EP1566462B1 - Chauffage de feuille d'alliage en métal par la conduction thermique - Google Patents

Chauffage de feuille d'alliage en métal par la conduction thermique Download PDF

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Publication number
EP1566462B1
EP1566462B1 EP04003803A EP04003803A EP1566462B1 EP 1566462 B1 EP1566462 B1 EP 1566462B1 EP 04003803 A EP04003803 A EP 04003803A EP 04003803 A EP04003803 A EP 04003803A EP 1566462 B1 EP1566462 B1 EP 1566462B1
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Prior art keywords
sheet
platens
heating
forming
heated
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German (de)
English (en)
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EP1566462A1 (fr
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John E. Carsley
Richard Harry Hammar
John Robert Bradley
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GM Global Technology Operations LLC
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GM Global Technology Operations LLC
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent

Definitions

  • This invention pertains to the heating of a cold worked metal alloy sheet to recrystallize its microstructure to a highly formable (e.g., superplastic) condition, and/or to raise its temperature for an immediate forming operation. More specifically, this invention pertains to a method using closely spaced heated platens to rapidly heat the cold worked sheet by conduction under controlled conditions for such recrystallization and/or heating and forming.
  • Body panels for automotive vehicles are currently being manufactured using a superplastic forming process applied to certain magnesium-containing aluminum alloy sheet stock.
  • the sheet stock is a specially prepared fine grain microstructure, aluminum alloy 5083.
  • AA5083 has a nominal composition, by weight, of about 4 to 5 percent magnesium, 0.3 to 1 percent manganese, a maximum of 0.25 percent chromium, about 0.1 percent copper, up to about 0.3 percent iron, up to about 0.2 percent silicon, and the balance substantially all aluminum.
  • the alloy is cast into a slab of a suitable thickness and subjected to a homogenizing heat treatment.
  • the slab is then gradually reduced in thickness by a series of hot rolling operations to a strip in the range of twenty to forty millimeters depending somewhat on the goal for the final thickness of the sheet.
  • the strip is then cold rolled, usually in stages with possible interposed anneals, to a final sheet thickness in the range of about one to three or four millimeters.
  • the result of the thermomechanical processing is a coil of smooth surface, aluminum sheet stock, the microstructure of which has been severely strained.
  • the smooth surface of the cold rolled sheet is very important.
  • the cold rolled surface must be free of visual defects and that surface quality must be retained in subsequent heating, forming and finishing steps so that the visible surface of the final part is commercially acceptable. In automotive manufacturing such a surface is called a "Class A surface.”
  • the cold rolled strip is not suitable for a high elongation forming operation. It must be reheated to recrystallize the elongated, strained grains that characterize its microstructure by the nucleation and growth of nearly strain-free grains.
  • the goal of the recrystallizing heat treatment in the case of AA5083 sheet is to produce a very fine grained microstructure characterized by a principal phase of a solid solution of magnesium in aluminum, with well distributed, finely disbursed particles of intermetallic compounds containing minor alloying constituents such as, Al 6 Mn.
  • the recrystallized grain size in the microstructure is uniformly about ten to fifteen micrometers.
  • the fine-grained sheet can be heated and superplastically formed into a complex part like an automotive body panel.
  • the sheet can sustain substantial elongation at a suitable strain rate and at a temperature in the range of about 440°C (825°F) to about 550°C (1020°F).
  • the '588 patent describes practices for forming aluminum alloy sheet metal using a pressurized working fluid such as air.
  • the sheet metal blank is first placed on a pre-bending and heating tool. The heated tool heats the sheet metal blank to its forming temperature and pre-bends it, if desired, for placement on a second tool configured for stretch-forming the heated sheet into a body panel or the like.
  • the heated blank is then clamped at its edges and gas pressure is applied which forces the sheet into the tool cavity to assume the requisite shape of the part.
  • gas pressure is applied which forces the sheet into the tool cavity to assume the requisite shape of the part.
  • the heating on the pre-heat tool may further the grain growth of its microstructure.
  • a blank is taken from a cold rolled coil supplied without heat treatment, e.g., in the H18 temper, the metal is not formable because it has experienced a cold rolling reduction of 74% or more as a last processing step.
