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Title:
ADDITIVE MANUFACTURING OF THREE-DIMENSIONAL ARTICLES
Document Type and Number:
WIPO Patent Application WO/2018/114142
Kind Code:
A1
Abstract:
A method is provided for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article. The method includes: providing at least one electron beam source emitting an electron beam; providing a leakage current detector for sensing a current through the anode and/or the Wehnelt cup; providing a low impedance voltage source connectable to the Wehnelt cup via a switch, where the voltage source is having a more negative potential than a negative potential applied to the cathode; and protecting the cathode against vacuum arc discharge energy currents when forming the three-dimensional article by providing the Wehnelt cup to the low impedance negative voltage by closing the switch when the leakage current detector is sensing a current through the anode and/or the Wehnelt cup which is higher than a predetermined value.

Inventors:
EKBERG, Christian (Hökvägen 8, Hindås, 43853, SE)
Application Number:
EP2017/079081
Publication Date:
June 28, 2018
Filing Date:
November 13, 2017
Export Citation:
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Assignee:
ARCAM AB (Krokslätts Fabriker 27A, Mölndal, 43137, SE)
International Classes:
H01J3/02; B22F3/105; B22F7/06; B29C64/153; B29C64/264; H01J37/06; H01J37/305
Foreign References:
EP2926926A22015-10-07
JP2014175173A2014-09-22
US20080153376A12008-06-26
Other References:
None
Download PDF:
Claims:
CLAIMS

1. A method for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, the method comprising the steps of:

emitting, via at least one electron beam source, an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and the anode;

applying a negative potential to the cathode;

sensing, via a leakage current detector, a current through at least one of the anode or the Wehnelt cup; and

responsive to the current through at least one of the anode or the Wehnelt cup exceeding a predetermined value, closing a switch to connect the Wehnelt cup to a low impedance voltage source, the voltage source having a negative potential that is more negative than the negative potential applied to the cathode, the closing of the switch protecting the cathode against vacuum arc discharge energy currents when forming the three- dimensional article.

2. The method according to claim 1 , wherein the cathode element is made of a rare earth metal oxide material.

3. The method according to claim 1, wherein the low impedance negative voltage source comprises a capacitor having a capacitance configured to maintain the more negative potential to the Wehnelt cup compared to the negative potential applied to the cathode for a time duration of a vacuum arc discharge.

4. The method according to claim 3, wherein the low impedance negative voltage source provides a negative voltage at least 1000V more negative than a negative voltage provided on the cathode when the leakage current detector senses a current through at least one of the anode or the Wehnelt cup higher than the predetermined value.

5. The method according to claim 1, wherein one or more of the steps recited therein are computer-implemented via at least one control unit or processor.

6. The method according to claim 1 , wherein the switch is closed automatically, via at least one control unit, upon sensing the current higher than the predetermined value.

7. An additive manufacturing apparatus for forming a three-dimensional article through successive fusion of parts of at least one layer of powder provided on a work table, which parts corresponds to successive cross sections of the three dimensional article, the apparatus comprising:

at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and the anode;

a leakage current detector configured for sensing a leakage current through at least one of the anode or the Wehnelt cup;

a low impedance voltage source selectively connectable to the Wehnelt cup via a switch, the voltage source having a more negative potential than a negative potential applied to the cathode; and

a controlling device,

wherein, responsive to the sensing a current through at least one of the anode or the Wehnelt cup greater than a predetermined value, the switch is closed, via the controlling device, so as to connect the voltage source to the Wehnelt cup.

8. The apparatus according to claim 7, wherein the low impedance negative voltage source is an electric circuit dedicated to maintain a negative potential during the vacuum arc discharge which is more negative than the negative potential applied to the cathode.

9. The apparatus according to claim 7, wherein the controlling device is configured for setting the Wehnelt cup potential to a more negative potential than the cathode potential.

10. The apparatus according to claim 7, wherein the cathode element is made of a rare earth metal oxide material.

1 1. The apparatus according to claim 7, wherein the low impedance negative voltage source comprises a capacitor having a capacitance configured to maintain a more negative potential to the grid compared to the cathode for a time duration of a vacuum arc discharge.

12. The apparatus according to claim 7, wherein the low impedance negative voltage source provides a negative voltage at least 1000V more negative than a negative voltage provided on the cathode when the leakage current detector senses a current through at least one of the anode or the Wehnelt cup higher than the predetermined value.

13. A computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions embodied therein, the computer-readable program code portions comprising at least one executable portion configured for:

emitting, via at least one electron beam source, an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and the anode;

applying a negative potential to the cathode;

sensing, via a leakage current detector, a current through at least one of the anode or the Wehnelt cup; and

responsive to the current through at least one of the anode or the Wehnelt cup exceeding a predetermined value, closing a switch to connect the Wehnelt cup to a low impedance voltage source, the voltage source having a negative potential that is more negative than the negative potential applied to the cathode, the closing of the switch being configured to protect the cathode against vacuum arc discharge energy currents when forming the three-dimensional article.

14. The computer program product according to claim 13, wherein the low impedance negative voltage source comprises a capacitor having a capacitance configured to maintain a more negative potential to the Wehnelt cup compared to the negative potential applied to the cathode for a time duration of a vacuum arc discharge.

15. The computer program product according to claim 13, wherein the low impedance negative voltage source provides a negative voltage which is at least 1000V more negative than a negative voltage provided on the cathode when the leakage current detector is sensing a current through the anode and/or the Wehnelt cup which is higher than a predetermined value.

