EP1216768A1 - Device and method for forming a metal sheet - Google Patents

Abstract

The assembly to shape metal sheets has a stretching mold (5) with a number of drillings (4), to carry compressed air (6) through vertically into the workpiece laying surface (8). The compressed air forms an air cushion (7) between the mold surface and the under side (11) of the metal sheet workpiece (2). The compressed air drillings are arranged in a uniform array. The drillings can be only in selected zones, to give a partial air cushion formation.

Description

The invention relates to an arrangement and a method for forming a Metal sheets according to the preamble of claims 1, 10 and 11. With it a metal sheet, that rests on a support surface almost without friction, changes shape plastically, which is also suitable for the forming of large sheet metal structures is suitable, with further processes that the separate intermediate and / or post-treatment of the metal sheet are expedient, is waived.

Known technologies undergo a sheet of metal on which is formed by mechanical forming a bulge is transferred, a stretch-pull process. Before performing this procedure there is a need for the metal sheet to be formed before stretching on the edge or pulling on the (over the) surface of a suitable stretch-traction means accordingly is greased to reduce the friction between the (shaped) to be transferred (to the sheet) Contour of the contact surface of the push-pull means, which is called "clamping claw" is common, and to reduce the sheet support surface lying on it to an acceptable level, to influence at least favorably. Traditionally, the classically known oil or Grease lubrication applied. There is often also a need for an intermediate annealing of the such pretreated metal sheet, the latter in a (so-called) another To reshape the calibration cable, resulting in a low springback of this metal sheet is obtained. Before this possible intermediate cooling, degreasing of the Formed sheet metal can hardly be avoided. You can probably assume that this known procedure for forming a metal sheet only with high Effort is coped with, at least the impression is given. Appropriate measures after which with appropriate measures an intermediate treatment of the metal sheet during the metal sheet will no longer be formed and there is no need for post-treatment of the curved metal sheet will not be known.

The invention is therefore based on the object of an arrangement and a method for To propose forming a metal sheet with which the plastic forming of the metal sheet without additional measures, according to which an improvement in plasticity of the material by heat treatment and no lubrication of the formed part which, at least during the forming phase (s), are almost frictionless and efficient is implemented.

This object is achieved by the measures specified in claims 1, 10 and 11. In the further subclaims there are expedient configurations of these measures specified.

Fig. 1

eine Anordnung zum Umformen eines Metallbleches mit dessen Luftkissenauflage;

Fig. 2

die Anordnung zum Umformen eines Metallbleches und dessen mechanische Befestigung an einem Streck-Zug-Mittel;

Fig. 3

eine Darstellung von Diagrammen des Umformprozesses, welche die Luftdruck-, Temperatur-und Weg-Veränderungen zeitabhängig veranschaulichen.

The invention is described in more detail in an exemplary embodiment with reference to the accompanying drawings. The shows

Fig. 1

an arrangement for forming a metal sheet with its air cushion pad;

Fig. 2

the arrangement for forming a metal sheet and its mechanical attachment to a stretch-pull means;

Fig. 3

a representation of diagrams of the forming process, which illustrate the air pressure, temperature and path changes as a function of time.

With a look at Fig. 1 you will see the basic structure of an arrangement 1 for forming perceive a metal sheet 2. Then a stretching die 5 is used, the so called stretching die support surface 8 has a curved shape. This stretching die support surface 8 is bulged outward in the horizontal direction, it is intended to be Transfer contour to the metal sheet 2. On this stretching die support surface 8 is (with suitable measures) the metal sheet 2, which (according to this illustration and also with an anticipation of later described method steps according to FIG. 3) in one (with the help a stretch-pull means 3 according to FIG. 2) biased at the edge of the sheet metal and in one on one Pre-bending level stretched condition. The stretching die 5 has several holes 4, which are arranged vertically exiting the stretching die support surface 8. Through this Bores 4 is in an intermediate space, the stretching die support surface 8 and Include sheet metal support surface 11, blown compressed air 6, within - through which localized (n) amount of compressed air - a (between) spatially spread air cushion 7 forms.

