Puyallup, Washington, U.S.A.Umesh Chandra, Ph.D. Modern Computational Technologies, Inc., Cincinnati,Ohio, U.S.A.Rafael Colas, Ph.D. Universidad Autonoma de Nuevo Leon, San Nicolas de losGarza, MexicoCarl E. Cross, Ph.D. The University of Montana, Butte, Montana, U.S.A.Shuvra Das, Ph.D. University of Detroit Mercy, Detroit, Michigan, U.S.A.D. Eskin, Ph.D. Netherlands Institute for Metals Research, Delft, The Netherlandsix

Bruce M. Griffin, B.S.M.E.T., M.S.M.E. The Boeing Company, St. Louis,Missouri, U.S.A.Robert Howard, B.Sc. Consolidated Engineering Company, Kennesaw, Georgia,U.S.A.I. S. Jawahir, Ph.D. University of Kentucky, Lexington, Kentucky, U.S.A.Kai F. Karhausen, Ph.D. VAW Aluminium AG, Bonn, GermanyLaurens Katgerman, Ph.D. Netherlands Institute for Metals Research, Delft, TheNetherlandsSerhat Kaya, M.Sc. Ohio State University, Columbus, Ohio, U.S.A.Antti S. Korhonen, D.Tech. Helsinki University of Technology, Espoo, FinlandHoward A. Kuhn, Ph.D. Scienda Building Sciences, Orangeburg, South Carolina,U.S.A.Stephen Liu, Ph.D. Colorado School of Mines, Golden, Colorado, U.S.A.D. Scott MacKenzie, Ph.D. Houghton International Incorporated, Valley Forge,Pennsylvania, U.S.A.Weimin Mao, Ph.D. University of Science and Technology Beijing, Beijing, ChinaKazuho Miyamoto, Dr.Eng. Miyamoto Industry Co. Ltd., Tokyo, JapanPer Thomas Moe, M.Sc.-Eng. Norwegian University of Science and Technology,Trondheim, NorwayJoseph W. Newkirk, Ph.D. University of MissouriRolla, Rolla, Missouri, U.S.A.Stanislav Prochorovich Nikanorov, Dr.Sc. A.F. Ioffe Physical Technical Institute ofRussian Academy of Sciences, Saint Petersburg, RussiaDavid L. Olson, Ph.D. Colorado School of Mines, Golden, Colorado, U.S.A.Ryotatsu Otsuka, Dr.Eng. Showa Aluminum Corporation, Osaka, JapanVsevolod Vladimirovich Peller A.F. Ioffe Physical Technical Institute of RussianAcademy of Sciences, Saint Petersburg, RussiaNorman Ridley, B.Sc., Ph.D., D.Sc., C.Eng., F.I.M. University of Manchester,Manchester, Englandx Contributors

Jeffrey R. Shenefelt, Ph.D. Mississippi State University, Mississippi State,Mississippi, U.S.A.Kichitaro Shinozaki National Institute of Advanced Industrial Science andTechnology, Tsukuba, JapanJames T. Staley, Ph.D.* Alcoa Technical Center, Alcoa Center, Pennsylvania,U.S.A.Henry W. Stoll, Ph.D. Northwestern University, Evanston, Illinois, U.S.A.Sigurd Stren, Ph.D. Norwegian University of Science and Technology, Trondheim,NorwayAlexey Sverdlin, Ph.D. Bradley University, Peoria, Illinois, U.S.A.Hans M. Tensi, Ph.D. Technical University of Munich, Munich, GermanyWilliam J. Thomas, Ph.D. General Motors, Troy, Michigan, U.S.A.Murat Tiryakioglu, Ph.D. Robert Morris University, Moon Township,Pennsylvania, U.S.A.George E. Totten, Ph.D., F.A.S.M. G.E. Totten & Associates, Inc., Seattle,Washington, U.S.A.Salvador Valtierra, Ph.D. Nemak Corporation, Monterrey, MexicoEulogio Velasco, Ph.D. Nemak Corporation, Monterrey, MexicoGlenn M. Webster, A.A.S. G.E. Totten & Associates, Inc., Seattle, Washington,U.S.A.*RetiredContributors xi