16. The computer program product according to claim 13, wherein the least one executable portion is configured to automatically close the switch upon sensing the current higher than the predetermined value.

17. The computer program product according to claim 13, wherein the cathode element is made of a rare earth metal oxide material.

18. The computer program product according to claim 13, wherein the low impedance negative voltage source is an electric circuit dedicated to maintain a negative potential during the vacuum arc discharge which is more negative than the negative potential applied to the cathode.

19. The computer program product according to claim 13, wherein the least one executable portion is further configured for setting the Wehnelt cup potential to a more negative potential than the cathode potential.

Description:
ADDITIVE MANUFACTURING OF THREE-DIMENSIONAL ARTICLES

BACKGROUND

Related Field

[0001] The present invention relates to a method for additive manufacturing of a three- dimensional articles by successively fusing individual layers of powder material.

Description of Related Art

[0002] Free-form fabrication or additive manufacturing is a method for forming three- dimensional articles through successive fusion of chosen parts of powder layers applied to a worktable.

[0003] An additive manufacturing apparatus may comprise a work table on which the three- dimensional article is to be formed, a powder dispenser or powder distributor, arranged to lay down a thin layer of powder on the work table for the formation of a powder bed, a high energy beam for delivering energy to the powder whereby fusion of the powder takes place, elements for control of the energy given off by the energy beam over the powder bed for the formation of a cross section of the three-dimensional article through fusion of parts of the powder bed, and a controlling computer, in which information is stored concerning consecutive cross sections of the three- dimensional article. A three-dimensional article is formed through consecutive fusions of consecutively formed cross sections of powder layers, successively laid down by the powder dispenser.

[0004] In additive manufacturing a short manufacturing time and high quality of the finalized product is of outmost importance. Desired material properties of the final product may depend on the ability to control the fusion process.

[0005] EBM (Electron Beam Melting) is one type of additive manufacturing where an electron emitting cathode in an electron acceleration column is the source for electron beam generation, which in turn is acting as an energy beam for melting the power material. One problem is that the cathode, as well as control electronics connected to the cathode is very sensitive to high discharge currents which may occur in an EBM machine. The discharge current is a result of vacuum arc discharges that is triggered by contamination particles that bridges the electric acceleration field between the cathode and an anode. The contamination particles may be material evaporated from the fusion process and/or contamination particles present in the vacuum chamber for other reasons. The discharge currents may destroy the cathode element and/or the electronics connected to the cathode element, which in turn will stop the additive manufacturing process.

BRIEF SUMMARY

[0006] An object of the invention is to provide a method and apparatus which prohibits that discharge currents will destroy the cathode element and/or the electronics connected to the cathode element in an EBM additive manufacturing machine. The above mentioned object is achieved by the features in the method and apparatus according to the claims recited herein.

[0007] In a first aspect of the invention a method is provided for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, the method comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and anode; providing a leakage current detector for sensing a current through the anode and/or the Wehnelt cup; providing a low impedance voltage source connectable to the Wehnelt cup via a switch, where the voltage source has a more negative potential than a negative potential applied to the cathode; and protecting the cathode against vacuum arc discharge energy currents when forming the three-dimensional article by providing the Wehnelt cup to the low impedance negative voltage by closing the switch when the leakage current detector is sensing a current through the anode and/or the Wehnelt cup which is higher than a predetermined value.

[0008] An exemplary and non-limiting advantage of various embodiments of the present invention is that the cathode and electronics connected to the cathode is protected from vacuum arc discharge currents which may greatly improve the reliability of the additive manufacturing process.

[0009] In various example embodiments of the present invention the low impedance negative voltage source may comprise a capacitor having a capacitance of a sufficient size so as to maintain a more negative potential to the grid compared to the cathode during a time duration of a vacuum arc discharge. An exemplary and non-limiting advantage of at least this embodiment is that it is simple and inexpensive to implement to make sure that the cathode elements or its electronics is not affected at any time during a vacuum discharge event. [0010] In various example embodiments of the present invention the low impedance negative voltage is always 200 - 1000V more negative than the grid cup potential for preventing formation of an electron beam current.

[0011] In still another aspect of the present invention it is provided an additive manufacturing apparatus for forming a three-dimensional article through successive fusion of parts of at least one layer of powder provided on a work table, which parts corresponds to successive cross sections of the three dimensional article, the apparatus comprising: at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and anode; a leakage current detector for sensing a leakage current through the anode and/or the Wehnelt cup; a low impedance voltage source connectable to the Wehnelt cup via a switch, where the voltage source is having a more negative potential than a negative potential applied to the cathode; and a controlling device for closing the switch when the leakage current detector is sensing a current through the anode and/or the Wehnelt cup which is higher than a predetermined value.

[0012] An exemplary and non-limiting advantage of at least this example embodiment is that the cathode and electronics connected to the cathode is protected from vacuum arc discharge currents which may greatly improve the reliability of the additive manufacturing apparatus.

[0013] All examples and exemplary embodiments described herein are non-limiting in nature and thus should not be construed as limiting the scope of the invention described herein. Still further, the advantages described herein, even where identified with respect to a particular exemplary embodiment, should not be necessarily construed in such a limiting fashion.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0014] Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0015] FIG. 1 depicts, in a schematic cross sectional side view, an example embodiment of an electron beam source according to the present invention;

[0016] FIG. 2 depicts, in a schematic view, an example embodiment of an apparatus for producing a three dimensional product which may have an electron beam source according to Figure i; [0017] FIG. 3 depicts a schematic flow chart of an example embodiment of the method according to the present invention.