It is provided that a largely completely perforated stretch-forming support surface 8 with a largely uniform borehole architecture of the bores 4 is arranged below the sheet metal support surface 11. It is also noted that below this sheet metal support surface 11, only certain sub-areas of the stretching mold support surface 8 are provided with bores 4, thereby realizing a partial construction of the air cushion 7. In order to ensure an almost frictionless movement of the metal sheet 2 during the forming process above the stretching die support surface 8, an air cushion 7 with a sufficiently constant forming air pressure P ₃ (according to FIG. 3) is to be built up, on which the metal sheet 2 floats during the forming. For this reason, the bores 4 mentioned are realized with cylindrical or non-cylindrical boreholes, the hole axis of which is arranged perpendicular to the stretching die support surface 8. Which borehole geometry is considered appropriate is up to the individual case. It is taken into account that the borehole cross section of the non-cylindrical boreholes 4 on the stretching die support surface 8 is larger than that which is located at an entry point of the compressed air 6 vertically upstream of it into the individual borehole 4. However, a non-cylindrical borehole exit on the stretching die support surface 8 will at least enjoy the advantage of better cleaning of the bores 4.

The compressed air source (not shown in the figure), from which the boreholes 4 are fed with compressed air 6, is arranged internally or externally of the drawing die 5 (depending on expediency). It is also added that the compressed air 6 will have a compressed air temperature of up to 350 degrees Celsius. The compressed air (which builds up the air cushion 7) is heated to this air temperature value and is later referred to as the heating temperature T ₂ . This heated temperature value (the heating temperature T ₂ ) is kept constant during the actual forming of the metal sheet 2, which can be achieved, for example, with a controllable heating source (not shown), which will pass the compressed air 6 (before it emerges at the stretching die support surface 8), implements. It is further added that the metal sheet 2 consists of a material which is made, for example, of an aluminum alloy which can be formed at room temperature T ₁ and which can be reshaped by the heating and consequent reduction in the yield stress during its loading. The material of the metal sheet 2 will mainly relate to a hardenable or non-hardenable aluminum alloy, which is largely used in aircraft construction. In principle, a process (described in more detail later) can be implemented with any metal (sheet 2), since almost all metals lose strength when heated. In practice, metal sheets 2 of a corresponding type will also be formed, which do not always have a flat appearance. The arrangement presented will also be able to form corresponding metal sheets 2, which are provided with an irregular surface curvature. Otherwise, these metal sheets 2 have a precisely specified surface curvature. In the worst case, the irregular appearance is understood to mean a creased sheet metal surface.

2 shows the arrangement 1 (presented with respect to FIG. 1) for shaping the metal sheet 2, which is expanded with a (indicated) stretch-pull means 3. The latter is required in order to fasten the side edges 9, 10 of the metal sheet 2 (lying horizontally on the stretching die support surface 8) on the output side of the (according to the example: convex) curvature. The stretch-drawing mold 5 will attack the metal sheet 2 on both sheet metal sides on these (opposing) side edges 9, 10 each with a tensile force F ₂₁ or F ₂₂ , provided that the metal sheet 2 is mechanically suitable on the edge of the stretch-pull means 3 in a suitable manner is attached. Based on the considerations mentioned above, the individual side edge 9, 10 will be clamped between the clamping surfaces of a (vertically lowerable) clamping device, which is known under the name "clamping claw". In this illustration, the air cushion 7 (mentioned with regard to FIG. 1) and the perforation of the stretching die support surface 8 with the (small) bores 4 machined into the stretching die 5 are not shown. Because FIG. 2 aims to explain stretch drawing in principle, it is further added that when the tensile forces F ₂₁ , F _{22 are applied,} the metal sheet 2 is first subjected to stretching over the (horizontal) sheet length above the drawing die support surface 8, as a result of which on the metal sheet 2 (also supported by its stretching) the surface contour of the stretching die 5 is transferred.

If the side edges 9, 10 of the metal sheet 2, which are fastened at the edges, are prestressed on the stretching die support surface 8 under the action of room temperature (T ₁ ) and atmospheric ambient air pressure P ₁ until a defined prestressing time (t ₁ ) has elapsed, it will be observed that this Metal sheet 2 (according to a process step specified later) is stretched from a rest position to the pre-bending level of a prestressing path s ₁ as a result of the mechanical prestressing on the side of the sheet.

