Method and apparatus for distortion control on additively manufactured parts using wire feed and magnetic pulses

Abstract

The invention provides a method and apparatus for forming a freeform metal structure by wire feed additive manufacturing. In accordance with the method, a holding structure is moved in at least one moving direction, the holding structure holding the metal structure. A metal wire end is fed along an area of deposition on the metal structure in the at least one moving direction. The metal wire end is heated to a melting temperature using a heat source, with the metal wire end as melted being deposited on the metal structure as a metallic build-up material. The metallic build-up material after heating and during the cooling is subjected in the at least one moving direction behind the area of deposition to at least one pulsed magnetic field using a magnetic coil arranged after the heat source, the at least one pulsed magnetic field effecting plastic deformation of the build-up material.

Claims

1. A method of forming a freeform metal structure by wire feed additive manufacturing, wherein the method comprises: moving a holding structure in at least one moving direction, the holding structure holding the metal structure; feeding a metal wire end along an area of deposition on the metal structure in the at least one moving direction; heating the metal wire end to a melting temperature using a heat source, the metal wire end as melted being deposited on the metal structure as a metallic build-up material; and subjecting the metallic build-up material after heating and during cooling in the at least one moving direction behind the area of deposition, when the metallic build-up material is non-liquid at 50%-80% of the melting temperature, to at least one pulsed magnetic field using a magnetic coil arranged after the heat source, wherein the at least one pulsed magnetic field produces opposite directed interaction to a current induced in the build-up material from deposition causing the build-up material to undergo plastic deformation with a strain rate in a range of 1000 l/sec-100 l/sec that influences grain refinement properties within the build-up material while reducing residual mechanical stress within the build-up material resulting from strain that provides mechanical stability within the build-up material during the plastic deformation.

2. The method of claim 1, wherein plastic strain of the build-up material caused by the at least one pulsed magnetic field is greater than 10% within the area of deposition.

3. The method of claim 1, wherein the at least one pulsed magnetic field has a pulse length of 1 μsec-1 msec.

4. The method of claim 1, wherein subjecting the metallic build-up material to at least one pulsed magnetic field comprises applying a pulse series of 2-10 pulses.

5. The method of claim 4, wherein a pulse of the pulse series comprises phases of alternating currents creating Lorentz forces in opposite directions.

6. The method of claim 1, wherein the method comprises subjecting the metallic build-up material to two magnetic fields simultaneously.

7. An apparatus to form a freeform metal structure by wire feed additive manufacturing, wherein the apparatus comprises: a holding structure moveable in at least one moving direction; a wire feeding means for feeding a metal wire end along an area of deposition on the metal structure in the at least one moving direction; a heating means for heating the metal wire end to a melting temperature, the metal wire end as melted being deposited on the metal structure as metallic build-up material; and at least one magnetic coil means arranged after the heating means for subjecting the build-up material after heating and during cooling in the moving direction behind the area of deposition, when the metallic build-up material is non-liquid at 50%-80% of the melting temperature, to at least one pulsed magnetic field, wherein the at least one pulsed magnetic field produces opposite directed interaction to a current induced in the build-up material from deposition causing the build-up material to undergo plastic deformation with a strain rate in a range of 1000 l/sec-100 l/sec that influences grain refinement properties within the build-up material while reducing residual mechanical stress within the build-up material resulting from strain that provides mechanical stability within the build-up material during the plastic deformation.

8. The apparatus of claim 7, wherein the holding structure is arranged on a handling arm allowing at least three translatory degrees of freedom of the holding structure.

9. The apparatus of claim 7, wherein the at least one magnetic coil means is planar in shape.

10. The apparatus of claim 7, wherein the magnetic coil means has a U-shaped cross section with a central portion and two adjacent side portions surrounding the build-up material from top and both sides, respectively.

11. The apparatus of claim 7, wherein two coil means are arranged to exert Lorentz forces from two distinct directions.

12. The method of claim 4, wherein the pulse series includes 3-5 pulses.

13. The apparatus of claim 7, wherein the apparatus comprises an electric energy supply means for supplying pulse shaped electric energy to the at least one magnetic coil means.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic diagram of an apparatus for performing a method according to the invention in a side-view perspective; and

(3) FIG. 2 is a schematic diagram of an apparatus for performing a method according to the invention in an isometric view.