[0018] FIG. 4 is a block diagram of an exemplary system 1020 according to various embodiments;

[0019] FIG. 5 A is a schematic block diagram of a server 1200 according to various embodiments; and

[0020] FIG. 5B is a schematic block diagram of an exemplary mobile device 1300 according to various embodiments.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0021] Various embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, embodiments of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly known and understood by one of ordinary skill in the art to which the invention relates. The term "or" is used herein in both the alternative and conjunctive sense, unless otherwise indicated. Like numbers refer to like elements throughout.

[0022] Still further, to facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as "a", "an" and "the" are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

[0023] The term "three-dimensional structures" and the like as used herein refer generally to intended or actually fabricated three-dimensional configurations (e.g., of structural material or materials) that are intended to be used for a particular purpose. Such structures may, for example, be designed with the aid of a three-dimensional CAD system. [0024] The term "electron beam" as used herein in various embodiments refers to any charged particle beam. The sources of charged particle beam can include an electron gun, a linear accelerator and so on.

[0025] The terms "Wehnelt cup" and "grid cup" have the same meaning and are used interchangeably in this document.

[0026] Figure 2 depicts an embodiment of a freeform fabrication or additive manufacturing apparatus 21 in which the inventive method according to the present invention may be implemented.

[0027] The apparatus 21 comprising an electron beam gun 6; deflection coils 7; two powder hoppers 4, 14; a build platform 2; a build tank 10; a powder distributor 28; a powder bed 5; and a vacuum chamber 20.

[0028] The vacuum chamber 20 is capable of maintaining a vacuum environment via a vacuum system, which system may comprise a turbo molecular pump, a scroll pump, an ion pump and one or more valves which are well known to a skilled person in the art and therefore need no further explanation in this context. The vacuum system is controlled by a control unit 8.

[0029] The electron beam gun 6 is generating an electron beam which is used for pre heating of the powder, melting or fusing together powder material provided on the build platform 2 or post heat treatment of the already fused powder material. The control unit 8 may be used for controlling and managing the electron beam emitted from the electron beam gun 6. At least one focusing coil (not shown), at least one deflection coil 7, an optional coil for astigmatic correction (not shown) and an electron beam power supply (not shown) may be electrically connected to the control unit 8. In an example embodiment of the invention the electron beam gun 6 may generate a focusable electron beam with an accelerating voltage of about 15-60kV and with a beam power in the range of 3-10kW. The pressure in the vacuum chamber may be 3x10 ~3 mbar or lower when building the three- dimensional article by fusing the powder layer by layer with the energy beam.

[0030] The powder hoppers 4, 14 comprise the powder material to be provided on the build platform 2 in the build tank 10. The powder material may for instance be pure metals or metal alloys such as titanium, titanium alloys, aluminum, aluminum alloys, stainless steel, Co-Cr alloys, nickel- based super alloys, and the like.

[0031] The powder distributor 28 is arranged to lay down a thin layer of the powder material on the build platform 2. During a work cycle the build platform 2 will be lowered successively in relation to a fixed point in the vacuum chamber. In order to make this movement possible, the build platform 2 is in one embodiment of the invention arranged movably in vertical direction, i.e., in the direction indicated by arrow P. This means that the build platform 2 starts in an initial position, in which a first powder material layer of necessary thickness has been laid down. Means for lowering the build platform 2 may for instance be through a servo motor equipped with a gear, adjusting screws, or the like. The servo motor may be connected to the control unit 8.

[0032] An electron beam may be directed over the build platform 2 causing the first powder layer to fuse in selected locations to form a first cross section of the three-dimensional article 3. The beam is directed over the build platform 2 from instructions given by the control unit 8. In the control unit 8 instructions for how to control the electron beam for each layer of the three- dimensional article is stored. The first layer of the three dimensional article 3 may be built on the build platform 2, which may be removable, in the powder bed 5 or on an optional start plate 16. The start plate 16 may be arranged directly on the build platform 2 or on top of a powder bed 5 which is provided on the build platform 2.

[0033] After a first layer is finished, i.e., the fusion of powder material for making a first layer of the three-dimensional article, a second powder layer is provided on the build platform 2. The thickness of the second layer may be determined by the distance the build platform is lowered in relation to the position where the first layer was built. The second powder layer is in various embodiments distributed according to the same manner as the previous layer. However, there might be alternative methods in the same additive manufacturing machine for distributing powder onto the work table. For instance, a first layer may be provided via a first powder distributor 28, a second layer may be provided by another powder distributor. The design of the powder distributor is automatically changed according to instructions from the control unit 8. A powder distributor 28 in the form of a single rake system, i.e., where one rake is catching powder fallen down from both a left powder hopper 4 and a right powder hopper 14, the rake as such can change design.

[0034] After having distributed the second powder layer on the build platform, the energy beam is directed over the work table causing the second powder layer to fuse in selected locations to form a second cross section of the three-dimensional article. Fused portions in the second layer may be bonded to fused portions of the first layer. The fused portions in the first and second layer may be melted together by melting not only the powder in the uppermost layer but also remelting at least a fraction of a thickness of a layer directly below the uppermost layer. [0035] Sometimes it may be necessary to consider the charge distribution that is created in the powder as the electrons hit the powder bed 5. The charge distribution density depends on the following parameters: beam current, electron velocity (which is given by the accelerating voltage), beam scanning velocity, powder material and electrical conductivity of the powder, i.e., mainly the electrical conductivity between the powder grains. The latter is in turn a function of several parameters, such as the non-limiting examples of temperature, degree of sintering and powder grain size/size distribution.