  • an unrecrystallized blank is placed on the preheat and pre-bend tool of the Rashid, et al, "588 patent disclosure, the sheet material is recrystallized as it is slowly heated to the panel forming temperature over a period of five to ten minutes.
  • the sheet Once the sheet has been recrystallized and reaches a forming temperature, for example, in the range of 825°F to 845°F (about 441°C to 452°C), it is bent and transferred to a heated forming press in which it is stretch formed into a vehicle body panel or the like.
  • a forming temperature for example, in the range of 825°F to 845°F (about 441°C to 452°C)
  • US 6,547,895 B2 discloses a method of forming a stack comprising at least two sheets of cold rolled superplastic metal alloy material, heating the stacked sheets and forming the sheets into the shape of the product.
  • US 6,211,497B1 discloses an apparatus for forming and consolidating organic matrix composites having an induction coil imbedded in a pair of dies.
  • a suitable forming temperature such as a stretch forming temperature.
  • one or two cold worked aluminum alloy sheets are placed between two massive, electrically heated platens.
  • the temperature of the platens is controlled at a pre-determined level at or just above the desired final temperature of the sheet.
  • the platens are suitably heated with inserted electrical resistance heating rods, which can be controlled to provide a uniform temperature over the entire heating surface of the massive plates.
  • One important application of the invention is to produce a recrystallized and formed sheet metal part with a Class A surface.
  • the hot platens are closed to a closely spaced position in which the cold worked sheet is not in full surface-to-surface contact with either platen.
  • the gap between the platens is suitably about 2.1 mm.
  • the nominal difference of 0.5 mm between the gap spacing and the thickness of the unheated sheet results in rapid heating of the sheet while protecting its surfaces. Reducing this difference promotes faster heating but increases the possibility of scratching of the sheet surface.
  • Shims located on the lower platen at the periphery of the sheet serve to retain the desired spacing. This close platen spacing permits three dimensional expansion of the sheet as it is rapidly heated, but the platens do not grip the sheet(s) and scratch or mar its surfaces. The sheet is supported by the lower platen but the expansion of the sheet causes it to move out of full surface contact with the lower platen. There is a thin layer of air between the opposing platens and the intervening sheet. But the air film is quiescent and heat transfer from the platens through the air is largely by conduction.
  • the sheet is suitably recrystallized to a microstructure for superplastic forming and heated to a suitable temperature for such forming within a period of, for example, thirty seconds or less. It was unexpected that the sheet could be suitably heat treated for superplastic forming in such a short time. Advantageously, this period is comparable to the actual panel forming operation so that the heating operation no longer slows the panel manufacturing process.
  • the platens are opened and the hot sheet is removed and, without intentional cooling, placed on a forming tool for pre-bending and/or final part formation.
  • This invention is likewise applicable to the static recrystallization of other pseudo single phase alloys such as aluminum alloys of the 2xxx series, other alloys of the 5xxx series, alloys of the 7xxx series and, for example, suitable magnesium, ferrous and titanium alloys.
  • Figure 1 is an oblique elevation view of a fixed upper heating platen and a movable lower platen, each supported on a framework.
  • the lower platen is shown in its lower, open position for removing a heated recrystallized sheet and loading a new cold worked metal sheet.
  • Figure 2 is a side view of a portion of the framework and upper and lower platens showing one of the air cylinders and a roller-rail system for raising and lowering the movable heating platen.
  • Figure 3 is an isolated side schematic view of the platens in their closed position for small gap conduction heating of a cold worked metal sheet. The relative size of the sheet and gap are not to scale.
  • Superplastic metals can undergo large uniform strains prior to failure.
  • the ability of a metal to deform superplastically depends primarily on its composition, grain size, strain rate, and deformation temperature. Metals that behave superplastically usually have a grain size less than about 10 micrometers and they are deformed within the strain rate range of 10 -5 to 10 -1 per second at temperatures greater than about half of their absolute melting temperature (0.5 T).
