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Title:
ELECTRON BEAM SOURCE AND THE USE OF THE SAME
Document Type and Number:
WIPO Patent Application WO/2019/121430
Kind Code:
A1
Abstract:
Provided is an electron beam source (200) for generating an electron beam comprising a cathode (240), an anode and a grid for regulating an electron beam current. The cathode has a base (242) and a protrusion (244) with sidewalls (247) and a top surface (248). The base surface and the top surface are essentially flat. The base surface and the top surface are arranged at a predetermined distance D from each other. The base is larger than the protrusion. The electron beam source further comprising a control unit adapted for changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base surface of the cathode.

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Inventors:
FAGER, Mattias (Steffenvägen 8, Onsala, 43931, SE)
Application Number:
EP2018/085082
Publication Date:
June 27, 2019
Filing Date:
December 14, 2018
Export Citation:
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Assignee:
ARCAM AB (Krokslätts Fabriker 27A, Mölndal, 43137, SE)
International Classes:
H01J1/13; B29C64/153; B33Y30/00; H01J1/16; H01J3/02
Foreign References:
JP2012069364A2012-04-05
US20030117054A12003-06-26
US20140169530A12014-06-19
US20150165525A12015-06-18
Other References:
None
Download PDF:
Claims:
CLAIMS

1. An electron beam source for generating an electron beam, the source comprising:

a cathode,

an anode, and

a grid for regulating an electron beam current,

wherein:

the cathode has a base and a protrusion with sidewalls and a top surface, the base having a base surface which is essentially in parallel with the top surface,

the base surface and the top surface are essentially flat and facing towards the anode,

the base surface and the top surface are arranged at a predetermined distance from each other,

the base is larger than the protrusion,

the sidewalls are essentially perpendicular to the base surface and the top surface, and

a control unit is configured for changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base surface of the cathode.

2. The electron beam source according to claim 1, wherein the base and the protrusion are circular.

3. The electron beam source according to claim 1 or 2, wherein the center of the protrusion is aligned with the center of the base element.

4. The electron beam source according to any one of claim 1-3, wherein the predetermined distance of the top surface and the base surface is 0.2-2mm.

5. 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 an electron beam, via at least one electron beam source and for at least one of heating or fusing the powder material, the at least one electron beam source comprising a cathode, an anode, and a grid between the cathode and anode, wherein the cathode is having a base and a protrusion with sidewalls and a top surface, the base having a base surface which is essentially in parallel with the top surface, the base surface and the top surface are essentially flat and facing towards the anode, the base surface and the top surface are arranged at a predetermined distance from each other, the base is larger than the protrusion, the sidewalls are essentially perpendicular to the base surface and the top surface, and

changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base surface of the cathode.

6. The method according to claim 5, further comprising the step of aligning a center of the protrusion with a center of the base element.

7. The method according to claim 5 or 6, wherein at least one of:

the base and the protrusion are circular,

the center of the protrusion is aligned with the center of the base element, or the predetermined distance of the top surface and the base surface is 0.2-2mm.

8. The method according to any one of claim 5-7, wherein one or more of the recited steps are executed via one or more computer processors within a control unit.

9. 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:

controlling an electron beam source when formation of a three-dimensional article, the electron beam source emitting an electron beam for at least one of heating or fusing individual layers of a powder material together so as to form the three-dimensional article, the electron beam source comprising a cathode, an anode, and a grid between the cathode and anode wherein the cathode is having a base and a protrusion with sidewalls and a top surface, the base and the top surface are essentially in parallel with each other, essentially flat and facing towards the anode, the base and the top surface are arranged at a predetermined distance from each other, the base is larger than the top surface, the sidewalls are essentially perpendicular to the base and the top surface; and

changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base of the cathode.

10. The computer program product according to claim 9, further configured to execute the step of aligning a center of the protrusion with a center of the base element.

1 1. The computer program product according to claim 9 or 10, wherein at least one of:

the base and the protrusion are circular,

the center of the protrusion is aligned with the center of the base element, or

the predetermined distance of the top surface and the base surface is 0.2-2mm.

12. An electron beam generating assembly ( 100) for an electron beam source, the assembly (100) comprising:

a cathode (140),

a grid (130), and

a heating circuit (180) for the cathode (140),

wherein:

the cathode (140) and the grid (130) are arranged electrically insulated from each other,

the cathode (140) is having a base (142) and a protrusion (144) with sidewalls (147) and a top surface (148),

the base (142) with abase surface (146) and the top surface (148) are essentially in parallel with each other, essentially flat and facing downwards,

the base surface (146) and the top surface (148) are arranged at a predetermined distance (D) from each other,

the base surface (146) is larger than the top surface (148), and

the sidewalls (147) are essentially perpendicular to the base surface (146) and the top surface (148).