[0036] Thus, for a given powder, i.e., a powder of a certain material with a certain grain size distribution, and a given accelerating voltage, it is possible, by varying the beam current (and thus the beam power) and the beam scanning velocity, to affect the charge distribution.

[0037] By varying these parameters in a controlled way, the electrical conductivity of the powder can gradually be increased by increasing the temperature of the powder. A powder that has a high temperature obtains a considerably higher conductivity which results in a lower density of the charge distribution since the charges quickly can diffuse over a large region. This effect is enhanced if the powder is allowed to be slightly sintered during a pre -heating process. When the conductivity has become sufficiently high, the powder can be fused together, i.e., melted or fully sintered, with predetermined values of the beam current and beam scanning velocity.

[0038] Figure 1 depicts, in a schematic cross sectional side view, an example embodiment of an electron beam source 100 according to the present invention. The electron beam source 100 comprises a cathode 101 , a grid cup or Wehnelt cup 102 and an anode 104. Electrons 106 emitted at the cathode, 101 being on negative potential, are accelerated towards the anode 104 and finally a target surface (not shown). The grid cup 102 is set at a predetermined distance from the cathode 101. The cathode 101 may be provided with a separate power supply which may be used to heat the cathode, where upon the cathode 101 releases electrons by thermionic emission.

[0039] An acceleration voltage 160 is provided between the cathode 101 and the anode 104. The acceleration voltage 160 causes the emitted electrons from the cathode 101 to accelerate towards the anode 104 thus establishing an electron beam 106. The electron beam 106 may impinge on a substrate surface, which may be a powder layer in an additive manufacturing process. In order to guide and focus the electron beam there may further be arranged at least one focusing coil and at least one deflection coil. [0040] In the electron beam source 100 the grid cup 102 is provided between the cathode 101 and the anode 104. The grid cup 102 may be arranged as a plate having an aperture 1 12. The aperture 112 may be aligned with the cathode 101. The size of the aperture 112 in the grid cup 102 may correspond to a cross section of the electron beam 106 at the position of the grid cup 102.

[0041] A grid cup voltage 180 may be provided between the grid cup 102 and the cathode 101 and may be adjusted between a negative blocking voltage and a full power voltage and thereby adjusting an electron beam current between 0 - maximum electron beam current. In Figure 1 the cathode 101 may be provided with a negative potential of -20kV to -lOOkV.

[0042] The grid cup voltage 180 may be varied between the negative blocking voltage and the full power voltage . A grid amplifier 124 may be controlling the grid cup voltage 180 in order to adjust the electron beam current to a desired value as well as the acceleration voltage 160.

[0043] The anode may be set to ground potential. The target surface may be set to ground potential or a positive potential. The electron beam source 100 may also comprise means for detecting the actual electron beam current. An example means for detecting the electron beam current on the target surface may be to detect the actual loading of the high voltage source providing the acceleration voltage 160. If the cathode is provided with a fixed negative potential of -60kV the negative blocking voltage may be around -61kV, i.e., the Wehnelt cup 102 itself is set at -61kV, for blocking the electrons by the grid cup 102. If starting to decrease the negative blocking potential, some of the electrons emitted from the cathode will be allowed to pass through the grid cup 102. By varying the grid cup potential in this example embodiment between -61kV to— 60kV, when the cathode is provided with a fixed negative potential of -60kV, the electron beam current may vary from 0mA - maximum electron beam current which may be 25mA for a predetermined size and shape of the cathode 101 and a predetermined size andshape ofthe aperture in the grid cup 102. Other acceleration voltages and/or other size, shape and emissivity ofthe cathode 101 and/or other size and shape of the aperture in the grid cup 102 may affect the maximum electron beam current to be higher or lower than the exemplified 25mA. The grid potential is in the example embodiment above referenced to the ground potential, however the grid potential may in another example embodiment be referenced to the cathode potential.

[0044] The grid cup 102 may be provided with a clamping potential 170 under special circumstances in order to diverge vacuum discharge arcs from the cathode 101 towards and onto the grid cup 102. [0045] In Figure 1 a pre-discharge channel 107 may be present between the anode 104 and the cathode 101 if no special measures are taken. However, a diverted discharge channel 108 between the anode 104 and the grid cup 102 may be present if the grid cup 102 is arranged with the clamping voltage which will have a more negative electric potential than the cathode 101 and the blocking voltage on the Wehnelt cup 102. A clamping voltage 170 may be fixed and connected to a bulk capacitance 105 of sufficient size to maintain its relative voltage to the cathode 101 during any possible vacuum discharge. The clamping potential 170 is what controls the electric field strength that attracts and diverges the developing pre-discharge arc channel 107 from the anode 104 to the cathode 101 into a diverted discharge channel 108 from the anode 104 to the grid cup 102.

[0046] The clamping potential 170 may be provided onto the grid cup under the special circumstances, which in an example embodiment may be when a leakage current detector 120, 122 detects a leakage current which is above a predetermined value. A first leakage current detector 120 may detect a leakage current at the anode 104. A second leakage current detector 122 may detect a leakage current at the grid cup 102. The leakage current through the anode and/or the grid cup may be a first sign in a build-up phase of a vacuum arc discharge event. This leakage current may be used as a trigger signal to a switch. If the leakage current is above a predetermined value a control unit 150 may send a control signal to the switch 130, which in turn will close the switch 130. A closure of the switch 130 means that the clamping potential is applied to the grid cup 102 and the vacuum arc discharge is redirected from the cathode to the grid cup. The second control unit 150 may be a physically separate control unit or integrated with control unit 8 in Figure 2.