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8ExtrusionSIGURD STVREN and PER THOMAS MOENorwegian University of Science and Technology, Trondheim, Norway1 INTRODUCTIONThis chapter is devoted to extrusion of aluminum alloys and divided into three mainsections. Section 2 covers the basic parameters of extrusion needed for designing analuminum section and a die, for understanding the processing steps, and foroptimizing productivity, cost and product quality. A specic section shape is usedto illustrate the interaction between these parameters. Section 3 is focused onthe commercial applications aspects of extruded sections, life cycle aspects, alloyselection and section design guidelines. Section 4 covers the extrusion process insome detail, focusing on the basics of quantitative modeling of metal ow in thecontainer and through the die. In the nal section, some of the outstanding researchchallenges in the theory of extrusion of thin walled aluminum sections are discussed:(1) 3D-modeling of thin-walled extrusion; (2) the bearing channel friction in inter-action with die deections and section surface formation; (3) stability of ow;and (4) limits of extrudability.The intention is that the chapter should give the reader an overview of thepractical aspects of extrusion as well as an understanding of the present state ofthe theoretical work and some challenges in this branch of metal forming scienceand technology. However, the study of extrusion as a process is both relativelycomplex and multidiciplinary, and this chapter can hardly give the answer to allproblems that may be encountered. Thus, before making detailed section designand alloy decisions, the reader is advised to contact an extrusion plant. Even thoughtheoretical and experimental work has managed to explain a number of relevantphenomena, the quality of an extruded prole and naturally also of a complete prod-uct based on extrusions is still mainly dependent on the experience of personnel close385

to or at the extrusion plant. One may also confer with more general works onextrusion [1,2].2 BASIC PARAMETERS OF EXTRUSION2.1 The ProcessThe most common method for producing aluminum proles is that of directextrusion (Fig. 1). Here, the ram is moving into the container at one end, and pushesthe billet through the opening of the die at the other end. The temperature of thedeforming aluminum alloy is in the range of 450^600C during the process cycle.In contrast to the extrusion of steel, aluminum extrusion is taking place in absenceof any lubrication of the die. Hence, the material sticks to the container and thedie, giving a highly inhomogeneous ow with large degree of visco-plastic shear ow(See Sec. 4). The material far a way from the wall is owing easier than that closer toit, with the surface of the billet remaining in the container. The billet and the con-tainer are normally circular cylindrical, but can in special cases be rectangular withrounded corners.A special feature in extrusion of aluminum alloys is the production of hollowsections (Fig. 2). In this case the metal ows into the opening between the dieand the mandrel. The mandrel is kept in position by bridges. The billet materialis forced, by the movement of the ram, into the portholes in the bridge die, calledthe feeder ports. Under the bridges, adjoining metal streams meet and areforgewelded together in the weld chamber, before owing through the bearingchannel, i.e. the opening between the die and the mandrel.Besides direct extrusion, two other special extrusion methods are used, indirectextrusion, and continuous extrusion, the Conform method [3]. In indirect extrusion(Fig. 3) the die is pushed into the container, where as the extrudate is owing inopposite direction through the hollow stem. In the continuous extrusion (Fig. 4)a continuous feedstock is fed into a groove in a rotating wheel. Pressure is builtFigure 1 Direct extrusion of an open section.386 Stpren and Moe

up by friction between the groove walls and the feedstock in the gap between thewheel groove, the feeder plate and the abutment. The metal is then forced to thedie opening in a continuous ow. Both open and hollow sections can be produced.Extrusion in rectangular containers, indirect extrusion and continuousextrusion are used for special products in limited quantities. Therefore, in the restof this chapter the direct extrusion of open and hollow sections are dealt with.The main parameters of the billet, the container and the extruded section are(Fig. 1):. Diameter of the container: Dc m. Cross section area of the container: Acontainer Ac p4D2c m2Figure 2 Direct extrusion of a hollow section.Figure 3 Indirect extrusion.Extrusion 387