3 shows a representation of (correlated) diagrams of the Forming process shown, which changes the air pressure, temperature and path illustrate time-dependent.

These diagrams are used to present the method for forming the conventional metal sheet 2, the method being implemented with the arrangement 1 (presented with reference to FIGS. 1 and 2). As mentioned - the metal sheet 2 is subjected to a stretch-pull procedure in order to transfer a single or double curved and convex or concave curvature (curvature) to the metal sheet 2. In order to act promisingly for the intended purpose, the process steps specified below with the arrangement 1 and including the additionally installed components, which relate to the (previously specified) heat source and an adjustable pressure booster with which the volume flow of the compressed air 6 fed in are pressure-adjusted , relate, realized in the order given. These components are not shown in Figures 1 and 2.
The following steps will become clear if you compare the information with the diagrams. The following steps are then implemented procedurally:

The conventional metal sheet 2 is first positioned over the stretching die 5 and then placed on the curved die-drawing support surface 8. Then the side edges 9, 10 of the metal sheet 2 lying opposite one another in the horizontal plane are fastened, preferably clamped, to the tension-stretching means (3) at the edges of the stretch-drawing mold 5 [ie near the beginning of the convex-shaped curvature of the stretch-drawing mold support surface 8 curved in this way, and then pretensioned on its curved stretching mold support surface 8 under the action of room temperature T ₁ and atmospheric ambient air pressure P ₁ until a defined pretensioning time t _{1 has} elapsed, the metal sheet 2 as a result of the mechanical pretensioning on the side of the sheet metal from a rest position to the prebending level of a pretensioning path s ₁ is stretched. A tempered compressed air 6, which will reach a heating temperature T ₂ after a heating time t ₂ has passed, is then passed through the bores 4 of the stretch-forming die 5 with a constant heating air pressure P ₂ . This compressed air 6 will then spread between the stretching die support surface 8 and the sheet metal support surface 11, as a result of which an air cushion 7 is formed between these two support surfaces. During the heating phase (t ₂ - t ₁ ) the metal sheet (2) under tension will absorb the heat of the heating temperature (T ₂ ), but will not experience any changes in the pre-bending level.

Then the opposite side edges 9, 10 of the metal sheet 2 are clamped with a constant forming air pressure P ₃ until a forming time t _{3 has} elapsed. At the same time, the metal sheet 2 is moved in the horizontal direction of motion above the air cushion 7 so that it is almost frictionless, as a result of which the metal sheet (2), the sheet temperature of which is kept constant at the heating temperature (T ₂ ). As a result of the sheet metal movement, after the forming time t _{3 has} elapsed (due to its edge-side tensile load with subsequent stretching of the sheet metal profile), the sheet metal 2 will assume a (for example convex) curvature which is adapted to the surface contour of the drawing die 5 and which will change within the forming phase t ₃ - t _{2 will change} iteratively to the forming level of a forming path s ₂ . Then the shape-altered metal sheet 2 is cooled by a compressed air 6 cooled to the room temperature T ₁ until a cooling time t _{4 has} elapsed, with a constant cooling air pressure which corresponds to the level of the heating pressure P ₂ . This cooled compressed air is also passed through the bores 4 of the stretching die 5 to the shaped metal sheet 2, the shape-changing metal sheet 2 not experiencing any changes in the level of deformation during the cooling phase t ₄ -t ₃ .

In addition, a slight modification of the method steps presented would initially be conceivable, according to which first the side edges 9, 10 of the metal sheet 2 lying opposite one another in the horizontal plane are fastened, preferably clamped, to the tension-stretching means (3) at the edges of the stretch-drawing mold 5. Subsequently, the metal sheet 2 fixed at the edge is positioned over the stretch-drawing mold 5, which is then lowered vertically until it is placed on the curved stretch-drawing mold support surface 8. Thereupon, the side edges 9, 10 of the metal sheet 2, which are fixed at the edges, are prestressed on the stretching die support surface 8 under the action of room temperature T ₁ and atmospheric ambient air pressure P ₁ until a defined pretensioning time t _{1 has} elapsed, the metal sheet 2 being released due to the mechanical tensioning on the sheet metal side a rest position is stretched to the pre-bending level of a prestressing path s ₁ . Only then is a tempered compressed air 6, which will reach a heating temperature T ₂ after the expiry of a heating time t ₂ , passed through the bores 4 of the stretching die 5 with a constant heating air pressure P ₂ . This compressed air will then spread between the stretching die support surface 8 and the sheet metal support surface 11, whereby an air cushion 7 is formed between these two support surfaces. During the heating phase t ₂ - t _1, the metal sheet 2) under pre-tension will absorb the heat of the heating temperature T ₂ , but will not experience any changes in the pre-bending level.