[0047] The leakage current detector may sense current anomalies in the range of μΑ to mA with a characteristic current derivative typical for a vacuum arc discharge build up. The time window for sensing the vacuum arc buildup is narrow, typically in the range of 100ns to a few μ&, and the switch 130 needs to be fully activated within this time window. The switch 130 may typically be realized by specialized power electronic devices such as triode electron tubes or high voltage power transistors.

[0048] In an example embodiment the detectors 120, 122 and clamping switch 130 may be realized as one unit possibly integrated with the cathode 101 and Wehnelt assembly 102.

[0049] If the grid cup potential is varied between -61kV- -60kV the clamping potential 170 needs to be around -61.5kV or higher if set to a fixed value. The clamping voltage potential is very much dependent of the geometries of the Wehnelt cup 102, cathode 101 and anode 104 as well as the acceleration voltage 160. In an example embodiment the clamping potential may be at least - 500V below the zero current threshold voltage on the Wehnelt cup 102.

[0050] In an example embodiment the cathode element may be made of a rare earth metal oxide such as lanthanum hexaboride. In another example embodiment the cathode element may be made of a wolfram element. The cathode element may be heated by a separate heating circuit (not shown) in order to set the cathode element 101 to a desired temperature at which electron emission is favourable. The clamping voltage source may need to have a low impedance and sufficient current handling capacity to withstand the vacuum arc discharge current without dropping more than negligible in clamping voltage in order to sustain a sufficient potential difference with reference to the cathode 101 to maintain the diverging electric field strength at the Wehnelt cup 102. In an example embodiment the capacitor 105 may be of a size in the range of a few μΡ up to ΙΟΟμΡ, where the size is dependent of the discharge energy and maximum allowed voltage drop during any foreseeable discharge.

[0051] The clamping voltage source may be a low impedance negative voltage source. In an example embodiment the clamping voltage source comprises a capacitor of sufficient size so as to maintain a more negative potential to the grid cup compared to the cathode during a time the vacuum discharge event take place. In an example embodiment the clamping voltage may be in the order of -500 to -2000V lower than the Wehnelt cup cut off voltage.

[0052] In an example embodiment the clamping voltage has at least 1 % more negative potential than the cathode element. In another example embodiment the clamping voltage has at least 2.5% more negative potential than the cathode element. In still another example embodiment the clamping potential is at least 1000V more negative than the cathode potential.

[0053] Figure 3 depicts a schematic flow chart of an example embodiment of the method for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article.

[0054] In a first step 310 at least one electron beam source is provided for emitting an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and anode.

[0055] In a second step 320 a leakage current detector is provided for sensing a current through the anode and/or the Wehnelt cup. [0056] In a third step 330 a low impedance voltage source is provided and connectable to the Wehnelt cup via a switch, where the voltage source is having a more negative potential than a negative potential applied to the cathode.

[0057] In a fourth step 340 the cathode is protected against vacuum arc discharge energy currents when forming the three-dimensional article by providing the Wehnelt cup to the low impedance negative voltage by closing the switch when the leakage current detector is sensing a current through the anode and/or the Wehnelt cup which is higher than a predetermined value.

[0058] In another aspect of various embodiments of the invention a program element is provided, configured and arranged when executed on a computer to implement a method for forming a three- dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, the method comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, wherein the electron beam source comprises a cathode, an anode, and a Wehnelt cup positioned between the cathode and anode; providing a leakage current detector for sensing a current through the anode and/or the Wehnelt cup; providing a low impedance voltage source connectable to the Wehnelt cup via a switch, where the voltage source is having a more negative potential than a negative potential applied to the cathode; and protecting the cathode against vacuum arc discharge energy currents when forming the three-dimensional article by providing the Wehnelt cup to the low impedance negative voltage source by closing the switch when the leakage current detector is sensing a current through the anode and/or the Wehnelt cup which is higher than a predetermined value.

[0059] The program may be installed in a computer readable storage medium. The computer readable storage medium may be the control unit 8, the control unit 150, or another separate and distinct control unit. The computer readable storage medium and the program element, which may comprise computer-readable program code portions embodied therein, may further be contained within a non-transitory computer program product. Further details regarding these features and configurations are provided, in turn, below.

[0060] As mentioned, various embodiments of the present invention may be implemented in various ways, including as non-transitory computer program products. A computer program product may include a non-transitory computer-readable storage medium storing applications, programs, program modules, scripts, source code, program code, object code, byte code, compiled code, interpreted code, machine code, executable instructions, and/or the like (also referred to herein as executable instructions, instructions for execution, program code, and/or similar terms used herein interchangeably). Such non-transitory computer-readable storage media include all computer-readable media (including volatile and non-volatile media).