13. The electron beam assembly according to claim 12, wherein the base surface (146) and the top surface (148) are circular.

14. The electron beam assembly according to claim 12 or 13, wherein the center of the protrusion (144) is aligned with the center of the base element (142).

15. The electron beam assembly according to any one of claim 12-14, wherein the predetermined distance (D) between the top surface (148) and the base surface (146) is 0.2-2mm.

16. The electron beam assembly according to any one of claim 12-15, wherein the cathode is made ofhafhium carbide, a rare earth metal hexaboride or an alkaline earth metal hexaboride.

17. An apparatus for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article wherein the apparatus comprises:

an electron beam source for generating an electron beam, the electron beam source comprising a cathode, an anode, and a grid for regulating an electron beam current; and a control unit,

wherein:

the cathode comprises a base and a protrusion with sidewalls and a top surface, the base has a base surface which is essentially in parallel with the top surface, the base surface and the top surface are essentially flat and facing towards the anode,

the base surface and the top surface are arranged at a predetermined distance from each other,

the base is larger than the protrusion,

the sidewalls are essentially perpendicular to the base surface and the top surface,

the control unit is configured for changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base surface of the cathode.

18. The electron beam source according to any one of claim 1 -4, wherein at least one of:

the base and the protrusion are circular,

the center of the protrusion is aligned with the center of the base element, or the predetermined distance of the top surface and the base surface is 0.2-2mm.

19. The electron beam source according to any one of claim 1 ,2, 3, 4 or 18, wherein the cathode is made of hafnium carbide, a rare earth metal hexaboride or an alkaline earth metal hexaboride.

Description:
ELECTRON BEAM SOURCE AND THE USE OF THE SAME

BACKGROUND

Related Field

[0001] Various embodiments of the present invention relate to an electron generating assembly, an electron beam source and a method for additive manufacturing of a three-dimensional article by successively fusing individual layers of powder material using such electron beam source.

Description of Related Art

[0002] Freeform 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] Designing high max power of electron beam triode guns may result in a tradeoff between intensity and power for a majority, for not saying all, of beam currents/grid voltages. An increase in emission area will deteriorate the possibility to achieve high beam intensity in the low current regime. Increased power can be achieved by moving to high brightness crystals such as LaB6/CeB6 or to use Schottky-guns. In many applications, and particularly in additive manufacturing, it is a problem that a larger cathode results in a lower intensity of the electron beam in the low electron beam current regime. In electron beam additive manufacturing it is of outmost importance that the electron beam source can be used with large power variations. Low beam currents (high intensity) may be used for network structures and/or contours, whereas high power (low intensity) may be used for heating.

BRIEF SUMMARY

[0005] Having this background, an object of the invention is to provide an electron beam source that is capable of achieving high max power and low intensity for large electron beam currents and high electron beam intensity for low electron beam currents.

[0006] In a first aspect of the invention it is provided an electron beam source for generating an electron beam comprising a cathode, an anode and a grid for regulating an electron beam current, wherein the cathode is having a base and a protrusion with sidewalls and a top surface, the base having abase surface which is essentially in parallel with the top surface, the base surface and the top surface are essentially flat and facing towards the anode, the base surface and the top surface are arranged at a predetermined distance from each other, the base is larger than the protrusion, the sidewalls are essentially perpendicular to the base surface and the top surface, the electron beam source further comprising a control unit adapted for changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base surface of the cathode.

[0007] A non-limiting advantage of the present invention is that a first and second spot size on a target surface may be achieved with one and the same setting of the beam shaping optics such as focus coil(s) and/or astigmatism coil(s). Electrons emitted from the base surface and the top surface have essentially the same beam trajectories and therefore can be focused and shaped with the same beam shaping optics settings.

[0008] In another example embodiment of the present invention the base and the protrusion are circular.

[0009] A non-limiting advantage of this embodiment is that any defects in the electron beam spot on the target surface may be easily detected.

[0010] In another example embodiment of the present invention the center of the protrusion is aligned with the center of the base element.

[0011] A non-limiting advantage of this embodiment is that a so called ghost spot may be arranged symmetrically around the melting spot. In an alternative embodiment the center of the protrusion is not aligned with the center of the base element. By arranging the protrusion non symmetrical in a direction of scan direction a post heating or pre heating may be more or less distinctive.