. Billet weight: Wb r p4D2bLb kg. Billet diameter Db m. Billet length Lb m. Density of aluminum: r 2700 kg=m3. The circumscribed diameter of the section: d m. Section thickness: t m. Cross sectional area of the section: Asection As m2. Weight of section per meter length: ws Asr kg=m. Reduction ratio: R AcAsThe most common values for the diameter of the container are 0.178 m and0.208 m. The billet diameter is usually 5^10 mm less than the container diameter,allowing the billet to enter the container easily. The circumscribed diameter ofthe prole is usually less than 0.9 times the diameter of the container, but speciallydesigned dies with a so-called expansion chamber may actually allow for d >Dc. The section thickness often varies over the cross section of the prole. Thereduction ratio is normally in the range of 20^80. If R is very high (R> 70) andthe section is of a proper shape, the die is usually designed with more than onedie opening (Fig. 5). In this case, the reduction ratio is:R AcAsnn number of die openingsWhen an extrusion press cycle is carried out (see Sec. 4 for details), a small partof the billet is left in the container, the discard (Fig. 6). The length of the discard isnormally around 10^20 mm.. Discard length: Ld. Discard weight: Wd r p4D2cLd kg. The weight of the extruded section: Ws Wb Wd kg. Length of the extruded section: Ls Wsws mFigure 4 Continuous extrusion.388 Stpren and Moe

2.2 The DieThe tooling package is to perform the deformation of the aluminum and must nat-urally withstand very large forces. Tools are generally made of high strength steelssuch as H11 and H13, and surface in direct contact with the owing material ishardened through nitriding prior to any use. Furthermore, the complete toolingpackage will be comprised of a great number of parts which all are meant to supportthe die when pressure is applied by the stem. The complete tooling package will beFigure 6 Billet, discard, and the extruded section.Figure 5 A multihole die.Extrusion 389

designed differently for the extrusion of hollow or open proles. In any case,however, a bolster will be situated directly behind the die and provide the mainsupport. The die and bolster will then be placed in a horseshoe clamp, which is rmlyattached to the press structure.In the case of extrusion of open sections one die design does not differ signi-cantly from another although the bolster may provide varying degrees of support.Various die designs have, however, been developed for the extrusion of hollowproles. The names of the most commonly used die types are porthole, spiderand bridge, and for the extrusion of 6XXX-alloys porthole dies have traditionallybeen most popular, partly due to the ease with which they can be cleaned afterextrusion.The design of a porthole die is displayed in Fig. 7. The outer contour of thesection is formed by the die plate (Fig. 7(a)). The tongue will be less stiff and weakerthan the rest of the plate because it supports the pressure from the deformingmaterial on the tongue only along one edge. The inner circumference of the sectionis formed by the mandrel (Fig. 7(b). The mandrel is an integrated part of the portholeFigure 7 Billet, die, and extruded section in the process of extrusion.390 Stpren and Moe

die, connected to the rest of the die by webs, or bridges. In the mandrel a groove ismachined out. This groove enables the internal rib in the hollow section to be for-med.The deforming alloy is owing over the bridges and down into the feeder ports.Under each bridge, in the weld chamber, the two neighboring metal streams areforge-welded together. In this process the temperature of the material will not exceedthat of melting, but welding will take place due to high pressures and diffusion rates.The alloy is also owing into the groove in the mandrel from two sides, and in thecenter of the groove the two streams of metal are forge-welded, before the materialows into the bearing channel. All such welds are denoted seam welds. If pressuresare not high enough in the weld zones, insufcient welding will take place.Furthermore, if material ows in an uncontrolled manner, one will not be ableto predict the exact position of the weld. All these phenomena are highly unwantedand, hence, detailed studies of such can be found in the literature [4].When designing mandrels one has to keep the following in mind:. The stiffness and strength of the bridges should be optimized. The feederports should at the same time be as large as possible in order to reducethe load on the mandrel and allow for higher extrusion speed. This will,however, result in a weak bridge construction with unwanted exibilityand an increased risk of die deection.. Controlled ow out of the bearing channel should be sought. The die andthe bearing channel should be designed so that the section leaves thebearings at a uniform speed and without generating excessive tensile orcompressive stresses. Of special importance is the control of metal owand die welding of the inner rib, because this cannot be inspected fromoutside during the press cycle.. The surface of the section should be homogeneous and leave the die withoutstreaks and stripes at the highest acceptable speed.Clearly, there is a complex, but a very fascinating design-optimizing challengehere. Today, die design competence exists mainly as practical knowledge by highlyskilled die designers, die producers and die correctors in the die shops. As willbe pointed out in Secs. 4 and 5, however, the development of 3D computer simu-lation of hot extrusion processes is approaching such a level of precision that itcan be used as a tool for die design. It must, however, be done in close cooperationwith skilled and experienced die specialists.2.3 The Manufacturing SystemSatisfactory control of the material ow may be viewed as the key element in a suc-cessful production of aluminum proles. In this context the last assertion hastwo alternative interpretations, and both are in fact equally correct. In order to pro-duce extrusions with the desired quality at an optimum pace, one has to establishsome sort of an understanding of the mechanisms of plastic ow of material inthe container and die. However, if an enterprise is to succeed economically inthe extrusion business, it is as important that it masters the logistics, that is thecontrol of the material ow in and around the production facilities. The extrusionprocess is carried out in an extrusion plant, which often has a lay out similar toExtrusion 391

