Method and arrangement for building metallic objects by solid freeform fabrication using plasma transferred arc (PTA) torches

Abstract

This invention relates to a method and arrangement for manufacturing objects by solid freeform fabrication, especially titanium and titanium alloy objects, wherein the deposition rate is increased by supplying the metallic feed material in the form of a wire and employing two gas transferred arcs, one plasma transferred arc for heating the deposition area on the base material and one plasma transferred arc for heating and melting the feed wire.

Claims

1. A system for building metallic objects by solid freeform fabrication, comprising: a first plasma transferred arc torch electrically connected to a base material and a second plasma transferred arc torch electrically connected to a feed wire; and a control system to control the first and second torches, and the feed wire to form an object by fusing successive deposits of a metallic material onto the base material.

2. The system of claim 1, wherein the electrical connection between the first plasma transferred arc torch and the base material is achieved by a first power source, and the electrical connection between the second plasma transferred arc torch and the feed wire is achieved by a second power source.

3. The system of claim 2, wherein the first and second power sources are direct current.

4. The system of claim 3, wherein the first and second direct current power sources include independent controls.

5. The system of claim 1, wherein the first plasma transferred arc torch preheats the base material at a position at which the metallic material is to be deposited.

6. The system of claim 1, wherein the second plasma transferred arc torch melts the feed wire.

7. The system of claim 1, wherein at least one of the first and second plasma transferred arc torches includes arc deflection control.

8. The system of claim 1, wherein the first plasma transferred arc torch is a gas tungsten arc welding torch.

9. The system of claim 1, wherein at least one of first and second plasma transferred arc torches is a gas metal arc welding torch.

10. The system of claim 1, further comprising an electrical connection between the second plasma transferred arc torch and the base material.

11. The system of claim 10, wherein the electrical connection between the second plasma transferred arc torch and the base material is achieved by a power source independent from that of first plasma transferred arc torch and second plasma transferred arc torch.

12. The system of claim 11, wherein the independent power source is direct current.

13. The system of claim 12, wherein the direct current independent power source includes controls independent from that of first plasma transferred arc torch and second plasma transferred arc torch.

14. The system of claim 13, wherein the independent controls include controls for a pulsating arc discharge between the second plasma transferred arc torch and the base material.

15. The system of claim 14, wherein the pulsating arc is pulsed with a frequency in the range from 1 Hz to 10 kHz.

16. The system of claim 1, wherein the first plasma transferred arc torch is electrically connected to a first power source such that an electrode of the first plasma transferred arc torch becomes a cathode and the base material becomes an anode.

17. The system of claim 1, wherein the second plasma transferred arc torch is electrically connected to a second power source such that an electrode of the second plasma transferred arc torch becomes a cathode and the feed wire of metallic material becomes an anode.

18. The system of claim 17, wherein the second plasma transferred arc torch is further electrically connected to a third power source such that an electrode of the second plasma transferred arc torch is also a cathode with the base material as a corresponding anode.

19. A method for manufacturing a three-dimensional object of a metallic material by solid freeform fabrication, the method comprising: preheating a deposition area in a base material using a first plasma transferred arc; feeding a feed wire to a position above the preheated deposition area in the base material; and melting a distal end of the feed wire using a second plasma transferred arc such that molten metallic material is deposited onto the preheated deposition area in the base material.

20. The method of claim 19, further comprising independently controlling the first and second plasma transferred arcs.

21. The method of claim 19, wherein the preheating of the deposition area in of the base material further comprises forming a molten pool in the base material.

22. The method of claim 19, further comprising moving the base material relative to the position of the first and second plasma transferred arcs in a predetermined pattern such that the successive deposits of molten metallic material drips on the preheated deposition area.

23. The method of claim 19, further comprising providing the first plasma transferred arc with a first plasma transferred arc torch electrically connected to the base material by a first power source, and providing the second plasma transferred arc with a second plasma transferred arc torch electrically connected to the wire by a second power source.

24. The method of claim 23, wherein the first and second power sources are direct current.

25. The method of claim 19, further comprising controlling the deflection of at least one of the first and second plasma transferred arcs.

26. The method of claim 19, wherein the first plasma transferred arc is generated by a gas tungsten arc welding torch.

27. The method of claim 19, wherein at least one of first and second plasma transferred arcs is generated by a gas metal arc welding torch.

28. The method of claim 19, further comprising preheating the deposition area in the base material using a third plasma transferred arc, wherein the second plasma transferred arc and the third plasma transferred arc are both provided by a single plasma transferred arc torch that is electrically connected to the wire via a power source, and to the base material via another power source.

29. The method of claim 28, further comprising independently pulsating arc discharge between the plasma transferred arc torch and the wire and the plasma transferred arc torch and the base material.

30. The method of claim 29, wherein each power source connected to the plasma transferred arc torch is a direct current power source pulsating with a frequency in the range from 1 Hz to 10 kHz.

31. The method of claim 28, wherein the preheating by the third plasma transferred arc forms a molten pool in the base material.