[0012] In another example embodiment of the present invention the predetermined distance of the top surface and the base surface is 0.2 -2mm.

[0013] A non-limiting advantage of this embodiment is that the sensitivity of a change in grid voltage may be chosen by a different distance. The smaller the distance the more sensitive the cathode will be for grid voltage variations, which in turn may result in a different electron beam spot sizes. By increasing the distance more variations in the grid voltage is allowed before changing from only electron beam emanating from the top surface to an electron emanating from the top surface plus the base surface. A larger distance will increase the electron beam current range from only the top surface before the base surface starts to add electrons to the electron beam spot on the target surface.

[0014] In another aspect of the present invention it is provided an apparatus for forming a three- dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article wherein the apparatus comprises an electron beam source according to any one of the embodiments mentioned above.

[0015] An advantage of this embodiment is that the electron beam spot may be switched between different spot sizes during manufacturing for different purposes very quickly and without the need of changing the setting of the beam shaping optics.

[0016] In still another aspect of the present invention it is provided an electron beam generating assembly for and electron beam source, the assembly comprising a cathode, a grid, a heating circuit for the cathode , the cathode and grid are arranged electrically insulated from each other, wherein the cathode is having a base and a protrusion with sidewalls and a top surface , the base with a base surface and the top surface are essentially in parallel with each other, essentially flat and facing downwards, the base surface and the top surface are arranged at a predetermined distance from each other, the base surface is larger than the top surface and the sidewalls are essentially perpendicular to the base surface and the top surface.

[0017] A non-limiting advantage of the present invention is that the inventive concept may be used in any existing triode electron beam source with little or no design modifications to the electron beam source as such. [0018] 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.

[0019] Further advantages and advantageous features of the invention are disclosed in the following description and in the claims provided herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0020] 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:

[0021] FIG. 1 depicts, in a schematic view, an example embodiment of an electron beam source with an inventive electron beam generating assembly;

[0022] FIG. 2 depicts, in a schematic view, an example embodiment of an electron beam generating assembly according to the present invention;

[0023] FIG. 3 depicts, in a schematic view, an example embodiment of an apparatus for producing a three-dimensional article which may have an electron beam generating assembly as depicted in figure 2.

[0024] FIG. 4 is a block diagram of an exemplary system 1020 according to various embodiments;

[0025] FIG. 5A is a schematic block diagram of a server 1200 according to various embodiments; and

[0026] FIG. 5B is a schematic block diagram of an exemplary mobile device 1300 according to various embodiments.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0027] 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.

[0028] Still further, to facilitate the understanding of this invention, a number of terms are defined below. T erms 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.

[0029] 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, etc. may, for example, be designed with the aid of a three-dimensional CAD system.

[0030] 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.

[0031] Figure 3 depicts an embodiment of a freeform fabrication or additive manufacturing apparatus 21 in which the electron beam generating assembly according to the present invention may be implemented.

[0032] 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.

[0033] 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.

[0034] 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 l5-60kV and with a beam power in the range of 3-l0kW. The pressure in the vacuum chamber may be lxl 0 3 mbar or lower when building the three- dimensional article by fusing the powder layer by layer with the energy beam.

[0035] 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, etc.

[0036] 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 engine equipped with a gear, adjusting screws, etc. The servo engine may be connected to the control unit 8.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Figure 1 depicts, in a schematic view, an exemplary embodiment of an electron beam source in which the inventive method may be implemented. The electron beam source 100 comprises a cathode 102, a grid 104 and an anode 106. Electrons emitted at the cathode 102 being on negative potential are accelerated towards the anode 106 and finally a target surface 118. A grid 104 is set at a predetermined distance from the cathode 102. The cathode 102 maybe provided with a voltage which may cause the cathode to heat up, where upon the cathode 102 releases electrons by thermionic emission. An aperture 105 o f the grid 104 may have about the same size and shape as a cross sectional area of the cathode along a plane taken along a line denote by A- A.

[0044] An accelerator voltage 160 is provided between the cathode and the anode 106. The accelerator voltage 160 causes the emitted electrons from the cathode 102 to accelerate towards the anode 106 thus establishing an electron beam 120. The electron beam 120 may impinge on a substrate surface 118, 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 (not shown).

