Method and apparatus for producing metal sheets from strand-shaped profiles

Abstract

A method for producing metal sheets from strand-shaped profiles having a low thickness made of magnesium or magnesium alloys, wherein an open or a closed extruded profile is produced in a preceding method step, wherein the extruded profile exiting the extrusion die of an extrusion press is shaped to form a planar metal sheet by the contactless action of electromagnetic forces.

Claims

1. A method for producing metal sheet of magnesium or a magnesium alloy, comprising: extruding the magnesium or magnesium alloy through an extrusion die to form a strand, that is continuous and elongated, of the magnesium or magnesium alloy, the die being so configured that the strand as it exits the die has a widthwise cross-section of closed or open profile including curvature; and proximate the strand exiting the extrusion die, applying pulsed electromagnetic force to the strand from a magnetic field source spaced from the strand to shape the strand into a planar metal sheet by pushing the strand against a planar surface acting as a counter bearing.

2. The method for producing metal sheet according to claim 1, further comprising: after said applying of electromagnetic force to obtain the planar metal sheet, smoothing the planar metal sheet by rolling or sizing; and winding the planar metal sheet into a coil.

3. The method for producing metal sheet according to claim 1, wherein the profile is open and comprises at least one sinusoidal contour.

4. The method for producing metal sheet according to claim 1, wherein the profile is closed and comprises a circle or approximately circular shape or includes at least one sinusoidal contour.

5. The method for producing metal sheet according to claim 1, wherein the profile is closed and as the magnesium or magnesium alloy is extruded to form the strand the strand is so formed as to facilitate breaking of the strand along a lengthwise line of the strand, the die being configured to form said lengthwise line on a peripheral surface of the strand.

6. The method for producing metal sheet according to claim 1, wherein the profile is closed and the method further comprises cutting the closed profile open along a line lengthwise of the strand.

7. The method for producing metal sheet according to claim 1, wherein the profile is closed and comprises a circle or approximately circular shape or includes at least one sinusoidal contour, further comprising: cutting the closed profile open along a line lengthwise of the strand; and after said applying of electromagnetic force to obtain the planar metal sheet, smoothing the planar metal sheet by rolling or sizing.

8. The method for producing metal sheet according to claim 1, wherein the profile is closed and comprises a lengthwise line of the strand to facilitate breaking of the strand along thereof, the method further comprising severing the closed profile by action of magnetic forces along the lengthwise line.

9. The method for producing metal sheet according to claim 1, further comprising winding the planar metal sheet into a coil.

10. The method for producing metal sheet according to claim 1, wherein the step of applying electromagnetic forces to shape the strand into the planar metal sheet is performed in less than 0.1 sec.

11. The method for producing metal sheet according to claim 1, wherein the magnetic field source generates a magnetic field by discharging a charged capacitor.

12. A method for producing metal sheet of magnesium or a magnesium alloy, comprising: extruding the magnesium or magnesium alloy through an extrusion die to form a strand, that is continuous and elongated, of the magnesium or magnesium alloy, the die being so configured that the strand as it exits the die has a widthwise cross-section of closed or open profile including curvature; proximate the strand exiting the extrusion die, applying electromagnetic force to the strand from a magnetic field source spaced from the strand thereby to shape the strand into a metal sheet; after said applying of electromagnetic force to obtain the metal sheet, smoothing the metal sheet; and winding the metal sheet into a coil.

13. The method as in claim 12, wherein smoothing the metal sheet is performed by rolling and sizing within a sizing unit.

14. The method as in claim 12, wherein the profile is closed and as the magnesium or magnesium alloy is extruded to form the strand, the strand is so formed as to facilitate breaking of the strand along a lengthwise line of the strand, the die being configured to form said lengthwise line on a peripheral surface of the strand, and wherein the closed profile is severed along said lengthwise line by the applied of magnetic forces.

15. The method for producing metal sheet according to claim 12, wherein the profile is closed and the method further comprises cutting the closed profile open along a line lengthwise of the strand.