that presented in Fig. 8. Although heat treatment in general is the most time con-suming part of the production system, other process steps may in fact constitutethe actual bottlenecks. The pressing of proles is one such as it is non-continuous,and as considerable time is spent on changing dies, reloading new material intothe container and performing maintenance tasks. Procedures are made even morecomplicated as new production orders for proles often may necessitate several trialruns on the press. If the material is not transported effectively, down times may easilybe long, and the most important parameter of all, productivity, will, consequently, below.As is seen on Fig. 8 the extrusion process is comprised of a great number ofsteps. One of the most important, however, is the production of raw materialfor the process, and this usually does not take place in the plant. Feed stock forthe process is logs, normally in lengths of 6^7 m. They are supplied from the casthouse of primary aluminum smelter or a secondary (recycled) aluminum cast house.The logs are produced as visualized in Fig. 9.The liquid metal at temperature above 700C is cleaned, added alloyingelements and grain rener before entering the casting table. By passing the castingmolds with direct water cooling, the liquid aluminum alloy solidies into a log. Aftercasting, the log is homogenized in a temperature cycle that secures the best possibleextrudability by establishing a homogeneous distribution of alloying elementsand by dissolving phases with low melting points, typically Mg2Si [5,6]. The logsare then transported to the extrusion plant.In the plant a number of distinct processing steps takes place (Fig. 8). The logsare rst taken one by one from the log stacker and transported to the inductionheater. Here, a certain temperature prole is imposed on the log, and it is thencut into billets of a prescribed weight. In some plants the logs are cut prior toany heating.Figure 8 Layout of an extrusion plant.392 Stpren and Moe

The billet is then loaded into the extrusion press, where the ram pushes it intothe container. The end of the billet surface in contact with the ram, has been givena coating so that it does not stick to the dummy block between the ram and thebillet. Because the billet has smaller diameter than the container bore, it is givenan upsetting in order to ll the container. In this phase there is a risk of entrappingair in the container, and, thus, the ram stops after upsetting, unloads, and movesa small distance backwards to let the possible entrapment leave. This is calledthe burb cycle.Thereafter, the extrusion process commences. The ram pushes the billetthrough the die opening. The load capacity of the press with a container diameterof 0.178 m is normally 16 MN, which corresponds to a specic pressure of 643 MPa.If the container diameter is 0.208 m, the load capacity is normally 22 MN and thespecic pressure 647 MPa. The temperature of the billet prior to extrusion is inthe range 450^470C. In the induction heater, the billet may have been given varyingtemperature along its length in order to compensate for the heat generation causedby the shearing along the container walls when it is pushed through the container(see also Sec. 4). This is called tapering, and the highest temperature is usuallyin the front end of the billet. The temperature of the section leaving the die is inthe range of 550^600C. The taper should be given in such a way that the runout temperature is constant as this will result in minimum variation of dimensionsand properties during the press cycle.As the section front leaves the die, it is gripped by a puller, which guides thesection out on the run out table. The prole is then quenched and further cooleddown when moving sideways along the table. The lengths of the proles upon leavingFigure 9 Direct chilling casting (DC-casting) of logs.Extrusion 393