  • the fine grain size is believed to allow grain boundary sliding and grain rotation to contribute to the large superplastic strains. Therefore, in order to deform superplastically, an aluminum alloy or other superplastic alloy of, for example, titanium, iron or magnesium must first be capable of being processed into a fine grain structure that remains stable during deformation.
  • This invention is applicable to superplastic metal sheet alloys that are statically recrystallized to a fine grain structure prior to a forming operation.
  • the practice of the invention will be illustrated in connection with magnesium containing, aluminum sheet alloys, specifically AA 5083.
  • Production of the alloy sheet includes a combination of hot rolling, cold rolling and finally a heat treatment to develop small recrystallized grains of aluminum-magnesium solid solution with dispersed insoluble materials.
  • An exemplary goal for this small gap conduction heating process may be to heat the cold worked sheet to a temperature of, 900°F (482°C) in less than 45 seconds.
  • This heating program is to transform the microstructure from severely strained, cold worked grains to a recrystallized fine grain, pseudo single phase, soft (e.g., O Temper), condition.
  • the sheet is to be heated to a temperature at which it can be stretched and/or drawn into a body panel or the like product of complex shape and with a high quality surface finish on its visible side.
  • a metal alloy blank for an automotive vehicle body panel may, for example, have dimensions of 1625 mm (64 inches) x 1117 mm (44 inches) x 1.6 mm (0.063 inch). It is often coated on one or both sides with a film of boron nitride lubricant particles to assist in a high temperature panel forming operation against a suitable forming tool. In order to heat such a blank, or pair of blanks, in accordance with this invention it is necessary to use larger heated plates or platens.
  • FIG. 1 illustrates a machine 10 for supporting horizontally disposed heated platens for the practice of an embodiment of this invention.
  • Machine 10 comprises base frame member 12 suitably formed of longitudinal steel beam frame members 14 with lateral support beams 16. Fixed at one end of base frame member 12 are two vertical I-beams 18. I-beams 18 serve as support columns for machine 10. Attached to the upper end of beams 18 and cantilevered over the base frame member 12 is an upper frame member 20.
  • the horizontal upper frame member 20 is also formed of two longitudinal steel beam frame members 22 welded or bolted to lateral support beam members 24. Cantilevered upper frame member 20 is further supported in its horizontal position by corner supports 26 welded to the upper ends of vertical beams 18.
  • upper frame member 20 Attached to upper frame member 20 by suitable hangers, not shown, is a horizontally disposed upper heating platen 28.
  • upper platen 28 is attached in a fixed position to upper frame 20.
  • a lower heating platen 30 is carried on lower frame member 12 and vertical beams 18 so that platen 30 can be moved from an open position as seen in Figures 1 and 2 to a closed position very near to the upper platen 28 as seen in Figure 3 .
  • lower heating platen 30 is in its open position a heated blank ready for immediate forming is mechanically removed from the hot platen 30 and a new cold worked blank is loaded onto it.
  • the lower platen 30 is raised to its closed position for heating the sheet metal blank 54.
  • Lower heating platen 30 is carried on a pair of horizontal beams 32 (one seen in Figures 1 and 2 ).
  • Several lateral tubes 33 are welded crossways between beams 32 to carry platen 30.
  • Beams 32 are fixed at their ends to vertical end plate 34 and further supported by corner plate 36.
  • Vertical end plate 34 spans between vertical beams 18. Attached to vertical end plate 34 at locations close to vertical beams 18 are two vertical side plates 38.
  • Each vertical side plate 38 carries three rollers 40, 42, and 44 located to movably secure vertical side plates 38 to the adjacent head portions of I-beams 18.
  • the upper and lower rollers 40 and 44 are placed in opposition to central roller 42.
  • the support structure for lower heating platen 30 permits it to be raised and lowered along the head webs of vertical I-beams 18.
  • Two high pressure air cylinders 46 one seen in the broken off side view of Figure 2
  • piston rods 48 one seen in Figure 3
  • Figure 3 shows a side view of upper heating platen 28 and lower platen 30 in their closed position. It is preferred that the heating platens be supported in a horizontal attitude to facilitate supporting and loading of the metal alloy sheets. In order to reduce heat loss, it is preferred that the platens only be opened enough to accommodate handling of the sheets. Typically, for the sheet sizes of this example, the lower platen 30 need only be lowered five or six inches from its closed position against the fixed upper platen 28. Shaft 48 is actuated by cylinder 46 to raise (close) and drop (open), lower platen 30. The main length of shaft 48 is broken out in Figure 3 to accommodate location of this illustration on the drawing page.