Subsequent to the step of cooling the deformed metal sheet 2, it would be conceivable for this metal sheet 2 to be calibrated [ie brought to an exact measure] under the action of room temperature T ₁ until the end of a completion time t ₅ , this metal sheet 2 during the calibration phase t ₅ - t ₄ will experience a change [of the forming level] to the calibration level of a calibration path s ₃ .

In addition, it is added that the opposite side edges 9, 10 of the Metal sheets 2 near the beginning of the curvature of the curved drawing mold support surface 8 the train-stretch means 3 are attached. It will be the relevant page margin 9, 10 of the Metal sheet 2 a gripping means of the pull-stretching means, which is variable in the vertical direction 3 clamp.

Furthermore, it is added that during the forming phase t ₃ - t ₂ a surface pressure of up to 200 bar / cm ² and an inflow of tempered compressed air 6 with a heating temperature T ₂ of up to 350 ° C. are implemented

Finally, it is also mentioned that the sheet-metal contact surface 11 will lift off from the stretch-drawing contact surface 8 at least during the forming phase t ₃ -t ₂ due to the air cushion 7 present.

The following can be summarized. With the device described and specified method is the reshaping of large structures in particular Vehicle construction are not uncommon, implemented, the production of which is currently only under Use of known lubrication methods and sometimes only possible with intermediate annealing becomes. With the proposed solution (s), the forming of such (large-area) Metal sheets (metal alloys, preferably aluminum alloys) smoothly on one Air cushion 7 take place. The latter is between the stretching die 5 and the metal sheet 2 by means of (Smaller) bores built in the stretch-drawing mold 5. Through a created opportunity that to blow blown compressed air 6, even metal alloys and difficult to form other materials (moldable at room air temperature) by reducing the yield stress allow the metal (sheet) to be formed. At the end of the molding process, the stretch-forming mold 5 and the metal sheet 2 cooled again by the cold air introduced. This measure has a positive effect on the springback and the contour accuracy of the deformed metal sheet 2. By the use of the presented solutions will be (in comparison with known solutions) Savings from stretching trains achieved. The complex lubrication processes (oil and Grease lubrication) and their elimination (before any intermediate annealing) omitted.

reference numeral

1

Arrangement for forming a metal sheet

2

metal sheet

3

Train stretching means

4

drilling

5

Stretch form die

6

compressed air

7

air cushion

8th

Stretch form die bearing surface

9

Side edge (of sheet metal 2)

10

Side edge (of sheet metal 2)

11

Sheet metal contact surface

F _Z1 , F _Z2

traction

P ₁

atmospheric air pressure

P ₂

Vorheizluftdruck

P ₃

Umformluftdruck

T ₁

room temperature

T ₂

heating temperature

t ₁

biasing time

t ₂

Heating time

t ₃

forming time

t ₄

cooling

t ₅

completion time

t ₂ - t ₁

heating phase

t ₃ - t ₂

forming phase

t ₄ - t ₃

cooling phase

t ₅ - t ₄

calibration

s ₁

preload

s ₂

forming path

s ₃

Kalibrierweg

Claims (16)