32. The method of claim 19, wherein the metallic material is titanium or alloyed titanium.

33. The method of claim 19, further comprising: creating a virtual three dimensional model of the object; dividing the model into a set of virtual parallel layers and further into a set of virtual quasi one-dimensional pieces for each parallel layer to form a virtual vectorized layered model of an object; loading the virtual vectorized layered model of the object into a control system able to regulate the position and movement of the base material, and the activation of the first and second plasma transferred arcs; engaging the control system to deposit and fuse a series of quasi one-dimensional pieces of the molten metallic material onto the base material in a pattern according to the first layer of the virtual vectorized layered model of the object; forming the second layer of the object by depositing and fusing a series of quasi one-dimensional pieces of the molten metallic material onto the previous deposited layer in a pattern according to the second layer of the virtual vectorized layered model of the object; and repeating the deposition and fusing process layer by layer for each successive layer of the virtual vectorized layered model of the object until an entire object is formed.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a facsimile of FIG. 1 of Taminger and Hafley [1] showing a schematic view of the principle of solid freeform fabrication.

(2) FIG. 2 is a facsimile of FIG. 1 of U.S. Patent Application Publication No.: 2006/0185473 showing a schematic view of the principle of plasma transferred arc solid freeform fabrication.

(3) FIG. 3 is a schematic drawing showing a cross-section view of the arrangement according to the second aspect of the present invention.

(4) FIG. 4 is a schematic drawing showing a cross-section view of a second embodiment of the invention including thermal pulsing.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

(5) The invention will be explained in greater detail by way of example embodiments. These examples should not be interpreted as a limitation of the general scope of the inventive idea of using two PTA-torches, one to form the molten pool in the base material and one to melt the feed material.

(6) First Example Embodiment

(7) The first example embodiment of the arrangement according to second aspect of the invention is shown schematically in FIG. 3. The figure shows a holding substrate 1 made of a Ti-6Al-4V alloy shaped as a rectangular cuboid, onto which a three-dimensional object made of the same Ti-6Al-4V alloy is to be formed by solid freeform fabrication. The figure displays the initial part of the deposition process where the first welding stripe 2 of Ti-6Al-4V alloy is being deposited.

(8) A wire 3 made of the Ti-6Al-4V alloy is continuously being supplied by a wire feeder 4 which positions the wire 3 such that its distal end is located above the molten pool 5 at the deposition area on the holding substrate 1. The wire 3 is given a velocity indicated by the upper arrow on the Figure which corresponds to the heating and melting rate of the distal end such that droplets 6 of molten wire are continuously being supplied to the molten pool 5.

(9) A first plasma transferred arc 7 is formed by a PTA-torch 8 which is electrically connected to a DC power source 9 such that the electrode 10 of the PTA-torch becomes the cathode and the holding substrate 1 the anode. The plasma transferred arc 7 is continuous and directed to heat and melt the base material (which at this stage of the SFFF-process is the holding substrate) at the deposition spot such that the molten pool 5 is obtained. The effect of the DC power source 9 is regulated to maintain a molten pool 5 with a constant size and extension by a control system (not shown). The PTA-torch 8 is a gas tungsten arc welding (GTAW) torch equipped with a magnetic arc deflector (not shown) to control the size and position of the arc 8.

(10) A second plasma transferred arc 11 is formed by a PTA-torch 12 which is electrically connected to a DC power source 13 such that the electrode 14 of the PTA-torch 12 becomes the cathode and the feed wire 3 the anode. The plasma transferred arc 11 is continuous and directed to heat and melt the distal end of the wire 3. The effect of the DC power source 13 is regulated to maintain a heating and melting rate in accordance with the feeding velocity of the wire such that the formation of the droplets 6 are timed to maintain a continuous drip of molten wire into the molten pool 5. The effect supplied by the DC power source 13 and the feeding velocity of the wire 3 exiting the wire feeder 4 are constantly regulated and controlled by the control system 17 such that the molten pool 5 is supplied with molten wire at a rate providing the intended deposition rate of the Ti-6Al-4V alloy. The control system 17 is simultaneously engaged to operate and regulate the engagement of an actuator (not shown) which constantly positions and moves the holding substrate 1 such that the molten pool is located at the intended deposition spot as given by the CAD-model of the object that is to be formed. At this stage of the SFFF-process, the holding substrate 1 is moved as indicated by the lower arrow.

(11) Second Example Embodiment

(12) The second example embodiment of the invention is the first example embodiment given above including additional means for forming thermal pulses in the molten pool 5.

(13) The means for forming thermal pulses is a DC power source 15 which is electrically connected to the second PTA-torch 12 such that the electrode 14 becomes the cathode and the holding substrate 1 becomes the anode. In addition, there are means 16 for pulsing the power delivered by DC power source 15 such that the arc 11 will in addition to heat and melt the wire 3, enter into the molten pool 5 with the same frequency as the pulsed power supply and thus deliver a pulsating heat flux to the molten pool. The means 16 may is regulated by the control system 17 and provides a pulsing arc discharge into the molten pool with a frequency of 1 kHz.

REFERENCE

(14) 1. Taminger, K. M. and Hafley, R. A., Electron Beam Freeform Fabrication for Cost Effective Near-Net Shape Manufacturing, NATO/RTOAVT-139 Specialists' Meeting on Cost Effective Manufacture via Net Shape Processing (Amsterdam, the Netherlands, 2006) (NATO). pp 9-25, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013538.sub.-20-08013396.pdf