  • Plates 28 and 30 are suitably made of steel for heating AA5083 cold worked blanks. Inserted across the width of each heating platen are several parallel electrical resistance heating rods 50. Heating rods 50 are connected to a suitable electrical power source and temperature controller, not shown. If, for example, the desired final temperature of the AA 5083 sheet is 900°F (482°C) the electrical power delivered to heating rods 50, collectively or individually, will be controlled so that each platen, 28 and 30, is maintained uniformly at a temperature in the range of about 900 to 910°F (482 to 488°C). The high temperature platen heaters rapidly heat each cold worked sheet in succession toward its specified temperature without overheating.
  • the spacing between the very flat surfaces of the platens 28 and 30 is maintained by the thickness of shims 52.
  • shims 52 are attached to the movable lower platen 30 to facilitate placement of the cold worked blank sheet on that platen.
  • shims For heating a sheet of 1.6 mm thickness, shims of about 2.0 to 2.2 mm thickness may be employed, especially when the surface quality of the cold rolled sheet is to be preserved.
  • Such a spacing allows the sheet 54 to freely expand as it is heated from ambient temperature to about 900°F (482°C). If two sheets are heated together the thickness of the shims will be suitably increased.
  • the intent is to provide sufficient space between the platens so that the expanding sheet is not grasped or impeded by the platens in a way that mars the surface of the sheets.
  • the space between the hot platen surfaces and the sheet 54 will be small. It is exaggerated in Figure 3 .
  • the time required to heat the 1.6 mm blank of cold worked AA5083 will be about 30 seconds. The time for a specific application is soon determined by trial, but typically less than 45 seconds depending on the thickness of the sheet(s) and the dimension of the gap between them and the platens.
  • shims 52 are shown at the edges of platen 30 while in Figure 1 the shims are inside the edges of that representation of the platen. It may be desired to place insulation around the steel heating platen to reduce heat loss. The insulation is not shown in Figure 3 for simplicity of illustration. However, the representation of platens 28 and 30 in Figures 1 and 2 contemplates that the edges and back surfaces of these heating plates may be embedded in a suitable insulating material.
  • the lower platen is 30 lowered by action of air cylinders 46.
  • the center portion, or other portion, of the heated sheet 54 can be raised by actuation of a series of ejector pins 56 located in the lower platen 30.
  • the sheet is then removed mechanically from the platen 30.
  • the hot sheet can then be placed on a forming tool to utilize its softened and formable condition. Since the heated sheet is at its forming temperature it is transferred without undue delay to the forming tool. If some delay and cooling is anticipated it may be desired to heat the sheet to a slightly higher temperature to compensate for such cooling before forming.
  • a controlled heating by conduction from heated platens is used to rapidly transform (recrystallize) a cold worked sheet of suitable metal alloy to a highly formable microstructure and heat it to a suitable forming temperature to utilize the newly acquired formability.
  • the heating period is typically less than 45 seconds and often less than 30 seconds.
  • the formability of the AA 5083 sheet typically exceeds 300 + % elongation by standard tensile test.
  • a gap is maintained between the sheet(s) to be heated and the hot platens to preserve a surface quality on the sheet(s).
  • the platens may closely engage the sheet for more rapid heating.
  • the heating platens in the above example were positioned for receiving and heating sheets in a horizontal position.
  • the platens can be supported for opening and closing in any attitude.
  • the arrangement of the heating platens can be set to accommodate sheet positioning required by other processing stations of a manufacturing line.
  • the platens have been illustrated as having flat heating surfaces. But the sheet may have been bent or otherwise formed prior to heating and the platens can be shaped to receive and heat such sheets.
  • an object of the invention is to accomplish the rapid heating by thermal conduction of a cold worked sheet of superplastic metal alloy composition to recrystallize the microstructure of the sheet and to heat it to a temperature suitable for superplastic forming.
  • a user of such sheet material may choose to have the cold rolling supplier perform the recrystallization step and supply the sheet in a superplastic formable condition.
  • the user of such sheet stock can still benefit from the use of this invention to rapidly heat the cold rolled and recrystallized material to a suitable superplastic forming temperature.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)