[0045] An electron beam generating cathode may be a thermionic cathode made of an alkaline earth metal hexaboride such as Lithium hexaboride, Sodium hexaboride, Potassium hexaboride, Rubidium hexaboride, Caesium hexaboride or Francium hexaboride. The cathode may also be made of a rare earth metal hexaboride such as Scandium hexaboride, Yttrium hexaboride, Lanthanum hexaboride, Cerium hexaboride, Praseodymium hexaboride, Neodymium hexaboride, Promethium hexaboride, Samarium hexaboride, Europium hexaboride, Gadolumium hexaboride, Terbium hexaboride, Dysprosium hexaboride, Holmium hexaboride, Erbium hexaboride, Thulium hexaboride, Ytterbium hexaboride or Lutetium hexaboride. The cathode may also be made of Hafnium carbide.

[0046] In the electron beam source 100 the grid 104 is provided between the cathode 102 and the anode 106. The grid 104 may be arranged as a plate having the aperture 105. The aperture 105 may be aligned with the cathode 102. The size of the aperture in the grid 104 may correspond to a cross section of the electron beam 120 at the position of the grid 104. [0047] A grid voltage 180 may be provided between the grid 104 and the cathode 102 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 102 may be provided with a negative potential of -20kV to -lOOkV. A first connection point 110 of the accelerator voltage 160 and a first connection point 114 of the grid voltage 180 may be fixed to the same potential of -20kV to -lOOkV. A second connection point 108 of the accelerator voltage 160 may be provided with ground potential. A second connection point 112 of the grid voltage 180 may be varied between the negative blocking voltage and the full power voltage. A second control unit 150 may be controlling the voltage on the second connection point 112 of the grid voltage in order to adjust the electron beam current to a desired value. The second control unit 150 may be a physically separate control unit in connection with the control unit 8 or fully integrated in the control unit 8.

[0048] The target surface 118 may be set to ground potential or a positive potential. The electron beam source 100 may also comprise means 170 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 accelerator voltage 160, indicated by box 170 in Figure 1. This may be done by simply measuring the electron beam passing between the first and second connection points 110 and 108 respectively. If the cathode is provided with a fixed negative voltage of -60kV the negative blocking voltage may be around -6lkV, i.e., the second connection point 112 of the grid voltage is set at -6lkV and the first connection point 114 is set to -60kV, for blocking the electrons by the grid 104. If starting to decrease the negative blocking voltage at the second connection point 112, some of the electrons emitted from the cathode will be allowed to pass the grid 104. By varying the grid voltage in this example embodiment between -6lkV 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 and a predetermined size and shape of the aperture in the grid 104. Other accelerator voltages and/or other size, shape and emissivity of the cathode and/or other size and shape of the aperture in the grid may affect the maximum electron beam current to be higher or lower than the exemplified 25mA.

[0049] When starting to decrease the grid voltage from the negative blocking voltage -6lkv, electrons starts to emanate from a top surface 248 of the cathode 240. Decreasing the grid voltage further, the cathode 240 will also start to emanate electrons from the base surface 246. With the inventive design of the cathode 240 an electron beam at a target surface may be steered to emanate from the top surface only or from the top surface 248 and the base surface 246.

[0050] The cathode 240 is having a base 242 on top of which a protrusion 244 is arranged. The protrusion having a top surface 248 and side walls 247. The base 242 have a base surface 246 which is the freely exposed surface beside the protrusion. The base 242 as such is larger than the protrusion 244. The total area of the top surface 248 and the base surface 246, correspond in this particular embodiment to the total surface of the base 242. The side walls 247 is essentially perpendicular to the base surface 246 and the top surface 248. The top surface and the base surface is essentially in parallel with each other. The distance between the top surface 248 and the base surface is denoted by D. The distance D may be in the range of 0,2-2mm. The smaller the distance D is the less change of grid voltage is required in order to switch from an electron beam emanating from the top surface only to an electron beam from the top surface plus the base surface. There are several benefits with a cathode having a stepwise increased area of actual electron beam emission area. The top surface 248 may be used for electron beam currents from 0-40mA, whereas the top surface 248 plus sad base surface 246 may be used for electron beam currents from 40-200mA. The top surface and the base surface may have a circular shape. In an example embodiment the diameter of the top surface may be 0,5mm and the diameter of the base surface may be 1 mm.

[0051] The top surface 248 of the protrusion 244 may be arranged 0,2-1 ,5mm into the aperture of the grid 104, i.e., the top surface 248 is further away from the target surface than the aperture of the grid 104

[0052] With a design of the cathode according to figure 2 it is possible to achieve a high maximum power of the electron beam at the target surface together with a high intensity for small currents <30-40mA.

[0053] If for instance carbon coating is added to the sidewall 247 of the protrusion 244, electron emission from the sidewall 247 may be eliminated.