Arrangement for forming a metal sheet, with a stretch-drawing mold (5) and a tension-stretching means (3), the metal plate (2) being positioned on a curved stretch-drawing mold support surface (8) which is curved outwards in the horizontal direction , whose side edges (9, 10) on the output side of the curvature are attached to the tension-stretching means (3), the tension-stretching means (3) the metal sheet (2) on both sheet metal sides on the opposite side edges (9, 10) will attack with a tensile force (F _Z1 , F _Z2 ) and the sheet metal (2) will be plugged over its sheet length above the stretching die support surface (8), which also supports the surface contour of the sheet metal (2) by its stretching the drawing die (5) is transferred,
characterized in that the stretching die (5) has a plurality of bores (4) which are arranged vertically emerging from the stretching die support surface (8), and above this stretching die support surface (8) an air cushion enclosed by a sheet metal support surface (11) (7) is spread, which is built up by a compressed air (6) guided through the bores (4). Arrangement according to claim 1, characterized in that below the sheet metal support surface (11) is arranged a largely completely perforated drawing die support surface (8) with a largely uniform borehole architecture of the bores (4). Arrangement according to claims 1 to 2, characterized in that below the sheet metal support surface (11) only certain sub-areas of the stretching mold support surface (8) are provided with bores (4) and a partial construction of the air cushion (7) is thereby realized. Arrangement according to claim 1, characterized in that the bores (4) are realized with cylindrical or non-cylindrical boreholes, the hole axis of which is arranged perpendicular to the drawing die support surface (8). Arrangement according to claim 4, characterized in that the borehole cross section of the non-cylindrical boreholes on the stretching die support surface (8) is greater than that which is located at an entry point of the compressed air (6) vertically upstream of it into the individual bore (4) , Arrangement according to claim 1, characterized in that an internal or external drawing die (5) of a compressed air source is arranged, from which compressed air (6) is guided through the bores (4). Arrangement according to claim 1, characterized in that an air temperature of the compressed air (6) with which the air cushion (7) is built up is up to 350 degrees Celsius. Arrangement according to claim 1, characterized in that the material of the metal sheet (2) is mainly a hardenable or non-hardenable aluminum alloy. Arrangement according to claim 1, characterized in that the metal sheet (2) is provided with an irregular or precisely specified surface or with a flat surface, which is largely adapted to the surface contour of the stretching die support surface (8). Method for forming a metal sheet with an arrangement according to claim 1, in which the metal sheet (2) is subjected to a stretch-pull procedure in order to transfer a single or double curved and convex or concave curvature to the metal sheet (2),
characterized by the following steps: a) a metal sheet (2) is positioned over the stretching die (5) and then placed on the curved stretching die support surface (8), b) thereupon the side edges (9, 10) of the metal sheet (2) lying opposite each other in the horizontal plane are attached to the draw-stretching means (3) at the edges of the stretch-drawing mold (5) and then on the curved stretch-drawing support surface (8) upon exposure from room temperature (T ₁ ) and atmospheric ambient air pressure (P ₁ ) to the end of a defined pre-stressing time (t ₁ ), whereby the metal sheet (2) is stretched from a rest position to the pre-bending level of a pre-stressing path (s ₁ ) due to the mechanical pre-stressing on the side of the sheet becomes, c) then a tempered compressed air (6), which will reach a heating temperature (T ₂ ) after the expiry of a heating time (t ₂ ), is passed through the bores (4) of the stretching die (5) with a constant heating air pressure (P ₂ ) , which will then spread between the stretching die support surface (8) and the sheet metal support surface (11), whereby an air cushion (7) is formed between these two support surfaces, during the heating phase (t ₂ - t ₁ ) the under tension located metal sheet (2) will absorb the heat of the heating temperature (T ₂ ), but will not experience any changes in the pre-bending level, d) then the opposite side edges of the metal sheet (2) are tensioned with a constant forming air pressure (P ₃ ) until a forming time (t ₃ ) has elapsed, at the same time the metal sheet (2) is moved in a floating manner with horizontal direction of motion over the air cushion (7) with almost no friction , whereby the metal sheet (2), the sheet temperature of which is kept constant at the heating temperature (T ₂ ), as a result of the sheet metal movement after the end of the forming time (t ₃ ) [due to its edge-side tensile load with subsequent stretching of the sheet metal profile), one of the surface contours of the stretching die (5) will adopt adapted curvature, which will change