Claims (8)

  1. Procédé de mise en forme d'une feuille d'une composition d'alliage métallique susceptible d'être mise en forme de manière superplastique, comprenant les étapes consistant à :
    fournir au moins une feuille oeuvrée à froid (54) de ladite composition ;
    commander la température d'une paire de plateaux chauffés opposés (28, 30) à un niveau prédéterminé pour recristalliser la microstructure oeuvrée à froid de ladite feuille de métal (54) pour donner une microstructure à grains fins pour la mise en forme superplastique ;
    lesdits plateaux (28, 30) étant mobiles entre une position ouverte pour recevoir ladite feuille (54) et une position fermée pour chauffage conductif de ladite feuille (54) de sorte qu'une surface latérale de ladite feuille (54) est face à un plateau (28, 30) et la surface latérale opposée de ladite feuille (54) est face au plateau opposé (28, 30) ;
    chauffer ladite feuille (54) entre lesdits plateaux (28, 30) par transfert de chaleur par conduction vers lesdites surfaces latérales pour recristalliser la microstructure oeuvrée à froid de ladite feuille de métal (54) et donner une microstructure à grains fins pour la mise en forme superplastique ;
    enlever ladite feuille (54) d'entre lesdits plateaux (28, 30) ; et
    mettre en forme la feuille chauffée (54).
  2. Procédé selon la revendication 1, dans lequel deux desdites feuilles (54) sont chauffées simultanément entre lesdits plateaux (28, 30).
  3. Procédé selon la revendication 1, dans lequel deux desdites feuilles (54) sont chauffées simultanément entre lesdits plateaux (28, 30), chacune desdites feuilles (54) ayant une surface latérale avec une qualité de surface désirée qu'il s'agit de maintenir pendant ledit chauffage, et lesdites feuilles (54) sont chauffées entre lesdits plateaux (28, 30) avec lesdites surfaces latérales présentant une qualité de surface mutuellement face-à-face, protégées d'un contact avec lesdits plateaux (28, 30).
  4. Procédé selon la revendication 1, dans lequel ladite feuille (54) est formée d'une composition d'alliage d'aluminium susceptible d'être formée de manière superplastique.
  5. Procédé selon la revendication 1, dans lequel ladite feuille (54) est formée d'une composition d'alliage d'aluminium contenant du magnésium susceptible d'être formée de manière superplastique.
  6. Procédé de mise en forme d'une feuille d'une composition d'alliage métallique susceptible d'être mise en forme de manière superplastique selon la revendication 1, dans lequel lesdits plateaux (28, 30) définissent, dans ladite position fermée, un intervalle avec les surfaces latérales de ladite feuille (54) qui ne dépasse pas 3 mm plus l'épaisseur de ladite feuille (54), ce qui permet l'expansion thermique de ladite feuille (54) dans ledit intervalle, et le chauffage de ladite feuille (54) par transfert de chaleur conductif à travers ledit intervalle depuis chaque plateau (28, 30) via les surfaces latérales face-à-face de ladite feuille (54).
  7. Procédé selon l'une des revendications 4 et 5, dans lequel ladite feuille (54) a subi une réduction par travail à froid jusqu'à un état de températion H18.
  8. Procédé selon l'une des revendications 4 et 5, dans lequel ladite feuille (54) a une épaisseur allant jusqu'à environ 2 mm et est recristallisée et chauffée à ladite température de mise en forme en 45 secondes.
EP04003803A 2004-02-19 2004-02-19 Chauffage de feuille d'alliage en métal par la conduction thermique Expired - Lifetime EP1566462B1 (fr)

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EP04003803A EP1566462B1 (fr) 2004-02-19 2004-02-19 Chauffage de feuille d'alliage en métal par la conduction thermique

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EP04003803A EP1566462B1 (fr) 2004-02-19 2004-02-19 Chauffage de feuille d'alliage en métal par la conduction thermique

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EP1566462B1 true EP1566462B1 (fr) 2012-03-28

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Publication number Priority date Publication date Assignee Title
EP2182081B1 (fr) 2008-10-29 2014-01-22 Neue Materialien Bayreuth GmbH Procédé destiné au traitement thermique d'un corps en tôle d'acier revêtu
DE102012110649C5 (de) * 2012-11-07 2018-03-01 Benteler Automobiltechnik Gmbh Warmformlinie sowie Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Kraftfahrzeugbauteils

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US5591370A (en) * 1991-04-05 1997-01-07 The Boeing Company System for consolidating organic matrix composites using induction heating
US6547895B2 (en) * 2001-01-25 2003-04-15 General Motors Corporation Superplastic multi-layer forming

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