[0061] In one embodiment, a non-volatile computer-readable storage medium may include a floppy disk, flexible disk, hard disk, solid-state storage (SSS) (e.g., a solid state drive (SSD), solid state card (SSC), solid state module (SSM)), enterprise flash drive, magnetic tape, or any other non-transitory magnetic medium, and/or the like. A non-volatile computer-readable storage medium may also include a punch card, paper tape, optical mark sheet (or any other physical medium with pattems of holes or other optically recognizable indicia), compact disc read only memory (CD-ROM), compact disc compact disc-rewritable (CD-RW), digital versatile disc (DVD), Blu-ray disc (BD), any other non-transitory optical medium, and/or the like. Such a nonvolatile computer-readable storage medium may also include read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory (e.g., Serial, NAND, NOR, and/or the like), multimedia memory cards (MMC), secure digital (SD) memory cards, SmartMedia cards, CompactFlash (CF) cards, Memory Sticks, and/or the like. Further, a non-volatile computer-readable storage medium may also include conductive -bridging random access memory (CBRAM), phase-change random access memory (PRAM), ferroelectric random- access memory (FeRAM), non-volatile random-access memory (NVRAM), magnetoresistive random-access memory (MRAM), resistive random-access memory (RRAM), Silicon-Oxide- Nitride-Oxide-Silicon memory (SONOS), floating junction gate random access memory (FJG RAM), Millipede memory, racetrack memory, and/or the like.

[0062] In one embodiment, a volatile computer-readable storage medium may include random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), fast page mode dynamic random access memory (FPM DRAM), extended data- out dynamic random access memory (EDO DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), double data rate type two synchronous dynamic random access memory (DDR2 SDRAM), double data rate type three synchronous dynamic random access memory (DDR3 SDRAM), Rambus dynamic random access memory (RDRAM), Twin Transistor RAM (TTRAM), Thyristor RAM (T-RAM), Zero-capacitor (Z-RAM), Rambus in-line memory module (REVIM), dual in-line memory module (DIMM), single in-line memory module (SIMM), video random access memory VRAM, cache memory (including various levels), flash memory, register memory, and/or the like. It will be appreciated that where embodiments are described to use a computer-readable storage medium, other types of computer-readable storage media may be substituted for or used in addition to the computer-readable storage media described above.

[0063] As should be appreciated, various embodiments of the present invention may also be implemented as methods, apparatus, systems, computing devices, computing entities, and/or the like, as have been described elsewhere herein. As such, embodiments of the present invention may take the form of an apparatus, system, computing device, computing entity, and/or the like executing instructions stored on a computer-readable storage medium to perform certain steps or operations. However, embodiments of the present invention may also take the form of an entirely hardware embodiment performing certain steps or operations.

[0064] Various embodiments are described below with reference to block diagrams and flowchart illustrations of apparatuses, methods, systems, and computer program products. It should be understood that each block of any of the block diagrams and flowchart illustrations, respectively, may be implemented in part by computer program instructions, e.g., as logical steps or operations executing on a processor in a computing system. These computer program instructions may be loaded onto a computer, such as a special purpose computer or other programmable data processing apparatus to produce a specifically-configured machine, such that the instructions which execute on the computer or other programmable data processing apparatus implement the functions specified in the flowchart block or blocks.

[0065] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including computer-readable instructions for implementing the functionality specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions that execute on the computer or other programmable apparatus provide operations for implementing the functions specified in the flowchart block or blocks. [0066] Accordingly, blocks of the block diagrams and flowchart illustrations support various combinations for performing the specified functions, combinations of operations for performing the specified functions and program instructions for performing the specified functions. It should also be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, could be implemented by special purpose hardware -based computer systems that perform the specified functions or operations, or combinations of special purpose hardware and computer instructions.

[0067] Figure 4 is a block diagram of an exemplary system 1020 that can be used in conjunction with various embodiments of the present invention. In at least the illustrated embodiment, the system 1020 may include one or more central computing devices 1 1 10, one or more distributed computing devices 1120, and one or more distributed handheld or mobile devices 1300, all configured in communication with a central server 1200 (or control unit) via one or more networks 1130. While Figure 4 illustrates the various system entities as separate, standalone entities, the various embodiments are not limited to this particular architecture.

[0068] According to various embodiments of the present invention, the one or more networks 1 130 may be capable of supporting communication in accordance with any one or more of a number of second-generation (2G), 2.5G, third-generation (3G), and/or fourth-generation (4G) mobile communication protocols, or the like. More particularly, the one or more networks 1 130 may be capable of supporting communication in accordance with 2G wireless communication protocols IS- 136 (TDM A), GSM, and IS-95 (CDMA). Also, for example, the one or more networks 1130 may be capable of supporting communication in accordance with 2.5G wireless communication protocols GPRS, Enhanced Data GSM Environment (EDGE), or the like. In addition, for example, the one or more networks 1 130 may be capable of supporting communication in accordance with 3G wireless communication protocols such as Universal Mobile Telephone System (UMTS) network employing Wideband Code Division Multiple Access (WCDMA) radio access technology. Some narrow-band AMPS ( AMPS), as well as TACS, network(s) may also benefit from embodiments of the present invention, as should dual or higher mode mobile stations (e.g., digital/analog or TDMA CDMA analog phones). As yet another example, each of the components of the system 1020 may be configured to communicate with one another in accordance with techniques such as, for example, radio frequency (RF), Bluetooth™, infrared (IrDA), or any of a number of different wired or wireless networking techniques, including a wired or wireless Personal Area Network ("PAN"), Local Area Network ("LAN"), Metropolitan Area Network ("MAN"), Wide Area Network ("WAN"), or the like.

[0069] Although the device(s) 1 1 10-1300 are illustrated in Figure 4 as communicating with one another over the same network 1 130, these devices may likewise communicate over multiple, separate networks.