[0054] An advantage with this design of the cathode is that the electron beam from the top surface and the base surface will have in general terms the same trajectories. This means that a high current large beam spot emanating from the base surface and the top surface of the cathode onto the target surface can be focused using the same setting of the focus and astigmatism coils as for an electron beam emanating from only the top surface of the cathode 240. One can with other words switch the electron beam between two spot sizes with different electron beam currents using the same setting of the beam shaping coils. This may be advantageous in a special case in for instance additive manufacturing when a defocused high energy beam, a so called“ghost spot, is arranged around a sharp focused melting sport without changing the focus coil. The“ghost spot” may be arranged with a certain frequency around the melting spot. The frequency is the switching frequency of the grid voltage between a first grid voltage allowing only electrons from the top surface to form an electron beam impinging on the target surface to a second grid voltage allowing electron from both the top surface and the base surface to form an electron beam to impinge on the target surface.

[0055] A cathode 102 at different temperatures may emanate different amounts of electrons.

[0056] The grid potential may be taken from a look-up table. During the fusion process of the three-dimensional article, i.e., when powder material is melted or fused by the electron beam impinging on the powder layer, the correct grid voltage may be extracted for achieving a desired electron beam current from the a look up table or a mathematical function. The electron beam current may be switched from a first predetermined electron beam current to a second predetermined electron beam current by just switching the potential on the grid from a first grid potential to a second grid potential. This may enable fast switching of the electron beam current during the fusion process with accuracy from a first electron beam current to a second electron beam current. This may be helpful when an electron beam current has to be switched from a first electron beam current to a second electron beam current during a scan line of the electron beam in order to achieve final material characteristics. By changing the grid potential from a first value to a second value, the electron beam current may instantaneously change from a first electron beam current to a second desired electron beam current. The fast response of the amendment of the grid potential and the corresponding electron beam current makes it suitable as an addressing method for electron beam current in an additive manufacturing process where the electron beam may need to be amended several times during a small time interval. A sufficiently quick change in the electron beam current may for some applications be the key factor for a successful 3-dimensional article with the desired material properties and dimensional tolerances.

[0057] A predetermined grid potential may be applied for achieving a predetermined electron beam current on the powder surface for fusing the powder. This may also enable a fast switching during a fusion process from a first electron beam current to a second electron beam current. This may be necessary during a scan line depending on which, when and/or where a specific type of structure to be melted. [0058] In another aspect of the invention it is provided a program element 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 heating and/or fusing the powder material, where the electron beam source comprising a cathode, an anode, and a grid between the cathode and anode, controlling the electron beam source in a first mode when the formation of the three dimensional article is in a first process step, controlling the electron beam source in a second mode when the formation of the three dimensional article is in a second process step, wherein an electron beam current from the electron beam source is controlled in a feed-forward mode in the first mode and the electron beam current is controlled in a feed-back mode in the second mode. 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.

[0059] 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).

[0060] 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 patterns 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 non volatile 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.

[0061] 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 (RIMM), 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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 1130 may be capable of supporting communication in accordance with 2G wireless communication protocols IS- 136 (TDMA), GSM, and IS-95 (CDMA). Also, for example, the one or more networks 1 130 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 (NAMPS), 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 5 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.

[0068] 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.

[0069] 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 1 1 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.

[0070] In various embodiments, the server 1200 includes various systems for performing 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.

[0071] 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.

[0072] 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.

[0073] 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 1200. 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.

[0074] 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 ofthe 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.

[0075] 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.

[0076] 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 ofthe 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. [0077] 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 1200 components may be combined, and/or additional components performing functions described herein may also be included in the server.

[0078] 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.

[0079] 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 ofthe 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.

[0080] 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. [0081] 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.

[0082] 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.

[0083] 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, add ons, and updates, for instance, to its firmware, software (e.g., including executable instructions, applications, program modules), and operating system.

[0084] 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.

[0085] 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 308). 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.

[0086] The mobile device 1300 can also include volatile storage or memory 1322 and/or non volatile 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.

[0087] 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.

[0088] The 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 a different source of energy beam than the exemplified electron beam such as a laser beam. Other materials than metallic powder may be used, such as the non-limiting examples of: electrically conductive polymers and powder of electrically conductive ceramics. [0089] Indeed, a person of ordinary skill in the art would be able to use the information contained in the preceding text to modify various embodiments of the invention in ways that are not literally described, but are nevertheless encompassed by the attached claims, for they accomplish substantially the same functions to reach substantially the same results. Therefore, it is to be understood that the invention is not limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.