DETAILED DESCRIPTION

(4) FIG. 1 shows in a schematic diagram the basic principle of an apparatus for performing a method according to the invention in a side-view perspective. An electric energy supply means 10 is connected to a capacitor bank means 12 by a wire system designed to handle high currents and to be low on inductance and resistance. The capacitor bank means 12 is preferably designed to include a variety of single capacitor devices being lagged to maximize the resulting capacity of the capacitor bank means 12. A typical capacitor device has a capacity of 50 μF up to 400 μF. The typical discharge energy is between 200 J and 2000 J. The typical initial capacitor voltage is between 5 kV and 25 kV.

(5) While the electric energy supply means 10 is arranged to charge the capacitor bank means 12, the capacitor bank means 12 can rapidly be discharged by activating a switch means 14 being designed to emit extremely short current pulses to at least one magnetic coil means 22 which is mounted close to a metal structure 26. Typical pulses are in the range of 1 μsec-1 msec.

(6) The metal structure 26 is mounted onto a holding structure 28 being able to move the metal structure 26 into at least one direction. The metal structure 26 itself includes an area of deposition 24, where a metal wire 20 is being fed from a wire feeding means 18 and heated by a heating means 16, both of them also being able to move into the at least one direction. The heating means 16 is preferably designed to be a laser source specified to locally generate temperatures sufficient to melt common types of metals such as iron, steel or aluminum, while the wire feeding means 18 is typically arranged to be a roll-shaped device mounted onto a supporting structure. The metal wire 20 has typically an elliptical or prismatic cross section with the semimajor of 0.25 mm to 4 mm. The dimension of the semiminor is typically between 0.25 mm and 4 mm, too.

(7) When the metal wire 20 is fed to the area of deposition 24 on the metal structure 26, it is immediately melted by the heating means 16 resulting in growth of build-up material on the metal structure 26. Shortly after deposition, the build-up material showing temperatures of 50% to 80% of its melting temperature in Kelvin is subjected to at least one pulsed magnetic field effecting plastic deformation caused by Lorentz forces within the build-up material as a response to the applied pulsed magnetic field and, thus, forcing the build-up material to alter shape according to a desired geometry. Preferably, a pulse series of 2 to 10, more preferably of 3 to 5 subsequent pulses is applied.

(8) The plastic strain of the material is preferably chosen to be at least 10% within the area of deposition 24 in order to achieve substantial relief of mechanical stress and, thus, a significant reduction of distortion within the build-up material once being fed to the metal structure 26. The at least one pulsed magnetic field preferably exhibits a pulse length of 1 μsec to 1 msec resulting in strain rates of 10000 l/s to 100 l/s within the build-up material. These very high strain rates as compared to those of mechanical rolling (in the order of l/s) will result in an increase in formability and a reduction in wrinkling.

(9) In a basic form of the invention, the magnetic coil means 22 is designed to be a planar-shaped, preferably disc-shaped, magnetic coil emitting pulsed magnetic fields into one preferred direction. In order to withstand high currents, the wires of the magnetic coil means 22 must be low on resistance. In order to be able to emit highly directed pulsed magnetic fields, the magnetic coils means 22 is also required to be low on inductance.

(10) In a further embodiment of the invention, the magnetic coil means 22 is designed to include two coil means arranged around the build-up material and thus being able to exhibit Lorentz forces from two distinct directions allowing the build-up material to be exhibited to spatially more complex plastic deformation. As a variation of the invention, it is also possible to design the magnetic coil means 22 to feature a U-shaped cross section with a central portion and two adjacent side portions, as shown in FIG. 2 and hinted in FIG. 1. The magnetic coil means 22 being designed in such way so as to exert Lorentz forces onto the build-up material from three distinct directions, allowing to force the build-up material into even more complex geometric forms.

(11) In FIG. 2, the apparatus to perform a method according to the invention is shown in an isometric view. In this figure, the holding structure 28 is mounted onto a handling arm 30 of a robotic device allowing the holding structure 26 to move into at least three translatory degrees of freedom and, thus, enabling the apparatus to create even more geometrically complex parts using the described combination of wire feed additive manufacturing and electromagnetic forming.

LIST OF REFERENCES

(12) 10—Electric energy supply means; 12—Capacitor bank means; 14—Switch means; 16—Heat source/heating means; 18—Wire feeding means; 20—Metal wire; 22—Magnetic coil means; 24—Area of deposition; 26—Metal structure; 28—Holding structure; and 30—Handling arm.