[0070] According to one embodiment, in addition to receiving data from the server 1200, the distributed devices 11 10, 1120, and/or 1300 may be further configured to collect and transmit data on their own. In various embodiments, the devices 11 10, 1 120, and/or 1300 may be capable of receiving data via one or more input units or devices, such as a keypad, touchpad, barcode scanner, radio frequency identification (RFID) reader, interface card (e.g., modem, etc.) or receiver. The devices 1 110, 1120, and/or 1300 may further be capable of storing data to one or more volatile or non-volatile memory modules, and outputting the data via one or more output units or devices, for example, by displaying data to the user operating the device, or by transmitting data, for example over the one or more networks 1130.

[0071] In various embodiments, the server 1200 includes various systems forperforming one or more functions in accordance with various embodiments of the present invention, including those more particularly shown and described herein. It should be understood, however, that the server 1200 might include a variety of alternative devices for performing one or more like functions, without departing from the spirit and scope of the present invention. For example, at least a portion of the server 1200, in certain embodiments, may be located on the distributed device(s) 1 110, 1 120, and/or the handheld or mobile device(s) 1300, as may be desirable for particular applications. As will be described in further detail below, in at least one embodiment, the handheld or mobile device(s) 1300 may contain one or more mobile applications 1330 which may be configured so as to provide a user interface for communication with the server 1200, all as will be likewise described in further detail below.

[0072] Figure 5 A is a schematic diagram of the server 1200 according to various embodiments. The server 1200 includes aprocessor 1230 that communicates with other elements within the server via a system interface or bus 1235. Also included in the server 1200 is a display/input device 1250 for receiving and displaying data. This display/input device 1250 may be, for example, a keyboard or pointing device that is used in combination with a monitor. The server 1200 further includes memory 1220, which preferably includes both read only memory (ROM) 1226 and random access memory (RAM) 1222. The server's ROM 1226 is used to store a basic input/output system 1224 (BIOS), containing the basic routines that help to transfer information between elements within the server 1200. Various ROM and RAM configurations have been previously described herein.

[0073] In addition, the server 1200 includes at least one storage device or program storage 210, such as a hard disk drive, a floppy disk drive, a CD Rom drive, or optical disk drive, for storing information on various computer-readable media, such as a hard disk, a removable magnetic disk, or a CD-ROM disk. As will be appreciated by one of ordinary skill in the art, each of these storage devices 1210 are connected to the system bus 1235 by an appropriate interface. The storage devices 1210 and their associated computer-readable media provide nonvolatile storage for a personal computer. As will be appreciated by one of ordinary skill in the art, the computer-readable media described above could be replaced by any other type of computer- readable media known in the art. Such media include, for example, magnetic cassettes, flash memory cards, digital video disks, and Bernoulli cartridges.

[0074] Although not shown, according to an embodiment, the storage device 1210 and/or memory of the server 1200 may further provide the functions of a data storage device, which may store historical and/or current delivery data and delivery conditions that may be accessed by the server. In this regard, the storage device 1210 may comprise one or more databases. The term "database" refers to a structured collection of records or data that is stored in a computer system, such as via a relational database, hierarchical database, or network database and as such, should not be construed in a limiting fashion.

[0075] A number of program modules (e.g., exemplary modules 1400-1700) comprising, for example, one or more computer-readable program code portions executable by the processor 1230, may be stored by the various storage devices 1210 and within RAM 1222. Such program modules may also include an operating system 1280. In these and other embodiments, the various modules 1400, 1500, 1600, 1700 control certain aspects of the operation of the server 1200 with the assistance of the processor 1230 and operating system 1280. In still other embodiments, it should be understood that one or more additional and/or alternative modules may also be provided, without departing from the scope and nature of the present invention.

[0076] In various embodiments, the program modules 1400, 1500, 1600, 1700 are executed by the server 1200 and are configured to generate one or more graphical user interfaces, reports, instructions, and/or notifications/alerts, all accessible and/or transmittable to various users of the system 1020. In certain embodiments, the user interfaces, reports, instructions, and/or notifications/alerts may be accessible via one or more networks 1130, which may include the Internet or other feasible communications network, as previously discussed.

[0077] In various embodiments, it should also be understood that one or more of the modules 1400, 1500, 1600, 1700 may be alternatively and/or additionally (e.g., in duplicate) stored locally on one or more of the devices 11 10, 1120, and/or 1300 and may be executed by one or more processors of the same. According to various embodiments, the modules 1400, 1500, 1600, 1700 may send data to, receive data from, and utilize data contained in one or more databases, which may be comprised of one or more separate, linked and/or networked databases.

[0078] Also located within the server 1200 is a network interface 1260 for interfacing and communicating with other elements of the one or more networks 1 130. It will be appreciated by one of ordinary skill in the art that one or more of the server 1200 components may be located geographically remotely from other server components. Furthermore, one or more of the server 1060 components may be combined, and/or additional components performing functions described herein may also be included in the server.

[0079] While the foregoing describes a single processor 1230, as one of ordinary skill in the art will recognize, the server 1200 may comprise multiple processors operating in conjunction with one another to perform the functionality described herein. In addition to the memory 1220, the processor 1230 can also be connected to at least one interface or other means for displaying, transmitting and/or receiving data, content or the like. In this regard, the interface(s) can include at least one communication interface or other means for transmitting and/or receiving data, content or the like, as well as at least one user interface that can include a display and/or a user input interface, as will be described in further detail below. The user input interface, in turn, can comprise any of a number of devices allowing the entity to receive data from a user, such as a keypad, a touch display, a joystick or other input device.