16. An apparatus, comprising: an extrusion press having a die profile configured to provide a strand of magnesium or magnesium alloy extruded therethrough with a cross-section which includes curvature; a source of a magnetic field laterally spaced from the die and immediately downstream from where the extruded magnesium or magnesium alloy exits the die, the magnetic field source comprising an electric coil and the magnetic field source being configured to apply electromagnetic forces to the strand to force the strand to move in a predetermined lateral direction; a body having a planar surface substantially orthogonally facing the direction in which the strand is forced to move and positioned to counter that movement whereby the surface is positioned and configured so that the electromagnetic forces applied by the magnetic field source push the strand against said planar surface thereby to flatten the strand into a sheet; and a rolling or sizing unit downstream of the magnetic field source and said body and configured to smooth a surface of the sheet, wherein the apparatus carries out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a representative illustration of a system for producing strand-shaped profiles by way of an extrusion press which are subsequently formed to obtain a planar metal sheet.

(2) FIG. 2 is a cross-sectional view along line A-A in FIG. 1.

(3) FIG. 3 is a cross-sectional view along line B-B in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

(4) The system is essentially composed of an extrusion press 1 for producing an extruded profile 8, a forming unit composed of a work coil 2 and a counter bearing 3, and a sizing unit 4.

(5) Using the extrusion press 1, a round billet is formed from a magnesium alloy to obtain an extruded profile 8, i.e., an elongated strand having a profiled widthwise cross-section, i.e., a cross-section which includes curvature, for example a profile 6 having three sinusoidal arcs in the cross-section. Thereafter, the profile 6 is positioned above the work coil 2 and formed under the action of a force of a pulsed magnetic field having very high intensity, wherein the profile 6 is formed against the counter bearing 3 to obtain a planar metal sheet 7. The force of the magnetic field acting on the profile 6 is illustrated in form of wide arrows in FIG. 2 and FIG. 3.

(6) A magnetic field that changes over time induces eddy currents in the electrically conducting profile 8. The magnetic field exerts forces on these currents. The intensity of the forces is dependent on the spatial gradients of the magnetic flux density and the magnitude of the induced currents. The profile 8 is subjected to forces directed toward a lower flow density. The magnetic fields necessary for forming the profiles 8 to obtain planar metal sheets 7 are generated by discharging charged capacitors over the course of a few microseconds via a coil that is adapted to the profile geometry. This creates a very high magnetic pulse on the profile surface, as a result of which a current flows in the profile 8, which is directed against the coil current, wherein the profile 8 is moved in a predetermined direction toward lower fields i.e., against a planar surface of a body acting as a counter bearing, the planar surface being substantially orthogonal to the aforementioned predetermined direction.

(7) The intensity of the induced currents and the attendant action of a force on the profile 8 depend on the electrical conductivity. Since magnesium or the magnesium alloy have relatively good electrical conductivity, high pressures act on the surface of the profile 8. These can amount to several thousand megapascals. This pressure only acts over a short time period, this being in the range of a few microseconds, for the duration of the discharge of the capacitors. During this time, the profile 6 takes up the required forming energy in the form of pulses. After an acceleration phase, the material of the profile 8 moves very quickly, due to the low mass thereof. It is possible for speeds of up to 300 m/s to be achieved. The stresses occurring in the profile 6 become so high that yielding occurs, within the meaning of metal forming technology, and the profile 6 is formed to obtain a planar metal sheet 7.

(8) Afterwards the metal sheet 7 passes through a sizing unit for smoothing and is wound to form a coil 5. Alternatively, it is possible to replace the winding to form the coil 5, with a stamping or cutting unit, with the aid of which components are stamped from the metal sheet 7 coming from the sizing unit, or the metal sheet 7 is cut into panels or strips.

(9) So as to form closed profiles 8 to obtain a metal sheet, these are either provided, by the configuration of the die, for example, with a predetermined breaking point along the peripheral surface line during production of the profile, or severed along the peripheral surface line using a cutting unit. Profiles 6 comprising an introduced predetermined breaking point are severed by the action of magnetic forces and formed to obtain a metal sheet 7.

(10) Particular advantages of the method according to the invention are that the magnetic fields and the magnetic forces act unimpaired by the material, whereby the magnetoforming process can also be employed under vacuum or in a protective gas atmosphere, and additionally that magnetoforming systems do not require any mechanical contact with the workpiece, whereby surface contamination and tool impressions are avoided. The short process times for the forming operation to obtain the metal sheet 7 are also advantageous, being less than 0.1 s.