the die may be from 20 to 50 m, depending on the length of the billet and thereduction ratio. Normally, a number of charges (billets) are performed with the samedie in a production set up. In this case, one may weld the prole from the new chargedirectly to the one produced in the foregoing charge, creating a so-called charge weld.This procedure simplies production, but necessitates cutting of the prole duringextrusion. On the cooling table the section is given a plastic deformation of 0.5^2%elongation in order to eliminate internal stresses due to uneven cooling over thecross section of the prole and straighten up possible bends and twists before goinginto the cutting saw. The extruded section is nally cut into prescribed lengths,normally 6 m. The process of cutting may vary somewhat from one plant to another.The cut sections are stacked in bins and transported through the aging ovenwhere they spend 3^6 hr at temperature in the range of 170^190C. After agingthe sections are inspected and packed before they are delivered to the customerfor further fabrication and surface treatment, followed by joining and assemblinginto the nished component or product.With a generic aluminum section (Fig. 10) some important features andcharacteristics of die design and productivity for aluminum extrusions will bedemonstrated.An order of 200 sections a' 6 m of alloy AA6060 (Al-MgSi0.5) shall be produced in a 16MN press with container diameter of 0.178 m and run out table length 42 m. Thefollowing typical process parameters can be calculated and controlled:. The cross sectional area of the container is:Ac p4 0:1782 24:9 103 m2. The cross sectional area of the extruded section isAs 0:084 0:02 2 0:028 0:016 0:0032 p 0:00152104 0:437 103 m2. The reduction ratio can, thus, be calculated to:R AcAs 24:8850:437 57Figure 10 A generic extruded aluminum section.394 Stpren and Moe

This is a reduction ratio within the acceptable range for a one hole die.. The circumscribed diameter of the section is:d 0:022 0:0842p 0:086 mThis is well bellow the maximum recommended diameter of 0:9 0:178 0:16m. Special features of the section shape that should be noticed, are a hollowrectangular section with constant wall thickness, an outer tongue andan inner rib. Furthermore, the prole is symmetric about the horizontalaxis.2.4 Productivity and CostA number of aspects are important to consider for a customer who is to choosebetween the many different suppliers of aluminum proles. As a great numberof sections ought to and have to be designed and manufactured for only one producttype, customer service stands out as particularly important. Furthermore, the sup-plier must of course be able to deliver the section requested within an agreed timelimit and to the specied quality. If the prole geometry is fairly complicated ora very high strength alloy is chosen, some suppliers may fall out of the race, butfor most proles one may not be able to differ on these grounds alone. And inthe end, thus, all usually comes down to money. The basic parameters in theextrusion business are the prices per meter or per kg extruded section. Thesemeasures are dependent on the choice of alloy and the geometry of the section,and one has to contact different suppliers in order to determine exact prices. Theseshould not differ too much since there is an active market mechanism working. Thismechanism will, however, also pressure the suppliers to continuously seek to increaseproductivity and cut costs. It is in the creative negotiations between the customer andthe supplier that the right price is agreed upon as a consequence of a section designwith the right balance between requirements for functionality and the cost efciencyin the extrusion plant. Important parameters that determine the productivity andcost of the extruded section are:. Length produced per press cycle. Length of end cuts that have to be scrapped. Number of cut lengths per billet. The discard weight per billet. Number of billets produced, i.e. gross weight delivered to the press. Net weight ordered. The dead cycle, i.e. the time between each press cycle. The ram speed. The acceleration time, i.e. the time to reach the full ram speed. Time for die change. The price of billet delivered at the press. Die cost. Production cost. Unpredicted press stopExtrusion 395

. Unpredicted quality scrap, i.e. the number of sections produced, which arenot conforming with the required quality.The production cost may be measured as cost per minute extrusion time spent.This measure contains all direct costs and man-hour costs in the plant, divided by theestimated availability of the press in minutes.The following example is meant to illustrate a typical calculation of the cost per meterand cost per kg extruded prole. The calculations are meant to refer to the sectionin Fig. 10, and data from the example of th