[0080] Still further, while reference is made to the "server" 1200, as one of ordinary skill in the art will recognize, embodiments of the present invention are not limited to traditionally defined server architectures. Still further, the system of embodiments of the present invention is not limited to a single server, or similar network entity or mainframe computer system. Other similar architectures including one or more network entities operating in conjunction with one another to provide the functionality described herein may likewise be used without departing from the spirit and scope of embodiments of the present invention. For example, a mesh network of two or more personal computers (PCs), similar electronic devices, or handheld portable devices, collaborating with one another to provide the functionality described herein in association with the server 1200 may likewise be used without departing from the spirit and scope of embodiments of the present invention.

[0081] According to various embodiments, many individual steps of a process may or may not be carried out utilizing the computer systems and/or servers described herein, and the degree of computer implementation may vary, as may be desirable and/or beneficial for one or more particular applications.

[0082] Figure 5B provides an illustrative schematic representative of a mobile device 1300 that can be used in conjunction with various embodiments of the present invention. Mobile devices 1300 can be operated by various parties. As shown in Figure 5B, a mobile device 1300 may include an antenna 1312, a transmitter 1304 (e.g., radio), a receiver 1306 (e.g., radio), and a processing element 1308 that provides signals to and receives signals from the transmitter 1304 and receiver 1306, respectively.

[0083] The signals provided to and received from the transmitter 1304 and the receiver 1306, respectively, may include signaling data in accordance with an air interface standard of applicable wireless systems to communicate with various entities, such as the server 1200, the distributed devices 11 10, 1120, and/or the like. In this regard, the mobile device 1300 may be capable of operating with one or more air interface standards, communication protocols, modulation types, and access types. More particularly, the mobile device 1300 may operate in accordance with any of a number of wireless communication standards and protocols. In a particular embodiment, the mobile device 1300 may operate in accordance with multiple wireless communication standards and protocols, such as GPRS, UMTS, CDMA2000, lxRTT, WCDMA, TD-SCDMA, LTE, E- UTRAN, EVDO, HSPA, HSDPA, Wi-Fi, WiMAX, UWB, IR protocols, Bluetooth protocols, USB protocols, and/or any other wireless protocol.

[0084] Via these communication standards and protocols, the mobile device 1300 may according to various embodiments communicate with various other entities using concepts such as Unstructured Supplementary Service data (USSD), Short Message Service (SMS), Multimedia Messaging Service (MMS), Dual-Tone Multi-Frequency Signaling (DTMF), and/or Subscriber Identity Module Dialer (SIM dialer). The mobile device 1300 can also download changes, addons, and updates, for instance, to its firmware, software (e.g., including executable instructions, applications, program modules), and operating system.

[0085] According to one embodiment, the mobile device 1300 may include a location determining device and/or functionality. For example, the mobile device 1300 may include a GPS module adapted to acquire, for example, latitude, longitude, altitude, geocode, course, and/or speed data. In one embodiment, the GPS module acquires data, sometimes known as ephemeris data, by identifying the number of satellites in view and the relative positions of those satellites.

[0086] The mobile device 1300 may also comprise a user interface (that can include a display 1316 coupled to a processing element 1308) and/or a user input interface (coupled to a processing element 1308). The user input interface can comprise any of a number of devices allowing the mobile device 1300 to receive data, such as a keypad 1318 (hard or soft), a touch display, voice or motion interfaces, or other input device. In embodiments including a keypad 1318, the keypad can include (or cause display of) the conventional numeric (0-9) and related keys (#, *), and other keys used for operating the mobile device 1300 and may include a full set of alphabetic keys or set of keys that may be activated to provide a full set of alphanumeric keys. In addition to providing input, the user input interface can be used, for example, to activate or deactivate certain functions, such as screen savers and/or sleep modes.

[0087] The mobile device 1300 can also include volatile storage or memory 1322 and/or nonvolatile storage or memory 1324, which can be embedded and/or may be removable. For example, the non-volatile memory may be ROM, PROM, EPROM, EEPROM, flash memory, MMCs, SD memory cards, Memory Sticks, CBRAM, PRAM, FeRAM, RRAM, SONOS, racetrack memory, and/or the like. The volatile memory may be RAM, DRAM, SRAM, FPM DRAM, EDO DRAM, SDRAM, DDR SDRAM, DDR2 SDRAM, DDR3 SDRAM, RDRAM, RIMM, DIMM, SIMM, VRAM, cache memory, register memory, and/or the like. The volatile and non-volatile storage or memory can store databases, database instances, database mapping systems, data, applications, programs, program modules, scripts, source code, object code, byte code, compiled code, interpreted code, machine code, executable instructions, and/or the like to implement the functions of the mobile device 1300.

[0088] The mobile device 1300 may also include one or more of a camera 1326 and a mobile application 1330. The camera 1326 may be configured according to various embodiments as an additional and/or alternative data collection feature, whereby one or more items may be read, stored, and/or transmitted by the mobile device 1300 via the camera. The mobile application 1330 may further provide a feature via which various tasks may be performed with the mobile device 1300. Various configurations may be provided, as may be desirable for one or more users of the mobile device 1300 and the system 1020 as a whole.

[0089] It should be understood that the present invention is not limited to the above -described embodiments and many modifications are possible within the scope of the following claims. Such modifications may, for example, involve using multiple energy beam sources instead of the exemplified single electron beam source. Additionally or otherwise, materials other than metallic powder may be used, such as the non-limiting examples of powder of polymers or powder of ceramics.