iteratively to the level of forming of a forming path (s ₂ ) within the forming phase (t ₃ - t ₂ ), e) then the shape-changed metal sheet (2) is cooled by a compressed air (6) cooled to room temperature (T ₁ ) until a cooling time (t ₄ ) has elapsed, with a constant cooling air pressure which corresponds to the level of the heating pressure (P ₂ ), cooled, which is also guided through the bores (4) of the stretch-forming mold (5) to the shaped metal sheet (2), the shape-changing metal sheet (2) not experiencing any changes in the level of deformation during the cooling phase (t ₄ - t ₃ ). Method for forming a metal sheet with an arrangement according to claim 1, in which the metal sheet (2) is subjected to a stretch-pull procedure in order to transfer a single or double curved and convex or concave curvature to the metal sheet (2),
characterized by the following steps: a) first, the side edges (9, 10) of the metal sheet (2) lying opposite one another in the horizontal plane are attached to the draw-stretching means (3) at the edges of the stretch-drawing mold (5) and then the metal sheet (2) attached to the edges above the stretch-drawing mold ( 5) positioned, which is then lowered vertically until it is placed on the curved drawing mold support surface (8), b) thereupon, the side edges (9, 10) of the metal sheet (2), which are fastened at the edges, are placed on the stretching die support surface (8) under the action of room temperature (T ₁ ) and atmospheric atmospheric pressure (P ₁ ) until a defined pretensioning time (t ₁ ) pretensioned, the metal sheet (2) being stretched from a rest position to the prebending level of a pretensioning path (s ₁ ) as a result of the mechanical prestressing on the side of the sheet, c) then a tempered compressed air (6), which will reach a heating temperature (T ₂ ) after the expiry of a heating time (t ₂ ), is passed through the bores (4) of the stretching die (5) with a constant heating air pressure (P ₂ ) , which will then spread between the stretching die support surface (8) and the sheet metal support surface (11), whereby an air cushion (7) is formed between these two support surfaces, during the heating phase (t ₂ - t ₁ ) the under tension located metal sheet (2) will absorb the heat of the heating temperature (T ₂ ), but will not experience any changes in the pre-bending level, d) then the opposite side edges of the metal sheet (2) are tensioned with a constant forming air pressure (P ₃ ) until a forming time (t ₃ ) has elapsed, at the same time the metal sheet (2) is moved in a floating manner with horizontal direction of motion over the air cushion (7) with almost no friction , whereby the metal sheet (2), the sheet temperature of which is kept constant at the heating temperature (T ₂ ), due to the sheet movement after the end of the forming time (t ₃ ) [due to its tensile load on the edge rope with subsequent stretching of the sheet metal profile) one of the surface contours of the stretching die (5) will adopt adapted curvature, which will change iteratively to the level of forming of a forming path (s ₂ ) within the forming phase (t ₃ - t ₂ ), e) then the shape-changed metal sheet (2) is cooled by a compressed air (6) cooled to room temperature (T ₁ ) until a cooling time (t ₄ ) has elapsed, with a constant cooling air pressure which corresponds to the level of the heating pressure (P ₂ ), cooled, which is also guided through the bores (4) of the stretch-forming mold (5) to the shaped metal sheet (2), the shape-changing metal sheet (2) not experiencing any changes in the level of deformation during the cooling phase (t ₄ - t ₃ ). Method for forming a metal sheet according to claims 10 or 11,
characterized in that, following step e), the pre-changed metal sheet (2), which is in the cooled state, is calibrated [bring to exact measure] under the action of room temperature (T ₁ ) until the end of a completion time (t ₅ ), this metal sheet (2 ) a change [of the forming level] to the calibration level of a calibration path (s ₃ ) is experienced during the calibration phase (t ₅ - t ₄ ). Method for forming a metal sheet according to claims 10 or 121,
characterized in that the opposite side edges (9, 10) of the metal sheet (2) near the beginning of the curvature of the curved die-forming support surface (8) are attached to the tension-stretching means (3). A method for forming a metal sheet according to claim 13,
characterized in that the relevant side edge (9, 10) of the metal sheet (2) is clamped into a gripping means of the tension-stretching means (3) which is variable in the vertical direction. Method for forming a metal sheet according to claims 10 or 11,
characterized in that during the forming phase (t ₃ - t ₂ ) a surface pressure of up to 200 bar and an inflow of tempered compressed air (6) with a heating temperature (T ₂ ) of up to 350 ° C are implemented. Method for forming a metal sheet according to claims 10 or 11,
characterized in that the sheet metal support surface (11) will lift off from the stretch-forming support surface (8) at least during the forming phase (t ₃ - t ₂ ) due to the air cushion (7) present.

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